Oops, replied to Dave instead of the list. ----- Original message ----- From: John Kasunich <jmkasun...@fastmail.fm> To: dave <dengv...@charter.net> Subject: Re: [Emc-users] LinuxCNC Week in Wichita Date: Mon, 22 Oct 2012 16:17:16 -0400
On Mon, Oct 22, 2012, at 03:44 PM, dave wrote: > On Mon, 2012-10-22 at 07:09 -0500, Stuart Stevenson wrote: > > Do you mean the G&L that had the Allen Bradley control on it? > > We found the X, Y and W (table) axes have a lot of backlash. We are > > replacing the balls in the ball nuts. This has tightened them very nicely. > > The X axis ball nut does not mount solidly to the table. We are working on > > that right now. > > The Y axis scale is broken beyond repair. I believe we can run just as > > accurate using the motor and compensation. > > > > On Sat, Oct 20, 2012 at 3:53 PM, Jon Elson <el...@pico-systems.com> wrote: > > > > > > > > > Stuart Stevenson wrote: > > > > > > > Oh, yeah, I've been meaning to ask what ever happened to the > > > K&T horizontal? Did you ever get the encoder fixed or replace > > > it with something more robust? > > > > > > Jon > > Hi Stuart, > Indeed I think you can especially with tight ball screws. In fact, if > you really want to be anal put a high count encoder eg. >= 10 K > counts/rev on the ballscrew for position and an encoder on the motor for > control; or emulate your 5 axis with I on the ballscrew and the rest on > the motor. > My ease of tuning increased considerably when I went from glass scales > to encoders on the ballscrew. Several years ago we did the experiment on the X axis. We used two PID loops, one with feedback from the motor encoder, the other with feedback from the glass scale. We set P, D, FF, etc on the one that used the motor encoder, and I on the one that used the glass scale. The outputs are summed before they go to the drive. It worked - the motor encoder loop keeps things stable, and the I gain from the glass-scale loop takes care of things like screw errors and screw growth from temperature changes. I haven't been active at all in EMC/LinuxCNC for the last few years, but if my work schedule permits, I think I will try to make it to Wichita next summer. Sounds like fun! John Kasunich -- John Kasunich jmkasun...@fastmail.fm ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_sfd2d_oct _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
