Subpixel Measurement Method for Surface Mount Devices Based on Edge Tracing

Visual inspection of surface mount devices is a prevalent practice in the field of electronic manufacturing. Among these components, rectangular pin devices, which include a variety of resistor, capacitor and transistors, constitute a significant portion. We propose a novel measurement method based on edge tracing for rectangular pin chips. The proposed method encompasses four primary steps: image preprocessing, edge tracing, subpixel optimization, and parameter measurement. Initially, the blob features of the pins are analyzed and categorized. Subsequently, an edge tracing approach is employed to examine the pin edges on a point-by-point basis, facilitating the extraction of the straight edges of all pins. Following this, the spatial moments are utilized to enhance the pixel-level edges to a subpixel level. Finally, by establishing a relationship between all pairs of straight lines and the principal axis of the pin group, a measurement line pair is constructed to derive the chip parameters. Experimental validation was conducted using a variety of rectangular pin chip images obtained from actual surface mount devices, and the results indicate that the proposed methodology is effective.