Identification and compensation of geometric errors of rotary axes in five-axis machine tools through constructing equivalent rotary axis (ERA)

This paper proposes a volumetric accuracy enhancement method of rotary axes in five-axis machine tools through constructing equivalent rotary axis (ERA). The influences of translational axes, setup errors of table ball and tool ball are simultaneously considered. A new concept named ERA, originated from the definition of axis of rotation, is proposed to globally describe the instantaneous position and orientation of rotary axes. Based on this concept, only six parameters are needed to describe the influences of geometric errors rather than ten parameters required by the existing concept of PDGEs and PIGEs. At the same time, the coupled relationship between the compensated motion commands of rotary axes and geometric error components is eliminated, and the geometric error compensation is realized by formulating analytical expressions. The typical characteristics of the proposed method lie in the following three aspects. First, the axis twists in the identification method naturally follow the constraint of rotary axis, and thus the normalization and iteration procedure required by existing literatures are avoided. Second, compact form of geometric error compensation is established and explicit equations are given to generate the compensated motion commands. Specially, the inverse kinematic model of five-axis machine tools can be well integrated into the proposed method. Third, besides machine tools with non-orthogonal rotary axes, the proposed method can also be easily applied to five-axis machine tools with non-orthogonal rotary axes just by modifying the ERA parameters. Simulation results and blade machining tests verify the effectiveness of the proposed method, and more than 70% machining precision improvement is observed.