Re: stepper pulse rate idea

["alex" <telecomt-at-tht.net>]

I think that the best way around it is to network EMC postprocessor to
DOS module which would work in real time, with encoder feedback.
If loop length limit for RT LINUX is 1ms, for DOS it can be easy .1 ms,
or less. Heck, it can be done in assembler even!
Technically it is quite easy to do as well - just requires recompiling some
modules for DOS.
Alex

----- Original Message -----
From: <jmkasunich-at-ra.rockwell.com>
To: Multiple recipients of list <emc-at-nist.gov>
Sent: Friday, March 14, 2003 9:55 AM
Subject: Re: stepper pulse rate idea


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> Ray's gearshifting idea has prompted me to float one of my own.
> I considered this a while ago but didn't post it or follow up.
>
> If I understand it correctly, the existing stepper routines
> can generate only one step pulse for every two executions of
> the high speed interrupt.  The first sets the output, the
> second clears it.  The maximum step rate could be doubled
> if we could generate a step pulse on every interrupt.
>
> There are at least two ways to reach that goal.  Both would
> require some external hardware, but it probably would be
> less than an pulse multiplier or gearshifter.
>
> 1)  Instead of setting the step bit in one pass of the
> code and clearing it in the next, set and clear it in
> the same pass.  This would result in a very short step
> pulse (1uS or less).  Then use an external one-shot to
> stretch the pulse enough to make the drive happy.
>
> 2)  Instead of outputing step and direction, use the same
> two pins to output a quadrature signal  (like an encoder
> signal).  Then use an external decoder circuit to generate
> step and direction signals from the quadrature signals,
> stepping on each quadrature transition.  A while back I
> designed a quadrature to step/dir circuit.  I don't have it
> handy, but I know it was pretty simple.  I have also seen
> a circuit from Mariss that is even simpler.  (He was using
> the circuit for encoder feedback on a servo version of the
> G2002.)  If you are a member of the Geckodrive group at
> Yahoo, you can see the circuit at:
> http://groups.yahoo.com/group/geckodrive/files/G2002-C.pdf
> It is in the upper left of the schematic, driving the 4029
> up/down counter.
>
> Pros and cons:
>
> Quadrature output from the parallel port can double the
> maximum step rate, where gearshifting could multiply it
> by 2, 4, 5, 8, 10 or more.  On the other hand, the software
> change needed to output quadrature (AKA Gray code) would
> be almost trivial, and the hardware is probably simpler too.
>
> Comments?
>
> John Kasunich
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