Rotary Position Monitoring

Discussion in 'General Electronics Chat' started by Dritech, Apr 10, 2014.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi all,

    I want to monitor the position on a DC motor which will be rotating 340° only (not full rotation). Is a potentiometer a prectival device to use for monitoring the position to the nearest 1° ? Will slight changes to Vcc have a significant effect on the position respective output voltage?

    Any help will be highly appreciated.
     
  2. mcgyvr

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    Oct 15, 2009
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You can get the incremental encoder in 360 pulses per rev.
    Did you also intend positioning to a degree? If so what control method are you using?
    CUI also have programmable capacitive detection versions quite cheap.
    Max.
     
  4. Zerotolerance

    Member

    Sep 18, 2011
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    Rotary Encoder Broski!
     
  5. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    Pots are how most ordinary servo motors for RC work, the 1degree precision might be an issue. Reading it is really simple.
     
  6. Bernard

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    Aug 7, 2008
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    US Digital, E5 rotary optical kit encoder available in 360 pulses/ rev. for $ 75. Quaduature signal output with index pulse.
     
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  7. #12

    Expert

    Nov 30, 2010
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    Pots usually only have 270 degrees or 300 degrees. Linearity is a problem. Repeatability depends on the driving current or voltage being stable (but we know how to do that). The encoder method seems a lot better for accuracy and being able to cover the whole range you need.
     
  8. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Thanks a lot for the replies. Where can I find to buy an optical encoder which is the same size of a standards potentiometer? Also, ere these similar sensors with a single channel (since I do not want to know the direction)?
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The CUI (DigiKey) are small, but if you don't want to use a quadrature encoder for directional indication, then you would need some absolute type of device.
    Encoders can be obtained in absolute, but alot more than a single input, it sounds as if you are limited to a single (analogue) input?
    Max.
     
  10. ronv

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  11. LDC3

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  12. ronv

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    Does it matter as long as when it is in the center you read 1/2 the voltage?
     
  13. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    5
    Hi,

    Sorry for the late reply. I was considering a potentiometer for two reason:
    1) because of space
    2) to eliminate the calibration process required when using an encoder.

    So lets say I use the potentiometer in the link below, will I be able to stop the motor in 1 degrees (2 degrees max.) intervals?
    Also, is a potentiometer reliable for repetitive positioning?

    http://www.bourns.com/data/global/pdfs/6637.pdf

    Thanks in advance.
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    The stated resistance rotation is 340 deg +- 3 deg. If you have some tolerance in motor rotation of 340 deg., then it might work. Stopping motor within +- 1 deg. is doughtfull, unless it is a gear reduced motor- just gut feeling.
     
  15. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi,

    I found a three turn potentiometer which I caqn use for this application. I can apply 15V as Vcc to get from 0V to 5V for a 360degrees rotation.

    The motor is with a planitary gear.
     
    Last edited: Apr 15, 2014
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