![Chapter 1
Introduction
1.1 Vision
As roboticists, we often use nature as inspiration for the way robots should look, act,
or think. For example, we have robots that attempt to reason like humans, run like
cheetahs [Park et al., 2014a], grasp with the dexterity of human hands [Deimel and
Brock, 2014], and fly with the agility of birds [Moore et al., 2014]. Accordingly, we
have a tendency to benchmark the performance of these robotic systems against their
biological counterparts. The manufacturing industry has demonstrated the ability of
robots to outperform humans when tasks are well-defined, uncertainty is negligible,
and the environment is sufficiently controlled. However, outside of these conditions
the capabilities of robots are often underwhelming with respect to nature. From a
technical perspective, there are many reasons for this apparent performance discrep-
ancy (e.g. limitations in design, fabrication, sensing, control, and motion planning).
One salient difference between the majority of current robots and natural systems is
the degree of body elasticity, and soft roboticists believe this material mismatch may
be a significant technical barrier inhibiting robots from reaching their full potential
[Trimmer, 2014, Majidi, 2014]. Natural systems frequently leverage body elasticity
to resiliently accommodate environmental variation (Fig. 1-la), passively conform
to spatial uncertainty (Fig. 1-1b), and continuously deform during dexterous tasks
(Fig. 1-1c). The goal of this thesis is to explore how autonomous robotic systems
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![:~ ~
(c)
Figure 1-1: Nature utilizes body elasticity to: (a) resiliently accommodate environ-
mental variation as illustrated by a tree branch bending to accommodate heavy snow,
(b) passively conform to spatial uncertainty as shown by an elephant's trunk conform-
ing to flat ground, and (c) continuously deform during dexterous tasks exemplified by
a fish contorting its body during an escape-response. The image in (a) is attributed
to Ville Turkkinen of Tampere, Finland and licensed under Creative Commons Deed
CCO. The image in (b) is "An elephant trunk" attributed to Jenny Downing of
Geneva, Switzerland and licensed under Creative Commons Attribution 2.0 Generic.
The image at (c) is reproduced with permission from Figure 1 A of Goldbogen et al.
2005]
can be designed to also incorporate and leverage softness. To do this, we develop ex-
tremely soft robot morphologies that are radically different from today's mainstream
rigid-body robotic platforms in an effort to break the mold on how we think about
designing, fabricating, and controlling such systems. That is, we build robotic sys-
20
(b)](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-24-320.jpg)
![tems with bodies made entirely from soft silicone elastomer and power these bodies
with pressurized compressible fluids; the robots in this thesis have approximately five
orders of magnitude, or 100,000 times, greater inherent elasticity than traditional
rigid-body robots (please refer to Fig. 1-2). These robots serve as archetypical soft
autonomous systems. By creating radically different platforms we can begin to solve
hard problems arising from the introduction of deformable materials into autonomous
systems and thus inform a future where robots are destined to be softer.
a FF Elastic (Young's)
KiYN ~Modulus:
- L.= + E =FL/A7
b
S P,
10. 161 104 15 106 107 108 109 10t 10" 1012
i kiloPascal i MegaPascal 1GigaPascal
Figure 1-2: (a) "The elastic (Young's) modulus scales with the ratio of the force F
to the extension d of a prismatic bar with length Lo and cross-sectional area A0.
(b) Young's modulus for various materials (adapted from Autumn et al. [2006])."
Reprinted with permission from SOFT ROBOTICS, Volume 1, Issue 1, 2014, pp.
5-11, published by Mary Ann Liebert, Inc., New Rochelle, NY. [Majidi, 2014].
1.2 New Capabilities
1.2.1 Safer Interactions
Imagine a future where robots work alongside humans to cooperatively perform tasks
[Edsinger and Kemp, 2007]; safety becomes an immediate concern [Markoff and Miller,
2014]. Although industrial-style manipulators have been transformative for structured
repetitive tasks, these robots are often considered too rigid for human-centered envi-
ronments where the tasks are unpredictable and the robots have to ensure that their
interaction with the environment and with humans is safe. At the moment, robots
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![are isolated from humans and confined to operate behind guarding in industrial envi-
ronments. Nevertheless, roboticists are constantly balancing the competing goals of
safety and performance [Wyrobek et al., 2008]. Much research is aimed at equipping
such hard robots with soft capabilities [De Santis et al., 2008]. For example, the
inclusion of compliant transmissions function to decouple actuator and link inertia
when necessary to minimize collision forces [Bicchi and Tonietti, 2004]. Common
approaches to variable-impedance actuation, reviewed by Vanderborght et al. [2013],
include series elastic actuators [Pratt and Williamson, 1995] and variable stiffness
actuators [Tonietti et al., 2005]. However, despite these safer design morphologies,
robots are still fundamentally composed of rigid components and rely on control soft-
ware to guarantee safety if collisions with humans or environments occur. Soft robots
offer an alternative approach. By incorporating highly deformable materials, soft
robots offer the potential for mechanical compatibility between robots and humans
and this offers better safety margins, as articulated by Lipson [20141. The time is ripe
for inherently soft machines.
1.2.2 Mitigating Uncertainty
Roboticists have optimal, time-tested solutions when tasks are well-defined and a
machine's motions and interactions with its environment are predictable. However,
outside of structured environments, robots must constantly deal with uncertainty.
For example, if a humanoid robot were to misperceive a flight of steps within a
residential home, it will likely fall and require a costly repair. Commonly we rely on
tools such as a suite of sensors [Kammel et al., 2008], state-estimation [Smith et al.,
1990], Bayesian models [Cassandra et al., 1996], robust controllers [Tedrake, 2009],
and robust probabilistic reasoning [Thrun et al., 2006] to mitigate uncertainty. These
are all very good but computationally complex solutions. An alternative approach is
to develop robust and durable machines that can mitigate some of this uncertainty
at the hardware level. Autonomous systems can offload computational complexity to
mechanical components by incorporating soft, elastic materials into their structure. It
is possible to then combine these machines with relatively simple models and control
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![algorithms to achieve performance.
1.2.3 Continuous Deformation
What if robots could exhibit the dexterity and rapid continuum motion displayed
by natural creatures? For example, fish can perform escape responses, or energetic
bursts characterized by rapid accelerations (16 - 151 m s- 2
) over very short durations
(30 - 210 ms). This often involves the fish's body initially bending into a "C" shape
exceeding 100 degrees [Domenici and Blake, 1997]. Among vertebrates, these are some
of the most rapid maneuvers [Jayne and Lauder, 19931. Although biomimetic robots
with finite degree-of-freedom (DOF) bodies and elctro-mechanical actuators show
promising capabilities, they often cannot match the speed nor the dexterity of their
natural counterparts. Such approaches only approximate naturally continuous body
motion with multiple discrete links separated by fixed joints. Soft robots offer the
potential to lift the limitations imposed by rigid-body kinematics, as their bodies can
deform continuously under actuation. Furthermore, fluid energy can be stored and
subsequently released directly into soft actuators without a costly energy conversion
stage. These features make soft robots well-suited to emulate the kinematics and
dexterity displayed by some natural systems.
1.2.4 Natural Form
Soft materials and fabrication processes allow soft robots to realize complex, amor-
phous forms [Lipson, 20141. It is prohibitively difficult to realize naturally occurring
features such as continuously varying spatial surfaces and internal non-convex cavi-
ties with rigid materials and standard power transmission components. Soft materials
can be casted into arbitrary shapes using similar processes to that which an artist
uses to create sculptures. Fluidic channels can be continuously embedded throughout
these soft machines to provide form-independent power transmission and actuation.
Such soft technologies profoundly expand the robotics community's ability to emulate
complex biologically inspired morphologies.
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![1.3 Challenges
Although soft robots offer a promising range of new capabilities, there are surprisingly
few soft machines, and even fewer soft autonomous systems. What are the technical
challenges inhibiting the growth of soft robotics? To begin answering this question
we can look at recent reviews of the field. As Trivedi et al. [2008] notes, soft robots
are designed with either a continuously deformable backbone or no backbone at all,
and although this feature provides these robots with theoretically infinite degrees
of freedom, it presents a variety of technical challenges. To paraphrase Trimmer
[2014], the engineering community lacks experience working with highly deformable
materials. Our current tools are well-suited for applications using rigid materials;
soft, nonlinear materials break many of the underlying assumptions. To paraphrase
Lipson (2014], eliciting benefits from soft robots is difficult for several reasons: (i)
we lack computational tools that can simulate the many DOF and nonlinear effects
of soft materials; (ii) we have limited intuition when designing soft systems and few
automated tools at our disposal; (iii) soft actuation methods are relatively inefficient,
specifically pneumatic systems require substantial supporting hardware; (iv) the low
structural impedance introduced by soft materials makes feedback control difficult
and new control strategies are likely needed; (v) lastly, manufacturing processes are
tailored for rigid rather than soft systems, and standardization of components is very
challenging.
In short, the softer we make robots the less predictable their motions become. To
combat this, we need to address technical challenges on many fronts. Specifically, this
thesis addresses challenges arising in the areas of (i) device design, (ii) manufacturing
processes, (iii) kinematic and dynamic modeling, as well as (iv) algorithms for control
and planning. By studying extreme examples of soft robots, i.e. ones made entirely
from soft elastomer and powered by fluids, this thesis begins to identify appropriate
morphologies, fabrication processes, motion models, computational tools, and control
strategies for a growing class of robots that are designed to incorporate softness.
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![1.3.1 Devices
The concept of using very soft elastic materials to construct autonomous robots is
relatively new compared to and radically different from the time-tested form and
structure of traditional robotic systems. As soft roboticists, we are in the process
of defining long-lasting morphologies for soft machines. Accordingly, a considerable
amount of innovation is required to design functional soft machines as well as mech-
anisms for driving their actuation.
Performance and autonomy are competing goals in soft mobile fluidic elastomer
robots. Some fluid-powered soft machines show promising capabilities like walking
[Shepherd et al., 2011] and leaping [Shepherd et al., 2013a] but are primarily driven
by cumbersome external hardware limiting their practical use. Conversely, there are
instances of self-contained fluidic soft robots [Onal et al., 20111 [Onal and Rus, 2013];
however, because of the constraints imposed by bringing all supporting hardware
onboard, the performance of these robots is severely limited when compared to rigid-
bodied robots. Accordingly, one of the primary technical challenges addressed by this
thesis work is:
How do we advance soft-bodiedfluidic robots to be capable of rapidlyachiev-
ing continuum body motion while simultaneously being self-contained?
Next, we address device challenges associated with soft manipulation. Although
in this design space we can relax the constraint of on-board supporting fluidic hard-
ware, we encounter the competing goals of task precision and body compliance. In
general, the designs of existing soft position controlled manipulators are not very
soft. A fundamental limitation in designing robots to be softer and more compliant
is that the robots become increasingly unconstrained, making predictable and con-
trolled movement difficult. In more traditional manipulator morphologies there is a
balance between compliance and internal kinematic constraints that make controlled
movement feasible; however, in soft robots low durometer elastic materials effectively
lower the systems' structural impedance.
What is the morphology of a manipulatorwhose body and actuators are
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![composed entirely of soft elastomer but that is used for tasks requiring
task-space control?
Even if we can devise an appropriate manipulator morphology, what mechanisms
do we use to drive its actuation? In order to continuously vary the curvature of a soft
fluidic elastomer robot, input fluid energy needs to be continuously varied. Most soft
robots use valves to pressurize and sequence their actuation. A common strategy is to
rely on the fluidic actuator's relatively long time constant in combination with high
frequency valve switching to approximate continuous fluid delivery. This strategy falls
within the domain of morphological control (see Section 2.2.2) and is fundamentally
limited by the fact that it uses a discrete pulse width modulation approach to control
continuous motion. Furthermore, this strategy can be prohibitive as it is difficult to
recover fluid energy once it is delivered to the actuator. To enable precise curvature
control for soft fluidic elastomer robots this thesis addresses the following challenge:
How do we deliver continuous closed-circuitfluid flow to a soft robot in
order to enable continuum configurationcontrol?
1.3.2 Hardware Processes
Such radically different robot morphologies cannot be built using the same processes
by which engineers build traditional, rigid-body robots. Innovative approaches to
fabrication are required in order to build robots composed of soft rubber and deform
under fluid pressure. In the absence of fasteners, hard chassis, mechanical linkages,
and other standardized components we generally rely on casting and lamination pro-
cesses to realize soft robots. Cho et al. [2009] review manufacturing processes for soft
robots and provide only one reference to the use of embedded molding by Dollar and
Howe [2006]. Perhaps this is testament to the novelty of such processes for robotics.
More recent work by Correll et al. [2010] and Onal and Rus [2012] suggests this pro-
cess is well-suited for creating fluidic elastomer robots. However, before such robots
can attain mainstream usage, it is necessary that we build on these contributions and
devise repeatable and general methods for constructing soft machines.
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![body segment while not artificially constraining the robot's spatial mobility. The
process is analogous to adding multiple integrated circuits (ICs) to a printed circuit
board. Here, the board designer must route traces to each IC in order to supply
power and connect signals while minimizing the board's overall footprint. It follows
that, a challenge addressed by this thesis is:
What is a scalable approachto fabricatingmulti-body soft fluidic elastomer
robots?
1.3.3 Models
In a 2008 review by Trivedi et al. [2008] the challenges associated with modeling soft
robots were articulated:
"Accurate control of soft robots requires model-based prediction of the
set of possible configurations. Dynamic models that accurately describe
large-scale deflections of soft robots and cover their entire workspace are
currently too complicated to be used for control. Current control ap-
proaches, based on simpler models, are not guaranteed to be stable or
effective for large deflections (Gravagene et al. 2001). Also, including dis-
tributed forces such as gravity, and structural stability of multiple section
robots into control schemes is a challenging problem."
This problem is further compounded by the fact that the soft robots in this the-
sis have body segments composed entirely from low durometer elastomer and are
actuated by fluids. This means the bodies of these soft robots undergo large and con-
tinuous circumferential and longitudinal deformation due to the low elastic modulus
of their material composition. Accordingly, a primary technical challenge addressed
in this thesis is:
What is an appropriatestatic model for the large-scaleelastic deformation
of a soft fluidic body segment?
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![this system, and we explore capabilities enabled by this new soft fluidic elastomer
manipulator. The arm extends our modular planar manipulator morphology and
fabrication process into three spatial dimensions. We build a prototype consisting
of four independently casted and serially concatenated modular segments that each
move in three spatial dimensions with two degrees of freedom. We use a piece-wise
constant curvature assumption to model the arm and validate this assumption on the
the physical prototype. We demonstrate the arm's ability to pass through confined
environments, achieved closed-loop configurations, and position itself in three dimen-
sions. Additionally, we provide a dynamic model of the spatial manipulation system
under a sagittal plane assumption as well as a process for identifying the model's
parameters. We develop planning algorithms that leverage this dynamic model to
perform new capabilities like dynamic grabbing. Experimentally, we demonstrate
task precision improvement using bracing as well as dynamic positioning accuracy of
4 centimeters outside of the arm's statically reachable envelope.
1.4.2 Single Segment Soft Robots
We address the following hypothesis:
Hypothesis 1: A soft-bodied fluidic robot can be both capable of rapid
continuum body motion and entirely self-contained ([Marchese et al.,
2014d], [Marchese et al., 20131, and [Marchese et al., 2011]).
We advance soft robotics by providing a method for creating and controlling au-
tonomous self-contained soft-bodied systems. Specifically, we introduce a novel self-
contained fluidic actuation system and control algorithms used to deliver continuum
motion in soft robots. We demonstrate this soft actuation in a case study by build-
ing an autonomous soft-bodied robotic fish powered by an on-board energy source;
see Figure 1-3 and 1-4. The fish is novel in that it uses a soft continuum body
and an innovative fluidic actuation system for the soft body. Additionally, it has
onboard autonomy. That is, all power, actuation, and computational systems are
located onboard. The continuum body has an embedded flexible spine and embedded
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![Figure 1-3: An autonomous soft-bodied robot that is both self-contained and capable
of rapid, continuum body motion. The robot employs a compliant body with em-
bedded actuators emulating the slender anatomical form of a fish. Photo courtesy of
Devon Jarvis for Popular Mechanics.
anatomically proportioned muscle-like actuators. The robot is capable of forward
1
swimming and performing agile maneuvers, scaled versions of an escape response
.
We illustrate our proposed technical approach by designing and building a soft
robot fish capable of emulating the escape response of fish. A fish was chosen as a case
study because it naturally exhibits: continuum body curvature, rapid motion during
an escape response [Domenici and Blake, 1997, Borazjani et al., 2012], a compliant
posterior that bends under hydrodynamic resistance [Wakeling and Johnston, 1999],
and an anterior suitable for housing rigid supporting hardware.
We evaluate the forward swimming and escape response maneuver of this soft
robot in a suite of experiments. Extensive kinematic data is collected on the escape
response and we compare the performance of the robot to various studies on biological
fish. We show our robotic system, although on a different time scale, is able to emulate
'Escape response maneuvers are characterized by rapid body accelerations over very short du-
rations and that often involve the body initially bending into a "C" shape Domenici and Blake
[19971. Among vertebrates, these are some of the most rapid maneuvers Jayne and Lauder [1993]
and subject of frequent study. The extremely agile behavior exhibited by fish during escape response
maneuvers is central to predator-prey interactions Webb and Skadsen [19801, and accordingly escape
response performance carries marked ecological significance Walker et al. [20051, Gibb et al. [2006],
Domenici et al. [2008], Bergstrom [2002]. Furthermore, the behavior serves as a neurophysiological
model Eaton et al. [1981, 1991]. Understanding this behavior can give scientists insights on ver-
tebrate evolution Hale et al. [2002] and physiology. Recently, the hydrodynamics of the maneuver
have been explored in great detail; see Borazjani et al. [2012].
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![Figure 1-4: Left: Soft-bodied robotic fish with hull and rubber anterior cowl re-
moved exposing the robot's onboard power, actuation, and computational subsys-
tems. Right: A close-up of the robot with its cowl removed showing the wireless
communication and control circuitry as well as the central fluid artery. Photos cour-
tesy of Devon Jarvis for Popular Mechanics.
the basic structure of an escape response and that the performed maneuvers have a
similar input-output relationship as observed in biological fish.
1.4.3 Multi-segment Planar Soft Robots
Additionally, in this thesis we address another important hypothesis:
Hypothesis 2: Planar manipulation is possible with a soft fluidic elas-
tomer robot. That is, a fluid powered multi-segment planar robot made
entirely from soft elastomer can be precisely positioned using a closed-loop
kinematic controller ([Marchese et al., 2015a], [Marchese et al., 2014c],
[Marchese et al., 2014a], and [Katzschmann et al., 2015]).
This thesis demonstrates that autonomous manipulation with soft fluidic elastomer
robots is possible. First, we present the design and characterization of three fluidic
elastomer manipulator morphologies. Each of the arm's serially connected body seg-
ments are fundamentally constructed from derivatives of fluidic elastomer actuators
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![Figure 1-5: Two planar soft fluidic elastomer manipulator morphologies. Left: a
manipulator prototype composed of six independently actuatable body segments.
Each cylindrical segment has actuated channels embedded in its outer layer enabling
the body segment to bend. Right: a six segment manipulator prototype where each
rectangular body segment generates curvature using two agonist fluidic elastomer
actuators separated by a thin inextensible spine.
(FEAs) [Correll et al., 20101 and these actuators deform by bending about a neutral
axis when pressurized [Onal et al., 2011]. Next, we provide three alternative fabri-
cation approaches for reliably fabricating these manipulators. Then, a method for
closed-loop positional control of these soft manipulators is developed. This capability
requires two critical innovations. First, we solve the previously unaddressed problem
of controlling the configuration of an entirely soft and highly compliant pneumatic
arm. That is, we develop real-time, closed-loop curvature controllers that drive the
bending of the manipulator's soft pneumatic body segments despite their high com-
pliance and lack of kinematic constraints. Specifically, to achieve curvature control
we use an array of cascaded PI and PID controllers as well as develop an array of
fluidic drive cylinders. Second, we apply a simplifying piece-wise constant curvature
(PCC) assumption to model the forward and inverse kinematic relationship between
the arm's configuration space (i.e., segment curvatures and lengths) and task space
(i.e., the pose of points along its backbone) in a manner consistent with traditional
continuum manipulation literature, as reviewed by Webster and Jones 2010]. Under
this assumption, we develop forward and inverse kinematics algorithms to transform
between configuration and task space.
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![We combine all these developments into an aggregate system for which we create a
suite of planning algorithms, and with this we achieve novel capabilities for this class
of robot. First, using a Jacobian-based approach to the inverse kinematics problem,
we experimentally evaluate the arm's ability to repeatably move to poses in free-space
as well as track linear end-effector trajectories.
Second, we provide an approach for autonomously moving a planar fluidic elas-
tomer arm through a confined, pipe-like environment. We provide a computational
approach to whole arm planning that finds a solution to the inverse kinematics prob-
lem for this class of arms. The solution considers both the primary task of advancing
the arm's end effector pose as well as the secondary task of positioning the whole
arm's changing envelope in relation to the environment. Specifically, we find a trans-
formation from the arm's task space to its arc space that is aware of the soft arm's
entire shape. We achieve this by posing a series of constrained nonlinear optimization
problems and solving for locally optimal arc space parameters. A key feature of our
approach is that we do not prevent collisions, but rather minimize their likelihood.
In fact, since we have designed an entirely soft and compliant robot, we can tolerate
collisions. Often, the arm's ability to passively comply with the environment allows
the primary task to be accomplished despite the collision. To experimentally validate
the soft robot's ability to successfully advance through a confined environment, we
carry out a series of experiments using a six segment soft planar manipulator. The
primary goal of these experiments is to validate the whole body planner's ability to
incrementally advance the robot through one of four distinct pipe-like sections.
Lastly, we present a fluid powered gripper for these soft manipulators that can con-
form to variations in object geometry while ensuring encapsulation of a round object.
The gripper is inspired by fingers developed by Polygerinos et al. [2013] and is ad-
vantageous for grasping because it exhibits high curvature, minimal radial expansion,
and remains compliant during actuation. We attach this gripper to a multi-segment
soft manipulator to enable grasp-and-place capabilities. We also present a planning
algorithm that advances the arm through all necessary states of the grasp-and-place
operation. The system first plans concentric approach circles shrinking from the ini-
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![tial end-effector pose to the object. Next, the system searches for locally optimal
manipulator configurations that constrain the end-effector to lie on these approach
circles so that the manipulator does not collide with the object. We experimentally
validate the system's ability to repeatably and autonomously grasp-and-place ran-
domly placed objects with a 7 DOF planar fluidic elastomer manipulator prototype.
1.4.4 Multi-segment Spatial Soft Robots
Lastly, in this thesis we address the hypothesis:
Hypothesis 3: Spatial manipulation is possible with an arm composed
entirely of low durometer elastomer and powered by fluid. That is, an
entirely soft fluid-powered multi-segment spatial robot subject to gravity
can be autonomously positioned to accomplish tasks ([Marchese and Rus,
2015] and [Marchese et al., 2015b]).
In this thesis we present a complete soft spatial manipulation system. That is, we
provide the design, fabrication, and kinematic modeling of a new manipulator mor-
phology: a fluid-powered three-dimensional multi-segment arm composed entirely of
soft elastomer. Additionally, we develop a power system as well as processing and
control algorithms that enable autonomous closed-loop control of the soft manipulator
despite the self-loading effects of gravity. We show how the fluidic elastomer manip-
ulator's continuum kinematics and soft material composition lead to several distinct
advantages when compared to traditional rigid body manipulators. First, we show
that the manipulator's soft segments deform according to constant curvature. With a
constant curvature assumption [Webster and Jones, 2010], we can parameterize this
N-link spatial soft manipulator with 2N joint variables. Second, the kinematics and
extreme compliance of such a soft manipulator enable it to fit within and advance
through confined environments. When the boundaries of the environment can be pa-
rameterized by curved cylinders and its curvature is non-zero, an idealized soft fluidic
elastomer manipulator will be more capable of advancing through a confined environ-
ment than a manipulator with rigid links and discrete joints. We demonstrate this
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![Micro NiTi coil actuators
Elastomer film
Constraint
Layer Pressurized
Channels
Depressurized
Channels
Figure 2-1: Common actuation approaches for soft robots. (a) Shape Memory Alloy
(SMA) actuators [Seok et al., 2010], (b) Pneumatic Artificial Muscle (PAM) actuators
[McMahan et al., 2006], (c) Fluidic Elastomer Actuators (FEAs) [Onal et al., 2011],
and (d) Fiber reinforced FEAs [Galloway et al., 2013].
Tendons
Originally, many hard hyper redundant and hard continuum robots [Hannan and
Walker, 2003, Cieslak and Morecki, 1999, Buckingham, 2002, Gravagne and Walker,
2002, McMahan et al., 2005, Camarillo et al., 2009] used an array of servomotors or
linear actuators to pull cables that move rigid connecting plates located between body
segments. Some softer robots have adopted a similar actuation scheme consisting of
tendons pulling rigid fixtures embedded within an elastomer body. For example, the
elastomer based bio-inspired octopus arm developed in Calisti et al. [2010], Laschi
et al. [2012] and Calisti et al. [2011] uses Shape Memory Alloy (SMA) actuation.
Further, Seok et al. [2010] use SMA actuators within a worm-like locomotory robot
(see Fig. 2-la). The basic operating principle behind SMA technology is that nickel
titanium (NiTi) wire contracts under joule heating. This heating is typically produced
by passing electrical current through the wire. The contracting wire can be used as an
agonist actuator, similar to the way one's bicep pulls the forearm towards the body
during a curl. There are also soft elastomer robots that use more traditional variable
tension cables. For example, the soft-bodied fish developed by Valdivia y Alvarado
and Youcef-Toumi [2006] as well as the soft arm developed by Wang et al. [2013] use
44](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-48-320.jpg)
![this actuation approach, but these both consist of only one actuated segment.
Pneumatic Artificial Muscles
Another common actuation scheme for soft robots involves distributed Pneumatic
Artificial Muscle (PAM) actuators (see Fig. 2-1b) also known as the McKibben actu-
ator. A PAM is fundamentally composed of an inflatable elastic tube surrounded by
a braided mesh. Depending on the weave pattern of the braided mesh the actuator
can be designed to contract or extend under input pressure. Typically these actuators
are operated with driving pressures between 50 and 100 psi. These actuators have
been used and studied extensively in Chou and Hannaford [1996], Tondu and Lopez
[20001 and Daerden and Lefeber [2002]. Notable semi-soft robots using PAMs include
[McMahan et al., 2006, Pritts and Rahn, 2004] and Kang et al. [2013].
Fluidic Elastomer Actuators
A softer alternative is the Fluidic Elastomer Actuator (FEA), which is used predom-
inantly throughout this thesis. The FEA is a bending actuator composed of low
durometer rubber and driven by relatively low-pressure fluid, 3 to 8 psi. Its basic
structure consists of two soft elastomer layers separated by a flexible but inextensible
constraint. Each of these elastomer layers contains embedded fluidic channels. By
pressurizing the fluid entrapped in these channels, stress is induced within the elastic
material producing localized strain. This strain in combination with the relative in-
extensibility of the constraint produces body segment bending (see Fig. 2-1c). FEAs
can be powered pneumatically or hydraulically.
Perhaps the earliest application of pneumatically actuated elastomer bending seg-
ments to robotics was by Suzumori et al. [1992]. Here fiber-reinforced Flexible Mi-
croactuators (FMAs) were developed and shown viable in a manipulator and multi-
fingered hand. Recently, these concepts have been extended and developed into the
FEA and used to build a variety of robotic systems [Shepherd et al., 2011, Ilievski
et al., 2011, Onal et al., 2011, Morin et al., 2012, Martinez et al., 2013, Onal and
Rus, 2013, Tolley et al., 2014a]. These robots use elastomers of varying stiffness as
45](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-49-320.jpg)
![well as cloth, paper, plastics, and even stiffer rubbers for their constraint layers. Fur-
thermore, Mosadegh et al. [20141 and Polygerinos et al. [2013] have investigated more
elaborate channel designs in order to reduce elastomer strain.
There are also less flexible, fiber-reinforced FEAs (see Fig. 2-1d) that occupy the
soft actuator space between purely elastomer FEAs and PAMs. These actuators
operate with driving pressures of between 25 and 35 psi and can accordingly apply
higher forces which is an advantage for many applications. There are several notable
examples of fiber-reinforced FEAs in the literature Galloway et al. [2013], Bishop-
Moser et al. [2012], Deimel and Brock [2013, 2014], Park et al. [2014b] and Suzumori
et al. [2007].
2.1.2 Power
Fluidic power sources present many challenges for soft robots. Recently, Wehner et al.
[2014] review existing pneumatic energy sources. Besides the use of compressed gas,
which was proposed to the community in Marchese et al. [2013] and Marchese et al.
[2014d] and detailed in Chapter 3, there are three viable alternatives. These are: (i)
microcompressors, (ii) explosive combustion, and (iii) peroxide monopropellants.
Microcompressors
Microcompressors, as used in Tolley et al. [2014b], Katzschmann et al. [2014], and
Onal and Rus [2013], are well-suited for low-flow applications where the duration of
the robot's operation is of primary concern. Typically, a microcompressor converts
electrical energy from lithium polymer batteries into fluid energy, and this approach
makes use of the high energy density of commercial battery technology. In general
the components of this power source are commercially available and easy to control.
Explosive Combustion
In contrast, explosive combustion, as used in Shepherd et al. [2013a] and Tolley et al.
[2014a], is well-suited for high-power, high-speed applications because chemicals like
46](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-50-320.jpg)
![butane and methane offer unmatched energy densities with respect to batteries and
compressed gas. However, considerable supporting hardware is required to prepare,
mix, and trigger such reactions. Besides producing noise and heat, the release of
energy can be difficult to control.
Peroxide Monopropellant
Alternatively, peroxide monopropellant, as used in Onal et al. [20111, leverages the de-
composition of hydrogen peroxide into water and oxygen. By carefully, but passively
controlling the introduction of a decomposition catalyst, a portable peroxide pump
has been shown to slowly release gas in order to sustain driving pressures suitable for
soft robot actuation.
Compressed Gas
Additionally, we show stored compressed gas is well-suited when high driving pressures
and high maximum flow rates are required, and accordingly rapid, quiet actuation
is required from a robotic system. This is primarily because fluid energy is stored
and released onboard, as opposed to generated. Accordingly, no energy is converted
between domains. However, because this strategy leverages compressed gas canisters
whose energy densities are significantly lower than both lithium polymer batteries
and the chemicals within the aforementioned reactions, the total available energy is
limited and therefore the system's duration of operation can be limited.
2.1.3 Design Tools
As mentioned in the introduction of this thesis, design tools for soft robots are limited
with respect to the availability of design tools for more traditional rigid-body robots.
Suzumori et al. [2007] use Finite Element Modeling (FEM) to analyze the bending
of fiber reinforced pneumatic tube-like actuators. Specifically, hyperelastic material
models are used to capture the nonlinear material properties of rubber, line elements
are used to represent radial inextensibility constraints due to fiber reinforcement,
47](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-51-320.jpg)
![and the simulation is performed using the software MARC. Outside of this example,
the community has generally found that iterative nonlinear finite element solvers are
limited to small deformations and of limited use when modeling very soft nonlinear
materials [Lipson, 2014]. VoxCAD and the Voxelyze physics engine, as used in Cheney
et al. [2013] and Lehman and Stanley [2011] and reviewed by Lipson [2014], are
simulation tools for very soft nonlinear materials. These tools use the concept of
nonlinear relaxation to effectively perform physically correct particle-based material
simulation. They have the advantage of allowing the user to individually set the
local material properties of each particle. The disadvantage is that many physical
parameters of active and passive material types must be experimentally derived.
2.1.4 Fabrication
Cho et al. [2009] review several manufacturing processes for soft biomimetic robots.
The vast majority of soft elastomer robots rely on the processes of soft lithography
[Xia and Whitesides, 1998] and/or shape deposition manufacturing [Cham et al.,
2002]. Specifically, for soft fluidic elastomer robots this fabrication process generally
consists of three steps as shown in Figure 2-2: (1) Two elastomer layers are molded
through a casting process using pourable silicone rubber. The mold used for the outer
layer contains a model of the desired channel structure. When cast, the outer layer
contains a negative of this channel structure. The mold used for the constraint layer
may contain fiber, paper, or a plastic film to produce the the inextensibility property
required for actuation. When the elastomer is poured, this material is effectively
embedded within the constraint layer. (2) The two layers are cured, removed from
their molds, and their joining faces are dipped in a thin layer of uncured elastomer.
(3) Lastly, the two layers are joined and cured together. The primary limitation of
this soft lithography fabrication process is that it is fundamentally 2.5D, meaning
that the robots are largely constrained to a planar morphology. This process limits
a soft robot's ability to achieve amorphous, 3D forms. Additionally, shape depo-
sition manufacturing (SDM) [Cham et al., 2002] is a cyclical, layering fabrication
process where material is iteratively deposited, shaped to the desired geometry, and
48](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-52-320.jpg)
![Molding
Dipping
Gluing
Figure 2-2: Soft lithography fabrication process for soft fluidic elastomer robots.
Reproduced with permission from Onal and Rus [2012].
embedded with components as necessary. This process enables multi-material struc-
tural assemblies that include actuators and supporting infrastructure. Additionally,
Umedachi et al. [2013] provide the first SMA actuated soft robot fabricated using 3D
printing. However, although 3D printing allows printing flexible materials in amor-
phous forms, these materials are relatively brittle with respect to casted rubbers and
are not well-suited for FEAs.
2.2 Computation and Control
Computational approaches to motion control and planning assist robots in performing
autonomous tasks. Previous research has explored computation-based approaches to
motion control and planning in the context of continuum robots with appreciable
levels of rigidity, and these are reviewed within this section. In contrast, elastomer-
based continuum robots are very well-suited to realize the concepts of morphological
computation [Pfeifer and lida, 2005] or embodied intelligence [Pfeifer et al., 2007] to
perform tasks. Morphological computation is the idea that a robot's morphology (i.e.
its form and structure) as well as material composition can be exploited to achieve
complex tasks in a computationally "cheap" manner. Embodied intelligence refers
to the theory that a robot or creature's physical embodiment (e.g. its morphology
and/or material composition) is closely coupled to its intelligence. For example,
consider the task of grasping a novel object from a bin. As opposed to precisely
49](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-53-320.jpg)
![perceiving and reconstructing the object using a suite of sensors and then planning a
fully actuated grasp where each joint of the hand is considered, embodied intelligence
would suggest combining the approximate location of the object with the capacity of
a compliant hand to passively conform to unknown object geometry to complete the
task. Existing work in this area is also reviewed here. However, to date, realizations of
body-brain control strategies for soft robots often exhibit a disproportionate reliance
on the robot's body and this translates to significant human intervention and trial-
and-error when performing novel tasks. We believe to fully realize the potential of
embodied intelligence for soft elastomer systems, equal parts computation (brain) and
body are required.
2.2.1 Models
Robot-Independent Kinematic Model
Despite the variability in continuum manipulator designs, their kinematics can of-
ten be represented using a piecewise constant curvature (PCC) model. This is the
message within a 2010 review of continuum robots by Webster and Jones [2010].
That is, Webster and Jones review several seemingly distinct kinematic modeling ap-
proaches, but show that when using a PCC modeling assumption, these approaches
yield identical robot-independent results. This assumption means each body segment
of a multi-segment arm is assumed to deform with constant curvature. An early use of
PCC modeling appears in Hannan and Walker [2003] where a bending robotic trunk
is developed.
Again as Webster and Jones [2010] describe, the transformation from configuration
space consisting of arc length L, curvature r., and plane orientation y (refer to Figure
2-3) to task space consisting of Cartesian position and orientation or pose can be
derived in multiple ways. Differential geometry [Hannan and Walker, 2003] or the
use of virtual links and a Denavit-Hartenberg (DH) approach [Jones and Walker,
2006a] are among a few of the derivations. The robot independent forward kinematic
50](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-54-320.jpg)
![The piece of ground[1] consisted of fifteen acres of cleared land, but
which, certainly, had not been cultivated for five years past; but
Herbold thought that the soil would only be the richer for that.
These fifteen acres were surrounded by a fence ten rails high, (but
which, probably, would require a little repair here and there,) and
further, a curing-house, a small kitchen, a stable, and a small crib for
Indian corn. All these edifices were detached—together with the
absolute property in one hundred and sixty acres of land covered
with splendid wood, which were to be sold at an average price of
four dollars per acre, or six hundred and forty dollars cash for the
whole, and the purchasers were to have a formal deed of
conveyance.
The price seemed extraordinarily reasonable; for, although it is true
that the so-called Congress-land, or the tract of country not yet
occupied by individuals, and belonging to the government of the
United States, is sold at the cheap price of a dollar and a quarter per
acre, yet it does not consist of any portion of cleared land, nor of
buildings, which undoubtedly must make a great difference. Dr.
Normann affirmed besides, that it was always a good sign of the
fertility of the soil of a tract of land, that people had formerly settled
on it, for that the whole surrounding district was open to them, and
of course they would not choose the worst. The committee
comprehended these reasons completely, and determined to lay the
plan before the next meeting, and make arrangements accordingly.
Young Werner had meanwhile settled himself in the same inn with
the Hehrmanns, although he had hitherto formed no definite
resolution as to his plans for the future. His heart urged him to
remain with the Society, and Dr. Normann also strongly counselled
this; but his former plans had been, first of all, to wait upon several
merchants in Philadelphia and Boston, and to deliver his letters of
introduction, in order to be enabled, under their guidance, easily and
surely to begin some new occupation, in a country where he was a
stranger. It was when things were in this position, on the second
evening, and whilst he with Pastor Hehrmann and other guests were](https://image.slidesharecdn.com/18643259-250605133057-dfe15520/85/Design-Fabrication-And-Control-Of-Soft-Robots-With-Fluidic-Elastomer-Actuators-Andrew-D-Marchese-75-320.jpg)
Design Fabrication And Control Of Soft Robots With Fluidic Elastomer Actuators Andrew D Marchese
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- 5. Design, Fabrication, and Control of Soft Robots with Fluidic Elastomer Actuators by Andrew D. Marchese B.S., B.S., Worcester Polytechnic Institute (2010) M.S., Massachusetts Institute of Technology (2012) ARCHNES MASSACHUSETTS INSTITUTE OF TECHNOLOLGY MAR 19 2015 LIBRARIES Submitted to the Department of Electrical Engineering and Computer Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering and Computer Science at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY February 2015 @ Massachusetts Institute of Technology 2015. All rights reserved. Author. .~ Signature redacted Department of Electrical Engineering and Computer Science January 16, 2015 Signature redacted Certified by ............ ..................... Daniela Rus Professor Thesis Supervisor Accepted by ............ Signature redacted j (,0 Leslie A. Kolodziej ski Chair, Department Committee on Graduate Theses
- 6. 2
- 7. Design, Fabrication, and Control of Soft Robots with Fluidic Elastomer Actuators by Andrew D. Marchese Submitted to the Department of Electrical Engineering and Computer Science on January 16, 2015, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering and Computer Science Abstract The goal of this thesis is to explore how autonomous robotic systems can be created with soft elastomer bodies powered by fluids. In this thesis we innovate in the design, fabrication, control, and experimental validation of both single and multi-segment soft fluidic elastomer robots. First, this thesis describes an autonomous fluidic elas- tomer robot that is both self-contained and capable of rapid, continuum body motion. Specifically, the design, modeling, fabrication, and control of a soft fish is detailed, focusing on enabling the robot to perform rapid escape responses. The robot employs a compliant body with embedded actuators emulating the slender anatomical form of a fish. In addition, the robot has a novel fluidic actuation system that drives body motion and has all the subsystems of a traditional robot on-board: power, actuation, processing, and control. At the core of the fish's soft body is an array of Fluidic Elastomer Actuators (FEAs). The fish is designed to emulate escape responses in ad- dition to forward swimming because such maneuvers require rapid body accelerations and continuum body motion. These maneuvers showcase the performance capabilities of this self-contained robot. The kinematics and controllability of the robot during simulated escape response maneuvers are analyzed and compared to studies on bio- logical fish. During escape responses, the soft-bodied robot is shown to have similar input-output relationships to those observed in biological fish. The major implication of this portion of the thesis is that a soft fluidic elastomer robot is shown to be both self-contained and capable of rapid body motion. Next, this thesis provides an approach to planar manipulation using soft fluidic elastomer robots. That is, novel approaches to design, fabrication, kinematic model- ing, power, control, and planning as well as extensive experimental evaluations with multiple manipulator prototypes are presented. More specifically, three viable ma- nipulator morphologies composed entirely from soft silicone rubber are explored, and these morphologies are differentiated by their actuator structures, namely: ribbed, cylindrical, and pleated. Additionally, three distinct casting-based fabrication pro- cesses are explored: lamination-based casting, retractable-pin-based casting, and lost- wax-based casting. Furthermore, two ways of fabricating a multiple DOF manipulator 3
- 8. are explored: casting the complete manipulator as a whole, and casting single DOF segments with subsequent concatenation. An approach to closed-loop configuration control is presented using a piecewise constant curvature kinematic model, real-time localization data, and novel fluidic drive cylinders which power actuation. Multi- segment forward and inverse kinematic algorithms are developed and combined with the configuration controller to provide reliable task-space position control. Building on these developments, a suite of task-space planners are presented to demonstrate new autonomous capabilities from these soft robots such as: (i) tracking a path in free-space, (ii) maneuvering in confined environments, and (iii) grasping and placing objects. Extensive evaluations of these capabilities with physical prototypes demon- strate that manipulation with soft fluidic elastomer robots is viable. Lastly, this thesis presents a robotic manipulation system capable of autonomously positioning a multi-segment soft fluidic elastomer robot in three dimensions while sub- ject to the self-loading effects of gravity. Specifically, an extremely soft robotic manip- ulator morphology that is composed entirely from low durometer elastomer, powered by pressurized air, and designed to be both modular and durable is presented. To understand the deformation of a single arm segment, a static physics-based model is developed and experimentally validated. Then, to kinematically model the multi- segment manipulator, a piece-wise constant curvature assumption consistent with more traditional continuum manipulators is used. Additionally, a complete fabrica- tion process for this new manipulator is defined and used to make multiple functional prototypes. In order to power the robot's spatial actuation, a high capacity fluidic drive cylinder array is implemented, providing continuously variable, closed-circuit gas delivery. Next, using real-time localization data, a processing and control algorithm is developed that generates realizable kinematic curvature trajectories and controls the manipulator's configuration along these trajectories. A dynamic model for this multi-body fluidic elastomer manipulator is also developed along with a strategy for independently identifying all unknown components of the system: the soft manipu- lator, its distributed fluidic elastomer actuators, as well as its drive cylinders. Next, using this model and trajectory optimization techniques locally-optimal, open-loop control policies are found. Lastly, new capabilities offered by this soft fluidic elas- tomer manipulation system are validated with extensive physical experiments. These are: (i) entering and advancing through confined three-dimensional environments, (ii) conforming to goal shape-configurations within a sagittal plane under closed-loop control, and (iii) performing dynamic maneuvers we call grabs. Thesis Supervisor: Daniela Rus Title: Professor 4
- 9. Acknowledgments This thesis was possible because of the support, guidance, and encouragement of many people. First, I have learned such an immense amount from my thesis advisor, Daniela Rus, that it is impossible to articulate. She has taught me everything from how to critically analyze, decompose, and properly address difficult technical problems to how the work we do in our lab has the potential to impact the world in profound ways. She has continually believed in my abilities as well as the vision of soft robotics. Her passion is contagious and her support is unwavering. I would also like to thank my committee members, Russ Tedrake, Rob Wood, and Tomis Lozano-P~rez for their time and guidance in developing my thesis. It is not often in life that you have the opportunity to receive counsel from such a brilliant and thoughtful group; for this I am beyond privileged. Despite everyone's schedule, my committee always found time for me and always made me feel as if I was the only item on their agenda. I owe a great deal of thanks to Russ for his patience in bringing me up to speed with Drake and for continually answering my questions no matter what time of day. Additionally, thank you to Cagdas Onal, my mentor in the Distributed Robotics Lab. He has had a profound influence on my development as a researcher and critical thinker, and most of all he was an incredible friend. Cagdas taught me everything from the casting of fluidic elastomer actuators to a holistic, integrative perspective to problem solving. With patience and plenty of proverbs, Cagdas meticulously passed on everything he knew in the area of soft robotics before leaving our lab. More recently, I owe a lot of gratitude to Robert Katzschmann for his continual help and for his extremely thorough review of my work. At a moments notice, he would stop what he was doing to review a paper, help with an experiment, or brainstorm ideas on a white board. Also, a thank you to Jose Lara, Jonathan Lambert, Yanni Coroneos, and Konrad Komorowski who all spent time as UROPs on the soft robotics project. I could not ask for a more supportive lab group than the Distributive Robotics Lab at CSAIL. In particular, colleagues like Marek Doniec, Brian Julian, Kyle Gilpin, 5
- 10. Ross Knepper, Danny Soltero, John Romanishin, Cindy Sung, Mikhail Volkov, and Andy Barry have made my doctorate a transformative experience. Outside of academia, I have my lovely wife to thank. Words really cannot begin to describe the ways in which she helped me achieve this, but I will try: On the surface, she handled every aspect of our daily lives, ensuring that I only ever had my work to worry about. To say she is selfless would be an understatement. She always listened intently, as I would explain every set-back and achievement in my work, for hours, day after day. You could go an entire lifetime and never meet a human that would give you so much of themselves. Our sauntering, conversations, and literal smelling of the roses gave me perspective and kept me living. Since I was in second grade, she has always brought out the best in me whether I was building a rocket ship out of cardboard, a Valentine's Day card out of maccaroni, or a soft robot from silicone elastomer; some things never change. Additionally, I would like to thank my entire family for their support and patience over the years and for always believing in me. Last, this work was done with support from the National Science Foundation, grant numbers NSF 1117178, NSF EAGER 1133224, NSF IIS1226883, and NSF CCF1138967 as well as NSF Graduate Research Fellowship Program, primary award number 1122374. We are grateful for this support. 6
- 11. Contents 1 Introduction 1.1 Vision . . 1.2 New C 1.2.1 1.2.2 1.2.3 1.2.4 1.3 Challen 1.3.1 1.3.2 1.3.3 1.3.4 1.4 Our A 1.4.1 1.4.2 1.4.3 1.4.4 1.5 Thesis 1.5.1 1.5.2 1.5.3 1.6 Thesis apabilities . . . . . . . . . . . . . . Safer Interactions . . . . . . . . . . Mitigating Uncertainty . . . . . .. Continuous Deformation . . . . . . Natural Form . . . . . . . . . . . . ges . . . . . . . . . . . . . . . . . . Devices . . . . . . . . . . . . . . . Hardware Processes . . . . . . . . . Models . . . . . . . . . . . . . . . . Algorithms . . . . . . . . . . . . . pproach . . . . . . . . . . . . . . . . Summary ... .............. Single Segment Soft Robots . . . . Multi-segment Planar Soft Robots Multi-segment Spatial Soft Robots Contributions . . . . . . . . . . . . Single-segment Soft Robots . . . . Multi-segment Planar Soft Robots Multi-segment Spatial Soft Robots Outline . . . . . . . . . . . . . . . . 7 19 19 21 21 22 23 23 24 25 26 28 29 30 30 32 34 37 39 39 40 41 42
- 12. 2 Related Work 43 2.1 Design and Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.1.1 Actuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.1.2 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 2.1.3 Design Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 2.1.4 Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.2 Computation and Control . . . . . . . . . . . . . . . . . . . . . . . . 49 2.2.1 M odels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.2.2 Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 2.2.3 Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 2.3 Robots: Systems and Applications . . . . . . . . . . . . . . . . . . . . 55 2.3.1 Locomotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 2.3.2 Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3 Single-Segment Soft Robots 63 3.1 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 3.2 Actuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.2.1 Fluidic Elastomer Actuator . . . . . . . . . . . . . . . . . . . 65 3.2.2 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.2.3 Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.2.4 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 3.3 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.3.1 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.3.2 Gas Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.4 Processing and Control . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.5 Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.5.1 Swimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.5.2 Escape Response . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 8
- 13. 4 Planar Multi-Segment Soft Robots 4.1 System Overview ................... 4.2 Actuation .... ....... ............ 4.2.1 Operating Principles . . . . . . . . . . 4.2.2 Actuator Morphologies . . . . . . . . . 4.2.3 Multi-Segment Manipulators . . . . . . 4.2.4 Fabrication . . . . . . . . . . . . . . . 4.3 Power . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Fluidic Drive Cylinder . . . . . . . . . 4.3.2 Fluidic Drive Cylinder Model . . . . . 4.3.3 Fluidic Drive Cylinder Implementation 4.4 Kinematic Modeling . . . . . . . . . . . . . . 4.4.1 Piecewise Constant Curvature..... 4.4.2 Single-segment Inverse Kinematics 4.4.3 Forward Kinematics . . . . . . . . . . 4.4.4 Multi-Segment Inverse Kinematics . . . 4.5 Control . . . . . . . . . . . . . 4.5.1 Main Controller..... 4.5.2 Configuration Controller 4.5.3 Configuration Tracking . 4.6 Capabilities . . . . . . . . . . . 4.6.1 Free Space Motion . . . 4.6.2 Whole Arm Planning . . 4.6.3 Grasp-and-Place . . . . 4.7 Experimental Results . . . . . . 4.7.1 Point-To-Point..... 4.7.2 Path Tracking . . . . . . 4.7.3 Confined Environment . 4.7.4 Grasp-and-Place . . . . 9 85 85 86 87 88 96 98 105 105 105 109 111 112 113 114 115 117 118 119 120 121 122 122 125 129 129 130 131 134
- 14. 5 Spatial Multi-Segment Soft Robots 5.1 System Overview . . . . . . . . . . . . . . 5.2 Actuation . . . . . . . .. . . . . . . . . . 5.2.1 Soft Manipulator Design . . . . . . 5.2.2 Alternative Designs Considered . . 5.2.3 Kinematic Modeling . . . . . . . . 5.2.4 Dynamic Model . . . . . . . . . . . 5.2.5 Manipulator Fabrication . . . . . . 5.3 Power . . . . . . . . . . . . . . . . . . . . 5.4 Processing and Control . . . . . . . . . . . 5.4.1 Kinematic Controller . . . . . . . . 5.4.2 System Identification . . . . . . . . 5.5 Capabilities . . . . . . . . . . . . . . . . . 5.5.1 Confined Environment . . . . . . . 5.5.2 Shape Fitting . . . . . . . . . . . . 5.5.3 Positioning . . . . . . . . . . . . . 5.5.4 Grabbing . . . . . . . . . . . . . . 6 Conclusion 6.1 Summary of Contributions . . . . . . . . . 6.1.1 Devices . . . . . . . . . . . . . . . 6.1.2 Hardware Processes . . . . . . . . . 6.1.3 Models . . . . . . . . . . . . . . . . 6.1.4 Algorithms . . . . . . . . . . . . . 6.2 Limitations and Near-Term Improvements 6.2.1 Single-Segment Soft Robots . . . . 6.2.2 Multi-Segment Planar Soft Robots 6.2.3 Multi-Segment Spatial Soft Robots 6.3 Lessons Learned. . . . .. . . . . . . . . . 6.4 Looking to the Future . . . . . . . . . . . 10 139 . . . . . . . . . . . . . . 139 . . . . . . . . . . . . . . 140 . . . . . . . . . . . . . . 140 . . . . . . . . . . . . . . 143 . . . . . . . . . . . . . . 144 . . . . . . . . . . . . . . 154 . . . . . . . . . . . . . . 158 . . . . . . . . . . . . . . 162 . . . . . . . . . . . . . . 163 . . . . . . . . . . . . . . 163 . . . . . . . . . . . . . . 164 . . . . . . . . . . . . . . 171 . . . . . . . . . . . . . . 171 . . . . . . . . . . . . . . 176 . . . . . . . . . . . . . . 182 . . . . . . . . . . . . . . 187 201 203 203 204 205 205 206 206 207 208 208 211
- 15. 6.4.1 How Soft is Too Soft? . . . . . . . . . . . . . . . . . . . . . . 212 6.4.2 3D Printing Soft Materials . . . . . . . . . . . . . . . . . . . . 212 6.4.3 Proprioceptive Sensing . . . . . . . . . . . . . . . . . . . . . . 212 6.4.4 Contact Modeling . . . . . . . . . . . . . . . . . . . . . . . . . 213 A Bracing 215 A.1 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 A.2 Bracing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 A.2.1 Condition I . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 A.2.2 Condition 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 A.2.3 Condition 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 A.3 Bracing Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 A.4 Bracing Simulations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 11
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- 17. List of Figures 1-1 Natural inspiration for soft machines . . . . . . . . . . . . . . . . . . 20 1-2 Elastic modulus of various materials . . . . . . . . . . . . . . . . . . . 21 1-3 An autonomous soft-bodied robot . . . . . . . . . . . . . . . . . . . . 33 1-4 Soft-bodied robotic fish with hull removed . . . . . . . . . . . . . . . 34 1-5 Two planar soft fluidic elastomer manipulator morphologies . . . . . . 35 1-6 Spatial soft fluidic elastomer manipulator and drive cylinders . . . . . 38 2-1 Common actuation approaches for soft robots. . . . . . . . . . . . . . 44 2-2 Soft lithography fabrication process . . . . . . . . . . . . . . . . . . . 49 2-3 Arc parameters used to model segment bending . . . . . . . . . . . . 51 2-4 Various soft locomotory robots. . . . . . . . . . . . . . . . . . . . . . 56 2-5 Various hard, semi-soft, and soft continuum manipulators. . . . . . . 60 3-1 Details of a soft-bodied robotic fish. . . . . . . . . . . . . . . . . . . . 64 3-2 Schematic representation of a tapered bidirectional FEA. . . . . . . . 66 3-3 Illustration of the soft fish body fabrication. . . . . . . . . . . . . . . 69 3-4 Pressure-volume profiles of fluid. . . . . . . . . . . . . . . . . . . . . . 71 3-5 Details of gas delivery mechanism . . . . . . . . . . . . . . . . . . . . 74 3-6 Robotic fish during forward swimming. . . . . . . . . . . . . . . . . . 78 3-7 Sequences depicting the soft robotic fish. . . . . . . . . . . . . . . . . 79 3-8 Escape response kinematics soft-bodied fish. . . . . . . . . . . . . . . 80 3-9 Fast-start kinematics of an angelfish. . . . . . . . . . . . . . . . . . . 81 3-10 Input-output relationship of escape response maneuvers. . . . . . . . 83 13
- 18. 4-1 An overview of the soft planar robotic manipulation system. . . . . . 86 4-2 Operating principle of a bending elastomer segment . . . . . . . . . . 87 4-3 Operative principle of producing material strain through fluidic power. 88 4-4 A conceptual representation of the ribbed segment morphology . . . . 90 4-5 A conceptual representation of the cylindrical segment morphology. 92 4-6 A conceptual representation of the pleated segment morphology. . . 94 4-7 Experimental characterizations of three actuated segment morphologies. 95 4-8 A ribbed soft manipulator prototype. . . . . . . . . . . . . . . . . . . 97 4-9 A cylindrical soft manipulator prototype. . . . . . . . . . . . . . . . . 99 4-10 A pleated soft manipulator prototype . . . . . . . . . . . . . . . . . . 100 4-11 Fabrication process for a ribbed manipulator morphology . . . . . . . 101 4-12 Fabrication process for the cylindrical manipulator morphology . . . . 102 4-13 Fabrication process for the pleated actuator morphology . . . . . . . 103 4-14 An overview of the fluidic drive cylinders . . . . . . . . . . . . . . . . 106 4-15 Parameters used in developing a simplified fluidic drive cylinder model. 107 4-16 Experimentally measured actuator compliance . . . . . . . . . . . . . 110 4-17 Experimental verification of the fluidic drive cylinder plant model . 111 4-18 Diagram depicting the driving states of the fluidic drive cylinders . 112 4-19 Visualization of the single segment inverse kinematics algorithm . 114 4-20 State flow diagram of the main controller. . . . . . . . . . . . . . . . 118 4-21 A block diagram of the manipulator's configuration controller. . . . . 120 4-22 Closed-loop curvature tracking of an arm segment . . . . . . . . . . . 121 4-23 Visualization of the Whole Arm Planning Algorithm . . . . . . . . . 124 4-24 State flow diagram of the grasp-and-place planner . . . . . . . . . . . 126 4-25 Grasp approach planner visualization . . . . . . . . . . . . . . . . . . 128 4-26 Point-to-point movement results. . . . . . . . . . . . . . . . . . . . . 130 4-27 A path tracking experimental trial. . . . . . . . . . . . . . . . . . . . 131 4-28 Line tracking results for ten trials. . . . . . . . . . . . . . . . . . . . . 132 4-29 Validation of navigation through a pipe-like environment. . . . . . . . 134 4-30 Complete set of experimental grasp-and-place trials. . . . . . . . . . . 136 14
- 19. 4-31 A time series representation of an experimental grasp-and-place trial .1 5-1 Overview of the spatial fluidic elastomer manipulation system. . . . . 140 5-2 The soft spatial manipulator. . . . . . . . . . . . . . . . . . . . . . . 141 5-3 A schematic of the spatial manipulator. . . . . . . . . . . . . . . . . . 143 5-4 Example design alternatives. . . . . . . . . . . . . . . . . . . . . . . . 144 5-5 Representation of a deformed soft spatial arm segment. . . . . . . . . 145 5-6 Verification of soft actuator model. . . . . . . . . . . . . . . . . . . . 147 5-7 True stress true strain relationship. . . . . . . . . . . . . . . . . . . . 148 5-8 Experimental validation of the proposed segment transformation. . . 152 5-9 Percent error in model predicted bend angle. . . . . . . . . . . . . . . 153 5-10 Visualization of the multi-segment dynamic model. . . . . . . . . . . 158 5-11 Spatial soft arm fabrication process. . . . . . . . . . . . . . . . . . . . 159 5-12 Multiple soft fluidic elastomer manipulators. . . . . . . . . . . . . . . 161 5-13 High capacity fluidic drive cylinders. . . . . . . . . . . . . . . . . . . 163 5-14 Reference curvature trajectory generated by controller. . . . . . . . . 165 5-15 Experimental identification of a fluidic drive cylinder. . . . . . . . . . 169 5-16 Experimental identification of a soft actuator. . . . . . . . . . . . . . 170 5-17 Passive system identification verification. . . . . . . . . . . . . . . . . 171 5-18 Minimum confining space concept . . . . . . . . . . . . . . . . . . . . 172 5-19 Soft and hard minimum confining environment comparison. . . . . . . 174 5-20 Soft and hard minimum confining volume comparison . . . . . . . . . 175 5-21 Pipe insertion experiment. . . . . . . . . . . . . . . . . . . . . . . . . 176 5-22 Results of pipe insertion experiment. . . . . . . . . . . . . . . . . . . 177 5-23 Several shape fitting error scenarios . . . . . . . . . . . . . . . . . . . 179 5-24 Shape fitting simulations . . . . . . . . . . . . . . . . . . . . . . . . . 181 5-25 Experimental evaluations of real-time configuration control . . . . . . 183 5-26 Experimental evaluations of real-time configuration control . . . . . . 184 5-27 Experimental evaluations of end-effector positioning. . . . . . . . . . 187 5-28 Feasible static solutions for spatial arm . . . . . . . . . . . . . . . . . 188 15 137
- 20. 5-29 Trajectory optimization simulations. . . . . . . . . . . . . . . . . . . 193 5-30 Locally-optimal generalized torque trajectories. . . . . . . . . . . . . 194 5-31 Cartesian state trajectories of end effector. . . . . . . . . . . . . . . . 197 5-32 Sequenced photographs from experiments two, three, and four. . . . 198 5-33 Experimental characterization of a dynamic grab maneuver. . . . . . 199 6-1 Baymax from Walt Disney's Big Hero 6. . . . . . . . . . . . . . . . . 201 A-1 Illustration of the first condition for normal force bracing . . . . . . . 217 A-2 Illustration of the second condition for bracing. . . . . . . . . . . . . 218 A-3 A depiction of the third condition for bracing. . . . . . . . . . . . . . 219 A-4 Simulation of static normal force bracing. . . . . . . . . . . . . . . . . 222 16
- 21. List of Tables 3.1 Elastic and Resistive Components of Work . . . . . . . . . . . . . . . 71 3.2 Robot Parameters Used in Modeling . . . . . . . . . . . . . . . . . . 75 4.1 Commercially Available Tools and Equipment . . . . . . . . . . . . . 104 4.2 Approximations of Fluidic Drive Cylinder Parameters . . . . . . . . . 109 4.3 Mean errors and S.D. for point-to-point movements. . . . . . . . . . . 129 4.4 Experimental Validation . . . . . . . . . . . . . . . . . . . . . . . . . 135 5.1 Segment Parameters Used in Simulation . . . . . . . . . . . . . . . . 146 5.2 Comparison between measured and model predicted deformation kine- matics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 5.3 Comparison between measured and model predicted deformation kine- matics for segment under external load . . . . . . . . . . . . . . . . . 153 5.4 Fabrication Tools and Materials . . . . . . . . . . . . . . . . . . . . . 161 5.5 Identification of Passive Arm . . . . . . . . . . . . . . . . . . . . . . 171 5.6 Dynamic motion planning with direct collocation . . . . . . . . . . . 195 5.7 Summary of Grabbing Experiments . . . . . . . . . . . . . . . . . . . 195 17
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- 23. Chapter 1 Introduction 1.1 Vision As roboticists, we often use nature as inspiration for the way robots should look, act, or think. For example, we have robots that attempt to reason like humans, run like cheetahs [Park et al., 2014a], grasp with the dexterity of human hands [Deimel and Brock, 2014], and fly with the agility of birds [Moore et al., 2014]. Accordingly, we have a tendency to benchmark the performance of these robotic systems against their biological counterparts. The manufacturing industry has demonstrated the ability of robots to outperform humans when tasks are well-defined, uncertainty is negligible, and the environment is sufficiently controlled. However, outside of these conditions the capabilities of robots are often underwhelming with respect to nature. From a technical perspective, there are many reasons for this apparent performance discrep- ancy (e.g. limitations in design, fabrication, sensing, control, and motion planning). One salient difference between the majority of current robots and natural systems is the degree of body elasticity, and soft roboticists believe this material mismatch may be a significant technical barrier inhibiting robots from reaching their full potential [Trimmer, 2014, Majidi, 2014]. Natural systems frequently leverage body elasticity to resiliently accommodate environmental variation (Fig. 1-la), passively conform to spatial uncertainty (Fig. 1-1b), and continuously deform during dexterous tasks (Fig. 1-1c). The goal of this thesis is to explore how autonomous robotic systems 19
- 24. :~ ~ (c) Figure 1-1: Nature utilizes body elasticity to: (a) resiliently accommodate environ- mental variation as illustrated by a tree branch bending to accommodate heavy snow, (b) passively conform to spatial uncertainty as shown by an elephant's trunk conform- ing to flat ground, and (c) continuously deform during dexterous tasks exemplified by a fish contorting its body during an escape-response. The image in (a) is attributed to Ville Turkkinen of Tampere, Finland and licensed under Creative Commons Deed CCO. The image in (b) is "An elephant trunk" attributed to Jenny Downing of Geneva, Switzerland and licensed under Creative Commons Attribution 2.0 Generic. The image at (c) is reproduced with permission from Figure 1 A of Goldbogen et al. 2005] can be designed to also incorporate and leverage softness. To do this, we develop ex- tremely soft robot morphologies that are radically different from today's mainstream rigid-body robotic platforms in an effort to break the mold on how we think about designing, fabricating, and controlling such systems. That is, we build robotic sys- 20 (b)
- 25. tems with bodies made entirely from soft silicone elastomer and power these bodies with pressurized compressible fluids; the robots in this thesis have approximately five orders of magnitude, or 100,000 times, greater inherent elasticity than traditional rigid-body robots (please refer to Fig. 1-2). These robots serve as archetypical soft autonomous systems. By creating radically different platforms we can begin to solve hard problems arising from the introduction of deformable materials into autonomous systems and thus inform a future where robots are destined to be softer. a FF Elastic (Young's) KiYN ~Modulus: - L.= + E =FL/A7 b S P, 10. 161 104 15 106 107 108 109 10t 10" 1012 i kiloPascal i MegaPascal 1GigaPascal Figure 1-2: (a) "The elastic (Young's) modulus scales with the ratio of the force F to the extension d of a prismatic bar with length Lo and cross-sectional area A0. (b) Young's modulus for various materials (adapted from Autumn et al. [2006])." Reprinted with permission from SOFT ROBOTICS, Volume 1, Issue 1, 2014, pp. 5-11, published by Mary Ann Liebert, Inc., New Rochelle, NY. [Majidi, 2014]. 1.2 New Capabilities 1.2.1 Safer Interactions Imagine a future where robots work alongside humans to cooperatively perform tasks [Edsinger and Kemp, 2007]; safety becomes an immediate concern [Markoff and Miller, 2014]. Although industrial-style manipulators have been transformative for structured repetitive tasks, these robots are often considered too rigid for human-centered envi- ronments where the tasks are unpredictable and the robots have to ensure that their interaction with the environment and with humans is safe. At the moment, robots 21
- 26. are isolated from humans and confined to operate behind guarding in industrial envi- ronments. Nevertheless, roboticists are constantly balancing the competing goals of safety and performance [Wyrobek et al., 2008]. Much research is aimed at equipping such hard robots with soft capabilities [De Santis et al., 2008]. For example, the inclusion of compliant transmissions function to decouple actuator and link inertia when necessary to minimize collision forces [Bicchi and Tonietti, 2004]. Common approaches to variable-impedance actuation, reviewed by Vanderborght et al. [2013], include series elastic actuators [Pratt and Williamson, 1995] and variable stiffness actuators [Tonietti et al., 2005]. However, despite these safer design morphologies, robots are still fundamentally composed of rigid components and rely on control soft- ware to guarantee safety if collisions with humans or environments occur. Soft robots offer an alternative approach. By incorporating highly deformable materials, soft robots offer the potential for mechanical compatibility between robots and humans and this offers better safety margins, as articulated by Lipson [20141. The time is ripe for inherently soft machines. 1.2.2 Mitigating Uncertainty Roboticists have optimal, time-tested solutions when tasks are well-defined and a machine's motions and interactions with its environment are predictable. However, outside of structured environments, robots must constantly deal with uncertainty. For example, if a humanoid robot were to misperceive a flight of steps within a residential home, it will likely fall and require a costly repair. Commonly we rely on tools such as a suite of sensors [Kammel et al., 2008], state-estimation [Smith et al., 1990], Bayesian models [Cassandra et al., 1996], robust controllers [Tedrake, 2009], and robust probabilistic reasoning [Thrun et al., 2006] to mitigate uncertainty. These are all very good but computationally complex solutions. An alternative approach is to develop robust and durable machines that can mitigate some of this uncertainty at the hardware level. Autonomous systems can offload computational complexity to mechanical components by incorporating soft, elastic materials into their structure. It is possible to then combine these machines with relatively simple models and control 22
- 27. algorithms to achieve performance. 1.2.3 Continuous Deformation What if robots could exhibit the dexterity and rapid continuum motion displayed by natural creatures? For example, fish can perform escape responses, or energetic bursts characterized by rapid accelerations (16 - 151 m s- 2 ) over very short durations (30 - 210 ms). This often involves the fish's body initially bending into a "C" shape exceeding 100 degrees [Domenici and Blake, 1997]. Among vertebrates, these are some of the most rapid maneuvers [Jayne and Lauder, 19931. Although biomimetic robots with finite degree-of-freedom (DOF) bodies and elctro-mechanical actuators show promising capabilities, they often cannot match the speed nor the dexterity of their natural counterparts. Such approaches only approximate naturally continuous body motion with multiple discrete links separated by fixed joints. Soft robots offer the potential to lift the limitations imposed by rigid-body kinematics, as their bodies can deform continuously under actuation. Furthermore, fluid energy can be stored and subsequently released directly into soft actuators without a costly energy conversion stage. These features make soft robots well-suited to emulate the kinematics and dexterity displayed by some natural systems. 1.2.4 Natural Form Soft materials and fabrication processes allow soft robots to realize complex, amor- phous forms [Lipson, 20141. It is prohibitively difficult to realize naturally occurring features such as continuously varying spatial surfaces and internal non-convex cavi- ties with rigid materials and standard power transmission components. Soft materials can be casted into arbitrary shapes using similar processes to that which an artist uses to create sculptures. Fluidic channels can be continuously embedded throughout these soft machines to provide form-independent power transmission and actuation. Such soft technologies profoundly expand the robotics community's ability to emulate complex biologically inspired morphologies. 23
- 28. 1.3 Challenges Although soft robots offer a promising range of new capabilities, there are surprisingly few soft machines, and even fewer soft autonomous systems. What are the technical challenges inhibiting the growth of soft robotics? To begin answering this question we can look at recent reviews of the field. As Trivedi et al. [2008] notes, soft robots are designed with either a continuously deformable backbone or no backbone at all, and although this feature provides these robots with theoretically infinite degrees of freedom, it presents a variety of technical challenges. To paraphrase Trimmer [2014], the engineering community lacks experience working with highly deformable materials. Our current tools are well-suited for applications using rigid materials; soft, nonlinear materials break many of the underlying assumptions. To paraphrase Lipson (2014], eliciting benefits from soft robots is difficult for several reasons: (i) we lack computational tools that can simulate the many DOF and nonlinear effects of soft materials; (ii) we have limited intuition when designing soft systems and few automated tools at our disposal; (iii) soft actuation methods are relatively inefficient, specifically pneumatic systems require substantial supporting hardware; (iv) the low structural impedance introduced by soft materials makes feedback control difficult and new control strategies are likely needed; (v) lastly, manufacturing processes are tailored for rigid rather than soft systems, and standardization of components is very challenging. In short, the softer we make robots the less predictable their motions become. To combat this, we need to address technical challenges on many fronts. Specifically, this thesis addresses challenges arising in the areas of (i) device design, (ii) manufacturing processes, (iii) kinematic and dynamic modeling, as well as (iv) algorithms for control and planning. By studying extreme examples of soft robots, i.e. ones made entirely from soft elastomer and powered by fluids, this thesis begins to identify appropriate morphologies, fabrication processes, motion models, computational tools, and control strategies for a growing class of robots that are designed to incorporate softness. 24
- 29. 1.3.1 Devices The concept of using very soft elastic materials to construct autonomous robots is relatively new compared to and radically different from the time-tested form and structure of traditional robotic systems. As soft roboticists, we are in the process of defining long-lasting morphologies for soft machines. Accordingly, a considerable amount of innovation is required to design functional soft machines as well as mech- anisms for driving their actuation. Performance and autonomy are competing goals in soft mobile fluidic elastomer robots. Some fluid-powered soft machines show promising capabilities like walking [Shepherd et al., 2011] and leaping [Shepherd et al., 2013a] but are primarily driven by cumbersome external hardware limiting their practical use. Conversely, there are instances of self-contained fluidic soft robots [Onal et al., 20111 [Onal and Rus, 2013]; however, because of the constraints imposed by bringing all supporting hardware onboard, the performance of these robots is severely limited when compared to rigid- bodied robots. Accordingly, one of the primary technical challenges addressed by this thesis work is: How do we advance soft-bodiedfluidic robots to be capable of rapidlyachiev- ing continuum body motion while simultaneously being self-contained? Next, we address device challenges associated with soft manipulation. Although in this design space we can relax the constraint of on-board supporting fluidic hard- ware, we encounter the competing goals of task precision and body compliance. In general, the designs of existing soft position controlled manipulators are not very soft. A fundamental limitation in designing robots to be softer and more compliant is that the robots become increasingly unconstrained, making predictable and con- trolled movement difficult. In more traditional manipulator morphologies there is a balance between compliance and internal kinematic constraints that make controlled movement feasible; however, in soft robots low durometer elastic materials effectively lower the systems' structural impedance. What is the morphology of a manipulatorwhose body and actuators are 25
- 30. composed entirely of soft elastomer but that is used for tasks requiring task-space control? Even if we can devise an appropriate manipulator morphology, what mechanisms do we use to drive its actuation? In order to continuously vary the curvature of a soft fluidic elastomer robot, input fluid energy needs to be continuously varied. Most soft robots use valves to pressurize and sequence their actuation. A common strategy is to rely on the fluidic actuator's relatively long time constant in combination with high frequency valve switching to approximate continuous fluid delivery. This strategy falls within the domain of morphological control (see Section 2.2.2) and is fundamentally limited by the fact that it uses a discrete pulse width modulation approach to control continuous motion. Furthermore, this strategy can be prohibitive as it is difficult to recover fluid energy once it is delivered to the actuator. To enable precise curvature control for soft fluidic elastomer robots this thesis addresses the following challenge: How do we deliver continuous closed-circuitfluid flow to a soft robot in order to enable continuum configurationcontrol? 1.3.2 Hardware Processes Such radically different robot morphologies cannot be built using the same processes by which engineers build traditional, rigid-body robots. Innovative approaches to fabrication are required in order to build robots composed of soft rubber and deform under fluid pressure. In the absence of fasteners, hard chassis, mechanical linkages, and other standardized components we generally rely on casting and lamination pro- cesses to realize soft robots. Cho et al. [2009] review manufacturing processes for soft robots and provide only one reference to the use of embedded molding by Dollar and Howe [2006]. Perhaps this is testament to the novelty of such processes for robotics. More recent work by Correll et al. [2010] and Onal and Rus [2012] suggests this pro- cess is well-suited for creating fluidic elastomer robots. However, before such robots can attain mainstream usage, it is necessary that we build on these contributions and devise repeatable and general methods for constructing soft machines. 26
- 31. Traditionally, roboticists sequentially construct robots. First, the frame of a robot is built and then components (e.g. motors, gears, pulleys, cables, etc) are installed on the frame to provide actuation. Fluid-powered soft robots provide the unique challenge of requiring the robot's body and actuators to be integrated, both in form and function, into one seamless system. This means at the time of forming the body we must simultaneously form actuated regions that have specific material properties and geometric profiles. The fabrication constraints and requirements of the actua- tors must fit within the fabrication constraints of the body such that both sets of constraints can be simultaneously satisfied. Accordingly, this thesis addresses the technical challenge of: How do we continuously integrate and embed fluidic actuatorsthroughout a soft-bodied robot? In order for soft robots to migrate from research environments to real-world op- erations, we must also devise a way for their bodies to take task-specific, three- dimensional forms. As within other engineering disciplines, form-function relation- ships are important in robotics. For example, in the case of building biomimetic robots, it is often necessary to emulate the anatomical form of the robot's natural counterpart to achieve proper functionality (i.e. a fish needs a slender form to reduce hydrodynamic forces such as drag). Additionally, in the case of robotic manipulators, it is often necessary to adjust the manipulator's mass, volume, and shape link by link to accomplish certain manipulation tasks (i.e. a base link may be larger than a distal link to minimize the effects of gravity). A major technical challenge addressed in this work is: How do we produce soft elastomer bodies that take on task-specific, three- dimensionalforms by means of casting and laminationprocesses? As we desire more functionality from a soft robot, we inevitably need to add more actuated DOF to their bodies. Such functional requirements increase the robot's kinematic capabilities but also add considerable complexity to the fabrication process. For example, we need ways to independently supply fluid to each actuator within each 27
- 32. body segment while not artificially constraining the robot's spatial mobility. The process is analogous to adding multiple integrated circuits (ICs) to a printed circuit board. Here, the board designer must route traces to each IC in order to supply power and connect signals while minimizing the board's overall footprint. It follows that, a challenge addressed by this thesis is: What is a scalable approachto fabricatingmulti-body soft fluidic elastomer robots? 1.3.3 Models In a 2008 review by Trivedi et al. [2008] the challenges associated with modeling soft robots were articulated: "Accurate control of soft robots requires model-based prediction of the set of possible configurations. Dynamic models that accurately describe large-scale deflections of soft robots and cover their entire workspace are currently too complicated to be used for control. Current control ap- proaches, based on simpler models, are not guaranteed to be stable or effective for large deflections (Gravagene et al. 2001). Also, including dis- tributed forces such as gravity, and structural stability of multiple section robots into control schemes is a challenging problem." This problem is further compounded by the fact that the soft robots in this the- sis have body segments composed entirely from low durometer elastomer and are actuated by fluids. This means the bodies of these soft robots undergo large and con- tinuous circumferential and longitudinal deformation due to the low elastic modulus of their material composition. Accordingly, a primary technical challenge addressed in this thesis is: What is an appropriatestatic model for the large-scaleelastic deformation of a soft fluidic body segment? 28
- 33. Next, in order to autonomously and accurately perform tasks such as point-to- point movements, pick-and-place operations, and trajectory following we must de- velop reasonably accurate multi-segment kinematic models of multi-body soft fluidic elastomer robots. Forward and inverse kinematic models are vital to virtually all manipulation motion primitives. Although these models must be accurate enough to capture the complexity of a highly compliant and highly deformable multi-segment manipulator, they must be simple enough to implement in real-time control routines. Consequently, this thesis addresses the following technical challenges: What are appropriateapproaches to modeling the forward and inverse kinematics of multi-segment soft fluidic elastomer manipulators? As articulated by Trivedi et al. [20081, to really make the concept of soft robotics a game changer we have to be able to model the dynamics of multi-body soft robots subject to gravity. This problem is exemplified by this thesis because again we are working with robots on the extreme soft end of the "soft" robotics spectrum. What are appropriateapproachesto modeling the dynamics of multi-segment soft fluidic elastomer manipulators? 1.3.4 Algorithms Soft robots are in need of automation. In order for soft fluidic elastomer robots to autonomously perform tasks we need to first develop appropriate motion control and planning algorithms for these robots. The extreme elasticity, body compliance, and fluidic power of this class of soft robots makes developing such algorithms a challenge. A fundamental requirement for automating the aforementioned soft robots is both open-loop and closed-loop control of body segment curvature. In the context of soft fluidic elastomer robots, open-loop control techniques are well-suited when desired body motions are required to be fast but not necessarily precise, whereas closed-loop techniques are favorable when desired body motions are required to be precise but not necessarily fast. Thus, this thesis must address the following challenge: 29
- 34. How do we provide open-loop and closed-loop body segment curvature con- trolfor soft fluidic elastomer robots? After the challenge of controlling a single segment's curvature is met, the next technical challenge is to have these robots position themselves within a Cartesian task- space. We need to develop algorithms that build on the capability of configuration control and leverage appropriate multi-body kinematic models to enable position control. That is: How do we repeatablyposition a multi-body soft fluidic elastomer robot? One of the primary advantages of a soft robot is that it can harmlessly conform to its environment. To enable this benefit, we must develop algorithms that build on positional controllers, devices that deliver continuously variable flow, as well as that leverage the soft material properties of this class of robots. A major question addressed by this work is: How do we autonomously allow soft fluidic elastomer robots to navigate confined environments? Additionally, soft robots should have capabilities beyond those provided by tradi- tional rigid-body robots. Our intent is to develop soft robot manipulators capable of autonomous, safe, and dynamic interactions with people and their environments. Ac- cordingly, we must develop algorithms for dynamically controlling soft robots acting under gravity in 3D environments: How do we develop algorithms that leverage a soft fluidic elastomer ma- nipulator's dynamics to increase its performance? 1.4 Our Approach 1.4.1 Summary This thesis addresses the technical challenges presented by soft robots by cyclically innovating solutions as we build multiple autonomous soft fluidic elastomer platforms. 30
- 35. These platforms gradually increase in complexity, and each platform builds upon the subsequent. First, we work with single segment soft-bodied robots and develop a fundamental understanding of this new technology. We present an autonomous and self-contained soft-bodied robot that is a significant advancement over the state of the art in this field, namely Shepherd et al. [20111 where the main innovation was fluidic actuation for a robot's body. All supporting hardware and computation was external to the mechanism. We provide a complete approach to creating autonomous soft-bodied robots with onboard computation, actuation, power, and control and describe how we achieve this through modeling, design, fabrication, and algorithms. This work brings all systems found in a traditional rigid-bodied robot onboard the soft robot: an actuation system, power system, driving electronics, and computation and control system. We develop a robotic fish to provide an instantiation of our approach to cre- ating autonomous soft-bodied robots capable of rapidly achieving continuum body motion. In this system, soft muscle-like actuators generate curvature in a continu- ously deformable, vertebrate-like body. Novel, form-independent actuator technology as well as miniaturization of supporting hardware enable the robot to take on the fun- damental anatomical structure of a fish while being self-contained and unconstrained. Next, we extend these concepts and create multi-segment planar soft fluidic elas- tomer robots. We outline an approach to designing, fabricating, and controlling pressure-operated soft robotic manipulators. Three alternative actuator morpholo- gies and three fabrication processes are explored. Forward and inverse kinematic models are presented and we show how they integrate into an autonomous control system for these robots. Arms consisting of six independently controllable segments are analyzed on their (i) single section curvature tracking, (ii) point-to-point move- ment accuracy, (iii) path tracking accuracy, and (iv) ability to maneuver in confined environments. Then, an arm is combined with a gripper and evaluated on its (v) ability to grasp and place objects. Lastly, we develop a multi-segment spatial soft manipulation system that oper- ates subject to gravity. We provide the design, fabrication, modeling, and control of 31
- 36. this system, and we explore capabilities enabled by this new soft fluidic elastomer manipulator. The arm extends our modular planar manipulator morphology and fabrication process into three spatial dimensions. We build a prototype consisting of four independently casted and serially concatenated modular segments that each move in three spatial dimensions with two degrees of freedom. We use a piece-wise constant curvature assumption to model the arm and validate this assumption on the the physical prototype. We demonstrate the arm's ability to pass through confined environments, achieved closed-loop configurations, and position itself in three dimen- sions. Additionally, we provide a dynamic model of the spatial manipulation system under a sagittal plane assumption as well as a process for identifying the model's parameters. We develop planning algorithms that leverage this dynamic model to perform new capabilities like dynamic grabbing. Experimentally, we demonstrate task precision improvement using bracing as well as dynamic positioning accuracy of 4 centimeters outside of the arm's statically reachable envelope. 1.4.2 Single Segment Soft Robots We address the following hypothesis: Hypothesis 1: A soft-bodied fluidic robot can be both capable of rapid continuum body motion and entirely self-contained ([Marchese et al., 2014d], [Marchese et al., 20131, and [Marchese et al., 2011]). We advance soft robotics by providing a method for creating and controlling au- tonomous self-contained soft-bodied systems. Specifically, we introduce a novel self- contained fluidic actuation system and control algorithms used to deliver continuum motion in soft robots. We demonstrate this soft actuation in a case study by build- ing an autonomous soft-bodied robotic fish powered by an on-board energy source; see Figure 1-3 and 1-4. The fish is novel in that it uses a soft continuum body and an innovative fluidic actuation system for the soft body. Additionally, it has onboard autonomy. That is, all power, actuation, and computational systems are located onboard. The continuum body has an embedded flexible spine and embedded 32
- 37. Figure 1-3: An autonomous soft-bodied robot that is both self-contained and capable of rapid, continuum body motion. The robot employs a compliant body with em- bedded actuators emulating the slender anatomical form of a fish. Photo courtesy of Devon Jarvis for Popular Mechanics. anatomically proportioned muscle-like actuators. The robot is capable of forward 1 swimming and performing agile maneuvers, scaled versions of an escape response . We illustrate our proposed technical approach by designing and building a soft robot fish capable of emulating the escape response of fish. A fish was chosen as a case study because it naturally exhibits: continuum body curvature, rapid motion during an escape response [Domenici and Blake, 1997, Borazjani et al., 2012], a compliant posterior that bends under hydrodynamic resistance [Wakeling and Johnston, 1999], and an anterior suitable for housing rigid supporting hardware. We evaluate the forward swimming and escape response maneuver of this soft robot in a suite of experiments. Extensive kinematic data is collected on the escape response and we compare the performance of the robot to various studies on biological fish. We show our robotic system, although on a different time scale, is able to emulate 'Escape response maneuvers are characterized by rapid body accelerations over very short du- rations and that often involve the body initially bending into a "C" shape Domenici and Blake [19971. Among vertebrates, these are some of the most rapid maneuvers Jayne and Lauder [1993] and subject of frequent study. The extremely agile behavior exhibited by fish during escape response maneuvers is central to predator-prey interactions Webb and Skadsen [19801, and accordingly escape response performance carries marked ecological significance Walker et al. [20051, Gibb et al. [2006], Domenici et al. [2008], Bergstrom [2002]. Furthermore, the behavior serves as a neurophysiological model Eaton et al. [1981, 1991]. Understanding this behavior can give scientists insights on ver- tebrate evolution Hale et al. [2002] and physiology. Recently, the hydrodynamics of the maneuver have been explored in great detail; see Borazjani et al. [2012]. 33
- 38. Figure 1-4: Left: Soft-bodied robotic fish with hull and rubber anterior cowl re- moved exposing the robot's onboard power, actuation, and computational subsys- tems. Right: A close-up of the robot with its cowl removed showing the wireless communication and control circuitry as well as the central fluid artery. Photos cour- tesy of Devon Jarvis for Popular Mechanics. the basic structure of an escape response and that the performed maneuvers have a similar input-output relationship as observed in biological fish. 1.4.3 Multi-segment Planar Soft Robots Additionally, in this thesis we address another important hypothesis: Hypothesis 2: Planar manipulation is possible with a soft fluidic elas- tomer robot. That is, a fluid powered multi-segment planar robot made entirely from soft elastomer can be precisely positioned using a closed-loop kinematic controller ([Marchese et al., 2015a], [Marchese et al., 2014c], [Marchese et al., 2014a], and [Katzschmann et al., 2015]). This thesis demonstrates that autonomous manipulation with soft fluidic elastomer robots is possible. First, we present the design and characterization of three fluidic elastomer manipulator morphologies. Each of the arm's serially connected body seg- ments are fundamentally constructed from derivatives of fluidic elastomer actuators 34
- 39. Figure 1-5: Two planar soft fluidic elastomer manipulator morphologies. Left: a manipulator prototype composed of six independently actuatable body segments. Each cylindrical segment has actuated channels embedded in its outer layer enabling the body segment to bend. Right: a six segment manipulator prototype where each rectangular body segment generates curvature using two agonist fluidic elastomer actuators separated by a thin inextensible spine. (FEAs) [Correll et al., 20101 and these actuators deform by bending about a neutral axis when pressurized [Onal et al., 2011]. Next, we provide three alternative fabri- cation approaches for reliably fabricating these manipulators. Then, a method for closed-loop positional control of these soft manipulators is developed. This capability requires two critical innovations. First, we solve the previously unaddressed problem of controlling the configuration of an entirely soft and highly compliant pneumatic arm. That is, we develop real-time, closed-loop curvature controllers that drive the bending of the manipulator's soft pneumatic body segments despite their high com- pliance and lack of kinematic constraints. Specifically, to achieve curvature control we use an array of cascaded PI and PID controllers as well as develop an array of fluidic drive cylinders. Second, we apply a simplifying piece-wise constant curvature (PCC) assumption to model the forward and inverse kinematic relationship between the arm's configuration space (i.e., segment curvatures and lengths) and task space (i.e., the pose of points along its backbone) in a manner consistent with traditional continuum manipulation literature, as reviewed by Webster and Jones 2010]. Under this assumption, we develop forward and inverse kinematics algorithms to transform between configuration and task space. 35
- 40. We combine all these developments into an aggregate system for which we create a suite of planning algorithms, and with this we achieve novel capabilities for this class of robot. First, using a Jacobian-based approach to the inverse kinematics problem, we experimentally evaluate the arm's ability to repeatably move to poses in free-space as well as track linear end-effector trajectories. Second, we provide an approach for autonomously moving a planar fluidic elas- tomer arm through a confined, pipe-like environment. We provide a computational approach to whole arm planning that finds a solution to the inverse kinematics prob- lem for this class of arms. The solution considers both the primary task of advancing the arm's end effector pose as well as the secondary task of positioning the whole arm's changing envelope in relation to the environment. Specifically, we find a trans- formation from the arm's task space to its arc space that is aware of the soft arm's entire shape. We achieve this by posing a series of constrained nonlinear optimization problems and solving for locally optimal arc space parameters. A key feature of our approach is that we do not prevent collisions, but rather minimize their likelihood. In fact, since we have designed an entirely soft and compliant robot, we can tolerate collisions. Often, the arm's ability to passively comply with the environment allows the primary task to be accomplished despite the collision. To experimentally validate the soft robot's ability to successfully advance through a confined environment, we carry out a series of experiments using a six segment soft planar manipulator. The primary goal of these experiments is to validate the whole body planner's ability to incrementally advance the robot through one of four distinct pipe-like sections. Lastly, we present a fluid powered gripper for these soft manipulators that can con- form to variations in object geometry while ensuring encapsulation of a round object. The gripper is inspired by fingers developed by Polygerinos et al. [2013] and is ad- vantageous for grasping because it exhibits high curvature, minimal radial expansion, and remains compliant during actuation. We attach this gripper to a multi-segment soft manipulator to enable grasp-and-place capabilities. We also present a planning algorithm that advances the arm through all necessary states of the grasp-and-place operation. The system first plans concentric approach circles shrinking from the ini- 36
- 41. tial end-effector pose to the object. Next, the system searches for locally optimal manipulator configurations that constrain the end-effector to lie on these approach circles so that the manipulator does not collide with the object. We experimentally validate the system's ability to repeatably and autonomously grasp-and-place ran- domly placed objects with a 7 DOF planar fluidic elastomer manipulator prototype. 1.4.4 Multi-segment Spatial Soft Robots Lastly, in this thesis we address the hypothesis: Hypothesis 3: Spatial manipulation is possible with an arm composed entirely of low durometer elastomer and powered by fluid. That is, an entirely soft fluid-powered multi-segment spatial robot subject to gravity can be autonomously positioned to accomplish tasks ([Marchese and Rus, 2015] and [Marchese et al., 2015b]). In this thesis we present a complete soft spatial manipulation system. That is, we provide the design, fabrication, and kinematic modeling of a new manipulator mor- phology: a fluid-powered three-dimensional multi-segment arm composed entirely of soft elastomer. Additionally, we develop a power system as well as processing and control algorithms that enable autonomous closed-loop control of the soft manipulator despite the self-loading effects of gravity. We show how the fluidic elastomer manip- ulator's continuum kinematics and soft material composition lead to several distinct advantages when compared to traditional rigid body manipulators. First, we show that the manipulator's soft segments deform according to constant curvature. With a constant curvature assumption [Webster and Jones, 2010], we can parameterize this N-link spatial soft manipulator with 2N joint variables. Second, the kinematics and extreme compliance of such a soft manipulator enable it to fit within and advance through confined environments. When the boundaries of the environment can be pa- rameterized by curved cylinders and its curvature is non-zero, an idealized soft fluidic elastomer manipulator will be more capable of advancing through a confined environ- ment than a manipulator with rigid links and discrete joints. We demonstrate this 37
- 42. Figure 1-6: A spatial soft fluidic elastomer manipulator composed entirely from low durometer rubber. The manipulator has four independently actuatable body seg- ments, each capable of 2 DOF bending. In this work, an external camera system is used to localize soft connectors between arm segments shown in green. Right: An array of high capacity fluidic drive cylinders are used to drive the manipulator's dis- tributed fluidic elastomer actuators. Each drive mechanism consists of a pneumatic cylinder (a) driven by an electric linear actuator (b). The primary benefits of this drive mechanism are that it is closed-circuit and allows realization of continuously variable flow profiles. concept experimentally. Third, the continuum kinematics of a soft fluidic elastomer manipulator enable a high degree of dexterity. Specifically, in an environment where a collision-free path is parameterized by a curved path, the continuum kinematics of a fluidic elastomer manipulator can generally fit the curvature of the path better than a rigid link manipulator with discrete joints and rigid links. In this thesis we also provide an approach for dynamically controlling soft robots. Through simulation and experiments we demonstrate repeatable positioning of the soft fluid-powered multi-segment spatial robot to states outside of the statically reach- able workspace in dynamic maneuvers we call grabs. Specifically, we begin by develop- ing a dynamic model for such a soft manipulation system as well as a computational strategy for identifying the model. Using this identified model and trajectory opti- mization routines, locally-optimal dynamic maneuvers are planned through iteration learning control and repeatably executed on a physical prototype. Actuation limits, 38
- 43. the self-loading effects of gravity, and the high compliance of the manipulator, phys- ical phenomena common among soft robots, are represented as constraints within the optimization. For example, consider a soft manipulator that can safely and dy- namically interact with humans by quickly grabbing objects directly from a human's hand. 1.5 Thesis Contributions The results presented in this thesis differ from prior work in design, fabrication, and control and enable new autonomous capabilities for soft robots. 1.5.1 Single-segment Soft Robots A primary contribution of this thesis is that we show a soft-bodied fluidic robot can be both capable of rapid continuum body motion and entirely self-contained. More specifically this contribution consists of: 1. A soft fluidic actuation system capable of rapidly achieving continuum body motion. 2. A static model for the non-constant bending deformation of a tapered planar fluidic elastomer actuator. 3. A method for fabricating amorphous soft bodies with embedded fluidic channel structures. 4. A self-contained soft-bodied fluidic robot with 3 DOF and 2 bidirectional ac- tuators that embodies our approach to mobile soft robotics and that emulates the planar forward swimming and escape maneuvers of biological fish. 5. Experimental evaluations with this robotic system that demonstrate the energy consumption, motion, and speed of the system and a comparison to biological fish. 39
- 44. 1.5.2 Multi-segment Planar Soft Robots Another contribution of this thesis is that we develop a soft fluidic manipulator capa- ble of grasp-and-place and planned continuous motion in environments with obstacles. This work shows that planar manipulation with soft fluidic elastomer robots is possi- ble and first to provide a comprehensive approach to design, fabrication, closed-loop control, and planning of such manipulators. Specifically this contribution consists of: 1. Three viable multi-segment manipulator morphologies that are (i) composed primarily of soft silicone rubber, (ii) powered by fluids, (iii) suitable for au- tomation; 2. Three fabrication processes for reliably manufacturing these soft fluidic elas- tomer manipulators; 3. The first method for closed-loop configuration control for a soft fluidic elastomer robot consisting of (i) a kinematic model and an algorithm for estimating the manipulator's configuration in real-time, (ii) a novel device for providing contin- uous, closed-circuit adjustment of the manipulator's fluid, and (iii) a cascaded curvature controller; 4. Task-space planning algorithms that solve the IK problem and enable these manipulators to autonomously (i) position their end-effector in free-space, (ii) maneuver in confined environments, and (iii) grasp and move objects; 5. Experiments with a soft multi-segment planar arm prototype made of 6 dis- tributed bidirectional rectangular fluidic elastomer actuators with 6 DOF demon- strating repeatable free-space positioning; 6. Experiments with a soft multi-segment planar arm prototype composed of 6 dis- tributed bidirectional cylindrical fluidic elastomer actuators with 6 DOF demon- strating repeatable maneuvering in confined environments; 7. Experiments with a soft multi-segment planar arm equipped with a gripper 40
- 45. prototype having 7 DOF demonstrating repeatable successful grasping demon- strations. 1.5.3 Multi-segment Spatial Soft Robots Another contribution of this thesis is the first autonomous three-dimensional fluidic elastomer manipulator. That is, we provide: 1. A novel multi-segment manipulator prototype (i) constructed 100% from soft silicone rubber, (ii) powered by four fluidic elastomer actuators per segment, and (iii) designed with a modular morphology suitable for automation; 2. A novel process to repeatably fabricate this manipulator; 3. A novel iterative physics-based model to understand a spatial segment's defor- mation; 4. A multi-segment kinematic model and processing and control systems that en- able the first autonomous capabilities for this manipulator type, e.g. (i) ad- vancing through a confined environment, (ii) following configuration trajectories within a sagittal plane, and (iii) positioning in 3D; 5. Evaluations in both simulation and physical experiments with a four-segment prototype evaluating capabilities i-iii above; 6. Experimental evaluations of one and two segment prototypes that quantify the accuracy of bending angle and center of mass model estimations. To the best of our knowledge, this thesis also provides the first instance of dynamic motion control for a soft fluidic elastomer robot. More specifically, we provide: 1. A dynamic model for a fluid powered spatial manipulator made entirely from soft elastomer as well as a process for fitting the model to experimental data 2. Dynamic control algorithms that allow such a 3D soft manipulator operating under gravity to be precisely positioned 41
- 46. 3. A manipulation primitive built on these dynamic control algorithms, grabbing. 4. Extensive dynamic experiments with a physical prototype demonstrating re- peatable grabbing. 1.6 Thesis Outline This thesis is organized as follows: First, in Chapter 2 we provide a current review soft robotics. Then, in Chapter 3 our work with locomotory soft fluidic elastomer robots composed of a single body segment is detailed. We develop this work in the context of a soft robotic fish, and we focus on addressing the open challenge of cre- ating a self-contained soft robot that is capable of rapid continuum body motion. Then, in Chapter 4 we extend this work to planar multi-segment soft robots. We focus on addressing the open challenges of creating and controlling multi-body flu- idic elastomer robots and develop manipulators that can advance through confined environments, grasp randomly placed objects, and track trajectories in free space. In Chapter 5 we extend our work to multi-segment soft robots that can move in three spatial dimensions subject to gravity. Here, we focus on addressing open challenges in design, fabrication, dynamic modeling, and control. We develop manipulators that can advance through confined environments, dynamically grab objects, and position an end-effector in free space. Lastly, in Chapter 6 we conclude with lessons learned and important areas for future research. 42
- 47. Chapter 2 Related Work Soft robotics is a nascent, interdisciplinary field. Just this year the journal of Soft Robotics was created to connect the rapidly growing community. This community is unique in that it merges the seemingly disjoint disciplines of biology, chemistry, robotics, artificial intelligence, material science, and biomedical engineering. Ar- guably, some of the field's most important work has just been published this year. In the following, we provide a current review of soft robotics, and when necessary, we narrow our focus to soft fluidic elastomer robots. Our review spans both the body and brains of such robots. That is, we review design and fabrication, computation and control, as well as robotic systems and applications. 2.1 Design and Fabrication 2.1.1 Actuation There are various approaches to actuating the body of a soft robot. One distinguishing feature of many soft robots is that actuators and/or power transmission systems are integrated within and distributed throughout the body. In the following we review four common actuator types, and these are also depicted in Figure 2-1. 43
- 48. Micro NiTi coil actuators Elastomer film Constraint Layer Pressurized Channels Depressurized Channels Figure 2-1: Common actuation approaches for soft robots. (a) Shape Memory Alloy (SMA) actuators [Seok et al., 2010], (b) Pneumatic Artificial Muscle (PAM) actuators [McMahan et al., 2006], (c) Fluidic Elastomer Actuators (FEAs) [Onal et al., 2011], and (d) Fiber reinforced FEAs [Galloway et al., 2013]. Tendons Originally, many hard hyper redundant and hard continuum robots [Hannan and Walker, 2003, Cieslak and Morecki, 1999, Buckingham, 2002, Gravagne and Walker, 2002, McMahan et al., 2005, Camarillo et al., 2009] used an array of servomotors or linear actuators to pull cables that move rigid connecting plates located between body segments. Some softer robots have adopted a similar actuation scheme consisting of tendons pulling rigid fixtures embedded within an elastomer body. For example, the elastomer based bio-inspired octopus arm developed in Calisti et al. [2010], Laschi et al. [2012] and Calisti et al. [2011] uses Shape Memory Alloy (SMA) actuation. Further, Seok et al. [2010] use SMA actuators within a worm-like locomotory robot (see Fig. 2-la). The basic operating principle behind SMA technology is that nickel titanium (NiTi) wire contracts under joule heating. This heating is typically produced by passing electrical current through the wire. The contracting wire can be used as an agonist actuator, similar to the way one's bicep pulls the forearm towards the body during a curl. There are also soft elastomer robots that use more traditional variable tension cables. For example, the soft-bodied fish developed by Valdivia y Alvarado and Youcef-Toumi [2006] as well as the soft arm developed by Wang et al. [2013] use 44
- 49. this actuation approach, but these both consist of only one actuated segment. Pneumatic Artificial Muscles Another common actuation scheme for soft robots involves distributed Pneumatic Artificial Muscle (PAM) actuators (see Fig. 2-1b) also known as the McKibben actu- ator. A PAM is fundamentally composed of an inflatable elastic tube surrounded by a braided mesh. Depending on the weave pattern of the braided mesh the actuator can be designed to contract or extend under input pressure. Typically these actuators are operated with driving pressures between 50 and 100 psi. These actuators have been used and studied extensively in Chou and Hannaford [1996], Tondu and Lopez [20001 and Daerden and Lefeber [2002]. Notable semi-soft robots using PAMs include [McMahan et al., 2006, Pritts and Rahn, 2004] and Kang et al. [2013]. Fluidic Elastomer Actuators A softer alternative is the Fluidic Elastomer Actuator (FEA), which is used predom- inantly throughout this thesis. The FEA is a bending actuator composed of low durometer rubber and driven by relatively low-pressure fluid, 3 to 8 psi. Its basic structure consists of two soft elastomer layers separated by a flexible but inextensible constraint. Each of these elastomer layers contains embedded fluidic channels. By pressurizing the fluid entrapped in these channels, stress is induced within the elastic material producing localized strain. This strain in combination with the relative in- extensibility of the constraint produces body segment bending (see Fig. 2-1c). FEAs can be powered pneumatically or hydraulically. Perhaps the earliest application of pneumatically actuated elastomer bending seg- ments to robotics was by Suzumori et al. [1992]. Here fiber-reinforced Flexible Mi- croactuators (FMAs) were developed and shown viable in a manipulator and multi- fingered hand. Recently, these concepts have been extended and developed into the FEA and used to build a variety of robotic systems [Shepherd et al., 2011, Ilievski et al., 2011, Onal et al., 2011, Morin et al., 2012, Martinez et al., 2013, Onal and Rus, 2013, Tolley et al., 2014a]. These robots use elastomers of varying stiffness as 45
- 50. well as cloth, paper, plastics, and even stiffer rubbers for their constraint layers. Fur- thermore, Mosadegh et al. [20141 and Polygerinos et al. [2013] have investigated more elaborate channel designs in order to reduce elastomer strain. There are also less flexible, fiber-reinforced FEAs (see Fig. 2-1d) that occupy the soft actuator space between purely elastomer FEAs and PAMs. These actuators operate with driving pressures of between 25 and 35 psi and can accordingly apply higher forces which is an advantage for many applications. There are several notable examples of fiber-reinforced FEAs in the literature Galloway et al. [2013], Bishop- Moser et al. [2012], Deimel and Brock [2013, 2014], Park et al. [2014b] and Suzumori et al. [2007]. 2.1.2 Power Fluidic power sources present many challenges for soft robots. Recently, Wehner et al. [2014] review existing pneumatic energy sources. Besides the use of compressed gas, which was proposed to the community in Marchese et al. [2013] and Marchese et al. [2014d] and detailed in Chapter 3, there are three viable alternatives. These are: (i) microcompressors, (ii) explosive combustion, and (iii) peroxide monopropellants. Microcompressors Microcompressors, as used in Tolley et al. [2014b], Katzschmann et al. [2014], and Onal and Rus [2013], are well-suited for low-flow applications where the duration of the robot's operation is of primary concern. Typically, a microcompressor converts electrical energy from lithium polymer batteries into fluid energy, and this approach makes use of the high energy density of commercial battery technology. In general the components of this power source are commercially available and easy to control. Explosive Combustion In contrast, explosive combustion, as used in Shepherd et al. [2013a] and Tolley et al. [2014a], is well-suited for high-power, high-speed applications because chemicals like 46
- 51. butane and methane offer unmatched energy densities with respect to batteries and compressed gas. However, considerable supporting hardware is required to prepare, mix, and trigger such reactions. Besides producing noise and heat, the release of energy can be difficult to control. Peroxide Monopropellant Alternatively, peroxide monopropellant, as used in Onal et al. [20111, leverages the de- composition of hydrogen peroxide into water and oxygen. By carefully, but passively controlling the introduction of a decomposition catalyst, a portable peroxide pump has been shown to slowly release gas in order to sustain driving pressures suitable for soft robot actuation. Compressed Gas Additionally, we show stored compressed gas is well-suited when high driving pressures and high maximum flow rates are required, and accordingly rapid, quiet actuation is required from a robotic system. This is primarily because fluid energy is stored and released onboard, as opposed to generated. Accordingly, no energy is converted between domains. However, because this strategy leverages compressed gas canisters whose energy densities are significantly lower than both lithium polymer batteries and the chemicals within the aforementioned reactions, the total available energy is limited and therefore the system's duration of operation can be limited. 2.1.3 Design Tools As mentioned in the introduction of this thesis, design tools for soft robots are limited with respect to the availability of design tools for more traditional rigid-body robots. Suzumori et al. [2007] use Finite Element Modeling (FEM) to analyze the bending of fiber reinforced pneumatic tube-like actuators. Specifically, hyperelastic material models are used to capture the nonlinear material properties of rubber, line elements are used to represent radial inextensibility constraints due to fiber reinforcement, 47
- 52. and the simulation is performed using the software MARC. Outside of this example, the community has generally found that iterative nonlinear finite element solvers are limited to small deformations and of limited use when modeling very soft nonlinear materials [Lipson, 2014]. VoxCAD and the Voxelyze physics engine, as used in Cheney et al. [2013] and Lehman and Stanley [2011] and reviewed by Lipson [2014], are simulation tools for very soft nonlinear materials. These tools use the concept of nonlinear relaxation to effectively perform physically correct particle-based material simulation. They have the advantage of allowing the user to individually set the local material properties of each particle. The disadvantage is that many physical parameters of active and passive material types must be experimentally derived. 2.1.4 Fabrication Cho et al. [2009] review several manufacturing processes for soft biomimetic robots. The vast majority of soft elastomer robots rely on the processes of soft lithography [Xia and Whitesides, 1998] and/or shape deposition manufacturing [Cham et al., 2002]. Specifically, for soft fluidic elastomer robots this fabrication process generally consists of three steps as shown in Figure 2-2: (1) Two elastomer layers are molded through a casting process using pourable silicone rubber. The mold used for the outer layer contains a model of the desired channel structure. When cast, the outer layer contains a negative of this channel structure. The mold used for the constraint layer may contain fiber, paper, or a plastic film to produce the the inextensibility property required for actuation. When the elastomer is poured, this material is effectively embedded within the constraint layer. (2) The two layers are cured, removed from their molds, and their joining faces are dipped in a thin layer of uncured elastomer. (3) Lastly, the two layers are joined and cured together. The primary limitation of this soft lithography fabrication process is that it is fundamentally 2.5D, meaning that the robots are largely constrained to a planar morphology. This process limits a soft robot's ability to achieve amorphous, 3D forms. Additionally, shape depo- sition manufacturing (SDM) [Cham et al., 2002] is a cyclical, layering fabrication process where material is iteratively deposited, shaped to the desired geometry, and 48
- 53. Molding Dipping Gluing Figure 2-2: Soft lithography fabrication process for soft fluidic elastomer robots. Reproduced with permission from Onal and Rus [2012]. embedded with components as necessary. This process enables multi-material struc- tural assemblies that include actuators and supporting infrastructure. Additionally, Umedachi et al. [2013] provide the first SMA actuated soft robot fabricated using 3D printing. However, although 3D printing allows printing flexible materials in amor- phous forms, these materials are relatively brittle with respect to casted rubbers and are not well-suited for FEAs. 2.2 Computation and Control Computational approaches to motion control and planning assist robots in performing autonomous tasks. Previous research has explored computation-based approaches to motion control and planning in the context of continuum robots with appreciable levels of rigidity, and these are reviewed within this section. In contrast, elastomer- based continuum robots are very well-suited to realize the concepts of morphological computation [Pfeifer and lida, 2005] or embodied intelligence [Pfeifer et al., 2007] to perform tasks. Morphological computation is the idea that a robot's morphology (i.e. its form and structure) as well as material composition can be exploited to achieve complex tasks in a computationally "cheap" manner. Embodied intelligence refers to the theory that a robot or creature's physical embodiment (e.g. its morphology and/or material composition) is closely coupled to its intelligence. For example, consider the task of grasping a novel object from a bin. As opposed to precisely 49
- 54. perceiving and reconstructing the object using a suite of sensors and then planning a fully actuated grasp where each joint of the hand is considered, embodied intelligence would suggest combining the approximate location of the object with the capacity of a compliant hand to passively conform to unknown object geometry to complete the task. Existing work in this area is also reviewed here. However, to date, realizations of body-brain control strategies for soft robots often exhibit a disproportionate reliance on the robot's body and this translates to significant human intervention and trial- and-error when performing novel tasks. We believe to fully realize the potential of embodied intelligence for soft elastomer systems, equal parts computation (brain) and body are required. 2.2.1 Models Robot-Independent Kinematic Model Despite the variability in continuum manipulator designs, their kinematics can of- ten be represented using a piecewise constant curvature (PCC) model. This is the message within a 2010 review of continuum robots by Webster and Jones [2010]. That is, Webster and Jones review several seemingly distinct kinematic modeling ap- proaches, but show that when using a PCC modeling assumption, these approaches yield identical robot-independent results. This assumption means each body segment of a multi-segment arm is assumed to deform with constant curvature. An early use of PCC modeling appears in Hannan and Walker [2003] where a bending robotic trunk is developed. Again as Webster and Jones [2010] describe, the transformation from configuration space consisting of arc length L, curvature r., and plane orientation y (refer to Figure 2-3) to task space consisting of Cartesian position and orientation or pose can be derived in multiple ways. Differential geometry [Hannan and Walker, 2003] or the use of virtual links and a Denavit-Hartenberg (DH) approach [Jones and Walker, 2006a] are among a few of the derivations. The robot independent forward kinematic 50
- 55. Another Random Scribd Document with Unrelated Content
- 56. behind him, and wearing a very thoughtful countenance; and he whistled so loud that at last Becher begged him, for Heaven's sake, to leave off. In the steerage, meanwhile, all seemed to be pacified again; the fact that Mr. Becher had offered to return them their money left no doubt as to his sincerity: and as to the other points, they were content to assent to them; all they wanted was, to have their equality acknowledged, and that the committee should see that they would not "put up" with anything. The wind blew pretty favourably from the south-southwest, and the ship flew along bravely, with all sails set, through the slightly ruffled waves. They were now off the so-called Bank of Newfoundland, and were approaching nearer and nearer to the American continent: the captain even had the lead sounded, but without as yet finding bottom. A glowing heat lay upon the water, and the burning sun shone almost perpendicularly down upon the travellers, who felt more and more the continued monotony of the voyage. Although squabbles occurred daily in the steerage, yet, in general, peace was easily restored; the spirits were at rest—almost too much at rest; for a portion of the Emigrants, especially the Oldenburghers, lay so immoveably in their berths all day, that there was no getting any fresh, healthy air below. Werner remained the whole day through upon deck, for he could not, as he declared, endure the stifling atmosphere below; and almost all the women complained bitterly of the want of pure air in their sleeping places. Pastor Hehrmann first tried to rouse these "immoveables," but in vain; then came Becher, who put to them a number of cases, showing the evil consequences of so much rest, as he called it. It was in vain. Even Siebert tried his luck, with the same want of success. The good folks lay still, and asserted quietly, "That they were quite comfortable— and that those who were not so, might go above; that they compelled no one to remain below, and could not understand why they should be compelled to go on deck." In fact, they remained
- 57. where they were; and the Committee, at their wits' end, turned at last to the Captain—he promised a remedy. At last, one fine morning, when the sun was shining warmly and refreshingly on deck, he had the idlers asked once more to come upon deck, and as the summons was unheeded, the word of command was given down both hatchways, "All on deck!—all on deck!" This, too, was unavailing; it had been tried several times already. But, when all the well-disposed had obeyed, and women and children had left the between-decks, several sailors simultaneously descended the two hatchways, four of them, provided with pots of tar and red hot irons, and two with pans of sulphur. When the latter had ignited their brimstone, the others dipped their irons in the tar, and such a vapour immediately filled the hold, that the sailors, familiar as they were with climbing up and down, could scarce find their way into the open air, where they were received with hurrahs by the Emigrants. Meanwhile, it fared very ill with the poor "immoveables," who tried in vain to find their way to the hatchways; they could neither find them nor their way back to their berths, but were obliged to wrap their jackets round their heads, and throw themselves on the ground, there, half suffocated, to await the drawing off of the dreadful smoke. But the remedy was effectual—for on the following morning, when the voices of the two sailors were heard at the hatchways, not one passenger was missing from on deck. All had now recovered—even the poor girl had got better under the careful nursing of the women, assisted by some medicines ordered by Werner, and she met with every assistance and sympathy which she could expect, under such circumstances and in such a position. But the longed-for coast now drew nearer and nearer, and the passengers, by this time grown impatient, expected daily to see the wished-for shore rise out of the blue distance; the lead had been
- 58. twice successfully cast, and the depth found announced the neighbourhood of the coast. One morning, the glad cry of "Land! land!" resounded in their ears, and before the eyes of those who were half awake could distinguish the low blue stripe, almost fading in the horizon, and stretching out towards the north-west, a charming little cutter shot towards them, with the speed of an arrow, through the waves; the flag of the United States, the stars and stripes, fluttered at the mast, and in a few minutes more the pilot, a tall, haggard-looking man, in a black dress coat, dazzling white linen, and a large gold watch-chain, sprang, with a bound, up the ship's side. With wonder, bordering upon awe, the steerage passengers gazed at the pilot, who was no sooner on board than he took upon himself the complete command of the ship, and ordered the sailors about as though he had made the whole voyage out with them. He was the first actual living American whom they had seen, and spoke real English. There remained, however, but short time for astonishment, for the wind was favourable, and the Captain announced that they should cast anchor that very evening. Hereupon every one had a variety of little matters to look after and get in order, and most of them scarcely cast another glance upon either the pilot or the land. The magnificent coast stood out more clearly and distinctly every minute; at first, the mere outline of the hills was discernible, and certain hollows and promontories—then darker and lighter spots could be distinguished—the eye was able to separate field from woodland. There a house started up—is it, perhaps, some farm, inhabited by Germans? Over yonder, there stand some single trees, and farther to the right—yes—something moves: it is a flock, there are living creatures on the shore, and the searching gaze might soon detect men—human beings—who moved backwards and forwards, and it soon even became a question of indescribable interest whether that man yonder, to the right of the projecting tree, and to
- 59. the left of the red roof, wore—a hat or a cap! Every trifle was narrowly examined, and it was only when they came nearer and nearer, and new objects were constantly crowding forward into notice, that they turned their attention to the grandeur of the whole scenery. It was a delightful view. That beautiful bay, with its meadows and its woods, fields and buildings, its forts and its many ships, bathed in the magic of a new, unknown, and long-desired country. None of the Emigrants knew yet the many cares and privations which, perhaps, awaited them there. None saw in the splendid landscape spread out before them, all the want, all the sorrow, that reign among the indwellers of this, as of every other country; they saw only the beautiful sparkling shell, and concluded that the kernel must of course be good. Towards evening, the heavy anchor rolled into the deep, and a little boat, bearing several medical men, and with a yellow flag flying, came up to them. The doctors examined the state of health of the passengers, and pronounced it satisfactory. Still, the "Hoffnung" remained this night without further communication with the shore, and it was not until the following morning that a little coasting vessel, with two schooner sails, came alongside, and took the steerage passengers on board, to conduct them to the Quarantine Buildings, where their luggage was to be examined, and they themselves were to remain for twenty-four hours longer. Here, again, their concord was near being disturbed; for the committee remained on board. Werner, however, pacified them, by the assurance that it could not be helped, for that they dared not even go on shore with them—that such was the regulation; but they would now shortly set foot on land, and every distinction would cease.
- 60. This consoled the people; they assisted to carry over their things to the Quarantine House, and were soon busily engaged studying the thousands of names which former emigrants had written in pencil upon the rough-hewn timbers of which the building was composed. Many a one found there the name of some old acquaintance, and hastened to incorporate his own in the general register. Pencils were in demand. But how many elegant verses, gnawed by the tooth of Time, passed into decay here in retirement! how many effusions of a pure poetical frenzy, seizing on the poor exile torn from his home to this foreign, friendless shore, disappeared, without a trace, among the mass of names! Werner copied some of them into his pocket book— "Now we'll all sing Hallelujah, For we are in America." Another— "For all that we've suffered I don't care one button, Now that we've plenty of fresh beef and mutton!" Although the Quarantine House was distant a few hundred yards only from the shore, (it was built like an island in the water,) yet the Emigrants had hitherto in vain asked for permission to go across. At last some boats came over, and the cheerful cry, "Ashore! ashore!" resounded from lip to lip. All, however, did not avail themselves of the permission; some would not leave their things, which stood there unprotected; others considered the fare demanded higher than suited their views; in short, there might be about fifteen, who, jumping joyously into the boat, were rowed ashore to their adopted country, whose soil they were now about to set foot on for the first time.
- 61. And now, no doubt, they fell down and kissed the longed-for land, hugged the trees, shook the Americans as their new brothers heartily by the hand, embraced them, and in their turn were received by these latter equally cordially and affectionately, and as newly acquired brethren and fellow citizens, who had just been endowed with sacred Liberty! No; they inquired for the nearest tavern, where some fresh bread, cheese, and beer, were to be had, and were laughed at by the Americans on account of their speech and their costume. But they found what they were looking for, and without bestowing a single glance at the town, which they said they should see enough of by and by, they stormed into the public room of the inn with joyful haste, "in order to get the salt taste out of their mouths," as the brewer expressed it. Their entrance was characteristic. The brewer stepped up to the bar, and in a deep, sonorous voice pronounced the single word "Beer," but with such emphasis, with such feeling, with such infinite longing, that one could see at a glance what the man had suffered since he had been deprived of its enjoyment. He knew besides that the same word signified beer in English as in his own language, and, indeed, had already intimated, on board ship, his conviction that in all languages it must be called "Beer," for that it could not be expressed otherwise. Several of the passengers had zealously studied English aboard ship; the tailor had been particularly industrious in this respect, and he now determined to make a trial of his acquirements, as he naturally supposed himself to be surrounded by Englishmen, or rather by persons who spoke nothing but English. With a face of great importance, therefore, he walked up to the bar, and asked loudly, and, as he supposed, distinctly, for a "A porschen hemm," (a portion or plateful of ham.) He was taken aback very much by the simple answer of the hostess, who, in broad German, smacking a good deal of the Swabian twang,
- 62. asked him, for Heaven's sake, to speak German, for she understood that much better than his English. The passengers were not a little pleased to meet with a countrywoman, who was already in America, and the evening passed with incredible swiftness, amidst full bowls, and good, strengthening, and long-missed food. Werner had remained but a short time beside them, and had gone and seated himself on the beach, gazing dreamily out upon the wide sea that had borne him thither. Long and steadfastly did his eye rest upon the proud ship whose red-and-white chequered flag fluttered in the fresh wind, resting upon the waters with sails taken in, like some wearied bird, and only slightly rocked by the gently heaving waves. Yonder structure contained all to which his heart was attached, and he felt almost impelled to swim across and climb up its side in infinite longing. He still sat there when deep night had sunk upon the misty expanse of waters, and the hull of the ship and the water on which it rested disappeared in the dull darkness; the sharp line of the masts alone stood out in relief against the lighter horizon, in which many a friendly star glanced through the driving clouds, when he thought that he heard something move in the bushes behind him—he looked round, he listened—all was quiet—only the lights shone from out the not distant houses, and human voices sounded from them over towards him. He arose; it began to grow cool; the night air was damp; he cast but another glance towards the peaceful ship, from whose cabin also a light now shone out, and turned towards the neighbouring inn, when two dark figures rushed upon him, and at the same instant a blow from a stick, narrowly missing his temples, at which it was aimed, descended upon him. "Help!" cried he, seizing one of his aggressors, who he now saw were negroes, by the throat; but a second better directed blow
- 63. descended with fearful force upon his forehead, protected only by a thin cap; his senses left him, and he sank down unconscious. How long he might have lain there he knew not; when he came to himself again he found himself in the midst of his travelling companions in the Quarantine-house, and the poor girl whom he had healed, and the woman whose child he had saved, supporting his head and bathing his wounds. He gazed around in astonishment, for in fact he did not at once discover where he was, and although awake, he thought he must be dreaming, when, looking up, he saw the room in which he was, from the roof of which, consisting of rough-hewn beams, a lantern was suspended, throwing a dim, indistinct light around—and he heard the words and the murmur of voices around him. But the women had observed his waking, and their cheerful call immediately brought all the emigrants round the couch of the sufferer. A hundred questions were directed to him simultaneously, and in vain did he ask himself for an explanation of what had taken place. It was some time before the tumult was allayed, and he learnt that his cry for assistance had fortunately been heard, and, as such attacks had occasionally been made in that quarter before, it had been attended to. The scoundrels, disturbed by the men who hurried towards them, had robbed him of nothing besides his purse. His pocket-book, which he carried in a coat-pocket behind, and which contained the whole of his little stock of money, had, fortunately, thanks to their speedy assistance, escaped. With his purse, he might have lost, according to his statement, some five or six dollars. But all attempts to overtake the robbers had proved vain; under cover of the night they had reached the neighbouring woods, and were secured by them from further pursuit.
- 64. Werner soon recovered, and—with a cool bandage round the wound received from the bludgeon—slept throughout the night softly and tranquilly. On the following morning a little boat carried him and two other steerage passengers to the steamboat, which was at hand, and merrily getting the steam up to start from Staaten Island for New York; but scarcely had he put foot upon its deck, before he met the eyes of Bertha, who, standing by her sister's side, had not noticed his arrival, until she caught sight of his pale face and the white handkerchief tied round his head. The blood left her cheeks, as she asked him, in a tremulous voice, what had happened; but, before he could reply, he felt the hand of Pastor Hehrmann on his shoulder, who heartily welcomed him, it is true, but also started back on seeing his pale face. Werner had to relate what had occurred, and Bertha listened with palpitating heart and half-opened lips. The remaining members of the committee now joined them, and pitied young Werner, heartily. Becher was of opinion that he had received a "striking" proof of the evil disposition of the negroes. At last, after the expiration of about half an hour, the steamer, passing rapidly through a number of small craft and vessels, went on its course towards the immense city of New York, which, with its mass of houses, surrounded by a forest of masts, spread itself out before them. The elder Siebert, who had formerly lived four years in the United States, undertook the care of their luggage, and gave directions to some carters, whose numbers he took, and then passed on, leading the way, with his travelling companions, through the, to him, familiar streets, towards Hudson-street, where they had obtained the address of a good French boarding-house; for, as Siebert assured them, there were few good German inns at New York, although their number extended to several hundreds.
- 65. Their sea voyage was thus happily accomplished, and they now only awaited the arrival of the rest of their fellow passengers, which was to take place on the following day, in order to discuss and execute their plans for the further journey, as all were agreed that too long a stay in New York was to be avoided—first, on account of the loss of time, and, secondly, of the considerable expense. Mr. Siebert promised to make inquiries forthwith as to the most advantageous neighbourhood for a settlement, and to communicate the information to the committee.
- 66. CHAPTER II. A WEEK IN NEW YORK. Hotly and oppressively did the sun shine down upon the mirror-like surface of Staaten Island Bay, the next day, when the boat, containing the steerage passengers of the Hoffnung, reached the Quay at New York, and threw its ropes ashore. The sailors had not had time to make fast before a complete flood of persons pressed forward from every side from which it was possible to get upon deck, and crowded every corner and gangway of the vessel. A great number of those who jumped on board to welcome the fresh-comers to their new home appeared to be actuated, not by curiosity only, but also by zeal to make themselves useful, and without looking round they seized upon boxes and chests, and seemed inclined to empty the whole vessel. "Hallo there! where are you off to with that chest," cried the brewer, seizing at the same time the above-mentioned article of luggage with both hands, and dragging it from the shoulders of a sturdy negro, who was just about to step on shore with it. The black, it is true, explained his intentions in few words, but as the brewer unfortunately could not understand a syllable of what he was saying, he merely shook his head, and carried back his chest to the remainder of his luggage. The same sort of thing occurred to all the rest, until at last the master of the boat interfered, drove the intruders back, and the few seamen on board, with the willing assistance of the Germans themselves, got the whole of the passengers' things on shore, and several of the emigrants kept watch by them. This last measure seemed a very necessary one, for, as carrion vultures surround a dying animal, so did carters, black
- 67. and white, surround the piled-up boxes, impatiently waiting the moment when each of them might carry off his load. Pastor Hehrmann, the elder Siebert, and Mr. Becher, now joined them, and after a hearty shaking of hands with their fellow travellers on the so longed-for terra firma, took counsel how best to lodge them properly, since they could not well all find room together in one tavern. Many had brought with them the addresses of "good" German inns in New York, obtained through acquaintances or relations who had formerly sojourned at them, and found them comfortable. Others were directed to a so-called "German Boarding House" in Pearl Street, and a large number, including nearly all the Oldenburghers, determined to remain on the Quay, where they saw three German public-houses side by side, as well to have a view of the shipping as to save the money required for the removal of their luggage, which they at once got on their own shoulders, and carried across into the "Schweitzer's Heimat," (the Switzer's Home.) Siebert advised them not to take up their quarters at these waterside public-houses, but they had made up their minds; they listened, it is true, patiently to his representations and arguments, but still went and did as they wished. Mr. Siebert now exhorted each of them to be careful in noting accurately the number of the cart which carried his property, so that, in the event of their being separated from it, they might not lose their little all, and he then started, with a portion of his fellow travellers, towards the boarding-house, whilst several two-wheeled carts, with their baggage, accompanied them. In less than two hours the whole company was scattered; and we will now follow the Oldenburghers for a moment, who, persecuted by the jokes and jeers of the carters plying on the quay, carried their heavy chests into the inn, in front of which hung a gaudy sign,
- 68. intended to represent a Swiss landscape, with the subscription "Schweitzer's Heimat." The landlord, who was a fat man, and who might have passed for a good-natured looking fellow, had it not been for a slight cast in his eye, met them at the door, and called to them, in a not-to-be- mistaken Swiss dialect, to carry their things up into the large saloon. The thing was sooner said than done—for it was no easy matter to get the colossal boxes and chests up the narrow and steep staircase. However, they succeeded at last, and found themselves in a very large roomy apartment, which might claim the title of a "saloon," and contained about twenty double beds, while beside these, in two long rows, there stood a number of boxes and bags. Immediately afterwards, their host followed, and indicated a particular corner for their luggage. "Are there more people to sleep here, then?" inquired one of the Oldenburghers, who began, perhaps, to think the thing rather uncomfortable. "Yes," replied our host, "we are a little crowded for the moment, but to-morrow many of them are going away, and if you will only make yourselves comfortable for to-night, the matter can be arranged." "And two have to sleep in one bed?" asked another. "It might happen," replied the landlord, "that we might be compelled to accommodate three in some of them; it's only for one night, and you are not spoiled—on board ship, things are worse, I know;" he laughed, and descended the steep stairs. "Yes, that's true enough—on board ship it's worse still. But upon my word, I don't see why on that account it should not be otherwise here in New York." The others comforted him with "Well, it's for one night only!" and easily pacified, they walked down to the bar-room, where a kind of barman, half sailor, half waiter, stood behind a counter covered with
- 69. unwashed glasses, and filled liquors for the guests out of pitchers and bottles. Tobacco smoke and noise filled the room, and the sound of curses and laughter, of violence and hallooing, met them at their entrance. They called for a can of cider, it is true, in an unoccupied corner—but they did not feel at home or comfortable there, and determined, at last, to go and have a look at New York. Meanwhile, Mr. Siebert had led his protegées to a somewhat more decent and better house; and the brewer, the little tailor, the shoemaker, and old Schmidt, the quondam ambassador to the committee, took a room together. But the shoemaker was in despair, for one of his chests, containing all the tools of his trade, and many other things, was nowhere to be found. He had last seen it upon the shoulders of a negro, who was walking behind the cart containing the other luggage, but distracted by the gaudily-ornamented shops, he had lost sight of the black suddenly, and neither him nor the chest did he ever see again. All inquiry was in vain, and he was now convinced how much reason Mr. Siebert had to recommend particular attention to their property. The others felt themselves the more comfortable, and the little tailor declared it was worth while to travel to America, if it were only to look at the streets and the people. Soon afterwards they were summoned to dinner, and in the large room of the house they found a long table spread, at which all of them, without distinction of rank, took their seats, and were allowed to torture their teeth with some very tough beef. The dinner was not particularly good; but a glass of cider, which they got with it, consoled them, and a stroll through the town was agreed upon by all the Germans immediately after dinner. The shoemaker alone remained behind, in order to prepare a pot of his new expeditious blacking, with which he hoped to earn something, and to reimburse himself somewhat for the loss of his chest.
- 70. But what splendour, exceeding anything they had imagined, met their eyes in the broad and handsome streets which they wandered through; what gold, and silver, and costly stuffs, gleamed in all the windows and shops; they could not gaze enough, and stopped continually at newly-discovered beauties with fresh astonishment. But they were particularly delighted with the number of small two- wheeled trucks, drawn about the streets by men, full of the finest pine-apples, cocoanuts, and oranges; and no sooner did the brewer learn that a pine-apple (which, in Germany, as he had heard, would cost a couple of dollars) might be bought here for as many groats, than he bargained for a whole armfull; the others were not behindhand, and they filled the vacuum which the dinner had left in their stomachs with fruit. The little tailor, on the other hand, could not get over his astonishment at the number of clothes'-shops, for in some streets every third house seemed to be a tailor's workshop; when stopping suddenly before one of these, as if petrified, he stared at a small shield, upon which there was this notice, both in English and German, "Five hundred Journeymen wanted." "Hallo!" he cried, "that's what I call a master. But by this and by that, he must pay good wages, if he can employ so many people! Hark ye, I'll go in and try." "What are you going to be at inside, then, Meier?" asked Schmidt, of the tailor; "haven't you engaged to go with us, and actually paid for your share of the new farm?" "Oh, that be hanged!" said the tailor; "if I could get work at such a master's, I should be much better off." "That don't signify," said the brewer; "your word is your word, and you must come with us! Who else is to sew all our clothes?" "Well," said the tailor, "but if brilliant prospects should present themselves to me here, the Committee would surely allow me to
- 71. accept them; for to remain all one's life a poor journeyman tailor ——" "All that don't matter," replied the brewer; "you've paid your deposit, and go you must! This was the object of having all the articles written down, in order that, afterwards, nobody might do as they pleased." "At all events, I'll ask the question," cried the little fellow, quickly; "a question can't hurt, and perhaps it may be of use hereafter." With these words he walked in, accompanied by the others, who were curious to see the interior of such a shop, and he was not a little astonished to find the master a German, and moreover an Israelite, who in very polite terms asked him what he wanted, and what articles he would allow him to show him? "Oh!" said the little man, rather abashed; "I'm only a tailor—and— should like to inquire after work; you have given notice outside that five hundred——" "Yes, that was three days ago," the clothes-dealer interrupted him, suddenly changing his tone altogether. "Since then, I've engaged four hundred and sixty—indeed, I should have liked to make up the five hundred, but as most of the work is already arranged, I could only pay the rest very small wages; besides, most of our summer clothing is made by sempstresses. However, you may work a week on trial. You're only just arrived, aint you?" The tailor answered in the affirmative, wondering at the same time how the man could know this. "Well, then," continued the other, "as I said, you may work a week on trial, and I'll pay your board—if we suit each other, at the end of the time, we can enter into an engagement." "We'll consider it, meanwhile," said the brewer, going away, and dragging the little tailor, who offered little resistance, after him, by his coat tails, out of the shop.
- 72. "What a lot of clothes were hanging in there!" said Schmidt, when they got outside again. "I wonder where he puts his four hundred and sixty journeymen to," said the little tailor, looking up towards the house; "that must be something like a workshop!" "He's no fool," the brewer rejoined; "he wants to get you to work a week for nothing—a pretty arrangement, that!" "But it may be the custom here, you know," said the tailor. "Oh, I wish they may get it!" replied the brewer; "if that's the custom, I won't stay in America. But, hallo! if there aint the Oldenburghers coming along!" It was them, in fact, who, like their fellow-travellers, staring into every shop, came up the street, and were not a little pleased to meet with their old acquaintances so suddenly. On board ship, they had almost ceased to look at each other, from anger and hatred; but here, in a foreign country, where everything met them coldly and indifferently, and everybody seemed to be only trying if they could squeeze money out of them in some way or other, their old quarrels had vanished, and they shook hands like brothers. Of course, they continued their stroll together, and for several hours more traversed the principal streets of New York; but who shall describe their embarrassment when the setting sun reminded them of their return, and not one of them could find their way back, or had even any idea in which direction their several inns were situate. They walked in vain, with quickened pace, through the straight streets, which all cross each other at right angles, no longer admiring the gaudy show of the wares exposed for sale—at last, not even honouring them with a glance. Suddenly, they met a man who certainly must be a German: the long blue coat—the high-crowned and broad-brimmed hat—the short pipe—there could be no mistake. Schmidt accordingly walked
- 73. confidently up to him, and taking off his hat, bade him good day, and inquired whether he had the honour to address a German. The man thus accosted, however, stared at him awhile, and seemed in doubt whether he should answer or not; at last, he drew a long whiff from his short pipe, stared at the Emigrants all round, one after the other, and answered, in a drawling tone—"Yes." "Oh, then, perhaps you can tell us the way to Perl, or Pirl Street?" (for they had all, by this time, noticed the meaning of the English word, "Yes.") "What number?" asked their countryman, who was sparing of words, looking this time upwards towards the roof of the houses. What number!—oh, yes, there they all were, but not one could remember it. Schmidt owned this at last, and added— "Well, the street can't be so very long; if we can only get to the one end of it—I know the house, if I see it again. Whereabouts is Pearl Street?" "There—and there—and there!" said their friendly countryman, pointing up the broad street in which they were standing, then down again, and then to the left, towards a cross street; and, puffing another long cloud from his pipe, left the Germans looking at each other. "There—and there—and there!" said the tailor, at last, after a pause. "Oh my! he must be making game of us—the street can't go all round about!" But the street did go all round about—at least, it took a large curve, and the poor devils might have stood there a long time, without knowing what to do, had not a more obliging countryman of theirs at last assisted them, and put them on their road again. The Committee, in the meanwhile, had made themselves pretty comfortable at the French tavern, in Hudson Street, whither several of the steerage passengers had followed them, and a large meeting
- 74. was convened to be held there on the fourth day, in order to agree upon the next measures to be taken, and to determine what was to be done. In the interim, the elder Siebert had been busily engaged collecting more accurate information concerning the interior of the country, and the fittest place for a settlement, and had made the acquaintance of a certain Dr. Normann, who promised to lend him a helping hand, as he had already, according to his own account, been serviceable to many Germans in this particular, and they could trust him the more implicitly as he did not make a business of it, but merely did it out of friendship for his countrymen. He accordingly accompanied Siebert to several vendors of land, and appeared at last, according to his statement, to have met with a particularly good thing for the emigrants. It was a piece of land in Tennessee, situate about thirty miles west of the lively little town of Jackson, where good water, a healthy locality, first-rate soil, and the neighbourhood of a navigable river, the Big Halchee, on which several mills were already erected, promised every possible advantage for settlement. Pastor Hehrmann objected that they could not very well undertake such a long land journey, because they had so much luggage; but the provident Doctor had an answer ready to this—he assured them, that their destination being only about fifteen miles from the Mississippi, they would have to travel that short distance only by land, but that every other quarter mile of their journey might be passed by water, and that either in a ship by sea to New Orleans, and thence up the Mississippi River to the mouth of the Big Halchee, which was known to every captain, or by steamer or canal-boat to the Ohio, and then down that river into the Mississippi. The latter route was determined upon unanimously by the Committee, for they would not expose themselves again to all the dangers and discomforts of a sea voyage; and the principal object of all only now remained to be fixed—viz., the price to be paid for the land. Here again there appeared to be no difficulty, for the terms were to be as follow:
- 75. The piece of ground[1] consisted of fifteen acres of cleared land, but which, certainly, had not been cultivated for five years past; but Herbold thought that the soil would only be the richer for that. These fifteen acres were surrounded by a fence ten rails high, (but which, probably, would require a little repair here and there,) and further, a curing-house, a small kitchen, a stable, and a small crib for Indian corn. All these edifices were detached—together with the absolute property in one hundred and sixty acres of land covered with splendid wood, which were to be sold at an average price of four dollars per acre, or six hundred and forty dollars cash for the whole, and the purchasers were to have a formal deed of conveyance. The price seemed extraordinarily reasonable; for, although it is true that the so-called Congress-land, or the tract of country not yet occupied by individuals, and belonging to the government of the United States, is sold at the cheap price of a dollar and a quarter per acre, yet it does not consist of any portion of cleared land, nor of buildings, which undoubtedly must make a great difference. Dr. Normann affirmed besides, that it was always a good sign of the fertility of the soil of a tract of land, that people had formerly settled on it, for that the whole surrounding district was open to them, and of course they would not choose the worst. The committee comprehended these reasons completely, and determined to lay the plan before the next meeting, and make arrangements accordingly. Young Werner had meanwhile settled himself in the same inn with the Hehrmanns, although he had hitherto formed no definite resolution as to his plans for the future. His heart urged him to remain with the Society, and Dr. Normann also strongly counselled this; but his former plans had been, first of all, to wait upon several merchants in Philadelphia and Boston, and to deliver his letters of introduction, in order to be enabled, under their guidance, easily and surely to begin some new occupation, in a country where he was a stranger. It was when things were in this position, on the second evening, and whilst he with Pastor Hehrmann and other guests were
- 76. sitting smoking a cigar, in the street before the inn, that he made the acquaintance of a young man, a German by birth, who, coming from Kentucky, had traversed nearly all the northern states, and now visited New York city for the first time. He had been in America from his childhood, and knew the country thoroughly; but he shook his head doubtfully when he heard, in the course of conversation, of the agreement which all the Germans had mutually entered into, to found a settlement in common. "My dear Mr. Hehrmann," said the young Kentuckian, "you must not be offended that a young man like myself should presume to offer you advice; but I have experience on my side. These settlements in common do no good, and you will live to see the result of yours. Somehow or other we Germans agree with difficulty (unless we absolutely must); and here, in America, there is no must in the case. The country is too large; the prospects and openings are too many and too various, and consequently societies generally dissolve themselves quickly, and for the most part in a very unpleasant manner; and besides," he continued, stepping closer, and in a suppressed voice, "I don't quite trust this Dr. Normann; I have an impression that I have met the man before somewhere, under no very honourable circumstances, but I can't exactly remember where, and therefore will not positively affirm it. However, be that as it may, take care, and pay particular attention that you have the so-called 'deed' or instrument conveying the right of property." "But come, Mr. Werner," said he to the latter, "we'll take a walk down to the quay together; there are many things to be seen there which will interest you, and besides you don't know enough of New York yet." With these words, he took Werner's arm, and lounged down Hudson-street towards the Battery, and then to the left to the waterside, to the same spot where the steerage passengers of the Hoffnung had landed a day or two before. As they were wandering along the narrow quay which separates the houses from the water, observing the arrival and departure of the shipping, they perceived an unusual crowd of people assembled in
- 77. front of one of the German taverns which stand there side by side— in fact, before that very one where the Oldenburghers had put up. They walked forward to ascertain the cause. Just as they had pressed on sufficiently to obtain a view of the entrance of the house, the door, which up to that time had been closed, was suddenly opened, and a man, who was received by the people outside with loud hurrahs, was violently ejected, and the door instantly closed behind him. A thousand different witticisms and jeers welcomed him; but he appeared neither to hear nor to see what was passing around him, but only tried to get out of the crowd. He was passing close to the two young men, when the Kentuckian laid his hand upon the man's shoulder, and exclaimed with surprise: "Müller! where do you come from? and in this blackguard hole? I thought you were quiet and contented in Indiana." "Oh, Mr. Helldorf, is that you?" replied the stranger. "Yes, bad enough to be here, and to go back thus; but the devil take this den of thieves—I've been cheated out of all that I could call mine." "But how is that possible?" asked Werner. "Possible!" said the other, laughing bitterly; "what is not possible in these German taverns in America? But come away from here; my blood boils, from merely breathing the air of the neighbourhood of this pestilent hole; come along, and I will relate to you my story, and that of thousands more, who have lost, and will lose, all they possess in the same way." The three men walked some paces in silence, side by side, when the poor German thus began:— "It is now two years since I landed here in a French ship from Havre; I had not a single acquaintance in all America, nor did I consider that I required one, but relied on my own strength and
- 78. perseverance, for I was healthy and strong, and called about fifteen dollars in ready money, and a large chest full of linen and clothes, my own: what more did I want? I went, as being near the landing- place, into this godless house. Had I only kept my eyes open, the first view must have betrayed the character of the crib to me; but, as it was, I thought I could make shift in it; paid my two dollars and a half per week for board, and tried to find work. In vain did I run about daily; the times were bad; I could not speak English, and besides I would not undertake any kind of work that I did not thoroughly understand, and thus months passed by, during which the landlord, when I returned of an evening, unsuccessful, consoled me, and obliged me to drink, at which he was always ready to give me the benefit of his company. It is true that I was not then aware that, according to an American custom, I had to pay for both glasses, as well for that which he drank as for my own; or, rather, that he chalked it up. "Ultimately, he got my last dollar, and I wanted to leave, with about fifty cents in my pocket, and go to work somewhere or other, if only for my board, but he still persuaded me to remain. He would arrange the matter, he said; something or other would turn up some of these days, and I was not to let my spirits droop; that I knew very well that I might have credit with him, and that I need have no anxiety about that. Fool that I was, I followed his advice. "Thus a fortnight more passed away, and my debt to him, for board and drink, might perhaps amount to six dollars, when, one Saturday evening, he called me aside, and declared that he could not feed me for nothing any longer, and that I must look about for a lodging elsewhere. I then informed him of my total inability to pay, which, besides, he knew very well before, and offered him some of my shirts in lieu of payment; for I told him he need not suppose that I wanted to cheat him; he declined this, on the pretence that he could not mix himself up with barter of that kind; that he wanted money, and not linen, to pay for his liquors and his provisions; and that if I were not in a position to pay money then, I had better look about
- 79. and see where I could earn some, and that, meanwhile, he should retain my chest as a security. "I was quite content—for the things would have been an incumbrance to me in my wanderings—took, therefore, two shirts and a couple of pairs of socks out of my box, and wrapped them in a pocket handkerchief, and left the remainder, with the key, in his hands, with the request to have the things occasionally taken out and exposed to the air, to prevent them from rotting. "I then left this place on foot, and, with a few cents in my pocket, made my way to Indiana, where, at last, I found work; and you know, Mr. Helldorf, how I worked there, in order to get my living honestly. When, at last, I had earned the necessary sum, beside enough to defray the journey, I came hither to redeem my box, for, meanwhile, my shirts were worn out. This morning I arrived, and went immediately to yonder rascal. Do you suppose that he knew me again? Do you suppose that he knew anything about a chest belonging to me? Confusion!—the fellow was wearing one of my own shirts at the very moment when he denied ever having seen them. I could contain myself no longer, but knocked him down; his accomplices, however, got hold of me, and turned me out of doors; and here I am again, with, the exception of a few dollars, and of much experience, as rich, or rather as poor, as before." "But you will go to a lawyer, surely," said Werner, indignantly—"won't you? That must be the shortest way." "Do you think so?" asked the German, looking sideways at him; "you have not been long in America, if you call that the shortest way; I should have costs to pay, and trouble and delay besides, and should never see an article of my linen either—that's lost; but Heaven have mercy on that rascal, if he ever crosses my path again." "Never mind, Müller," said Helldorf, deprecatingly; "like thousands of others, you have paid dearly for your experience, and should rather feel obliged to the rogue, on that account, than otherwise; another
- 80. time, keep a better look out; you know the American saying: 'No German can earn, or rather save, a cent in America until he has got rid of his last European penny.' You have now done with your European property: work hard, and you'll soon earn something again." Müller shook his head; acknowledged, however, the truth of what he heard, and, after a little reflection, shook hands with Helldorf; bowed to Werner, and went up Broadway back into the town. Young Helldorf related to his newly acquired friend many other things concerning the German inns, not only in New York, but throughout the whole United States, and which being, for the most part, established by people who are afraid of work, appear in no way to serve the convenience of travellers, but are merely money-boxes for their landlords, into which every passer-by may cast his mite, without receiving the least service, or even thanks in return. At last the two young people reached the boarding-house, in Hudson- street, and separated for the night. The Committee had undoubtedly chosen one of the best, as well as one of the most reasonable inns in New York; nevertheless, all its members were compelled to submit to the custom prevailing throughout nearly all the United States—that two people should sleep in one bed—which is only tolerable when several friends are together; and highly repulsive when one is thrown among strangers. The Committee at first refused to comply with this custom on any condition, and M. Von Schwanthal said that it was opposed to all propriety and manners; but it was of no use, the house was pretty full, and though they might perhaps have had a bed each, they would have been obliged to make room in their beds for any stranger who might chance to arrive during the night. They chose the less disagreeable alternative of being among friends, at all events, and agreed, as well as they could, about their couches. Hehrmann's family took possession of a little room to themselves.
- 81. Meanwhile it fared dreadfully with the poor Oldenburghers, at the Switzer's home, where, with admirable stoicism, packed three and three in a bed, they exposed themselves to the attacks of innumerable squadrons of bugs. They had not even wherewithal to get a light, in order to see the extent of their misery. Grumbling and swearing, they lay till morning. Sleep was out of the question; and it was only towards the approach of dawn, when their tormentors withdrew, that, completely exhausted, they fell into an uneasy, unrefreshing sleep, out of which they were shortly awakened by the screeching voice of the maid, who called them to breakfast. They reproached the landlord bitterly, and assured him that it was impossible that they could endure such another night. He, too, promised a change, and gave them his word that they should sleep more quietly next night; but, to their by no means agreeable surprise, they learned how he usually kept his word. They certainly lay somewhat more quietly, for they were so wearied that the exhausted body compelled sleep, but everything else remained as before; even their position, three in a bed, was not bettered. They, therefore, came to the heroic resolution, on the ensuing morning, to shift their quarters, cost what it might; it cost, however, the amount of a week's board, which they had been obliged to pay in advance, and of which the landlord refused to return one cent; on the contrary, he abused them besides, and told them his opinion that his house was much too good for such peasant fellows as they. Notwithstanding, they carried out their determination, and aided by a carter (a German who had spoken to them in the street,) removed to the tavern of their fellow-travellers, the situation of which they had by this time discovered. But they found these latter in no enviable condition, for the fruit, of which they had partaken so heartily, had made them all ill; and the poor little tailor was so bad that, as he said himself, "he could hardly support himself on his pins." Besides this, the brewer had met with a peculiar mishap, for when the alarm of fire arose, for the first time in the night, (which hitherto had been the case twice each night) he
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