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angular opto sensor

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  • Day_Walker
    Hi group, I need to measure angle using angular opto sensor, do any body have idea about some kind of them, or how to use them? Thanks ...
    Message 1 of 4 , Mar 29 11:58 AM
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      Hi group,
      I need to measure angle using angular opto sensor, do any body have
      idea about some kind of them, or how to use them?
      Thanks ...
    • PeterBalch
      ... What kind of angular opto sensor? Gray-code? Quadrature pulses (like a mouse sensor)? What accuracy do you need? The cheapest is crossed polaroids - but
      Message 2 of 4 , Mar 31 2:06 PM
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        > I need to measure angle using angular opto sensor, do any body have
        > idea about some kind of them, or how to use them?

        What kind of angular opto sensor? Gray-code? Quadrature pulses (like a
        mouse sensor)?

        What accuracy do you need?

        The cheapest is crossed polaroids - but they will only meaure (approximate)
        angles up to 90deg.

        Peter
      • jone jordan
        Hi, Thanks for yoyr response, i dont know exactly, im having course called instruments and measurements, and i must make a device to measure the angle using
        Message 3 of 4 , Mar 31 2:30 PM
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          Hi,
          Thanks for yoyr response, i dont know exactly, im having course called instruments and measurements, and i must make a device to measure the angle using light, or anyhing optical, if you could give me some links or guidlines i will be helpfull.
          Thanks ....

          ----------------------------------------------------------------

          PeterBalch <PeterBalch@...> wrote:

          > I need to measure angle using angular opto sensor, do any body have
          > idea about some kind of them, or how to use them?

          What kind of angular opto sensor? Gray-code? Quadrature pulses (like a
          mouse sensor)?

          What accuracy do you need?

          The cheapest is crossed polaroids - but they will only meaure (approximate)
          angles up to 90deg.

          Peter




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        • PeterBalch
          ... instruments and measurements, and i must make a device to measure the angle using light, or anyhing optical, if you could give me some links or guidlines
          Message 4 of 4 , Apr 1, 2005
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            > Thanks for yoyr response, i dont know exactly, im having course called
            instruments and measurements, and i must make a device to measure the angle
            using light, or > anyhing optical, if you could give me some links or
            guidlines i will be helpfull.

            You can buy rotary shaft encoders that produce two streams of pulses with a
            90deg phase shift between them. You count the pulses to know how far the
            shaft has rotated. A mechanical computer mouse works the same way. You know
            which way the shaft is rotating because of the phase of the two signals.
            Any decent robot book will explain it. The problem is that you only get the
            angle relative to where you started - not absolute angle.

            If you have to build it yourself that's probably the easiest. make a
            cylinder 2cm dia out of transparent sheet plastic (from some sort of
            packaging). Paint two or four longitudinal black stripes in it. Put a
            flashlight bulb inside the cylinder. Arrange two light sensors around it to
            give you the quadrature signals. Years ago I made a tracker-ball like that
            (using a billiard ball) and it worked well.

            You can also buy rotary shaft encoders that produce 10 or 12 bits of
            (parallel) binary output which is an absolute measure of the angle (e.g.
            BAV0G.24K 4096 65 from RSWWW.com for £378). The usual output is Gray Code
            which is like binary but only one digit ever changes between adjacent
            numbers (unlike binary where e.g. 3 to 4 becomes 011 to 100 and two bits
            have changed). Again, any decent robot book will explain it.

            You could try making one of those with perhaps 4-bit output. One lightbulb,
            four sets of stripes and four light sensors. A typical four-bit gray-code
            is

            1000
            1001
            1011
            1010
            1110
            1111
            1101
            1100
            0100
            0101
            0111
            0110
            0010
            0011
            0001
            0000

            "1" is black and "0" is clear.

            Crossed polariser filter is the easiest of all. You can buy polariser
            filter from any scientific supplier or just use old sunglasses. Arrange two
            filters so one filter rotates with the shaft and one is fixed. Shine a
            light through them and measure the output with an LDR. I think the output
            is proportional to cos(2*a) - can anyone remember the formula? Anyway, it
            goes from dark to light in 90deg so to measure a full circle you'd have to
            arrange several sets of crossed polarisers.

            I used to do research in crab locomotion and used crossed polarisers to
            measure the positions of the joints of the gantry that supported the crabs.
            It worked well but crossed polarisers are too bulky to measure the
            positions of the individual leg joints. For that I attached a "grain of
            wheat" bulb to one side of the joint and a light-sensitive transistor to
            the other side. As the joint moved, the bulb's distance from the transistor
            varied.

            So there you have four methods of measuring angles using optical
            techniques.

            Peter
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