Servo Motor Control Demonstration

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

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?

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.

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

NI USB-6009

Interface to Computer

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

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

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

ground channel A channel B +5V power

Encoder Demo Program

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

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

Interface to Computer

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

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?

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

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).

Interface to Computer

Interface to Computer

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

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

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

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