Dual sliding mode contouring control with high accuracy contour error estimation for five-axis CNC machine tools

• A dual sliding mode contouring control method is proposed for five-axis CNC machine tools.
• The contour error can be analytically estimated by definition in real-time with high accuracy.
• The contouring controller is designed for each axis separately to avoid complex kinematic calculations.
• The dual sliding surface integrates tracking, contouring sliding surfaces and input signal together.
• The contouring controller can avoid the chattering in the actual control input as well.

Five-axis CNC machine tools are widely used in the manufacturing of the complex parts, and the contour error is the key indicator for the accuracy of the final product. Contour error, by definition, is a geometrical quantity solely dependent on the current actual tool pose and the reference trajectory. Contouring control is the main method to reduce or eliminate it. In this paper, based on the geometrical information of the reference trajectory, a high accuracy contour error estimation method for five-axis machine tools is proposed. Then, to avoid the time-consuming calculation of the inverse and derivative of the Jacobian matrix, to reduce tracking and contour errors simultaneously as well as suppress the chattering in the control signal, a dual sliding mode contouring control method is proposed. The dual sliding surface is selected for each drive separately, which integrates the traditional PD-type tracking sliding surface, a PD-type contouring sliding surface consisting of the axis component of the contour errors, and the input signal together. Experiments are conducted on a tilting-rotary-table type five-axis CNC machine tool. The results demonstrate that the contour errors estimated using the proposed method are very close to the true ones, and compared with the traditional sliding mode controller, the proposed method can reduce the contour error and the chattering behavior effectively.