Re: [CAD_CAM_EDM_DRO] Re: rotary hand encoder wheels with detent

Perhaps, at last, this is a use for the encoder wheel out of a mouse!!! ;o)
Hand wheel with clicks, and a rubber band drive from the hand wheel shaft to
the encoder spindle to gear it up in a suitable ratio.....

Best wishes,
Ian
--

Ian W. Wright
Sheffield, UK

----- Original Message -----
From: "mariss92705" <mariss92705@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Thursday, February 14, 2002 6:33 PM
Subject: [CAD_CAM_EDM_DRO] 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!
> > -------------------------------------------
>
>
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