Rob Jansen wrote: > Jon Elson wrote: > > This is, in general, a bad idea to have a rigid tandem axis. > > > Define "rigid". Even a 1-foot steel I beam has some flex... As opposed to a gantry that is suspended on bearings from the sides. Big machines, like vertical boring mills, bed planing mills, etc. have a bearing at one end, and a sliding fit (single axis constraint) at the other, so the gantry ends can be fairly far out of sync with no strain on the machine parts. I'm guessing they have some limit switches to shut it down if the gantry beam gets too far out of line. This allows you to drive the gantry toward home with the sides out of sync until it reaches the home position, where the two motors are synchronized by the home position.
> I have combines home/limit switches on one side and with some standard > combinatorial logic I make sure that the motor is stopped as soon as the > home is reached (and the axis is moving towards the home/limit switch. > Only when both axes are homed, the home signal will be sent to EMC2. > As soon as both axes are homed, EMC will back off from the home switch > and the direction signal allows both motors to move again. > > In this way both X-axes are homed on a 90 degrees angle from the Y-axis. > No steps are lost so there is no way the axes will become miss-aligned. > Only reason for miss-alignment could be during start-up of the motor > drivers where both axes may move to a different full-step location. So > in theory there is a max. 0.03 mm difference in the position of both > sides of the X axis during startup. The OP has some industrial servo drives, and I have no idea how far they move when powered on. Then, the drives need to stay in sync while moving toward home. The drives use analog velocity command, so unless the drives are extremely well matched, they could drive at slightly different velocities. So, some scheme needs to be figured out to maintain the right sync between the two sides' encoder positions until they reach home. Jon ------------------------------------------------------------------------- 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
