Resonance Fixture. Crazy Idea? 2

[dktoao]

We have a spec for a sine dwell on a project that I am working on. The level is higher than we can do at our local test facility which is where we would prefer to test. So my question is... Is it unheard of to design a fixture that will resonate at or near the test frequency so that you can push the table at a percentage of the required input and still fully test the part? Or are there just too many risks associated with doing a test this way? I attached a rough sketch of the idea.

 

[GregLocock]

In an engineering, problem solving sense, that may be a reasonable solution. In the hidebound world of test rigs you may meet with some resistance. My guess is that if it is for an internal project you should be able to persuade management. If it is for an external customer, you may be able to charm them.

Incidentally it may not be as easy as you think to get that effect, over a braod frequency range.

Cheers

Greg Locock


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[IRstuff]

Just because you can do it is not a reason to do so. Forcing a system to handle a resonance that it was not intended to could potentially damage bearings and surfaces. There might even be potential damage to the actuator.

TTFN

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[dktoao]

It is a sine dwell at a single frequency, there is not a broad spectrum of frequencies. IR, I guess I am not fully following your point. If we design the resonance and shoot for the ramp up rather than the peak of the resonance. Say assuming a Q of 4 I could just multiply the weight of the part and the fixture by 4 to figure out the size shaker that can handle the resonance. Of course there will have to be surveys done and the whole 9 but that is good practice for any vibe test.

 

[GregLocock]

Add a third acc to the baseplate, then you can see if you are upsetting the table.

Cheers

Greg Locock


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[MAGNAFEAMAN]

hi,
I have design such a fixture way back but we call it mechanical signal amplifier. The main reason is to increase the signal that the DUT is experiencing. The material for the fixture and the way to control the gain take more work in the analysis side. Good knowledge of damping coefficient for material is very important as well as shape of elastomer to control the gain on a particular bandwidth. Resonance can be change by change the damper resonance (made of elastomer with or without fluid).

This type of fixture has been done and can also be qualified as a standard test fixture for a given DUT mass.

Good luck in your endeavor.