METHOD FOR DETECTING FOREIGN MATTER ON THE SURFACE OF LONG BODY AND FOR MEASURING SIZE THEREOF

PURPOSE:To detect foreign matter on the surface of a long body and to measure the sizes thereof automatically, by jetting a gas on the surface of the running long body, projecting the light from a specified light source on the jetted part, and picking up the image of the projected part as an electric signal. CONSTITUTION:A gas is jetted from a blower 3 on the surface of a long body 1 which is guided with guide rollers 2 and moved, and dust and the like are blown out. Then, the part of the long body 1 which is jetted with the blower 3 is lit with stroboscopes 9 and 9'. Thereafter, the part which is lit with the stroboscopes 9 and 9' is picked up as an electric signal with a TV camera 4. Then, the sizes of the part which is lit with foreign matter at the part lit with the stroboscopes 9 and 9' in the direction X and in the direction Y are measured with a processing circuit 7 based on the electric signal obtained in the camera 4. Thus, the foreign matter on the surface of the long body can be detected automatically and the sizes thereof can be detected automatically.