JP2804320B2 - Plating weight control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method for controlling the amount of plating to control the amount of plating by spraying a gas from a wiping nozzle onto the surface of a strip plated through a molten metal bath,
In particular, the present invention relates to a plating amount control method capable of automatically switching between feedback control and feedforward control, thereby preventing control hunting and improving the control accuracy of the plating amount.

[Prior art]

When a galvanized steel sheet is produced in a continuous hot-dip galvanizing line, as shown in FIG. 1, gas is applied from a wiping nozzle 14, 16 to the surface of a strip 12 plated through a hot-dip galvanizing bath 10. The amount of zinc deposition is adjusted by spraying. That is, zinc attached to the surface of the strip 12 is
By pressing and pushing down with the jet of the wiping gas, the attached zinc is squeezed. In the figure, reference numeral 18 denotes a sink roll. As a method for controlling the amount of zinc deposition in such a hot-dip galvanizing line, Japanese Patent Publication No. 46-14521 discloses a wiping nozzle 14, 16 in accordance with the line speed LS of the strip 12.
Feed-forward control that adjusts the interval D between the strip 12 and the strip 12, and feedback control that adjusts the interval D between the wiping nozzles 14, 16 and the strip 12 by adjusting the wiping gas pressure P according to the actual amount of plating. Combinations are disclosed. JP-A-49-32821 also discloses wiping nozzles 14, 16
Feedback control that corrects the pressure P of the wiping gas in accordance with the deviation between the set plating amount and the actual plating amount after fixing the distance D between the strip and the strip 12 to an appropriate condition; A combination of feedforward control for setting the wiping gas pressure according to the speed is disclosed. In these control methods, in order to accurately control the actual coating weight with respect to the set coating weight with good responsiveness, the coating weight and the line speed LS, the distance D between the wiping nozzle and the strip, the wiping The relationship with the gas pressure P needs to be constant. However, in an actual operation, it is extremely difficult to satisfy this condition for a long time. That is, the wiping nozzle is usually replaced or repaired after using it for an appropriate period of time, but even if the distance D between the wiping nozzle and the strip is correctly reset, the slit gap or the intermediary of the replaced or repaired wiping nozzle is usually used. Since the injection angle and the like fluctuate without always being kept under the same condition, the relationship between the coating amount and the wiping gas pressure P or the line speed LS is
It changes every time the wiping nozzle is replaced or repaired. Further, it is actually difficult to accurately reset the distance D between the wiping nozzle and the strip. Furthermore, the actual amount of plating changes not only due to variations in the line speed LS, the spacing D between the wiping nozzle and the strip, and the wiping gas pressure P, but also due to variations in strip thickness, plating bath temperature, air temperature, and the like. . Therefore, it has been difficult to stably and accurately control the amount of plating over a long period of time by the methods disclosed in JP-B-46-14521 and JP-A-49-39821. To solve such problems, Japanese Patent Publication No. 55-
34861 has feedforward control to set the wiping gas pressure P according to the set plating amount and the line speed LS, and corrects the wiping gas pressure P according to the deviation between the set plating amount and the actual plating amount. In the coating weight control in combination with the feedback control, the feedforward control characteristic is corrected based on the measured values of the coating weight, the line speed LS, the wiping gas pressure P, and the distance D between the wiping nozzle and the strip. In addition, it is disclosed that it can follow not only the fluctuation of the line speed LS, the interval D between the wiping nozzle and the strip, the fluctuation of the wiping gas pressure P, but also the fluctuation of other fluctuation factors. Also, Japanese Patent Publication No. 56-12316 shows that the wiping gas pressure P
Is expressed as a function of the spacing D of the wiping nozzle, the height and angle, the line speed LS, and the amount of plating adhesion. Before changing the operating conditions such as the operation conditions, the wiping gas pressure P, the nozzle-strip interval D, the nozzle height H, the nozzle angle, the line speed LS, and the plating adhesion amount, which were previously found before the feedback control, were performed. Based on the relational expression (experimental formula) between the working conditions, when any of the above working conditions is changed, other working conditions that maintain the target plating adhesion amount are calculated according to the working conditions. However, these conditions are changed at the same time, and other working conditions such as the wiping gas pressure are quickly changed and set according to changes in the target coating weight and the line speed due to the type change. Those capable manner is disclosed. Further, in Japanese Patent Publication No. 57-10948, the large adjustment of the wiping gas pressure P and the interval D between the wiping nozzle and the strip is mainly set by the preset control. When it is necessary to change these conditions, the pressure P and / or the interval D or one of the conditions is greatly adjusted in a short time, and the fine adjustment based on the information of the plating thickness from the line is adjusted by feedback control. Since there is a certain correlation between the plating thicknesses, there is disclosed one in which the responsiveness is enhanced by adjusting this by proportional control.

[Problems to be solved by the invention]

However, usually, since the distance between the wiping nozzle and the adhesion meter is close to 100 m, in the conventional control mainly based on the actual value feedback, it takes a long time to respond, and when the operating conditions such as the line speed change, The amount of adhesion changes to a hunting tendency and falls outside the management range, so that high control accuracy cannot be expected. Further, even in the case where the feed forward control such as the preset is used in combination, there is a problem that the response is not sufficient especially when the line speed is increased. The present invention has been made to solve the above-mentioned conventional problems, and by automatically switching between feedback control and feedforward control, it is possible to prevent hunting of control and improve the accuracy of controlling the amount of plating applied. An object of the present invention is to provide a method for controlling the amount of plating applied, which is possible.

[Means for achieving the object]

The present invention relates to a method for controlling the amount of plating by spraying a gas from a wiping nozzle onto the surface of a plated strip passing through a molten metal bath, in which a distance between a strip and a wiping nozzle, a wiping gas pressure and a line speed change. In an unstable state in which at least one of the rates exceeds a predetermined value, the feedforward control is performed, and the stable state in which the change rates are all equal to or less than a predetermined value continues, and when the attached amount information is received a predetermined number of times or more, The object has been achieved by enabling feedback control.

[Action and effect]

In the present invention, when the gas is blown from the wiping nozzle to the surface of the plated strip passing through the molten metal bath to control the amount of plating, each of the strip-wiping nozzle distance, the wiping gas pressure, and the line speed is used. In an unstable state in which at least one of the rate of change exceeds a predetermined value, feedforward control is performed, the stable state in which the rate of change is all equal to or less than a predetermined value continues, and the attached amount information has been received a predetermined number of times or more. Sometimes feedback control is made possible. In this way, by automatically switching between the feedback control and the feedforward control according to the stability determination result, hunting of the control can be prevented, and the accuracy of controlling the amount of plating applied can be improved.

【Example】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, the present invention is applied by spraying a gas from wiping nozzles 14 and 16 onto the surface of a strip 12 plated through a molten zinc bath 10 as shown in FIG. This is applied to a hot-dip plating line that controls the temperature. As shown in FIG. 2, the apparatus for controlling the amount of plating applied according to the present embodiment, for example, during plating with pure zinc, in a state where the strip 12 is cooled downstream of the wiping nozzles 14 and 16 (upper side in FIG. 1). A coating weight meter (thickness gauge) 20 for measuring the coating weight (thickness) of the plating, and an alloying method for measuring the content of the base iron in the strip 12 and the coating weight of the alloyed plating, for example, in the case of alloy plating. Meter 22, a coating weight control device 24 for controlling the coating weight according to the present invention based on the output of the coating weight meter 20 or the alloying meter 22, a coating weight control device 24 and the coating weight meter 20 or a signal input from the alloying degree meter 22, a process computer 26 for setting a coating amount set value and a plating type, an off-line regression calculation computer 28, and a display device 28A and a line printer 28B. ing. Hereinafter, the operation of the embodiment will be described. First, various results data used for controlling the amount of adhesion are collected for each predetermined sampling circumference by the adhesion amount meter 20, the alloying degree meter 22, and the like, and stored in the memory of the process computer 26 to create a result collection table. As the actual data to be collected, for example, the actual distance value D _P between the strip and the nozzle,
Wiping nozzle height H _P, wiping gas pressure actual value
P _P , actual line speed value LS _P , strip thickness t at the wiping nozzle portion, strip plate width W at the wiping nozzle portion, zinc bath temperature actual value Tz, nozzle type, nozzle angle, dull / bright classification, standard grape number, There are a set value of plating weight Ms, a measured value of plating weight M _P , zinc bath components (Al, Pb, Fe), gas types (air, nitrogen), plating types, and the like. At the time of data collection, upper and lower limits are checked, and abnormal data is left blank, and data is stored in the results collection table. Next, a regression calculation is performed by the regression calculation computer 28 using the actual data for the regression calculation.
Find b and c. M = aX ² + bX + c (1) Here, M: Plating amount setting value or actual value X: Plating amount equivalent value The regression calculation is performed based on the model formula level by updating the parameters a, b, and c. This is for the purpose of examining an adhesion amount model formula having a higher hit ratio and a change in the layering method of the parameters a, b, and c in the model formula. This regression calculation is
It is desirable to perform the calculation offline using a development computer, but it is also possible to perform regression calculation in parallel even when the online process computer 26 is controlling the amount of adhesion. If a part of the regression calculation result data is abnormal, it is excluded from the regression calculation target data,
Regression accuracy can be improved. Specifically, the inventors found out by examining the actual operation data, for example, the following basic model formula X = (1 / lnH) · (LS · D / P) ^1/2 × L ₁ · L ₂ …… (2) where LS: line speed, D: distance between strip and wiping nozzle P: wiping gas pressure, H: wiping nozzle height from molten metal bath surface, L ₁ , L ₂ : constant ( The following regression equation is set as a constant L ₁ = L ₂ = 1 (reference value) of the correction coefficient), and the regression coefficients a, b, and c are obtained by substituting the actual data for regression calculation therein. . _{X = (1 / lnH P)} × {(LS P · D P) / P P} 1/2 ...... (3) M P = aX 2 + bX + c ...... (4) where _the subscript _P is indicating an actual value It is. The regression calculation computer 28 is a process computer
Data of the set conditions are read from the regression calculation result data table 26 and stored in the regression data table in the regression calculation computer 28. Next, the data items to be used for the actual regression calculation are specified, the data under the corresponding conditions are read, and the regression calculation is performed. After performing a correlation check as necessary, a regression calculation is performed using the data in the regression data table, and the calculation result is displayed on the display device 28A. Further, regression calculation parameters, regression calculation setting contents, data stored in the regression data table, regression calculation results, and the like can be output to the line printer 28B. In the feedforward control, firstly, supra (2) the following equation (5) obtained by solving the wiping gas pressure P the equation P = (LS · D · L 1 2 · L 2 2) / (X · lnH) 2 ...... (5) and also (2) the strip - following equation (6) D = P · (X · lnH ) was solved for the distance D between the wiping nozzle ^{_{2 / (LS · L 1 2}} · L 2 2 With the constant L ₁ = L ₂ = 1 in (6), the wiping gas pressure P and the nozzle interval D are determined by the equations (5) and (6), and the adhesion amount is controlled by feedforward control. At this time, when obtaining the set value of the wiping gas pressure P,
For the line speed LS, the nozzle interval D, and the nozzle height H, the actual values up to that point are used. When calculating the nozzle interval D, the wiping gas pressure P is a constant corresponding to the nozzle pressure during ideal operation determined after the line is operated, and the line speed LS and the nozzle height H are actual values.
The value X of the following equation obtained by solving the above equation (1) is used as the plating adhesion amount equivalent value X. If b ² −4a (c−Ms) is negative, this value is set to zero. Since the above equation (1) always increases monotonically,
As the plating adhesion amount X, the larger value of X ₁ and X ₂ is used. The regression coefficients a, b, and c used in the equation (7) are, for example, gas type, nozzle type, nozzle angle, dull material or bright material, hot material or cold material, and plating adhesion set value.
Ms, the nozzle height H _P, the line speed LS _P, thickness, plate width, the strip unit tension, zinc bath temperature, by layering depending on the zinc bath prior to sheet temperature, etc., is possible to improve the accuracy of the regression calculation it can. Which of the stratified regression coefficients a, b, and c is used is automatically determined by command information from the process computer 26. Also, it can be set by the designation of the operator. According to the calculation result by the above-mentioned formula (6), the strip-
When moving the distance D between nozzles, it is not preferable in terms of operation if the distance D is changed every moment. Therefore, in practice, as shown in FIG. 3, for example, the distance D can be changed stepwise at intervals of 10 mm. y = f (x) (8) where x is a calculation result by the equation (6), and y is an actual nozzle position. In the present embodiment, hysteresis is provided when the nozzle interval D is increased and when the nozzle interval D is reduced.
Hunting is prevented. When the nozzle interval D is set, a correction according to a change in the thickness of the strip 12 is also performed. On the other hand, when there are no fluctuations in various actual values around the wiping nozzle such as the line speed LS, the plating amount M, the wiping gas pressure P, and the nozzle position, and the line is operating stably, the feedback control is performed. Specifically, the wiping gas pressure P is feedback-corrected based on the information of the plating adhesion meter 20 or the alloying degree meter 22 downstream of the wiping nozzles 14 and 16. The difference of the feed-forward control and the feedback control is in whether the constant L ₂ is updated, the other functions are basically the same. This feedback control is realized by correcting the model formula used for the feedforward control. Correction factor L ₂ in the feedback control,
It is calculated by the following equation. L ₂ = (X · lnH / L ₁ ) × {P / (LS · D)} ^1/2 (9) Here, the value X corresponding to the amount of coating applied is calculated by the above formula (7). . Incidentally, coating weight M used in calculation of the time in (7) is the actual value M _P rather than setting value Ms. Further, the nozzle height H, the wiping gas pressure P, the line speed LS, and the nozzle interval D are all time average values of the actual values from the previous control timing to the current control timing. The correction coefficient L ₁ is used is stored in the learning parameter table value (initial value is 1). Correction coefficient L ₂ calculated by the equation (9), while being stored in the feedback correction table, the following wiping gas pressure calculations, the strip - is used in the distance calculation between the nozzles. When the feedback control is being performed, the contents of the learning parameter table are not updated. This is the updating of the correction coefficient L ₁ by the learning control, because the update by the feedback control of the correction coefficient L ₂ is overcorrected to occur simultaneously. The calculation of the wiping gas pressure P and the strip-to-nozzle distance D during the feedback control is performed in the same manner as in the feedforward control. The correction factor L ₂ used at this time becomes the value calculated by the supra not 1 (9). Also, the manner of moving the strip-to-nozzle distance D according to the calculation result can be the same as in the case of feedforward control. The correction factor L _2, since the deposition amount information from the coating weight meter 20 or alloyed meter 22 is updated every transmitted, layering not is a single parameter. Switching between the feedforward control and the feedback control according to the present invention is performed as follows. That is, as shown in FIG. 4, a predetermined time t, which is variable in one second, for example, as shown in FIG. 4, with respect to three actual values of the actual value of the strip-wiping distance Dp, the actual value of the wiping gas pressure Pp, and the actual value of the line speed Lsp. For each, the change rate ln / t of each actual value (for example, l ₁ : Dp, l
₂ : Pp, l ₃ : LSp), and when all the change rates are equal to or less than the predetermined value xn, it is determined that the state is stable. or,
When the stable state is not established, the unstable state is determined. This stable state means that the operation around the wiping nozzle is stable, and does not mean that the amount of zinc deposited at the place where the weight meter is installed is stable. When the unstable state has occurred a predetermined number of times (for example, once) after the state has changed from the stable state to the unstable state,
Automatically switches from feedback control to feedforward control. Conversely, when the state changes from an unstable state to a stable state, the control is not immediately switched to the feedback control, but as shown in FIG. )), A predetermined distance (for example, 100 m) corresponding to the arrangement interval between them, and then, when the adhesion amount information is transmitted from the adhesion amount meter or the like a predetermined number of times (for example, twice), the feed-forward control is automatically switched to the feedback control. Switch to At this time, the influence of the unstable part may remain in the adhesion amount information of the first figure.
Feedback control is started using the attached amount information after the second time. Note that, even if the switching to the feedback control becomes possible, the switching to the feedback control may not always be performed depending on the setting state of the control mode. Further, in the present embodiment, the model equation (1) used in the feedforward control and the feedback control,
Learning is also performed to automatically improve the accuracy of (2). That is, (2) calculated from the various actual values of the correction coefficients L ₁ of formula, stored in the learning parameter table, at the time of feed-forward control and feedback control, using the data L ₁ stored in the learning parameter table.
The timing of the learning control is when the adhesion information is transmitted from the plating adhesion meter or the alloying degree meter 22, and is in a stable state in which feedback control is possible. Although this learning control and the feedback control is very similar functions, according to the learning control, is capable of long-term model type auto-tuning, correction coefficients L ₁ have been layering by other various parameters It has the feature of. In contrast, the feedback control may be considered a model formula auto-tuning function of the short term, the feedback correction coefficient L ₂ is not layering, it has become a single parameter. This learning control is based on the learning parameters in the model formula used in feedforward control.
It is achieved by calculating the L _1. Learning parameters L ₁ is calculated as follows. That is,
Assuming that the feedback correction coefficient L ₂ = 1, the following equation is derived from the above equation (2). L ₁ = X · LnH _P × {P _P / (LS _P · D _P )} ^1/2 (10) Here, the plating adhesion amount X is calculated by the above equation (7). At the time of this learning, the plating adhesion amount M
Is the actual value M _P rather than the set value Ms. Also, the regression coefficient a,
b, layering of c also to the actual value M _P coating weight as a parameter. Also, nozzle height H _P , wiping gas pressure P _P ,
Each of the line speed LS _P and the nozzle interval D _P is a time average value of each actual value in a period from the previous control timing to the current control timing, and is calculated from the actual result collection table. Note that blank data is excluded from the average value calculation. (10) the learning correction coefficient L ₁ calculated by equation, after filtering calculation shown in the following indicates, are stored in the learning parameter temporary table (not the learning parameter table itself). _{L 1 (n) = (1} -α) · L 1 + α · L 1 (n-1) ...... (11) where, L _{1 (n),} the value stored in the learning parameter temporary table, L ₁ Is calculated by equation (10), L
_{1 (n-1)} is a value read from the temporary learning parameter table before storing L _{1 (n)} , and α is a filtering constant (α = 0
Is no filter), α = 1 is filter infinity). When the feedback control is not performed, the contents of the learning parameter temporary table are stored in the learning parameter data. This process prevents concurrent updates of the learning correction coefficient L ₁ and the feedback correction coefficient L ₂ is, oversteering can be prevented. The learning control result data is stored in the regression calculation result data table immediately after the learning parameter calculation. If the target data does not exist or if the data is an upper / lower limit abnormal value, a blank column is stored in the regression calculation result data table. In the present embodiment, since there is provided a correction coefficient L ₂ by the feedback control in the model equation for the feed-forward control can be performed based on the feedforward control and the feedback control to a common expression, the control is simplified is there. FIG. 6 shows control results obtained by the method of the present invention and the conventional method in comparison with FIG. Operating conditions are as follows: speed 85m / min, plate thickness 1.2mm, plate width 850 ~
1200 mm, a basis weight target value 80 → 60g / m ^2. In the conventional method using only feedforward (FF) control, Fig. 6 (A)
As shown in (1), the transition is made with the deviation remaining. On the other hand, in the conventional method using only feedback (FB) control, as shown in FIG. In contrast, according to the method of the present invention, as shown in FIG.
Good results were obtained. In the above embodiment, the present invention is applied to pure zinc plating and alloy plating, but the type of plating to which the present invention is applied is not limited to this.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing the principle of plating weight control using a wiping gas, and FIG. 2 is a plating weight control method for performing a plating weight control method according to the present invention. FIG. 3 is a block diagram showing the overall configuration of the apparatus, FIG. 3 is a diagram showing a method of moving the strip-to-nozzle distance in an embodiment of the present invention, and FIG. FIG. 5 is a diagram for explaining a state in which feedback control is possible, and FIGS. 6 (A), (B) and (C) are diagrams for comparing control results obtained by the conventional method and the present invention method. FIG. 10 ... molten zinc bath, 12 ... strip, 14, 16 ... wiping nozzle, 20 ... plating weight meter, 22 ... alloying degree meter, 24 ... weight control device, 26 ... process computer, 28 Regression calculation computer.

Claims (1)

(57) [Claims] When a gas is sprayed from a wiping nozzle onto a surface of a plated strip passing through a molten metal bath to control the amount of plating, each of a strip-wiping nozzle distance, a wiping gas pressure and a line speed is controlled. In an unstable state in which at least one of the change rates exceeds a predetermined value, the feedforward control is performed, and the stable state in which the change rates are all equal to or less than a predetermined value continues, and the adhesion amount information has been received a predetermined number of times or more. A plating amount control method characterized in that feedback control is sometimes enabled.