English：

Robots with large arm spans and high⁃altitude working capabilities have been appliedincrementally in construction industry in recent years. This could effectively improve the efficiency ofhigh⁃altitude operations, reduce safety risks, and address issues such as the shortage and aging ofconstruction workers. However, in the scenario of bridge painting, the robots often rely on three⁃dimensional modeling of the scene to analyze the bridge’s shape before they can paint on the sides andunderside of the bridge, especially the curved surface of the side. On account of the relatively simple andregular shapes of the bridge’s sides and underside, a device structure that adopted laser rangefindersinstead of expensive LiDAR and other scanning and modeling instruments was proposed. It could adjustitself to be perpendicular to the side of the bridge, measure the distance of multiple points on the contourof the bridge side and underside, and obtain a series of coordinates of the points relative to the robot. Acalculation method was also proposed, which could synthesize the contour into a combination of linesegments and arcs based on the coordinates of the measured points, and obtain the lengths and positionsof each line segment and arc. Then, the robot’s painting path could be planned based on the processrequirements. Finally, the collaborative robotic arm could be driven to paint the side and underside of thebridge according to the planned path. The device and the calculation method were tested in a practicalengineering project, and the average deviation of the actual painting path from the designed path wasmeasured to be 31. 08mm. Both construction efficiency and painting quality fulfilled the requirements andstandards, verifying the effectiveness of this method.