Jeshua Lacock wrote: > I captured a big spike event (16 encoder counts!), but for the life of me, I > cannot figure which came first (the seem to be at the same instant?). I have > two screen captures online, 1 so you can see the whole event and the second > zoomed in as far as possible at the beginning of the event: > > > <http://3DTOPO.com/spike-event-zoom.png> > OK, I think that is the Gecko 320, or possibly noise pickup on the encoder inputs. Since the encoder velocity seems to be fairly well-behaved, this is more likely to be real movement, not noise. When you see movement in a single sample, or + movement in one sample and - movement in the VERY next one, that is hard to believe as a real motion in the physical world. This move extends over 3 samples, an acceleration, deceleration, and finally the PID commands a gentle return to the commanded position. But, you see the error and PID output follow the delta, they don't precede it - so it was not a commanded move, ie. LinuxCNC didn't tell the G320 to move, it responded to the sudden movement with a command to move back. (Depending on how you have everything wired, these polarities can work either way.) > Yes, deadband did help remove most of the jitter I was experiencing, so I > started trying to tune the P and D (again!) - but I think I might have made > the "spikes" worse. > Well, it introduces a discontinuity in the transfer function, and should be used sparingly. > Can I hire you to VNC on the machine while I have you on the phone? I think > if I watched you tune one drive I would learn a great deal. > Boy, without the audible feedback, I'd have a lot less confidence in what I was doing. And, I'm not sure you can get this a whole lot better. If the G320 is responding to electrical noise on the encoder inputs, no amount of PID tuning will fix it.
Jon ------------------------------------------------------------------------------ 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-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
