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stepper motor speed ramp

Discussion in 'Beginner Electronics' started by david austin, Nov 20, 2003.

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  1. david austin

    david austin Guest

    This site has a pdf with a neat method to generate timings for a linear
    ramp.
    It is quick enough to do in real time in a timer-comparator ISR on a PIC.

    http://mysite.freeserve.com/stepper

    Dave Austin
     
  2. Bill Sloman

    Bill Sloman Guest

    A linear ramp isn't all that helpful in accelerating a stepper motor.

    If your maximim stepping rate is higher than the first resonance
    frequency of the stepper motor you are using, you do have to chose
    your acceleration sequence with the resonant frequency in mind, and an
    arbitrary linear ramp probably won't serve. Read Douglas W. Jones on
    the subject.

    http://www.cs.uiowa.edu/~jones/step/physics.html
     
  3. david austin

    david austin Guest

    The method can cope with Bill Sloman's objection by building a
    piecewise-linear acceleration profile.
    My experience is that this is not necessary
    Dave Austin
     
  4. Well that's all very well, but I've never heard of a stepper motor
    driver that does anything other than linear or s-curve accelerations,
    but then I guess I've only seen about half a dozen :)

    --
    Trevor Barton
    Isotek Electronics Ltd, 9 Clayton Wood Bank, Leeds, LS16 6QZ, UK.
    Tel: +44 (113) 275 1339, Fax +44 (113) 224 9827
    Remove X from before replying.
    Views expressed are my own and not necessarily those of Isotek Electronics Ltd.
     
  5. Bill Sloman

    Bill Sloman Guest

    I hope your lucky break continues. A lot depends on how dissipative
    your load is. Several of the steppers I've played with had a fairly
    high-Q first resonances, and the starting sequence that worked
    involved enegergising the coils for several cycles of the resonant
    period, until the rotor had settled down aligned with the magnetic
    field, then making the first step period one quarter of the inverse of
    the resonant frequency.

    Do it wrong, and the rotor doesn't rotate, it just sits there buzzing
    at the stepping frequency, which isn't helpful.
     
  6. Stephen Pelc

    Stephen Pelc Guest

    A long, long time ago I did the software for a six axis machine
    that cut patterns on glasses and decanters. The first time we
    tried an S-curve, we hit the low-frequency resonance problem
    and the motors stalled. Both resonant regions are important.

    Stephen
    --
    Stephen Pelc,
    MicroProcessor Engineering Ltd - More Real, Less Time
    133 Hill Lane, Southampton SO15 5AF, England
    tel: +44 (0)23 8063 1441, fax: +44 (0)23 8033 9691
    web: http://www.mpeltd.demon.co.uk - free VFX Forth downloads
     
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