Actuators

Jussi SuomelaHUT/Automation 1
Actuators are used in order to produce mechanical
movement in robots.
Slides from Braunl and Jussi Suomela
Actuators
 In this lecture we will present:
 Motor and Encoder
 H-Bridge
 Pulse-Width-Modulation (PWM)
 Servos
 Other robotic actuators
Actuator TypesActuator Types
 Electrical
 Hydraulic
 Pneumatic
 Others
Jussi SuomelaHUT/Automation 3
Actuators
 Actuators can be built in may different ways, most
prominently:
 electrical motors
 pneumatics and valves.
 In this course we will only deal with electrical motors
 In past we built pneumatic robots which you can still find in
the lab.
 We will build them again after purchasing air compressor
 My first robot was very strong and it was hydraulic. It pissed
hot oil at students in Warsaw.
Servo SystemServo System
Servo is mechanism based on
feedback control.
The controlled quantity is
mechanical.
Jussi SuomelaHUT/Automation 5
Servo Control of an
Electrical Motor
Jussi SuomelaHUT/Automation 6
Properties of Servo
 high maximum torque/force allows high (de)acceleration
 high zero speed torque/force
 high bandwidth provides accurate and fast control
 works in all four quadrants
 robustness
Jussi SuomelaHUT/Automation 7
ElectricalElectrical
ActuatorsActuators easy to control
 from mW to MW
 normally high velocities 1000 - 10000 rpm
 several types
 accurate servo control
 ideal torque for driving
 excellent efficiency
 autonomous power system difficult
Jussi SuomelaHUT/Automation 8
Electric actuators
•Mainly rotating but also
linear ones are available
•linear movement with
gear or with real linear
motor
Electrical Actuator Types
 DC-motors
 brushless DC-motors
 asynchronous motors
 synchronous motors
 reluctance motors (stepper motors)
Jussi SuomelaHUT/Automation 10
DC-Motors
 simple, cheap
 easy to control
 1W - 1kW
 can be overloaded
 brushes wear
 limited overloading
on high speeds
Jussi SuomelaHUT/Automation 11
DC-motor control
 Controller + H-bridge
 PWM-control
 Speed control by
controlling motor
current=torque
 Efficient small
components
 PID control
H-BridgeH-Bridge
Actuators
H-Bridge
 Hardware Implementation with
Microcontroller:
 2 Digital output pins from microcontroller,
[one at Gnd, one at Vcc] feed into a power
amplifier
 Alternative: use only 1 digital output pin plus
one inverter, then feed into a power amplifier
Power AmplifierPower Amplifier
Actuators
Brushless DC-Motors
(pm synchronous motor)
 no brushes  no wearing parts  high speeds
 coils on cover => better cooling
 excellent power/weight ratio
 simple
 needs both speed and angle feedback
 more complicated controller
 From small to medium power (10W – 50kW)
Jussi SuomelaHUT/Automation 18
Asynchronous Motors
 very simple, very popular in industry
 0,5kW - 500kW
 More difficult to control (frequency)
 nowadays as accurate control as DC-motors
 In mobile machines also (5kW )
Jussi SuomelaHUT/Automation 19
Structure of an Asynchronous
motor
Jussi SuomelaHUT/Automation 20
Synchronous Motors
 usually big 100 kW - XXMW
 also small ones ~ brushless DC-motors from
50W to 100 kW
 controlled like as-motors (frequency)
 ships
 industry
 Mobile machines
Jussi SuomelaHUT/Automation 21
StepperStepper
MotorsMotors
Reluctance (Stepper) Motors
 angle control
 slow
 usually no feedback used
 accurate positioning
 with out feedback not servos
 easy to control
Jussi SuomelaHUT/Automation 23
Principle of Stepper Motor
Jussi SuomelaHUT/Automation 24
Stepper Motors
 Stepper motors are another kind of motors that do not require feedback
 A stepper motor can be incrementally driven, one step at a time, forward or
backward
 Stepper motor characteristics are:
 Number of steps per revolution (e.g. 200 steps per revolution = 1.8° per
step)
 Max. number of steps per second (“stepping rate” = max speed)
 Driving a stepper motor requires a 4 step switching sequence for full-step
mode
 Stepper motors can also be driven in 8 step switching sequence for half-
step mode (higher resolution)
 Step sequence can be very fast, the the resulting motion appears to be very
smooth
Actuators
Actuators
Stepper Motors
 Advantages
 No feedback hardware required
 Disadvantages
 No feedback (!)
Often feedback is still required,
e.g. for precision reasons, since a stepper motor can “lose” a step signal.
 Requires 2 H-Bridges plus amplifiers instead of 1
 Other
 Driving software is different but not much more complicated
 Some controllers (e.g. M68332) support stepper motors in firmware
(TPU)
Motor and EncoderMotor and Encoder
Actuators
Actuators
Actuators
Motor and Encoder
 Motor speed determined by:
supplied voltage
 Motor direction determined by:
polarity of supplied voltage
 Difficult to generate analog power signal
(1A ..10A) directly from microcontroller
→ external amplifier (pulse-width modulation)
Motor and Encoder
 Encoder disk is turned once for each rotor revolution
 Encoder disk can be optical or magnetic
 Single detector can determine speed
 Dual detector can determine speed and direction
 Using gears on motor shaft increases encoder accuracy
Pulse-Width ModulationPulse-Width Modulation
 A/D converters are used for reading analog
sensor signals
 Why not use D/A converter for motor
control?
 Too expensive (needs power circuitry)
 Better do it by software, switching power on/off
in intervals
 This is called “Pulse-Width Modulation” or PWM
Actuators
Pulse-Width Modulation
 How does this work?
 We do not change the supplied voltage
 Power is switched on/off at a certain pulse ratio
matching the desired output power
 Signal has very high frequency (e.g. 20kHz)
 Motors are relatively slow to respond
 The only thing that counts is the supplied power
 ⇒ Integral (Summation)
 Pulse-Width Ratio = ton / tperiod
ServosServos
Servos
Actuators
Servos
 Terminology:
 Do not confuse “servos” with “servo motors”
 DC motors (brushed or brushless) are also sometimes also
referred to as “servo motors”
 See: http://www.theproductfinder.com/motors/bruser.htm
 “So when does a motor become a servo motor? There are
certain design criteria that are desired when building a servo
motor, which enable the motor to more adequately handle the
demands placed on a closed loop system.
 First of all, servo systems need to rapidly respond to changes in
speed and position, which require high acceleration and
deceleration rates.
 This calls for extremely high intermittent torque.
Servos
 As you may know, torque is related to current in the brushed servo
motor.
 So the designers need to keep in mind the ability of the motor to
handle short bursts of very high current, which can be many times
greater than the continuous current requirements.
 Another key characteristic of the brushed servo motor is a high
torque to inertia ratio.
 This ratio is an important factor in determining motor
responsiveness.
 Further, servo motors need to respond to small changes in the
control signal.
 So the design requires reaction to small voltage variations.”
HydraulicHydraulic
ActuatorsActuators linear movement
 big forces without gears
 actuators are simple
 in mobile machines
 Bad efficiency
 motor, pump, actuator combination is lighter
than motor, generator, battery, motor & gear
combination
Jussi SuomelaHUT/Automation 43
Hydraulic actuators
Hydraulic motor
Jussi SuomelaHUT/Automation 45
Hydraulic Valves
 servo valves
 complicated structure, expensive
 good control
 proportional valves
 simple, cheap
 robust
 more difficult to control
 Digital hydraulics, new!
 several fast on/off valves (2n
)
 digital control of the flow
Jussi SuomelaHUT/Automation 46
Servo Valve
Jussi SuomelaHUT/Automation 47
Proportional Valve
Jussi SuomelaHUT/Automation 48
Pneumatic ActuatorsPneumatic Actuators
like hydraulic except power from compressed
air
fast on/off type tasks
big forces with elasticity
no leak problems
Jussi SuomelaHUT/Automation 49
Other Actuators
 piezoelectric
 magnetic
 ultra sound
 SMA
 inertial
Jussi SuomelaHUT/Automation 50
ExamplesExamples
Arska
Workpartner
Shape Memory Alloy Robot
Practically
 In this class we will use only servos
 In past we used DC motors with H-bridge,
pneumatic actuators, nintinol wires and
hydraulic actuators.
 So far, if you want to build rather small robots
and you want to concentrate on intelligence and
sensing, RC servos are the best choice. Many
new types arrive every year, from very small to
big powerful ones. Look to internet.
 We will learn about some new actuators if time
will allow at the end of the class.
1 von 55

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Actuators

  • 1. Jussi SuomelaHUT/Automation 1 Actuators are used in order to produce mechanical movement in robots. Slides from Braunl and Jussi Suomela
  • 2. Actuators  In this lecture we will present:  Motor and Encoder  H-Bridge  Pulse-Width-Modulation (PWM)  Servos  Other robotic actuators
  • 3. Actuator TypesActuator Types  Electrical  Hydraulic  Pneumatic  Others Jussi SuomelaHUT/Automation 3
  • 4. Actuators  Actuators can be built in may different ways, most prominently:  electrical motors  pneumatics and valves.  In this course we will only deal with electrical motors  In past we built pneumatic robots which you can still find in the lab.  We will build them again after purchasing air compressor  My first robot was very strong and it was hydraulic. It pissed hot oil at students in Warsaw.
  • 5. Servo SystemServo System Servo is mechanism based on feedback control. The controlled quantity is mechanical. Jussi SuomelaHUT/Automation 5
  • 6. Servo Control of an Electrical Motor Jussi SuomelaHUT/Automation 6
  • 7. Properties of Servo  high maximum torque/force allows high (de)acceleration  high zero speed torque/force  high bandwidth provides accurate and fast control  works in all four quadrants  robustness Jussi SuomelaHUT/Automation 7
  • 8. ElectricalElectrical ActuatorsActuators easy to control  from mW to MW  normally high velocities 1000 - 10000 rpm  several types  accurate servo control  ideal torque for driving  excellent efficiency  autonomous power system difficult Jussi SuomelaHUT/Automation 8
  • 9. Electric actuators •Mainly rotating but also linear ones are available •linear movement with gear or with real linear motor
  • 10. Electrical Actuator Types  DC-motors  brushless DC-motors  asynchronous motors  synchronous motors  reluctance motors (stepper motors) Jussi SuomelaHUT/Automation 10
  • 11. DC-Motors  simple, cheap  easy to control  1W - 1kW  can be overloaded  brushes wear  limited overloading on high speeds Jussi SuomelaHUT/Automation 11
  • 12. DC-motor control  Controller + H-bridge  PWM-control  Speed control by controlling motor current=torque  Efficient small components  PID control
  • 15. H-Bridge  Hardware Implementation with Microcontroller:  2 Digital output pins from microcontroller, [one at Gnd, one at Vcc] feed into a power amplifier  Alternative: use only 1 digital output pin plus one inverter, then feed into a power amplifier
  • 18. Brushless DC-Motors (pm synchronous motor)  no brushes  no wearing parts  high speeds  coils on cover => better cooling  excellent power/weight ratio  simple  needs both speed and angle feedback  more complicated controller  From small to medium power (10W – 50kW) Jussi SuomelaHUT/Automation 18
  • 19. Asynchronous Motors  very simple, very popular in industry  0,5kW - 500kW  More difficult to control (frequency)  nowadays as accurate control as DC-motors  In mobile machines also (5kW ) Jussi SuomelaHUT/Automation 19
  • 20. Structure of an Asynchronous motor Jussi SuomelaHUT/Automation 20
  • 21. Synchronous Motors  usually big 100 kW - XXMW  also small ones ~ brushless DC-motors from 50W to 100 kW  controlled like as-motors (frequency)  ships  industry  Mobile machines Jussi SuomelaHUT/Automation 21
  • 23. Reluctance (Stepper) Motors  angle control  slow  usually no feedback used  accurate positioning  with out feedback not servos  easy to control Jussi SuomelaHUT/Automation 23
  • 24. Principle of Stepper Motor Jussi SuomelaHUT/Automation 24
  • 25. Stepper Motors  Stepper motors are another kind of motors that do not require feedback  A stepper motor can be incrementally driven, one step at a time, forward or backward  Stepper motor characteristics are:  Number of steps per revolution (e.g. 200 steps per revolution = 1.8° per step)  Max. number of steps per second (“stepping rate” = max speed)  Driving a stepper motor requires a 4 step switching sequence for full-step mode  Stepper motors can also be driven in 8 step switching sequence for half- step mode (higher resolution)  Step sequence can be very fast, the the resulting motion appears to be very smooth
  • 28. Stepper Motors  Advantages  No feedback hardware required  Disadvantages  No feedback (!) Often feedback is still required, e.g. for precision reasons, since a stepper motor can “lose” a step signal.  Requires 2 H-Bridges plus amplifiers instead of 1  Other  Driving software is different but not much more complicated  Some controllers (e.g. M68332) support stepper motors in firmware (TPU)
  • 29. Motor and EncoderMotor and Encoder
  • 33. Motor and Encoder  Motor speed determined by: supplied voltage  Motor direction determined by: polarity of supplied voltage  Difficult to generate analog power signal (1A ..10A) directly from microcontroller → external amplifier (pulse-width modulation)
  • 34. Motor and Encoder  Encoder disk is turned once for each rotor revolution  Encoder disk can be optical or magnetic  Single detector can determine speed  Dual detector can determine speed and direction  Using gears on motor shaft increases encoder accuracy
  • 35. Pulse-Width ModulationPulse-Width Modulation  A/D converters are used for reading analog sensor signals  Why not use D/A converter for motor control?  Too expensive (needs power circuitry)  Better do it by software, switching power on/off in intervals  This is called “Pulse-Width Modulation” or PWM
  • 37. Pulse-Width Modulation  How does this work?  We do not change the supplied voltage  Power is switched on/off at a certain pulse ratio matching the desired output power  Signal has very high frequency (e.g. 20kHz)  Motors are relatively slow to respond  The only thing that counts is the supplied power  ⇒ Integral (Summation)  Pulse-Width Ratio = ton / tperiod
  • 41. Servos  Terminology:  Do not confuse “servos” with “servo motors”  DC motors (brushed or brushless) are also sometimes also referred to as “servo motors”  See: http://www.theproductfinder.com/motors/bruser.htm  “So when does a motor become a servo motor? There are certain design criteria that are desired when building a servo motor, which enable the motor to more adequately handle the demands placed on a closed loop system.  First of all, servo systems need to rapidly respond to changes in speed and position, which require high acceleration and deceleration rates.  This calls for extremely high intermittent torque.
  • 42. Servos  As you may know, torque is related to current in the brushed servo motor.  So the designers need to keep in mind the ability of the motor to handle short bursts of very high current, which can be many times greater than the continuous current requirements.  Another key characteristic of the brushed servo motor is a high torque to inertia ratio.  This ratio is an important factor in determining motor responsiveness.  Further, servo motors need to respond to small changes in the control signal.  So the design requires reaction to small voltage variations.”
  • 43. HydraulicHydraulic ActuatorsActuators linear movement  big forces without gears  actuators are simple  in mobile machines  Bad efficiency  motor, pump, actuator combination is lighter than motor, generator, battery, motor & gear combination Jussi SuomelaHUT/Automation 43
  • 46. Hydraulic Valves  servo valves  complicated structure, expensive  good control  proportional valves  simple, cheap  robust  more difficult to control  Digital hydraulics, new!  several fast on/off valves (2n )  digital control of the flow Jussi SuomelaHUT/Automation 46
  • 49. Pneumatic ActuatorsPneumatic Actuators like hydraulic except power from compressed air fast on/off type tasks big forces with elasticity no leak problems Jussi SuomelaHUT/Automation 49
  • 50. Other Actuators  piezoelectric  magnetic  ultra sound  SMA  inertial Jussi SuomelaHUT/Automation 50
  • 52. Arska
  • 55. Practically  In this class we will use only servos  In past we used DC motors with H-bridge, pneumatic actuators, nintinol wires and hydraulic actuators.  So far, if you want to build rather small robots and you want to concentrate on intelligence and sensing, RC servos are the best choice. Many new types arrive every year, from very small to big powerful ones. Look to internet.  We will learn about some new actuators if time will allow at the end of the class.