Bruce Klawiter wrote: > Jon Elson <elson@...> writes: > > >> Yeah, actually, I'd like to see one of these spikes zoomed in on the >> time scale so it is >> > > See image 9 here: https://sites.google.com/site/bmklawt/home/pid-tuning > OK, this is clearly a real movement of the machine, not any sort of error between encoder - PPMC - computer. Smooth acceleration and then a nicely damped return. One interesting thing is the time scale. Although it could be a damped response to a single servo cycle transient, the initial acceleration seems like it may last for several cycles. > >> Bruce says he has run it back >> and forth for >> a half hour, and it was within one encoder count of proper position >> (.0005") It seems VERY >> unlikely it could do that without errors accumulating. >> > > I am not following this, why can't it do this without errors accumulating. > If it was a misread of encoder counts due to electrical noise, it is very unlikely that any errors causing positive miscounts would be balanced by exactly the same number of miscounts in the negative direction. There usually is a bias in the system caused by slight difference from perfect 90 degree quadrature of the encoder, so that counts accumulate more in one direction. > >> I think Bruce has an oscilloscope, >> > > I do not have one, wouldn't have a clue how to use it if I did. > Ah, sorry, I must have you confused with another of my customers. > I unhooked the Y and Z axis amps and only had the X axis plugged into the DAC > board and when running the X axis it still had random jerks. > > Here are two videos of the jitter I get in the Z and Y axis. > The > first one showing the Z axis jitter when the X axis is moving back and forth. > The knob is on the end of the servo motor. > http://www.youtube.com/watch?v=7wZQwee8bec > OK, well, this is looking like there is a problem in the servo amps. Maybe you need to check the + and - 15 Volts, or whatever the servo amps use as the supply for their op-amps. Capacitors may have deteriorated and there is noise on these supplies. There could also be dirty connectors or wipers on the adjustment pots. Possibly you have grounded a circuit that should not be grounded to the machine's common ground. Another thought is that the logic signal that enables the servo amps is not being held at the right voltage, so the servo amps are right on the edge of enabling/disabling. This can cause a transient every time the amp enables that causes it to jump.
Jon ------------------------------------------------------------------------------ All of the data generated in your IT infrastructure is seriously valuable. Why? It contains a definitive record of application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-d2dcopy2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
