On Mon, 2008-11-03 at 18:58 -0600, Dave Merriman wrote: Welcome Dave.
> I'm new to EMC and CNC, and have been trying to get my head around what's > going on with EMC and a CNC machine. Good plan. Don't try to think that it will all come to you at once but let it soak in a chunk at a time. There are several layers here that all work in concert to produce a properly working EMC2 system. > I've gone through (read) the CNC setup process a couple of times, and I have > to admit that I'm still a bit confused. > > What I'm not understanding, really, is just exactly _what_ EMC is dispensing > through the parallel port. It makes sense that the level of detail/control > varies with the sophistication of the CNC machine; what I'm not real clear on > is *how*. At the core of EMC2 there is a data model of the current state of the machine being controlled. State meaning current position, what signals are true or false, and such. There is also a set of what to do if (something) changes. Pressing an Estop switch will cause a comparison between the current state and that expected for an estopped condition and will develop and send a set of messages to conform the machine to that condition. Initiate a change of position command and it will cause commands that produce the desired motion. But all this is at the center of the system. Actual changes in the machine depend on the specific configuration available. In a stepper system it produces step and direction pulses and assumes that the machine is moving and will continue until the new position is achieved. With a servo system it sends a velocity command and watches feedback to see motion. We call most step and direction machines open loop. Meaning that there is no "real" way for EMC's state to check that actual position has been achieved. We tend to call full servo systems closed loop. That means that EMC can see actual position and issue velocity commands to achieve that position. HTH Rayh ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
