Positioning accuracy enhancement of a robotic assembly system for thin-walled aerostructure assembly

Aircraft assembly demands efficient and accurate drilling and fastening of a large number of complex thin-walled aircraft parts. In this paper, a robotic assembly system is developed. The machine design and component functions of the robotic system are first discussed. Subsequently, the formation of the relative positioning error between the end-effector and an aircraft part is analyzed and modeled. Measuring instruments are used for relative error measurement to compensate for drilling positions. To achieve high positioning accuracy, we theoretically compare relative positioning errors across instrument configurations from a tolerance management perspective to recommend a good hand-eye configuration. Besides, the impact of hand-eye offset on positioning accuracy is explored based on positioning error Jacobian to guide the end-effector design and the setting of the vision coordinate system. After that, the on-machine hand-eye calibration and system positioning methods are proposed and modeled, eliminating the effect of the dissimilarity of the robot's absolute positioning error. For positioning and processing, the control system of the multifunctional robotic assembly system is built. Finally, experiments for accurate positioning are conducted on the robotic assembly system developed to assemble an aircraft. With the recommended hand-eye configuration, the minimized hand-eye offset, and the on-machine hand-eye calibration, the maximal positioning error is 0.08 mm, which can adequately meet the accuracy standard of the aircraft assembly.