On Thu, 15 Feb 2007, Jon Elson wrote: > Date: Thu, 15 Feb 2007 15:53:16 -0600 > From: Jon Elson <[EMAIL PROTECTED]> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> > Subject: Re: [Emc-users] Hardware step generator for 5I20 > > [EMAIL PROTECTED] wrote: > >> Jon Elson's boards use the servo scheme - his step outputs are sent to >> an encoder counter as well as to the drive, and the encoder counter >> feedback is used to close the loop. >> >> >> > It seems to me you HAVE to do this. Unless the clock of the FPGA is somehow > linked to the clock of the CPU, or the FPGA is generating a "servo" update > interval for the CPU, then there is always the possibility of a step > pulse either > being sent or not, before the next update. Eventually, these errors will > multiply to large position errors.
Actually works fine for me... In other words the host filling the FIFOs knows exactly how many (whole+fractional) steps are output each frame. This was mainly done for people using Windows so that real time reponse was not required to get a perfectly timed output stream. I'm working on an alternate step gen for EMC that will be free running and unbuffered. Its a little more involved because you cant avoid the direction setup time problem as easily as the buffered approach and therefore requires a dir change deadtime step accumulater-deccumulator. I should have something tommorow or Monday. > >> It is true that the buffered approach is theoreticaly a tiny bit more >> accurate. A perfect forward transfer function is more accurate (if >> less robust) than using feedback to compensate for imperfections. >> Maybe we (EMC) should investigate the possibilities. If we limit >> ourselves to a maximum of one "frame" in the buffer, perhaps the >> delay issue can be avoided. Something to think about. >> >> > Well, some discussion might be warranted, but it seems that in a real-world > machine control, where the operator may need to change feedrate or even > abort the procedure at any time, this is just unworkable. Maybe if the > counters are there, and are only used to recover position from an abort, > it would be functional. > >> >> >> > Jon > > ------------------------------------------------------------------------- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to share your > opinions on IT & business topics through brief surveys-and earn cash > http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
