Robotics & CNC Machines Lecture no 3.ppt

Robotics & CNC
Robotics & CNC
Machines
Machines
Lecture 3
Lecture 3
By
By
Muhammad Asim Rehmat
Muhammad Asim Rehmat
(Assistant Professor CS&E
(Assistant Professor CS&E
UET Lhr.)
UET Lhr.)

Robotics & CNC Machine by Asim rehmat
Actuator
Actuator

An actuator is sort of the opposite of a sensor.
An actuator is sort of the opposite of a sensor.
actuator is a transducer that helps you get
actuator is a transducer that helps you get
information from a system out into the "real
information from a system out into the "real
world." actuator sort of implies physical motion.
world." actuator sort of implies physical motion.
Electromagnetic Actuators
Electromagnetic Actuators

Solenoid
Solenoid
Optical
Optical

LED, LCD
LED, LCD
Switches
Switches

Transistor, Relay, Optocoupler
Transistor, Relay, Optocoupler
Motors
Motors

DC Motor, AC Motor, Servo Motor, Stepper Motor
DC Motor, AC Motor, Servo Motor, Stepper Motor

Displacement Actuator
Displacement Actuator

An actuator that brings about the
An actuator that brings about the
mechanical movements
mechanical movements

e.g. Solenoid, motors etc.
e.g. Solenoid, motors etc.
Solenoid
Solenoid

A solenoid is an electromechanical
A solenoid is an electromechanical
device that converts electrical energy
device that converts electrical energy
into linear or rotary mechanical
into linear or rotary mechanical
motion.
motion.


When current flows in the coil,
When current flows in the coil,
a magnetic field is generated
a magnetic field is generated
around the coil.
around the coil.

The frame serves to
The frame serves to
concentrate the magnetic field
concentrate the magnetic field
such that the maximum
such that the maximum
magnetic force is exerted on
magnetic force is exerted on
the plunger.
the plunger.

The magnetic force causes the
The magnetic force causes the
plunger to be attracted to the
plunger to be attracted to the
rear of the frame or the back
rear of the frame or the back
stop and close
stop and close

All solenoids include a coil for conducting current
All solenoids include a coil for conducting current
and generating a magnetic field
and generating a magnetic field

An iron or steel shell or case to complete the
An iron or steel shell or case to complete the
magnetic circuit
magnetic circuit

And a plunger or armature for translating
And a plunger or armature for translating
motion.
motion.

Solenoids can be actuated by either DC or AC.
Solenoids can be actuated by either DC or AC.

Motors
Motors
 DC motors
DC motors
 Servo Motors
Servo Motors
 AC motors
AC motors
 Stepper Motors
Stepper Motors
 All electric motors use electromagnetic induction
All electric motors use electromagnetic induction
to generate a force on a rotational element called
to generate a force on a rotational element called
the rotor
the rotor
 The moment to rotate the rotor is created due to
The moment to rotate the rotor is created due to
the interaction of magnetic fields generated by
the interaction of magnetic fields generated by
the rotor, and the part surrounding it, which is
the rotor, and the part surrounding it, which is
fixed, and called the stator.
fixed, and called the stator.

DC and AC Motors
DC and AC Motors

In DC motors, the
In DC motors, the electromagnetic field in
electromagnetic field in
both, the rotor as well as the stator
both, the rotor as well as the stator are
are
generated by passing the DC current through the
generated by passing the DC current through the
electric
electric wire coils in them
wire coils in them. The orientation of
. The orientation of
the coils with respect to each other, and a
the coils with respect to each other, and a
commutator (which essentially changes the
commutator (which essentially changes the
direction
direction of the electromagnetic field in the rotor
of the electromagnetic field in the rotor
as the motor rotates) ensures that the interacting
as the motor rotates) ensures that the interacting
fields maintain a torque.
fields maintain a torque.

In AC motors, only the
In AC motors, only the stator has coils
stator has coils through
through
which current passes. This current creates an
which current passes. This current creates an
alternating electromagnetic field, which induces
alternating electromagnetic field, which induces
an alternating current in the rotor. The interaction
an alternating current in the rotor. The interaction
of the two electromagnetic fields is used to create
of the two electromagnetic fields is used to create
the driving torque.
the driving torque.

DC Motors
DC Motors

DC motors are widely used in
DC motors are widely used in
robotics for their small size and high
robotics for their small size and high
energy output.
energy output.

They are excellent for powering the
They are excellent for powering the
drive wheels of a mobile robot as
drive wheels of a mobile robot as
well as powering other mechanical
well as powering other mechanical
assemblies.
assemblies.

Ratings and Specifications
Ratings and Specifications
 Several characteristics are important in selecting
Several characteristics are important in selecting
a DC motor.
a DC motor.
 Operating Voltage
Operating Voltage. If batteries are the source
. If batteries are the source
of power for the motor, low operating voltages
of power for the motor, low operating voltages
are desirable because fewer cells would be
are desirable because fewer cells would be
needed to obtain the specified voltage. However,
needed to obtain the specified voltage. However,
the electronics to drive motors are typically more
the electronics to drive motors are typically more
efficient at higher voltages.
efficient at higher voltages.
 Typical DC motors may operate on as few as 1.5
Typical DC motors may operate on as few as 1.5
volts on up to 100 volts.
volts on up to 100 volts.
 Roboticists often use motors that operate on 6,
Roboticists often use motors that operate on 6,
12, or 24 volts
12, or 24 volts

Operating Current.
Operating Current.

Ideally one would like a motor that produces a
Ideally one would like a motor that produces a
great deal of power while requiring a minimum of
great deal of power while requiring a minimum of
current. Typically however the current rating (in
current. Typically however the current rating (in
conjunction with the voltage rating) is a good
conjunction with the voltage rating) is a good
indication of the power output capacity of a motor.
indication of the power output capacity of a motor.

Motors that draw more current will deliver more
Motors that draw more current will deliver more
power.
power.

A low voltage (e.g., 12 volt or less) DC motor may
A low voltage (e.g., 12 volt or less) DC motor may
draw from 100 milliamps to several amps at stall,
draw from 100 milliamps to several amps at stall,
depending on its design.
depending on its design.
Speed.
Speed.

Usually this is specified as the speed in rotations
Usually this is specified as the speed in rotations
per minute (RPM) of the motor when it is unloaded,
per minute (RPM) of the motor when it is unloaded,
or running freely at its specified operating voltage.
or running freely at its specified operating voltage.

Typical DC motors run at speeds from several
Typical DC motors run at speeds from several
thousand to ten thousand RPM.
thousand to ten thousand RPM.

Torque
Torque

The torque of a motor is the rotary force
The torque of a motor is the rotary force
produced on its output shaft.
produced on its output shaft.
 When a motor is stalled it is producing the
maximum amount of torque that it can
produce. Hence the torque rating is
usually taken when the motor has stalled
and is called the stall torque.
Power
Power

The power of a motor is the product of its
The power of a motor is the product of its
speed and torque.
speed and torque.
 The power output is greatest somewhere
between the unloaded speed (maximum
speed, no torque) and the stalled state
(maximum torque, no speed).

DC Brush Motor
DC Brush Motor

DC brush motors convert applied current into output
DC brush motors convert applied current into output
mechanical motion.
mechanical motion.

DC brush motors have smooth motion and higher peak
DC brush motors have smooth motion and higher peak
torque and can be used at higher speeds than stepper
torque and can be used at higher speeds than stepper
motors
motors

DC brush motors incorporate a stator with either
DC brush motors incorporate a stator with either
permanent magnets or windings and a
permanent magnets or windings and a rotor with
rotor with
windings.
windings.

Windings in the stator are known as field windings or
Windings in the stator are known as field windings or
field coils
field coils.
.

DC motors using permanent magnets in the stator are
DC motors using permanent magnets in the stator are
known as
known as permanent magnet DC motors
permanent magnet DC motors.
.

DC motors with windings in the stator are known as series-
DC motors with windings in the stator are known as series-
wound or shunt-wound motors depending upon the
wound or shunt-wound motors depending upon the
connectivity of the windings in relation to rotor windings.
connectivity of the windings in relation to rotor windings.

Series-wound
Series-wound motors have the field windings in series
motors have the field windings in series
with the rotor
with the rotor

Shunt-wound
Shunt-wound motors have the field windings in parallel
motors have the field windings in parallel
with the rotor.
with the rotor.

 All DC brush motors include conductive brushes
All DC brush motors include conductive brushes
which make sliding contact with a commutator as
which make sliding contact with a commutator as
the rotor turns.
the rotor turns.
 The commutator is attached to the rotor shaft
The commutator is attached to the rotor shaft
and the rotor windings are connected to the
and the rotor windings are connected to the
individual sections of the commutator.
individual sections of the commutator.
 The commutator has as many sections as there
The commutator has as many sections as there
are poles in the rotor.
are poles in the rotor.

DC Brushless Motor
DC Brushless Motor

A DC brushless motor is like a DC brush motor
A DC brushless motor is like a DC brush motor
turned inside out because the rotor contains a
turned inside out because the rotor contains a
permanent magnet and the stator contains
permanent magnet and the stator contains
windings.
windings.

The windings are electronically commutated so
The windings are electronically commutated so
that the mechanical commutator and brushes are
that the mechanical commutator and brushes are
no longer required as in a DC brush motor
no longer required as in a DC brush motor

 DC brushless motors are commonly used in
DC brushless motors are commonly used in
robotics applications because of their high speed
robotics applications because of their high speed
capability, improved efficiency, and low
capability, improved efficiency, and low
maintenance in comparison with DC brush
maintenance in comparison with DC brush
motors.
motors.
 They are capable of higher speeds because of
They are capable of higher speeds because of
the elimination of the mechanical commutator.
the elimination of the mechanical commutator.
 They are more efficient because heat from the
They are more efficient because heat from the
windings in the stator can be dissipated more
windings in the stator can be dissipated more
quickly through the motor case.
quickly through the motor case.
 They require less maintenance because they do
They require less maintenance because they do
not have brushes that require periodic
not have brushes that require periodic
replacement.
replacement.
 The total system cost for brushless motors is
The total system cost for brushless motors is
higher than that for DC brush motors due to the
higher than that for DC brush motors due to the
complexity of electronic commutation.
complexity of electronic commutation.

Brushless Motor Advantages
Brushless Motor Advantages

Brushless DC motors have some
Brushless DC motors have some
advantages over brush type DC motors.
advantages over brush type DC motors.
•
• There is no need to replace brushes.
There is no need to replace brushes.
• Electromagnetic interference (EMI) is
Electromagnetic interference (EMI) is
minimized by replacing mechanical
minimized by replacing mechanical
commutation, the source of unwanted radio
commutation, the source of unwanted radio
frequencies, with electronic commutation.
frequencies, with electronic commutation.
•
• Brushless motors can run faster and more
Brushless motors can run faster and more
efficiently with electronic commutation. Speeds
efficiently with electronic commutation. Speeds
of up to 50,000 rpm can be achieved vs. the
of up to 50,000 rpm can be achieved vs. the
upper limit of about 5000 rpm for brush-type
upper limit of about 5000 rpm for brush-type
DC motors.
DC motors.

Brushless DC Motor
Brushless DC Motor
Disadvantages
Disadvantages
 There are some disadvantages of brushless DC
There are some disadvantages of brushless DC
motors.
motors.
• Brushless PM DC servomotors cannot be reversed by
Brushless PM DC servomotors cannot be reversed by
simply reversing the polarity of the power source. The
simply reversing the polarity of the power source. The
order in which the current is fed to the field coil must be
order in which the current is fed to the field coil must be
reversed.
reversed.
• Brushless DC servomotors cost more than comparably
Brushless DC servomotors cost more than comparably
rated brush type DC servomotors.
rated brush type DC servomotors.
• The motion controller and driver electronics needed to
The motion controller and driver electronics needed to
operate a brushless DC servomotor are more complex
operate a brushless DC servomotor are more complex
and expensive than those required for a conventional
and expensive than those required for a conventional
DC servomotor. Consequently, the selection of a
DC servomotor. Consequently, the selection of a
brushless motor is generally justified on a basis of
brushless motor is generally justified on a basis of
specific application requirements.
specific application requirements.

Servo Motors
Servo Motors
AC SERVO MOTORS
AC SERVO MOTORS

Large ac motors are too inefficient for servo use.
Large ac motors are too inefficient for servo use.

To move large loads, the ac motor draws excessive amounts of
To move large loads, the ac motor draws excessive amounts of
power, and is difficult to cool.
power, and is difficult to cool.

Hence, ac servo motors are used primarily to move light loads.
Hence, ac servo motors are used primarily to move light loads.

Most of the ac servo motors are of the two-phase or split-phase
Most of the ac servo motors are of the two-phase or split-phase
induction type.
induction type.

Fundamentally, these motors are constant-speed devices,
Fundamentally, these motors are constant-speed devices,
although their speeds can be varied within limits by varying the
although their speeds can be varied within limits by varying the
amplitude of the voltage to one of the motors stator windings.
amplitude of the voltage to one of the motors stator windings.
DC SERVO MOTORS
DC SERVO MOTORS

The control characteristics of dc servo motors are superior to
The control characteristics of dc servo motors are superior to
those of ac servo motors.
those of ac servo motors.

The dc servo motor can control heavy loads at variable speeds.
The dc servo motor can control heavy loads at variable speeds.

Most dc servo motors are either the permanent magnet type,
Most dc servo motors are either the permanent magnet type,
which are used for light loads, or the shunt field type, which are
which are used for light loads, or the shunt field type, which are
used for heavy loads.
used for heavy loads.

The direction and speed of the dc motor's rotation is determined
The direction and speed of the dc motor's rotation is determined
by the armature current. An increase in armature current will
by the armature current. An increase in armature current will
increase the motor's speed.
increase the motor's speed.

Servo Motors
Servo Motors
 Servo motors incorporate several components
Servo motors incorporate several components
into one device package:
into one device package:
• a DC motor;
a DC motor;
• a gear reduction drive for torque increase;
a gear reduction drive for torque increase;
• an electronic shaft position sensing and control circuit
an electronic shaft position sensing and control circuit

Stepper Motors
Stepper Motors
 These are most directly adaptable for digital
These are most directly adaptable for digital
controlling methods.
controlling methods.
 The stepper motor is driven by feeding it a
The stepper motor is driven by feeding it a
stream of electric pulses.
stream of electric pulses.
 Each pulse makes the motor rotate by a fixed
Each pulse makes the motor rotate by a fixed
angle (e.g. 1.8º).
angle (e.g. 1.8º).
 Moves in discrete steps.
Moves in discrete steps.
 controlled with two signals step and direction
 They are commonly used in laser positioning, pen
They are commonly used in laser positioning, pen
positioning, disc and CDROM drives, robots,
positioning, disc and CDROM drives, robots,
positioning tables etc.
positioning tables etc.

Operating Principle
Operating Principle

The rotor is a
The rotor is a permanent magnet
permanent magnet, configured so as to
, configured so as to
have a
have a series of equally spaced (angularly) sets of
series of equally spaced (angularly) sets of
poles
poles along the circumference. The stator has a
along the circumference. The stator has a
corresponding number of coils.
corresponding number of coils. For a required motion,
For a required motion,
only one of the stator coils is activated
only one of the stator coils is activated, causing the
, causing the
rotor to align its poles in opposition to the electromagnetic
rotor to align its poles in opposition to the electromagnetic
poles of the energized coil.
poles of the energized coil.

Further,
Further, by activating a combination of coils
by activating a combination of coils, the
, the
selection of the right combination gives further resolution in
selection of the right combination gives further resolution in
the steps taken by the motor. Yet another method used by
the steps taken by the motor. Yet another method used by
stepper motor drive units is
stepper motor drive units is application of pulses of
application of pulses of
different voltages to different coils
different voltages to different coils. By proper selection
. By proper selection
of the voltage levels applied, smaller steps can be
of the voltage levels applied, smaller steps can be
produced, thus making the motor more precise.
produced, thus making the motor more precise.

Stepper Motor Types and Modes

3 Types
3 Types
• Permanent magnet
Permanent magnet
• Variable reluctance
Variable reluctance
• Hybrid
Hybrid

3 Step Modes
3 Step Modes
• Wave Drive i.e. 1 phase on
Wave Drive i.e. 1 phase on
• Full step i.e. 2 phase on
Full step i.e. 2 phase on
• Half step i.e. 1 and 2 phase on ( x2 i.e. 400 steps/revolution)
Half step i.e. 1 and 2 phase on ( x2 i.e. 400 steps/revolution)
• Microstep i.e. continuously varying motor current ( x N with N
Microstep i.e. continuously varying motor current ( x N with N
up to 256,upto 50,000 step/ revolution)
up to 256,upto 50,000 step/ revolution)
 Motor Windings
• Unifilar ( 4 wires)
• Bifilar ( 6 or 8 wires)
Note: (Def. of Reluctance: The characteristics of a magnetic field
which resists the flow of magnetic lines of force through it.)

Variable Reluctance (VR)
Variable Reluctance (VR)
This type of motor consists of a soft iron multi-toothed
rotor and a wound stator. When the stator windings are
energized with DC current the poles become magnetized.
Rotation occurs when the rotor teeth are attracted to the
energized stator poles.

Permanent Magnet (PM)
Permanent Magnet (PM)
 Rotor is a permanent magnet. The rotor is magnetized
with alternating north and south poles situated in a straight
line parallel to the rotor shaft.
 These magnetized rotor poles provide an increased
magnetic flux intensity

Hybrid Motors
Hybrid Motors
 The hybrid stepper motor combines the best features of
both the PM and VR type stepper motors.
 The rotor is multi-toothed like the VR motor and contains
an axially magnetized concentric magnet around its shaft.

1-Phase On Motor
1-Phase On Motor

2-Phase On Motor
2-Phase On Motor

1 and 2 phase on , Half Step Motor
1 and 2 phase on , Half Step Motor

Unifilar and Bifilar
Unifilar and Bifilar

Unifilar, as the name implies, has only one winding per
Unifilar, as the name implies, has only one winding per
stator pole. Stepper motors with a unifilar winding will have
stator pole. Stepper motors with a unifilar winding will have
4 lead wires.
4 lead wires.

Bifilar wound motors means that there are two identical
Bifilar wound motors means that there are two identical
sets of windings on each stator pole. This type of winding
sets of windings on each stator pole. This type of winding
configuration simplifies operation in that transferring
configuration simplifies operation in that transferring
current from one coil to another one, wound in the opposite
current from one coil to another one, wound in the opposite
direction, will reverse the rotation of the motor shaft.
direction, will reverse the rotation of the motor shaft.

Advantages of Stepper Motors
The rotation angle of the motor is
proportional to the input pulse.
 The motors response to digital input
pulses provides open-loop control, making
the motor simpler and less costly to
control.
 Large savings in sensor (measurement
Large savings in sensor (measurement
system) and controller costs are possible
system) and controller costs are possible
when the open-loop mode is used.
when the open-loop mode is used.
 Because of the incremental nature of
Because of the incremental nature of
command and motion, step motors are
command and motion, step motors are
easily adaptable to digital control
easily adaptable to digital control
applications.
applications.

Disadvantages of Stepper
Motors
 Stepper motors provide a system that is not
much accurate due to the feedback.
 Not easy to operate at extremely high speeds.
 They have low torque capacity (typically less than
They have low torque capacity (typically less than
2,000 oz-in) compared to DC motors.
2,000 oz-in) compared to DC motors.
 They have limited speed (limited by torque
They have limited speed (limited by torque
capacity and by pulse-missing problems due to
capacity and by pulse-missing problems due to
faulty switching systems and drive circuits).
faulty switching systems and drive circuits).
 They have high vibration levels due to stepwise
They have high vibration levels due to stepwise
motion.
motion.
 Large errors and oscillations can result when a
Large errors and oscillations can result when a
pulse is missed under open-loop control
pulse is missed under open-loop control

Motor Drive Circuits
Motor Drive Circuits

All motors require drive circuitry
All motors require drive circuitry
which controls the current flow
which controls the current flow
through the motor windings. This
through the motor windings. This
includes the direction and magnitude
includes the direction and magnitude
of the current flow.
of the current flow.

Direction control……H-Bridge
Direction control……H-Bridge

Speed control…PWM
Speed control…PWM

Direction Control
Direction Control

The H-bridge derived its name from
The H-bridge derived its name from
the common way the circuit is
the common way the circuit is
drawn. This is the only solid state
drawn. This is the only solid state
way to operate a motor in both
way to operate a motor in both
directions.
directions.

H-Bridge consists of 4 switches that
H-Bridge consists of 4 switches that
form a shape like H.
form a shape like H.

Relay Drives
Relay Drives

Relay circuits requires a diode across
Relay circuits requires a diode across
the coil of the relay. This will keep
the coil of the relay. This will keep
the spike voltage (back EMF),
the spike voltage (back EMF),
coming out of the coil of the relay
coming out of the coil of the relay


But if we want to be able to control
But if we want to be able to control
the motor in both forward and
the motor in both forward and
reverse with a processor, we need
reverse with a processor, we need
more circuitry, H-Bridge
more circuitry, H-Bridge


The "high side drivers" are the relays
The "high side drivers" are the relays
that control the positive voltage to
that control the positive voltage to
the motor. This is called
the motor. This is called sourcing
sourcing
current
current.
.

The "low side drivers" are the relays
The "low side drivers" are the relays
that control the negative voltage to
that control the negative voltage to
sink current to the motor called
sink current to the motor called
Sinking current
Sinking current.
.

 So, if we turn on the upper left and
So, if we turn on the upper left and
lower right circuits, and power flows
lower right circuits, and power flows
through the motor forward, i.e.: 1 to
through the motor forward, i.e.: 1 to
A, 0 to B, 0 to C, and 1 to D.
A, 0 to B, 0 to C, and 1 to D.

 Then for reverse you turn on the
Then for reverse you turn on the
upper right and lower left circuits
upper right and lower left circuits
and power flows through the motor
and power flows through the motor
in reverse, i.e.: 0 to A, 1 to B, 1 to
in reverse, i.e.: 0 to A, 1 to B, 1 to
C, and 0 to D.
C, and 0 to D.

Be Careful
Be Careful

You should be careful not to turn on
You should be careful not to turn on
both circuits on one side or the
both circuits on one side or the
other, or you have a direct short
other, or you have a direct short
which will destroy your circuit;
which will destroy your circuit;
Example: A and C or B and D both
Example: A and C or B and D both
high (logical 1).
high (logical 1).

Semiconductor H-Bridges
Semiconductor H-Bridges

We can better control our motor by using
We can better control our motor by using
transistors or Field Effect Transistors
transistors or Field Effect Transistors
(FETs)
(FETs)

These solid state circuits provide power
These solid state circuits provide power
and ground connections to the motor, as
and ground connections to the motor, as
did the relay circuits. The
did the relay circuits. The high side
high side
drivers
drivers need to be current
need to be current "sources"
"sources"
which is what
which is what PNP transistors and P-
PNP transistors and P-
channel FETs
channel FETs are good at. The
are good at. The low side
low side
drivers
drivers need to be current
need to be current "sinks"
"sinks" which
which
is what
is what NPN transistors and N-channel
NPN transistors and N-channel
FETs
FETs are good at
are good at

 To be nice to your transistors, we should
To be nice to your transistors, we should add
add
diodes
diodes to catch the back voltage that is
to catch the back voltage that is
generated by the motor's coil when the power is
generated by the motor's coil when the power is
switched on and off. This fly-back voltage can be
switched on and off. This fly-back voltage can be
many times higher than the supply voltage. If we
many times higher than the supply voltage. If we
don't use diodes, transistors can burn out.
don't use diodes, transistors can burn out.


Transistors, being a semiconductor device,
Transistors, being a semiconductor device,
will have some resistance, which causes
will have some resistance, which causes
them to get hot when conducting much
them to get hot when conducting much
current. This is called not being able to
current. This is called not being able to
sink or source very much power, i.e.: Not
sink or source very much power, i.e.: Not
able to provide much current from ground
able to provide much current from ground
or from plus voltage.
or from plus voltage.

Mosfets are much more efficient, they can
Mosfets are much more efficient, they can
provide much more current and not get as
provide much more current and not get as
hot. They usually have the flyback diodes
hot. They usually have the flyback diodes
built in so we don't need the diodes
built in so we don't need the diodes
anymore
anymore

Bridge Devices
Bridge Devices
 The L 293 has 2 H-Bridges, can provide
The L 293 has 2 H-Bridges, can provide
about 1 amp to each and occasional peak
about 1 amp to each and occasional peak
loads to 2 amps
loads to 2 amps
 The L298 has 2 h-bridges on board, can
The L298 has 2 h-bridges on board, can
handle 1amp and peak current draws to
handle 1amp and peak current draws to
about 3amps
about 3amps
 The LMD18200 has one h-bridge on board,
The LMD18200 has one h-bridge on board,
can handle about 2 or 3 amps and can
can handle about 2 or 3 amps and can
handle a peak of about 6 amps
handle a peak of about 6 amps

Speed Control
Speed Control
 The process of adjusting the power
to the motor to maintain constant
velocity is called speed control
 The motors operate using pulse
width modulated (PWM) signals. A
PWM signal has a fixed frequency
and variable duty cycle.

Controlling Motor Speed
Controlling Motor Speed
 By turning our transistors (switches) ON
By turning our transistors (switches) ON
and OFF really fast, we change the
and OFF really fast, we change the
average voltage seen by the motor
average voltage seen by the motor
 This technique is called
This technique is called
Pulse-Width Modulation (
Pulse-Width Modulation (PWM
PWM).
).

PWM Basics
PWM Basics

The higher the voltage seen by the
The higher the voltage seen by the
motor, the higher the speed.
motor, the higher the speed.

Robotics & CNC Machines Lecture no 3.ppt

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Robotics & CNC Machines Lecture no 3.ppt