That's not problem of friction at all!. The worst you have is 'sticky' axis. That means you need a lot more power to start to move axis and when already moving the required power is a way smaller. And if that ratio is big then tuning PID is near imposible. You can have low static error or low (or none) overshots but not the both!. So in this point of view the mechanics is bad nad electronic's can't do the job. The ratio can be measured with spring scalle. Just make arm on screw and then pull that arm with scale. Slowly pull until axis move then stop pulling and you have reading just at the point before start and when stoped. (you need some support for pulling as if you pull with bare hand then the 'stop' can't be measured as hand is to 'springy') And if ratio is biger than 1:2 then you have serrious problem.
2011/1/26 Igor Chudov <ichu...@gmail.com> > I have a rotary table (4th axis) that has considerable friction. > > I know this because the DC servo motor requires at least about 4 amps, to > turn the table. > > The rotary table has a tight worm drive, not some sort of a ballscrew, and > the drive is hard to turn. I did try that without the motor, by hand, and > it > was clearly a bit hard to move. > > I finally got the table work with EMC2 (thanks to Jon), and have a problem > with is a high following error. The error is 0.04 degrees. Since there is a > considerable reduction ratio in the work drive, the following error amounts > to something like 5 degrees of a turn of the motor (I may be off with my > math VERY easily, but clearly it is huge with that much reduction). > > Right or wrong, I attribute this to the friction in the worm drive system > -- > the servo motor develops following error when working against friction. > > I have AMC DC drives working in torque mode. > > My question is what servo tuning parameters could I use to compensate for > high friction. It seems that I almost need FF(-1) or something like that? > > Thanks > > i > > ------------------------------------------------------------------------------ > Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! > Finally, a world-class log management solution at an even better > price-free! > Download using promo code Free_Logger_4_Dev2Dev. Offer expires > February 28th, so secure your free ArcSight Logger TODAY! > http://p.sf.net/sfu/arcsight-sfd2d > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
