Re: [CAD_CAM_EDM_DRO] Re: Home switches.

----- Original Message -----
From: "turbulatordude" <dave_mucha@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, July 10, 2005 12:21 AM
Subject: [CAD_CAM_EDM_DRO] Re: Home switches.


> Are you asking to use the existing end or home switch in combination
> with an encoder ?

That's right. I have separate home and limit (or end) switches and the home
switch operates just before the limit switch.

> As I understand, some encoders have a 3rd channel. a single point per
> revolution.

My encoders have a channel that provides a single pulse per revolution.

> It would appear that one could run the axis to the end switch and then
> until that encoder point changed state.

That is what I want to do. In principal I could run the encoders index pulse
throught the home microswitch NO contacts to get a signal at the same
position. In practice I don't have enought wires in the cables between the
controller and the mill to do this. Both signals are in the controller box
and I would like to combine them elctronically (AND gate?). I can solder the
bits together and make it work but I can't design the circuit from scratch.
I am hoping that someone has already done this and can help me out.

> That would represent the motor being in one exact location, and not
> necessarly the screw or table. But, it does eleminate a chip or dirt
> from influencing the home point.

All the positioning of the table relies on the position of the motor and
ignores backlash etc in the screw and timing belt drives. I would be much
happier with the encoder and microswitch defining the home point than
relying on the microswitch alone.

> Dave
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "David Micklethwaite"
> <d.micklethwaite@o...> wrote:
> > At the moment my mill uses microswitches for homing the X and Y axes.
This
> > sort of works but does not allow exactly reproducible positioning. The
axes
> > are driven by servos with encoders. I would like to combine the index
pulse
> > from the encoder with the microswitch to get a more accurate indication
of
> > the home position. Can anyone give me some advice, preferably with a
circuit
> > diagram, on the electronics needed to achieve this.
> >
> > The microswitch operates with 5 volts as do the encoders and the
combined
> > signal has to go into a PMDX-120 breakout board.
> >
> > Thanks in advance,
> >
> > Dave Micklethwaite
>