Download H-Bridge

MOTION CONTROL
ECE 105 Industrial Electronics
Engr. Jeffrey T. Dellosa
College of Engineering and Information Technology
Caraga State University
Ampayon, Butuan City
MOTOR CONTROL
APPLICATIONS :
ENCODER
•
A motion control system generally
consists of the following:
 Motion Controller
 Motor Driver / Amplifier
 Motion Sensor (for feedback)
MOTOR CONTROL
Motion
Controller
Motor
Driver
Motion
Sensor
Block Diagram of a typical
Motion Control System
Motor
Computer
MOTOR CONTROL
Description
Computer /
Motion
Controller
Function
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 /
Decodes PWM (magnitude) & DIR (Sign) signal and
Power Amplifier 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.
ENCODER
A 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

ENCODER
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.

MOTOR CONTROL
Motion
Controller
Motor
Driver
ENCODER
Motion
Sensor
Block Diagram of a typical
Motion Control System
Motor
Computer
ENCODER BLOCK
ENCODER
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.

ENCODER
Slot
(Figure 1)
A 16 count per revolution Code Disk
PHOTO INTERRUPTER
Code Disk
A pulse is given out
whenever the light is
blocked
Slot Sensor
ENCODER-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.

ENCODER-MOTOR CONTROL
Code
Disk
Comparators
A
Signal
Processing
Circuitry
LEDs
+
A
B
+
B
Channel A
Channel B
Photo
Diodes
(Figure 2)
90
Block Diagram of a 2-Channel Incremental Encoder
ENCODER-MOTOR CONTROL
By 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 photointerrupter.

ENCODER-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.

ENCODER-MOTOR CONTROL
• Output waveforms of the 2-channel incremental
encoder and the corresponding direction of
rotation.
Ch A
Ch A
Ch B
Ch B
Ch A leads Ch B,
Code disk is rotating
clockwise
Pulses Phase
Ch B leads Ch A,
Code disk is rotating
anti-clockwise
ENCODER-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 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:
ENCODER-MOTOR CONTROL
Motor Position
=
=
Pulses Counted
CPR
1250 count
500 count/rev
=
Pulses Counted
2.5 revolutions
ENCODER-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:
ENCODER-MOTOR CONTROL
Motor Speed
=
=
Pulses Frequency
=
=
Output Frequency
CPR
5000 count/sec
500 count/rev
10 rev/sec
600 rev/min
SUMMARY - ENCODER
Motor Position
 Pulse Count
Motor Speed
 Pulse Frequency
Motor Direction
 Pulse Phase
Questions
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?
Questions
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
Questions
1. A motor has a 500 count-per-revolution incremental
encoder attached to its shaft. If the output pulsetrain 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
Questions
1. A motor has a 500 count-per-revolution incremental
encoder attached to its shaft. If the output pulsetrain 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
MOTOR CONTROL
APPLICATIONS :
H-BRIDGE

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 CONTROL
Sends signals
Amplifies signals
H-BRIDGE
Motion
Controller
Motor
Driver
Motor
Computer
ENCODER
Motion
Sensor
Feedback actual situation
Block Diagram of a typical Motion Control System
H-BRIDGE
S3
S1
+
T1
+
T2
Motor
Supply Voltage
Vss
-
-
S2
H-Bridge Driver with Motor
S4

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.
H-BRIDGE
H-BRIDGE
Speed &
S1
open
+
Direction
T1
open
T2
+
Supply Voltage
Vss
S3
Motor
-
S2
open
H-Bridge Driver with Motor
S4
open
H-BRIDGE
S3
S1
+
T1
T2
+
Supply Voltage
Vss
Motor
-
S2
H-Bridge controls Motor for Forward Rotation
S4
S1 – S4
H-BRIDGE
S3
S1
open
closed
+
T1
T2
+
Supply Voltage
Vss
Motor
-
S2
open
H-Bridge controls Motor for Forward Rotation
S4
closed
H-BRIDGE
S3
S1
open
open
+
+
Supply Voltage
Vss
Motor
-
T1
-
T2
S2
open
H-Bridge controls Motor for Reverse Rotation
S4
open
S2 – S3
H-BRIDGE
S3
S1
closed
open
+
+
Supply Voltage
Vss
Motor
-
T1
-
T2
S2
closed
H-Bridge controls Motor for Reverse Rotation
S4
open

S1, S2, S3 and S4 are all open,
the motor will freewheel.
H-BRIDGE
H-BRIDGE
S1
Free-Wheeling
open
open
+
S3
+
Supply Voltage
Vss
Motor
-
T1
-
T2
S2
open
H-Bridge releases control of Motor
S4
open
S1 and S3 or S2 and S4 are closed,
the motor will brake.
H-BRIDGE
H-BRIDGE
Braking
S1
S3
closed
closed
+
+
Vss
Supply Voltage
Vss
Motor
Vss
-
T1
-
T2
S4
S2
open
open
H-Bridge brakes Motor
H-BRIDGE
Braking
S1
S3
open
open
+
+
0V
Supply Voltage
Vss
0V
Motor
-
T1
-
T2
S4
S2
closed
closed
H-Bridge brakes Motor

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.
H-BRIDGE

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.
H-BRIDGE

The Magnitude signal controls the speed of the
motor
The Sign signal controls the direction of the
motor.
 Sign = “1” clockwise
 Sign = “0” anti-clockwise

H-BRIDGE
H-BRIDGE
Magnit
Sign
ude
S1
S2
S3
S4
VT1
VT2
1
1
close
open
open
close
Vss
0V
1
0
open
close
close
open
0V
Vss
0
X
close
open
close
open
Vss
Vss
Logic Truth Table for Sign/Magnitude PWM
S1 – S4
closed
H-BRIDGE
S3
S1
open
closed
+
T1
T2
+
Supply Voltage
Vss
Motor
-
S2
open
H-Bridge controls Motor for Forward Rotation
S4
closed
S2 – S3
closed
H-BRIDGE
S3
S1
closed
open
+
+
Supply Voltage
Vss
Motor
-
T1
-
T2
S2
closed
H-Bridge controls Motor for Reverse Rotation
S4
open
H-BRIDGE
Magnit
Sign
ude
S1
S2
S3
S4
VT1
VT2
1
1
close
open
open
close
Vss
0V
1
0
open
close
close
open
0V
Vss
0
X
close
open
close
open
Vss
Vss
Logic Truth Table for Sign/Magnitude PWM
H-BRIDGE
Vss
Magnitude
S1
S3
Motor
Sign
T1
S2
T2
S4
Combinational Logic Circuit with H-Bridge Drive
H-BRIDGE
Forward
Direction
Reverse
Direction
Mag
Sign
VT1
VT2
VT1-VT2
Sign/Magnitude Pulse Width Modulation
APPLICATION :
MICRO-MOUSE
Thank You
for listening.
MOTION CONTROL
INDUSTRIAL ELECTRONICS