초록 열기/닫기 버튼
In a strip steel production line, the preceding and following coils are joined by a flash butt, mash seam, or laser welding at the entrance of the line for continuous processing. These coils are fed to the subsequent processing stages and finally cut again to be separated into each coil. Therefore, a welding point detection device is an essential part of the production line. Detecting the welding point is preferable to the conventional scheme that involves detecting punched holes in the coil because the punched hole causes several problems owing to the burr. Although an optical detection device that utilizes the change in the reflected light distribution around the welding point has been developed, malfunction may occur owing to the harsh environments involving vapor, dust, and other elements. Therefore, there is an increasing need to develop robust welding point detection devices. This paper proposes a robust and compact welding point detection device based on MFL (Magnetic Flux Leakage) inspection. The device consists of two separate magnetic sensor arrays which have eight linearly arranged Hall sensors, a small magnetizer with a permanent magnet, and data processing hardware. Considering the vertical vibration of the strip, the lift-off distance between the sensor array and strip should be larger than that of the usual MFL inspection case. A larger lift-off distance corresponds to a less intense MFL signal. The weak MFL signal of the welding point can be effectively detected by applying a summing amplifier to 8 MFL signals of each sensor array. The welding point can be detected based on the difference in these output signals of the summing amplifiers. The performance of the proposed device was validated experimentally.
