Proper sensor for accurate positioning...

Discussion in 'The Projects Forum' started by bhargav shankhalpara, Oct 24, 2013.

  1. bhargav shankhalpara

    Thread Starter Member

    May 9, 2010
    Hello everyone...

    i need some help for my project. actually i made up automatic link changer system.

    now my problem is...

    in my project i used stepper motor for accurate sliding movement. so for reach and stop at some fixed position is required. for that i have used TCRT5000 (REFLECTIVE OPTICAL SENSOR) datasheet of that can be download from here

    problem with this sensor is its not giving accurate position all the time. in my case aluminum surface as a reflective surface so i think due to oxidation process surface property will change with time and due to that i can't obtain accurate position. so i stick mirror at reflective surface but due to that also i can't obtain accurate position.

    so i cant understand what is actually going on...?

    please suggest me other method of accurate positioning(without any touching physically like limit switch).

    Last edited by a moderator: Oct 24, 2013
  2. MrChips


    Oct 2, 2009
    You need a photo interrupter.
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
    The flex coupling shown on your stepper motor looks to be aluminum. The aluminum couplings can "wind-up" in use, due to torsion build up in the 'spring' part of the coupling and friction in the screw and slide. When the motion of the slide stops this torsion un-winds and moves the screw a slight amount, giving a extra amount of movement. I'd guess your inaccuracy gets worse with a longer movement of the slide.

    The Lovejoy style couplings are better when accuracy is needed. There is no "wind-up" in them.
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    paint the block area or attach another material (plastic,etc..) that won't cause the problems you are seeing..
    Why is a regular contact type limit switch is out of the question?

    Are you also sure that the stepper isn't missing steps or binding too?
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
    It appears (to me) that you are bouncing the signal off the end of the block.
    Instead, try pointing the sensor at right angles to the slide (towards the leadscrew) so it detects the edge (corner) of the slide block. Maybe paint the area flat black as suggested, except for a narrow stripe at the corner of the block.
  6. bertus


    Apr 5, 2008

    It could be that the sensor is looking OVER the moving plate.
    In the PDF you linked to is also given that the surface should be like a mirror:


  7. MaxHeadRoom


    Jul 18, 2013
    Also Aluminum Helical coupling is not ideal for stepper or servo, They fracture prematurely.
    This can be corrected by using the helical Stainless Steel version.
    Last edited: Oct 24, 2013
  8. MaxHeadRoom


    Jul 18, 2013
    I would tend to use a slotted Opto sensor, they are a little more accurate for that application, also there is the miniature Honeywell SS400 proximity series that work well.