This paper presents a novel compensation methodology for nonlinearities in table drive system of machine tools, providing the high-precision contouring control. The nonlinearities in a target system are mainly composed of the lost motion between motor and table and the nonlinear friction on the table sliding surface with standard lubricants. In the research, the lost motion is especially modeled as a nonlinear spring/damping component at the velocity reversal motion, which causes the response delay in acceleration torque. The deterioration in table contouring performance due to the lost motion and the nonlinear friction can be separately compensated in a mode switching control manner, by superimposing the motor torque based on the lost motion model or the disturbance observer according to the system stiffness at the velocity reversal. Experimental results using a prototype show the significant performance improvements of the proposed approach in precise table contouring control.
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