Re: rotary hand encoder wheels with detent

Hi,

I don't mean to pour cold water on the idea of using a step motor as
an encoder but I don't think it will work.

At speeds above 0.5 revs/sec it's a piece of cake. The winding
voltages are sine/cosine. A pair of simple zero-crossing comparators
give a clean quadrature output.

The rub, and where it all falls apart, is at speeds below that.

I did some quick experiments. Where detent torque can be felt, moving
the motor in single detent increments produces narrow 50 mV, near
simultaneous pulses on both channels. It would require
differentiation of the pulses to retrieve phase timing info from them
which then could be "assembled" into a quadrature output.

When a "real world" inertial and frictional load is coupled to the
motor (a 4" dia, .125" aluminum disk and 10 oz-in friction), it
washes out the detent and the voltage outputs fall below 2 mV.

This signal is below the "noise" level. The motor is microphonic;
simply tapping a pencil on the bench next to it produces 10 mV of
signal.

The result would be an encoder that has no output if the handwheel
were turned at a rate less than 0.25 revs/sec. Above that speed the
quadrature output would suddenly start running at 50 counts per
second. That would be very irritating.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Scot Rogers <scotr@b...> wrote:
>
> Hey all,
>
> I think someone could be on to something with using a stepper for a
> jogwheel. I'm currently waiting on a lathe with just such a
device, and the
> wheel is great.
>
> One thing though. Wouldnt it be best, since the graduations of
jogs are in
> decimal, to use a 3.6 degree stepper instead of a standard 1.8
degree? It
> would make exactly 100 marks and big, well defined dentents at
that. If the
> pulses could be generated with the motor, there could be a way to
hack the
> mouse if the device were used in a program like EMC.
>
> Scot
>
>
>
> /?*$#@%!&*
> -------------------------------------------
> Give me open source, or give me open sores!
> -------------------------------------------