Re: [CAD_CAM_EDM_DRO] Limit and Homing switches

Hi Ian,

Yes, you've got it! A better and more complete explanation to what I
was saying about using a motor phase in combination with a mechanical
switch. The Schmitt trigger is a nice point; I'm trying to remember if
it might already be included in the opto switches.

Another method I have just been reminded about is to use a "vane"
attached to the SERVO or stepper shaft that passes through an opto
switch. This setup can be used somewhat like an index. Could be useful
on a SERVO where there isn't a motor phase, or the encoder is too high
resolution to use it's phases.

Best Regards,

Alan KM6VV


"Ian W. Wright" wrote:

>
> Hi Alan,
>
> Surely the whole point of using a combined limit switch/motor pulse is that
> you don't need any really accurate components. I haven't actually tried it
> yet but the way I see it working is that you use a normal microswitch as the
> limit and the signal from this is taken to an AND gate / schmitt trigger
> which also has an input from the power to one phase of the stepper motor.
> So, as the axis travels to one end, it closes the microswitch and holds it
> closed then, as soon as power is next applied to the appropriate motor coil,
> in the correct phase, the edge of this pulse triggers the schmitt trigger
> and a signal is delivered to the home switch input. On normal systems, of
> course, the motor will then reverse and back away to a preset distance which
> places it clear of the microswitch. The only real 'accuracy' required is
> that the microswitch closes before the relevant motor pulse. Using, say, the
> rising edge of the power pulse should give extremely precise positioning of
> the home or limit location.
>
> Best wishes,
> Ian
> --
>
> Ian W. Wright
> Sheffield, UK
> ----- Original Message -----
> From: "Alan Marconett KM6VV" <KM6VV@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Thursday, March 07, 2002 1:13 AM
> Subject: Re: [CAD_CAM_EDM_DRO] Limit and Homing switches
>
> > Hi Carlos,
> >
> > I have used a "phase" of the motor signal before in an RDF project. The
> > Optical switch must be narrow enough to only "gate" one phase signal or
> > index signal. So if the optical or mechanical switch was 3 steps wide,
> > one could position the switch so that the combined signal (sw AND index)
> > would now only be as wide as the index.
>