Trajectory-Based Identification of Rotary-Axis Position-Independent Geometric Errors Considering Excitation Projection Effects

Improving the identification accuracy of geometric errors in five-axis machine tools is a critical requirement in advanced manufacturing. Although rotary axes enhance machining flexibility and productivity, they introduce additional geometric errors, among which position-independent geometric errors (PIGEs) are a dominant source of accuracy degradation. Existing studies have paid limited attention to how excitation projection associated with test trajectories affects identification accuracy. This study proposes a trajectory-based identification method using a single setup and systematically investigates the influence of excitation projection on the identification accuracy of rotary-axis PIGEs. An error model and a double differential identification scheme are developed and validated through simulation and experimental studies. For the AC-type machine tool, both simulation and experimental results demonstrate that the accurate identification of all rotary-axis PIGEs is achieved after the second differential under a favorable excitation projection. In contrast, the simulation results for a BC-type machine tool indicate that the optimal excitation projection differs due to its kinematic configuration. Compensation results further confirm the effectiveness of the identified PIGEs, showing a significant reduction in trajectory errors. The results reveal that identification accuracy is governed by the relationship between excitation projection and machine tool structural configuration rather than by the physical test trajectory itself. The proposed method, which requires only a single setup, provides an effective and practical approach for improving the identification accuracy of rotary-axis PIGEs in five-axis machine tools.