Title of Invention

METHOD AND COATING PLANT FOR COATING A METAL STRIP

Abstract

Method for coating a metal strip with a coating metal, in particular for coating a steel strip with zinc or a zinc/nickel compound, by means of at least one galvanic cell through which, current flows and which contains an electrolyte through which the metal strip is led, the current effecting the disposition of a layer of coating metal on the metal strip, and the current being controlled by means of a monitor controller that has a process model and a controller part in such a way that a layer of a desired intended thickness is deposited on the metal strip, in the event of changes in the state of the coating plant, in particular when a new metal strip runs in or the coating falls below a minimum intended thickness, the controller part is matched to the altered state of the coating plant.

Full Text

-1A — Description The invention relates to a method and a coating plant for coating a metal strip with a coating metal, in particular for coating a steel strip with zinc or a zinc/nickel compound. A coating plant usually has one or more galvanizing cells, in which there is an electrolyte which contains the metals for the coating of the metal strip. The metal strip is led through the electrolyte liquid. In addition, anodes are arranged in the electrolyte. The metal strip is coated by means of an electric current between the anodes and the metal strip, which acts as cathode. In the process, the current is controlled in such a way that a layer of a desired intended thickness is deposited on the metal strip. However, in the industrial coating of metal strips there are two conflicting requirements. On the one hand, a predefined coating weight set point should, as far as possible, not be exceeded, since too thick a coating consumes an unnecessarily large amount of material and leads to higher costs. However, in order to be able to guarantee the desired properties of the metal strip, it must be ensured that the coating weight does not fall below a specific lower limit at any point on the strip. The object of the invention is to specify a method and an apparatus for coating a metal strip with coating metal which makes it possible to keep as accurately as possible to a predefined coating weight set point. In this case, compliance with a specific coating weight lower limit in particular is to be guaranteed, without the metal strip being coated to an unnecessarily high degree. According to the invention, the object is achieved by a method according to Claim 1 and an apparatus according to Claim 15. The current through the GR 97 P 3129 - 2 - galvanic cell is controlled as a function of the properties of the galvanic cell by means, of a monitor controller that has a process model and a controller part in such a way that a layer of a desired intended thickness is deposited on the metal strip, in which case, in the event of changes in the state of the coating plant, in particular when a new metal strip runs in or the coating falls below a minimum intended layer thickness, time constants of the controller part are matched to the altered state of the coating plant. In this way, it is possible to suppress measurement noise, and large controller movements, which can be caused by the process model not being an exact image of the coating plant, are adequately smoothed, and at the same time it is possible to react rapidly to external events, such as a new strip running into the plant or the occurrence of critical states, such as the coating weight falling below a minimum value. To this end, in a particularly advantageous way, the current is controlled by means of a dynamic low-pass filter as a function of the coating weight mean value, in particular as a function of the ratio of coating weight mean value and coating weight value ascertained by the process model, it being the case that when a new metal strip runs into the coating plant, the time constant of the dynamic low-pass filter for controlling as a function of the coating weight mean value is reduced and subsequently enlarged. In the case of a simple low-pass filter, the time constant, once set, would be effective from the start. Accordingly, the dynamic low-pass filter used according to the invention operates in such a way that it initially constitutes direct access at each strip start. After this, a time constant is set which rises slowly to a specific value guaranteeing adequate smoothing. The result of this is that the monitor controller sets the predefined coating weight set point at the strip start as rapidly as is at all possible, that is to say without any kind of smoothing. With an increase in the measured values, the dynamic low-pass filter then GR 97 P 3129 - 3 - changes into a mode of operation which smooths large control movements, in particular those caused by measurement noise and differences between the process model and the real process. In a further advantageous refinement of the invention, the current is controlled by means of a dynamic low-pass filter as a function of the coating weight minimum value, in particular as a function of the ratio of coating weight minimum value and coating weight value ascertained by the process model, it being the case that, when the coating weight falls below the minimum value, the time constant of the dynamic low-pass filter is reduced to a very small value, and above the coating weight minimum value is set to a large value ensuring adequate smoothing. In this case, it is particularly advantageous, when the coating weight exceeds the minimum value, initially to keep the output from the dynamic low-pass filter constant for a specific waiting time, and after this waiting time has expired to control the said output as a function of the coating weight minimum value, in particular as a function of the ratio of coating weight minimum value and coating weight ascertained by the process model, the time constant of the dynamic low-pass filter being set to a value ensuring adequate smoothing. Further advantages and inventive details emerge from the following description of exemplary embodiments, using the accompanying drawings and in conjunction with the subclaims. In detail: FIG 1 shows a coating plant, FIG 2 shows a coating weight control system having a monitor control system according to the invention, FIG 3 shows the structure of a monitor controller according to the invention. FIG 1 shows the basic structure of a coating plant in which rolled steel strips 2 can be coated with zinc or zinc/nickel. In the coating plant there are several, for example 10, galvanizing cells 1, in which GR 97 P 3129 - 4 - there is an electrolyte 12 which contains the metals for the coating. Different electrolytes are used for the coating with zinc (Zn mode) and for the coating with zinc/nickel (ZnNi mode). An electrolyte control system (not shown) ensures that the composition and the parameters of the respective electrolyte remain constant, so that good quality of the galvanizing is always ensured. The steel strip 2 which is to be coated is led through rollers 6, 7, 8, 9, 10 and runs through the individual galvanizing cells 1 at a specific speed in the direction of the arrow designated by reference symbol 13. Fitted in each cell are 4 anodes 4, 5, 2 anodes 5 for the top side and 2 anodes 4 for the bottom side of the strip 2. The current rollers 8, 9 above the cells 1 transmit the negative pole to the strip, which in this way becomes the cathode. The coating of the strip is carried out electrolytically, in that a specific current is impressed into the anodes 4, 5 with the aid of rectifiers. The effect of this current is that the zinc or zinc/nickel contained in the electrolyte is deposited on the strip surface. The currents are set separately for the anodes of the top side and the bottom side of the strip 2. As a result, the thicknesses of the coatings for the top side and the bottom side may be fixed separately. It is therefore possible not only to coat a strip 2 with equal thicknesses on both sides, but also to coat the top side and the bottom side with different thicknesses, independently of each other, by means of differently set currents . There is also the possibility of coating only one side of the strip. In this case, the first galvanizing cell is fed with a so-called flash current for the side which is not intended to be coated. A minimum coating is thus produced on this side, and is dimensioned such that it is just pickled off again in the remaining cells by the acid of the electrolyte. This prevents the acid of the electrolyte from dissolving iron out of the uncoated side of the strip. GR 97 P 3129 - 5 - In order for it to be possible to operate the coating plant continuously, the individual strips are welded to one another upstream of the plant. The welds produced in this way are tracked, so that it is known at any time in which part of the plant the old strip is still located and where the new strip is already to be encountered. Downstream of the plant, the strips are separated again. Each strip is either wound onto a coil or is further subdivided and wound onto several coils. The coating plant is intended to apply a coating with a precisely fixed thickness in each case to the top side and the bottom side of the strip. These set points are to be complied with as precisely as possible. In particular, the thickness must not fall below a specific minimum at any point on the strip, since otherwise the required properties of the strip cannot be guaranteed. On the other hand, too high a thickness is not desired, since it consumes material unnecessarily and leads to higher costs. A coating weight control system ensures compliance with these stipulations. Therefore, at a specific distance downstream of the galvanizing cells 1, there is a coating weight gauge 3, which registers the thicknesses of the coatings on the top side and the bottom side of the strip 1. Based on these measured values, the coating weight control system influences the coating, by calcu-lating for the anodes 4, 5 of the galvanizing cells 1 the necessary currents, which are then fed as manipulated variables to the appropriate rectifiers. The coating weight control system controls the coating of the top side and the bottom side of the strip 1 separately. In addition, when there is a weld in the plant, the said system has to control the old strip and the new strip separately. Therefore, the coating weight control system must be present a total of four times. The coating weight control system has the task of setting the currents for the anodes 4, 5 of the galvaniz-ing cells 1 continuously in such a way that the desired coating weight of the strip 1 is always reached, specifi- GR 97 P 3129 - 6 - cally irrespective of which operating conditions prevail at that time. The quantity of zinc or zinc/nickel, which is precipitated from the electrolyte and coats the strip 1, is proportional to the product of current and time. i The strip area coated per unit time is the product of strip width and strip speed. If it is therefore desired to calculate the coating weight, measured in g/m2, then the current, the strip width and the strip speed must be taken into account. The coating weight control system has the converse task, namely of calculating the current required for a predefined coating weight set point. This is performed by means of the following equation: where Itotal is the total rectifier current [A] G*mean is the coating weight set point [g/m2] bstriP is the strip width [m] vstrip is the strip speed [m/min] cs is the separation equivalent [g/Ah] ηcells is the cel1 efficiency kcontrol is the controller output. The significant influencing variables in the current calculation are thus the coating weight set point, the strip width and the strip speed. The factor 60 arises from the units used as a result of the conversion min/h. The separation equivalent cs is 1.2193 g/Ah for zinc. Since the acid of the electrolyte in the galvanizing cells dissolves part of the coating from the strip again, the actual coating weight is somewhat lower than that calculated theoretically. This effect is taken into account by the cell efficiency ΗCELLS • The coating weight control system determines this cell efficiency ηcells and adapts it to the prevailing operating conditions with the aid of the variable kcontrol. In this case, kcontrol serves as a controller output to set the current and hence the coating weight in GR 97 P 3129 - 7 - such a way that the predefined coating weight set point is reached. FIG 2 shows how this takes place in principle. The current calculation 25, which is supplied with the variables G*mean, bstrip, vstrip# ηcells and Kcontrol ,sets the coating weight at the entry to the coating plant via the current. At the exit, a coating weight gauge 22 registers the actual coating weight and makes the measured values Gmin and Gmean available, Gmin being the coating weight minimum value and Gmean the coating weight mean value. The following set points are associated with these measured values: G*min coating weight lower limit G*mean coating weight set point Based on these measured values and set points, the coating weight control system controls the coating weight and, for this purpose, calculates the controller output kcontrol. When setting up the control concept of the coating weight control system, it has transpired that it is expedient to perform a subdivision into the following 3 components: - monitor controller 27 - fuzzy system 28 - on-line training 29 of the fuzzy system The monitor controller controls the coating weight. To this end, it evaluates the measured values Gmin and Gmean . points G*min and G*mean and, from these, calculates the controller output kcontrol. This is effected in such a way that the conditions Gmin ≥ G*min and Gmean = G*mean are complied with as well as possible. The first condition states that the coating weight must not fall below the lower limit. The second condition expresses the fact that the predefined coating weight set point is to be complied with. The cell efficiency ηcells depends on the respective operating conditions of the plant. The variables GR 97 P 3129 - 8 - that are taken into account for its calculation are in this case: - current density of the anodes - pH of the electrolyte - temperature of the electrolyte These 3 variables are used as input variables of a fuzzy system 28, which provides the cell efficiency ηFuzzy at its first output. The higher-order automation level, which is not illustrated in FIG 2, also calculates for each strip a cell efficiency, which is designated by ηLevel2. At each strip start, the difference between these two cell efficiencies ηmemory = ηLevel2 - ηFuzzy is stored and subsequently, during the coating of the strip, added to the cell efficiency of the fuzzy system: ηcells = ηmemory + ηFuzzy The result of this is that each strip starts with the cell efficiency ηcells = ηLeve12 Predefined by the higher-order automation system, and thereafter the fuzzy system 28 can change this cell efficiency ηcells • At the beginning, the fuzzy system 28 is pre-filled with simple, verbally formulated expert knowledge. During the operation of the plant, the on-line training 29 ensures automatic adaptation of the fuzzy system 28 to the actual plant behaviour. To this end, in the present example, the prevailing situation is fed to the on-line training 29 in the form of the variable iFuzzy of the fuzzy system 28. In addition, the prevailing cell efficiency used in the current calculation is taken into account. This efficiency is identified by the variables ηcells and Kcontrol, which are also fed to the on-line training 29. In order for it to be possible to assess the coating behaviour of the plant, the coating weight set point G*mean and the measured coating weight Gmean are also fed to the on-line training. The actual cell efficiency of the plant is calculated from all these variables. This efficiency is used in order to adapt the fuzzy system step by step, so that it represents the actual plant behaviour better and GR 97 P 3129 - 9 - better. As a result, the fuzzy system is always able to determine the optimum cell efficiency. The present coating process extends from the galvanizing cells as far as the coating weight gauge 22. The strip 20 running through is coated in the galvanizing cells. The monitor controller 27 influences the coating by means of controller outputs which are converted in the current calculation. However, the effects of these controller outputs are only registered when the relevant strip section has been transported as far as the gauge. Depending on the arrangement of the gauge, and depending on the strip speed, the result may be relatively long transport times. The monitor controller 27 used is designed in such a way that it has good control dynamics, even given long transport times. Its structure is shown by FIG 3. The strip 3 0 runs through the coating plant in the direction of the arrow 33. The coating weight gauge 31 registers the actual coating weight and provides the measured values Gmin and Gmean. The monitor controller fixes the controller outputs kcontrol which are used in the current calculation. A plant model 38 operates in parallel with the coating plant. This model is supplied, at its input, with the quotient This quotient is also contained in the current calculation. It is a measure of the coating weight applied at any one time. The plant model simulates the behaviour of the coating plant. It continuously calculates the coating weight of the strip applied in the galvanizing cells and tracks this as far as the coating weight gauge. The coating weight GM is then output at the output of the plant model. By means of the plant model 38, the two coating weights Gmean and GM are synchronized, so that they can be - 10 - placed in a relationship with each other. If the cell efficiency used in the current calculation is correct, it is then true that Gmean = GM. Otherwise, the cell efficiency must be corrected using This value kmean could in principle be output directly as manipulated variable kcontrol. However, it is particularly advantageous to perform smoothing, which is done by the dynamic low-pass filter 39. The output variable kLpl from the latter is the manipulated variable which is needed in order to control the coating weight mean value Gmean, in order to achieve Gmean - G*mean. A further measured value, namely the coating weight minimum value Gmin, comes from the coating weight gauge. The procedure with this measured value is exactly the same as that with the coating weight mean value Gmean. Hence, the value is calculated and smoothed in a particularly advantageous way using the dynamic low-pass filter 40. The output variable kLP2 from the latter is further multiplied by G*mean and divided by G*min, in order that the measured value Gmin is compared not with the set point G*mean, which is contained in GM, but with G*min: This value is the manipulated variable which is needed in order to control the coating weight minimum value Gmin, in order to achieve Gmin = G*min. The minimum of this manipulated variable and of the abovementioned manipulated variable kLpl is the manipulated variable kcontrol, which is output by the monitor controller: - 11 - The monitor controller thus controls both the coating weight mean value Gmean and the coating weight minimum value 6min. It thus contains two controllers. Of the two manipulated variables, the smaller is output, since this leads to a higher coating weight. This achieves the situation where, in normal circumstances, the monitor controller controls the coating weight mean value, in order to achieve Gmean = G*mean. However, if in this case the coating weight minimum value would lie below the coating weight lower limit, then the monitor controller controls the coating weight minimum value, in order to achieve Gmin = G*min. In this case, however, Gmean > G*mean. The plant model 38 simulates the behaviour of the coating plant. It consists of the following three partial models: - coating model 35 - transport model 36 - averaging 37 The coating model calculates the coating weight of the strip that is applied in the galvanizing cells. The transport model tracks the coating weight of the strip from the galvanizing cells as far as the coating weight gauge. As already explained, the monitor controller contains two controllers, one for the coating weight mean value Gmean and a second for the coating weight minimum value Gmin. The dynamics of the first controller are set by the dynamic low-pass filter 39, and the dynamics of the second controller are set by the dynamic low-pass filter 40. These two dynamic low-pass filters fulfil the following functions: - Errors and noise in the measured values are smoothed. - In general, the behaviour of the plant model does not agree exactly with the behaviour of - 12 - the coating plant. In particular, slight inaccuracies in the transport time may result. When the coating weight then changes, the variables Gmean and Gmin, on the one hand, and the variable GM, on the other hand, do not change synchronously. As a result, pulses occur in the variables Kmean and Kmin.These pulses are smoothed by the low-pass filters and hence reduced in size. - Changes in the manipulated variable kcontrol are made after smoothing. The dynamic low-pass filter 39 has its parameters set by the smoothing constant nLpl. This smoothing constant corresponds to a time constant. It specifies the number of measured values over which the smoothing extends. If, for example, the coating weight gauge supplies new measured values after 1 min in each case and nLP1 = 3 then the low-pass filter operates with a time constant of 3 min. In the case of a simple low-pass filter, the smoothing constant nLP1 set as a parameter would be effective at any time from the start. Accordingly, the dynamic low-pass filter 39 used according to the invention operates in such a way that it initially permits direct access at each strip start. After this, use is made of a smoothing constant which rises slowly from 1 to nLP1. This rise is implemented by means of a further low-pass filter with the smoothing constant nLP1. This means that at each strip start, as soon as the first measured values have arrived, kLpl = kmean because of the direct access. The result of this is that the monitor controller sets the predefined coating weight set point at the strip start as rapidly as at all possible, that is to say without any smoothing. After this, the smoothing effect of the low-pass filter increases slowly. The dynamic low-pass filter 40 has its parameters set by the following values: nLP2 down smoothing constant downwards - 13 - nLP2 up smoothing constant upwards nLP2 wait wait constant, following a downward movement, until an upward movement is possible again. The smoothing constant downwards nLP2 down is used when the output variable kLP2 of the low-pass filter becomes smaller. This is the case, for example, when the coating weight minimum value Gmin suddenly falls below the coating weight lower limit G*min. In order that in this case kLP2 and hence kcontrol can be reduced rapidly, as a result of which the coating weight increases, the smoothing constant downwards nLP2 down should be selected to be relatively small. The smoothing constant upwards nLP2 up is used when the output variable kLp2 of the low-pass filter becomes larger. This smoothing constant can have its parameters set such that adequate smoothing is achieved. In order that the coating weight is not reduced immediately again in the event of an increase in the measured value Gmin ,the wait constant nLP2 wait ensures that this only takes place after a further nLP2 wait measured values have arrived. A significant property of the monitor controller is that it operates without a persistent control deviation, which may be demonstrated by the following consideration. It is initially assumed that kcontrol = kl The plant model then outputs the value If the coating weight mean = K2 . G*mean is now measured in the plant, then the value - 14 - is calculated in the monitor controller and, following the transient response of the dynamic low-pass filter 1, is output as manipulated variable kcontrol = kl . k2 Kcontrol is therefore multiplied by the factor k2 as com-pared with the original value. As a result, both the coating weight in the galvanizing cells of the plant and the input variable of the plant model decrease by the factor k2. Following the transport of the strip through the plant, the coating weight gauge registers this decrease and makes the measured value Gmean = Gmean available. At the same time, the plant model also outputs the reduced value Hence, the value is also calculated and output as manipulated variable Kcontrol = Kl . K2 The monitor controller therefore controls out deviations from the set point without a persistent control deviation. It thus has an integrating behaviour. In this case, the monitor controller uses the plant model to a certain extent as a memory for the previous controller outputs, in order to calculate new controller outputs based on these. Furthermore, the monitor controller presented according to the invention is characterized by the following properties and advantages with respect to conventional controllers: - At the strip start, deviations from the set - 15 - point are controlled out as rapidly as at all possible, that is to say without any smoothing. After this, the smoothing effect of the dynamic low-pass filters sets in slowly. If a simple I controller were to be used as monitor controller, then, because of the transport time in the coating plant, this could be set only to be very slow. The greater the transport time, the slower an I controller would have to be set. This disadvantage is avoided by the monitor controller presented here. Its dynamics can be fixed as desired, irrespective of the transport time, that is to say, for example, in accordance with technological aspects. The result of the plant model contained in the monitor controller is that the calculated values kmean and kmin do not depend on the output manipulated variable kControl, since kcontrol influences the measured values Gmean and Gmin and the variable GM in the same way, and these influences compensate one another. The stability of the monitor control system is thus ensured. This is true irrespective of how the dynamics of the monitor controller are set by means of the dynamic low-pass filters 1 and 2. Changes in the set point G*mean are directly implemented without a time delay, since they enter directly into the current calculation. In parallel with this, they are also present at the input of the plant model. This means that they influence the values Gmean, Gmin and GM to the same extent, so that the values kmean and kmin are not influenced here either. This means that, in the case of set point changes, no transient-response processes occur. This is also true if the coating weight lower limit G*min is changed. 16. We Claim: 1. Method for. coating a metal strip with a coating metal, in a coating plant, in particular for coating a steel strip with zinc or a zinc/nickel compound, by means of at least one galvanic cell through which current flows and which contains an electrolyte through which the metal strip is led, the current effecting the deposition of a layer of coating metal on the metal strip, and the current being controlled by means of a monitor controller that has a process model and a controller part in such a way that a layer of a desired intended thickness is deposited on the metal strip, characterized in that, in the event of changes in the state of the coating plant, in particular when a new metal strip runs in or the coating falls below a minimum intended layer thickness, a time constant of the controller is adjusted to match the altered state of the coating plant. 2. Method as claimed in claim 1 wherein the current is controlled by means of a dynamic low-pass filter (39) as a function of the coating weight mean value (G mean), in particular as a function of the ratio of coating weight mean value (G mean) and coating weight value (GM) ascertained by the process model. 3. Method as claimed in claim 2, wherein, when a new metal strip runs into the coating plant, the time constant of the dynamic low-pass filter (39) for controlling as a function of the coating weight mean value (G mean) is reduced and subsequently enlarged. 4. Method as claimed in claim 3, when a new metal strip runs into the coating plant, the time constant of the dynamic low-pass filter (39) for controlling as a function of the coating weight mean value (G mean) is set to zero and subsequently, particularly continuously, enlarged. Method as claimed in claim 4, wherein when a new metal strip runs into the coating plant, a smoothing constant nLP1 that is equivalent to the time constant of the dynamic low-pass filter (39) for controlling as a function of the coating weight mean value (G mean) is set to one and subsequently enlarged in accordance with the relationship. 17. CK being a constant, Lstrip being the length of the metal strip from the entry into the galvanic cell as far as the coating weight gauge, Vstrip being the speed of the metal strip and ∆tM being the time interval at which the coating weight gauge supplies measured values. 6. Method as claimed in claim 5, wherein said CK is at least equal to one, advantageously at least equal to two. 7. Method as claimed in claims 1, 2, 3, 4, 5 or 6, wherein the current is controlled by means of a dynamic low-pass filter (40) as a function of the coating weight minimum value ( Gmin), in particular as a function of the ratio of coating weight minimum value (Gmin) and coating weight value ( GM) ascertained by the process model. 8. Method as claimed in claim 7, wherein when the coating weight falls below the lower limit set point ( G *min ), the time constant of the dynamic low -pass filter (40) for controlling as a function of the coating weight minimum value (Gmin) is reduced, in particular to a very small value. 9. Method as claimed in claims 7 or 8, wherein the time constant of the dynamic low- pass filter(40) for controlling as a function of the coating weight minimum value (Gmin) above the coating weight lower limit set point ( G *min) is set to a large value ensuring adequate smoothing. 10. Method as claimed in claims 7 , 8 or 9, wherein after the coating weight has exceeded the lower limit set point ( G *min ) , the output from the dynamic low-pass filter (40) for controlling as a function of the coating weight minimum value (Gmin) is kept constant for a specific waiting time ( nLP2, wait)- 11. Method as claimed in one of the preceding claims, wherein the calculation of the current ( itotal) is carried out as a function of at least one of the variables coating weight set point ( G *mean) , strip width ( bstrip), strip speed ( Vstrip) , separation equivalent ( CS), efficiency ( ncellS) of the galvanic cell (1) or controller output (KControl) from the current-control system. 12. Method as claimed in claim 11, wherein the calculation of the current ( itotal ) is carried out as a function of the variables coating weight set point ( G *mean ) , strip width ( bstrip) , strip speed ( Vstrip), separation equivalent ( Cs) efficiency ( ŋcells) of the galvanic cell (1) or controller output ( Kcontrol) from the current control system. 18. 13. Method as claimed in claim 12, wherein the calculation of the total rectifier current (itotal) is carried out in accordance with the relation-ship: Where I total is the total rectifier current ( A). G *mean is the coating weight set point (g/m2). bstrip is the strip speed (m/min). Cs is the separation equivalent (g/Ah) ηcells is the efficiency of the galvanic cell. Kcontrol is the controller output from the current control system. 14. Coating plant for coating a metal strip with a coating metal, for carrying out the method as claimed in one of the preceding claims, comprising at least one computing device and at least one galvanic cell through which the metal" strip is led, the current effecting the deposition of a layer of coating metal on the metal strip, and the computing device controlling the current by means of a monitor controller having a process model and a controller part in such a way that a layer of a desired intended thickness is deposited on the metal strip, characterized in that, in the event of changes in the state of the coating plant, in particular when a new metal strip runs in or the coating falls below a minimum intended layer thickness, a time constant of said controller is adjusted to the altered state of the coating plant.

Documents:

00292-cal-1998 abstract.pdf

00292-cal-1998 claims.pdf

00292-cal-1998 correspondence.pdf

00292-cal-1998 description(complete).pdf

00292-cal-1998 drawings.pdf

00292-cal-1998 form-1.pdf

00292-cal-1998 form-2.pdf

00292-cal-1998 form-3.pdf

00292-cal-1998 form-5.pdf

00292-cal-1998 general power of attorney.pdf

00292-cal-1998 letters patent.pdf

00292-cal-1998 priority document.pdf

292-CAL-1998-(10-10-2012)-FORM-27.pdf

292-CAL-1998-CORRESPONDENCE.pdf

292-CAL-1998-FORM-27.pdf

292-cal-1998-granted-abstract.pdf

292-cal-1998-granted-acceptance publication.pdf

292-cal-1998-granted-claims.pdf

292-cal-1998-granted-correspondence.pdf

292-cal-1998-granted-description (complete).pdf

292-cal-1998-granted-drawings.pdf

292-cal-1998-granted-examination report.pdf

292-cal-1998-granted-form 1.pdf

292-cal-1998-granted-form 2.pdf

292-cal-1998-granted-form 3.pdf

292-cal-1998-granted-form 6.pdf

292-cal-1998-granted-gpa.pdf

292-cal-1998-granted-letter patent.pdf

292-cal-1998-granted-others.pdf

292-cal-1998-granted-priority document.pdf

292-cal-1998-granted-reply to examination report.pdf

292-cal-1998-granted-specification.pdf

292-cal-1998-granted-translated copy of priority document.pdf

292-CAL-1998-PA.pdf