Servo Motor Control

1. Servo Motor Control

2. Design Problem • You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide. • Tasks • determine puck location • position blocker

3. Concepts • You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide. • Tasks • determine puck location • camera placed abovetable • position blocker

4. Concepts • You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide. • Tasks • determine puck location • camera placed abovetable • position blocker • linear motion of blockerpiece using belt andpulleys • linear motion of blockerusing screw • linear motion of blockerusing slider crank mechanism • rotational motion of blocker piece

5. Concepts • You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide. • Tasks • determine puck location • camera placed abovetable • position blocker • linear motion of blockerpiece using belt andpulleys • linear motion of blockerusing screw • linear motion of blockerusing slider crank mechanism • rotational motion of blocker piece

6. Concepts • You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide. • Tasks • determine puck location • camera placed abovetable • position blocker • linear motion of blockerpiece using belt andpulleys • linear motion of blockerusing screw • linear motion of blockerusing slider crank mechanism • rotational motion of blocker piece

7. Concepts • You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide. • Tasks • determine puck location • camera placed abovetable • position blocker • linear motion of blockerpiece using belt andpulleys • linear motion of blockerusing screw • linear motion of blockerusing slider crank mechanism • rotational motion of blocker piece

8. Concept Selection • list the pro’s and con’s of each design • formulate concept evaluation table

9. Other Design Choices • power • electric servo motor • electric stepper motor • hydraulic actuator • pneumatics • open or closed loop control • open loop • closed loop • closed loop control requires a feedback sensor to measure the motor’s rotation

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

11. How to pick a motor? • How much power isneeded? • Is a speed reducer needed?

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

13. 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

14. gear box worm gear drive

15. epicyclic gear train ball screw drive

16. 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

17. 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 move the goalie; further the rotational speed will be very low) • Is a speed reducer needed? • yes • Open-loop or closed-loop control? • closed-loop

18. 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?

19. Motor and Gear Box how is the motor connected to the steering shaft?

20. Motor and Gear Box

21. motor with gear reducer flex coupling

22. Servo Motor Control select means of angle measurement • optical encoder • incremental • absolute • potentiometer • resolver how does the computer know the current steering angle?

23. 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)

24. Incremental Optical Encoder

25. Incremental Optical Encoder you can count pulses, but which way is it rotating?

26. Incremental Optical Encoder an encoder will typically also have anindex that will ‘blink’ once each revolution

27. 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

28. Incremental Optical Encoder note: many encoders will have an index that will pulse once per revolution

29. Honeywell / Clarostat 600128CN1 Allied Electronics part # 753-0059 cost: $41.67

30. Incremental Optical Encoder problem: - you start up the device - where are you when you start?

31. Absolute Optical Encoder BEI brand encoder $455

32. Homing and Limit Protection • for an incremental optical encoder, we need to add a switch to set the homing position • we also need to have limit switches

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

34. 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

35. How does the computer control the motor? control the current (via the voltage)

43. 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