Ok, so if I have this right: Servo thread periods of 1000us - 2000us are fine for 3/4 axis mill cutting steel / aluminium with rapids of say 120ipm. Benefit of hardware stepgens is improved resolution of accelerating / decelerating pulse trains - makes better use of stepper motors are high rpm.
7i43 on a parallel port should cope with 1 to 2kHz servo thread BUT there is an issue with setting the EPP parallel port mode on the D510MO when running Ubuntu 10.04. The other option is 5i20 or 5i23 PCI cards which don't have the EPP issue but are >x2 more expensive than the 7i43. Life is never easy :( Regards Andy -------------------------------------------------- From: "Jon Elson" <el...@pico-systems.com> Sent: Saturday, October 23, 2010 7:14 PM To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Subject: Re: [Emc-users] 7i43 or 5i20 > Andy Pugh wrote: >> Possibly. I have read somewhere that a sane (200uS) servo-thread >> _execution_ period is only enough time to shift 50 bytes through a >> parallel port. That is potentially limiting, but has not been a >> problem I have noticed with my 4-axis machine. The software stepgens >> running in the base thread and twiddling pins individually are >> effectively shifting one word per thread cycle. >> > At first I was going to take major exception to your numbers, but if > your servo loop has > to read position, compute PID, etc. and then write velocity out to the > device, > actually, you may be just about right! Using a PCI parallel port in EPP > mode, > 200 us should allow up to 250 bytes or so to be transferred, but that > would take up > the entire SERVO_PERIOD. You have to leave some slack for timing > variation, > and also for computation. So, the 50-byte figure might be quite close. > > For my USC board, for instance, there are 4 axes, with 3 bytes of > position and > 3 bytes of velocity for each. Plus a little digital I/O. So, it reads > 14 bytes and write > 13, plus setup and control overhead. Total of about 35 I/O operations > per servo > cycle. You could easily run a 10 KHz servo cycle with 4 axes, or 5 KHz > with 8 > axes on a modern CPU and PCI parport. > > Jon > > ------------------------------------------------------------------------------ > Nokia and AT&T present the 2010 Calling All Innovators-North America > contest > Create new apps & games for the Nokia N8 for consumers in U.S. and Canada > $10 million total in prizes - $4M cash, 500 devices, nearly $6M in > marketing > Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store > http://p.sf.net/sfu/nokia-dev2dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Nokia and AT&T present the 2010 Calling All Innovators-North America contest Create new apps & games for the Nokia N8 for consumers in U.S. and Canada $10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store http://p.sf.net/sfu/nokia-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
