Machining, Measurement, and Control Laboratory

Contour error compensation for NC machine tools based on synchronized measurement of tool-tip motion and error analysis
Kotaro Nagaoka, Atsushi Matsubara, Cefu Hong

Feed drive systems of NC machine tools have several error factors that are caused by the control and mechanical system. Those errors prevent improvement of the motion accuracy. Geometric errors such as straightness error and squareness error can be compensated for by subtracting the amount of the tool tip error from the reference position. However, by considering position reference changes time-by-time during the tracking control, the compensated result of the actual position becomes different from the compensating command because of delayed servo response. In this research, we propose a compensating method using the expanded two-degrees-of-freedom control structure. The proposed controller possesses two reference models; one is for the original position reference and the other is for the compensating command for the position. The effectiveness of the proposed method is verified by a numerical simulation and an experiment.
Keywords: NC machine tools, motion accuracy, measurement, compensation, reference model