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! 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... -- Ed ------------------------------------------------------------------------- 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
