On Thu, Sep 17, 2009 at 03:42:41PM -0600, David Braley wrote: > > This means that at a modest 100ipm of table travel speed, the position > pulse stream is 16,666.67 pulses per second. I just had trouble > imagining a parallel port dealing with something like this. Even if the > table encoder position output stream was fed to a counter, how can the > system know where it's at without looking (through the parallel port) at > the output of the counter value at least 16K+ times a second?
The smart hardware, whether it be on the other side of an EPP (parallel port) bus or a PCI bus does only the things that need to be done fast. Generally for servos this is counting the quadrature from the encoders, and generating PWM to make an analog output for servo amps. Every millisecond, EMC reads the encoder count so far (NOT the raw encoder signals which care changing way too fast) and commands velocities for the axes that are valid for the next millisecond. Your calculations are certainly valid if you want to read the raw encoder signals with the parallel port directly. You can quickly see why you have a nasty resolution - top speed tradeoff when you do that. The smart hardware eliminates this tradeoff. This page gives a general idea of the hardware that works with EMC2: http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Emc2HardwareDesign > Now, I know that I don't need those kinds of speed for actual machining. > It's just nice to be able to get the table to move that quick on a rapid > move without loosing it's position. You bet. My HNC lathe has an encoder resolution of 1/204800 inch (about 0.1 micron) and rapids at 250 inch (about 6m)/minute. No tradeoffs here! ------------------------------------------------------------------------------ Come build with us! The BlackBerry® Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9-12, 2009. Register now! http://p.sf.net/sfu/devconf _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
