Plate thickness control device and plate thickness control method

1. A plate thickness control device for controlling the plate thickness in a hot rolling mill with a rolling stand, the plate thickness control device comprising:

a pyrometer disposed on an entry side of the rolling stand;

a difference calculation part configured to output a difference temperature between a lock-on temperature of a plate-to-be-rolled measured by the pyrometer and a measurement value other than a head end portion of the plate-to-be-rolled measured by the pyrometer;

a tracking part configured to transfer the difference temperature from a first position of the pyrometer to a second position immediately below the rolling stand based on a plate speed of the plate-to-be-rolled; and

a computation part configured to calculate a screw-down amount of the rolling stand based on the difference temperature transmitted from the tracking part, wherein

the computation part includes

a control part configured to perform, at least, differential control on the difference temperature, and

a screw-down amount calculation part configured to calculate the screw-down amount based on an output value of the control part.

2. The plate thickness control device according to claim 1 ,

wherein the rolling stand includes

an oil pressure type screw-down device, and

an oil pressure sensor configured to measure an oil pressure of the screw-down device, and

wherein the plate thickness control device further comprises

a screw-down control part that controls the screw-down device based on the oil pressure measured by the oil pressure sensor and the screw-down amount calculated by the computation part.

3. The plate thickness control device according to claim 1 , wherein

the hot rolling mill does not include a load cell configured to detect rolling force of the rolling stand.

4. The plate thickness control device according to claim 1 , wherein

the control part is configured not to include an integral control part for performing integral control on the differential temperature.

5. A plate thickness control device for controlling a plate thickness in a hot rolling mill with a rolling stand, the plate thickness control device comprising:

a skid mark detecting part configured to detect temperature information representing a first position of a skid mark included in a plate-to-be-rolled rolled at the rolling stand based on a measurement value of a pyrometer disposed on an entry side of the rolling stand;

a tracking part configured to transfer the temperature information to a second position immediately below the rolling stand based on a plate speed of the plate-to-be-rolled; and

a computation part configured to calculate a screw-down amount of the rolling stand so as to determine force applied to the skid mark by the rolling stand based on the temperature information transferred at the tracking part, wherein

the computation part includes

a control part configured to perform, at least, differential control on the temperature information, and

a screw-down amount calculation part configured to determine the force applied to the skid mark based on an output value of the control part.

6. A plate thickness control method comprising:

obtaining a measured value of a pyrometer disposed on an entry side of a rolling stand of a hot rolling mill;

outputting a difference temperature between a lock-on temperature of a plate-to-be-rolled measured by the pyrometer and a measured value of a portion other than a head end portion of the plate-to-be-rolled measured by the pyrometer;

transferring the difference temperature from a first position of the pyrometer to a second position immediately below the rolling stand based on a plate speed of the plate-to-be-rolled;

performing, at least, differential control on the differential temperature which is transferred to the second position; and

calculating a screw-down amount of the rolling stand based on the difference temperature on which the differential control is performed.