I think it's always best to go back to first principles when you have this sort of problem.
I'd try and isolate the problem from the application first. Set up a short G-Code program that runs the Z axis up and down at the feed rates used for your project. Set the loop count to 6000 and attach a dial indicator to the Z axis. Move a distance that is results in an even number of full steps of the stepper motor based upon the lead screw and micro-stepper. If the dial indicator shows an error I'd make sure the set screws holding lead screws and pulleys etc. are tight and try again. Ideally there should be two screws on each shaft. Not just one. If it's still out it will be out an integral number of steps. So if you are microstepping 10 steps per step it will be out 10 steps. Another thing to look at if the system doesn't lose any steps after that experiment is your power supply. Do a similar test but zero the dial indicator on a gauge block that you can move out of the way. Now run the same 6000 loop program but add simultaneous moves of XY and A. At the end of it insert the gauge block under the dial indicator and you shouldn't have lost any steps. If you have you may have power supply problems where multiple axis motion results in a dropout on the supply that causes a missed step. It makes sense it would be upwards because then you have to move against gravity. Some things to try. John Dammeyer > -----Original Message----- > From: Gregg Eshelman [mailto:g_ala...@yahoo.com] > Sent: December-11-15 3:09 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Z axis stepper gradually losing position > > > On 12/11/2015 2:03 PM, J. wrote: > > First hunch: > > Sloppyness in the z movement or in the spindle bearings. With lost steps > as a result. > > > > Because when you increase the 'load' the sloppyness is taken up by the > back pressure from the cutter. > > > > This problem has been the downfall of many stepper motor artists. A > stepper might lag as much as 2 steps from the driver output in certain > conditions, and yet recover again if running conditions are normal. But any > mechanical upset in that phase will result in lost steps. > > > > Happy hunting. > > What's the precision rating of the stepper motors? > > The smaller setting could be less than the motors+mechanicals of the Z > axis can handle, and gravity is conspiring with the system to ensure the > error is always downward. > > Can you incorporate a Z height probe/setter and have it automatically > recalibrate Z height before each pass? > > > --- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > > > ---------------------------------------------------------------------------- -- > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
