The most satisfactory tuning I've gotten on loose ballscrews , i.e. 0.003, is with a 2500 cpr encoder on the end of the ball screw. In order of increasing ease of tuning, smoothness, etc. the linear scale was worst, an encoder on the servo motor shaft was next and the best results were obtained with the encoder coupled to the end of the ball screw. I've not tried other resolution encoders nor attempted to tighten up the backlash between the servo motor and the ball screw ( the drive is a 2:1 timing belt into a worm gear ). Sorry I can't be more helpful. $$$ spent in the right place can be really effective.
Good Luck. Dave On Jan 8, 2008, at 10:45 AM, Kirk Wallace wrote: > 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 ------------------------------------------------------------------------- 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
