Ideas for tension / compression test stand

[qu1nn]

Hello,
I currently work for a company that manufactures weigh scale devices. A majority of the devices are either patient weight scales ( the kind you stand on at the doctors ) or a tension load cell (displays patient weight when on a lifter). Typically the devices can weigh up to 1000lbs full scale.
My job usually consists of performing engineering test / evaluation of these devices. A majority of the testing involves me slinging massive amounts of weight all day… I usually have to do repeatability testing, linearity runs (ascending / descending), etc. Currently this technique is purely physical… I am looking for ideas to make it a LabView controlled technique that is relatively CHEAP.

Desired:
1) Relatively accurate (at 1000 lbs) accurate AND REPEATABLE to 0.05 lbs
2) Once at a particular load it must remain stable to 0.00 lbs ( sometimes air compression devices oscillate)
3) Can be configured for tension loads or compression loads (can be manual to configure)
4) Automation – Would like to run either tension testing OR compression testing but to be able to just walk away and have the system automagically perform the repeatability/linearity runs, etc.

Ideas so far:
A) A lever arm whose fulcrum point changes based on a linear motor and a known load.
B Some kind of linear motor that can be securely mounted vertically: would have to have various types of attachments to configure tension / compression testing.

I haven’t even begun to research linear motors… I don’t even know if they are appropriate or not for the application.

Any brainstorming ideas would be greatly appreciated



Thank you for your time


Qu1nn

 

[jdonville]

Qu1nn,

It seems to me that researching, building, testing and refining your envisioned test automation system to the point where you can be comfortable with the results (in terms of overall reliability, accuracy and throughput), will eat up a lot of time and resources. In addition, maintenance and periodic verification of the envisioned setup will demand more time and resources.

Unless there's a HUGE demand for increased throughput in your testing and evaluation, my feeling is that there are likely better ways for your company to spend the money.

Just my opinion.

Jeff

 

[ScottyUK]

You're essentially looking for a means of providing a force to load your measuring instrument with. Pneumatics or hydraulics exert force directly proportional to pressure, so for that idea to work you would require an accurately controlled source of pressure and an accurate means of measuring it. Accuracy depends on the accuracy you calibrate your instruments to. I have some experience on air-operated actuators for control valves in the process industry, and my gut feeling is that pneumatics may be the way to go - there is a forum dedicated to fluid power where you'll find a lot of knowledgable people who might have some more solid ideas of how to implement this idea: forum1083.

Depending on where you're located in the world, many of the H&S regulatory bodies are hugely in favour of reducing manual handling by employing automation, and this could be used to leverage your position with the management when trying to get funding.


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[m777182]

I would construct a lever, where its one end is supported in such a way, that it is completely and almost without friction rotatable in the vertical plane. Somewhere in the middle of the lever lenght fasten an adaptable rod or cylinder thet will exert pressure (force) on your load cell or add a hook that will produce a pulling action downwards providing that your load cell is fastened on a rigid frame over the lever.
On the right side of the lever you will be loading fixed weights by some pneumatic actuators. Calculate the distance from the axis of rotation and the particular weight at that distance in such a way that you will cover the entire range linearly in N steps or more. Look at the concept of binary number: with 4 weights you can span your range linearly in the range 1:16;with 7 weights even 1:128.The actuators will be switched on/off ellectrically so you can program your test for cyclic work.
I am sorry that my description is perhaps due to linguistic reasons not very good but I hope that you will get the concept.
m777182