Method and device for controlling strip thickness in rolling mills

A device for controlling a thickness of a strip in a rolling mill which has a plurality of rolling stands, comprising:

• a roll gap adjusting device for adjusting a roll gap of a given one of said plurality of rolling stands, through which said strip is passed for being rolled, giving the rolled strip a desired value of thickness;
• a rolling speed adjusting device for adjusting a rolling speed of said strip at a preceding one of said plurality of rolling stands which precedes said rolling stand;
• roll force detecting means for detecting a variation of a roll force exerted on said rolling stand;
• upstream thickness detecting means for detecting a variation of a thickness of said strip on an upstream side of said rolling stand;
• downstream thickness detecting means for detecting a variation of a thickness of said strip on a downstream side of said rolling stand;
• tension detecting means for detecting a variation of a tension of said strip on said upstream side of said rolling stand;
• and
• arithmetic means receiving outputs of said roll force detecting means, said downstream and upstream thickness detecting means, and said tension detecting means, so as to classify rolling enviroment disturbances received by said rolling mill into a first disturbance for which only said rolling speed should be compensated, a second disturbance for which only said roll gap should be compensated, and a third disturbance for which both said roll gap and said rolling speed should be compensated, said arithmetic means estimating values of said first, second and third disturbances, based on the detected variation of said roll force, said thicknesses of said strip and said tension, and producing output signals for operating said roll gap adjusting device and said rolling speed adjusting device, depending upon the estimated values of said first, second and third disturbances, to thereby control the thickness of said strip, such that only said rolling speed is adjusted by said rolling speed adjusting device for said first disturbance, while only said roll gap is adjusted by said roll gap adjusting device for said second disturbance, and such that both said rolling speed and said roll gap are adjusted for said third disturbance.