Brian wrote: > I may give that a shot as a band-aid to the problem. I suspect that > when reversing direction, the backlash is going to drive the PID nuts > and cause the table to jerk. > > If you have sizable backlash in your machine, then it becomes very hard for any CNC system to work right, either open- or closed-loop. The problem is the motor can't get from one side of the backlash to the other instantly, so it always leaves the axis uncontrolled for a moment. There is just no way to get around that fact. > I appreciate everyone's interest to find a workable solution for me, > but what I would like to focus on more is making EMC2 a more logical > and 'unified' system. Specifically adding the option to use a direct > reading scale for joint-pos-fb, instead of inferring this from the > motor position minus the screw comp. Lots of robots and machines use > a direct reading scale for measuring joint position, in addition to > having a scale on the actual servo motor. I really think there should > be a provision to utilize it, the way it was intended to be used. > Honestly, looking at the architecture of the axis HAL pins, I am > surprised that it hasn't been implemented already. > > This has already been done, and is well documented on the Wiki. You can start here : http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Combining_Two_Feedback_Devices_On_One_Axis Stuart Stevenson may also have some info on his web pages, he has the first machine done that way. Here's one link to that project, from the Linuxcnc.org links area : http://jmkasunich.com/cgi-bin/blosxom/shoptask/wichita-trip-02-20-08.html
Jon ------------------------------------------------------------------------------ This SF.net email is sponsored by Make an app they can't live without Enter the BlackBerry Developer Challenge http://p.sf.net/sfu/RIM-dev2dev _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
