Servo Motor Control

1. Servo Motor Control Demonstration

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

3. Closed-Loop Control How does the computer do this? 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 How does the computer ‘read’ the encoder information?

5. Computer Interface • To command the motor: • The computer must be able to generate an analog voltage signal that is somehow interpreted by the motor. • To ‘read’ the encoder: • The computer must be able to read the +5V and 0V pulses coming from the two light detectors on the optical encoder.

6. Interface to Computer • We will use a National Instruments USB-6009 data acquisition (DAQ) device • specs • USB interface to PC • 8 channels of analog input, 0-5V • 2 channels of analog output 0-5V5 mA each • 12 channels of digital input/outputs0 or 5V, (8.5 mA for outputs) • 1 counter

7. NI USB-6009

8. Interface to Computer

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

10. Computer Interface • Let’s start with digital inputs to interface to the optical encoder. notice that there are four wires

12. channels A & B will be either 0V or 5V depending on whether that light detector detects light through a slit or not ground channel A channel B +5V power

13. ground channel A channel B +5V power

14. Encoder Demo Program

16. Closed-Loop Control How does the computer do this? 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

17. Computer Interface to Motor • To control the motor: • the computer must be able to generate an analog voltage signal • however, the typical analog voltage signal that a computer generates does not have sufficient current to power the motor • an amplifier is used • a power supply provides 24V (7.5 amp max for our case) to the amp • the computer generates an analog voltage in the range of-5V to +5V; 0V means the motor is to stop ; -5V means the motor is to turn at a maximum speed CCW ; +5V means the motor is to turn at a maximum speed CW

18. Interface to Computer

19. command analog signal emergency stop to motor from 24V power supply

20. Issue with USB-6009 & Amp The analog command signal to the amp must be from -5V to +5V. A negative voltage causes the motor to turn in the opposite direction. The USB DAQ can only output from 0 to +5V. How can we reverse the direction of the motor?

21. When we want the motor to go in the other direction, switch these two wires. command analog signal emergency stop to motor from 24V power supply

22. Change motor direction To go CW, set this digital output pin to TRUE (+5V). To go CCW, set this digital output pin to FALSE (0V).

23. Interface to Computer

24. Interface to Computer

25. Homing Switch 0V +5V to input pin on USB DAQ

26. Interface to Computer 0V from USB-6009 +5V from USB-6009

27. digital signal E stop switch input power analog signal computer controls the current going to the motor USB connection desired steering angle compared to current steering angle gear reducer and flex couplings (if needed) connect motor to steering shaft USB connection incremental optical encoder (with homing switch to initialize position) feeds back current motor position digital signal homing switch 2 digital signals

29. Design Project • If you decide to use a servo motor in your design: • include an optical encoder for motor position feedback • include a homing switch to initialize your position • include E-stop switches as needed