Robust band tension control

A computer program, which comprises machine code recorded on a non-transitory recording medium, and the machine code is processable by a control unit for a rolling train;

• wherein a metal strip is firstly rolled in a front roll stand of a multi-stand rolling train and then in a rear roll stand of the multi-stand rolling train;
• wherein a strip tension (Z), which prevails in the metal strip between the front roll stand and the rear roll stand, is detected by means of a looper applied to the metal strip between the front roll stand and the rear roll stand;
• wherein the processing of the machine code by the control unit causes;
• the control unit to accept the detected strip tension (Z);
• the control unit to implement a first tension controller, to which the strip tension (Z) is supplied and which determines an adjustment additional setpoint value (δs*, δF*);
• the control unit furthermore to implement a second tension controller, to which the strip tension (Z) is supplied and which determines a velocity additional setpoint value (δv*);
• the control unit to implement the second tension controller such that the second tension controller (9) determines a value less than 0 as the velocity additional setpoint value (δv*) if the strip tension (Z) lies below a lower strip tension limit (Z1), determines a value greater than 0 as the velocity additional setpoint value (δv*) if the strip tension (Z) lies above an upper strip tension limit (Z2), and returns the velocity additional setpoint value (δv*) to the value 0 if the strip tension (Z) lies between the lower and the upper strip tension limits (Z1, Z2);
• the adjustment additional setpoint value (δs*, δF*) to act on the rear roll stand, and the velocity additional setpoint value (δv*) to act with positive sign on the front roll stand or to act with negative sign on the rear roll stand;
• and
• wherein the processing of the machine code by the control unit causes the first tension controller to determine the adjustment additional setpoint value (δs*, δF*) using a determination rule on the basis of the deviation of the strip tension (Z) from a setpoint tension (Z′), which lies between the lower and the upper strip tension limits (Z1, Z2), and the determination rule also to permit a value not equal to 0 as the adjustment additional setpoint value (δs*, δF*) if the strip tension (Z) is between the lower and the upper strip tension limits (Z1, Z2).