> > Sure there is Jon. Timestamp the last 4 edges so you can develop an > average speed over the total time period of those 4 stamps. Then add the > last few digits for the position it is expected to be at the servo threads > time. The only thing to complicate that would be a motion reversal within > that 4 sample period. > > Or maybe I don't fully appreciate the problem. No explanation offered so > far seems to explain why the encoders rps output, at a mechanical speed of > 20 rps, has +- 3.xxx or more from the 20 its actually doing, flickering in > the halmeter output. And this 'noise' does not seem to be all that much > effected by the actual speed regardless of the speed as long as its over > about 1 rps. > > Cheers, Gene
Thats an awful lot of jitter (>15 %). I certainly dont see that with our hardware that timestamps the encoder edges in conjunction with the driver doing a counts/time_between_counts calculation of estimated velocity. The software velocity estimation works the same as the hardware AFAIK, so should have reasonably good jitter performance. So there are a couple of possibilities I see 1. Are you use the encoder components velocity output? 2. Is this wired to the PID comps feedback-deriv input? 3. Do you actually have a good signal from the encoder? (things like HF tortional vibrations can play hell with velocity estimation by causing apparent reversals at low speeds) Note that Scott Hasse in his using the encoder counter for a A-D scheme with a V-F thought there was a problem with the encoder comp but found out jitter in his signal was the problem, and that the encoder comp performed as well as it could given the jitter and resolution of the basethread timestamp http://www.mail-archive.com/emc-users@lists.sourceforge.net/msg37885.html Can you connect a signal generator to the encoder comp and "bifurcate" the problem? Peter Wallace Mesa Electronics ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
