An automated in-situ alignment approach for finish machining assembly interfaces of large-scale components

Alignment is a crucial issue for finish machining the assembly interfaces of a large-scale component before final assembly in the aviation industry, as it affects the distribution of machining allowance and is time and effort consuming in the current manual way. This study presents an automated and in-situ alignment approach with the assistance of computer numerical controlled (CNC) positioners and laser trackers. The aligning process mainly consists of three steps, that is, measurement, posture evaluation, and posture adjustment. For measuring using laser tracker, a closed-loop method is proposed to establish a global reference frame (GRF) on the shop floor to unify measuring results from multi-stations based on the machine tool coordinate system. Therefore, the large-scale component is aligned to the machine tool as long as it is adjusted to the nominal posture in the GRF. As regards posture evaluation, the key characteristics (KCs) of the large-scale component are considered in the evaluation process based on the geometrical meaning of the singular value decomposition (SVD) to reduce the residual error of the KC with higher importance. An in-process calibration method is proposed during the adjustment process to calculate the actual position of the sphere hinge center and avoid the alignment accuracy loss in the kinematic backward transformation. A vertical tail of a certain large passenger aircraft is then used to validate the proposed alignment system and methods. The experimental results show that: (1) the GRF is accurately established on the shop floor; (2) the proposed posture evaluation algorithm enhances the transformation accuracy of the KC with greater importance; (3) the center position of the sphere hinge is calibrated, such that it hardly affects the alignment accuracy; and (4) the large component is aligned to the machine tool, satisfying all the tolerance requirements.