Download Motor Control Lab

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
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
motor
gear reducer and flex
couplings (if needed)
connect motor to
steering shaft
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.
EML 2023
Department 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 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
desired steering angle
compared to current steering angle
incremental optical
encoder (with homing
switch to initialize
position) feeds back
current motor position
gear reducer
motor
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
-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
EML 2023
Department of Mechanical and Aerospace Engineering
Interface to Computer
EML 2023
Department of Mechanical and Aerospace Engineering
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?
EML 2023
Department of Mechanical and Aerospace Engineering
When we want the motor to go
in the other direction, switch
these two wires.
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
Interface to Computer
EML 2023
Department of Mechanical and Aerospace Engineering
Interface to Computer
EML 2023
Department of Mechanical and Aerospace Engineering
Homing Switch
0V
+5V
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
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
USB connection
homing switch
incremental optical
encoder (with homing
switch to initialize
position) feeds back
current motor position
digital
signal
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