Subpixel Vision Measurement Method for Rectangular-Pin SMDs Based on Asymmetric Gaussian Gradient Edge Profile

In mounting machines, vision measurement of surface mount devices (SMDs) is a crucial task, widely used for size calculation and defect detection. However, current vision measurement methods focus on specific SMDs, such as quad flat packages. There is no unified method for measuring all kinds of rectangular-pin components, which account for more than half of the SMDs processed in mounting machines. This article presents an automatic and universal method for measuring with subpixel accuracy the parameters of rectangular-pin SMDs, which can be applied to different types of SMDs. First, an edge gradient model is proposed in the form of asymmetric Gaussian function. After that, line segments of SMDs are extracted and a line adjacency matrix is obtained that describes the relationship between lines. Then, segments are combined into long lines by searching through the line adjacency matrix. Finally, pixel line pairs are refined to subpixel level. Experimental results on the surface mount hardware platform for different components under different angles and light conditions demonstrate the high accuracy and strong robustness of the proposed method.