At 09:06 AM 3/25/2010, you wrote: >Mark Wendt (Contractor) wrote: > > At 08:43 AM 3/25/2010, you wrote: > > > >> Mark Wendt (Contractor) pravi: > >> > >>> 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, > >>> > >>> > >> This can be only mechanical then... Check backlash and endplay of nut... > >> check coupler too.. If motor make step and gantry not then don't blew > >> software :D > >> > >> Slavko. > >> > > This is on a rack and pinion system, pulley mounted directly on > > stepper, pinion has pulley mounted directly to it, with cogged timing > > belt driving the pinion. All these numbers were with the gantry > > moving in one direction, jog and hold, jog and hold, while watching > > the dial indicator for movement between jogs, which there was > > none. Does backlash come into play when all moves are in the > same direction? > > >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. Even if it doesn't have the resolution to move .001" shouldn't the resolution on the .1" moves be a little closer? 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
