Servo Motor Control
Demonstration

motor with gear reducer flex coupling incremental optical encoder homing switch limit switch
EML 2023
Department of Mechanical and Aerospace Engineering

Closed-Loop Control
How does the computer do this?
computer controls the current going to the motor gear reducer motor desired steering angle compared to current steering angle incremental optical encoder (with homing switch to initialize position) feeds back current motor position
How does the computer
‘read’ the encoder information?
gear reducer and flex couplings (if needed) connect motor to steering shaft

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
EML 2023
Department of Mechanical and Aerospace Engineering

NI USB-6009
EML 2023
Department of Mechanical and Aerospace Engineering

Interface to Computer
EML 2023
Department of Mechanical and Aerospace Engineering

Honeywell / Clarostat 600128CN1
Allied Electronics part # 753-0059 cost: $41.67
EML 2023
Department of Mechanical and Aerospace Engineering

Computer Interface
• Let’s start with digital inputs to interface to the optical encoder.
notice that there are four wires
EML 2023
Department of Mechanical and Aerospace Engineering

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
EML 2023
Department of Mechanical and Aerospace Engineering

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

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
-0 to +5V; 0V means the motor is to stop ; +5V means the motor is to turn at a maximum speed
• a digital signal will give the desired direction (0 V, CCW, 5 V CW)
EML 2023
Department of Mechanical and Aerospace Engineering

Interface to Computer
EML 2023
Department of Mechanical and Aerospace Engineering

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).
EML 2023
Department of Mechanical and Aerospace Engineering

0V
+5V
Homing Switch to input pin on USB DAQ
EML 2023
Department of Mechanical and Aerospace Engineering

Interface to Computer
0V from USB-6009
+5V from USB-6009
EML 2023
Department of Mechanical and Aerospace Engineering

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

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
EML 2023
Department of Mechanical and Aerospace Engineering

EML 2023
Department of Mechanical and Aerospace Engineering

EML 2023
Department of Mechanical and Aerospace Engineering

EML 2023
Department of Mechanical and Aerospace Engineering

EML 2023
Department of Mechanical and Aerospace Engineering