A Probe With Less Plastic

[Graham S]

http://www.ems.k.u-tokyo.ac.jp/morit..._Kanda2000.pdf

[Mariss Freimanis]

Exactly! You know when you are moving, the pezio device sends a signal, you stop moving and log the coordinates when you get the contact signal. It tails off afterwards alright but you still get a sharp rising edge at the instant of contact. That's what you are after.

Mariss

[turmite]

Mariss would this be any safer on the probe itself than one of the units that have been discussed here? I suppose I'm asking if the axis would continue to move slightly after receiving the signal or would this still be software related?

Mike

[Mariss Freimanis]

I always like to simply. I saw the break-away drawing with the 4 balls and everything for a contact probe. I thought what an elegant but complex solutiuon. You jostle the balls, they break contact with a circuit. It does what it's supposed to do.

Meanwhile I'm getting hung up with the "complex" part. Shouldn't it be easier where something gives an electronic "clang" when contact is made? Something with no moving parts at all? Like a toothpick in your ear touching your eardrum? Your'e OK until the faintest pressure touches the end of the toothpick. Lateral or on-axis, it doen't matter: you'll scream.

Same thing here but very simple mechanically. Just a probe rod afixed to a pezio-electric crystal. Touch it slightly and it screams "contact!".

Sorry for the gruesome analogy but it works.

Mariss

[strat]

just did some playing around with a buzzer i had from ratshack i noticed i get lower readings if i tap like the center was under 1 volt then if i have it push and bend the crystal bending was sending anywhere 12 to 15 volt

[vacpress]

Oh Mariss.

That is so romantic! Perfect... You are, of course, describing the subtle sliding back-n-forth of a piezo-electric elements intermeshed current producing chrystalene structure..

I havent spent much time with digital edge finders and 3d probes, but i have played drums for years. Electronic drums, especially those from before 1998 are based on simple piezo transducers and op-amp based amplification circuitry.

If the 10uM deflection for a 4.5v pulse is a real rating, a simple probe based on a pizeo element seems very interesting, yeah.. No moving parts is a bit of a oversight, considering some sort of actuator must still impact the pizeo disc...

Why dont you do some experiments.. It could be fun...


Everyone likes new products. Especially if they are appropriately engineered, and priced for the man on the street.


Robert

[Graham S]

Originally Posted by Mariss Freimanis Exactly! You know when you are moving, the pezio device sends a signal, you stop moving and log the coordinates when you get the contact signal. It tails off afterwards alright but you still get a sharp rising edge at the instant of contact. That's what you are after. Mariss

Fine for bed of nails but not so good for adaptive feedplane when you need to know when the probe has left the surface.

You need some give in the system for axis deceleration I don't suppose that would be too hard to do but it needs to give in all directions.

Jostle the balls? There clamped!

Graham

[Barry_ward]

Mariss and all,

Just use one of the piezo disks that have 3 terminals. You conect it to a single npn transistor and a couple of resistors and you have a ceramic resonator-oscillator.

Glue the probe to it, tweak in the gain to get it to run at some frequency.

Monitor the input current or the oscillator (ac) output voltage. When the probe is touched (any axis), the gain is reduced, the oscillator stops and you detect the current draw change or the AC output.

I'd use a light weight probe rod and a rigid glue to get good coupling to the ball. The piezo disk mount could be the part that had the flexture that prevents destruction in the event of a crash or over-deflection.

Where do I get the ruby ball?

Barry

[braidmeister]

Barry,
Why does it have to be ruby?

-Brady

[Barry_ward]

Dunno - maybe the tempco. Seems like they are always ruby on CMMs. Maybe it has something to do with Kansas.

[lerman]

Ruby is hard (almost as hard as diamond) and cheap.

Get Replacement Styli and Accessories for Renishaw CMM Probes from www.mcmaster.com -- $35 for a 5mm ball end probe.

Quoting from the web page.
(E-J) Styli— Have Grade 10 ruby balls with a sphericity tolerance of ±.000025" and a diameter tolerance of ±.0001

I consider that pretty reasonable.

Ken