Hey Kirk what kind of linear encoders were u using? Do you know what kind of signal they produce ? square edge (quad) or sin ? Sin wave signal encoders can be subdivided to produce more counts. .0005 inches per count is too course for pid tuning. Also I found that when i stopped the slide would very slowly oscillate. eventually I decided it was because The PID component which has a deadband setting didn't work as I thought it would. If I remember right it kills the P but not the I or P. so the I and D would slowly more the motor though the backlash till it moved the slide past the deadzone. But my backlash was something like .005-.007 , probably more because the encoder head was not bolted down very well. This was just a test-I wanted to see something move! When I finish the machine The rotary encoders will be on the motor (Thats the oem way), and I will fix the backlash, which I'm pretty sure is a bearing. I will also toy with dual encoders since the mounts are there using t he idea talked about - setting P with the linear scale (at least .0001 inches per count I would like more) and I and D with the rotary. At the very least i will try mapping the back lash with the linear scale.
Chris Morley ---------------------------------------- > From: [EMAIL PROTECTED] > Date: Tue, 8 Jan 2008 11:33:36 -0800 > To: emc-users@lists.sourceforge.net > Subject: Re: [Emc-users] DRO scales and EMC2 > > 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 _________________________________________________________________ Read what Santa`s been up to! For all the latest, visit asksantaclaus.spaces.live.com! http://asksantaclaus.spaces.live.com/ ------------------------------------------------------------------------- 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
