INTRODUCTION TO ROBOTICS
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This document provides an overview of robot fundamentals including: - The three laws of robotics which govern robot behavior to protect humans. - A timeline of major developments in robotics from the 1920s to the 1990s. - The main components of an industrial robot including the manipulator, end effector, drive source, control system, and sensors. - Common robot programming methods like manual teaching, walkthrough, and offline programming. - Applications of industrial robots in areas like materials handling, machine loading, welding, and assembly. - Performance specifications that characterize robots like work volume, speed, accuracy, load capacity, and repeatability.
INTRODUCTION TO ROBOTICS
- 1. UNIT 1 FUNDAMENTALS OF ROBOTS Mr.R PREM KUMAR , ME MECHANICAL ENGINEERING KALAIGNAR KARUNANIDHI INSTITUTE OF TECHNOLOGY COIMBATORE - 641402
- 2. 2 Robotics History Three Laws of Robotics: 1. A robot may not injure a human being, or, through inaction, allow a human being to come to harm. 2. A robot must obey the orders given it by human beings except where such orders would conflict with the First Law. 3. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.
- 3. Robotics Timeline • 1922 Czech author Karel Capek wrote a story called Rossum’s Universal Robots and introduced the word “Rabota”(meaning worker) • 1954 George Devol developed the first programmable Robot. • 1955 Denavit and Hartenberg developed the homogenous transformation matrices • 1962 Unimation was formed, first industrial Robots appeared. • 1973 Cincinnati Milacron introduced the T3 model robot, which became very popular in industry. • 1990 Cincinnati Milacron was acquired by ABB
- 5. ROBOT • Defined by Robotics Industry Association (RIA) as – a re-programmable, multifunctional manipulator designed to move material, parts, tools or specialized devices through variable programmed motion for a variety of tasks • Possess certain anthropomorphic characteristics – mechanical arm – sensors to respond to input – Intelligence to make decisions
- 6. Robot Accessories A Robot is a system, consists of the following elements, which are integrated to form a whole: • Manipulator / Rover : This is the main body of the Robot and consists of links, joints and structural elements of the Robot. • End Effector : This is the part that generally handles objects, makes connection to other machines, or performs the required tasks. It can vary in size and complexity from a endeffector on the space shuttle to a small gripper
- 7. Accessories • Acutators : Actuators are the muscles of the manipulators. Common types of actuators are servomotors, stepper motors, pneumatic cylinders etc. • Sensors : Sensors are used to collect information about the internal state of the robot or to communicate with the outside environment. Robots are often equipped with external sensory devices such as a vision system, touch and tactile sensors etc which help to communicate with the environment • Controller : The controller receives data from the computer, controls the motions of the actuator and coordinates these motions with the sensory feedback information.
- 8. Motivation for using robots to perform task which would otherwise be performed by humans. • Safety • Efficiency • Reliability • Worker Redeployment • Cost reduction The Advent of Industrial Robots
- 9. – Arm or Manipulator – End effectors – Drive Source – Control Systems – Sensors Main Components of Industrial Robots
- 10. Arm or Manipulator • The main anthropomorphic element of a robot. • In most cases the degrees of freedom depends on the arm • The work volume or reach mostly depends on the functionality of the Arm
- 11. End Effectors Grippers – Mechanical Grippers – Suction cups or vacuum cups – Magnetized grippers – Hooks – Scoops (to carry fluids) Device attached to the robot’s wrist to perform a specific task
- 12. Tools – Spot Welding gun – Arc Welding tools – Spray painting gun – Drilling Spindle – Grinders, Wire brushes – Heating torches End Effectors Device attached to the robot’s wrist to perform a specific task
- 13. Sensors in robotics Types of sensors : – Tactile sensors (touch sensors, force sensors, tactile array sensors) – Proximity and range sensors (optical sensors, acoustical sensors, electromagnetic sensors) – Miscellaneous sensors (transducers and sensors which sense variables such temperature, pressure, fluid flow, thermocouples, voice sensors) – Machine vision systems
- 14. Sensors in robotics Uses of sensors: – Safety monitoring – Interlocks in work cell control – Part inspection for quality control – Determining positions and related information about objects
- 15. Sensors in robotics Desirable features of sensors: Accuracy Operation range Speed of response Calibration Reliability Cost and ease of operation
- 16. Work Envelope concept • Depending on the configuration and size of the links and wrist joints, robots can reach a collection of points called a Workspace. • Alternately Workspace may be found empirically, by moving each joint through its range of motions and combining all space it can reach and subtracting what space it cannot reach
- 18. WRIST • typically has 3 degrees of freedom – Roll involves rotating the wrist about the arm axis – Pitch up-down rotation of the wrist – Yaw left-right rotation of the wrist • End effector is mounted on the wrist
- 19. WRIST MOTIONS
- 20. Point-to-Point Control • Only the end points are programmed, the path used to connect the end points are computed by the controller • user can control velocity, and may permit linear or piece wise linear motion • Feedback control is used during motion to ascertain that individual joints have achieved desired location
- 21. • Often used hydraulic drives, recent trend towards servomotors • loads up to 500lb and large reach • Applications – pick and place type operations – palletizing – machine loading
- 22. Continuous Path Controlled • In addition to the control over the endpoints, the path taken by the end effector can be controlled • Path is controlled by manipulating the joints throughout the entire motion, via closed loop control • Applications: – spray painting, polishing, grinding, arc welding
- 23. Robot Anatomy • Manipulator consists of joints and links – Joints provide relative motion – Links are rigid members between joints – Various joint types: linear and rotary – Each joint provides a “degree-of-freedom” – Most robots possess five or six degrees-of- freedom • Robot manipulator consists of two sections: – Body-and-arm – for positioning of objects in the robot's work volume – Wrist assembly – for orientation of objects Base Link0 Joint1 Link2 Link3Joint3 End of Arm Link1 Joint2
- 24. Manipulator Joints • Translational motion – Linear joint (type L) – Orthogonal joint (type O) • Rotary motion – Rotational joint (type R) – Twisting joint (type T) – Revolving joint (type V)
- 25. Joint Notation Scheme • Uses the joint symbols (L, O, R, T, V) to designate joint types used to construct robot manipulator • Separates body-and-arm assembly from wrist assembly using a colon (:) • Example: TLR : TR • Common body-and-arm configurations …
- 26. Polar Coordinate Body-and-Arm Assembly • Notation TRL: • Consists of a sliding arm (L joint) actuated relative to the body, which can rotate about both a vertical axis (T joint) and horizontal axis (R joint)
- 27. Cylindrical Body-and-Arm Assembly • Notation TLO: • Consists of a vertical column, relative to which an arm assembly is moved up or down • The arm can be moved in or out relative to the column
- 28. Cartesian Coordinate Body-and-Arm Assembly • Notation LOO: • Consists of three sliding joints, two of which are orthogonal • Other names include rectilinear robot and x-y-z robot
- 29. Jointed-Arm Robot • Notation TRR:
- 30. SCARA Robot • Notation VRO • SCARA stands for Selectively Compliant Assembly Robot Arm • Similar to jointed-arm robot except that vertical axes are used for shoulder and elbow joints to be compliant in horizontal direction for vertical insertion tasks
- 31. Wrist Configurations • Wrist assembly is attached to end-of-arm • End effector is attached to wrist assembly • Function of wrist assembly is to orient end effector – Body-and-arm determines global position of end effector • Two or three degrees of freedom: – Roll – Pitch – Yaw • Notation :RRT
- 32. Example • Sketch following manipulator configurations • (a) TRT:R, (b) TVR:TR, (c) RR:T. Solution: T R T V (a) TRT:R R T R T R TR R (c) RR:T(b) TVR:TR
- 33. •Manual Cams, stops etc •Walkthrough (Lead-through) Manually move the arm, record to memory • Manual teaching Teach pendant • Off-line programming Similar to NC part programming VAL, RAPT Programming Robots
- 34. • Material Handling/Palletizing • Machine Loading/Unloading • Arc/Spot Welding • Water jet/Laser cutting • Spray Coating • Gluing/Sealing • Investment casting • Processing operations • Assembly • Inspection Applications
- 35. • Size of the working envelope • Precision of movement – Control resolution – Accuracy – Repeatability •Lifting capability •Number of robot axes •Speed of movement – maximum speed – acceleration/deceleration time •Motion control – path control – velocity control •Types of drive motors – hydraulic – electric – pneumatic Performance Specifications of Industrial Robots
- 36. Determined by – Physical configurations – Size – Number of axes – The robot mounted position (overhead gantry, wall- mounted, floor mounted, on tracks) – Limits of arm and joint configurations – The addition of an end-effector can move or offset the entire work volume Work Volume Spatial region within which the end of the robot’s wrist can be manipulated
- 37. Depends on the position control system, feedback measurement, and mechanical accuracy Spatial Resolution Smallest increment of motion at the wrist end that can be controlled by the robot
- 38. • One half of the distance between two adjacent resolution points • Affected by mechanical Inaccuracies • Manufacturers don’t provide the accuracy (hard to control) Accuracy Capability to position the wrist at a target point in the work volume
- 39. • Repeatability errors form a random variable. • Mechanical inaccuracies in arm, wrist components • Larger robots have less precise repeatability values Repeatability Ability to position back to a point that was previously taught
- 40. • The lifting capability provided by manufacturer doesn’t include the weight of the end effector • Usual Range 2.5lb-2000lb • Condition to be satisfied: Load Capability > Total Wt. of workpiece +Wt. of end effector + Safety range Weight Carrying Capacity
- 41. •Acceleration/deceleration times are crucial for cycle time. •Determined by – Weight of the object – Distance moved – Precision with which object must be positioned Speed of Movement Speed with which the robot can manipulate the end effector
- 42. • Path control - how accurately a robot traces a given path (critical for gluing, painting, welding applications); • Velocity control - how well the velocity is controlled (critical for gluing, painting applications) • Types of control path: - point to point control (used in assembly, palletizing, machine loading); - continuous path control/walkthrough (paint spraying, welding). - controlled path (paint spraying, welding). Motion Control
- 43. • Degree of freedom - one joint one degree of freedom • Simple robots - 3 degrees of freedom in X,Y,Z axis • Modern robot arms have up to 6 degrees of freedom • XYZ, Roll, Pitch and Yaw • The human arm can be used to demonstrate the degrees of freedom. • Crust Crawler- 5 degrees of freedom Degrees of Freedom
- 44. Robot Applications (Configurations/Characteristics) SCARA Robot (Selective Compliance Assembly Robot Arm) Characteristics: •Repeatability: < 0.025mm (high) •No. of axes: min 4 axes • Vertical motions smoother, quicker, precise (due to dedicated vertical axis) • Good vertical rigidity, high compliance in the horizontal plane. •Working envelope: range < 1000mm •Payload:10- 100 kg •Speed: fast 1000-5000mm/s Applications: •Precision, high-speed, light assembly
- 45. Robot Applications (Configurations/Characteristics) Cylindrical Coordinate Robot Characteristics: •Wide range of sizes •Repeatability: vary 0.1-0.5mm •No. of axes: min 3 arm axes (2 linear) •Working envelope: typically large (vertical stroke as long as radial stroke) • The structure is not compact. •Payload: 5 - 250kg •Speed: 1000mm/s, average •Cost: inexpensive for their size and payload Applications: •Small robots: precision small assembly tasks •Large robots: material handling, machine loading/unloading.
- 46. Robot Applications (Configurations/Characteristics) Vertical Articulated Arm Robot Characteristics: •Repeatability: 0.1-0.5mm (large sizes not adequate for precision assembly) •No. of axes: 3 rotary arm-axes, 2-3 additional wrist axis (excellent wrist articulation) •Working envelope: large relative to the size, Structure compact, but not so rigid •Payload: 5-130kg •Tool tip speed: fast 2000mm/s Applications: Welding, painting, sealing, deburring, and material handling
- 47. Robot Applications (Configurations/Characteristics) Spherical Coordinate Robot Characteristics: •Repeatability: poor 0.5-1mm •No. of axes: 3 arm-axes (1 linear radial), 1-2 additional wrist-axes. •Working envelope: large vertical envelope relative to the unit size •Payload: 5-100 kg •Speed: low (linear motions are not smooth and accurate- require coordination of multiple axes) Applications: Material handling, spot welding, machine loading
- 48. Robot Applications (Configurations/Characteristics) Cartesian Coordinate Robot Characteristics: •Repeatability: high (0.015-0.1) •No. of axes: 3 linear arm-axis, •Working envelope:relative large •Payload:5- 100kg •Speed: fast Applications: Precise assembly, arc welding, gluing, material handling
- 49. Robot Applications (Configurations/Characteristics) Gantry Robot Characteristics: •Repeatability: 0.1-1mm •No. of axes: 3 linear traverse-axes, 1-3 additional wrist axes •Working envelope: very large •Payload: vary function of size, support very heavy 10-1000kg •Speed: low for large masses Applications: Handling very large parts, moving material on long distances, welding, gluing.
- 50. Types of robots • Industrial robots(welding, handling, painting, AGV) • Domestic robots(vacuum cleaners, surveillance) • Medical robots(surgery) • Service robots(data gathering, lifting) • Military robots(bomb disposal, transportance) • Entertainment robots(toy, motion simulator) • Space robots(space station) • Hobby and competition robots • Explorer robots(underground mine, walking undersea) • Laboratory robots(pharmaceutical robots) • Sequence robots • Playback robots
- 51. Thank you
- 52. UNIT II ROBOT DRIVE SYSTEMS AND END EFFECTORS R.PREM KUMAR AP – MECH KIT , CBE
- 54. 2004 3 There are basically Four types of power sources 1. Pneumatic drive • Preferred for smaller robots • Less expensive than electric or hydraulic robots • Suitable for relatively less degrees of freedom design • Suitable for simple pick and place application • Relatively cheaper
- 55. Pneumatic drive
- 56. 2004 5 2. Hydraulic drive • Provide fast movements • Preferred for moving heavy parts • Preferred to be used in explosive environments • Occupy large space area • There is a danger of oil leak to the shop floor
- 57. Hydraulic drive
- 58. 2004 7 3. Electric drive • Slower movement compare to the hydraulic robots • Good for small and medium size robots • Better positioning accuracy and repeatability • Stepper motor drive: open loop control • DC motor drive: closed loop control • Cleaner environment • The most used type of drive in industry
- 59. Electric drive
- 61. 4. Mechanical drives • When the various driving methods like hydraulic, pneumatic, electrical servo motors and stepping motors are used in robots, it is necessary to get the motion in linear or rotary fashion. • When motors are used, rotary motion is converted to linear motion through rack and pinion gearing, lead screws, worm gearing or bail screws.
- 62. Mechanical drives Rack and Pinion Movement: • The pinion is in mesh with rack (gear of infinite radius). If the rack is fixed, the pinion will rotate. • The rotary motion of the pinion will be converted to linear motion of the carriage.
- 63. Ball Screws: • Sometimes lead screws rotate to drive the nut along a track. But simple lead screws cause friction and wear, causing positional inaccuracy. • Therefore ball bearing screws are used in robots as they have low friction. The balls roll between the nut and the screw. • A cage is provided for recirculation of the balls. The rolling friction of the ball enhances transmission efficiency to about 90%.
- 64. Gear Trains: • Gear trains use spur, helical and worm gearing. A reduction of speed, change of torque and angular velocity are possible. • Positional errors are caused due to backlash in the gears.
- 65. Moments and Forces • There are many forces acting about a robot • Correct selection of servo - determined by required torque • Moments = Force x Distance • Moments = Load and robot arm • Total moment calculation • Factor of safety- 20%
- 66. Actuators Actuators – Converts some form of energy to mechanical work . Motors - Control the movement of a robot. Identified as Actuators there are three common types • DC Motor • Stepper Motor • Servo motor Servo motor
- 67. DC MOTORS • Most common and cheapest • Powered with two wires from source • Draws large amounts of current • Cannot be wired straight from a Peripheral Interface Controller • Does not offer accuracy or speed control
- 68. STEPPER MOTORS • Stepper has many electromagnets • Stepper controlled by sequential turning on and off of magnets • Each pulse moves another step, providing a step angle • Example shows a step angle of 90° • Poor control with a large angle • Better step angle achieved with the toothed disc
- 70. Step 2 Stepper motor operation
- 73. • 3.6 degree step angle => 100 steps per revolution • 25 teeth, 4 step= 1 tooth => 100 steps for 25teeth • Controlled using output Blocks on a Peripheral Interface Controller • Correct sequence essential • Reverse sequence - reverse motor DISADVANTAGES • Low efficiency - Motor draws substantial power regardless of load. • Torque drops rapidly with speed (torque is the inverse of speed). • Low accuracy. • No feedback to indicate missed steps. • Low torque to inertia ratio. Cannot accelerate loads very rapidly. • Motor gets very hot in high performance configurations. • Motor is audibly very noisy at moderate to high speeds. • Low output power for size and weight. Stepper Motor
- 74. SERVO MOTORS • Servo offers smoothest control • Rotate to a specific point • Offer good torque and control • Ideal for powering robot arms etc. • Degree of revolution is limited • Uses Encoders for feedback • Not suitable for applications which require continuous rotation
- 75. Servo Motors Operation • Pulse Width Modulation (0.75ms to 2.25ms) • Pulse Width takes servo from 0° to 150° rotation • Continuous stream every 20ms • Pulse width and output pin must be set to the controller • Pulse width can also be expressed as a variable
- 76. AC SERVO AND DC SERVO • There are two types of servo motors, AC servos and DC servos. • The main difference between the two motors is their source of power. • AC servo motors rely on an electric outlet, rather than batteries like DC servo motors. • While DC servo motor performance is dependent only on voltage. • AC servo motors are dependent on both frequency and voltage.
- 77. Open and Closed Loop Control All control systems contain three elements: (i) The control (ii) Current Amplifiers (iii) Servo Motors • The control is the Brain - reads instruction • Current amplifier receives orders from brain and sends required signal to the motor • Signal sent depends on the whether Open or Closed loop control is used.
- 78. Open Loop Control For Open Loop Control: • The controller is told where the output device needs to be • Once the controller sends the signal to motor it does not receive feedback to known if it has reached desired position • Open loop much cheaper than closed loop but less accurate
- 79. Closed Loop Control • Provided feedback to the control unit telling it the actual position of the motor. • This actual position is found using an encoder. • The actual position is compared to the desired. • Position is changed if necessary
- 80. The Encoder • Encoders give the control unit information as to the actual position of the motor. • Light shines through a slotted disc, the light sensor counts the speed and number of breaks in the light. • Allows for the calculation of speed, direction and distance travelled.
- 81. End Effectors Correct name for the “Hand” that is attached to the end of robot • Used for grasping, drilling, painting, welding, etc. • Different end effectors allow for a standard robot to perform numerous operations. • Two different types - Grippers as EE & Tools as EE End Effector
- 83. End Effectors Grippers : Mechanical, Hydraulic, Magnetic , Pneumatic etc Tools : Tools are used where a specific operation needs to be carried out such as welding, painting drilling etc. - the tool is attached to the mounting plate. Mechanical: • Two fingered most common, also multi-fingered available • Applies force that causes enough friction between object to allow for it to be lifted • Not suitable for some objects which may be delicate / brittle
- 85. Pneumatic Grippers • Suction cups from plastic or rubber • Smooth even surface required • Weight & size of object determines size and number of cups
- 86. Vacuum grippers • It also called as suction cups, can be used as gripper device for handling certain type of objects and it made up of with rubber and soft plastic. • The usual requirements on the objects to be handled are that they be flat, smooth, and clean.
- 87. Magnetic Grippers • Ferrous materials required • Electro and permanent magnets used
- 88. Magnetic grippers • Variations in part size can be tolerated • Pickup times are very fast • They have ability to handle metal parts with holes • Only one surface is required for gripping • Magnetic grippers can use either electromagnets or permanent magnets. • Electromagnetic grippers are easier to control, but require a source of dc power and an appropriate controller. • Permanent magnets do not require an external power and hence they can be used in hazardous and explosive environments, because there is no danger of sparks which might cause ignition in such environments.
- 89. Adhesive Grippers • It uses adhesive substance to grasping action on fabrics and light weight materials. • One of the potential limitation of an adhesive gripper is that the adhesive substance loses its tackiness on repeated usage. • To overcome the limitation, the adhesive material is loaded in the form of a continuous ribbon into a feeding mechanism that is attached to the robot wrist.
- 90. 2 Fingers and 3 Fingers Gripper THREE FINGERS TWO FINGERS
- 91. Hooks , Scoops as Grippers • Hooks can be used to handle containers of parts and to load and unload parts hanging from overhead conveyors. • Scoops can be used to handle certain materials in liquid or powder form.
- 92. PAINTING DRILLING WELDING Tools as End Effectors
- 93. External and Internal Grippers
- 94. Selection and Design Considerations • The industrial robots use grippers as an end effector for picking up the raw and finished work parts. • A robot can perform good grasping of objects only when it obtains a proper gripper selection and design. • Therefore, Joseph F. Engelberger, who is referred as Father of Robotics has described several factors that are required to be considered in gripper selection and design.
- 95. Selection and Design Considerations • The gripper must have the ability to reach the surface of a work part. • The change in work part size must be accounted for providing accurate positioning. • During machining operations, there will be a change in the work part size. As a result, the gripper must be designed to hold a work part even when the size is varied. • The gripper must not create any sort of distort and scratch in the fragile work parts. • The gripper must hold the larger area of a work part if it has various dimensions which will certainly increase stability and control in positioning.
- 96. Selection and Design Considerations • The replaceable fingers can also be employed for holding different work part sizes by its interchangeability facility. • Consideration must be taken to the weight of a work part. • It must be capable of grasping the work parts constantly at its centre of mass. • The speed of robot arm movement and the connection between the direction of movement and gripper position on the work part should be considered. • It must determine either friction or physical constriction helps to grip the work part. • It must consider the co-efficient of friction between the gripper and work part.
- 97. THANK YOU
- 98. Sensors and Machine vision system
- 99. Robotic Sensors Sensors provide feedback to the control systems and give the robots more flexibility. Sensors such as visual sensors are useful in the building of more accurate and intelligent robots. The sensors can be classified as follows: 2004 2
- 100. Sensor Types A. Based on power requirement: 1. Active: require external power, called excitation signal, for the operation 2. Passive: directly generate electrical signal in response to the external stimulus B. Based on sensor placement: 1. Contact sensors 2. Non-contact sensors
- 101. Why do Robots need sensors? Provides “awareness” of surroundings What’s ahead, around, “out there”? Allows interaction with environment Robot lawn mower can “see” cut grass Protection & Self-Preservation Safety, Damage Prevention Gives the robot capability to goal-seek Find colorful objects, seek goals Makes robots “interesting”
- 102. What can be sensed? Light Presence, color, intensity, direction Sound Presence, frequency, intensity, direction Heat Temperature, wavelength, magnitude, direction Chemicals Presence, concentration, identity, etc. Object Proximity Presence/absence, distance, bearing, color, etc. Physical orientation/attitude/position Magnitude, pitch, roll, yaw, coordinates, etc. Magnetic & Electric Fields Presence, magnitude, orientation Resistance Presence, magnitude, etc. Capacitance Presence, magnitude, etc. Inductance Presence, magnitude, etc.
- 103. Characteristics of sensor Range The range of a sensor indicates the limits between which the input can vary. For example, a thermocouple for the measurement of temperature might have a range of 25-225 °C. Accuracy The accuracy defines the closeness of the agreement between the actual measurement result and a true value of the measured. Sensitivity Sensitivity of a sensor is defined as the ratio of change in output value of a sensor to the per unit change in input value that causes the output change. Size, weight and volume. linearity The linearity indicates the relationship between the i/p variations and o/p variations.
- 104. • Resolution The small change in measured variable and it need minimum input. • Response time It is time to sensor o/p requires to reach certain percentage of total change. • Frequency response Range in which the system ability to resonate to the i/p remains high. • Reliability Ratio between the no. of times a system operates properly and no. of times it is tired. • Repeatability Same i/p if the o/p is different each time is to get poor.
- 105. 1. Position sensors: Position sensors are used to monitor the position of joints. Information about the position is fed back to the control systems that are used to determine the accuracy of positioning. 2004 8
- 106. Types of position sensor Piezoelectric sensor LVDT Resolvers Optical encoders Pneumatic position sensors
- 107. Piezoelectric sensor Piezoelectric sensors: a microscopic crystal structure is mounted on a mass undergoing acceleration; the piezo crystal is stressed by acceleration forces thus producing a voltage When an external electric field is applied to the crystal, the ions in each unit cell are displaced by electrostatic forces, resulting in the mechanical deformation of the whole crystal.
- 108. A piezoelectric sensor is a device that uses the piezoelectric effect to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge. The prefix piezo- is Greek for 'press' or 'squeeze'.
- 109. Application of Piezoelectric sensor
- 110. LVDT Linear variable differential transformer (LVDT) is a primary transducer used for measurement of linear displacement. It has three coils symmetrically spaced along an insulated tube. The central coil is primary coil and the other two are secondary coils. Secondary coils are connected in series in such a way that their outputs oppose each other. A magnetic core attached to the element of which displacement is to be monitored is placed inside the insulated tube. Due to an alternating voltage input to the primary coil, alternating electro-magnetic forces (emf) are generated in secondary coils. When the magnetic core is centrally placed with its half portion in each of the secondary coil regions then the resultant voltage is zero.
- 112. LDVT is a robust and precise device which produce a voltage output proportional to the displacement of a ferrous armature for measurement of robot joints or end-effectors. It is much expensive but outperforms the potentiometer transducer. A rotary variable differential transformer (RVDT) can be used for the measurement of rotation. LVDT
- 113. Applications of LVDT sensors Measurement of spool position in a wide range of servo valve applications To provide displacement feedback for hydraulic cylinders For automatic inspection of final dimensions of products being packed for dispatch To measure distance between the approaching metals during Friction welding process To continuously monitor fluid level as part of leak detection system To detect the number of currency bills dispensed by an ATM
- 114. Resolvers It has two stator windings positioned at 90 degrees. The output voltage is proportional to the sine or cosine function of the rotor's angle. The rotor is made up of a winding. A resolver is a type of rotary electrical transformer used for measuring degrees of rotation. It is considered an analog device, and has digital counterparts such as the digital resolver, rotary (or pulse) encoder.
- 115. Optical encoders It generates pulses proportional to the rotation speed of the shaft. grating light emitter light sensor decode circuitry - direction - resolution A B A leads B
- 116. The Encoder Encoders give the control unit information as to the actual position of the motor. Light shines through a slotted disc, the light sensor counts the speed and number of breaks in the light. Allows for the calculation of speed, direction and distance travelled.
- 117. Pneumatic sensor It uses the principle of a gas nozzle to detect the presence of an object without any mechanical contact. Low pressure air is supplied through angular converging nozzle surrounding a sensing hole, called o/p port. Nozzle may also be of the converging-diverging type. Sensing hole communicates through hose with switch chamber, which contains an elastic diaphragm switch, or other type of pressure-sensitive switch. Nozzle converts some of the energy of the supply air into kinetic energy
- 119. 2. Range sensors: Range sensors measure distances from a reference point to other points of importance. Range sensing is accomplished by means of television cameras or sonar transmitters and receivers. 2004 22
- 120. The distance between the object and the robot hand is measured using the range sensors Within it is range of operation. The calculation of the distance is by visual processing. Range sensors find use in robot navigation and avoidance of the obstacles in the path. In these cases the source of illumination can be light- source, laser beam or based on ultrasonic
- 121. Types of range sensors Triangulation principle Structured lighting approach Time of flight range finders Laser range meters
- 122. Triangulation principle This is the simplest of the techniques, which is easily demonstrated in the Figure. The object is swept over by a narrow beam of sharp light. The sensor focused on a small spot of the object surface detects the reflected beam of light. If ‗8‘ is the angle made by the illuminating source and ‗b‘ is the distance between source and the sensor, the distance ‗c of the sensor on the robot is given as
- 124. Structured lighting approach This approach consists of projecting a light pattern the distortion of the pattern to calculate the range. The intersection of the sheet with objects in the‘ work space yields a light stripe which is viewed through a television camera displaced a distance B from the light source. The stripe pattern is easily analyzed by a computer to obtain range information. For example, an inflection indicates a change of surface, and a break corresponds to a gap between surfaces.
- 125. In this, arrangement, the light source and camera are placed at the same height, and the sheet of light is perpendicular to the line joining the origin of the light sheet and the center of the camera lens.
- 126. Laser Ranger Finder Range 2-500 meters Resolution : 10 mm Field of view : 100 - 180 degrees Angular resolution : 0.25 degrees Scan time : 13 - 40 msec. These lasers are more immune to Dust and Fog http://www.sick.de/de/products/categories/safety/
- 127. Range Finder Time of Flight The measured pulses typically come form ultrasonic, RF and optical energy sources. D = v * t D = round-trip distance v = speed of wave propagation t = elapsed time Sound = 0.3 meters/msec RF/light = 0.3 meters / ns (Very difficult to measure short distances 1-100 meters)
- 128. 4. Proximity Sensors: They are used to sense and indicate the presence of an object within a specified distance without any physical contact. This helps prevent accidents and damage to the robot. Inductive type sensors Hall effect sensors Capacitive type sensors Ultrasonic sensors Optical sensors 2004 31
- 129. Inductive type sensors The ferromagnetic material brought close to this type of sensor results in change in position of the flux lines of the permanent magnet leading to change in inductance of the coil. The proximity inductive sensor basically consists of a wound coil located in front of a permanent magnet encased inside a rugged housing. The lead from the coil, embedded in resin is connected to the display through a connector. The effect of bringing the sensor in close proximity to a ferromagnetic material causes a change in the position of the flux lines of the permanent magnet.
- 131. Hall effect sensor • Hall effect sensors work on the principle that when a beam of charge particles passes through a magnetic field, forces act on the particles and the current beam is deflected from its straight line path. • Thus one side of the disc will become negatively charged and the other side will be of positive charge. • This charge separation generates a potential difference which is the measure of distance of magnetic field from the disc carrying current.
- 132. Capacitive type sensors Tactile sensors within this category are concerned with measuring capacitance, which made to vary under applied load. The capacitance of a parallel plate capacitor depends upon the separation of the plates and their area, so that a sensor using an elastomeric separator between the plates provides compliance such that the capacitance will vary according to applied load. Advantages: 1. Wide dynamic range 2. Linear response 3. Robust Disadvantages: 1. Susceptible to noise 2. Some dielectrics are temperature sensitive 3. Capacitance decreases with physical size ultimately limiting spatial resolution.
- 134. Ultrasonic Sensors Basic principle of operation: Emit a quick burst of ultrasound (50kHz), (human hearing: 20Hz to 20kHz) Measure the elapsed time until the receiver indicates that an echo is detected. Determine how far away the nearest object is from the sensor D = v * t D = round-trip distance v = speed of propagation(340 m/s) t = elapsed time Bat, dolphin, …
- 135. Ultrasonic Sensors Ranging is accurate but bearing has a 30 degree uncertainty. The object can be located anywhere in the arc. Typical ranges are of the order of several centimeters to 30 meters. Another problem is the propagation time. The ultrasonic signal will take 200 msec to travel 60 meters. ( 30 meters roundtrip @ 340 m/s )
- 136. Ultrasonic Sensors Polaroid ultrasonic ranging system It was developed for auto-focus of cameras. Range: 6 inches to 35 feet Ultrasonic transducer Electronic board Transducer Ringing: transmitter + receiver @ 50 KHz Residual vibrations or ringing may be interpreted as the echo signal Blanking signal to block any return signals for the first 2.38ms after transmission http://www.acroname.com/robotics/info/articles/sonar/sonar.html
- 137. Ultrasonic Sensors Applications: Distance Measurement Mapping: Rotating proximity scans (maps the proximity of objects surrounding the robot) chair Robot chair Doorway Scan moving from left to right LengthofEcho Scanning at an angle of 15º apart can achieve best results
- 138. Optical proximity Sensor Light sensors are used in cameras, infrared detectors, and ambient lighting applications Sensor is composed of photoconductor such as a photoresistor, photodiode, or phototransistor p n I + V -
- 139. Touch sensors It used to indicate that contact has been made b/w two objects without regard to the magnitude of the containing force. Simple devices are used such as limit switches, micro switches. For e.g.. They can be used to indicate the presence or absence of parts in a fixture at the pickup point along a conveyor.
- 140. Vision is the most powerful robot sensory capabilities. Enables a robot to have a sophisticated sensing mechanism that allows it to respond to its environment in intelligent and flexible manner. Therefore machine vision is the most complex sensor type. Robot vision may be defined as the process of extracting, characterizing, and interpreting information from images of a three-dimensional world. This process, also known as machine or computer vision may be subdivided into six principle areas 43
- 141. Sensing : The process that yields visual image Preprocessing : Deals with techniques such as noise reduction and enhancement of details Segmentation : The process that partitions an image into objects of interest Description: Deals with that computation of features for example size or shape, suitable for differentiating one type of objects from another. Recognition: The process that identifies these objects (for example wrench, bolt, engine block, etc.) Interpretation: Assigns meaning to an assembled recognized objects. 44
- 142. The imaging component, the “eye” or sensor, is the first link in the vision chain. Numerous sensors may be used to observe the world. There are four type of vision sensors or imaging components: 1. Point sensors It is capable of measuring light only at a single point in space. These sensor using coupled with a light source (such as LED) and used as a noncontact ‘feeler’ It also may be used to create a higher – dimensions set of vision Information by scanning across a field of view by using mechanisms such as orthogonal set of scanning mirrors 45 IMAGING COMPONENTS
- 144. 47 Image scanning using a point sensor and oscillating deflecting mirrors
- 145. 2. Line Sensor Line sensors are one- dimensional devices used to collect vision information from a real scene in the real world. The sensor most frequently used is a “line array” of photodiodes or charger-couple- device components. It operates in a similar manner to analog shift register, producing sequential, synchronized output of electrical signals, corresponding to the light intensity falling on an integrated light-collecting cell. 48 Circular and cross configurations of light sensors
- 146. 3. Planar Sensor A two dimensional configuration of the line-scan concept. Two generic types of these sensors generally in use today are scanning photomultipliers and solid-state sensors. Photomultipliers are represented by television cameras, the most common of which is the vidicon tube, which essentially an optical-to-electrical signal converter. In addition to vidicon tubes, several types of solid-state cameras are available. Many applications require the solid- state sensors because of weight and noise factor (solid- state arrays are less noisy but more expensive). This is important when mounting a camera near or on the end- effector of a robot. 49
- 147. 4. Volume Sensor A sensor that provide three- dimensional information. The sensor may obtain the information by using the directional laser or acoustic range finders. 50 Schematic representation of a triangulation range finder
- 148. IMAGE REPRESENTATION From the diagram below. F(x,y) is used to denote the two- dimensional image out of a television camera or other imaging device. “x” and “y” denote the spatial coordinates (image plane) “f” at any point (x,y) is proportional to the brightness (intensity) of the image at that point. In form suitable for computer processing, an image function f(x,y) must be digitized both spatially and in amplitude (intensity). Digitization of the spatial coordinates (x,y) will be known as image sampling, while amplitude digitization is known as intensity or grey-level quantization. The array of (N, M) rows and columns, where each sample is sampled uniformly, and also quantized in intensity is known as a digital image. Each element in the array is called image element, picture element (or pixel). 51
- 149. Effects of reducing sampling grid size. a) 512x512. b) 256x256. c) 128x128. d) 64x64. e) 32x32. 52
- 150. Effect produced by reducing the number of intensity levels while maintaining the spatial resolution constant at 512x512. The 256-, 128- and 64-levels are of acceptable quality. a) 256, b) 128, c) 64, d) 32, e) 16, f) 8, g) 4, and h) 2 levels 53
- 151. ILLUMINATION TECHNIQUES Illumination of a scene is an important factor that often affects the complexity of vision algorithms. A well designed lighting system illuminates a scene so that the complexity of the resulting image is minimised, while the information required for object detection and extraction is enhanced. Arbitrary lighting of the environment is often not acceptable because it can result in low contras images, specular reflections, shadows and extraneous details. 54
- 152. ILLUMINATION TECHNIQUES The angle of incidence of light on the object also influences the result. There are several different techniques, such as front illumination or backlighting, direct or diffuse illumination, bright-field or dark-field illumination. Direct front illumination (a ring light illuminates the objects directly, more or less parallel to the optical axis of the camera). The image appears non-uniform and mottled.
- 153. Diffuse bright-field illumination: The image appears more uniform. There is a strong contrast between the object and background, but the reflective surface of the connector 'floods' the camera, i.e. the camera is "dazzled" and no longerdetects some details. Furthermore, shadows are formed over the upper part of the connector. Diffuse dark-field illumination: Light with an oblique angle of incidence from a ring light with an angle between the front illumination unit and the object. Further detail can be seen on the connector and no shadows are formed.
- 154. Dark-field illumination: Shallow angle of incidence of the light on the object plane. The top edges of the pins, the connector and the holes appear as bright circles and can thus be easily identified busing image analysis software. The missing pin (no bright circle) and the bent pin (incorrect position) are more easily visible when compared to front illumination.
- 155. Backlighting: Light is aimed towards the camera from the rear of the object. The light only penetrates where there is nothing to obstruct it. This allows the drill holes on each side of the connector to be measured accurately. An easily detected bright spot appears in place of the missing pin.
- 157. Machine Vision It is the process of applying a range of technologies and methods to provide imaging-based automatic inspection, process control and robot guidance in industrial applications. The primary uses for machine vision are automatic inspection and robot guidance. Common MV applications include quality assurance, sorting, material handling, robot guidance, and optical gauging. creates a model of the real world from images recovers useful information about a scene from its two dimensional projections
- 158. Stages of machine vision:
- 159. Image formation Perspective Projection Orthographic projection
- 160. Image Processing Filtering, Smoothing, Thinning , Expending ,Shrinking ,Compressing
- 161. Image Segmentation Classify pixels into groups having similar characteristics
- 162. Image analyses Measurements: Size, Position, Orientation, Spatial relationship, Gray scale or color intensity
- 163. Sensing and digitizing Image sensing requires some type of image formation device such as camera and a digitizer which stores a video frame in the computer memory. We divide the sensing and digitizing into several steps. The initial step involves capturing the image of the scene with the vision camera. The image consists of relative light intensities corresponding to the various portions of the scene. These light intensities are continuous analog values which must be sampled and converted into digital form. The second step of digitizing is achieved by an analog –to –digital converter. The A/D converter is either a part of a digital video camera or the front end of a frame grabber. The choice is dependent on the type of hardware system. The frame grabber, representing the third step is an image storage and computation device which stores a given pixel array.
- 164. Image processing and analysis Fingerprint sensor Fingerprint sensor Feature Extractor Feature Extractor ID Enrollment Identification Template database
- 165. Arch Loop Whorl
- 167. THANK YOU