On Monday 25 August 2014 21:59:43 rayj did opine And Gene did reply: > Greetings, > > I'm wondering if anyone on this list has used a stepper motor as an > encoder to monitor a shaft position and used it as input to LCNC? > I have a box in the basement with 4 ea small steppers designed to run from a 24 volt supply, and a bunch of comparators to convert the induced voltages into an A/B signal, was going to use them as jog wheels, but the one time I tried to setup a test to see if the idea had merit, I found that by the time I had added enough hysteresis to the comparators, the minimum speed at which a reliable signal could be obtained was faster than I had envisioned for fine control. Doable, yes, practical for the job, no.
> A related question, has anyone used a stepper in a setup that uses it > as an encoder to measure how much the shaft has been rotated and then > used the stepper to rotate the shaft back to the original position. The stepper motors lack of a Z(index/home) signal unless one cobbles up a separate mechanical method would I believe lead to pretty poor accuracy, not to mention that the higher voltage motor needed to make an encoder, makes for a generally very poor speed vs torque. Because we need good repeatable accuracy, most of the "home made" encoders are either hall effect devices sensing ferrous gear teeth as they go by, or some sort of an optical system. Often resembling magnum sized versions of the motion encoders that were used in the now ancient rolling ball computer mice. But we add a third 'index' signal in case an axis needs a true 'home' signal. A slotted disk, with 3 opto-interrupters, one of which is positioned to see only the one long slot works well. I am using such a method as a spindle encoder on my 7x12 lathe. A 50 slot disk with one slot extending inward, has 3 opto devices in a straight line so the center one sees the long slot, works quite well for those lathe operations that normally use the change gears by making sure the carriage's motion is locked to the spindle at least as accurately as the backlash in the change gears would do it. My accuracy is 360/200 or 1.8 degrees of spindle rotation. Not by any means good enough for a positioning servo, but it sure cuts nice threads. Ad it removes totally, any limits the machine may have due to a lack of the right gear to cut the needed thread. Its all done in the math driving the G76 or one of the G33 operations. > TIA Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. Stuff that matters. http://tv.slashdot.org/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
