Edge drop control device

1. An edge drop control device, comprising:

low response actuators provided in a rolling stand that rolls a strip, including a first low response actuator and a second low response actuator, and making a different amount of change to each of roll gaps at edges of the strip according to a combination of operation of the first low response actuator based on a correction manipulated amount A and operation of the second low response actuator based on a correction manipulated amount B;

a high response actuator provided in the rolling stand, having a higher response than the first low response actuator and the second low response actuator, and making a same amount of change to each of the roll gaps at the edges of the strip based on a correction manipulated amount C;

an edge drop meter provided at least either upstream or downstream of the rolling stand and measuring an edge drop amount for each of the both edges of the strip; and

a processor configured to:

calculate a calculated manipulated amount A_calc of the first low response actuator and a calculated manipulated amount B_calc of the second low response actuator for bringing a difference between the measured edge drop amount and a target amount close to zero without using the high response actuator;

calculate a calculated manipulated amount C_calc of the high response actuator for bringing a difference between the measured edge drop amount and the target amount to zero without using the low response actuators;

when a determination condition is established, output the calculated manipulated amount A_calc as the correction manipulated amount A to the first low response actuator and outputting the calculated manipulated amount B_calc as the correction manipulated amount B to the second low response actuator; and

when the determination condition is not established, output the calculated manipulated amount C_calc as the correction manipulated amount C to the high response actuator.

2. The edge drop control device according to claim 1 , wherein

the processor is configured to:

when the determination condition is not established,

output the calculated manipulated amount C_calc as the correction manipulated amount C to the high response actuator;

output a difference between an amount that corresponds to the calculated manipulated amount C_calc and the calculated manipulated amount A_calc as the correction manipulated amount A to the first low response actuator; and

output a difference between an amount that corresponds to the calculated manipulated amount C_calc and the calculated manipulated amount B_calc as the correction manipulated amount B to the second low response actuator.

3. The edge drop control device according to claim 2 , wherein

the determination condition is established when the calculated manipulated amount A_calc and the calculated manipulated amount B_calc are within an allowable range, and

the determination condition is not established when at least either the calculated manipulated amount A_calc or the calculated manipulated amount B_calc is out of the allowable range.

4. The edge drop control device according to claim 2 , wherein

the determination condition is established when the amount of change per unit time of a rolling speed of the rolling stand is within an allowable range, and

the determination condition is not established when the amount of change per unit time of the rolling speed is out of the allowable range.

5. The edge drop control device according to claim 1 , comprising:

a memory that stores a control map defining a relation between a rolling speed of the rolling stand and a regulated manipulated amount C_reg of the high response actuator, the regulated manipulated amount not causing a change in the edge drop amount of the strip at rolling speed change,

wherein

the calculated manipulated amount C_calc is a difference between two of the regulated manipulated amount C_reg, one being obtained from the control map at a present control timing and related to the rolling speed of the present control timing, another being obtained from the control map at a previous control timing,

the determination condition is established when the amount of change per unit time of the rolling speed is within an allowable range, and

the determination condition is not established when the amount of change per unit time of the rolling speed is out of the allowable range,

and wherein

the processor is configured to:

when the determination condition is not established,

output the calculated manipulated amount A_calc as the correction manipulated amount A to the first low response actuator;

output the calculated manipulated amount B_calc as the correction manipulated amount B to the second low response actuator; and

output the calculated manipulated amount C_calc as the correction manipulated amount C to the high response actuator.