Rotational Position Sensor

Discussion in 'The Projects Forum' started by 360modina, Dec 11, 2008.

  1. 360modina

    Thread Starter New Member

    Oct 22, 2008
    9
    0
    At the moment I am mentoring a high school robotics building team and I came across a problem that I need a little help with. For a potential sensor we are considering using a digital semicircular sensor capable of measuring angular position.

    The sensor must have be able to measure the angular position to a precision of 0.3 degrees.

    My questions are:

    What is the number of concentric rings and on-off sensors are needed to achieve this precision?

    Is their a simple formula that I'm missing here, it appears like this could be easily solved with some knowledge of this type of sensor.

    I apologize that I cannot give too much detail on the subject, It just so happens that I am actually a chemistry teacher and don't have much experience behind the formulas that govern digital rotation sensors.

    Regards,
    Mr. Evans
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    It depends on the type you look for.
    With an absolute you need th number of rings dependend on the resolution.
    Witn an incremental sensor you are counting the number of marks after the indexmark.
    You say that you want to detect changes of 0.3 degrees.
    A full circle has 360 degrees. so the number of positions you need is 360 / 0.3 = 1200 positions.

    Binairy coding looks like this.
    1,2,4,8,16,32 ... 1024 for 2^0 , 2^1 , 2^3 , 2^4 , 2^5 ... 2 ^ 10 so you need 11 rings to encode 1200.

    See also this link from the EDUCYPEDIA.
    http://mechatronics.mech.northwestern.edu/design_ref/sensors/encoders.html

    This link comes from this page in encoders and resolvers from the EDUCYPEDIA.
    http://www.educypedia.be/electronics/sensorsencoders.htm

    Greetings,
    Bertus
     
  3. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    If you are referring to something like this [​IMG] (a 1°/step for the steering in an autonomous robot), there is indeed a formula.

    ceil(log(n)/log(2))

    Where
    n = number of segments
    and ceil means "if not integer, round up to nearest (higher) integer"

    log(1200)/log(2) = 10.229 (to 3 decimal places)
    Rounding up gives you the number of rings and sensors needed = 11
     
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