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1. Introduction
Transport planes, carrier rockets, missile launchers and other aerospace products are large-span thin-walled structures, which are constructed by crisscrossed girders and stringers as skeletons and covered by metal or carbon fiber-reinforced polymer (CFRP) panels as skins. Commonly, the skeletons and skins are mainly fastened by riveting joints; thus, the position accuracy of the fasteners is one of the main factors that affect the service life and safety of the products (Mei et al., 2015; Bi et al., 2013; Mei et al., 2018). Usually, the nominal positions of the fastener holes are directly obtained through the theoretical digital models of the products prescribed by designers (Robert, 2001). However, the actual fastener positions of the products are often deviated from the theoretical digital models due to assembly tolerances, gravity deformation errors, etc. (Bi et al., 2013; Bi and Liang, 2011). Once there are deviations between the nominal and actual positions of the fastener holes, the stress evenness around riveting fasteners is changed and the fatigue life of the aerospace products is reduced (Li et al., 2021). Hence, such position deviations or errors need to be eliminated to ensure the position accuracy of the fastener holes.
Generally, the skeletons and skins of aerospace products are first fixed on the assembly fixture to establish their relative position prior to connecting. Then, small reference holes are made to preassemble them together, followed by drilling and riveting operations (Zhang et al., 2018). More importantly, the reference holes are also used as geometric features to compare with theoretical digital models to correct for the deviations between them. That is, the positions of the reference holes in ready-to-assembly components are detected through the vision system; then, position deviations of the fastener holes are calculated by the position deviation of reference holes (Zhu et al., 2014; Tian et al., 2014). Based on the position deviation of the reference holes and the position relationship between the reference holes and the fastener holes, an error function is established, and the position errors of the fastener holes are compensated to improve the drilling accuracy (Zhao et al., 2017). Thus, correction results are significantly related to the selection of reference holes, and it could work better...