Actuators
Actuators
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Introduction
Solenoids, Relays, & Voice Coils
DC Motors
AC Motors
Stepper Motors
Hydraulics
Pneumatics
Servomechanisms
Actuators
Mechatronic System
Mechanical System
Sensors
Input Signal Conditioning
& Interfacing
Actuators
Control Architecture
Output Signal Conditioning
& Interfacing
Operator
Display System
Actuators
Introduction
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Most electromechanic systems involve motion of
some sort
This motion is created by a force or torque and result
in
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Displacement
Velocity
Acceleration
Actuators are devices used to produce motion
An important aspect of mechatronic system design is
selecting the appropriate type of actuator
Actuators
Electromagnetism
The discovery of relationship
between electric current flow and
magnetic field is the foundation of
electromagnetism and plays a
crucial role in the development of
electromechanic actuators
Electromagnetism owes a lot to the
pioneering work of Michael Faraday
in the early 19th century
Actuators
Electromagnetic Principles
Magnetic Flux Density
Force
F = I×B
Current
Fleming’s Left Hand Rule
- For motors
- Force is developed from electric
current & magnetic flux
Fleming’s Right Hand Rule
- For generators
- Electric current is developed from
magnetic flux & force
Actuators
Solenoids
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Solenoid comprises
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Coil
Armature (moveable iron core)
When current flows in coil, core moves to increase the flux
linkage by closing the gap between the cores
The armature is usually spring loaded to allow the core to
retract when current is switched off
Solenoids are inexpensive and limited to on-off applications
Actuators
Circuit Breaker
A circuit breaker is an automatically-operated
electrical switch designed to protect an
electrical circuit from damage caused by
overload or short circuit.
Unlike a fuse, which operates once and then
has to be replaced, a circuit breaker can be
reset (either manually or automatically) to
resume normal operation.
Circuit breakers do not offer personal
protection for electric shock.
Actuators
Circuit Breaker Cut-Out
1. Actuator lever - used to manually trip and reset
the circuit breaker. Also indicates the status of the
circuit breaker (On or Off/tripped). Most breakers are
designed so they can still trip even if the lever is held
or locked in the on position. This is sometimes
referred to as "free trip" or "positive trip" operation.
2. Actuator mechanism - forces the contacts
together or apart.
3. Contacts - Allow current to flow when touching
and break the flow of current when moved apart.
4. Terminals
5. Bimetallic strip
6. Calibration screw - allows the manufacturer to
precisely adjust the trip current of the device after
assembly.
7. Solenoid
8. Arc divider / extinguisher
Actuators
Safety Switch
Safety switches monitor the flow of
electricity through a circuit.
They automatically shut off the electricity
supply when current is detected leaking
from faulty switches, wiring or electrical
appliances.
This stops the chance of current flowing to
earth, through a person.
07-01-HighvoltageSafetySwitch.wmv
Actuators
Relay
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An electromechanical relay is
a solenoid used to make or
break mechanical contact
between electrical leads
A small voltage can be used
to control a relatively large
current through relay
contacts
A relay operates like power
transistor, except that
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It handles higher current
Input circuit is electrically
isolated from output circuit
It switches more slowly
Actuators
Voice Coil
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A voice coil is a coil that
is moved in magnetic
field produced in core
Force is proportional to
current in coil
Linear response &
bidirectional nature
makes voice coil
attractive for control
The best example of a
voice coil is a
loudspeaker
07-02-VoiceCoil.wmv
07-03-HardiskVoiceCoil.wmv
Actuators
Electric Motors
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A vast majority of electromechical devices
depend on electric motors as actuators
The general classification of motors includes
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Direct current (DC)
Alternating current (AC)
Stepper
The type of motor to be used depends on the
application
Actuators
Electric Motor Construction
Stator
Stationary outer housing that
supports magnetized poles
Poles consist of field coils
(permanent magnets or wire coils)
wrapped around laminated iron cores
Stator poles provide radial magnetic
fields
Iron core intensifies the magnetic
field in the coils
The core is laminated to reduce eddy
current effects
Rotor Part of motor that rotates. Consists of rotating shaft supported by bearings &
armature windings. Has an iron core that intensifies fields in windings
A small air gap exists between stator & rotor where magnetic field interacts
Actuators
DC Motor
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DC motor are often used in electromechanics applications
Generates torque directly from DC power supplied to the
motor by using internal commutation, stationary
permanent magnets, and rotating electrical magnets
Advantages
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Low initial cost
High reliability
Simple control of motor speed
Disadvantages
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High maintenance
Low life-span for high intensity uses
07-04-DcMotorComponents.wmv
Actuators
DC Motor Operation
Electric current flowing in the armature of rotor
creates electromagnetic field
Attracts and repels magnet in the stator
Results in rotation of the rotor
http://www.physclips.unsw.edu.au/jw/electricmotors.html
Actuators
DC Permanent Magnet Motor
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Stator fields are provided by permanent magnets
Is lighter and smaller because field strength of permanent magnets
is high
Easily reversed by switching the direction of the applied voltage –
current and field changes only in the rotor
Ideal for control applications due to linear torque speed relationship
Actuators
DC Shunt Motor
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Have armature and field windings connected in parallel and powered
by same supply
Total load current is sum of the armature and field currents
Exhibit nearly constant speed over a large range of loading
Have starting torque 1.5 times the rated operating torque
Speed can be adjusted by placing potentiometer in series with field
windings
Actuators
DC Series Motor
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Have armature and field windings connected in series
Armature and field currents are equal
Exhibit very high starting torques
Highly variable speed depending on load
High speed when load is small
Can fail catastrophically if suddenly unloaded
Actuators
DC Compound Motor
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Have both shunt and series field windings
Part of load current passes through armature & series windings
Rest of load current passes through shunt windings only
Maximum speed is smaller than series motor
Speed regulation is not as good as shunt motor
Torque is not as constant as shunt motor
Actuators
Homopolar DC motor
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It is arguably the simplest type of DC
motor using a battery and two button
magnets
The electric circuit completed by
attaching metal rails on the magnets
07-05-HomopolarMotor.wmv
Actuators
AC Motors
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Involves the interaction of magnetic fields varying in time
with AC excitation
Advantages
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Can provide higher power ratings
Low maintenance
Disadvantages
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Requires a more complicated circuit
Typically more expensive
07-06-ACInductionMotorWaterPump.wmv
Actuators
AC Motor Operation
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Synchronous motor
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AC voltage applied to the stator, rotor is permanent or DC electromagnet
The rotor follows the changing magnetic field of stator
Induction motor
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AC field of stator produces a changing flux in rotor wire loop to produce
current
This creates a magnetic field in rotor that interacts with magnetic field of
stator
Synchronous Motor
Induction Motor
Actuators
Stepper Motors
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Functions on the sequencing of a series of discrete rotational steps
Advantages
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Can be rotated to a specific angle with ease
Provides easy control for low precision applications
Can be controlled by inexpensive circuitry
Disadvantages
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Exhibit additional vibration due to stepping
Limited rotation speed
07-07-StepperMotorResponse.wmv
Actuators
Stepper Motor Operation
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Continuous rotation is achieved by an input of train pulses to
change magnetic polarity of stator
Rotational rate is determined by
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Number of steps per revolution
Rate at which pulses are applied
Maintaining the magnetic field will keep rotor in fixed angular
position with holding torque
Actuators
Motor Selection Factors
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Starting (stall) torque (maximum torque
motor can produce at zero speed)
α = (T – T ) / J
Angular acceleration
T : motor torque
T : load torque
Operating speed(s)
J: polar moment of inertia
Output power
Current requirement
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Actuators
Molecular Motors
With the ability to access and arrange
molecules, scientists are beginning to
develop gears for motors that can
function at the molecular level
Actuators
Hydraulics
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Hydraulic systems move large loads by controlling high
pressure fluid
Consists of
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Pump (driven by motor) to deliver high pressure fluid
Pressure regulator to limit pressure
Valves to control direction, flow rate, & pressure
Distribution system of pipes and actuators
Valve switching positions
07-09-HydraulicGearPump.wmv
Actuators
Hydraulic Press
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A press is used to
compress objects during
manufacture
The force applied from a
motor will not be sufficient
in most cases
Hydraulic systems are able
to provide sufficient forces
for such applications
Actuators
Pneumatics
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Pneumatic systems move loads by controlling
compressed air
Consists of
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Compressor (driven by motor) to deliver compressed air
Pressure regulator to limit pressure
Valves to control direction, flow rate, & pressure
Distribution system of pipes and actuators
07-08-PneumaticExerciseMachine.wmv
Actuators
Pneumatic Door Opener
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Doors need to be opened
automatically in hospitals
and disability access
places
Motors and hydraulic
systems generally are not
able to provide rapid
enough responses
Pneumatic systems
however provide very
rapid response
Actuators
Servomechanism
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A servomechanism (servo) is a device
which uses error-sensing feedback to
correct the performance of a mechanism
A common type of servo provides position
control.
Servos are commonly electrical or partially
electronic in nature, using an electric
motor as the primary means of creating
the mechanical force.
Other types of servos use hydraulics,
pneumatics, or magnetic principles
The science of trying to get a servo to
perform desirably is called control theory
07-10-Servomotor_with_PWM.wmv
07-11-Servo_motor_system.wmv
Small servo mechanism
1. electric motor
2. position feedback potentiometer
3. reduction gear
4. actuator arm
Actuators
Robotic Manipulators
The field of robotics makes
extensive use of
servomechanisms.
A robotic manipulator has to
provide precise position, velocity &
acceleration.
This will be impossible achieve
without actuating components with
error-sensing feedback.
07-12-ManufacturingRobotsFuture.wmv
Actuators
Control Theory
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A servomechanism uses error-sensing feedback to correct
the performance of a mechanism
Its performance can be depicted using control theory
(science that deals with monitoring and controlling
processes)
It has three main categories: 1) adaptive control, 2)
predictive control, 3) proportional-integral-derivative (PID)
Actuators
PID Controller
Generic control loop feedback
mechanism widely used in
industrial control systems.
In this example, the amplitude is stabilized
within 2 seconds