Abstract: In the five-axis machining, due to the non-linear relationship between the tool orientation vector and the rotary axis coordinates, smooth interpolation movement of rotary axes cannot be ensured by smooth transition of the tool axis vector. Especially when the vectors pass through the singular point or its neighborhood, the strenuous mechanical vibration of the rotary axis causes the servo alarm, even damages the machine parts. The tool posture error model is constructed by analyzing the changing situation of the tool posture in the process of the rotary axis linear interpolation and vector interpolation. According to the allowable tool posture error in five-axis machining process, the linear interpolation segment is inserted into the vector interpolation segment to avoid the rapid rotation movement of the rotary axes close to the singular point. Then the limiting velocity is determined according to the linear interpolation segment and the performance of rotary axes. Finally, a cubic spline curve is used to eliminate the discontinuity of speed produced on the boundary of the range which performs linear interpolation and the range which interpolates by the vector interpolation, and smooth operation is realized. Experimental results show that the fast smooth interpolation of rotary axes is feasible, while maintaining accuracy required with respect to the tool posture error, and is applied to the batch process of a certain structural part.

Key words: Five-axis CNC system, Motion control, Singular point, Tool posture error