Kirk Wallace wrote: > > I mean that when the motor is commanded to take a step the shaft will > try its best to reach the new step, overshoot and then settle down. If > this over shoot is large enough, it might cause the cutter to cut too > deep for an instant. At moderate speeds, I suspect this isn't a problem > because the motor might never come to rest between steps. I got this > thought when I saw that with increasing speed the inhibit signal got > smaller as a percentage of the already decreasing step pulse length and > went away at mid speed. If the inhibit were for electrical protection > the inhibit signal would get larger, relative to the pulse width. > Hmm, it is more sophisticated than I had thought! It apparently gradually goes from half-step to full-step as speed increases. Very ingenious!
Well, as for stair-step motion, there is no simple cure. You can gear down the stepper with a belt and pulleys, but then you lose top speed, rather severely with steppers. This is why a lot of higher-end systems go to servo motors. You can get encoders with an arbitrary number of counts/rev. and the speed limit is much higher. > > Micro-stepping and Geckos sound like a good thing, except they're not > exactly cheap and are in the budget. It would almost be cheaper to go > with a UnivPWM system, which would be even better. If I can get my old > stepper drivers sorted out, the conversion to EMC2 will be basically > free. I will only need a PC and breakout card that I already have. If > these drivers don't work, a servo system may not be possible because > there is no room for a belt reduction on X, unless I tolerate the loss > of some travel on one side. > Microstepping doesn't solve the problem, either. The microsteps build up force until the machine moves (some amount) in a jump. Might be less than, could be even more than, a full step. You'll never know. With a servo system that feeds back to the CPU, you can always check the performance, and at least read the jumpiness of movements as seen at the encoder. There are all sorts of ways to re-rig motors to clear moving parts. If you use a big enough motor, you CAN direct-drive the screws. Just select a high resolution encoder there. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
