On Fri, 2008-04-18 at 12:17 -0500, Jon Elson wrote: ... snip > Hmm, it is more sophisticated than I had thought! > It apparently gradually goes from half-step to full-step as > speed increases. Very ingenious!
Yes, I think it is half stepping because I got EMC hooked up to the mill and it only travels in .001" steps whereas before, at least .0005". It also sounds more aggressive. The machine rumbles at low speed. I can get up to the previous max. of 100 IPM or more. > 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. ... snip I think I am not getting my point across, fortunately it is only an academic pursuit. What I am concerned about, is axis travel due only to position oscillation as the motor settles into its new step position. With a properly tuned servo, the position is always arrived at from the starting point. If P is too high, the axis will over shoot and try to correct. If you are cutting material at this time, you will have taken off too much, even if you finally arrive to the desired position. I imagine that steppers do this on every step, but will never ring or over shoot more than a half step making the effect negligible. > ... > 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. > I am thinking that micro-stepping is like high servo encoder resolution and is for dynamic control, not positional control. I would think you would want full or half steps to set your positional accuracy and micro-stepping allows a means to work all the nasties while moving between the steps. This is pure speculation on my part. > 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 On the Bridgeport, I compromised and split the difference between full travel and no spacers between the motor mount and table end. The Bridgeport has a fair amount of binding on the ends so I wanted use the ends to help eventually even out the wear. I lust after getting all of the ways reground. The Shizuoka seems to have no wear, but time will tell. -- 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
