JPS6225446B2 - - Google Patents

Description

Detailed Description of the Invention The present invention detects the gap between the rolls and the tension applied to the plate material when passing the plate material between the rolls of a rolling mill and winding it up with a reel motor, and drives the mill motor according to the detected value. The present invention relates to an automatic plate thickness control method in rolling, in which the thickness of a plate material to be rolled is automatically controlled by adjusting the thickness.

The thickness of the plate material rolled by this type of rolling mill is usually as shown in Figure 1, with long-period fluctuations T ₁ and short-period fluctuations.
T ₂ occurs in a superimposed manner, but conventionally only compensation for long-period fluctuations has been considered, and compensation for short-period fluctuations has not been performed at all. In other words, the conventional automatic plate thickness control method for this type of rolling detects the exit side thickness of the plate material passed through the rolling mill, and then removes the deviation between the detected value and the target value of the exit side thickness. In order to do this, the gap between the rolls of the rolling mill is opened and closed in proportion to this amount of deviation, and the tension applied to the plate is adjusted by driving the reel motor that winds the plate or by controlling the speed of the front and rear stands. The thickness of the plate to be rolled was controlled by feedback.

Recently, a thickness gauge has been installed on the entrance side of the rolling mill to detect the entrance thickness of the plate material entering the rolling mill, and adjust the roll gap of the rolling mill in proportion to the deviation of the input thickness from the planned amount. Feed forward control was also performed to open and close. This type of conventional control method mainly aims only at eliminating long-period sheet thickness deviations, and the causes of sheet thickness deviations include fluctuations in constant deformation resistance (dP/dR・ΔR), entrance side sheet thickness, etc. variation (dP/dHΔ
H) was the main factor, and other causes of deviation were changes in the coefficient of friction between the plate and roll that occur during acceleration and deceleration of rolling, and changes in the thickness of the oil film on the bearing. It has been completely impossible to control short-term plate thickness deviations caused by causes other than the above-mentioned causes using conventional methods. Therefore, hunting occurs due to interference between the stand of the rolling mill and the take-up reel or adjacent stands, so long-period disturbances can be removed, but short-period disturbances cannot be removed, so fluctuations in factors occur during acceleration and deceleration. It had drawbacks such as being too large to be applied.

However, in addition to the above-mentioned causes, plate thickness deviations are caused by high-frequency fluctuations in the plate tension of the plate material due to mutual interference between the rolling mill system including the rolling mill and the reel. In addition to changes in the longitudinal direction as variations in plate thickness and deformation resistance,
This is caused by vibrations in the rolling mill system caused by disturbances caused by acceleration and deceleration of the reel motor. Since the cycle of high-frequency fluctuations caused by plate tension is shorter than the fluctuation cycle of deformation resistance and the fluctuation cycle of entry-side plate thickness, conventional automatic plate thickness control systems configured for the purpose of eliminating fluctuations in deformation resistance and entry-side plate thickness However, these high-frequency fluctuations remained as deviations in the thickness of the outlet side even after control, so there was a drawback that the thickness of the outlet side could not be accurately controlled.

In order to eliminate the drawbacks of the above-mentioned conventional methods, the method of the present invention
In order to eliminate high-frequency variations in plate thickness due to plate tension and obtain more accurate plate thickness, the thickness of the plate that is automatically rolled through the rolling mill is controlled by compensating for tension changes corresponding to high-frequency variations. It was designed to do so. According to the method of the present invention, high frequency fluctuations in this type of rolling mill system are caused by the inertia of the reel and rolling mill, causing load fluctuations due to disturbances, and this fluctuation changes the rolling speed of the sheet material, so that the rolling speed of the sheet material changes. It is assumed that thickness deviation occurs, and therefore, in order to suppress this high frequency fluctuation, load fluctuation due to disturbance is compensated for.

That is, the present invention extracts factors of plate thickness variation from changes in rolling load of each rolling mill when rolling a plate material wound from a rewinding reel to a take-up reel through at least one rolling mill. In the method of controlling the detected rolling load fluctuation ΔP
Calculates the roll eccentricity contribution ΔPe based on the frequency due to roll eccentricity from rolling load fluctuations sampled over time, calculates the contribution due to friction coefficient fluctuations ΔPμ from the rolling speed change ΔV, and calculates the difference between rolling mills or Detect or calculate the tension between the rolling mill and the reel and use the tension to calculate the tension fluctuation contribution Δ
After calculating Pt and calculating the fluctuation contribution ΔPs due to roll gap fluctuation, these contributions ΔPe,
By subtracting the rolling load fluctuation ΔP from ΔPμ, ΔPt, and ΔPs to calculate the contribution ΔP ₁ of the entrance plate thickness fluctuation and/or the deformation resistance change of the rolling mill, the rolling load fluctuation is separated for each factor, and the above-mentioned Among the rolling load fluctuation components, ΔPμ is controlled by current compensation for the reel motor or the mill motor of the adjacent stand, and the detected or calculated tension between the rolling mills or between the rolling mill and the reel is combined with the ΔPμ. The tension change value generated due to current compensation is integrated to calculate the tension change due to the vibration frequency component of the rolling mill between the rolling mills or between the rolling mill and the reel, and the calculated value is used to control the reel motor or adjacent stand. In addition, for ΔPe, the plate thickness is controlled by the roll gap, and for ΔP ₁ , the plate thickness is controlled by the roll gap and/or load compensation control is applied to the mill motor of the relevant stand. The rolling method is characterized in that high-frequency changes in plate thickness due to mutual interference of plate tension in a rolling mill system consisting of a rolling mill and a reel are eliminated at the same time as changes in plate thickness on the exit side due to the various causes described above. This paper provides a new automatic plate thickness control method. It should be noted that the automatic plate thickness control method according to the present invention can of course be applied to a single stand type mill, but is particularly suitable for a tandem type mill consisting of multiple stands.

In FIG. 2, reference numeral 1 denotes a rolling mill, and the gap between a pair of work rolls 2, 2 is freely adjusted by the operation of a mill motor 3, and a plate material 4 to be rolled is passed between the rollers 2, 2. do. 5 is a back-up roll. The plate material 4 passes from the unwinding reel 6 to the rolls 2, 2 of the rolling mill 1, and is wound onto a take-up reel 8 driven by a reel motor 7. Therefore, the thickness of the plate material rolled through the rolling mill 1 depends on the adjustment of the gap between the work rolls by the operation of the mill motor 3 and the rotational speed of the take-up reel 8 driven by the reel motor 7. Since it depends on the plate tension, a desired plate thickness can be obtained by adjusting these with the control circuit C. Control circuit C
The factors that influence the thickness of the plate material rolled through the rolling mill 1 are speed change ΔV, friction coefficient change Δμ, and deformation resistance change Δ.
R, entrance plate thickness variation ΔH, rolling load change ΔP, exit plate thickness variation Δh, roll gap variation command change Δu, roll gap change ΔS, tension change Δtb, reel current change ΔIR, roll eccentricity ΔSo, main motor current change ΔI _H , Mill's constant K, etc.

In addition, the causes of load fluctuation L during rolling include changes in roll gap due to roll eccentricity, changes in deformation resistance, changes in inlet plate thickness, changes in inlet tension, changes in outlet tension, and changes in the roll gap between the rolled material and the rolls. Changes in the friction coefficient and opening/closing of the roll gap are mentioned, and the influence of each of these items on the rolling load can be expressed by the following formula.

ΔP=ΔP ₁ +A ₁・ΔSec+A ₂・ΔS+A ₃・Δt _f +A ₄・Δt _b +A ₅・Δμ ...(1) In equation (1), ΔP ₁ =ΔP _H +ΔP _K ...(2). However, in equations (1) and (2), A ₁ to A ₅ are the influence coefficients of each factor on the load change, ΔSec is the roll eccentricity,
ΔS is roll gap change, Δtf is exit tension change, Δ
t _b is the change in tension on the entry side, Δμ is the change in friction coefficient, ΔP _H
is the change in rolling load due to change in plate thickness on the entry side, ΔP _K is change in rolling load due to change in deformation resistance, ΔP ₁ is ΔP
The sum of _H and ΔP _K is the rolling load change due to changes in the entrance plate thickness and deformation resistance.

In the following, we will explain the factors of load fluctuations mentioned above, and for the case of a single-stand mill equipped with a take-up reel, we will separate the amount of rolling load fluctuation for each factor in equation (1) above and control each separately. , each factor will be explained.

(i) Contribution to roll eccentricity: ΔPe First, out of the rolling load change, a variation equal to the rotation period of the back-up roll is extracted. That is, for example, I ₁ = 1/T∫ ^T _O (ΔP−Asin(ωt+φ)) ² dt……(
3) However, ω is the rotational angular velocity of the back-up roll, and is calculated by calculating the eccentricity amplitude A and the vibration phase angle φ so that equation (3) is minimized.

As a result, the roll eccentricity contribution ΔSec can be extracted as ΔPe=Asin(ωt+φ)=ΔSec (4). Therefore, first, the sampling data of ΔP is accumulated using the load cell, and ΔP is
From the P signal, extract the waveform that matches the rotation period of the back-up roll from 1/ _{T∫ TO} ⁽ ΔP−Asin(ωt+φ))Min, and calculate ΔPe=Asin(ωt+φ) as the roll eccentricity equivalent. Later, roll gap control can be used with ΔSe=-K+M/K·ΔPe/K.

(ii) Friction coefficient contribution: ΔPμ The amount of load change is calculated assuming that the friction coefficient changes only with speed. That is, for example, μ = μo-a・V ... (5) However, μo is the reference friction value when V = 0, V is the work roll speed, and a is a mill-specific coefficient, and as a result, the friction coefficient The contribution Δμ is ΔPμ=A ₅・Δμ=−A ₅・a・ΔV
...It can be calculated using (6). Therefore, by understanding the rolling speed and calculating the change in the friction coefficient due to the rolling speed, and calculating the change in rolling load due to the friction coefficient ΔP.
After calculating μ and correcting the tension change accompanying the ΔPμ, the drive current of the reel or the front and rear stands can be corrected.

(iii) Roll gap change contribution: ΔPs Assuming that the roll gap change amount ΔS can be measured, the roll gap change contribution ΔPs can be calculated as ΔPs=A ₂ ·ΔS (7).

(iv) Contribution of tension: ΔPt Assuming that the tension changes Δt _f and Δt _b between reel unwinding tension and winding tension can be detected, the contribution of tension ΔPt is ΔPt=A ₃・Δt _f +A ₄・Δt _b can be calculated using (8).

These Δt _f and Δt _b are the fluctuations in the measured tension,
A ₃ and A ₄ are tension influence coefficients.

Note that t _f = t _f1 + t _f2 However, there is the following relationship: t _f2 = b ₀ + b ₁ sin ω ₁ t + b ₂ cos ω ₁ t (18) t _b2 = c ₀ + c ₁ sin ω ₂ t + c ₂ cos ω ₂ t (19).

Therefore, the sampling data is accumulated by comparing the calculated value of the tension change due to the tension ΔPμ,
And from the signal of Δt′ _f , a waveform that matches the synchronization of ω ₁ = Vf/L ₁ is obtained as Δt′ _f =b ₀ +b ₁ Sinω ₁ t
+b ₂ Cosω ₁ t, and on the other hand, from the signal of Δt′ _b , the waveform matching the period of ω ₂ = Vb/L ₂ is extracted as Δt′ _b =C ₀ +C ₁ Sinω ₂ t
After extracting as +C ₂ Cosω ₂ t+C ₂ Cosω ₂ t, Δt′ _f and Δt′ _b can be corrected by the currents of the front and rear stands or reels.

(v) Contribution of change in entrance plate thickness and deformation resistance: ΔP ₁ Using equation (1) above, contribution of change in entrance plate thickness and deformation resistance ΔP ₁ is ΔP ₁ = ΔP− (ΔPe + ΔPs + ΔPμ + ΔPt)
... can be extracted using (9). Therefore, ΔP of the rhodle
(Contribution to roll eccentricity + contribution to roll gap change +
After comparing the load changes (tension change contribution + friction coefficient change contribution) and extracting ΔP ₁ , ΔS=gain
*ΔP ₁ /K is calculated, and roll gap control is performed from the ΔS, while load fluctuation calculation is performed using Δ=2λldΔP ₁ to correct the drive motor current.

With the above procedure, changes in rolling load can be separated by factor.

Next, the control of plate thickness according to the method of the present invention is performed according to the above-mentioned factors, and each control will be explained below.

(i) Control of entry side plate thickness and deformation resistance Contribution of entry side plate thickness and deformation resistance obtained in (9) above ΔP ₁
For this purpose, the conventionally used plate thickness control using the gap between rolls, so-called BISRA control, is performed. That is, u1=-g1·(ΔS+ΔP ₁ /K) (10) However, u1 is the roll gap opening/closing command by BISRA control, and g1 is the BISRA control gain. Conventionally, the load change ΔP was used in equation (10), but in the method of the present invention, ΔP ₁ is used as described above.

(ii) Compensation control of friction coefficient (acts during acceleration/deceleration) The reel unwinding tension and winding tension obtained from equation (6) above are compensated. That is, ΔI _Rb1 = -g2・Δt _b1 ...(11) Δt _b1 = α・ΔPμ/(dP/dt _b )...(12) ΔI _Rf1 = g3・Δt _f1 ...(13) Δt _f1 = (1 −α)・ΔPμ/(dP/dt _b )
...(14) However, ΔI _Rb1 is the motor current compensation amount of the winding reel, ΔI _Rb1 is the motor current compensation amount of the take-up reel, g2 and g3 are the compensation gains, and α is 0 and 1.
is a constant between . Compensation control using the friction coefficient can be performed using equations (12) and (14).

(iii) Roll eccentricity effect removal control Using ΔPe determined by the above equation (4), Control with. However, K is a mill constant, g4 is a control gain, and u2 is a roll gap opening/closing command.

(iv) Correction of tension fluctuations Regarding the contribution ΔPt of tension fluctuations calculated using the above equation (8), Δt _f2 = Δt _f −β・Δt _f1
...(16) Δt _b2 = Δt _b −β・Δt _b1
...(17) However, β is a weight constant. Furthermore, t _f2 = b0 + b1 · sinω1t + b2 · cosω1t (18) t _b2 = c0 + c1 · sinω2t + c2 · cosω2t (19) ω1 = Vf / L ₁ ... (20) ω2 = Vb / L ₂ ... (21) However, ω1 and ω2 are constants determined by the distance between the stands or between the stands and the reel. Using these equations (18) to (21),
If b0, b1, b2, c0, c1, c2 are evaluation functions from moment to moment, I ₂ = 1/T∫ ^T ₀ (Δt _f2 −b0−b1sinω1t −b2cosω1t) ² dt ...(22) and I ₃ = 1/ T ^T ₀ (Δt _b2 −c0−c1·sinω2t −c2·cosω2t) ² dt (23) is determined so as to be minimized.

However, in equations (20) and (21), Vf is the rolling mill exit plate speed, L ₁ is the distance between the rolling mill and the take-up reel, Vb is the rolling machine entrance plate speed, and L ₂ is the rolling mill and unwinding reel. is the distance between.

The motor currents of the winding and unwinding reels are compensated using the tension fluctuation amounts Δt _f2 and Δt _b2 determined by the above equations (18) and (19). That is, ΔI _Rf2 =-g5·Δt _f2 (24) ΔI _Rb2 =-g6·Δt _b2 (25). In equations (24) and (25), ΔI _Rf2 and ΔI _Rb2 are the motor current compensation amounts of the take-up and unwinding reels, respectively, and g5 and g6 (where 0<g<
1) is a compensation gain.

(v) Correction of speed change due to load fluctuation Regarding the load fluctuation of the rolling mill, the influence of ΔP ₁ caused by the change in the entrance plate thickness determined by the above equation (9) and the change in deformation resistance is compensated. That is, the load fluctuation Δτ is as follows: Motor load = 2 * Torr Comb coefficient * Projected contact length * Rolling load, that is, Δτ = 2・λ・ld・ΔP ₁ (26).

The rotational speed change Δn of the DC motor is calculated using the motor current change ΔI _M and the load torque fluctuation Δτ, Δn=−ΔI _M /K _V −Δτ/K _T・K _V (K _V : Voltage coefficient K _T : Torque coefficient ) becomes.

In order to keep the rotational speed unchanged even if the load fluctuates, Δn should be set to 0.

Therefore, ΔI _M = -Δτ/K _T = -Δτ/K ₁・if In _practice , by multiplying by a gain, the current of the rolling mill is calculated as ΔI _M = −g ₇・Δτ/K ₁・_if (27 ) will be corrected and compensated.

However, in equations (26) and (27), λ is the torque arm coefficient of the rolling mill, ld is the contact arc length, if is the reel field current, _K1 is the torque current conversion constant, and g7 is the correction gain. Now, if ΔI _M >0, the speed changes and becomes ΔV<0, but in order to reduce this to 0, the motor's armature current is lowered so that ΔI _M <0. As detailed in the above embodiments, the present invention focuses on the following points.

In other words, (1) Disturbances during acceleration and deceleration (roll gap changes due to oil film thickness, friction coefficient changes) cause mutual interference between the rolling stand and reel through tension between the two, and prevent phenomena that lead to sheet thickness fluctuations.

(2) Among tension fluctuations, some of them are due to interference between the rolling stand and the reel, even when not accelerating or decelerating.
This leads to high frequency plate thickness fluctuations. The present invention extracts the interference between the rolling stand and the reel from the total tension fluctuation, and controls to push this in.
Prevents plate thickness variation due to mutual interference between the two.

(3) First extract the contributions of roll eccentricity, acceleration/deceleration disturbances, and tension fluctuations to the rolling load, then remove the above contributions from the total rolling load, and calculate the contributions of deformation resistance and entrance plate thickness fluctuations. ing.

That is, the method of separating roll eccentricity, deformation resistance, etc. is special.

Note that variations in tension due to roll eccentricity, changes in entrance plate thickness, etc. are the result of interference between the stand and the reel.

That is, for example, when the roll gap opens and closes due to roll eccentricity, the mass flow is disrupted, causing tension fluctuations.

These tension fluctuations cause changes in the rolling load, which may apparently cancel out the contributions of the entrance plate thickness and deformation resistance to the load.

In order to obtain a good plate thickness, it is necessary to accurately separate and recognize the causes of plate thickness fluctuations by factor, and to control each factor using an appropriate method. For this reason, in the present invention, load changes due to tension are separated from the total rolling load.

Moreover, the tension fluctuation that is the object of control in the present invention is I ₂ = 1/T∫ ^T ₀ (Δt _f −b ₀ −b ₁ sinω ₁ t −b ₂ cosω ₁ t) ² dt→ Min (22) I ₃ = 1/T∫ ^T ₀ (Δt _f −c ₀ −c ₁ sinω ₂ t −c ₂ cosω ₂ t) ² dt→Min (23) The delay period contribution between the reel and the stand Only minutes.

In other words, with the present invention, the various causes of sheet thickness fluctuations are correctly identified and all of them are eliminated using the roll gap. For this purpose, data on tension fluctuations are used. What remains is the tension fluctuation caused by the delay between the reel and the stand, and between the stand and the reel. This is removed by separately controlling the reel current.

Furthermore, regarding the separation method, each of the following contributions is extracted respectively.

(1) Extract ΔPe=Asin(ωt+φ) ……(4) so that the roll eccentricity contribution becomes I ₂ = 1/T∫ ^T ₀ {ΔP−Asin(ωt+φ)} ² dt →Min ……(3) do.

(2) Extract the friction coefficient contribution using ΔPμ=-A ₅・a・ΔV (6).

(3) Extract the roll gap change contribution using ΔPs=A ₂・ΔS (7).

(4) Extract the contribution of tension using ΔPt=A ₃・Δt _f +A ₄・Δt _b (8).

(5) The contribution of the entrance plate thickness and deformation resistance is ΔP ₁ = ΔP− (ΔPe + ΔPμ + ΔPs + ΔPt)
...Extract by (9).

The control system of the method of the present invention described above is illustrated in FIG.

In other words, as an automatic plate thickness control method in rolling, in a single type or tandem type rolling mill with take-up and unwinding reels, changes in rolling load are extracted and controlled from changes in rolling load. As shown in Fig. 3, the load change ΔPe due to roll eccentricity, the load change ΔPμ due to the friction coefficient, the load change ΔPt due to tension change, and the load due to changes in entry side plate thickness and deformation resistance. The change ΔP is separated into ₁ , and the roll eccentricity effect removal control μ2 is applied to the contribution of roll eccentricity ΔPe.
Reel current compensation ΔI _Rf1 is applied to the friction coefficient contribution ΔP, reel current control ΔI _Rf2 and ΔI _Rb2 is applied to the tension change contribution ΔPt, and the input side plate thickness and deformation resistance change contribution are
Regarding the BISRA control μ1 and the load fluctuation of the rolling mill, load compensation control ΔI _M of the mill motor is performed, and in particular, according to the change in the rolling load mentioned above, current compensation control of the reel motor is performed with the load change due to the tension change. On the other hand, due to load changes due to changes in plate thickness and deformation resistance on the entry side and roll eccentricity,
By performing BISRA control and load compensation control of the rolling mill motor, the plate thickness changes at the exit side due to the various causes mentioned above, and at the same time, high-frequency changes in plate thickness due to mutual interference of plate tension in the rolling mill system consisting of the rolling mill and reel. It is designed to remove. Therefore, by using the method of the present invention, it is possible to eliminate plate thickness fluctuations due to high frequency changes, which cannot be removed by conventional automatic plate thickness control systems.

FIG. 4a shows the thickness of a plate rolled by the conventional method, and FIG. 4b shows the thickness of a plate rolled by the method of the present invention. As can be seen from FIG. 4, according to the method of the present invention in FIG. 4b, there is less variation in the plate thickness due to high frequencies compared to the result of the conventional method shown in FIG. 4a, and good plate thickness accuracy can be obtained. In other words, in the case of Fig. 4b, the short-term plate thickness variation is reduced, for example, the conventional plate thickness variation of 10μ is reduced to 4 to 5μ,
It has great practical value, as it improves plate thickness accuracy, improves quality, and improves manufacturing yield.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram showing plate thickness fluctuations, Figure 2 is a schematic explanatory diagram when the control method of the present invention is applied to a single stand mill, and Figure 3 is a block diagram of the control circuit used in Figure 2. , and FIGS. 4a and 4b show actual measured values of the thickness of plates rolled by the method of the present invention and the conventional method, respectively. 1...Rolling mill, 2...Work roll, 3...Mill motor, 4...Plate material, 7...Reel motor, C...
...control circuit.

Claims (1)

[Scope of Claims] 1. When rolling a plate material that is wound up from the unwinding reel to the take-up reel through at least one or more rolling mills, the factor of variation in plate thickness can be determined from the change in the rolling load of each of the rolling mills. In the extraction and control method, the roll eccentricity contribution ΔPe is calculated based on the frequency due to roll eccentricity from the rolling load fluctuation sampled over time from the detected rolling load fluctuation ΔP, and the friction coefficient is calculated from the rolling speed change ΔV. Calculate the contribution ΔPμ due to fluctuations, detect or calculate the tension between rolling mills or between the rolling mill and the reel, calculate the tension fluctuation contribution ΔPt using the tension, and calculate the fluctuation contribution due to roll gap fluctuations. After calculating ΔPs, these contributions ΔPe, ΔPμ, ΔPt
By subtracting ΔPs from the rolling load fluctuation ΔP to calculate the contribution ΔP ₁ of the entrance plate thickness fluctuation and the deformation resistance change of the rolling mill, the rolling load fluctuation is separated into each factor, and each rolling load fluctuation component is Of these,
Regarding ΔPμ, current compensation control is performed on the reel motor or the mill motor of the adjacent stand, and the tension generated between the detected or calculated tension between the rolling mills or between the rolling mill and the reel and the tension generated due to the current compensation of the ΔPμ is The tension variation due to the vibration frequency component of the rolling mill between the rolling mills or between the rolling mill and the reel is calculated by integrating the change values, and the calculated value is used to perform current compensation for the reel motor or the mill motor of the adjacent stand. In addition, for ΔPe, the plate thickness is controlled by the roll gap, while for ΔP ₁ , the plate thickness is controlled by the roll gap and the load compensation control for the mill motor of the relevant stand is performed to reduce the output caused by the various causes mentioned above. An automatic plate thickness control method in rolling, characterized in that high-frequency changes in plate thickness due to mutual interference of plate tension in a rolling mill system consisting of a rolling mill and a reel are removed simultaneously with changes in side plate thickness. 2. A method of extracting and controlling plate thickness variation factors from changes in rolling load of each rolling mill when rolling a plate material wound from a rewinding reel to a take-up reel through at least one or more rolling mills. In , the roll eccentricity contribution ΔPe is calculated based on the frequency due to roll eccentricity from the rolling load fluctuation obtained by sampling the detected rolling load fluctuation ΔP in time series, and the contribution due to the friction coefficient fluctuation is calculated from the rolling speed change ΔV. Calculate ΔPμ, detect or calculate the tension between the rolling mills or between the rolling mill and the reel, and calculate the tension fluctuation contribution ΔPt using the tension,
After calculating the fluctuation contribution ΔPs due to roll gap fluctuation, these contributions ΔPe, ΔPμ, Δ
By subtracting Pt and ΔPs from the rolling load fluctuation ΔP to calculate the contribution ΔP ₁ of the entrance plate thickness fluctuation or the deformation resistance change of the rolling mill, the rolling load fluctuation is separated for each factor, and each rolling load fluctuation is Among the components, for ΔPμ, current compensation control is performed for the reel motor or the mill motor of the adjacent stand, and the tension between the rolling mills or between the rolling mill and the reel detected or calculated is adjusted based on the current compensation for ΔPμ. The tension variation value due to the vibration frequency component of the rolling mill between the rolling mills or between the rolling mill and the reel is calculated by integrating the tension change value generated by the rolling mill, and the calculated value is used to generate a current for the reel motor or the mill motor of the adjacent stand. In addition, for ΔPe, the plate thickness is controlled by the roll gap, and for ΔP ₁ , the plate thickness is controlled by the roll gap or the load compensation control of the mill motor of the relevant stand is performed. An automatic plate thickness control method in rolling, characterized in that high-frequency changes in plate thickness due to mutual interference of plate tension in a rolling mill system consisting of a rolling mill and a reel are eliminated at the same time as variations in the plate thickness on the exit side due to various causes. .