motion control ece 105 industrial electronics
DESCRIPTION
MOTION CONTROL ECE 105 Industrial Electronics. Engr. Jeffrey T. Dellosa College of Engineering and Information Technology Caraga State University Ampayon, Butuan City. A motion control system generally consists of the following: Motion Controller Motor Driver / Amplifier - PowerPoint PPT PresentationTRANSCRIPT
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.
MOTOR CONTROLMOTOR CONTROL
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
Computer Motion Controller
Motor Driver
Motor
Block Diagram of a typical Motion Control System
MOTOR CONTROLMOTOR CONTROL
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
ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL
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.
ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL
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
ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL
Pulses Phase
ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL
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.
ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL
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
ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL
Pulses Counted
ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL
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
ENCODER-MOTOR CONTROLENCODER-MOTOR CONTROL
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
Computer Motion Controller
Motor Driver
Motor
Block Diagram of a typical Motion Control System
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
H-Bridge controls Motor for Forward Rotation
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
H-Bridge controls Motor for Reverse Rotation
+
-
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
H-Bridge controls Motor for Forward Rotation
closed
closedopen
open
+
-
S1 – S4 closed
+
Supply Voltage Vss
-
T2T1
Motor
HH--BRIDGEBRIDGE
H-Bridge controls Motor for Reverse Rotation
+
-
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