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Ultrasonic Drill Suggestions Needed

Discussion in 'Electronic Basics' started by jimbo, Dec 14, 2005.

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  1. jimbo

    jimbo Guest

    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
     
  2. Bob Masta

    Bob Masta Guest

    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
    www.daqarta.com
    Home of DaqGen, the FREEWARE signal generator
     
  3. jimbo

    jimbo Guest

    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
     
  4. Something like these?
    http://www.lauralee.com/chrisdunn/article.htm
    Scroll about 1/3 of the way down the page for s 6,000 year old example
    of this. :)

    Cheers!
    Rich
     
  5. 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
     
  6. jimbo

    jimbo Guest

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

    --jim
     
  7. Jasen Betts

    Jasen Betts Guest

    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
     
  8. Bob Masta

    Bob Masta Guest

    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.
    <snip>
    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
    www.daqarta.com
    Home of DaqGen, the FREEWARE signal generator
     
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