Help for system vibration coupling problem
Help for system vibration coupling problem
(OP)
We have optical plate, in which one pair of scanning mirrors (8KHz and 13Hz each) and some optical lenses are mounted. The optical plate is mounted on an isolated stage. My question is, assuming the stage is isolated so well that no vibration is from ground, what kind of vibration (frequency) we should measure on the optical plate? Only 8KHz and 13Hz from scanner? Does it have anything to do with the way of mounting?





RE: Help for system vibration coupling problem
OK, what is a linear system? All compliances must be linear. No clearances.So your mounting may be at fault if you are seeing (especially) 3rd harmonics of either of your 2 frequencies.
It is possible to generate phantom waves (not the correct terminology) for instance if you mix 12900 and 13000 Hz you will see a 100 Hz envelope on a scope, and be able to hear it as well. None the less, correct FFT analysis will show that there is no 100 Hz present in the system.
What other frequencies are present? Did you mean 8 kiloHertz and 13 Hertz in your post?
Cheers
Greg Locock
RE: Help for system vibration coupling problem
If the scanning motions are more like sawtooth, then you will see many harmonics on a FFT (decomposition in sines).
If the motion involves shocks, as if for example, there are brutal changes in the scanning direction (sawtooth) then broadband noise will appear too, maybe able to excite the suspension modes of the assembly..You will then see them on the responses.
Then, it has to deal with the mounting : all sx natural frequencies o the suspended body can appear...
Thomas.
RE: Help for system vibration coupling problem
Be that as it may, a dynamic system with a high Q will tend to suppress the relative magnitude of any harmonics when operated around its resonant frequency. (It's acting as a narrowband filter.)
Charlie Bright, PE