> 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? _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
