Has anyone tried to make a probe utilizing a piezo element instead of mechanical switches?

the piezos I have seen react only to very quick actuation, i.e. hit them with a hammer and they will show an output voltage swing.

for probing I assume you would want a signal even when the probe very gently and slowly begins touching the probing surface.

If you can find a piezo that reacts to these slow small changes then why not...

The piezo element in a musical instrument pickup is quite sensitive, especially the 'ribbon' type which I believe is actually a polymer film of some sort.

-al

I have a piezo element off of a ultrasonic die bonder. Already probe shaped. Maybe hooking it up to a high gain amp and see...

You know they make accelerometers that are piezo based and are rather sensitive. They can pick up pretty low g's.

I have a piezo element off of a ultrasonic die bonder. Already probe shaped. Maybe hooking it up to a high gain amp and see...
Darn it! there goes another idea someones already thought of!

Oh well. As I just mentioned in the touch probe thread, how about using gramaphone needles (with a softer tip)

I think you'd need some pretty good filtering or noise reduction though.
Especially with the steppers whirring away.

Another idea i hazily recall is a method for making bump sensors for
robots using a bent fiber optic (one of those cheap Tina Tuner lamp sort of ones) bend around to a sensor (something to do with interference patterns?). They were supposed to be quite sensitive.

And last (but not least) mount a probe to the centre of a thin Y shaped metal thing with small strain guages on each arm of the Y. They are very sensitve and read absolute (piezo just pulses).

I've already tested the piezo version, it was investigated long time ago. The output signal is just a quick peak and it will need some sort of amplifier, possibly also an echo device that makes the signal longer.

Regards,
Sven

I've already tested the piezo version, it was investigated long time ago. The output signal is just a quick peak and it will need some sort of amplifier, possibly also an echo device that makes the signal longer.

Regards,
Sven
Alright then, how about this...
http://catalog.sensing.honeywell.com/printfriendly.asp?FAM=force&PN=FSG15N1A
They are quite pricy (~£40) but I think you'd only need one (if probe tip was epoxied to the sensor).
0.2mV per gram force (up to 1500g), 30 microns full scale deflection.
Maybe as a cheaper alternative, pull apart one of those micro-scales you can get fairly cheaply these days and use the sensor from that.

Just another thought on the piezo idea. I know the piezo will give a voltage pulse if stressed (piezoelectricity), but does not also it's resistance change with applied force (piezo resistance)? If you put one in a wheatstone bridge I wonder if that would fly (using it as a strain gauge in effect).

Don't forget that there are requirements other than the low force requirement. My requirements list looks something like:

1 -- It must have a mount that "self centers" in three dimensions.

2 -- It must detect displacement in three dimensions.

3 -- It must permit a large motion (so that it won't break when the machine overshoots) in three dimensions. It should be possible to overshoot and break a probe without destroying the probe body. It must have replaceable probes so that when it crashes, the probe can be replaced.

4 -- It must be repeatable.

5 -- It must apply a minimal force to the object being probed (not required for all applications).

6 -- It must give repeatable measurements, independent of temperature, barometric pressure, humidity, etc. It shouldn't wear significantly in use (ruby tips are inexpensive and generally used).

7 -- The measuring probe must be concentric with the spindle axis; either machined that way or adjustable. (Adjustable is probably better so that cheap probes can be interchanged.)

Whether mechanical contacts (rods and balls), strain gauges, piezo for sensors, optical, or other means of sensing is used, the above requirements still exist. I don't think it likely that the simple rod and ball kinematic mount where the rods and balls complete the circuit can be beat for my application.

Ken

Maybe you should consider a ring gyro setup.....

This has already been successfully done by Roland DGA with their Picza series of scanners. The one I have has what appears to be a very long sewing needle attached to the piezo by means of solder. Instead of reinventing the wheel, you might want to just buy a replacement piezo/probe sensor from Roland directly. They've already done all of the research to engineer a working probe...you'll have to come up with your own electronics.

-Brady

Look at their site. Ohh.. Active piezo. Hadnt thought of that, Much more sensitive. But much more electronics.

Argh.. One project at a time... One project at a time...