Enhanced calibration method for robotic flexible 3D scanning system

Large-sized components with numerous small key local features are essential in advanced manufacturing. Efficient product quality control requires efficient and accurate three-dimensional (3D) measurements. A flexible measurement system integrating a fringe-projection-based 3D scanner with an industrial robot is developed to enable the rapid measurement of large object surfaces. To enhance overall measurement accuracy, we propose an online calibration method utilizing a multidimensional ball-based calibrator to simultaneously calibrate for hand-eye transformation and robot kinematic parameters. Firstly, considering the measurement error compensation in observation points completed by the angular-constrain-based optimization method, a preliminary hand-eye calibration method is proposed, based on a virtual single point calculated using the barycenter method. Subsequently, a distance constraint-based calibration method is proposed to simultaneously estimate the hand-eye and robot kinematic parameters. Specifically, a distance error model is derived for associating the parameters errors with the deviations in the measured coordinates of the single virtual point. Finally, the corresponding calibration experiments were performed, and the accuracy verification experiment was conducted. The experimental results demonstrate that the maximum and mean overall measurement errors decreased from 1.041/0.809 mm to 0.428/0.394 mm, verifying the effectiveness of the proposed method.