SourceForge.net wrote: > Initial Comment: > As I worked with positioning systems there ware always cascade loops > consisted of outer position and inner velocity loop. > The most simple system is a proportional (P-regulator only) loop for position > error-> output=Kp*(Position_setpoint-Position_encoder); > Output of position regulator is of course the needed velocity. The velocity > loop consists of proportional-integral (PI) regulator . > > Utilizing only PID regulator for position loop as used in EMC2 is not the > right approach, It cannot work good. I had never seen PID regulator for > positioning tasks and professional servo systems use cascaded position and > velocity loops only. If you truly believe a positioning-only loop can't work, please have a look at this document : http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?PWM_Servo_Amplifiers and especially the last graph. I'm sorry the scale unit doesn't show there, but it is 200 uInch per division. This was moving at 40 IPM, I think, during the continuous part of the jog. I think the loop control is excellent, and far better than the physical machine can deliver at the cutting tool. Note that the D term has a velocity component in it, so you get some of that velocity-loop response. I agree that a straight positioning-only loop is a little less stable than nested position/velocity/torque loops. You have to run with a lower gain to remain stable, and so feedforward help to keep error under control.
Of course, if you have a velocity servo amplifier with a DC tachometer, that will also work well. We use the same PID logic for both velocity and pseudo-torque servo systems. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
