On Friday 01 December 2006 00:32, Don Labriola wrote: >There have been a couple of articles describing this reverse motion > effect. A motor with a disturbed motion, either from a scrambled pulse > stream or from an external disturbance, can spin with significant > torque, in the opposite direction to the pulse stream at a speed of > three times that which would be expected from the pulse rate. The > combination of a motion of 3 full steps in the wrong direction by the > rotor with an advance of the magnetic pull of the stator in the wanted > direction causes the rotor and stator to again be in sync and to > produce torque. > >A single reversed direction pulse when the motor is running can easily > cause a two step position error (one from the error the step was about > to correct to keep producing torque, the second one from the wrong > pulse). Particularly at lower speeds, the rotor will oscillate after > each step. If the wrong direction step happens to occur as this ringing > is rebounding from an overshoot, the motor will continue in this > reverse direction locking in at the 3x rate as described above. > >Look for the single reversed pulse problem - it may well be the whole >problem! > While I can envision that effect if the motor was full stepping, I can't quite buy it if it was being microstepped at the 8x commonly used with the xylotex drivers. A single step in the wrong direction when its actually a 1/8th step just doesn't fit into the magnetic theory as I know it. But then my field is more electronics (I'm a C.E.T. since 1972, been chasing electrons for a living since 1949) than pure magnetics.
I would assume the motor(s) in question are being microstepped? >Don Labriola > >-----Original Message----- >From: Ed Nisley [mailto:[EMAIL PROTECTED] >Sent: Thursday, November 30, 2006 10:58 AM >To: [email protected] >Subject: Re: [Emc-users] Mysterious direction-signal changes >-SNIP- >One possibility is that my controller / motors are unduly >sensitive to starting out in the wrong direction. You can >convince a stepper to spin the wrong way if you torque it >enough; it doesn't sound happy, but it'll run the wrong way >at least for a while after you spin it up. > >What may be happening is that the motor gets up enough steam >in the wrong direction and loses lock when the direction >suddenly flips over. At that point it ramps up in the wrong >direction; the fractional stepping torque isn't enough to >overcome being in backwards sync with the whole-step poles. > >Also, I have seen on the real 'scope (but not recorded, so >apply a salt shaker here) invalid direction signals lasting >for tens to hundreds of milliseconds. That'd be enough to >ramp up to speed the wrong way, then go -thunk- when the >direction signal flips back the right way. > >Throw in another blast from my footgun and it might all be >the same problem under the covers. > >Onward... -- 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) Yahoo.com and AOL/TW attorneys please note, additions to the above message by Gene Heskett are: Copyright 2006 by Maurice Eugene Heskett, all rights reserved. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
