Identification and compensation of position-independent geometric errors for the rotary axes of large five-axis gantry machine tools

The accuracy improvement of five-axis gantry machine tools is constrained by position-independent geometric errors (PIGEs) introduced between the rotary axis components due to the influence of assembly processes. To rapidly and accurately compensate for these PIGEs in rotary axes, a method for identifying PIGEs based on the R-test instrument is proposed, using a five-axis gantry machine tool as the research object. Firstly, according to the definition of PIGEs, a kinematic model of rotary axis errors is established utilizing the multi-body system theory and homogeneous coordinate transformation. Secondly, leveraging the measurement characteristics of the R-test instrument, a continuous measurement trajectory is designed, incorporating two measurement modes, and a set of equations for identifying PIGEs is formulated. Finally, through detection and compensation experiments, it is verified that after compensation, the extreme difference of tool tip errors in the X-direction along the AK4 trajectory decreased by 27%, and the extreme difference in the Y-direction decreased by 22.5%. This confirms the effectiveness of the proposed method, which can be used to guide the accuracy assurance of rotary axes in five-axis gantry machine tools.