Method for controlling strip thickness in strip mill

In a strip mill comprising a rolling mill for rolling a strip, a screw down position control device for adjusting the distance between the rolls of said rolling mill, a tension adjusting device for adjusting the tension applied to the strip, and a speed meter for detecting the speed of movement of the strip, a method for controlling thickness of the strip, comprising the steps of:

• providing a thickness meter on the entrance side of the rolling mill for measuring deviations in the strip thickness from a predetermined thickness;
• sampling an output of the thickness meter for each predetermined time period .DELTA.t which is in a range which is equal to or smaller than 1/5 of the period of the cut-off frequency of at least one of the screw down position control device and the tension adjusting device;
• storing, in a memory means having a plurality of storage locations, the deviations in the strip thickness measured by the thickness meter and existing at a plurality of positions located between the thickness meter and the rolling mill, the measured thickness deviations being stored in specific storage locations in the memory means on the basis of the speed of movement of the strip as measured by the speed meter;
• computing a control signal for adjusting at least one of the screw down position control device and the tension adjusting device, using at least two of the stored thickness deviation values and the measured speed of the strip for each time period .DELTA.t;
• and
• outputting the computed control signal to at least one of the screw position control device and the tension adjusting device.