Synchronous Measurement and Verification of the Position-Independent Geometric Errors of Dual Rotary Axes on Five-axis Machine Tools

The machining accuracy of five-axis machine tools is greatly influenced by the geometric errors associated with the two rotary axes. To effectively measure these rotary axis geometric errors, the precision industry commonly utilizes precise measurement systems like double ball-bar systems and R-test systems. However, it's worth noting that the majority of commercial measurement devices are designed to measure only one axis at a time. As a result, this paper proposes a dual-axis synchronized measurement system for eight position-independent geometric errors (PIGEs) of two rotating axes in a five-axis machine tool. The system is based on the MF400U five-axis machine tool from Bede Machinery and uses a touch-trigger probe with two standard calibration spheres to measure the standard characteristics of the calibration spheres and infer the machine tool's errors. This paper focuses on developing a measurement system for simultaneously identifying the eight PIGEs of rotary axes in a five-axis machine tool. By analyzing the errors from a single experimental path, the error terms of both axes can be obtained, which improves the limitation of previous research that could only measure one axis at a time. The calculation process includes mathematical modeling of machine errors, derivation of forward and inverse kinematics, establishment of error analysis equations, and solution of linear overdetermined systems using the least squares method with geometric errors as variables. During the experimental process, the calibration procedure of the trigger-type probe is performed, and the data of the reference spheres obtained from the experimental measurement are input into the program. After completing the measurement, the compensation table of the Heidenhain controller is utilized to compensate for the PIGEs of the rotary axes. The difference before and after compensation is then compared through actual measurements to verify the measurement results and discuss the advantages and disadvantages of the compensation.