Hugh Wylie wrote: > This is a request for assistance from those who understand the code > structure of LinuxCNC better than I do, and arises from some (historic) > frustration trying to set MIN_FERROR & FERROR parms to achieve best results. > First, MIN_FERROR and FERROR define limits which cause LinuxCNC top stop with a following error message, but have nothing to do with the servo response. The way these work is that MIN_FERROR sets a base limit when standing still. Then, FERROR defines an additional sliding limit that is proportional to velocity. So, of you set MIN_FERROR to 0.001 and FERROR to 0.0005 and were moving at 1 inch/second, the total limit tolerance would be .001 + (.0005 X 1) = .0015"
Now, there has recently arisen a debate about how these errors should be calculated, and it was shown that the following error used in the PID calculation is different from the one used for the following error trip point. This made optimal tuning difficult, as the error trip is looking at a different calculated error than the PID is using. So, you could get an incredibly low pid.0.error and yet get following error trips at several times larger values. I think there is an optional setting to unify these two ways of computing error, but they may not enter the mainline code until rev 2.6 The [TRAJ] settings only affect the maximum velocity and acceleration that the trajectory planner will request. Then, it is up to the PID for each specific axis to close the loop based on the settings in the [AXIS_n] section. Jon ------------------------------------------------------------------------------ Symantec Endpoint Protection 12 positioned as A LEADER in The Forrester Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" in the endpoint security space. For insight on selecting the right partner to tackle endpoint security challenges, access the full report. http://p.sf.net/sfu/symantec-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
