Abstract: The rat hole formed by the assembly and welding of sheet metal parts in the design and manufacturing process of automobile body affects the safety performance and spatial structure of the whole vehicle to some extent. In order to solve the problems of complex procedures and low efficiency for inspecting rat hole size, a method of rat hole inspection for vehicle body based on fitting projection was proposed. Firstly, the contour curve was fitted and projected to the section by creating the rat hole edge contour section. Secondly, the grid partition mechanism of equidistant space within the projection contour was established, and mesh nodes were selected by using the principle of “minimum sum of squares of residual errors” of the least square method. Finally, the best approximation definition was employed to extract the center track point and the maximum radius of the inner tangent circle. Using CATIA software as the development platform and combined with CAA framework structure, the rat hole inspection function was realized. The example analysis shows that the inspection result can attain high accuracy, efficient function strong self-adaptability, and effectively shortened cycle of product research and development.  

Key words:  , rat hole, curve fitting, projection, grid partition, central locus point