Hi all,
I run a machine called a prototrak DPM. It's a bed mill that makes use of both linear scales and rotary encoders. The ball screw in the X axis currently has about .003" backlash. The machine compensates very well. The motor tuning is automatic. I just type a service code into the control and it jogs the axis and measures rotary feedback against the linear feedback and the machine configures itself. Not too shabby for a DOS based system.
Motor hunting is an issue in this type of system. While taking heavy cuts across the Y axis I can see the X hand-wheel jogging back and forth to comp for the slack in the system.
I use the machine for 3D surfacing of permanent mold cavities and it performs very well. Even with the backlash it will still interpolate a circle within .0005 out of round. It's all in the tuning.
I just wanted to let you all know that it can be and has been done. How to apply it in a home built system I don't know. It would appear that you will need real time feedback monitoring by the control not just a closed loop driver with a "blind" control.
hope this gets the wheels turning  |