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hard drive header position

Discussion in 'Electronic Basics' started by doddy, Mar 28, 2007.

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  1. doddy

    doddy Guest

    Hi,

    I have a little project that I am undertaking that requires accurate
    position feedback and I thought of using a similar approach to the way
    hard drive headers are used for positioning, afterall they are
    extremely accurate and fast. The difference is that I need to be able
    to adapt it into a linear position sensor.

    The other option I have been considering is using similar technology
    used in digital vernier calipers but again I am struggling to find any
    good information.

    Can anyone point me to some good resources, I am finding it a little
    hard to find good places. I am also fairly new to electronics.

    Any help woud be appreciated thanks.

    mark
     
  2. But you've missed a step. It would be far better to start with what it
    is you are trying to do. Because this may be a false start with the
    hard drive scheme, but we won't know that unless we know what you are
    trying to do.

    Time after time, people ask for solutions that they "know" will work,
    and it turns out what they thought was a solution wasn't valid because
    they missed some intermediate step.

    Michael
     

  3. So what your saying Michael is that you don't have a clue about what he's
    asking?
     
  4. Guest

    Right, so now all you need is embedded servo information in whatever
    you're trying to position over, and make sure that it's constantly
    moving.
    It's just a foil pattern. An accurately etched PCB.
    What exactly are you trying to do? Sounds like what you want is a
    LVDT.
    http://en.wikipedia.org/wiki/LVDT
     
  5. Guest

    As mentioned regarding LVDTs we may be able to help you www.macrosensors.com
    Contact Harold Schaevitz
     
  6. doddy

    doddy Guest

    Thanks for the information I will certainly take a look at the LVDT
    suggestion.

    Just to explain a little more about what I am trying to do:
    I currently have a moving body controlled by a stepper motor that
    traverses along a bar (not lead screw), the problem is that I can't
    rely on the number of steps of the motor to garauntee movement because
    the system can (and does slip) intentionally along the bar. The
    current feedback mechanism comprises of a type of potentiometer
    (printed carbon ink), this carbon ink process is proving difficult to
    manufacture linearly down to the accuracies I require (need to detect
    at least 0.1mm movements over 100mm travel), I am calibrating most of
    the inaccuracies out but still needs to be improved. So, I am
    researching any other avenues that I could take with this project. I
    was looking to perhaps make use of the current guide bar in some way
    (hence the suggestion of digital vernier technology), the guide bar
    turns with the step of the stepper motor, which forces the body to
    move along the bar (rolling ring technology).

    Another option I had thought of (albeit a little far fetched and
    limited by my konwledge) is to use some type of piezo system with the
    guide bar. The guide bar is clamped tightly by the moving body so
    perhaps measuring the time it takes for a sound wave to travel along
    the bar and back again. I am currently ruling this out as I am
    thinking the 100mm travel in 0.1mm increments is too small to measure
    accurately in this way and the electronics probably too comlicated and
    expensive.

    Space is also a limiting factor too.

    regards,

    mark
     
  7. Rich Grise

    Rich Grise Guest

    How about a piece of nichrome wire?
    NC (Numerically Controlled, i.e. CAM (Computer Aided Manufacturing))
    machines use some kind of optical quadrature position transducer, and
    they do very long distances, of which you need only 10 cm (isn't that
    about 4 inches?), with 0.0005 accuracy, which might or might not be
    close enough to .1 mm - I'm WAY too lazy to do THAT math. ;-)
    Isn't it always? <sigh> ;-)

    Cheers!
    Rich
     
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