CHARACTERISATION OF GEOMETRIC ERRORS OF A FIVE-AXIS MACHINE TOOL BASED ON LINEAR-ROTARY AXES COORDINATED MOTION

Position Independent Geometric Errors (PIGEs) of rotary axes, which are caused by imperfections during assembly of machine tools, are proved to be a major error source of a five-axis machine tool. In this paper, a PIGEs characterisation method using a Double Ball Bar (DBB) is proposed. The method is used to characterise the PIGEs based on the coordinated motion involving linear and rotary axes of a five-axis machine tool. Based on the machine tool kinematic topological structure and the screw theory, the comprehensive error model of the machine tool is established and the decoupling of PIGEs is realized. This method does not require the definition of local coordinate frames, which greatly simplifies the machine tool modeling process. The DBB is employed as the data sampling tool to capture the error information during the coordinated motion. The PIGEs are calculated based on the machine tool comprehensive error model and simulated with a Matlab program. Using the machine inverse kinematics, the machine tool is compensated for by the error values. The effectiveness of the proposed characterisation method is proved by the compensation results.