Abstract: For the missing fault of brake shoe in trouble of moving freight car detection system,a staged matching algorithm based on radian step is proposed.A regional image which contains normal brake shoe is intercepted as the template,then the contour moment invariants are calculated after template is preprocessed.In the image to be inspected,the excircle of wheel was extracted.The center point of the circle was set as another origin,where a new coordinates was established.Circular arc in the forth quadrant is chosen,from which the points regarded as determinative ergodic path are calculated by selected radian step.During the first stage of ergodic process,corresponding matching similarity of each ergodic points measured by normalized correlation algorithm is calculated between template and template window in the image to be inspected.Then the second stage of ergodic process’ region was calculated according to the maximum similarity and its coordinate.Finally the region of brake shoe is located.The experiment results has shown that the algorithm can avoid the interference of complex background effectively,make inspection on brake shoe more accurate and much quicker,and can satisfy the instantaneity of the inspection on brake shoe.

Key words: brake shoe, matching, Hu invariant moments, radian step