Roger wrote: > It's unfortunate that there isn't a way to approximate closed loop control > with > steppers and encoders in EMC2. I have read that EMC2 can detect a following > error using steppers with encoders and trigger a fault which is great but this > doesn't really allow the use of steppers in larger or high performance > machines. > > Yes, of course there is! Use the Pico Systems Universal Stepper Controller board. Wire the encoders to the USC board and verify EMC sees the motion in correct direction. Wire step/Dir outputs to step drivers. Set .ini file parameters INPUT_SCALE to match encoder resolution, and OUTPUT_SCALE to match step driver resolution. > It would be great if you could run a stepper like a brushless servo. Steppers > and drivers are cheap and easy to interface. > The problem with this is that a step motor driver has no power command, just step and direction. So, it always applies maximum power to the motor, that's why they run hot. There is no way to tell a Gecko, Rutex, Xylotex, etc. driver to run at lower or higher current. So, when the position falls behind, you KNOW you have a problem, but there is no real remedy for it. You can't ask the drive to go to peak power for a moment to catch up. The only thing that would work is to ask EMC to slow the feed rate to prevent a stall. Usually these things happen so quickly that the stall would happen before the feeds could be slowed.
You will note that (as far as I can tell) Gecko has dropped the "unstallable stepper" project. Mariss found it pretty easy to prevent ONE stepper from stalling, although it would deviate from the commanded path. The problem is that you have to slow ALL axes in a coordinated manner, and when one axis starts to stall, the others need to be decelerated abruptly to maintain the coordinated movement. That risks creating a stall on the other axes! What sounds like such a simple and brilliant idea in theory gets bogged down in real physics, like mass and inertia. Jon ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
