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Measuring the surface speed of a bearing — Parallax Forums

Measuring the surface speed of a bearing

MJHanaganMJHanagan Posts: 189
edited 2013-11-23 09:39 in Accessories
I have a 7 mm wide x 22 mm OD bearing whose outside surface is in contact with a spinning wheel. I would like to measure the rotational speed of the bearing using some type of optical encoder. Maximum speed is in the 100's of RPM but I am also interested in measuring very slow speeds down to about 1-2 RPM. The bearing is stainless steel so I was wondering if some of these IR optical encoder detectors would be able sense the smooth surface rotation if I painted small black lines on the outer surface or even side of the rim (say 30 to 60 lines). Does anyone know if these optical encoder sensors can use metal surface/painted surface for detection?

The bearing is 22 mm OD so the backup plan will be to glue on a 1" OD optical wheel.

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-09-29 11:53
    Bare metal reflects IR well. The trick can be finding something to absorb the IR. A black Sharpie won't do it. I used black masking tape on a brass gear in my recent encoder experiment. Some sort of flat black paint should also work.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2013-09-29 12:02
    Anything you adhere to the outer surface of the bearing will wear off. You could add an idler shaft in contact with the other side of the bearing to which you can attach a slotted wheel. Then it becomes easy.

    -Phil
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-09-29 12:16
    Could the black stripes be applied to the side of the bearing where it won't be worn off?

    If a slotted wheel is used should one of these type of sensors be used with it? IIRC, the S2 has uses a small version of the photo interrupter sensor I just linked to.
  • MJHanaganMJHanagan Posts: 189
    edited 2013-09-29 16:31
    Thanks for all the inputs. I will try the black tape on the edge to see if the sensor can detect it and I can get enough lines to detect the slow speeds. If not I will have to attach an encoder wheel and use a photointerrupter.

    Thanks everyone!
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-09-29 16:57
    At slow speeds you can use the time between transitions to compute speed rather than using number of transitions per unit of time.
  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2013-10-16 05:08
    Something I have always wanted to try, and I don't know if it will work in your situation, is to use an optical sensors from a mouse as a distance/velocity measuring instrument. I understand the way they work is taking high speed "pictures" and suing the delta in the "image" to computer distance and orientation. This would probably only work in slow speeds.
  • prof_brainoprof_braino Posts: 4,313
    edited 2013-11-23 09:39
    Timothy D. Swieter wrote: »
    Something I have always wanted to try, and I don't know if it will work in your situation, is to use an optical sensors from a mouse as a distance/velocity measuring instrument. I understand the way they work is taking high speed "pictures" and suing the delta in the "image" to computer distance and orientation. This would probably only work in slow speeds.

    I saw a demo at the sensor expo a couple years back that use this principle. The guy said it could sample faster than the shaft could spin. Of course, the unit he was showing cost a big pile of money. I suppose the sampling frequency of the optical mouse parts wold be the controlling factor.
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