On 11/03/2011 6:21 PM, Dave wrote: > >> Using gantrykins with a gantry that cannot be out of square more than about >> 3/4", how can we home the 2-jointed Y axis? >> >> We cannot move in World Mode before homing. We cannot move in Joint Mode >> without racking. We cannot understand how to select one encoder to find >> index pulse on. Can we home to one of the two index pulses or is this >> impossible? >> >> OK, I think the whole problem here is allowing EMC to know there are two joints on the gantry. Since they must never be moved independently, then EMC should only know about one axis. The motion control side can know about them, but should always keep them in sync once homed, ie the same axis position is sent to both PID modules, which drive the two joints. This is easy to do in HAL.
So, the only trickiness is getting the joints homed. I am sure a relatively simple HAL component could handle this. One joint is the "master", and obeys EMC directly. The other is the 'slave". The offset between the slave and master is recorded when you come out of Estop (when not homed) and then this offset is maintained until one of the joints hits the home switch. The master joint is homed by EMC as usual, then, with the master sitting on the index pulse, the slave would be adjusted until it is also on the index. Now, of course, the question is, which way do you move to find home? I guess a move similar to the homing sequence could be performed, with the HAL component setting the home index signal and watching for it to go back to zero. This will cause the encoder count to jump to zero, so the PID needs to handle that jump. Jon ------------------------------------------------------------------------------ RSA(R) Conference 2012 Save $700 by Nov 18 Register now http://p.sf.net/sfu/rsa-sfdev2dev1 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
