MOTION CONTROL ECE 105 Industrial Electronics

MOTION CONTROLMOTION CONTROLECE 105 Industrial ElectronicsECE 105 Industrial Electronics

Engr. Jeffrey T. DellosaCollege of Engineering and Information Technology

Caraga State UniversityAmpayon, Butuan City

MOTOR CONTROLMOTOR CONTROLAPPLICATIONS :APPLICATIONS :ENCODERENCODER

• A motion control system generally consists of the following:

Motion Controller Motor Driver / Amplifier Motion Sensor (for feedback)

Motion Sensor

Computer Motion Controller

Motor Driver

Motor

Block Diagram of a typical Motion Control System

MOTOR CONTROLMOTOR CONTROL

Description Function

Computer / Motion Controller

The motion control system determines the desired velocity profile of the motor under control and monitors the actual motor velocity via the motion sensor and makes the necessary adjustments.

Motor Driver / Power Amplifier

Decodes PWM (magnitude) & DIR (Sign) signal and provides an amplified signal with the necessary higher voltages and higher currents required to power the motor.

Motion Sensor Usually a rotary shaft encoder that provides the motor’s positional, speed and directional information as feedback to the Motion Controller.


ENCODERENCODERA shaft encoder is a sensor that measures the

position or rotation rate of a motor’s shaft. Typically, a shaft encoder is mounted on the output shaft of a drive motor.

There are basically two types of shaft encoders:

• Absolute Encoders • Incremental Encoders

ENCODERENCODER

The output signal of an absolute encoder is a code that corresponds to a particular orientation or position of the shaft.

The output signal of an incremental encoder is a pulse train that indicates the rotation of the shaft.

Motion Sensor


Motor Driver

Motor



ENCODER

ENCODER BLOCKENCODER BLOCK

ENCODERENCODER

The rate at which the pulses are produced corresponds to the rate at which the shaft turns.

An incremental shaft encoder contains a spinning code disk (Figure 1) that has slots cut in it, this code disk is attached to the motor shaft and spins with it.

Slot

(Figure 1)

A 16 count per revolution Code Disk

ENCODERENCODER

PHOTO INTERRUPTERPHOTO INTERRUPTER

A pulse is given outwhenever the light is

blocked

Code Disk

Slot Sensor

ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL

An LED is placed on one side of the code disk’s slots and a phototransistor or photodiode on the other side. (Figure 2)

As the code disk spins, the moving slots interrupts the light passing through the code disk and a signal in the form of a pulse train is produced at the output of the phototransistor.

(Figure 2)

Block Diagram of a 2-Channel Incremental Encoder


Photo Diodes

Signal Processing Circuitry

LEDs

Channel A A

Channel B

Comparators Code Disk

A

B

B+

+

90

ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROLBy counting these pulses, we can tell how much

the motor has rotated.The combination of such a LED emitter and a

photo-detector, packaged for the purpose of being mounted on either side of a shaft encoder’s code disk, is called a photo-interrupter.


In 2-channel incremental encoder, there are 2 outputs, Channel A and Channel B with two pulse trains.

These 2 pulse trains are 90o out of phase, and the relative phase difference between them corresponds to the direction of rotation of the code disk and thus the motor shaft.

• Output waveforms of the 2-channel incremental encoder and the corresponding direction of rotation.

Ch A

Ch B

Ch A

Ch B

Ch A leads Ch B, Ch B leads Ch A, Code disk is rotating Code disk is rotating

clockwise anti-clockwise


Pulses Phase


The number of slot / bar pairs on the code disk determines the resolution of the incremental encoder.

One slot on the code disk gives one output pulse (or count) and more slots or counts per revolution (CPR) increases the resolution.


Example 1 A 500-count per revolution incremental

encoder mounted on the shaft of a motor will output 500 pulses when the motor shaft has rotated 1 complete revolution. If there were a total of 1250 pulses counted, the motor shaft would have rotated:

2.5 revolutionscount/rev500

count1250

CPR

Pulses CountedMotor Position


Pulses Counted


Example 2 A 500-count per revolution incremental

encoder mounted on the shaft of a motor.

If the output of the incremental encoder has an output frequency of 5 kHz, then the speed of the motor shaft is:

600 rev/min10 rev/sec

count/rev500

count/sec5000

CPR

Output FrequencySpeedMotor


Pulses Frequency

SUMMARY - ENCODERSUMMARY - ENCODER

Motor Position

Motor Speed

Motor Direction

Pulse Count

Pulse Frequency

Pulse Phase

QuestionsQuestions

1. A motor has a 512 CPR incremental encoder attached to it. The output of the encoder is connected to a counter, which counts the pulses. After the motor has moved and come to a complete halt, the counter indicates a total of 35,840 counts.

What is the total amount the shaft has rotated?

QuestionsQuestions

1. A motor has a 512 CPR incremental encoder attached to it. The output of the encoder is connected to a counter, which counts the pulses. After the motor has moved and come to a complete halt, the counter indicates a total of 35,840 counts.

What is the total amount the shaft has rotated?

70 revolutions

QuestionsQuestions

1. A motor has a 500 count-per-revolution incremental encoder attached to its shaft. If the output pulse-train of the encoder has a frequency of 43 kHz.

What is the rotational speed of the motor shaft? rps

What is the rotational speed of the motor shaft? rpm

QuestionsQuestions

1. A motor has a 500 count-per-revolution incremental encoder attached to its shaft. If the output pulse-train of the encoder has a frequency of 43 kHz.

What is the rotational speed of the motor shaft? rps

86 rps

What is the rotational speed of the motor shaft? rpm

5160 rpm

A microprocessor or motion controller cannot drive a motor directly since it cannot supply enough voltage and current.

There must be some intermediate or interfacing circuitry used to control the motor. It is a Motor Driver.

MOTOR CONTROLAPPLICATIONS :

H-BRIDGE

Motion Sensor


Motor Driver

Motor


MOTOR CONTROLMOTOR CONTROLSends signals Amplifies signals

Feedback actual situation

H-BRIDGE

ENCODER

HH--BRIDGEBRIDGE

S4

S3S1

S2

+

Supply Voltage Vss

-

T1 T2 Motor

H-Bridge Driver with Motor

+

-

HH--BRIDGEBRIDGE

The switches in the H-bridge can be implemented using relays, bipolar transistors or field effect transistors.

The control signals from the motion controller are used to open or close these switches to achieve speed and direction control.

HH--BRIDGEBRIDGE

S1

S2

+

Supply Voltage Vss

-

T2T1

S4

S3

Motor

H-Bridge Driver with Motor

open

openopen

open

+

-

Speed &

Direction

HH--BRIDGEBRIDGE

S1

S2

+

Supply Voltage Vss

-

T2T1

S4

S3

Motor

H-Bridge controls Motor for Forward Rotation

+

-

HH--BRIDGEBRIDGE

S1

S2

+

Supply Voltage Vss

-

T2T1

S4

S3

Motor


closed

closedopen

open

+

-

S1 – S4

+

Supply Voltage Vss

-

T2T1

Motor

HH--BRIDGEBRIDGE

H-Bridge controls Motor for Reverse Rotation

+

-

S1

S2

open

openS4

S3

open

open

+

Supply Voltage Vss

-

T2T1

Motor

HH--BRIDGEBRIDGE


+

-

S3

open

closedS1

S2

open

closed

S2 – S3

S4

HH--BRIDGEBRIDGE

S1, S2, S3 and S4 are all open, the motor will freewheel.

+

Supply Voltage Vss

-

T2T1

Motor

HH--BRIDGEBRIDGE

H-Bridge releases control of Motor

+

-

S3

open

openS1

S2

open

open

Free-Wheeling

S4

HH--BRIDGEBRIDGE

S1 and S3 or S2 and S4 are closed, the motor will brake.

+

Supply Voltage Vss

-

T2T1

Motor

HH--BRIDGEBRIDGE

H-Bridge brakes Motor

+

-

S3

open

closedS1

S2

closed

open

Braking

S4

Vss Vss

+

Supply Voltage Vss

-

T2T1

Motor

HH--BRIDGEBRIDGE

H-Bridge brakes Motor

+

-

S3

closed

openS1

S2

open

closed

Braking

S4

0V 0V

HH--BRIDGEBRIDGE

To control the speed of the motor, the switches are opened and closed at different rates in order to apply different average voltages across the motor.

This technique is called pulse-width modulation.

HH--BRIDGEBRIDGE

One of the more popular forms of PWM for motor control is Sign / Magnitude PWM.

This consists of separate direction (Sign) and amplitude (Magnitude) signals with the Magnitude signal duty-cycle modulated as a normal pulse-width modulated signal.

HH--BRIDGEBRIDGE

The Magnitude signal controls the speed of the motor

The Sign signal controls the direction of the motor.

Sign = “1” clockwiseSign = “0” anti-clockwise

Magnitude

Sign S1 S2 S3 S4 VT1 VT2

1 1 close open Vss 0V

1 0 0V Vss

0 X Vss Vss

Logic Truth Table for Sign/Magnitude PWM

HH--BRIDGEBRIDGE

close

closeclose

closeclose

open

open open

openopen

HH--BRIDGEBRIDGE

S1

S2

+

Supply Voltage Vss

-

T2T1

S4

S3

Motor


closed

closedopen

open

+

-

S1 – S4 closed

+

Supply Voltage Vss

-

T2T1

Motor

HH--BRIDGEBRIDGE


+

-

S3

open

closedS1

S2

open

closedS4

S2 – S3 closed

Magnitude

Sign S1 S2 S3 S4 VT1 VT2

1 1 close open Vss 0V

1 0 0V Vss

0 X Vss Vss

Logic Truth Table for Sign/Magnitude PWM

HH--BRIDGEBRIDGE

close

closeclose

closeclose

open

open open

openopen

HH--BRIDGEBRIDGE

Combinational Logic Circuit with H-Bridge Drive

T2T1

Vss

Sign

Magnitude

Motor

S1

S2

S3

S4

Sign

Mag

VT1-VT2

VT1

VT2

Forward Direction

Reverse Direction

HH--BRIDGEBRIDGE

Sign/Magnitude Pulse Width Modulation

APPLICATION :MICRO-MOUSE

Thank You Thank You for listening.for listening.

MOTION CONTROLMOTION CONTROLINDUSTRIAL ELECTRONICSINDUSTRIAL ELECTRONICS

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MOTION CONTROL ECE 105 Industrial Electronics