Mark Wendt (Contractor) wrote: > [snip] >> Hmmm. >> >> My first thought was also that it's a mechanical issue. I can imagine >> the rack geometry causing a problem like backlash. The thing I think of >> (and this is pure conjecture, I don't know that anyone would actually >> manufacture a rack with this "feature") is that there are "rest >> positions" as the pinion moves over the rack. >> >> You should try the moves with extremely slow acceleration and velocity. >> Take the numbers you're using and divide them by 5 or 10. If you still >> have position errors, then it's pretty much got to be mechanical. You >> can also test by repeatedly doing MDI moves like "G91 F10 G1 X0.001". >> The acceleration may be different for jogs vs. coordinated moves. >> >> One other thing, what's the axis scale? A small pinion (say 1.5 inches) >> moves ~4.7 inches per rev, which with a standard stepper, 10x >> microstepping, and 2:1 gearing is under 1000 steps/inch. You may not >> have the resolution to move 0.001 inches exactly. >> >> - Steve >> > Steve, > > It doesn't seem to matter where along the length of the rack the > gantry is, it happens whether it's in the middle of the rack or at > either end (the rack is 6' long). > > The pinion diameter is 1", according to the maker of the R&P > setup, and when I measured the OD of the pinion it was slightly > larger than 1" which makes sense if the pitch diameter is 1". Works > out pretty easy in my case since with a 1" pitch diameter, the pinion > moves 3.14159 per revoultion. Microstepping was set to 8, gearing is > 3:1 reduction, and if I remember right there was a scale of somewhere > around 1579.xxxxx or something close. > OK, 1527.xxx is what you'd get there. The thing is, microsteps don't really increase your resolution, they're mostly there to prevent resonance. The number of real steps you have, where the motor has full torque, is 190.985/inch. That translates to a 0.005-ish step size. I think that might also explain the 0.001 moves - nothing happens until you get to the next full step (or close enough that it's the closer one), when the motor then clicks over to that full step position.
- Steve ------------------------------------------------------------------------------ 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
