On 05/05/2012 05:19 PM, Jon Elson wrote: > 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.
I agree that should work with what's in Linuxcnc. I'm game to try them on the machine I have access to. It is a 3-axis machine with servos and encoders (~40K counts/inch) on the lead screws. It does have some backlash (0.003" in X and 0.009" in Y), and I'm curious how that affects table motion. This is partly why I was thinking of using a geophone to measure high-frequency components. It might be interesting to also see how backlash affects table motion in Linuxcnc. Karl ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
