Re: [CAD_CAM_EDM_DRO] Limit and Homing switches

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.