On Thu, 2008-04-17 at 20:47 -0500, Jon Elson wrote: > Kirk Wallace wrote: ... snip > If step overshoot is a common stepper problem, is there a > > common way to fix it? > > > > Do you mean jumping steps?
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. > The worst cause of this is mid-band > resonance, where the (full) step frequency matches the rotor's > pendulum-like natural frequency due to rotor mass and the > magnetic pull of the motor's poles. The Gecko drive detects an > electrica phase shift in the motor's waveform and counteracts > it. Otherwise, you can have the controller skip over the > resonant frequency, install viscous dampers, or try to come up > with other electronic damping solutions (RC dampers, etc.) > None of these schemes is perfect, I think the latter RC dampers > are almost certainly a disaster due to component size. The > Gecko also greatly solves the problem with microstepping, as it > reduces the excess energy supplied at the full-step frequency so > as not to excite the resonance. > > Jon 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. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/Bandit CNC) ------------------------------------------------------------------------- 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
