Re: [CAD_CAM_EDM_DRO] Homing switches

Probably the most common homing switch I've seen is one of the little
photinterrupter modules - a black plastic case with a slot in the
middle and two leads coming out of each side - one set is for the
infrared LED and the other a phototransistor. You connect a little
tab to the moving slide that blocks the gap. They seem to be pretty
good and repeatable, provided that you always approach them in the
same direction and while traveling slowly. For more accuracy, you
could use the optical module anded with a particulary quadrature phase
of your encoder that you figure out is located just after the optical
switch trips...

Commonly available at surplus houses, probably digikey, and maybe even
radio shack. You'll need a series resitor on the diode to run it off
say 5v. Connect the phototransistor between your logic output and
ground, with a pullup resistor to +5v.

We have some really nice ones on a machine which have a visible LED on
them so you can tell when they are triggered (and powered)... very
nice for debugging when the optoisolator on the PMAC motion control
card decides to give up the ghost and ignore the home input...

Chris

>
> There are overlimit switches on the Series I. I understand they are
> not accurate enough to be homing switches. What are examples of
> good homing switches? If I'm going through the trouble of building
> the control, I thought I might include this feature. I'm fortunate
> enough to have Tom Kulaga (Mr. PC DRO) in my back yard, and
> we've met and chatted a bit about a closed loop Stepper system.
>

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT