Servo Motor Control - PowerPoint PPT Presentation

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Servo Motor Control

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Title: Motor Control Lab Author: carl Last modified by: ccrane Created Date: 10/19/2005 10:24:15 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: Servo Motor Control


1
Servo Motor Control
2
Design Project
  • You are to design a mechanical device that can
    tilt a given labyrinth board in two directions.

3
One Concept
  • Could use two motors.
  • Must be able to control the rotation angle of
    each.

4
Another Example
  • Control the steering angle of an autonomous
    ground vehicle.
  • Must be able to control the rotation angle.

5
Design Choices
  • What power source will be used?
  • How much power is needed?
  • Is a speed reducer needed?
  • Open-loop or closed-loop control?

6
Design Choices
  • What power source will be used?
  • electric servo motor
  • electric stepper motor
  • hydraulic actuator
  • pneumatics

7
Design Choices
  • How much power is needed?
  • determine the maximum product of motor torque
    times angular velocity

8
Design Choices
  • Is a speed reducer needed?
  • a typical DC motor can rotate at a top speed of
    2600 rpm (43? rev/sec)
  • gear box
  • epicyclic gear train
  • ball screw drive

9
gear box
worm gear drive
10
epicyclic gear train
ball screw drive
11
Design Choices
  • Open-loop or closed-loop control?
  • open-loop
  • well suited for remote control using a joystick
  • computer control can be implemented using a
    stepper motor
  • closed-loop
  • requires a sensor to measure the motors rotation
    angle

12
Design Choices
  • What power source will be used?
  • electric servo motor
  • How much power is needed?
  • experiment or perform analysis(very little
    torque will be needed to rotate the labyrinth
    board further the rotational speed will be very
    low)
  • Is a speed reducer needed?
  • yes
  • Open-loop or closed-loop control?
  • closed-loop

13
How does this work?
motor
gear reducer
desired steering angle
how is the motor connected to the steering shaft?
how does the computer cause the motor to turn?
how does the computer know the current steering
angle?
14
Motor and Gear Box
how is the motor connected to the steering shaft?
15
Motor and Gear Box
16
motor with gear reducer
flex coupling
17
Servo Motor Control
  • select means of angle measurement
  • optical encoder
  • incremental
  • absolute
  • potentiometer
  • resolver

how does the computer know the current steering
angle?
18
Incremental Optical Encoder
  • this disk has 12 slots (30º resolution)
  • typical incremental encoders have up to 2540
    counts per revolution (0.142º resolution) (488.
    41 each at McMaster-Carr)

19
Incremental Optical Encoder
20
Incremental Optical Encoder
you can count pulses, but which way is it
rotating?
21
Incremental Optical Encoder
an encoder will typically also have anindex that
will blink once each revolution
22
Incremental Optical Encoder
quadrature - there are 4n events per one
revolution of the disk - the resolution can in
effect be four times the number of slots
23
Incremental Optical Encoder
note many encoders will have an index that will
pulse once per revolution
24
Honeywell / Clarostat 600128CN1 Allied
Electronics part 753-0059
cost 41.67
25
Incremental Optical Encoder
problem - you start up the device - where are
you when you start?
26
Absolute Optical Encoder
BEI brand encoder 455
27
How does this work?
motor
gear reducer
desired steering angle
how is the motor connected to the steering shaft?
how does the computer cause the motor to turn?
gear reducer and flex couplings (if needed)
how does the computer know the current steering
angle?
computer controls the current going to the motor
incremental optical encoder with homing switch to
initialize position
28
How does the computer control the motor?
control the current (via the voltage)
29
motor with gear reducer
flex coupling
optical encoder
30
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36
Servo Motor Control
  • we will use a Galil motor control card to vary
    the current to the motor based on the error in
    the steering shaft angle

37
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38
Homing and Limit Protection
  • we need to add a switch to set the homing
    position
  • we need to have overshoot switches

39
terminal program provides a user interface where
we can send commands to change the steering angle
desired angle
40
motor with gear reducer
flex coupling
optical encoder
41
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42
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