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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