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Piezo-electric Actuators

  1. Jan 7, 2008 #1

    G01

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    Hi guys.

    I'm trying to use a piezo-electric actuator in a project of mine to move a sample a very small displacement. I am currently working with a ThorLabs AE0203D08F. I'm trying to detect the displacement of the device at a specified DC Voltage, somewhere around the range of 100V. Currently, I am placing a while above a test stage on top of the actuator. I put the wire as close as optically possible using a telescope and increase the voltage on the actuator until a short is detected between the stage and the wire. Using this method I would be able to see if the device is actually displacing the way it should.

    Anyway, I have yet to detect any displacement anywhere from 0-140V. I was wondering if maybe I am doing something incorrectly, since I am somewhat new to piezos. The max displacement of the piezo is 9.1 microns at 150V. Does anyone have any ideas as to why I am not detecting an displacement with this device?

    Thanks for any advice you guys can offer. Also, I did not know what forum this would best fall under, so if a mentor can move this to the best suited forum, it would be much appreciated. Thanks again!
     
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  3. Jan 7, 2008 #2

    mda

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    This may seem silly, but have you checked the polarity?
    You imply that you can optically resolve the initial separation, so why not just watch to see what happens?
     
  4. Jan 7, 2008 #3

    Danger

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    I have zero experience with piezos, but I was under the impression that they aren't proportional. Doesn't it take a certain threshold voltage to trigger one, and then it goes to full deflection?
     
  5. Jan 7, 2008 #4

    G01

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    Yes, the piezo is marked so we know we have the correct polarity.

    The thing is that I can optically see any displacement of the piezo. If I apply an AC voltage to the stack, it vibrates and you can hear it if the frequency is in the audible range, but I can't seem to detect any DC displacement.

    This piezo stack is built to be able to displace different amounts within a range of voltages. This piezo stack deflects a certain amount for a given voltage and deflects around 60 microns per volt. As you up the voltage, you up the displacement of the piezo, or so it should be, but that is what I cannot seem to detect.
     
  6. Jan 7, 2008 #5

    Danger

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    By 'piezo stack', then, do you mean that you have several crystals layered, each with its own voltage input? If so, perhaps it's simple mechanical insulation between them that's messing things up. Or (way out on a limb) maybe there's an electrical delay that's causing them to react out of phase with each other?
     
  7. Jan 7, 2008 #6

    G01

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    Honestly I am not quite sure, I'm working on figuring it out right now. Here is a link to the device's page on the ThorLab's website for more information until I figure it out for myself.

    http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=61&visNavID=655

    I have the AE0203D08F piezo stack.

    From the website I learned:

    So, it seems that the separate layers of crystals each have their own inputs, but the voltage for each will be equal since they are wired in parallel to the main voltage source.
     
    Last edited: Jan 7, 2008
  8. Jan 7, 2008 #7

    Danger

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    Okay, I misunderstood. I thought that you had assembled the stack yourself using normal single-plane (my term) crystals. Since it's a commercial unit, have you tried contacting the manufacturer? It might be either a factory defect in your particular stack, or a misinterpretation of the wiring specifications on your part. It can't hurt to give them a call.
     
    Last edited: Jan 8, 2008
  9. Jan 7, 2008 #8

    mda

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    Ok, I've never built anything with a piezo, and I can't see your equipment, so these may sound silly but here goes... (I'm sure you know more than me)

    Firstly, can you actually see any displacement under DC?
    What about with and without the stage?
    If you force the wire to contact the stage, does it actually make a circuit?
    (maybe the stage is anodized, etc etc)

    Also be aware that piezos have a few non-linearities (e.g. hysteresis) that make things more challenging.
     
  10. Jan 7, 2008 #9

    G01

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    No, I can't see any displacement under DC. I didn't expect to since 9.1 microns is very hard to see, even with a telescopic lenses. I expected to be able to detect it when the circuit was completed by the rise. (I know that the wire and stage do indeed make a circuit when touched.)

    Here is what I think may be possibilities as to what is wrong.

    1. I don't have the wire close enough to the stage, so that even at max displacement, the wire and stage still do not touch.

    2.The piezo, for some reason unknown to me, does not displace under a DC bias.

    Possibly it is the first one, but I do not know of a reason why the piezos shouldn't react to a DV voltage. What do you guys think?
     
  11. Jan 7, 2008 #10

    Danger

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    Sorry, but I'm out. I don't know enough about it to carry on with any suggestions. I'll continue to monitor the thread, though, because I'm interested to see what happens.
     
  12. Jan 8, 2008 #11
    I've worked with one of the Thorlabs piezoelectric actuators and used DC Voltage. And I could measure a displacement, though I didn't use your method but used the actuator in a laser setup.

    Maybe you find this pdf useful. In the pdf a laboratory work about piezoelectric actuators is described, in particular how to measure the displacement.

    My suggestion would be to do the following (I don't know if it works):
    Take the piezo and squeeze it gently with your fingers. Observe if you can measure a negative voltage. If yes, this could provide a possibility to measure a displacement.

    Take two piezos now and clamp them together in a mount (gently).

    [piezo1] [piezo2]

    The left piezo1 serves as measurement device, so just measure if some voltage occurs.
    For the right piezo2 you apply your voltage, but go from 0V to 100V and observe if a voltage at piezo1 occurs.

    ---

    Note: When squeezing the piezo with your finger, I don't know if you measure a voltage only for a short moment or as long as you squeez the piezo.
     
  13. Jan 8, 2008 #12

    Danger

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    Okay, I'm back for a moment. It's the displacement of the crystal lattice that causes the electrical output, so it's a one-shot deal. (At least, with any piezo device that I've dealt with.) You get a jolt when you squeeze it, and maybe another when you release it, but nothing in between.
     
  14. Jan 8, 2008 #13

    Claude Bile

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    I think you should seriously consider this possibility. If your optical system is not good enough to see the displacement of the stage, chances are you aren't getting close enough. Even with a really good optical system, positioning something manually within 9 micron of something without touching requires surgical precision.

    The piezo, if it is working properly should displace under a DC voltage unless its movement is being restricted somehow. There is a fairly low probability that the device has failed I would think (ThorLabs piezos are fairly robust in my experience), also the arrangement of piezo elements into stacks greatly reduces the hysteresis problem, to the point where hysteresis generally will not be an issue over distances of a few 10s of nanometers or more.

    Claude.
     
  15. Jan 8, 2008 #14

    G01

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    Thanks Claude. I'm currently trying to think of another way we can test the displacement of the piezo. Our optical system is nowhere near perfect, believe me, and none of us have surgical precision in anything we do!:rolleyes: I tried Edgardo's method with another piezo, one from a buzzer since I don't have another Thor Labs one yet. (The point was to test the first one and see if it worked decently.) I was not able to detect a voltage from the buzzer piezo, but this may be because it is not sensitive enough. Do you think I'd need to get another piezo stack from Thor to get results with his method? Also, If you have any advice on alternate means of testing the device, feel free to share.
     
    Last edited: Jan 9, 2008
  16. Jan 9, 2008 #15

    Claude Bile

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    The piezo specs should tell you the maximum force the piezo can apply. I would venture that it would not be much, since the piezo is designed to operate with high precision, such piezos generally aren't designed to push very hard.

    The piezo should have a characteristic resonance specified by the manufacturer where the impedance is lowest. I would suggest putting an AC signal across the piezo elements and seeing if you can observe this resonance.

    Another test you could try (in the same vein as Edgardo's method) is to glue a quartz tuning fork (watch crystal) to the piezo, then putting an AC signal over the piezo and measuring the response of the tuning fork. If the piezo is working, it should vibrate the tuning fork at the frequency its being driven at.

    Claude.
     
  17. Mar 4, 2010 #16
    The AE type piezo stacks are polarity sensitive and care must be used to connect + to the correct color wire from the stack (red). Do not reverse this polarity. In other words do not apply a negative potential at any time to the stack. Negative potential will more then likely remove the piezo effect and all you have left is a quartz crystal. Piezo stacks want to be pre-loaded, typically at around 400Nm. Then the applied potential will exert roughly about 800/900Nm. You should see the deflection, motion, as the piezo expands.
     
  18. Mar 5, 2010 #17
    You are trying to measure 9 microns with a switch? Better re-think that one! Just put a mirror on the actuator and set up an interferometer with a laser. If you can't see fringes moving like mad as you vary the voltage then the actuator is defective. OK?
     
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