Karl Cunningham wrote: > On 05/04/2012 07:26 PM, Jon Elson wrote: > >> You'd need a swept >> sine wave generator to stimulate the system, and record the response of >> the system, both amplitude and phase to the stimulus. Just add the sine >> wave excitation to a constant position and feed this to the PID, and >> record position. Then, feed that to a Fourier analysis. > I have a few geophones (mentioned earlier in this thread) which might be > usable for collecting vibration data. I don't have a good > high-sample-rate ADC, but perhaps some scope traces would suffice. > > If someone has any specific tests they would like done with this on a > 3-axis knee mill, I could give it a go. > Actually, as I hinted above, I think this could be done with a script and features built into LinuxCNC. There is a waveform generator as part of HAL, and a module that will record traces from the RT component of Halscope into a numerical file. So, the only thing needed is a little piece of code to extract amplitude and phase info from the halscope trace and create a spreadsheet data file from the same measurement over a range of frequencies. So, if you have a machine with encoder feedback to the PC, you should be able to do this. Assuming a 1 KHz servo cycle, you should be able to detect resonances up to almost 500 Hz.
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