On Sun, 2009-01-04 at 06:17 +0000, 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. > > It would be great if you could run a stepper like a brushless servo. > Steppers > and drivers are cheap and easy to interface. > > Roger
With only step and direction signals on stepper driver inputs, EMC has no way of modifying the stepper driver behavior. The driver would need something like a step bias or correction input, which EMC could probably be configured to work with. If you want to compensate for missed steps, EMC can send more steps as needed, but you will most likely end up with just more missed steps until you get a following error, just like when a servo stalls. Those that have encoders on there stepper machines, may correct me on this. Also, any other motor driver/controller, be it DC or AC, that has step and direction inputs has the same problem. Usually the encoders for these systems are for display and, if configured, for following error alarm from "missed" steps or motor stall. The key with normal stepper systems is to configure EMC to never operate the steppers in a way that causes missed steps. There may be some homing issues with steppers with encoders and limit switches, which make it easier to home the machine. On second thought, an axis screw flag or index instead of an encoder is needed for homing. ------------- Kirk http://www.wallacecompany.com/machine_shop/ ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
