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)

Motion Sensor Computer Motion Controller Motor Driver Motor Block Diagram of a typical Motion Control System MOTOR CONTROL

DescriptionFunction 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 SensorUsually a rotary shaft encoder that provides the motor’s positional, speed and directional information as feedback to the Motion Controller. MOTOR CONTROL

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.

Motion Sensor Computer Motion Controller Motor Driver Motor Block Diagram of a typical Motion Control System MOTOR CONTROL ENCODER

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.

Slot (Figure 1) A 16 count per revolution Code Disk ENCODER

PHOTO INTERRUPTER A pulse is given out whenever the light is blocked Code Disk 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.

(Figure 2) Block Diagram of a 2-Channel Incremental Encoder ENCODER-MOTOR CONTROL Photo Diodes Signal Processing Circuitry LEDs Channel A A Channel B Comparators Code Disk A B B 

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 photo- interrupter.

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 90 o 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 CONTROL Pulses Phase

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:

2.5 revolutions  count/rev500 count1250  CPR Pulses Counted Motor Position  ENCODER-MOTOR CONTROL Pulses Counted

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:

600 rev/min  10 rev/sec  count/rev500 count/sec5000  CPR Output Frequency SpeedMotor  ENCODER-MOTOR CONTROL Pulses Frequency

SUMMARY - ENCODER Motor Position  Motor Speed  Motor Direction  Pulse Count Pulse Frequency 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 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

Questions 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 CONTROL APPLICATIONS : H-BRIDGE

Motion Sensor Computer Motion Controller Motor Driver Motor Block Diagram of a typical Motion Control System MOTOR CONTROL Sends signalsAmplifies signals Feedback actual situation H-BRIDGE ENCODER

S4 S3 S1 S2 + Supply Voltage Vss - T1T2 Motor H-Bridge Driver with Motor + -

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.

S1 S2 + Supply Voltage Vss - T2 T1 S4 S3 Motor H-Bridge Driver with Motor open + - Speed & Direction

S1 S2 + Supply Voltage Vss - T2 T1 S4 S3 Motor H-Bridge controls Motor for Forward Rotation + -

S1 S2 + Supply Voltage Vss - T2 T1 S4 S3 Motor H-Bridge controls Motor for Forward Rotation closed open + - S1 – S4

+ Supply Voltage Vss - T2 T1 Motor H-Bridge controls Motor for Reverse Rotation + - S1 S2 open S4 S3 open

+ Supply Voltage Vss - T2 T1 Motor H-Bridge controls Motor for Reverse Rotation + - S3 open closed S1 S2 open closed S2 – S3 S4

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

+ Supply Voltage Vss - T2 T1 Motor H-Bridge releases control of Motor + - S3 open S1 S2 open Free-Wheeling S4

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

+ Supply Voltage Vss - T2 T1 Motor H-Bridge brakes Motor + - S3 open closed S1 S2 closed open Braking S4 Vss

+ Supply Voltage Vss - T2 T1 Motor H-Bridge brakes Motor + - S3 closed open S1 S2 open closed Braking S4 0V

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.

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.

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

Magnit ude SignS1S2S3S4V T1 V T2 11 closeopen Vss0V 1 0 Vss 0X Logic Truth Table for Sign/Magnitude PWM close open

S1 S2 + Supply Voltage Vss - T2 T1 S4 S3 Motor H-Bridge controls Motor for Forward Rotation closed open + - S1 – S4 closed

+ Supply Voltage Vss - T2 T1 Motor H-Bridge controls Motor for Reverse Rotation + - S3 open closed S1 S2 open closed S4 S2 – S3 closed

Magnit ude SignS1S2S3S4V T1 V T2 11 closeopen Vss0V 1 0 Vss 0X Logic Truth Table for Sign/Magnitude PWM close open

Combinational Logic Circuit with H-Bridge Drive T2 T1 Vss Sign Magnitude Motor S1 S2 S3 S4

Sign Mag V T1 -V T2 V T1 V T2 Forward Direction Reverse Direction Sign/Magnitude Pulse Width Modulation

APPLICATION : MICRO-MOUSE

Thank You for listening. MOTION CONTROL INDUSTRIAL ELECTRONICS