A Low Cost Sensing Technique For Detecting Defects On Metal Sheets

This paper presents a simple yet effective technique for detecting defects on metal sheets that are used for making outer bowls of washing machines. The proposed technique uses two arrays of strategically aligned infra-red diodes (IRD) and photo-diodes (PD) to detect the defects on metal sheets through the use of variation of emissivity of reflective surfaces. The sensor system, consisting two arrays of optical diodes, is mounted on top of a conveyer belt that carries the metal sheets to identify the defects that exist on metal sheets as they pass under the sensor. A prototype system with twenty optical diodes per array is built and a microprocessor based controller is used to detect the defected sheets and to signal the operator with their origin of location. The proposed system is simple and suitable for industrial use as experimental results suggest that it can identify defects that are moving faster than 1 m/s and as small as 2 mm times 1 mm.