This clears up some Questions that I have been wondering about. I was referring to the accumulated error in the ball screw, not backlash. The ball screws that I have are decent ground ones, so they should be ok. I'm not worried about thermal expansion, that usually only comes into play on runs longer than I will be doing. I appreciate the info, I wanted to make sure I was going down the right path before starting this project. Terry
On Sat, Jul 3, 2010 at 9:28 PM, Jon Elson <[email protected]> wrote: > Terry Neilson wrote: > > Gentlemen, > > So would it be safe to assume that the best place for an encoder to be > > mounted would be on the screw and not mounted to the motor shaft? > > Also once tuned using linear compensation, with other factors being even, > > rotary encoders will be at least as accurate as linear scales. True? > > > > > If you are using a belt reduction, then putting the encoder on the end > of the leadscrew > eliminates any error introduced by the belts and pulleys. There is > always some cyclical > error in these parts. There should be no backlash between motor and > encoder in this setup, > so it should not complicate servo tuning. If you have a belt drive, the > end of the leadscrew > should be available for mounting a shaft encoder. You want the drive > pulley to be between > two bearings, and then the encoder can be driven using a helical-slit > coupler. > > If your leadscrew is a ground screw in good condition, then this should > cause no significant > loos of accuracy. Thermal expansion of the screw will still affect > accuracy, but most home > shops don't run into that problem. > > If your leadscrew is a crummy rolled screw with some backlash, then the > shaft encoder will > not directly correct for this. The machine error compensation table can > help with this. > > > Jon > > > ------------------------------------------------------------------------------ > This SF.net email is sponsored by Sprint > What will you do first with EVO, the first 4G phone? > Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
