An automatic surface inspection system for grading hot slabs during the direct rolling process is described. The system, based on an optical method, employs CCD (Charge Coupled Device) line-scan cameras and real-time signal processors. CCDs can take hot radiant images of the moving slabs with high resolution. The signal processors, which use advanced image processing techniques, can perform the following functions. Firstly, the background level of the image of the slab can be correctly detected. Secondly, ill-defined signals caused by harmful defects can be discriminated with high signal-to-noise ratio. Thirdly, two-dimensional patterns associated with defects can be recognized.
The effects obtained when the system is applied to operation are discussed. The ability of the system to detect dark and gray defects is comparable with that of human visual inspection. The system is now in successful operation in the direct rolling process.
