AUTOMATIC EXPOSURE CONTROL FOR SURFACE DEFECT DETECTION OF HOT METAL MATERIAL

摘要

PURPOSE:To eliminate overlooking of defects, by controlling the light receiving time by varying the scanning cycle of a linear array image sensor to always keep the exposure sensitivity level of the linear array sensor constant. CONSTITUTION:An input signal converted into electricity from light from a linear array image sensor 1 for sensing heat radiation and a linear array image sensor 2 for sensing reflected light of an externally illuminated light on the surface of a cast billet is fed to an LPF7 to determine the extra polation line of the signal. From this extra polation line, readings during one scan are obtained by a pulse applied from a quantity of light data sampling control circuit 12 through a quantity of light sampling 8 and the data points averaged with an averaging circuit 9 to calculate the difference from the target quantity of light with a gain setting circuit 10. The alteration value of the necessary exposure time is calculated based on the deviation. The results of the calculation are inputted into a exposure time controlling circuit 11 to control the exposure time by changing the interval of the photoelectric conversion start pulse of linear array image sensors 1 and 2 and thus, the output signal of a flaw detection camera can be outputted with a fixed signal level.