Ultrasonic Drill Suggestions Needed

Greetings,

The way the device works is that the drill bit is a soft metal tube driven by the piezo unit in a slurry of cutting grit (~100 grade silicon carbide) in liquid (mineral oil or water). The action of the tube pounding grit against the substrate (jewelry bead, gem, or anything with a hardness lower than that of the grit) simultaneously eats away at the bit and the substrate, thus drilling the desired hole.

From the design specs of manufactured multi-thousand dollar units, it appears that I want something that drives a piezoelectric transducer at around 40kHz.

I'm starting from square one. I can wield a soldering iron and have played with the 300-in-1 type electronics kits a bit over the years, but am not at the point of being able to design a circuit for anything like this.

It appears that I need suggestions for:

  1. a signal generator capable of operating at 40kHz (am willing to experiment with different waveforms to see which is most efficient at cutting)
  2. an amplifier - capable of good slew rates at 40kHz - high input resistance matched to the piezo transducer
  3. good candidate piezo transducer

Thanks for any help in advance.

--jim

Reply to
jimbo
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Many industrial piezo devices typically run at high voltages (1000 V is not uncommon), which makes the amp design a problem even if you are a pro. One alternative might be to tear apart a plastic piezo horn tweeter. Some of these have decent response up to 40 kHz, although the response has many dips and peaks. You'd want to tune to the nearest peak, whatever the frequency. That will depend on the mechanical structure that you come up with to couple it to the cutter bit. My guess is that despite herculean efforts to reduce mass, this is not going to be in the same ballpark as the commercial units as far as cutting speed. The piezo tweeters just can't handle all that much power. But it might be fun to experiment with!

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

Bob,

Thanks for responding!

Big voltages but relatively small current?

The suggestion of the horn tweeter appeals to me. Looks like 50W tweeters can be had for about $5 a piece from surplus sources. A cheap op-amp delivering less than 50W over a good frequency range might do the trick for initial testing--since I don't know what drilling rates commercial setups are achieving, I won't know how much better it could be. ;)

Apologies for this naive question: Big voltages ... can they be done using voltage multipliers after the amplification stage? Um, a cursory glance at simple voltage multipliers gives a few questions:

1) At what point (frequency and/or voltage) does the cost of suitable caps leave practical reality. 2) Are there diode issues, i.e. noise or voltage, that will impact the system at higher voltages? 3) Am I looking at voltage multiplier circuits that are too simplistic? 4) For boosting the voltage (also at the expense of the current) what about a good old transformer operating in the low ultrasonic range? The smaller form-factor, the better, I'd assume.

Further down this road, another possibility that comes to mind is using another piezo transducer as a sensor that gives feedback so the circuit can drive itself to an (albeit probably local) maximum efficiency in terms of internal physical resonance.

UGH, I'm going to have to find someone to lend me a scope.

Thanks again,

--jim

Reply to
jimbo

Something like these?

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Scroll about 1/3 of the way down the page for s 6,000 year old example of this. :-)

Cheers! Rich

Reply to
Rich Grise, but drunk

These days, if you want to bore a hole in hard stuff using a copper tube, they just typically chuck the tube in a drill press and suspend the grit in the coolant stream.

Have Fun! Rich

Reply to
Rich Grise, but drunk

Not if you want the option of non-circular holes.

--jim

Reply to
jimbo

yes, if operating at 5W

a transformer would be ideal. for working at 5W a 40KHz transformer could probab;y be wound on a toroid from a dead computer PSU.

yes, you need AC to drive the piezo, those capacitor-diode devices produce DC. use a transformer.

aha.

Bye. Jasen

Reply to
Jasen Betts

The piezo material looks like a capacitor, so it only draws current when the voltage changes. The currents are "low" compared to typical magnetic-type transducers, but at 1000 V there is still a lot of power.

Note that "consumer" tweeters are typically rated for the power of the overall music program, not the power actually handled by the tweeter itself. In a 50W system, most of the power is going to the woofer and midrange. The tweeter itself is probably seeing well under 10W. So don't expect you can put anything close to 50W into this tweeter.

One problem with voltage mutipliers (besides efficiency) would be that they rectify while multiplying. So you would need to impose your 40 kHz on a much higher carrier, and do some tricks if you want a bipolar response.

Also, remember that the load is a capacitor, so whatever you drive it with has to remove the voltage as well as supply it when the input voltage changes. It's not like a power supply that mostly runs at a fixed voltage and just uses a bleeder resistor to discharge the output caps on shut-down.

A simple transformer would make much more sense. Electrostatic speakers use high voltages at low currents, and they typically use transformer drive.

But all that assumes you can get hold of industrial piezoceramic materials that need the high voltages. The horn tweeters don't need (and can't handle) any of that.

The industrial piezo material I messed with many years ago was tubular, about 1/4 inch in diameter, designed as a linear actuator. Seems like it would be ideal for your project, except that the original device was not intended for high frequency use: It was for positioning microelectrodes under a microscope, so the power supply wasn't anything too fancy in the response department. The whole instrument was from a company called Burleigh, which may not be in business any more, and they bought the piezo material from somebody else. (I got some samples from a Burleigh engineer, but never really got them to do anything on my own.)

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

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