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 > > OK, base period is 62.5 us. For safety, we should never have encoder counts coming faster than twice that period. So, that is 125 us or 8000 Hz. Just to pick round numbers, 3600 RPM is 60 rev/second, or 16.67 ms. So, we can read no more than 8000 counts/second, and need to fit that into .01667 seconds. 8000 * .016667 = 133. So, you need a 128 or 100 count/rev encoder. Encoders are usually specified as cycles/rev (also written pulses/rev) and that is 4 x less than the count rate. So, you need a 25 or 32 cycle/rev encoder! That's why people use hardware assist to handle these encoder counting chores.
Jon ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
