We were having a problem running a G33 command to do knurling (using a cutting tool, not knurling tool) on the Emco lathe today. It is essentially a very small TPI thread (on the order of 0.68 TPI run with a very slow spindle speed). It turned out that I had the acceleration set too high in the .ini file and the Z-axis motor was cogging and losing position. I set the acceleration down and am able to run the command. But, as I up'd the acceleration to find the appropriate setting i am getting a vibration and noise that isn’t there if I issue a NOP G33 (I don’t move position with the G33, just do it in order to wait for index) and then use G1 moves to do the same knurling. So we were graphing with Halscope the commanded velocity, encoder velocity, and encoder position and were playing with filters to see if we could get rid of the vibration. It appears that G33 completely ignores encoder velocity (or motion-spindle-speed-in (which is net’d to encoder velocity) and instead uses motion-spindle-revs.
However, on my lathe the encoder position seems to be varying but probably on a very small scale. I don’t know if the variance is the VFD or caused by the mass (inertia) of the spindle or what but it is not steady and so while G1 is rock solid straight line on the commanded position plot, G33 is a signal that varies quite a bit and i am sure this is where the vibration comes from. If I look at the Halscope plot of the position command it is a fairly straight line that increases to 3 and then resets. But I am sure if I could set the Halscope to see something more fine grained than one servo-period (1ms) I would see the same variance I see in the motion-spindle-speed-in. Is it expected that the spindle on a lathe driven by a VFD would have a variance in it’s velocity and position? I trust the encoder (1024ppr quadrature US Digital optical) is correct and believe there really is a small variation in the spindle but not sure why or how to deal with it so that G33 (spindle coord movements) don’t try to track it so close as to cause wild requests for speed changes during moves... -Tom ------------------------------------------------------------------------------ Monitor Your Dynamic Infrastructure at Any Scale With Datadog! Get real-time metrics from all of your servers, apps and tools in one place. SourceForge users - Click here to start your Free Trial of Datadog now! http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
