Abstract
Horizontal docking assembly is a fundamental process in the aerospace assembly, where intelligent measurement and adjustable support systems are urgently needed to achieve higher automation and precision. Thus, a laser scanning approach is employed to obtain the point cloud from a laser scanning sensor. And a method of section profile fitting is put forward to solve the pose parameters from the data cloud acquired by the laser scanning sensor. Firstly, the data is segmented into planar profiles by a series of parallel planes, and ellipse fitting is employed to estimate each center of the section profiles. Secondly, the pose of the part can be obtained through a spatial straight line fitting with these profile centers. However, there may be some interference features on the surface of the parts in the practical assembly process, which will cause negative effects to the measurement. Aiming at the interferences, a robust method improved from M-estimation and RANSAC is proposed to enhance the measurement robustness. The proportion of the inner points in a whole profile point set is set as a judgment criterion to validate each planar profile. Finally, a prototype is fabricated, a series of experiments have been conducted to verify the proposed method.
Highlights
In the field of aerospace assembly and pipeline welding, it is usually necessary to dock one cylindrical part with another within tolerance [1]
Measurement approaches for the cylindrical parts and the robustness in the actual environment should be discussed in depth at the very beginning because many problems exist in engineering, such as the complex on-site environment and interference features on the parts
The results show that the measured angle deviation between the prototype and the laser tracker system (LTS) is less than 0.02◦, the position deviation of the axis is less than 0.3 mm
Summary
In the field of aerospace assembly and pipeline welding, it is usually necessary to dock one cylindrical part with another within tolerance [1]. The frequently used pose measurement in the automation field can be divided into target-based measurement and non-target measurement according to whether the measurement target or marker is used or not [2]. For target-based measurement, it is required to mount additional targets or spray markers on the surface of the object. In aircraft assembly, the laser tracker system (LTS) is usually employed to measure the spatial pose of large-sized parts such as aircraft cabins [3], and the cabins can be aligned through 3-DOF support systems [4]
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