System for controlling strip thickness in rolling mills

A system for controlling a thickness of a strip being rolled by a rolling mill having more than two rolling stands, a final stand being a matt roll stand and the remaining stands being bright roll stands, in tandem configuration, comprising:

• subcontrol means for controlling a rolling speed and a rolling load of the final rolling stand according to a predetermined control schedule;
• a plurality of tension gauge means installed between adjacent rolling stands for detecting a tension of the strip;
• a plurality of thickness gauge means including at least second thickness gauge means installed on an output side of a penultimate rolling stand, and final thickness gauge means installed on an output side of the final rolling stand, for detecting a deviation in the thickness of the strip from a predetermined value;
• and
• thickness control means, connected to each of the tension gauge means and each of the thickness gauge means, for controlling the thickness and the tension of the strip to respective predetermined values by adjusting roll gaps and rolling speeds of each of the rolling stands except the final rolling stand, based on the detected tensions and the detected deviations in the thickness of the strip, the thickness control means including feedback means for adjusting a rolling speed of an antepenultimate rolling stand according to the detected deviation in the thickness of the strip by the second thickness gauge means, said deviation being corrected by a value calculated from the deviation in the thickness of the strip detected by the final thickness gauge, to control the thickness of the strip at the output side of the final rolling stand to the predetermined value;
• the feedback means including a first control unit for determining a first corrected amount by which a desired value of a strip thickness on the output side of the penultimate rolling stand is to be corrected according to the deviation in the thickness of the strip detected by the final thickness gauge means, and a second control unit for determining a second corrected amount representing a corrected strip thickness deviation at the penultimate rolling stand and an amount by which the rolling speed of the antepenultimate rolling stand is to be corrected to control the strip thickness at the output side of the penultimate rolling stand to a desired value, based on the deviation in the thickness of the strip detected by the second thickness gauge means and the first corrected amount.