2012/11/1 Peter C. Wallace <p...@mesanet.com>
> > interesting. Can you give your preferred technical reference for the > > PID error calculation for review? I am sure I can dredge several up, > > but you might have a clearer reference. Also, have you located the > > offending code? If so what file and line number? > > This is not a PID issue. The issue is that the ferror is calculated > differently than the PID error. So if you tune the PID loop properly the > ferror is larger then the PID error by an amount proportional to velocity. > > > The normal processing sequence that causes the problem is this: (and all > the > HAL files I looked at are arranged this way, that is, > read/motion/pid/write) > > encoders are read to get current position > motion does ferror calculation (on previous waypoint but current encoder > position) > motion calculates next waypoint (TP) > PID uses difference in motions new waypoint and current encoder position > to calculate error > > The problem is that if the PID loop is tuned so it has close to 0 error > (its > error, which is the difference in the new waypoint and the current > position) > you will have a calculated ferror thats equal to (velocity * sample period) > because the ferror was calculated from different data (current encoder > position and previous waypoint) than the PID error (calculated from current > encoder position and next waypoint) > and this is just plain wrong. > > Peter, I guess that in torque mode PID loop actually uses velocity but ferror is position error. While in velocity mode both PID and ferror use position. Why is it substantial to use torque mode? I never used it, but there must be some technique to minimize ferror rather than PID error. Andrew ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_sfd2d_oct _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
