DETECTING METHOD OF MEANDERING

PURPOSE:To detect accurately the meandering direction of a sheet in an early stage, by irradiating light to the vicinity of a rolling reduction part at the inlet side of the sheet wrapped around the upper and lower rolls of a differential speed rolling mill and detecting the amount of the light reflected from the roll and the sheet. CONSTITUTION:A luminous source 4 is provided to the front of a roll 2 wrapping part of a sheet 3 running while being wrapped around upper and lower rolls 1, 2, and image sensors 5, 5' incorporating a large number of sensitive parts respectively are also provided to both sides of the source 4. When light is irradiated to the vicinity of the rolling reduction part of a roll 2 wrapping part; because the light is reflected by the roll 2 and the sheet 3 at the inlet side, the reflected light is detected by the sensors 5, 5' to measure the amount of the light. At that time, there is a difference in the amount of reflected light between the sheet 3 and the surface of roll 2 because of the difference in luminosity between them, accordingly the amount of reflected light of one of the sensors 5, 5' is increased and that of the other one is decreased when the sheet 3 at the inlet side deviates to one side either left or right in the width direction. In this way, the direction of meandering of the sheet 3 at the inlet side is obtained, and the meandering of sheet 3 is leveled by changing the rolling down forces at the left and right sides, etc. of the rolls 1, 2.