DC Motor Speed control

Discussion in 'The Projects Forum' started by embpic, Jul 15, 2014.

  1. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
    Which is best method for controlling dc motor speed.?
    PWM, ENCODER, PID???
    I never used the Encode and PID so no idea which method is good to use.
    I need bit precise movement.
     
  2. Bill G

    New Member

    Jul 14, 2014
    8
    2
    A little more info would be helpful such as, horsepower and torque, voltage, type of motor - series, shunt, etc., power supply - battery or power supply application - heavy starting torque or light
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
    2,369
    All three, PWM, smoother than Triac/SCR using mains frequency.
    Encoder for position feedback.
    PID to control the loop.
    You could also design for velocity feedback using a DC tach, or digital tach converted for summing with the control signal.
    What type of control method did you have in mind?
    The current popular methods are ±10vdc analogue or step/direction pulses.
    What is the purpose of the control?
    Max.
     
  4. Alberto

    Active Member

    Nov 7, 2008
    169
    36
    PWM is the way you control the speed of the DC motor. Modifying the dutycycle you you apply more power or you reduce it.

    Encoder is the way to know at which speed your motor is turning, counting the number of pulses it can tell you also how much travell you have done. In other words is your velocity feedback.

    PID is an algoritm that collects information coming from the encoder and compare them with your velocity input and elaborate which is the best Duty CYCLE to keep the velocity you have input ( setpoint)

    In conclusion you will need all three for a close loop velocity controller.

    Cheers

    Alberto
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
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    I would not necessarily agree, there are velocity drives out there that operate purely with a DC tach, although they have dropped in favour of torque mode drives when used in position control.
    Encoder is required for precise positioning, Tach if just used for precise rpm control.
    Up until the early 70's velocity drives were the norm in CNC or servo positioning.
    The encoder went back to the controller.
    Max.
     
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  6. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
    Thank you sir.
    which type of encoder's are used normally.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Resolution Depends mainly on the application, and type depends on what the controller is designed to receive.
    The most common being the optical incremental quadrature encoder.
    For very low resolution one can be constructed with a dual Opto slot sensor and a slotted disc.
    If the controller is designed for it, the resolution can be increased by x4 in a fairly simple manner.
    Max.
     
  8. embpic

    Thread Starter Member

    May 29, 2013
    187
    3
    i need to measure 2000rpm
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
    2,369
    If just RPM control a single pulse tach could be used, this could be a single slot opto and a disc with one or more slots.
    This is the method that most Treadmill motors use.
    You would need to decode it at the processor or controller end of course.
    One method used with the Picmicro is the timer1 capture input (CCP module).
    This method does not give position or direction though.
    Max.
     
  10. IC-Man

    New Member

    Jan 3, 2012
    26
    4
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