On Sunday 06 June 2010, Neil Baylis wrote: >Just wanted to point out that there are millions of inkjet printers and >plotters in operation right now that use this exact technique.
And I would point out that those are 100% steppers, driving the carriage by toothed belts with solid plastic stops at the end of the carriage travel. They would have no problem backing away from such a stop as there is zero chance of binding the drive screw. Not to mention that those are generally mouse powered steppers, with only 1-2% of the power available that we use as a matter of fact. I only know of two printers in a history span of 50 years that actually had servos, and I own one of them, a xerox 1650-ro, the worlds fastest daisy wheel ever, and both the carriage return and the daisy wheel driver are servos. Stout ones too, it does 40cps so the daisy motor is pretty decent, and the carriage can do a full 18" return in about 80 milliseconds. It will make the table dance and eventually loosen every glue joint in it. Great printer, but I can't get its film ribbon cartridges anymore. The other was an IBM printer about the size of a 20' chest freezer. We had to place it over a wall, so the carriage moved in line with the wall, or it jiggled coffee cups out of the cabinets in the kitchen, 50 feet down the hall. Poorest quality dot matrix printer I ever saw. >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 <[email protected]>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 <[email protected]>: >> > 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 >> >> [email protected] >> >> 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 >> > [email protected] >> > 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. 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