stepper motor speed ramp

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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




Re: stepper motor speed ramp
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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

-------
Bill Sloman, Nijmegen

Re: stepper motor speed ramp

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A linear (or S curve or low jerk etc etc) ramp is just fine for a stepper as
long as you use microstepping so that you do not exite the resonance. Any
kludge that limits your flexibility in choosing acceleration or velocity
would be extremely painful to deal with in a multi axis system...


Peter Wallace

Re: stepper motor speed ramp

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Here's a nice kludge on a 343-axis stepper farm.

http://taomc.com/stepperarray/stepperarray.htm

It sure was fun fun fun!!!

MAN, 100 Amps at 4.25 Volts takes BIG wire.



--
- Alan Kilian <alank(at)timelogic.com>
Director of Bioinformatics, TimeLogic Corporation 763-449-7622

Re: stepper motor speed ramp
On Tue, 25 Nov 2003 02:37:42 GMT, snipped-for-privacy@raceme.UUCP (Alan Kilian)

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Dang, I love it! Neat hack.

--
Rich Webb   Norfolk, VA

Re: stepper motor speed ramp
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Agreed. Microstepping almost always allows you to operate at stepping
frequencies well above the motor resonances, and if by chance you do
happen to hit a resonance anyway, the amplitude of the oscillation is
almost certanly going to be too low to drive the system out of its
piece-wise linear range.

I was in involved in a cheapish stepper-motor controller development
back in 1992, where we used a bottom-of-the-line Transputer chip to
get the processing band-width to calculate micro-step up-dates in real
time in a single processor.

Regular microcontroller chips of that period couldn't hack it. I would
have preferred to use a decent-sized programmable logic device, but
the software guys found the Transputer to be much more congenial
programming environment.

Knowing the resonant frequencies of your motor-load combination can
let you use cheaper,dumber controllers, but it takes work, and you
have to be reasonably confident that these resonance freqencies aren't
going to change when the buyers find a cheaper stepper motor ....

--------
Bill Sloman, Nijmegen

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