Re: [CAD_CAM_EDM_DRO] Re: Digitizers, Renishaw

Roman Black wrote:

>
> I would stay well away from electrical contacts.
> To get reliable conduction requires pref silver
> plated contacts, and high contact pressure and
> velocity. Switch theory is all old hat. Just
> lightly touching two contacts together will
> NOT give a reliable confirmation. Sometimes
> it will work, sometimes not. As you increase
> the voltage the contact detection gets better
> but arcing starts, which is a whole new problem.
> All pushbuttons, switches and relays are
> designed to have high velocity and good pressure
> at the contacts. You are not going to get that.
> :o) Opto's or other non-contact sensing is the
> best. Optos and circuit are maybe $10 tops.

Well, there's the rub. The Renishaw design causes an open
circuit when the contact probe is moved .0002" in ANY
direction. I can see how this will work with an electrical contact
between two hard, rigid parts. I can also see how bad contact
could occur, as you say.

I don't see an easy way to make a low-force probe that will detect
such tiny motion in any direction by optical means.

Renishaw obviously solved this problem, and have been making
these devices for many years.

Jon