Kinematic calibration method with high measurement efficiency and robust identification for hybrid machine tools

Geometric error is the main factor affecting the machining accuracy of hybrid machine tools. Kinematic calibration is an effective way to improve the geometric accuracy of hybrid machine tools. The necessity to measure both position and orientation at each pose, as well as the instability of identification in case of incomplete measurements, severely affects the application of traditional calibration methods. In this study, a kinematic calibration method with high measurement efficiency and robust identification is proposed to improve the kinematic accuracy of a five-axis hybrid machine tool. First, the configuration is introduced, and an error model is derived. Further, by investigating the mechanism error characteristics, a measurement scheme that only requires tool centre point position error measurement and one alignment operation is proposed. Subsequently, by analysing the effects of unmeasured degrees of freedom (DOFs) on other DOFs, an improved nonlinear least squares method based on virtual measurement values is proposed to achieve stable parameter identification in case of incomplete measurement, without introducing additional parameters. Finally, the proposed calibration method is verified through simulations and experiments. The proposed method can efficiently accomplish the kinematic calibration of the hybrid machine tool. The accuracy of the hybrid machine tool is significantly improved after calibration, satisfying actual aerospace machining requirements.