Re: [CAD_CAM_EDM_DRO] Re: Digitizers, Renishaw

Hi Alan,

The way I read it is that the balls are in pairs set into some kind of
insulating medium (resin?) to probably about half their depth. They are set
as 3 sets of 2 at 120 degree angular spacing around a circle and the balls
with wide spaces between are electrically connected together (except 2 of
them. This makes 3 sets of contacts in series. The 'star' has downturned
arms with pointed ends which rest on the pairs of balls which are close
together and so make a continuous closed circuit. Now, any movement of the
'star' will break contact with one or more of the balls and so provide a '0'
signal. Having the balls and the star with pointed arms will make the star
self centring but I wonder if the star would also need some other restraint
to stop it moving around if it is deflected too much - probably not. The
sensitivity of the whole thing will depend on the ball circle diameter and
its relationship to the length of the measuring arm.....or will it? My brain
is not in gear enought to cope with difficult concepts like this at
midnight!!

Ian
--
Ian W. Wright
Sheffield UK
www.iw63.freeserve.co.uk

----- Original Message -----
From: "Alan Marconett KM6VV" <KM6VV@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: 04 January 2001 23:55
Subject: [CAD_CAM_EDM_DRO] Re: Digitizers, Renishaw


> Gordon,
>
> I would think the "star" has an insulating layer (pcb), with the "tips"
> of the star metal for contacts. The three "pairs" of balls are wired in
> series. That should do it, but 6 4mm balls on a 30mm ring circle don't
> have 2mm spacing (is my math ok?), so we'll have to work on that. a foam
> "spring" (non conductive) presses on the top of the star.
>
> Patented? Probably so. But as I understand it, we can make a model of
> it for our own use. We just couldn't SELL them without a license
> (someone can correct me if I'm wrong).
>
> This would be good for the "auto origin" hardware we were talking about
> also!
>
> DEFIANTLY not 1000's of $$ to make!
>
> Alan KM6VV
>
> Smoke wrote:
> >
> > The only thing I can't visualize from the description Peter provided, is
how
> > the actual electrical circuit is constructed.
> >
> > A skecth would be real helpful here. I think this system could be built
for
> > a whole lot less than $1000. Is it patented?
> >
> > Smoke
> >
> > >That's just the kind of information we're looking for! And it doesn't
> > >sound too hard to make! It would be useful to get a better idea what
> > >the "star" looks like, but I just drew the balls and star up in Vector,
> > >and with a few tries, we should be able to get a star that works (good
> > >contact angles). Pictures would help! Do you have any? Also, do you
> > >have a URL for CNCDIGIT?
> > >
> > >Thanks for the contribution!
> > >
> > >Alan KM6VV
> > >
> > >
> > >
> > >PMeinhard@... wrote:
> > >>
> > >> Hi
> > >> I´m digitizing on a little stepper-driven mill using a Renishaw. (got
a
> > >> broken one from the company I worke for and repaird it). The
innerparts a
> > >> quite simple and there ist no need for high accuracy . So I think
it´s no
> > big
> > >> thing to built one. Basic thing: The Probing Arm has to be able to
move
> > in
> > >> every direction to avoid breaking . They manage it that way: 6 little
> > >> Steel-ball (4mm) are fixed in a circle of 30mm diameter. always two
with
> > gap
> > >> of 2mm between them , half buried in electric isolating material. on
> > them
> > >> lies a 3-arm-Star of 4mm matrial making an electrical connection
while it
> > is
> > >> pressed with a soft spring on them . This is now forming an
electrical
> > >> circuit . Lifting an arm of the star would break the circuit. In the
> > center
> > >> of the star ist an arm leading straight down through a much bigger
hole
> > in
> > >> the center of the isolating material ,60mm long with a little ball
on
> > the
> > >> end. The star is always centering itself, drawing the ball in each
> > direktion
> > >> makes one star-arm lift off the balls and breaking the circuit. And
that
> > >> simple thing costs about 1000$- but the idea is great.
> > >> The accuracy is about 0.005 mm.
> > >> ( the dimensions are as kept them in my mind and might vary a little)
> > >> The Software I use is simple but good, CNCDIGIT. cost about 150$( as
far
> > as I
> > >> remember) remeber
> > >> Regards
> > >> Peter
> > >
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