Hi, First, I assume the 1024 PPR indicates that the resolution of the encoder is 1024 cycles per revolution as defined in http://www.motion-control-info.com/encoder_glossary.html Hence 1024 full AB cycles per revolution.
When using a 1024 PPR encoder, there will be 1024 A and 1024 B pulses per revolution. Since the A/B signals are directly read by the PC (via the parallel port), we have to make sure that every of the 4 phases of each pulse is sampled at least once by the PC in the time of one pulse. When pulses change faster than the PC samples, the PC will not see the changes, or loose track of the phase relation between the signals, and miss pulses. To compensate for possible fluctuations and inaccuracy of the phase and symmetry of the A/B pulses, we have to sample more often, e.g. 8 times per pulse-cycle (my guess). When running at 3500 rpm, there are (3500/60) * 1024 = 59733 pulses per second. When we want to sample 8 times per such pulse, we have to sample at least at 59733 * 8 = 477867 or about 480 000 times per second. That is once every 2.1 microseconds. Since your BASE_PERIOD = 62500 nanoseconds (62.5 microseconds) the sampling is about 30 times too low to be safe. When you keep the BASE_PERIOD = 62500 unchanged, and if you want to sample 8 times per pulse, the maximum number of pulses per revolution is: 1 / ((3500/60) * 8 * BASE_PERIOD) = 1 / ((3500/60) * 8 * (BASE_PERIOD / 1000000000)) = 34 Hence, i think that your encoder should have no more than 34 PPR when keeping the rest unchanged and when using the safety factor of 8 pulse-reads per pulse (which still gives not too much safety). So, i am surprised that you can go up to about 600rpm without loosing pulses. Can anyone check this, please? Luc Steve Blackmore wrote: > Hi Guys, what's a realistic number of PPR for a lathe spindle encoder > via a parallel port in EMC. Spindle is capable of 3500 rpm. > > My home made encoder had 90, but I've altered the drive system and > fitted a 1024 PPR encoder with index. Output is via differential line > drivers. > > I've changed the scale factor but it starts loosing pulses at 600 rpm or > so?? > > Here's what's in my ini file > > [EMCMOT] > EMCMOT = motmod > COMM_TIMEOUT = 1.0 > COMM_WAIT = 0.010 > BASE_PERIOD = 62500 > SERVO_PERIOD = 1000000 > > Hal file reads > > setp encoder.0.position-scale 360.000000 > net spindle-position encoder.0.position => motion.spindle-revs > net spindle-velocity encoder.0.velocity => motion.spindle-speed-in > net spindle-index-enable encoder.0.index-enable <=> > motion.spindle-index-enable > net spindle-phase-a encoder.0.phase-A > net spindle-phase-b encoder.0.phase-B > net spindle-index encoder.0.phase-Z > > Steve Blackmore ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
