Jon Elson wrote: > Kenneth Lerman wrote: >> Jon Elson wrote: >> >>> Ray Henry wrote: >>> >>>> Are there swivel joints between the two screws so that the motors can >>>> move independent of each other? >>> Excellent point, and no, there do not appear to be any joints >>> between the two sides. (Dr. Lie has sent me photos of the >>> machine.) That is going to make it MUCH harder to properly home >>> the thing without bending the rails or ballscrews. >>> >>> I wonder if it would work better to home one side, with the >>> other side's servo amp disabled, and then home the second side >>> the last few encoder counts. Or, home the system with the servo >>> P gain turned WAY down, just high enough to get movement, and >>> then turn it up after the axes are in sync. >> >> That solution assumes that one side can back drive the other. That isn't >> necessarily the case. >> > Right. I've seen pictures of the machine, it looks quite rigid, > a welded steel box-tube frame with round slider ways bolted > every 100 - 200 mm. A modestly robust gantry, although it looks > like 80-20 extrusion plus several round ways between the two ends. >> It might be worth considering a home switch on just one side and a >> squareness indicator on the other side. (Somehow, measure the offset or >> flexing between the two screws.) Then drive one side to make the axis >> square. Then lock the two axes to each other and home the whole thing. > Well, the problem is when the thing fires up, the two servo > drives will be fighting each other and distorting the frame. > It needs some scheme to keep the two drives from fighting > against each other, even BEFORE the axes are homed. It is not > real clear how you do this, especially since it is relatively > rigid. How do you determine the flex in the frame? Strain > gauges? Wire-spool encoders on each side? Absolute encoders? > Actually, matching up absolute encoders sounds like a possible > solution. > > Jon
Well, if one side can back drive the other, a possible sequence is: 1 -- Float side B and home side A. Side A will drag side B along with it. 2 -- Side B will be off of its home switch. Now lock side A (keep the servo active) and home side B. 3 -- Now both sides are homed. At this point, (electrically, logically) lock the two sides together. It's a little more tricky than that because homing involves back and forth motion. Step two, above, must be such that side B is off the switch. Ken -- Kenneth Lerman Mark Kenny Products Company, LLC 55 Main Street Newtown, CT 06470 888-ISO-SEVO 203-426-7166 ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
