I think what you're missing is that printers have an encoder strip that is only marginally wider than the paper.
Going full left is not a decoded exercise. It just runs the motor 'left' for longer than a full stroke. Now when the motor moves right again, there will be some movement along the blank part of the encoder strip. As soon as the counts start, it knows where it is. So the end of the striped area is really the 'home' position. If it is printing full width, when it goes right, and past the end of the strip, the counts will stop coming, so now it will reverse the motor, and wait for the counts to start again, so a new reference is obtained from the opposite travel direction. A simple DC motor is fine since the velocity can be computed from the count rate. Regards Roland On 6 June 2010 22:51, Neil Baylis <neil.bay...@gmail.com> wrote: > Just wanted to point out that there are millions of inkjet printers and > plotters in operation right now that use this exact technique. It's > certainly practical. I think the reason they do it is to lower the cost. I > imagine it also improves reliability by eliminating failure-prone parts > (switches, connectors, etc). > > The reason I would do it is to lower the moving mass, as I'm attempting to > build a very agile machine, and every ounce counts. If it's too complicated > though, I'll rig up some optical sensor that can have low mass. On the > other > axis, I already have a reflective optical sensor that adds no moving mass > and works well, but that's more difficult on this axis. > > Sam's point about the Integral term is important, and raises another > question: is it possible to alter the PID tuning parameters after the .ini > file has been read. I think the answer must be yes, because the calibration > tool in the GUI does this, but not having read the code yet, I don't know > how that works. But even assuming that's possible, I don't have a clear > idea > of where I would need to hook into EMC to do what I want. > > Neil > > On Sun, Jun 6, 2010 at 1:25 PM, Viesturs Lācis <viesturs.la...@gmail.com > >wrote: > > > Can You explain the reason, why would You want to do it this way? I > > think that such approach is breaking machine, it creates unnecesary > > loads and stresses to the construction of machine and simple switches > > are cheap and wiring them is easy. I think that it is trying to > > reinvent the wheel in some painful way. > > No offense, just my personal opinion :)) > > > > Viesturs > > > > 2010/6/6 sam sokolik <sa...@empirescreen.com>: > > > I could maybe see monitoring following error... When the servo hit the > > > limit - the error would increase. You could then use some logic that > > > says when the following error reaches a certain amount - trip the > > > 'virtual' limit switch. Maybe.. I could see lots of issues and as > > > gene says - you would want to limit the output to the servos. If you > > > have any I (in the pid) the pid loop will 'wind up' pretty quick > sending > > > the servos to maximum. > > > > > > Big picture it seems possible... :) (but I am just thinking out loud) > > > > > > sam > > > > > > On 6/6/2010 11:09 AM, Neil Baylis wrote: > > >> Many printers& plotters do not use limit switches. Instead, they move > > the > > >> print head slowly towards the end stop until the motor stalls, and > then > > back > > >> off from that point a certain distance and that's the home position or > > soft > > >> limit. > > >> > > >> What, roughly, do I need to do with EMC to get this behavior? > > >> > > >> Neil > > >> > > > ------------------------------------------------------------------------------ > > >> ThinkGeek and WIRED's GeekDad team up for the Ultimate > > >> GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the > > >> lucky parental unit. See the prize list and enter to win: > > >> http://p.sf.net/sfu/thinkgeek-promo > > >> _______________________________________________ > > >> Emc-users mailing list > > >> Emc-users@lists.sourceforge.net > > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > >> > > >> > > > > > > > > > > > > ------------------------------------------------------------------------------ > > > ThinkGeek and WIRED's GeekDad team up for the Ultimate > > > GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the > > > lucky parental unit. See the prize list and enter to win: > > > http://p.sf.net/sfu/thinkgeek-promo > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > > ------------------------------------------------------------------------------ > > ThinkGeek and WIRED's GeekDad team up for the Ultimate > > GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the > > lucky parental unit. See the prize list and enter to win: > > http://p.sf.net/sfu/thinkgeek-promo > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > -- > http://www.pixpopuli.com > > ------------------------------------------------------------------------------ > ThinkGeek and WIRED's GeekDad team up for the Ultimate > GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the > lucky parental unit. See the prize list and enter to win: > http://p.sf.net/sfu/thinkgeek-promo > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ ThinkGeek and WIRED's GeekDad team up for the Ultimate GeekDad Father's Day Giveaway. 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