Mark, I just looked through this thread and perhaps the discussion is getting a bit off the rails (in my humble opinion) Many many moons ago I also worked on stepper systems and they drove me nuts, exactly because of this:
> I tried it at .001, .05, .01 and .1 on the jog movement. At >.001, sometimes I'd get no movement (I'd here stepper motor noise but >no movement on the dial indicator), other times I'd get a half-thou, >and other times it would jump .002" - .004". My take on it is that there is resonance in the stepper, and exactly when EMC tells it to step forward, the rotor has resonated so far to the next step backwards that the step impulse in the stator windings make it jump the wrong way i.e. backwards. What happens from there on is anybody's guess sometimes you just lose that step, sometimes the motor stops and hums sometimes it might even move some more backwards. The cause of the resonance needs to be addressed, it can be one of: 1. acceleration to big, the rotor moves still syncronous but lags on the edge of the rotating field. Any disturbance kicks it out of syncronism. 2. acceleration change too sudden. vaguely the same as above and the sudden change in acceleration is the disturbing mechanism. 3. not enough mechanical damping. The rotor resonates all the time as it moves, the stepper frequency powers the resonance. Microstepping should solve this. 4. sloppy or loose rack and pinion movement. I.e. there is not enough damping in the region of the play. See 3. 5. Too much power. See 3 6. Too little power. See 1. the rotor lags too much. 8. And last but not least noise from the steppermotor power cables getting into the signal cable to the drive. One step out of time and synchronism is lost. 9. and lastlast: lousy stepper electronics / pc interface card. With not enough capacitance in the right place to feed the electronic circuits and so cause spikes. So the first line of attack to me would be to add a bit of friction to the motor and see if it gets better. I say this since it is a rack and pinion. Else check for noise in the signal cable. You might also want to see that there are no irregularities in the rack. Wind the thing by hand with the motor shaft! So well, good luck! Cheers, Jan de Kruyf. On Thu, Mar 25, 2010 at 11:59 AM, Mark Wendt (Contractor) < [email protected]> wrote: > Mornin' Gents, > > Had a little time to play yesterday evening to play around with my > machine, so I decided to stick a dial indicator on both my X and Z > axes (I only have those two, it's a gantry machine that cuts tapered > triangular bamboo strips for making bamboo fly rods). The Z axis was > dead nuts on, but I was get varied responses to jogs on the X > axis. I tried it at .001, .05, .01 and .1 on the jog movement. At > .001, sometimes I'd get no movement (I'd here stepper motor noise but > no movement on the dial indicator), other times I'd get a half-thou, > and other times it would jump .002" - .004". At .01, the first > couple of jogs would show about .001" - .002" short of the full .01" > movement, then occasionally move the full .01", and then sometimes > slightly more than .01". About the same for the .05" movement. At > .1", the movement for the first few times was .003" - .004" short, > but then would move almost dead nuts on to .1" each jog. I don't > think backlash would come into play since all the moves were in the > same direction. > > I disconnected the pinion gears from the racks, moved the gantry > back and forth the length of the X axis a few times by hand, and > didn't really notice any binding. It seemed pretty smooth, and > relatively easy to move a 165 lb gantry on the rails. > > I thought maybe it was a software setting, so I futzed around with > the MAX_VELOCITY, MAX_ACCELERATION, and the STEPGEN_MAXACCEL. It is > pretty cool to see a heavy gantry zipping back and forth on the > machine at 180 inches a minute... ;-) > > Anything else I should look at? Or should I keep concentrating on > tuning with the three variables above? > > Thanks, > Mark > > > > > > ------------------------------------------------------------------------------ > Download Intel® Parallel Studio Eval > Try the new software tools for yourself. Speed compiling, find bugs > proactively, and fine-tune applications for parallel performance. > See why Intel Parallel Studio got high marks during beta. > http://p.sf.net/sfu/intel-sw-dev > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
