>>> The idea is that you drive it with 10x its rated current, but just for >>> about 1/2 the time it would take to move, and drive it in reverse just as >>> hard to stop it at the target point, then hold it in that position with >>> the servo feedback at its normal current until its time to make the next >>> move. One can also move it at slower speeds, with that speed totally >>> under control if the feedback is fine grained enough. One can mix the >>> back emf of its velocity with the feedback and get pretty smooth motions >>> down to the stop, but the stop would always be at an encoder count, not >>> completely analog. But then neither is the r2r idea. >> >> Thats pretty much just what Accelleration feed forward does. Dont know what >> its called in EMC, FF2? >> > I'll have to let someone else more fam with the terms comment on this aspect, > Peter. My setup with steppers doesn't use it. > > My familiarity with that sort of thing comes from many years of tuning the > servo's in a 2" broadcast videotape machines, reading up on the theory as it > was practiced then in the 70's & 80's. > > Ampex, in the AVR-1 & 2 models, at one time had some truly hellacious servos, > able to bring a 2" diameter headwheel into full servo-lock with maybe 5 > microseconds (that's arc-second accuracy) worth of rotational error at 14,400 > rpm in 400 milliseconds from a dead stop. I'd guess at 4 to 5 ounces of > rotational mass in that thing. The servo amps were built tough, but the > power supplies could have anchored the Forrestal if the wind wasn't too > strong.
I do like the open loop idea of full force for 1/2 of the time and then reversing the the force (I've known people who drive like that) Also with the galvanometer, absolute angular accuracy is probably less important that repeatbility. For something frictionless, repeatable, having constant mass and no distrurb forces like a galvanometer, Feed forward will get you a long way, maybe even with a pre stored time based force profile. (HP was doing this on their 14" disk drive head positioners in the 70's) > > -- > Cheers, Gene > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Q: What's the difference between a car salesman and a computer > salesman? > > A: The car salesman can probably drive! > > -- Joan McGalliard ([EMAIL PROTECTED]) > > ------------------------------------------------------------------------- > SF.Net email is sponsored by: The Future of Linux Business White Paper > from Novell. From the desktop to the data center, Linux is going > mainstream. Let it simplify your IT future. > http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 > _______________________________________________ > Emc-users mailing list > [email protected] > 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. ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
