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  1. #1

    Unhappy Stepper motor positioning error

    Any help with be useful for me as I'm stuck .So, I have a machine with a stepper motor which I can control using an HMI having two parameters, 1) number of pulses and 2) speed of motor( i.e PPS or Freq). Now I have used microstepping and further subdivided my 200 steps per revolution motor to 4000 steps per revolution with "microstepping for each step" as 20.
    Now I want my stepper motor to make half a rotation. If I'm not wrong, if I give 4000 pulses it would make a full rotation. So, for half a rotation, i am setting the first parameter 1) number of pulses to 2000. As far I know, the second parameter (PPS) should have nothing to do with motor positioning and only have to do with speed. But, when I am changing the PPS, the stepper motor final positioning changes. If I keep the PPS as 2000, it is making a half rotation but very slowly. If I am changing it to say 13000 (to improve the speed), my stepper motor is only rotating around 40 degree instead of 180 degree intended. Why is the second parameter changing my motor position? What am I doing wrong here. I checked my stepper driver and it supports upto 200kHz frequency. I just want the motor to make a half rotation but faster. Please help me as I have tried everything but couldn't do it.

  2. #2
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    Mar 2009
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    1674

    Re: Stepper motor positioning error

    A bit basic:
    stepper motor makes one step per one pulse. If you will generate 1kHz you will get 1000 steps per second.

  3. #3

    Re: Stepper motor positioning error

    That's right. That's what I am saying, the PPS has everything to do with the speed, the higher I keep the frequency, more the steps will be per second. So, that means it will complete the PPR (pulse per revolution) faster. But, the PPS should not govern the motor position, right? as the number of steps is not changing just the number of steps in a second is. Am i missing something here?

  4. #4
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    Nov 2013
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    1373

    Re: Stepper motor positioning error

    Hi,

    So, that means it will complete the PPR (pulse per revolution) faster. But, the PPS should not govern the motor position, right? as the number of steps is not changing just the number of steps in a second is. Am i missing something here?
    Yes, that is correct.

    The main reason we use microstepping is for smoothness of motion. Its tempting to believe that it also increases the resolution but in doesn't work out that way in practice. In fact at half stepping, that is 400 steps/rev is about as good a resolution
    you can get with a stepper. The torque between micro steps reduces dramatically thereafter so 400 steps/rev is the best practical resolution. Smoothness of motion however gets better with more microsteps. As the microsteps go
    up however, to get any reasonable speed requires ever faster pulse rates from your controller.

    In practice 8 microsteps per fullstep, ie 1600 pulse/rev, is a good compromise. Its gains smooth motion WITHOUT demanding ridiculous pulse speeds. It would suggest setting the microstepping to somewhere between 5 microsteps per
    fullstep (1000 steps/rev) , 8 microsteps per fullstep (1600 steps/rev) or 10 microsteps per fullstep (2000 steps/rev) and leave it there. If you want the motor to spin faster you'll have to increase the pulse rate. Its the total number of
    steps that determine the final position but the rate of steps that determines the speed.

    Craig

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