Motor Control Lab
Servo Motor Control
Design Problem
• You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide.
• Tasks – determine puck location – position blocker
EML 2023 Department of Mechanical and Aerospace Engineering
Concepts
• You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide.
• Tasks – determine puck location • camera placed above
table
– position blocker
EML 2023 Department of Mechanical and Aerospace Engineering
Concepts
• You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide.
• Tasks – determine puck location • camera placed above
table
– position blocker • linear motion of blocker
piece using belt and pulleys
• linear motion of blocker
using screw
• linear motion of blocker
using slider crank mechanism
• rotational motion of blocker piece
EML 2023 Department of Mechanical and Aerospace Engineering
Concepts
• You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide.
• Tasks – determine puck location • camera placed above
table
– position blocker • linear motion of blocker
piece using belt and pulleys
• linear motion of blocker
using screw
• linear motion of blocker
using slider crank mechanism
• rotational motion of blocker piece
EML 2023 Department of Mechanical and Aerospace Engineering
Concepts
• You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide.
• Tasks – determine puck location • camera placed above
table
– position blocker • linear motion of blocker
piece using belt and pulleys
• linear motion of blocker
using screw
• linear motion of blocker
using slider crank mechanism
• rotational motion of blocker piece
EML 2023 Department of Mechanical and Aerospace Engineering
Concepts
• You are to design an automated goalie for an air hockey table. The goalie can be 1 inch wide.
• Tasks – determine puck location • camera placed above
table
– position blocker • linear motion of blocker
piece using belt and pulleys
• linear motion of blocker
using screw
• linear motion of blocker
using slider crank mechanism
• rotational motion of blocker piece
EML 2023 Department of Mechanical and Aerospace Engineering
Concept Selection
• list the pro’s and con’s of each design • formulate concept evaluation table
EML 2023 Department of Mechanical and Aerospace Engineering
Other Design Choices
• power – electric servo motor – electric stepper motor – hydraulic actuator – pneumatics • open or closed loop control – open loop – closed loop • closed loop control requires a feedback sensor to measure the motor’s rotation
EML 2023 Department of Mechanical and Aerospace Engineering
Another Example
• Control the steering angle of an autonomous ground vehicle.
• Must be able to control the rotation angle.
EML 2023 Department of Mechanical and Aerospace Engineering
How to pick a motor?
• How much power is needed?
• Is a speed reducer needed?
EML 2023 Department of Mechanical and Aerospace Engineering
Design Choices
• How much power is needed?
• determine the maximum product of motor torque times angular velocity
EML 2023 Department of Mechanical and Aerospace Engineering
Design Choices
• Is a speed reducer needed?
• a typical DC motor can rotate at a top speed of 2600 rpm (43⅓ rev/sec) • gear box • epicyclic gear train • ball screw drive
EML 2023 Department of Mechanical and Aerospace Engineering
gear box worm gear drive
epicyclic gear train ball screw drive
Design Choices
• Open-loop or closed-loop control?
• open-loop • well suited for remote control using a joystick • computer control can be implemented using a stepper motor • closed-loop • requires a sensor to measure the motor’s rotation angle
EML 2023 Department of Mechanical and Aerospace Engineering
Design Choices
• What power source will be used?
• electric servo motor • How much power is needed?
• experiment or perform analysis (very little torque will be needed to move the goalie; further the rotational speed will be very low) • Is a speed reducer needed?
• yes • Open-loop or closed-loop control?
• closed-loop
EML 2023 Department of Mechanical and Aerospace Engineering
How does this work?
motor gear reducer desired steering angle how does the computer cause the motor to turn?
how is the motor connected to the steering shaft?
how does the computer know the current steering angle?
EML 2023 Department of Mechanical and Aerospace Engineering
Motor and Gear Box
how is the motor connected to the steering shaft?
EML 2023 Department of Mechanical and Aerospace Engineering
Motor and Gear Box
EML 2023 Department of Mechanical and Aerospace Engineering
motor with gear reducer flex coupling
EML 2023 Department of Mechanical and Aerospace Engineering
Servo Motor Control
select means of angle measurement – optical encoder • incremental • absolute – potentiometer – resolver how does the computer know the current steering angle?
EML 2023 Department of Mechanical and Aerospace Engineering
Incremental Optical Encoder • this disk has 12 slots (30º resolution) • typical incremental encoders have up to 2540 counts per revolution (0.142º resolution) ($488.41 each at McMaster-Carr)
EML 2023 Department of Mechanical and Aerospace Engineering
Incremental Optical Encoder
EML 2023 Department of Mechanical and Aerospace Engineering
Incremental Optical Encoder you can count pulses, but which way is it rotating?
EML 2023 Department of Mechanical and Aerospace Engineering
Incremental Optical Encoder an encoder will typically also have an index that will ‘blink’ once each revolution
EML 2023 Department of Mechanical and Aerospace Engineering
Incremental Optical Encoder quadrature: there are 4n ‘events’ per one revolution of the disk - the resolution can in effect be four times the number of slots
EML 2023 Department of Mechanical and Aerospace Engineering
Incremental Optical Encoder note: many encoders will have an index that will pulse once per revolution
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
Incremental Optical Encoder problem: - you start up the device - where are you when you start?
EML 2023 Department of Mechanical and Aerospace Engineering
Absolute Optical Encoder BEI brand encoder $455
EML 2023 Department of Mechanical and Aerospace Engineering
Homing and Limit Protection
• for an incremental optical encoder, we need to add a switch to set the homing position • we also need to have limit switches
EML 2023 Department of Mechanical and Aerospace Engineering
motor with gear reducer flex coupling optical encoder homing switch limit switch
EML 2023 Department of Mechanical and Aerospace Engineering
How does this work?
motor gear reducer desired steering angle computer controls the current going to the motor how does the computer cause the motor to turn?
how is the motor connected to the steering shaft?
gear reducer and flex couplings (if needed) how does the computer know the current steering angle?
incremental optical encoder with homing switch to initialize position
EML 2023 Department of Mechanical and Aerospace Engineering
How does the computer control the motor?
control the current (via the voltage)
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
EML 2023 Department of Mechanical and Aerospace Engineering
Summary of Closed-Loop Control
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
