On vacation and reading AoE3 at the beach. (watching all the "bathing" women too!) Section 5.10.12 does a composite piezo drive. I was most interested by footnote 46, pg. 333
Here's a link,
George H.
I've thought about it, but the fly in the ointment is the low frequency response. I haven't used piezo actuators in a design for some years, but IIRC the main win was to notch out the lowest resonance (f_res) with an LC filter. That allowed the loop bandwidth to increase from 0.02 f_res to 0.25 f_res, even though the resonance had a Q of about 30.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
DC-wise (1 - 10Hz) piezo's have lots of hysteresis. It would be nice to get rid of some of that.
I think to make the above work I'd have to split the frequency response.. it needs some DC feedback below
0.1 Hz.At "high" frequencies (100-1kHz) voltage drive seems just fine. (I can lock the laser to the sides of spectra.)
George H.
It might be fun to add a high frequency voltage to the piezo drive to maybe shake up the hysteresis.
-- John Larkin Highland Technology, Inc lunatic fringe electronics jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I agree. Long ago when I was a post-doc, I was trying to make attractive-mode atomic- and magnetic-force microscopes using resonant cantilevers made of tungsten or nickel wire, electro-etched down to a few microns' diameter (with tips that were atomically sharp or very nearly, also courtesy of electro-etching).
The cantilevers were mounted on small PZT bimorphs, which supplied both the Z actuation and the AC tip excitation to make the cantilevers vibrate.
Even the best material (PZT-5A iirc) had ~1% hysteresis, and the high sensitivity stuff (PZT-5H) was much worse. So I feel your pain.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
If you have position feedback you could use charge control for the inner loop, with position for the outer.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Oh no real pain. I drive it with a triangle wave and that's just fine except right near the ends.
I thought the idea of charge control was interesting.
The piezo I use is a multilayer thing from NEC/tolkin If not the same as the one referenced in AoE3 then it's smaller sister.
George H.
Yeah, This is in a diode laser system, and when I lock the laser (via the piezo) to the side of an atomic absorption line then just voltage control works fine.
George H.
Would stochastic noise help?
The hysteresis is pretty big. Maybe 5-10% I think it would have to be a large voltage swing. (ditto for Bob R's noise voltage.) Cure is worse than the disease,
George H.
Piezo hysteresis resembles a B-H curve rather than, say backlash in a gear train. That makes it pretty benign unless you're trying to use it for a position readout.
Cheers
Phil Hobbs
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