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
