Servo Motor Control

EML 2023 Department of Mechanical and Aerospace Engineering 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

gear box worm gear drive

epicyclic gear train ball screw drive

EML 2023 Department of Mechanical and Aerospace Engineering 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 the computer cause the motor to turn? How does this work? desired steering angle motor gear reducer 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 ground? 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 how does the computer cause the motor to turn? How does this work? desired steering angle motor gear reducer 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 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) ($ each at McMaster-Carr)

EML 2023 Department of Mechanical and Aerospace Engineering Incremental Optical Encoder

EML 2023 Department of Mechanical and Aerospace Engineering you can count pulses, but which way is it rotating? Incremental Optical Encoder

EML 2023 Department of Mechanical and Aerospace Engineering an encoder will typically also have an index that will ‘blink’ once each revolution Incremental Optical Encoder

EML 2023 Department 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

EML 2023 Department of Mechanical and Aerospace Engineering note:many encoders will have an index that will pulse once per revolution Incremental Optical Encoder

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

EML 2023 Department of Mechanical and Aerospace Engineering problem:- you start up the device - where are you when you start? Incremental Optical Encoder

EML 2023 Department of Mechanical and Aerospace Engineering Absolute Optical Encoder BEI brand 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 optical encoder motor with gear reducer flex coupling limit switchhoming switch

EML 2023 Department of Mechanical and Aerospace Engineering how does the computer cause the motor to turn? How does this work? desired steering angle motor gear reducer how is the motor connected to the steering shaft? how does the computer know the current steering angle? incremental optical encoder with homing switch to initialize position gear reducer and flex couplings (if needed) computer controls the current going to the motor

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

computer controls the current going to the motor Summary of Closed-Loop Control desired steering angle compared to current steering angle motor gear 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