Re: Digitizers, Renishaw

Good idea Smoke, I think an aperture
system would be a good way of doing it.

But it has occured to me that nobody
really got what I meant by optos.
Imagine the optos that are used to break
a light beam when your x-travel gets to
home position.

But they don't have to be on/off light
beams. Shine one at an angled or curved
surface and it returns a analogue value
in volts. ANY movement of the reflecting
surface will cause the exact amount of
light to change, up or down, giving a
"hit".

You don't need to make it so it measures
the movement, just detects it. This is
easy, the signal can be "zeroed" every
time, then as the probe is lowered ANY
change in signal from the opto(s) will
give a "hit".

--- In CAD_CAM_EDM_DRO@egroups.com, "Smoke" <Smoke@5...> wrote:
> I think you might be able to use a gunsmithing/potography trick with
those
> opto set ups.
>
> First you mask (black out) the end of the pick up unit with some
sort of
> disk (or possibly a short length of "rod") glued in place. Put a
VERY TINY
> pinhole in the disk (rod) to allow light to come thru.
>
> Mount mirror on the end of the probe, with the probe free to move
angularly
> when it contacts a surface. With a small enough pinhole thru a thick
enough
> disk, the angular movement should be enough to block light return to
the
> opto unit. The probe would need to be free enough to move yet be
able to
> return to center position CONSISENTLY when the probe has been moved
away
> from contact with the part. It might be necessary to increase the
movement
> of the mirror by mounting it on the end of a "multiplier arm"
between the
> probe and the sensor rather than directly on the end of the probe.
>
> How much "adjusting" it would take remains to be seen.
>
> Smoke
>
>
> -----Original Message-----
> From: Ian Wright <Ian@i...>
> To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
> Date: Thursday, January 11, 2001 5:12 PM
> Subject: Re: [CAD_CAM_EDM_DRO] Re: Digitizers, Renishaw
>
>
> >Hi Jon,
> >
> >The only way you could get a similar accuracy using an opto set-up
would be
> >to make the disk very wide relative to the length of the probe and
put tiny
> >shutters at its periphery between LED/opto sensors. This would
probably
> work
> >but, you would have a big problem in preventing the disk rotating
whilst
> >keeping the movement light enough.
> >
> >Ian
> >--
> >Ian W. Wright
> >Sheffield UK
> >www.iw63.freeserve.co.uk
> >----- Original Message -----
> >From: "Jon Elson" <jmelson@a...>
> >To: <CAD_CAM_EDM_DRO@egroups.com>
> >Sent: 11 January 2001 19:56
> >Subject: Re: [CAD_CAM_EDM_DRO] Re: Digitizers, Renishaw
> >
> >
> >>
> >> 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
> >>
> >>
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