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Thread: mN Radial Measurement

  1. #1
    Associate Engineer
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    Feb 2014
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    mN Radial Measurement

    We have a component shaped like an ‘open helical spring’ for which radial force characteristics are required. The diameter at which we would like to measure force is 0.271”(6.9 mm) although the spring itself expands to 0.375” O.D. (9.4 mm) in its free/ unconstrained state. We think the force the spring exerts would be ~ 100 mN at the target diameter. Our hope is to measure this within a ± 20 mN error. Also note the component is 1” long. The profile and the low force range are currently proving to be challenges, any ideas?
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  2. #2
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by parisp3 View Post
    The profile and the low force range are currently proving to be challenges, any ideas?
    To manufacture, measure, analyze?

  3. #3
    Associate Engineer
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    Measurement has been the issue. One approach using fixtures with semi-circular channels machined and a load cell at one end does not give us the resolution we need. Perhaps there is a displacement technique or a better direct force measurement alternative to a standard strain gauge load cell??

  4. #4
    Senior Engineer
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    Jan 2014
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    Are you looking to measure a quantity of parts for statistical or inspection purposes or are you just trying to verify your calculations?
    Additionally, I would think that using semicircular channels would introduce a static friction error which my gut tells me would be high and difficult to characterize. After all, a strain gauge load cell implies some displacement.
    Last edited by Timelord; 02-09-2014 at 01:41 AM.

  5. #5
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    Hello,
    I have the same question as yours, could anyone help me ?

  6. #6
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    To measure the force as you have depicted in the attached image at that very low magnitude, you need a scale with very high sensitivity and precision. You could build a weighing scale. I would suggest building the scale such that the length of the spring is well distributed on a measurement platform. Then you can attach a strain gauge to that platform such that when the platform is deformed, the strain gauge is deformed. The platform should be a material soft enough to transmit the force to the strain gauge and hard enough not to cut or break. Also, you can attach multiple strain gauges to the platform to increase the accuracy and precision of the system.

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