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constant torque on rotating shaft

Discussion in 'Physics' started by praondevou, Oct 2, 2011.

  1. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011

    I recently started to work on a test setup for torque sensors. I realized that it is difficult to maintain a constant torque on a rotating shaft. If you rotate it manually you have of course the irregular force applied by the person who is turning the shaft. When using AC servo motors, it also generates torque ripple.

    Question is: anyone here worked with torque sensors and has an idea on how to apply a constant torque on them while rotating?

    (These are steel shafts with two magnetized bands that develop magnetic poles when torque is applied. The test determines if the shaft's magnetisation is uniform and also if there are irregularities in gear and or in the magnetic field capturing unit (fluxgate sensor))
    RRITESH KAKKAR likes this.
  2. BillO

    Distinguished Member

    Nov 24, 2008
    A hydraulic motor comes to mind.
    RRITESH KAKKAR likes this.
  3. someonesdad

    Senior Member

    Jul 7, 2009
    A DC servo motor popped into my mind. We used to use the ElectroCraft brand for running wear and stiction tests on head/disk interfaces.
  4. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
    We currently use AC servo motors. The proper way to distinguish between torque ripple caused by gears etc and the one caused by uneven torque applied from a motor is not quite clear to me. I guess FFT analysis of the sognal coming from the attached torque sensor would do the job, but I still would need at least ONE method to apply the constant torque to the shaft.

    I'm gonna have a look into the hydraulic motor thing, never worked with something alike.

  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    You could drive the shaft with a DC motor that typically has quite a small amount of torque ripple when driven with a constant current, and use some mechanical filtering to reduce the torque ripple.

    Or for the next step up use force gauges on the motor frame mountings and closed loop feedback to control the current to give a very constant torque.
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    How about some sort of eddy current brake?