A novel accurate positioning method of reference hole for complex surface in aircraft assembly

In the digital drilling and riveting process of complex surfaces such as aircraft panels, the reference hole is pre-drilled on the skin surface. Generally, four laser displacement sensors (LDSs) are used as a group for normal adjustment. The camera vision is used to determine the position of the reference hole to obtain the accurate positioning of the drilling position. However, while dealing with large curvature complex panel surface and panel edge, four LDSs have the problem of reflection laser disappearance or matching failure. Applying two LDSs for normal adjustment on one side, the projection of the reference hole on the camera focal plane is an ellipse which means a further normal adjustment is desired in the direction of the ellipse’s minor axis. Therefore, this paper proposes a 3-dimensional pose estimation method (TDPEM) combining multi-sensor fusion and space geometry to realize the normal adjustment and position measurement of reference holes with a monocular camera and two LDSs. Firstly, two LDSs are used to adjust the reference hole’s horizontal (or vertical) direction. And then, an ellipse contour extraction algorithm is proposed to determine the ellipse parameters. Finally, the pose of the reference hole on the panel is determined by a spatial circle reverse algorithm. The experiment proves that the position error and angle error between this algorithm and the traditional four-LDS–based measurement method are within 0.03 mm and 0.2°, respectively, which verifies the feasibility and reliability of this algorithm.