servo motor control. eml 2023 department of mechanical and aerospace engineering design project you...

Servo Motor Control

EML 2023Department of Mechanical and Aerospace Engineering

Design Project

• You are to design a mechanical device that can tilt a given labyrinth board in two directions.

EML 2023Department of Mechanical and Aerospace Engineering

One Concept

• Could use two motors.• Must be able to control

the rotation angle of each.

EML 2023Department 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 2023Department of Mechanical and Aerospace Engineering

Design Choices

• What power source will be used?

• How much power is needed?

• Is a speed reducer needed?

• Open-loop or closed-loop control?

EML 2023Department of Mechanical and Aerospace Engineering

Design Choices

• What power source will be used?

• electric servo motor• electric stepper motor• hydraulic actuator• pneumatics

EML 2023Department of Mechanical and Aerospace Engineering

Design Choices

• How much power is needed?

• determine the maximum product of motor torque times angular velocity

EML 2023Department 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 2023Department 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 2023Department 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 rotate the labyrinth board ; further the rotational speed will be very low)

• Is a speed reducer needed?• yes

• Open-loop or closed-loop control?• closed-loop

EML 2023Department of Mechanical and Aerospace Engineering

how does the computer cause the motor to turn?

how does the computer cause the motor to turn?

How does this work?

desired steering angle

motorgear reducer

how is the motor connected to the steering shaft?

how is the motor connected to the steering shaft?

how does the computer know

the current steering angle?

how does the computer know

the current steering angle?

EML 2023Department of Mechanical and Aerospace Engineering

Motor and Gear Box

how is the motor connected to the steering shaft?

how is the motor connected to the steering shaft?

EML 2023Department of Mechanical and Aerospace Engineering

Motor and Gear Box

EML 2023Department of Mechanical and Aerospace Engineering

motor withgear reducer

flex coupling

EML 2023Department 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?

how does the computer know

the current steering angle?

EML 2023Department of Mechanical and Aerospace Engineering

Incremental Optical Encoder

• this disk has 12 slots (30º resolution)

• typical incremental encodershave up to 2540 counts perrevolution (0.142º resolution)($488.41 each at McMaster-Carr)

EML 2023Department of Mechanical and Aerospace Engineering

Incremental Optical Encoder

EML 2023Department of Mechanical and Aerospace Engineering

you can count pulses, but which way is it rotating?

Incremental Optical Encoder

EML 2023Department of Mechanical and Aerospace Engineering

an encoder will typically also have anindex that will ‘blink’ once each revolution

Incremental Optical Encoder

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

EML 2023Department of Mechanical and Aerospace Engineering

note: many encoders will have an index that will pulse once per revolution

Incremental Optical Encoder

EML 2023Department of Mechanical and Aerospace Engineering

cost: $41.67

Honeywell / Clarostat 600128CN1Allied Electronics part # 753-0059

EML 2023Department of Mechanical and Aerospace Engineering

problem: - you start up the device- where are you when you start?

Incremental Optical Encoder

EML 2023Department of Mechanical and Aerospace Engineering

Absolute Optical Encoder

BEI brand encoder $455

EML 2023Department of Mechanical and Aerospace Engineering

how does the computer cause the motor to turn?

how does the computer cause the motor to turn?

How does this work?

desired steering angle

motorgear reducer

how is the motor connected to the steering shaft?

how is the motor connected to the steering shaft?

how does the computer know

the current steering angle?

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 2023Department of Mechanical and Aerospace Engineering

How does the computer control the motor?

control the current (via the voltage)

EML 2023Department of Mechanical and Aerospace Engineering

optical encoder

motor withgear reducer

flex coupling

limit switchhoming switch

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

EML 2023Department of Mechanical and Aerospace Engineering

EML 2023Department of Mechanical and Aerospace Engineering

Servo Motor Control

• we will use a Galil motor control card to vary the current to the motor based on the error in the steering shaft angle

motorDesired angle Angle error controller ampDesired Current current signal Steering angleSteering angle

motorDesired angle Angle error controller ampDesired Current PWM signal Steering angleSteering angle

desired position

EML 2023Department of Mechanical and Aerospace Engineering

Homing and Limit Protection

• we need to add a switch to set the homing position• we need to have overshoot switches

desired angle

motorDesired angle Angle error controller ampDesired Current PWM signal Steering angleSteering angle

terminal program providesa user interface where we cansend commands to changethe steering angle

EML 2023Department of Mechanical and Aerospace Engineering

optical encoder

motor withgear reducer

flex coupling

limit switchhoming switch

EML 2023Department of Mechanical and Aerospace Engineering