On Mon, 6 Aug 2007, Dale wrote: > Date: Mon, 06 Aug 2007 08:40:26 -0400 > From: Dale <[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] USB Wireless Network & Steppers with encoders? > > While I can't comment on the wireless network other than it should work. > I do have some comments on steppers and encoders. Unless you have some > real high rent stepper drives capable of running your steppers at > rediculess micro step counts encoder feedback is poimtless. First thing > a proper stepper setup should NOT lose steps! Second if you add all the > variables, tolerances, assembly, and missalignments in the machine you > still probably can't justify using encoder feedback. Unless your machine > is extremely accurate and near perfectly aligned, you would need drives > and motors capable of very high microstep counts. Then your steppers > could be run with encoder feedback and would act more like servos than > steppers. IMO it would be much more cost effective and practical to just > switch to actual servo drives. Less burden on the computer (EMC) and > easier to implement. Glass scales are also expensive at high > resolutions. To use Glass scales for position feedback requires a very > tight positioning system with zero or near zero backlash. I'm sure that > encoder feedback is possible to setup, I just don't see the need or > benefit of it. Last words, a properly setup stepper system should NOT > LOSE STEPS! And minor amounts of backlash can probably be ignored. I > have .002" ~ .003" backlash. It's not really backlash but more of a > windup due to motor coupling and the extra load of spring loaded anti > backlash nuts. It doesn't present a problem as the machine repeats > within .001 or better so the windup issue get's ignored and I have no > problems with it. > > Just my 25 cents, (inflation) > Dale
Actually we can (and have) done encoder-feedback stepper systems in SoftDMC pretty well, but its hardly worth the trouble because: 1. Even with a 1000 line (4000 count) line encoder, you only have 20 encoder counts for the full range of PID output - pretty lumpy 2. This also means encoder - stepper alignment is very fussy, making it hard to get symmetrical drive, 3. When you are all done you get a stepper that acts just like a brushless servo, except its a 50 pole 2 phase servo which means the drive frequencies are much higher than a normal (2 or 4 pole) 3 phase brushless motor. This is not a good thing... Peter Wallace ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users