JPH0647128B2 - Rolling mill plate thickness fluctuation prevention device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate thickness fluctuation prevention device for preventing a plate thickness fluctuation of a material to be rolled due to roll eccentricity of a rolling mill.

(Prior Art) For example, a quadruple pressure rolling apparatus includes a pair of upper and lower work rolls and a pair of backup rolls that reinforce each of the work rolls. Rolling is performed by passing a material to be rolled such as a hot strip between upper and lower work rolls, but in order to prevent the plate thickness fluctuation of the material to be rolled, it is absolutely necessary to keep the interval between them constant. Becomes That is, the separating force generated between the upper and lower work rolls due to the passage of the material to be rolled must be offset. For this reason,
The rolling apparatus is equipped with a pressure mechanism for applying pressure between the upper and lower work rolls via a backup roll.

In this case, the pressurizing mechanism applies a very large pressure to the rotating backup roll, and therefore the engagement portions thereof are required to have wear resistance. In other words, it is necessary to use a material with excellent wear resistance for at least the engaging portion between the backup roll and the pressure mechanism, but in general, due to problems such as replacement at the time of abrasion and manufacturing problems, this type of material is used. A method of attaching a sleeve or the like to the engaging portion is adopted.

When the sleeve is attached to the engagement portion of the backup roll with the pressing mechanism, the rotation stopper of the sleeve is provided to prevent abrasion of the engagement portion around the sleeve. However, by providing this detent, the elasticity of the engaging portion and the sleeve becomes non-uniform and the backup roll is eccentric.

Although the above is the main cause of the eccentricity of the backup roll, this eccentricity affects the applied pressure of the pressurizing mechanism, and causes a variation in the interval between the upper and lower work rolls, that is, a variation in the plate thickness of the material to be rolled.

In order to prevent the plate thickness variation due to the eccentricity of this type of backup roll, a delay element is not allowed, so predictive control utilizing its periodicity is exclusively adopted. That is, the eccentricity amount is stored by using the rotation angle of each backup roll as an address, and the eccentricity amount corresponding to the rotation angle of each backup roll at that time is read to correct the applied pressure and affect the plate thickness. Control to remove
For example, it is disclosed in JP-A-55-117510, JP-A-58-6718 and JP-A-59-45013.

(Problems to be Solved by the Invention) By the way, the eccentric amount of the backup roll is not only related to the rotation angle thereof, but is also deeply related to the pressure applied from the pressing mechanism. However, no consideration has been given to this point in any of the conventional techniques. The pressure applied from the pressurizing mechanism varies greatly depending on the thickness of the material to be rolled and the target plate thickness, but the prior art cannot eliminate the effect of the eccentricity of the backup roll on the plate thickness in such cases. become.

(Object of the Invention) The present invention provides a plate thickness variation prevention apparatus for a rolling mill, which accurately removes the influence of the eccentricity of the backup roll on the plate thickness even when the thickness of the material to be rolled or the target plate thickness is different. The purpose is to do.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, first and second work rolls for sandwiching a material to be rolled; first and second work rolls for reinforcing the first and second work rolls, respectively. In a rolling mill comprising a second backup roll; and a pressurizing means for applying a pressure between the first work roll and the second work roll via the first and second work rolls: a first backup roll and the above When the second backup roll is at the reference angle, the pressure applied by the pressurizing means is used as the reference pressure, and the deviation of the applied pressure with respect to the reference pressure or the applied pressure is calculated for each reference pressure as the rotation angle of the first backup roll. And stored in association with the rotation angle of the second backup roll, and during rolling, the reference pressure at that time and the rotation of the first backup roll are stored. It reads the angle and associated data to the rotation angle of the second backup roll is assumed to increase and decrease control of the application output.

In this case, the reference pressure may be the average value of the applied pressures of the first backup roll and the second backup roll during rotation.

(Operation) According to this, since the correction data corresponding to the rotation angle of the first backup roll and the rotation angle of the second backup roll is stored for each reference pressure, the thickness of the material to be rolled and the target plate thickness are stored. Even when the values are different, it is possible to effectively suppress the plate thickness variation caused by the eccentricity of the backup roll.

In particular, since the elastic change due to the rotation stop of the sleeve attached to the engaging portion with the pressurizing means of the backup roll as described above becomes non-linear, the effect of providing the correction data for each reference pressure is large and the rolling accuracy is high. It is possible to provide a plate thickness variation prevention device for a machine.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a quadruple pressure rolling apparatus for carrying out the present invention as an example. However, it should be understood that FIG. 1 shows only one of the configurations which are completely symmetrical in the width direction.

This device can be roughly classified into a mechanical system and an electrical system.

The mechanical system includes a housing 11 and a pair of upper and lower work rolls (WR) 12u, 12d, work rolls 12u, which are supported by the housing 11.
Backup role (BU
R) 13u, 13d, the chocks 14u, 14d respectively engaged with the backup rolls 13u, 13d, and the pressure 15 are main components.

The housing 11 is a highly rigid frame body, and is carefully reinforced especially in regard to its longitudinal extension, and is sufficiently reinforced.

The work rolls 12u and 12d face each other, and the hot strip SLP passes between them as shown in the drawing during rolling.

The backup rolls 13u and 13d are in pressure contact with the work rolls 12u and 12d, respectively. The pressure received by the upper backup roll 13u is absorbed by the housing 11 via the upper chock 14u and the pressure 15, and the pressure received by the lower backup roll 13d is absorbed by the housing 11 via the lower chock 14d.

Here, the engagement relationship between the upper backup roll 13u, the upper chock 14u, and the pressure 15 will be described with reference to FIG. This FIG. 2 corresponds to a part of the vertical cross section of the mechanical system shown in FIG. 1. However, in FIG. 1, a schematic view is used to simplify the configuration, so that the shapes of the respective parts do not match. Please understand that.

The upper backup roll 13u has a taper neck 131u extending in the axial direction, and a sleeve 132u is attached thereto. The sleeve 132u is a cylinder of wear resistant material,
It is fixed in the axial direction by a sleeve stopper 133u and in the rotational direction by a key 134u.

A bushing 142u fitted to the body 141u of the upper chock 14u is attached to the outer peripheral surface of the sleeve 132u. Like the sleeve 132u, the bushing 142u is a cylinder of wear resistant material, and has an inner diameter slightly larger than the outer diameter of the sleeve 132u.

The body 141u has a cap 143u and a sleeve stopper 133u.
Bearings such as 144u that rotatably support the hydraulic chamber 14
Make up 5u. Oil is pressed into the hydraulic chamber 145u. This oil is applied to the outer peripheral surface of the sleeve 132u and the bushing.
Although it penetrates into a gap between the inner peripheral surface of 142u and the gap is closed by a seal 146u provided at the other end, an oil film 147u is formed here. This oil film 14
7u reduces the friction between the sleeve 132u and the bushing 142u.

The upper surface of the body 141u is flat, and the pressure 15 acts on it.

The pressure 15 includes a screw 151, a nut 152, and a hydraulic cylinder 153.

Since the nut 152 is fixed in the rotation direction by the housing 11, the screw 151 moves up and down by rotation. As shown in FIG. 1, this rotation is given by the motor M via the wheel 16w fixed to the head and the pinion 16p meshing with the wheel 16w.

The tip of the screw 151 doubles as a piston and is housed in the cylinder chamber 1531 of the hydraulic cylinder 153. As shown in FIG. 1, a pump P is connected to the cylinder chamber 1531 via a solenoid valve 17. The solenoid valve 17 connects / disconnects between the intake port of the cylinder chamber 1531 and the output port of the pump P and between the discharge port of the cylinder chamber 1531 and the drain (not shown).

It should be noted that the engagement relationship between the lower backup roll 13d and the lower chock 14d is substantially the same except for the pressure 15 shown in FIG.

Referring again to FIG.

The electric system mainly includes a controller 21, a servo motor driver 22, sensor drivers 23, 24, 25, a solenoid driver 26, and various sensors.

A motor M and a position sensor (PS) 221 are connected to the servo motor driver 22. Position sensor 2
A potentiometer 21 outputs a voltage corresponding to the position of the screw 151. Servo motor driver
22 monitors the voltage output and energizes the motor M in the forward and reverse directions to position the screw 151 at the position designated by the controller 21.

A stroke sensor 231 is connected to the sensor driver 23. This stroke sensor 231 is an inductive type,
Tip of screw 151 (that is, piston) and cylinder chamber 1
The inductance changes according to the distance between the inner wall of 531 and the inner wall (hereinafter referred to as the stroke of the cylinder 153). The sensor driver 23 converts this inductance into digital data representing the stroke of the cylinder 153 and gives it to the controller 21.

An upper load cell 241u and a lower load cell 241d are connected to the sensor driver 24. The upper load cell 241u is inserted between the housing 11 and the nut 152, and the lower load cell 241d is inserted between the lower surface of the lower chock 14d and the housing 11. Strain gauges are used for these load cells, and their resistance values change according to the pressure applied to the elements sandwiched between the upper and lower surfaces of the inner wall of the housing 11. The sensor driver 24 reads the resistance value of each load cell, converts the resistance value between the housing 11 and the nut 152, and the pressure between the lower surface of the lower chock 14d and the housing 11 into digital data, which is supplied to the controller 21. In controller 21,
The true pressure (“true” means the most certain) is calculated by using these data.

An upper resolver 251u and a lower resolver 251d are connected to the sensor driver 25. Upper resolver 25
The input shaft of 1u is connected to the rotation shaft of the upper backup roll 13u, and the input shaft of the lower resolver 251d is connected to the rotation shaft of the lower backup roll 13d. The sensor driver 24 reads the outputs of these resolvers, converts them into digital data indicating the rotation angle of each backup roll, and gives it to the controller 21. In this case, each backup roll is given an address obtained by dividing one rotation into 32, and each rotation angle is represented by a numerical value of 0 to 31.

The solenoid driver 26 controls the solenoid valve 17 in response to an instruction from the controller to communicate between the intake port of the cylinder chamber 1531 and the output port of the pump P and the discharge port of the cylinder chamber 1531. Cut off.

The controller 21 adjusts the interval between the work rolls 12u and 12d, that is, the rolling thickness in response to an instruction from the host computer, and adjusts the stroke of the cylinder 153 while monitoring the outputs of various sensors during rolling. This adjustment is made based on a correction table stored in advance.

The correction table is a table in which the correction value of the pressure fluctuation caused by the eccentricity of the backup rolls 13u and 13d is associated with the address (rotation angle) of each backup roll,
In the present embodiment, three types prepared under different conditions, that is, the first, second and third correction tables are prepared.

The first correction table shows the kiss roll state (work roll 12
In the condition that there is no pinching between u and 12d), set the addresses of backup rolls 13u and 13d to 0, and the true pressure is
Tighten the screw 151 until it reaches 700 [ton], then
The true pressure fluctuation (deviation from 700 [ton]) is measured while rotating the backup rolls 13u and 13d, and arranged in association with each address. Therefore, this table is a 32 × 32 matrix.

Explaining further the manner of creating the first correction table, one rotation of each of the backup rolls 13u and 13d is divided into 32, and the angle between the rotations is represented by 0 to 31, as described above. Since 0 is the base point, for example, when the angle of the backup roll 13u is 0, the angle of the backup roll 13d is 0 to 31, and therefore there are 32 combinations of the rotation angles of the backup rolls 13u and 13d. There is. That is, the address (rotation angle) of the backup roll 13u is i (i = 0,
1, 2, ... 31) and the address of the backup roll 13d is j (j = 0, 1, 2, ... 31), the combination (i, j) is (0, 0), ( 0,1), (0,
2), ... (1,0), (1,1), (1,2), ...
.. (2,0), (2,1) ... (31,0), (31,
1), (31, 2), ... (31,31) and 1024 (= 32 x 32)
It becomes a street. The first correction table is the backup roll
The combination of the address i = 0 of 13u and the address j = 0 of the backup roll 13d (0, 0) is used as the base address, and (3
It is assumed to have addresses up to 1,31). The address (rotation angle) of the backup roll 13u i =
0 and the address J = 0 of the backup roll 13d, the screw 151 is tightened and held until it reaches 700 [ton], and after the hold, the pressure reduction position information of the screw 151 is saved, and the backup roll 13u and the backup roll 1 are saved.
While rotating 3d, the backup roll measured loads at the combinations (0,0), (1,1), (2,2), ... (31,31) of those rotation angles are measured. Next, the rotation angles of the backup roll 13u and the backup roll 13d are relatively shifted by one step (if the screw 151 needs to be loosened for this shifting, the screw 15 is loosened to rotate relatively, and the screw 15 is rotated. 151
Tighten up to the saved rolling position information),
While rotating the backup roll 13u and the backup roll 13d, a combination of their rotation angles (0, 1),
Measure the actual load of the backup roll at (1, 2), (2, 3), ... (31, 0). And so on
Measure the actual load of the backup roll up to the combination of (0,31), (1,0), (2,1) ... (31,30). As described above, the measured loads of (0,0) to (31,31) (total 32 × 32 pieces) are obtained. 700 from the measured load from (0,0) to (32,32)
The remaining value obtained by subtracting [ton], that is, the reference point (0,0)
Each point (0,0) to (31,31) for a load of 700 [ton]
The actual measured load deviation (hereinafter referred to as pressure deviation) of the first correction table address (0,0) to (31,31) corresponding to each point
Write to. In this state, for example, if the roll actual load is 710 [ton] at the backup roll address (0, 1), the backup roll reference address (0, 0)
Since it is +10 compared to, the pressure deviation +10 [ton] is written in the address (0, 1) of the first correction table,
If the roll actual load at the backup roll address (0, 31) is 690 [ton], the pressure deviation −10 [ton] is written at the address (0, 31) of the first correction table. In this way, the first correction table has 1024
(= 32 × 32) pressure deviations are stored.

The second and third correction tables are created by using 1500 [ton] and 2000 [respectively] instead of 700 [ton] described above when the combination of addresses (rotation angles) of the backup rolls 13u and 13d is (0, 0). [ton]] and is otherwise created in the same manner as the creation of the first correction table described above.

Address of backup rolls 13u and 13d (rotation angle)
Data (pressure deviation) of the first, second and third correction tables in one (i, j) of the combination (1024 ways)
Is the reference pressure (load value retained at address (0,0))
On the graph with the horizontal axis as the horizontal axis and the pressure deviation as the vertical axis,
The black circles shown in FIG. 4 are obtained. For example, when the backup roll address (0, 1) is set, the reference pressure is 700 [ton].
When the roll actual load is 710 [ton], the pressure deviation is +10 [ton] (black circle on the left side of Fig. 4), and when the backup roll address (0, 1) is, the reference pressure is 1500 [ton]. Roll actual load is 1520 [ton]
Then, the pressure deviation is +20 [ton] (black circle in the middle of FIG. 4), and the backup roll address (0,
In the case of 1), if the roll actual load is 2030 [ton] at the standard pressure of 2000 [ton], the pressure deviation is +30 [to].
n] (the black circle on the right side of FIG. 4).

The graph shown in FIG. 4 can be set to one for each address based on the data of the first correction table, the second correction table, and the third correction table, for a total of 1024 (= 32 × 32).

As shown in FIG. 4, a straight line connecting the pressure deviation (black circle) of the reference pressure 1500 [ton] and the pressure deviation (black circle) of the reference pressure 700 [ton] is extended to a region less than 700 [ton],
Reference pressure 1500 [ton] pressure deviation (black circle) and reference pressure
A straight line connecting the pressure deviation (black circle) of 2000 [ton] is 2000
Rolling load can be increased by extending to the area where [ton] can be obtained.
Even when the rolling load F is other than 700, 1500, 2000 [ton], the pressure deviation ΔF at the address (i, j) with respect to the rolling load F can be calculated by the interpolation method or the extrapolation method. For example, backup roll address (0, 1)
When the reference pressure is 1750 [ton], it is estimated that the roll actual load is 1775 [ton] and the pressure deviation is +25 [ton].

Therefore, even when the rolling load F is other than the rolling loads 700, 1500, 2000 [ton], the backup rolls 13u and 1u
3d rotation angle (address) combination (0,0) ~ (31,31)
For all of the above, it is possible to obtain pressure deviations equivalent to the pressure deviations of the first to third correction tables.

Next, the control process of the controller 21 will be described with reference to the flowcharts shown in FIGS. 3a and 3b.

When the controller 21 is powered on and a predetermined voltage is supplied to each part, the controller 21 initializes the input / output ports and internal registers in S1 (corresponding to the numbers given to the steps in the flowchart: the same below), and waits in S2. Set the mode. In this standby mode, when receiving the control start instruction from the host computer, the standby mode is released,
In S3, the mill constant M of the rolling mill transferred simultaneously, the plastic deformation rate Y of the hot strip SLP, the target plate thickness t
Then, the advance angle constant α ₁ of the upper backup roll 13u and the advance angle constant α ₂ of the lower backup roll 13d that compensate for the response delay of the cylinder 153 according to the transport speed of the hot strip SLP are read.

In S4, the position P of the screw 151 that makes the distance between the work rolls 12u and 12d equal to the target plate thickness t is determined by the function p having variables of the mill constant M, the plastic deformation rate Y, and the target plate thickness t prepared in advance. Then, in step S5, the servo motor driver 22 is instructed to perform position control. As a result, the servo motor driver 22 positions the screw 151 at the position P while monitoring the output of the position sensor 221.

S6 is a loop that waits for lock-on, that is, hot strip SLP biting. The biting of the hot strip SLP acts as a separating force of the work rolls 12u and 12d, and a large pressure is applied to each load cell. When it is detected, the process proceeds to S7, in which the upper load cell
Pressure F ₁ detected by _241U, pressure F ₂ was detected in Rowarodoseru 241 _d, address theta ₁ of the upper backup roll _13u, read the strokes G of the lower backup address roll 13d theta ₂ and the cylinder 153.

In S8, the true pressure (hereinafter referred to as the current pressure) F is obtained from the detection outputs F ₁ and F ₂ using the function f ₁₂ prepared in advance.

S9 to S20 are processes for estimating the true pressure (hereinafter referred to as reference pressure) F ₀ when the address of each backup roll is 0.

In this case, first, the pressure deviation ΔF at that time is assumed to be 0 in S9, it is saved as ΔF ′ in S10, and the pressure deviation ΔF is subtracted from the current pressure F in S11 to assume the reference pressure F ₀ .

In this embodiment, since only three types of correction tables are prepared as described above, the data between them are interpolated by linear approximation as shown in FIG. In this case, if the assumed reference pressure F ₀ is 1500 [ton] or less, the correction values (pressure deviation) of the first correction table and the second correction table are used.
If it exceeds 00 [ton], the correction values of the second correction table and the third correction table are used. That is, the proportional distribution constant K for linear interpolation is obtained in S13 or S15, and the first correction table and the second correction table or the second correction table and the third correction table are referred to in S14 or S16, and the proportional correction constant K is calculated. The correction value (pressure deviation) corresponding to each backup roll address θ ₁ and θ ₂ is read out, and the reference pressure F _{0 is} assumed by proportional distribution in S17.
The pressure deviation ΔF corresponding to is calculated.

In S18 and S19, the newly obtained pressure deviation ΔF
And the difference from the pressure deviation ΔF ′ before that are compared with a predetermined value ε ₀ .

By repeatedly executing the processing of S10 to S19, this difference becomes small and converges to a value equal to or smaller than the predetermined value ε _{0. At} that time, the process proceeds to S20 and the pressure deviation Δ from the current pressure F is determined.
Decrease F to establish reference pressure F ₀ .

In S21 to S23, it obtains the proportional distribution constant K using the reference pressure F ₀ which finalized.

In S24, the pressure deviation ΔF prepared in advance is set to the cylinder.
Substituting the mill constant M, the plastic deformation rate Y and the pressure deviation ΔF into the function g for converting the stroke of 153, the deviation ΔG of the stroke is obtained, and in S25, the deviation ΔG is subtracted by the stroke G at that time and each backup is performed. A stroke (hereinafter referred to as a reference stroke) G ₀ when the roll address is ₀ is estimated.

The above is the process in the preparatory stage, and the plate thickness variation prevention control process during rolling is performed in the following S26 to S39.

In S26, the address θ _{1 of} each backup roll
And θ ₂ are read, and in S27, the advance angle constant α ₁
And α ₂ are used to correct these values.

In S28 to S31, the first correction table and the second correction table, or the second correction table and the third correction table are referred to read the correction values corresponding to the corrected backup roll addresses θ ₁ and θ _2. , The pressure deviation ΔF to be compensated is obtained by proportionally distributing the reference pressure F ₀ .

In S32 to S33, the deviation ΔG of the stroke to be compensated is obtained by substituting the mill constant M, the plastic deformation rate Y and the pressure deviation ΔF into the function g described above, and the reference stroke G ₀
In addition to the above, the target stroke G'is determined.

In S34 to S39, while controlling the stroke G of the cylinder 153, the solenoid valve 17 is controlled via the solenoid driver 26, and the cylinder 153 is expanded / contracted to move within the allowable range (± δ) of the target stroke G '. Set.

The above steps S26 to S39 are repeated until the rolling process is completed.

In the embodiment described above, the true pressure when the address of each backup roll is 0 is set as the reference pressure of each correction table, but the screw 151 is fixed in an arbitrary state and each backup roll is rotated, The true pressure for one cycle may be averaged to obtain the reference pressure. Further, in the above embodiment, each correction table is created by the correlation between the address of each backup roll and the pressure deviation, but it may be created by the correlation between the address of each backup roll and the pressure. All of these differ in the way they handle data, and do not require any change in control.

Further, in the present embodiment, the true pressure is calculated by providing two load cells, but this is not a necessary process, and if only one of the load cells is used for detection, the true pressure is detected. Only pressure should be used.

(Effects of the Invention) As described above, according to the present invention, since the correction data associated with the rotation angle of the first backup roll and the rotation angle of the second backup roll is stored for each reference pressure, it is possible to perform rolling. Even when the material thickness and the target plate thickness are different, it is possible to effectively suppress the plate thickness variation due to the eccentricity of the backup roll.

In particular, as described in the embodiment, when the sleeve is attached to the backup roll and the rotation stopper is provided, since the elastic change due to the non-rotation becomes non-linear, the correction data is provided for each reference pressure so that high accuracy can be obtained. A plate thickness variation prevention device for a rolling mill can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a quadruple pressure rolling apparatus for carrying out the present invention as an example, and FIG. 2 is a partially enlarged sectional view showing a part thereof in detail. 3a and 3b show the controller shown in FIG.
22 is a flowchart showing a control operation of 21. FIG. 4 is a graph showing data interpolation by linear approximation. 11: Housing 12u, 12d: Work roll 13u, 13d: Backup roll 14u, 14d: Chock 15: Pressure 11,14,15: (pressurizing means) 16w, 16p: Gear 17: Solenoid valve 21: Controller (control means, Memory means) 22: Servo motor driver 23, 24, 25: Sensor driver 231: Stroke sensor 241u, 241d: Load cell (detection means) 251u, 251d: Resolver (rotation angle detection means) 26: Solenoid driver SLP: Strip (rolled) Material) M: Motor P: Pump

Claims (4)

[Claims] 1. A first work roll and a second work roll provided opposite to each other for sandwiching a material to be rolled; at least one first work roll for reinforcing the first work roll.
Backup roll; at least one second reinforcing roll for the second work roll
Backup roll; pressurizing means for applying pressure between the first work roll and the second work roll via the first backup roll and the second backup roll; detecting pressure applied by the pressurizing means Detection means for detecting the rotation angle of the first backup roll
Rotation angle detecting means; Second for detecting the rotation angle of the second backup roll
Rotation angle detection means; deviation of the pressure detected by the detection means with respect to the reference pressure for each reference pressure indicating the pressure detected by the detection means when the first backup roll and the second backup roll are at the reference angle. Is stored in association with the rotation angle of the first backup roll and the rotation angle of the second backup roll; and, during rolling, from the storage means, the reference pressure at that time, the first backup roll Of the rolling angle of the second backup roll and the deviation of the pressure associated with the rotation angle of the second backup roll, and instructing the pressurizing means to increase or decrease the applied pressure to offset the deviation, the control means; Plate thickness variation prevention device. 2. The storage means stores the pressure detected by the detection means for each reference pressure indicating the pressure detected by the detection means when the first backup roll and the second backup roll are at a reference angle. , The rotation angle of the first backup roll and the rotation angle of the second backup roll are stored in association with each other, and the control unit stores the reference pressure at that time and the first backup roll of the first backup roll during rolling. The pressure associated with the rotation angle and the rotation angle of the second backup roll is read, and the pressurizing means is instructed to increase or decrease the applied pressure that offsets the deviation from the reference pressure at that time. A rolling thickness variation prevention device for a rolling mill as set forth in (1). 3. The detecting means detects the reference pressure for each reference pressure indicating an average of the pressures detected by the detecting means when the first backup roll and the second backup roll rotate. The pressure deviation,
Rotation angle of the first backup roll and the second
Stored in association with the rotation angle of the backup roll, the control means, during rolling, from the storage means to the reference pressure at that time, the rotation angle of the first backup roll and the rotation angle of the second backup roll. The strip thickness variation prevention device for a rolling mill according to claim (1), wherein the associated pressure deviation is read out, and an instruction is given to the pressurizing means to increase or decrease the applied pressure to offset the deviation. 4. The storage means stores the pressure detected by the detection means for each reference pressure indicating an average of the pressures detected by the detection means when the first backup roll and the second backup roll are rotated. The rotation angle of the first backup roll and the rotation angle of the second backup roll are stored in association with each other, and the control means stores the reference pressure at that time and the rotation angle of the first backup roll at the time of rolling. And the pressure associated with the rotation angle of the second backup roll is read, and the pressurizing means is instructed to increase or decrease the applied pressure that offsets the deviation of the pressure and the reference pressure at that time. ) A device for preventing variation in plate thickness of a rolling mill as described in the paragraph.