On Wednesday 27 May 2020 11:20:46 N wrote: > > On Tuesday 26 May 2020 16:29:17 Chris Albertson wrote: > > > Gene, > > > > > > I'm also looking at using a closed-loop stepper for a z-axis > > > drive. On my system the z-motor's torque holds the full weight of > > > the head. With a standard open loop motor full current is used and > > > the motor gets hot because there is more current than needed. The > > > closed loop system puts only as much current into the motor as is > > > required to hold position. > > > > > > My calculation says that the force of gravity pulling the head > > > down will generate roughly just under 1.2 Nm of static torque on > > > the ball screw. That is the price one pays for using ball screws > > > vs acme lead screws. The ball screw is back drivable with very > > > little friction. But it has zero measurable backlash. (The cheap > > > $50 Chinees screw is perfect as far as my dial indicator can > > > tell.) > > > > If its loaded by head weight, and the gibs are well adjusted and > > wet, the weight preload cancels the backlash. Too much there will > > make sloppy rigid threads. > > > > > The build-in z-motor encoder has 1000 lines per revolution, so I > > > assume if I use 1/4 micro-steps that the motor will always have at > > > most 1/1000 of a revolution position error. The z-axis lead > > > screw is 5mm pitch so hopefully, I get 0.005 mm resolution (Yes, > > > this is better than needed) > > > > Absolutely, theres more spring in the frame iron than that. > > Have any idea how much spring there is in the iron? > That will take far more math than I am capable of doing.
> > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
