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Thread: Precise rotation of a turntable

  1. #1
    Associate Engineer
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    Sep 2020
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    Precise rotation of a turntable

    Hello, I have to design a turntable, that holds 3 PCBs, and stops at 120 degrees, for a piston to test the PCBs.

    My problem is, I am using a stepper motor and a photosensor to control the rotation of the turntable in 120 degrees increments, but the inertie makes it unaccurate, and I cannot think of a way to turn the table precisely 120 degrees at a time ( especially at high speeds) . Any thoughts?

    Thanks a lot!

  2. #2
    Principle Engineer
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    May 2015
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    Why do they have to be on a turn table? Or why can't they be moved in a straight line? How accurate do they have to be for measurement?

  3. #3
    Principle Engineer Cragyon's Avatar
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    Feb 2013
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    Retractable mechanical stop at 120 deg. increments? Have you considered a programable stepper motor control electronics like Rambo board?

  4. #4
    Technical Fellow jboggs's Avatar
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    Back in the day engineers used mechanical indexers to drive dial indexing tables for all kinds of automated assembly processes. I used Camco indexers on several successful projects. Like these:
    https://www.destaco.com/products/mec...ttribute-stops

  5. #5
    Associate Engineer
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    No it cannot

    Quote Originally Posted by Hudson View Post
    Why do they have to be on a turn table? Or why can't they be moved in a straight line? How accurate do they have to be for measurement?
    First of all, thank you Hudson for your reply.

    The project is specific for a turntable, I cannot change the scope, even if it's not the best way.

    The piston(it's up to me to use an pneumatic piston, or something else that moves in a straight line) has to have pogo pins that touch some pads, testing PCBs. it has to be very exact, within the 1mm.

  6. #6
    Associate Engineer
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    Sep 2020
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    After the table has turned 120 degrees, a sensor stops the stepper motor, and a claw that I made drops into her slot on the turntable, and keeps it fixed, fixing any small error of rotation, and then the PCB is tested, that is how I approached this and it worked.

    Thank you all for the replies, I really appreciate it Cragyon, Jboggs and Hudson.

    Have a great day fellows,
    Alex.

  7. #7
    Principle Engineer
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    May 2015
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    The indexer jboggs mentions is a good idea. Also investigate shot pins to position. The name Ferguson drive comes to mind as well.

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