关键词: 航空发动机, 气膜孔, 视觉测量, 对焦评价函数

Abstract:  functions is executed. Firstly, characteristics and requirements which are necessary for a well qualified focusing evaluation function are analyzed, as well as the advantages and disadvantages of typical functions. In this procedure, the gray gradient functions are selected to evaluate the sharpness of image sequence. Afterwards, 5 representative gray gradient functions such as Brenner gradient function, Tenengrad gradient function and Laplacian gradient function etc are investigated by experiments, in which their function curves are derived and then normalized to carry on comparisons and analysis. Finally, Laplacian gradient function is chosen as the focusing evaluation function of the system, whose repeatability is verified by experiments. As the experimental results show, Laplacian gradient function could be utilized to determine the focusing position of the target film cooling hole and the focusing repeatability is smaller than 0.005mm, which could satisfy the inspecting requirements of the film cooling holes.

Key words: Aero engine, Film cooling hole, Vision measurement, Focusing evaluation function