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MOTION CONTROL ECE 105 Industrial Electronics

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

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MOTION CONTROL ECE 105 Industrial Electronics

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  1. MOTION CONTROLECE 105 Industrial Electronics Engr. Jeffrey T. Dellosa College of Engineering and Information Technology Caraga State University Ampayon, Butuan City

  2. A motion control system generally consists of the following: • Motion Controller • Motor Driver / Amplifier • Motion Sensor (for feedback) MOTOR CONTROLAPPLICATIONS :ENCODER

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

  4. MOTOR CONTROL Description Function Computer / Motion Controller The motion control system determines the desired velocityprofile 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.

  5. 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

  6. 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. ENCODER

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

  8. ENCODER BLOCK

  9. 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

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

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

  12. 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

  13. ENCODER-MOTOR CONTROL Code Disk Comparators A + Signal Processing Circuitry Channel A A LEDs B + Channel B B Photo Diodes 90 (Figure 2) Block Diagram of a 2-Channel Incremental Encoder

  14. 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

  15. 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

  16. ENCODER-MOTOR CONTROL Ch A Ch A Ch B Ch B • Output waveforms of the 2-channel incremental • encoder and the corresponding direction of • rotation. Ch A leads Ch B, Ch B leads Ch A, Code disk is rotating Code disk is rotating clockwiseanti-clockwise Pulses Phase

  17. 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

  18. 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

  19. ENCODER-MOTOR CONTROL 1250 count = 500 count/rev Pulses Counted Motor Position = CPR = 2.5 revolutions Pulses Counted

  20. 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

  21. ENCODER-MOTOR CONTROL 5000 count/sec = 500 count/rev = 10 rev/sec = 600 rev/min Output Frequency = Motor Speed CPR Pulses Frequency

  22. SUMMARY - ENCODER Motor Position  Motor Speed  Motor Direction  Pulse Count Pulse Frequency PulsePhase

  23. Questions • 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?

  24. Questions • 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

  25. Questions • 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

  26. Questions • 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

  27. MOTOR CONTROLAPPLICATIONS : 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.

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

  29. H-BRIDGE S3 S1 + T1 T2 Motor + Supply Voltage Vss - - S4 S2 H-Bridge Driver with Motor

  30. The switchesin the H-bridge can be implemented using relays, bipolar transistors or field effect transistors. • The control signals from the motion controller are used to openor close these switches to achievespeedanddirection control. H-BRIDGE

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

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

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

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

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

  36. S1, S2, S3 and S4 are all open, the motor will freewheel. H-BRIDGE

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

  38. S1 and S3orS2 and S4 are closed, the motor will brake. H-BRIDGE

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

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

  41. 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

  42. 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

  43. 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

  44. H-BRIDGE Magnitude Sign S1 S2 S3 S4 VT1 VT2 1 1 close open open close Vss 0V open close close open 0 1 0V Vss close open close open 0 X Vss Vss Logic Truth Table for Sign/Magnitude PWM

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

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

  47. H-BRIDGE Magnitude Sign S1 S2 S3 S4 VT1 VT2 1 1 close open open close Vss 0V open close close open 0 1 0V Vss close open close open 0 X Vss Vss Logic Truth Table for Sign/Magnitude PWM

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

  49. H-BRIDGE Forward Direction Reverse Direction Mag Sign VT1 VT2 VT1-VT2 Sign/Magnitude Pulse Width Modulation

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