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 (43⅓ 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 motor’s 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. how is the motor connected to the steering shaft?
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. how does the computer know the current steering angle?
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) ($ 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 an index 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 #
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
limit switch
homing switch
optical encoder

36. Closed Loop Control

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

38. motor with
gear reducer
flex coupling
limit switch
homing switch
optical encoder

41. Summary of Closed-Loop Control
computer controls the current going to the motor
motor
gear reducer
desired steering angle
compared to current steering angle
gear reducer and flex couplings (if needed) connect motor to steering shaft
incremental optical encoder (with homing switch to initialize position) feeds back current motor position