Eric H. Johnson wrote: > My question now is about angular axes. While the X and Y axes have on the > order of 5000 counts per inch, the rotational axis only has 51.1 counts per > degree (18400 per revolution) If I use 18400 for my INPUT_SCALE, I can tune > the axis rather easily. Of course in this case if I issue: > G1 A1 F50 > It will turn 360 degrees rather than 1 degree. > > If I set INPUT_SCALE to 51.1 and adjust MAX_VELOCITY and MAX_ACCELERATION > proportionately, tuning again becomes much more difficult, ISTM due to the > granularity of the scaling. IOW, for the linear axes X and Y I get roughly > 5000 counts per machine unit (inch), but with the angular A axis I only get > 51 counts per machine unit (degree). Is this the correct way to set up an > angular axis? > Yup, I have observed the same problem with a Sherline rotary table and a 500 cycle/rev encoder directly on the motor shaft. The coarse resolution made it a problem to get good tuning. One thing is this low resolution makes the D term of the PID very dominant, so very small amounts of D work best. You can use FF1 and FF2 to improve the following error, but it won't do anything for stiffness.
I think this might be a place where velocity estimation base on arrival time of the last encoder count is the only thing that will really help. Jon ------------------------------------------------------------------------------ Come build with us! The BlackBerry® Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9-12, 2009. Register now! http://p.sf.net/sfu/devconf _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
