I think his method would work for your mill. Yes the tool pushed the table and the table moves. What he does is not just a double loop. He models the movement of the table and predicts how it will move. To do this on a mill you would need encoders on the table and then run a calibration cycle that measure table movement as a function of force.
Then as the mill cuts he can update the model parameter in real time by seeing if the predicted table motion matches the actual table motion. In this video he loads a pencil. He says (in comments some place) the reason for the initial slow movement is that the system is measuring flex vs. force applied as it puts the lead in the pencil. after a second or so the data is good enough the system can move faster. You can see the rate of lead insertion gets faster. It is because he has better data. https://youtu.be/GCHXNcpq3OA On Mon, Jan 3, 2022 at 7:02 PM John Dammeyer <jo...@autoartisans.com> wrote: > Interesting concept. I notice that although he showed his finger pushing > on the jaws (and text said compensation turned off) we never saw him > disturb the jaws with compensation on. That he can position accurately is > pretty cool. But backlash on my X axis results in the milling cutter > pulling or pushing the table under heavy cuts. > > The only real solution is ball screws or double nut ACME. > > Now for a robot arm that does pick and place of work "on to"/"off of" the > mill or a conveyor belt maybe it's not an issue? > John > > > > > -----Original Message----- > > From: Chris Albertson [mailto:albertson.ch...@gmail.com] > > Sent: January-03-22 6:40 PM > > To: Enhanced Machine Controller (EMC) > > Subject: [Emc-users] Very good software backlash control demo. > > > > 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
