Rolling Mill

The present invention relates to a rolling mill which includes a processing unit in the feedback control loop to provide improved rolling accuracy. More particularly, this invention relates to a rolling mill for compensating with a high accuracy the mill modulus of a rolling mill and the offset value of the roll gap of the mill.

In order to improve the rolling accuracy, it is necessary to know with a high accuracy the mill modulus of a mill under rolling process and the offset value of the roll gap of a rolling mill. However, since the mill modulus, the offset value and the reaction force at the start and during rolling are different, it is necessary to update those values with the most reliable and latest values in accordance with the actual rolling state, which is discussed in the paper entitled "Mill modulus variation and hysteresis - Their effect on hot strip mill AGC" by G. E. Wood published in Iron and Steel Engineer, January 1977, pages 65-70. Further in the paper entitled "Adaptive control" by Torsten Cegrell, ASEA JOURNAL, 1978, Vol. 51, No. 3, pages 75-77: says "it is possible to determine the parameter values with the aid of the technique of recursive least squares," and shows therein theoretical grounds of this statement.

Referring to FIG. 1, there is shown a sectional view of a rolling mill in an ordinary rolling process, in which a top work roll (TR) 1 and a bottom work roll (BR) 2 of the rolling mill are opposed to each other with a gap S forming therebetween. A rolling material (m) 3 is rolled to a plate of thickness h as it moves to the right in the figure. At this time, the rolls receive a reaction force F from the material to force the gap S to be changed. The relationship between the roll gap S and the reaction force F is shown in FIG. 2, in which the roll gap S increases as the reaction force increases, as indicated by line A and in which the gradient M of the line represents a mill modulus which corresponds to the magnitude of rigidity of the rolling mill. The plate thickness h has the following relationship with the roll gap S and the reaction force F:

wherein K represents an offset value of the roll gap.

In conventional rolling mills, however, the mill modulus M and the offset value K are fixedly given, even if those values may change in the actual rolling state so that a high rolling accuracy has heretofore been unobtainable.

It is the object of the present invention to provide a rolling mill having an improved rolling accuracy by calculating the most reliable value of a mill modulus and an offset of the roll gap during the actual rolling state of the rolling mill so as to successively feed back those values to a rolling control system.

The present invention is a rolling mill for rolling an elongated transferring material continuously through at least a pair of rolls opposed to each other with a gap formed therebetween, in which the size of the rolling material and the reaction force therefrom exerted to the rolls are successively provided as data to a processing unit, which in turn determines by an arithmetic operation the most reliable mill modulus of the rolling mill and offset of the roll gap, this data being obtained during respective sampling periods, and provides those resultant values as the present size and reaction force of the material to a rolling control system for controlling the rolls.

FIG. 1 is a sectional view of rolls which are rolling a rolling material;

FIG. 2 is a graph showing the relationship between the roll gap and the reaction force induced during rolling;

FIG. 3 is a block diagram of rolls and a control system in a rolling mill according to a first embodiment of the present invention;

FIG. 4 is a block diagram of plural sets of rolls and associated control systems in a rolling mill according to a second embodiment of the present invention; and

FIG. 5 is a block diagram of plural sets of rolls and associated control systems in a rolling mill according to a third embodiment of the present invention.

Referring to FIG. 3, there is shown a block diagram of a rolling mill embodying the present invention, in which a rolling material 3 which is being rolled by a pair of a top roll (TR) 1 and a bottom roll (BR) 2 is measured for its thickness h by means of a thickness measuring unit (TMU) 5 disposed on the outgoing side of a rolling mill 4. The thickness h thus measured is provided as data to a processing unit (CPU) 8. A roll gap S formed between the rolls 1 and 2 and a reaction force F exerted to those rolls are measured by a gap measuring unit (GMU) 6 and a reaction force measuring unit (RMU) 7 attached thereto respectively, which are also provided to the processing unit 8. The processing unit, which comprises for example a computer which thus receives the output signals indicative of the plate thickness h, roll gap S and reaction force F then calculates the mill modulus M and the offset value K of the roll gap in accordance with the equation shown below, which are fed back to a roll controlling section (not shown) of the rolling mill.

The arithmetic operation of the processing unit 8 will now be explained. The foregoing equation (1) may be rewritten as follows:

The equation (2) may be expressed with a following determinant: ##EQU1## Therefore, the following equation is established for F, h and S of n (=1, 2, . . . ) sample data obtained at predetermined time intervals during rolling: ##EQU2## 1/M and K as desired most reliable values can be obtained using the equation (4) and in accordance with the following equation: ##EQU3##

Thus, the processing unit calculates the mill modulus M and offset value K as the present most reliable values successively using plate thickness h.sub.1 -h.sub.n, roll gap S.sub.1 -S.sub.n and reaction force F.sub.1 -F.sub.n of the n (=1, 2, . . . ) sample data obtained under actual rolling conditions, and those values are provided to the roll controlling section to improve the rolling accuracy.

Referring now to FIG. 4, there is shown a block diagram of a rolling mill according to a second embodiment of the present invention, in which sets of rolls are disposed in series and the same components to that of FIG. 3 are indicated by the same reference numeral, and for the purpose of making distinction between them, a suffix of "a", "b" or "c" is attached thereto. Processing units 8a, 8b and 8c receive output signals indicative of plate thicknesses h.sub.a, h.sub.b, h.sub.c, roll gaps Sa, Sb, Sc and reaction forces Fa, Fb, Fc from the respective associated thickness measuring units 5a, 5b, 5c, gap measuring units 6a, 6b, 6c and reaction force measuring units 7a, 7b, 7c, and execute the arithmetic operation of the equation (5) to calculate mill moduli Ma, Mb, Mc and offset values Ka, Kb, Kc.

Referring now to FIG. 5, there is shown a block diagram of a rolling mill according to a third embodiment of the present invention, in which plural sets of rolls are disposed in series and the same components to that of FIG. 4 are indicated by the same reference numerals as in FIG. 4. It should be noted that no thickness measuring unit is disposed on the outgoing sides of rolls 4a and 4b. However, on the outgoing sides of rolls 4a, 4b, 4c and along the material 3, there are disposed speed measuring units (SMU) 9a, 9b and 9c for measuring transferring velocities Va, Vb and Vc, respectively, of the rolling material 3. Further, arithmetic and logic units (ALU) 10a and 10b are provided, which respectively receive velocities Va, Vc, thickness hc and velocities Vb, Vc, thickness hc. The arithmetic and logic units determine the thicknesses h.sub.a and h.sub.b on the outgoing sides of rolls 4a and 4b by a trial calculation in accordance with the following equation (6): ##EQU4## The plate thicknesses h.sub.a and h.sub.b thus obtained by the arithmetic and logic units 10a and 10b are fed to the respective processing units 8a and 8b, which in turn execute the arithmetic operation of the equation (5).

Although in the foregoing embodiments the absolute value of plate thickness is measured by the thickness meter, there may used a known X-ray thickness meter to measure a deviation from a reference plate thickness, and the plate thickness as an absolute value may be obtained by the addition of the reference plate thickness and the deviation by means of a processing unit.

Further, although in the embodiment of FIG. 5 the moving speed of the material is detected by means of a speed detector, it may also be detected by multiplying the peripheral speed of the work rolls of the rolling mill by the advancing factor of the rolled plate.

In the above embodiments, moreover, although the rolls are controlled through the parameters associated with thickness of the material, it may also controlled through the parameters associated with the width of the material. In this case, the thickness h and gap S in the equations (1)-(6) may be read as plate width W and roll gap in the width direction, respectively. And in the embodiments shown in FIGS. 1-5, the thickness h, the top and bottom work rolls and the thickness measuring unit may be read as plate width W, work rolls in the width direction and width measuring unit, respectively.

Further, although the arithmetic and logic units 10a and 10b are provided in the embodiment of FIG. 5, their functions may alternatively be executed by the processing units 8a and 8b.