Machining Allowance Calculation for Robotic Edge Milling an Aircraft Skin Considering the Deformation of Assembly Process

Aircraft skin parts are a typical kind of large size and thin wall parts which are easily deformed in both clamping and assembly. The edge of skin parts needs to be machined before assembly to control the clearances between adjacent skins after assembly. A frontier way is using a robot system to carry out large-range three-dimensional scanning, intelligentized calculation of machining allowance and automatic robotic edge milling. A necessary premise for robotic machining is accurately calculating the edge machining allowance of the skin part. In this article, a novel approach for accurately calculating the edge machining allowance based on onsite measurement points under the case of large bending deformation is proposed. This method solves two key problems in calculating the machining allowance. First, a method for accurately reconstructing the skin surface after assembly based on the extremely incomplete measurement points of the vacant area on a fuselage is proposed. Second, based on the reconstructed surface, a non-rigid registration method to construct the mapping relation between the skin surfaces before and after assembly is proposed to accurately calculate the edge machining allowance. To show the feasibility of the proposed method, simulations and experiments are carried out. It is proved that the proposed method can reconstruct the skin surface with a high degree of realism, and can achieve accurate non-rigid mapping between skin surfaces with large bending deformation. The skin parts are successfully milled with a robotic system based on the reconstructed surface and calculated machining allowance.