A Design Study of an Automatic System for On-line Detection and Classification of Surface Defects on Cold-rolled Steel Strip

In collaboration with the British Steel Corporation, Sira Institute Ltd is currently pursuing the development of sophisticated equipment for the automatic inspection of cold rolled steel strip. This paper will examine the special difficulties associated with the application of optical inspection techniques to a dull metallic surface at line speeds of up to 50 ms m 1. The development work has centred on the use of high-speed scanned laser systems, unique in their ability to provide diffraction-limited resolution with intrinsically high optical throughput. In order to detect and delineate all significant defects down to the most subtle imperfections, the polar scattering characteristics of the surface have been exploited and optimum signal processing techniques are being identified. The paper will discuss some of the optical, mechanical and electronic constraints imposed by the inspection requirement.