Accurate Kinematics Calibration Method for a Large-Scale Machine Tool

Laser tracker has been often adopted to measure the orientation and position of rotary axes for the calibration of a machine tool due to its high accuracy and fast execution. However, when dealing a large-size machine tool, the existing single station method of laser tracker placement leads to high measurement error of orientation and position, which results in the inaccurate calibration. To this end, this article proposed an accurate kinematics calibration method by a laser tracker at single station with angle selection and measurement weightings for kinematic calibration. The principle of the proposed method is based on the anisotropic and in-homogeneous measurement property of the laser tracker, which leads to nonuniform measurement error distribution. Specifically, first, the error sources of fitted plane normal measured by laser tracker is analyzed and the angle selection method is proposed to improve orientation calibration accuracy; second, the position measurement error by laser tracker is analyzed and the weightings for coordinates are applied to improve position calibration accuracy. Therefore, the kinematics calibration accuracy of machine tool is improved by the accurate orientation measurement and position weighting. Simulations and experiments were conducted to verify the proposed method with the uncertainty of kinematic parameters and with the measured absolute and relative error of end-effector's position and orientation. The results of simulations and experiments illustrate the effectiveness of our proposed method.