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accurate angle measurement

Discussion in 'Electronic Design' started by mario, Sep 6, 2006.

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  1. mario

    mario Guest

    Hi everybody,

    Can anyone suggest me some idea for measuring angles up to seconds? or
    Where can I find the principle used by theodolites in measuring angles?

    Thanks a lot
     
  2. That is a bit little information. There can
    be optical masks with micrometer resolution.
    Is your problem a scientific problem to be
    solved once, a technical problem to be
    solved repeatedly or a business problem to
    be solved cheapest in numbers.

    Rene
     
  3. default

    default Guest

    Wow.

    Theodolites implies angle - more of less.

    A rate gyro, on a chip?
     
  4. Joerg can make it cheaper :)


    martin
     
  5. Fred Bartoli

    Fred Bartoli Guest

    martin griffith a écrit :
    But only Philips and Infineon make that dreadfully required component.
     
  6. mario

    mario Guest

    Rene, I want to measure the angle position of a 4~6 cm radius disc.
    Does it help?
    Thanks

    Rene Tschaggelar ha escrito:
     
  7. Dave

    Dave Guest

    Avago (was Agilent (was HP)) make some quite nice absolute and incremental
    encoders (14 bit). ( If you have real money there are some laser based
    encoders that work down to a few arc seconds, and also some rotary
    transformer based solutions. )

    You need to specify:-

    Absolute or Incremental ?

    Accuracy?

    Angular speed and acceleration?

    Do you require 360 degree revolution ?

    How much do expect to spend ?

    Dave
     
  8. Guest

    Quartz crystal cut angles are measured to seconds of arc to get optimum
    temperature coefficient. Xray defraction and rugged mechanical
    construction are key elements.
    For a cheap system two a radial gratings and count the fringes as the
    transparent upper grating is rotated over a lower grating could do it.
     
  9. Guest

    A little calculation shows that a pointer/scale one-arcsecond system on
    the disk requires alignment
    precision (and also axis-of-rotation position) of 0.14 microns. That's
    not possible
    with simple light-readout systems.

    For reference, a CD squeezes about 6170 bits into one degree of disk
    rotation,
    with good diffraction-limited optics and lotsa tricks (like
    servo-controlled tracking
    mechanisms). That's 1.7 bits per arcsecond of rotation.

    One can just about use lightbeam interferometry to measure a triangle's
    sides to this
    precision, but it's not gonna be a simple measurement.
     
  10. mario

    mario Guest

    Hi Dave,

    My needings are: incremental, accuracy half second or second at most,
    speed 1.5 revs/sec at most, yes 360 degree, $ 500 to 700 approx
    Thanks

    Dave ha escrito:
     
  11. Steve

    Steve Guest

    Add a 'k' to those values and you just might do it.

    Do you really mean seconds ? To put what you've said in context, that's
    less than the width of a motorway measured from the centre of the earth.

    - Steve
     
  12. John Perry

    John Perry Guest

    Another way: you're asking for 1 part in 1296000 _accuracy_. Even that
    kind of _resolution_ is not easy.

    John Perry
     
  13. joseph2k

    joseph2k Guest

    Apparently you have never worked with any high resolution angle measurement
    systems. I can do that using 1950's technology, all gears and some tubes
    as needed. Back in the 1970 i saw 30 bit per revolution systems, i expect
    that better can be readily achieved today.
     
  14. A rotary transformer based solution is the Inductosyn (Farrand Controls
    http://www.ruhle.com/). It's typically 360 speed (cycles per rev).

    To encode the Inductosyn position, you can get an Inductosyn to digital
    converter or design your own.

    In a former life we did our own encoder. Using a 16 bit ADC, we encoded
    position to 18 bits per degree, or about 0.01 arc-seconds. Accuracy
    however was not better than the Inductosyn, which was about 0.5 - 1
    arc-second for IIRC a 12 inch diameter model. Achieving this level of
    accuracy required the use of patented calibration techniques.

    Marc
     
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