1. Servo Motor Control
Demonstration

2. incremental optical encoder
motor with
gear reducer
flex coupling
limit switch
homing switch
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: To ‘read’ the encoder:
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 0-5V 5 mA each
12 channels of digital input/outputs 0 or 5V, (8.5 mA for outputs)
1 counter

7. NI USB-6009

8. Interface to Computer

9. Honeywell / Clarostat 600128CN1
Allied Electronics part #
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? motor gear reducer
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. desired steering angle compared to current steering angle
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