Obtaining Higher Accuracy for Machine Tools by Nonlinear Disturbance Observer

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(1) A Positioning device using a DC servomotor and ball screw with 1 nm positioning resolutions is manufactured. As a result of 100μm stroke step response by PID control, a deviation error of 3.1 nm and a dispersion error of 2.2 nm are obtained, considering the nonlinear spring behavior of all rolling elements on the device.(2) After the nonlinear spring behavior of all rolling elements on the above positioning device is measured by a newly-developed method, the friction model can be obtained by the application of a blush model of the sliding elements.(3) On the XY table driven by the linear motor, the trajectory contouring of circular interpolations at the quadrant changes is analyzed by use of the above friction model for the linear ball guideways.(4) The nonlinear disturbance observer using the above friction model is newly developed. The method of the feedback system using the observer is theoretically effective. But its practical effect cannot be made sure by the experiment because of lack of time.