eml 2023 – motor control lecture 3 – feedback sensor optical encoder
TRANSCRIPT
EML 2023 – Motor Control
Lecture 3 – Feedback SensorOptical Encoder
EML 2023Department of Mechanical and Aerospace Engineering 2
Closed Loop Control
Motor Driver
desired position current
Computer and DAQ
Motor
analog speed signal
digital direction signal
Encoder
sensed actual position
EML 2023Department of Mechanical and Aerospace Engineering 3
Let’s answer 3 questions.
1. How is the motor held in place and how is it connected to the shaft that it is to rotate?
2. How does the encoder work and how is it physically connected to the motor?
3. How do the DAQ and motor driver work?
Motor Driver
desired position
currentComputer and
DAQMotor
analog speed signal
digital direction signal
Encoder
sensed actual position
EML 2023Department of Mechanical and Aerospace Engineering
Servo Motor Control
means of angle measurement– optical encoder
• incremental• absolute
– potentiometer– resolver
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rotary encoder linear encoder
EML 2023Department of Mechanical and Aerospace Engineering
Incremental Optical Encoder
• this disk has 12 slots (30º resolution)
• typical incremental encodershave 2500 counts perrevolution (0.144º resolution)($298.74 each at McMaster-Carr)
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EML 2023Department of Mechanical and Aerospace Engineering
you can count pulses, but which way is it rotating?
Incremental Optical Encoder
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EML 2023Department of Mechanical and Aerospace Engineering
Incremental Optical Encoder
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EML 2023Department of Mechanical and Aerospace Engineering
quadrature: - there are 4n ‘events’ per one revolution of the disk- the resolution can in effect be four times the number of slots
Incremental Optical Encoder
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EML 2023Department of Mechanical and Aerospace Engineering
note: many encoders will have an index that will pulse once per revolution
Incremental Optical Encoder
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EML 2023Department of Mechanical and Aerospace Engineering
cost: $41.67
Honeywell / Clarostat 600128CN1Allied Electronics part # 753-0059
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EML 2023Department of Mechanical and Aerospace Engineering
problem: - you start up the device- where are you when you start?
Incremental Optical Encoder
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EML 2023Department of Mechanical and Aerospace Engineering
Absolute Optical Encoder
BEI brand encoder $455
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EML 2023Department of Mechanical and Aerospace Engineering
Homing Switch
• for an incremental optical encoder, we need to add a switch to set the homing position
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EML 2023Department of Mechanical and Aerospace Engineering 14
Limit Switches
• If there is a limited range of motion, then limit switches must also be added.
• homing switches are wired to and monitored by the control computer
• limit switches are wired so that they immediately shut off the power to the motor if they are pressed
EML 2023Department of Mechanical and Aerospace Engineering
optical encoder
motor withgear reducer
flex coupling
limit switchhoming switch
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EML 2023Department of Mechanical and Aerospace Engineering 16
EML 2023Department of Mechanical and Aerospace Engineering 17
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EML 2023Department of Mechanical and Aerospace Engineering 19
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EML 2023Department of Mechanical and Aerospace Engineering 21
EML 2023Department of Mechanical and Aerospace Engineering 22
Let’s answer 3 questions.
1. How is the motor held in place and how is it connected to the shaft that it is to rotate?
2. How does the encoder work and how is it physically connected to the motor?
3. How do the DAQ and motor driver work?
Motor Driver
desired position
currentComputer and
DAQMotor
analog speed signal
digital direction signal
Encoder
sensed actual position