This has been done at a bigger scale... (2 feedback loops) https://web.archive.org/web/20160222165548/http://jmkasunich.com/cgi-bin/blosxom/shoptask/wichita-trip-02-20-08.html
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Combining_Two_Feedback_Devices_On_One_Axis On Mon, Jan 3, 2022, 8:42 PM Chris Albertson <albertson.ch...@gmail.com> wrote: > CNC is about precision motion control. Here is a new idea where this > builder gets 0.05mm accuracy but uses hobby level R/C servo Not only that, > but he connects three of these in series, one to the next to the next so > all the backlashes and poor tolerances add together. Then he uses this to > do precise motion. He loads a mechanical pencil with this chain of cheap > parts. > > What does this means for LCNC? It means that someone has found a software > solution to backlash. What he does is place a quadrature encoder on both > the motor and the output shaft. The difference in encoder reading is an > exact measure of mechanical backlash and effective gear ratio. He can > measure the backlash under different conditions and store the > measurements. Then he places a cascaded PID controller and Kalman filter > over this hardware. > > Technically the problem with backlash control via software is the delay > from input to output pays poorly with the PID algorithm. He applies a > predictive model. > > Checkup this video. It is unimpressive if you have a $100,000 CNC milling > machine, but he is using a linked chain of hobby servos. The novel idea is > his software. It is on github, you can read it. > https://youtu.be/gq-P39rfRqU > > He explains it here. Notice in the video he shows the backlash. The > gear-slop is at the 1/4 inch level but using his software backlash > correction you can see the results in the dial indicator is about 0.05mm > (or about 0.002 in American units) Not bad given the truly horrible > mechanics. > https://youtu.be/SioCwvR_PYY > > Why do I care? I have a robot-dog leg here on my workbench using hobby > servos, let's say performance could be improved. But the anti-lash > technique might be used on a real milling machine. Maybe one of the > experts here could look and see if it could be applied? I will use parts > of his idea on my dog-bot. > > -- > > Chris Albertson > Redondo Beach, California > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
