aaron moore wrote: > Hi Jon > Can you tell me what midband resonance is. Could it have anything to do with > leadscrews that vibrate/ whip around a bit > Stepper motors have "poles", where the magnets and coils interact to form the full-step positions. With the magnets pulling on the toothed stator plates, there are those detents you can feel in the motor. (When the coils are energized, these detents get a LOT stronger.) So, the motor has fixed positions built into it by the magnetic circuits inside. These act like springs, when the rotor is deflected from the center of the "detent" it will return when you let up on the shaft. Now, the rotor also has mass, therefor angular momentum. Add momentum to a spring, and you have something that can bounce back and forth. When the step rate approaches this natural resonant frequency, you have a very unstable condition. If the motor is driven at that frequency for a while, without enough damping, the resonance builds until it is strong enough to jump over 4 full step positions. Then, the motor is capable of running backwards, stalling, or all sorts of erratic behavior.
Gecko has a patented scheme to damp this resonance electronically, and all I can say is it really works! Due to that, I have a strong suspicion you are not using a Gecko drive, or any other with mid-band damping. Back in the old days, before microstepping, there were a variety of fluid dynamic dampers that were attached to stepper motor shafts to fight this. Many of them were basically a thick disc with an annular cavity with a big steel washer sealed inside, with a bunch of grease packing the cavity. Others had a steel washer attached to a thin disc with a rubber pad. All involved some kind of viscous damping scheme. If you are using a full- or even half-step drive, I think this definitely is your problem, and you may find it hard to fix with that type drive. Jon ------------------------------------------------------------------------------ Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are powering Web 2.0 with engaging, cross-platform capabilities. Quickly and easily build your RIAs with Flex Builder, the Eclipse(TM)based development software that enables intelligent coding and step-through debugging. Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
