Hi Marc I was working long time on an six axis gantry laser system with about 2.7 to 1.8 meters travelling range. As I understood from the machine builder, they used also two "independent" servos fore both gantry sides, one was the master servo, and the other was tracking to the master. Both axis had linear encoders, home and end switches. For reference, the moved parallel to the home position and the linear encoder was used to adjust the home position final, because the have also some repetitive pattern (Ca all 10 mm) to get home position to about 1/1000 mm precise. If the home position was not found for both axis in some window, an emergency shutdown occurred. If you had bad luck, You had to loosening both gantry sides, and pre- adjust the gantry manually (even the technician moved once the servos controlled in opposite direction to get the machine working again after an bad crash.)
I can not tell wich is the best solution for EMC2, but maybe you get some hints from my descriptions. Hansjakob Am 21.01.2007 um 00:08 schrieb Marc Bodmer: > Hello > I am on my way on building a gantry table for a plasma cutter and > setting up EMC. So far i am very impressed with EMC, thanks for > that great work. > > I am thinking about adding a second servo motor to the X Axis so > that it would be driven on both supported sides of the gantry. > However I am not so sure about how I could best do that. > > First I would like to explain my setup so you can imagine the > situation. The servos have planetary gearheads and drive the > gantry supports by timing belts. There are no linear encoders on > this axis, but the servos give resolver feedback to the servodrives > (Baldor Microflex). The drives convert the feedback to encoder > signals wich are fed to a Motenc Lite Card and EMC. > > 1. The first idea is to create a fourth servo PID position loop > for the new X1 axis and connect it to Xpos-cmd together with > axis X0. In the ini file I wouldn't add another axis, but > take the values for X1 and X0 from the X axis parameters. > For the feedback to the motion controller I would only attach > the X0 PID position feedback Xpos-fb. X1 Feedback wouldn't be > connected. > The problem I see in this setup is that first the feedback > of X1 isn't connected and I see no way for homing X1. > > 2. The second way would be to use the gantrykins component. > I had a look at the code, but did not see right away whether > there is a solution for the homing problem. The synchronisation > of these 2 axis however seems to be handled. > Did anybody use this module already? Any experiences? > > 3. Another way I would see is similar to the first way, except > that there wouldn't be a position loop for X1 axis. I have a > master-slave setup in mind where the master axis would be X0 > and the slave axis X1. The controller loop would control > position difference between these axis. Similar to the > HAL component "encoder_ratio". However I see no way again > in homing the slave axis. > > The homing problem is the following: Since there is always > a small position error between those 2 axis it would accumulate > up everytime X0 is homed, if X1 is dumbly homed at the same time. > There should be a way in first home X0 (of course both axis have > to move together) then X1 and instead of zeroing X1 it should > correct it's position in respect to X0. This way the error > would be eliminated in every homing cycle and not accumulate > up. I don't know if there are any "professional" ways of > solving this. (Would be interested in it if anybody knows about). > > Did anybody do such a gantry setup with a second servomotor > already? Any experiences? How to best do it? > I am pretty unsure where I should start. > > Thanks for any replies in advance > > regards > Marc > > > > > > > ---------------------------------------------------------------------- > --- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to > share your > opinions on IT & business topics through brief surveys - and earn cash > http://www.techsay.com/default.php? > page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
