Servo Motor Control

Demonstration

EML 2023Department of Mechanical and Aerospace Engineering

motor withgear reducer

flex coupling

incremental optical

encoder

limit switchhoming switch

computer controls the current going to the

motor

computer controls the current going to the

motor

Closed-Loop Control

desired steering anglecompared to current steering angle

motorgear reducer

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 do this?

How does the computer ‘read’ the encoder information?

EML 2023Department of Mechanical and Aerospace Engineering

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 2023Department of Mechanical and Aerospace Engineering

NI USB-6009

EML 2023Department of Mechanical and Aerospace Engineering

Interface to Computer

EML 2023Department of Mechanical and Aerospace Engineering

cost: $41.67

Honeywell / Clarostat 600128CN1Allied Electronics part # 753-0059

EML 2023Department 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

+5V power

ground

channel A

channel B

channels A & B will be either 0V or 5V depending on whether that light detector detects light through a slit or not

+5V power

ground

channel A

channel B

EML 2023Department of Mechanical and Aerospace Engineering

Encoder Demo Program

computer controls the current going to the

motor

computer controls the current going to the

motor

Closed-Loop Control

desired steering anglecompared to current steering angle

motorgear reducer

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 do this?

EML 2023Department of Mechanical and Aerospace Engineering

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 2023Department of Mechanical and Aerospace Engineering

Interface to Computer

EML 2023Department 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 2023Department of Mechanical and Aerospace Engineering

Homing Switch

to input pin on USB DAQ

+5V

0V

EML 2023Department of Mechanical and Aerospace Engineering

Interface to Computer

0V from USB-60090V from USB-6009

+5V from USB-6009+5V from USB-6009

computer controls the current going to the

motor

computer controls the current going to the

motor

desired steering anglecompared 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

USB connection

analogsignal

2 digitalsignals

USB connection

digitalsignal

digitalsignal

input power

homing switch

E stopswitch

EML 2023Department of Mechanical and Aerospace Engineering

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 2023Department of Mechanical and Aerospace Engineering

EML 2023Department of Mechanical and Aerospace Engineering

EML 2023Department of Mechanical and Aerospace Engineering

EML 2023Department of Mechanical and Aerospace Engineering