Separation and compensation of geometric errors of rotary axis in 5-axis ultra-precision machine tool by empirical mode decomposition method

In machining of a microstructure on a free form surface, a five-axis ultra-precision machine tool has a great advantage in its flexibility and efficiency compared to a conventional machine tool. However, rotary axes in the five-axis machine tools are sensitive to geometric errors due to their complicated structures. Therefore, the geometric errors of the rotary axes must be identified and compensated. Due to the nonlinear coupling and inevitable mutual influence between position independent geometric errors (PIGEs) and position dependent geometric errors (PDGEs), it is difficult to separate and compensate PIGEs and PDGEs accurately and effectively through conventional modeling and compensation methods, and there is no unified standard to judge whether the results are accurate. This paper first proposed an empirical mode detection (EMD) method to identify PIGEs and PDGEs of the rotary axis of a five-axis ultra-precision machine tool directly and simultaneously without any objective function, which solves the problem of mutual influence between mixed errors that cannot be avoided by conventional methods. The geometric errors are regarded as the mixed signals related with the rotation angle of the rotary axis, which are brought into the EMD procedure to calculate the error components. Cutting experiments were carried out on an Al6061 workpiece, and the results were analyzed to verify the proposed method.