On Tue, 2008-01-08 at 11:16 -0600, Witek GB wrote: > I am a newbie to EMC2 but not to machining. I am thinking about > creating a CNC Mill with EMC2 however, my problem is with backlash > compensation. Is it possible to use DRO scales with EMC2 to have the > feed back that would allow you to know exactly the tool position? > > Thanks > > WGB
I recently set up my Bridgeport with linear scales, new ballscrews with .002 backlash and EMC. It was basically un-tunable. For my DC servo system at least, at the beginning of a move, feedback would indicate no movement, so EMC would crank up the signal to the servo until the backlash was taken up. Then the feedback would indicate too much movement and pullback the signal, creating an oscillation. Kind of like trying to tow a car with a rope. I could tune in reasonable performance, which always stopped within the accuracy of my scales (.0005"), but the accuracy during the path was awful, and slow speeds were un-tunable. Currently, the only practical way to live with backlash, is to have an encoder connected to the servo motor in a way that has no backlash (on the motor shaft, or by belt). Then tune out the backlash with EMC's backlash compensation feature. It would be nice to have a system that could mix the motor feedback and the linear feedback, but so far, the current solution works well enough to not justify the effort to change it. I am guessing, but I think the current system works because backlash is fairly predictable, and encoders generally have a much higher resolution than linear scales. You can see my project at the link below. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending) ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
