On-line posture measurement for automatic positioning of foldable-wing with priority-based multi-constraints

Abstract

The digital assembly system is widely used in the automatic positioning of large aircraft components. Accurate posture measurement of the components remains challenging for high-precision assembly of the components with various engineering constraints. Existing methods often require repeated measurements of key features and are susceptible to the pronounced coupled effect, where various constraints mutually influence the solution of pose parameters. To enhance the efficiency and precision of posture measurement, this study proposes an on-line measurement method for the Foldable-wing Digital Assembly System. The key features and several reference points are measured once by the laser tracker. According to the assembly task sequence, a novel posture evaluation model with priority-based multi-constraints is established to calibrate these reference points which will be utilized as the new datum of posture measurement instead of the traditional key features. This model separately satisfies the various engineering constraints, such as coaxiality, gap, and basic positioning accuracy, in order of priority to avoid the coupling effect between different types of constraints. Consequently, features with higher priority can achieve higher accuracy without weight setting. Next, the reference points are automatically measured to calculate the posture parameters. Considering the uncertainty characteristics of the measuring instrument, the registration algorithm based on weighted total least squares adjustment is applied to reduce measurement uncertainty. Monte Carlo simulation results demonstrate the proposed method's ability to enhance positioning accuracy and reduce posture uncertainty, outperforming conventional methods. Finally, the practical application was successfully implemented, and all key features remained within tolerance.