An accurate calibration method of a combined measurement system for large-sized components

Abstract

Large-sized components with numerous supports are essential in advanced manufacturing. Efficient product quality control requires accurate three-dimensional (3D) measurements and error control. For 3D shape and spatial position measurements of the key local features on the support mounting surface, we propose an accurate measurement method combining a global laser tracker, local scanning system, and mobile robot system comprising an industrial robot and a mobile platform. To enhance the measurement accuracy, an accurate calibration method was introduced based on prior knowledge which establishes correlation constraints between local and global calibration. The local calibration method, including rail orientation and extrinsic parameters calibration based on a multi-dimensional combined collaboration target, achieves accurate calibration of both rail orientation and extrinsic parameters. Additionally, the enhanced global calibration method based on multi-dimensional cooperative calibrators constructs correlation constraints among global control points and provides an accurate global measurement field. We constructed a combined measurement system and conducted large-scale measurement experiments. As shown by the accuracy verification results of the proposed system, the maximum and mean measurement errors decreased from 0.142 and 0.132 mm to 0.111 and 0.095 mm within 8 m, respectively, which is highly accurate. Moreover, the large-scale scanning instance of a large-sized spacecraft cabin has also demonstrated that the developed method can significantly expand the measurement range as well as improve the measurement flexibility.