electro-mechanical application of a constant force

I am investigating the possibility of the application of a CONSTANT force
upon a deflecting material using a electro-mechanical device getting
feedback from an S-type load cell. The desired force would be keyed in and
the device would load to say 1000 lbs and monitor the load cell readings.
Then like a thermostat it would apply or remove force by some servo motor
advancing or reversing direction. This process would have to take place at
least once a second and be monitored over a few days if not longer. The
size of the equipment I would estimate be able to fit on a desk.
I am not an electrical or mechanical engineer so could someone point me in
the right direction
on where to start investigating this process.
Thanks in advance
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Standard PID control problem / application, start with a google search for PID control:
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(several tutorial links)
As to the best of many ways to implement this, you need to supply info as to scope of project. Is it a one of a kind or a few custom unit situation or a mass produced product? Could be done with a few op amps, uPC, micro PLC, I/O card in PC or something like this:
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Several ways to GET'er DONE! Depends on your needs, and PID is not the only way to do it.
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First you need to decide how you are going to apply force to your specimen. My first reaction is you will need either a screw driven actuator or a hydraulic actuator to develop 1000 lbs of force. Once you decide what type of actuator you want to use it is fairly easy to work backwards to design your control system. Also take a look at the tensile testing machines manufactured by Instron for hints on designimg a screw driven machine and MTS for hints on designing a hydraulic driven machine for applying a constant load to a specimen.
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This is what I have in mind:
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There are several failure modes you need to consider. Some of them may influence the initial design.
· How will the device ride out power failures of various durations? · What happens to the specimen if there is a sensor failure? · What happens to the device if there is a sensor failure? · Is there an expeditious expeditious way to free something caught in the device, even without power?
These considerations indicate to me the desirability of a screw jack.
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Jerry Avins

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