Re: Steppers: detecting lost steps

From: Nico Coesel (nico_at_puntnl.niks)
Date: 08/01/04 

Date: Sun, 01 Aug 2004 23:07:17 GMT

Ian Stirling <root@mauve.demon.co.uk> wrote:

>Winfield Hill <Winfield_member@newsguy.com> wrote:
>> Ian Stirling wrote...
>>>
>>> Winfield Hill wrote:
>>>>
>>>> My own efforts to use waveform detection to reliably observe the
>>>> loss of steps (four steps), met with failure three decades ago.
>>>
>>> It seems likely that this is probably fairly easy - given nice fast
>>> A/Ds, sensing currents, and a nice simple load. (say a mirror glued
>>> to the shaft).
>>
>> That's what I thought until I tried it. My load was very simple
>> (a capstan pulling magnetic tape), and I was using current-source
>> drives (so the voltage waveforms were not externally disturbed),
>> but I found the dominant parts of the waveform was not directly
>> responsive to stepping activity, leaving a small part that was,
>> riding on top of different types of very messy normal waveforms.
>
>I wouldn't call that simple.
>You'll have all sorts of nasty resonances from everything from bearing
>slop to tape acting like a rubber band, and probably lots of noise from
>the tape running over the head.
>
>For something really simple - a mirror or something mounted very
>rigidly to the shaft, which has a known predictable response to an
>input, maybe.

If the response is predictable (in other words, the load is constant),
you can design the driver in a way it will never let the motor slip.

Still, there might be an option which I haven't tried: If you drive
the motor with sine waves instead of pulses, missing a step would
propably cause higher harmonics in the current because the anchor will
jump into sync with the sine waves when it can. 

-- 
Reply to nico@nctdevpuntnl (punt=.)
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