Re: [CAD_CAM_EDM_DRO] Re: Re: Re: Digitizers,

Ian Wright wrote:

> Hi Bill,
>
> Just a thought re:the use of piezo crystals. If you are intending to use
> them as strain gauges or couple the probe tip to them in some way, you
> should be aware that they are quite brittle. Consequently, any sudden
> jarring or side loading would just snap them. If I were going to try such a
> system I would probably mill a groove in a small block of aluminium and glue
> both ends of the piezo across the gap (making sure I didn't short out the
> plated on contacts). Then I would glue the end of the probe to the centre of
> the piezo using a flexible adhesive like hot-melt glue. You may need a
> fairly sensitive amplifier this way but it should make the piezo last
> longer. (In the record player pickups, one end of the piezo 'rod' is held in
> a clip and the free end rests against a soft rubber link which 'connects' it
> to the stylus)

I think the way the real ones must work is the probe is free-floating
(like in the Renishaw unit that has been discussed) with some method
of securing a highly repeatable reference position. The piezo chip is
attached to the top of the probe, and thin, flexible wires connect it to
the electronics. When the probe hits something, the probe is deflected
up to some limit, without putting any strain on the piezo element. but, the
electronics can detect the contact by changes in the resonant performance
of the piezo element. The tricky part is setting it up so that the
piezo element is coupled to the probe tip, but not coupled to whatever
the probe sits on that sets the reference position.

Alternatively, you could do the opposite, which is sense that the probe
has been knocked out of contact with that support. Maybe that is easier!

Jon