stepper motor speed ramp

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

 

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

 

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

 

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
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Views expressed are my own and not necessarily those of Isotek Electronics Ltd.

 

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.

 

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
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