Method for measuring thickness of workpieces in rolling mills

Abstract

To provide a method for determining the present thickness of a workpiece while it is processed in a rolling mill (100).SOLUTION: The method includes acquiring a data signal reflecting the time dependence of eddy current decay in the workpiece caused by an applied pulsed magnetic field (S102), determining a thickness parameter value based on the acquired signal, the thickness parameter value being determined from samples in the data signal, the thickness parameter value being dependent on the ratio between the thickness of the workpiece and the resistivity of the workpiece (S104), computing the ratio between a reference thickness value of the workpiece and the thickness parameter value to thereby provide an instantaneous resistivity value (S106), determining a mean resistivity value based on the instantaneous resistivity value (S108), and providing an output signal based on the mean resistivity of the workpiece and the thickness parameter value, the output signal indicative of the determined present thickness of the workpiece (S110).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for determining the thickness of a workpiece while it is being processed in a rolling mill, a control unit and a rolling mill. [Background technology]

[0002] Metal rolling generally involves producing a metal workpiece having a reduced and uniform thickness by rolling the metal workpiece between two rotating work rollers.

[0003] To ensure high product quality, the thickness of workpieces is accurately monitored and controlled. It is particularly important to monitor rapid thickness variations in workpieces such as metal plates, even very thin metal plates. Based on the measured thickness, the operation of rolling mills can be controlled. In particular, to ensure the quality of the final product, rolling mills in the final position, i.e., the last rolling mill in a rolling mill process line, can be controlled based on thickness measurements upstream of the final position.

[0004] Commonly used pulsed eddy current measurement techniques are based on measuring the eddy currents induced in a metal plate by a rapidly changing magnetic field applied to the plate, from which the resistivity and thickness of the metal plate can be extracted.

[0005] However, for significantly thinner plates, conventional methods are not sufficiently accurate and often suffer from noisy measurements, thereby limiting their applicability below the lower limit of metal plate thickness.

[0006] It is therefore desirable to improve the accuracy of thickness measurements in rolling mills, especially for relatively thin metal plates. Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above and other drawbacks of the prior art, it is an object of the present invention to provide a method for determining with improved accuracy the thickness of a workpiece while it is being processed in a rolling mill. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided a method of determining the current thickness of a workpiece while it is being processed in a rolling mill, the method comprising the step of obtaining a data signal reflecting the time dependence of eddy current decay in the workpiece caused by an applied pulsed magnetic field.

[0009] The method further includes determining a thickness parameter value based on the acquired signal, the thickness parameter value being determined from samples in the data signal, and the thickness parameter value being dependent on the ratio of the thickness of the workpiece to the resistivity of the workpiece.

[0010] The method further includes calculating a ratio of the reference thickness value of the workpiece to the thickness parameter value, thereby providing an instantaneous resistivity value.

[0011] Additionally, an average resistivity value is determined based on the instantaneous resistivity values, and an output signal is provided that is indicative of the current thickness of the workpiece based on the average resistivity of the plate and the thickness parameter value.

[0012] The present invention is based, at least in part, on an implementation for processing a thickness parameter value, which reflects the ratio of the thickness of a workpiece to the resistivity of the workpiece, to determine the thickness of the workpiece. Thus, rather than attempting to derive thickness directly from the thickness parameter value and an uncertain resistivity value that is, for example, temperature-dependent, the thickness parameter value can be used together with a reference thickness value to obtain an instantaneous resistivity value that can depend on thickness variations of the workpiece, e.g., a metal plate, depending on how the reference thickness value is obtained. Based on this instantaneous resistivity value, the actual average resistivity value of the plate can be determined, thereby eliminating the need to use the uncertain resistivity value involved in the thickness parameter value dependency.

[0013] The proposed method allows thickness measurements to be obtained with improved accuracy, at least for thin workpieces, which in turn leads to improved control of the thickness of the workpieces being rolled in the rolling mill, which can result in increased production speeds and ultimately improved quality of the processed workpieces.

[0014] The dependence of the thickness parameter value on the ratio of workpiece thickness to resistivity means that the thickness parameter value reflects this ratio. The thickness parameter value depends almost entirely on this ratio, which is thickness divided by resistivity, although there may be a few other dependencies.

[0015] Preferably, the thickness parameter value can be determined from samples in the data signal after a predetermined time delay. This time delay is sufficiently long so that any initial large signal transients caused by the pulsed magnetic field are avoided in the sampled data signal. Furthermore, this time delay is sufficiently long so that the time dependence of eddy current decay in the workpiece depends primarily on the ratio of thickness to resistivity, but also on the distance to a measuring device that detects the magnetic field generated by the eddy currents to determine the decay, which is often provided as a receiver coil. Thus, the thickness parameter value can be calculated based on the time dependence of eddy current decay.

[0016] More precisely, the thickness parameter value is preferably determined from the time derivative of the magnetic flux generated by the eddy currents in the workpiece after a predetermined delay and the distance between the workpiece and the measuring device. For example, if this distance is constant, the thickness parameter value can be determined by detecting the time dependence of the eddy current decay and then using a model that relates the time dependence of the eddy current decay to the thickness parameter value, i.e., the ratio of the thickness to the resistivity of the workpiece. This model may be established theoretically, but may also be based on a large amount of conventional measurements.

[0017] As mentioned above, eddy currents can be detected by a receiver coil positioned at a distance from the workpiece. In such cases, the time derivative of the magnetic field generated by the eddy currents in the workpiece induces a voltage signal in the receiver coil. This voltage signal is preferably amplified and integrated to produce the acquired signal.

[0018] The thickness parameter value can be determined based on a theoretical model.

[0019] However, according to one embodiment, the thickness parameter value is determined based on an empirically derived model relating the time dependence of eddy current decay to the ratio of workpiece thickness to workpiece resistivity. Through multiple measurements or observations of the time dependence of eddy current decay versus thickness parameter value for various workpieces of varying thickness and resistivity, an empirical model relating the thickness parameter to the derivative of eddy current decay can be formed. To develop an accurate model, an empirical model is advantageously used.

[0020] According to an embodiment, the time dependence of eddy current decay can be measured by a magnetic field measuring device arranged at a distance from the workpiece, and this distance is determined from samples in the data signal during the initial stage of eddy current decay, and in this case, the thickness parameter value is further determined based on the determined distance. Thus, the distance between the measuring device and the workpiece can be advantageously determined from the data signal itself. As is well known, the magnetic field strength decays with the distance to the source. This knowledge can be used to calculate the distance from the measuring device to the workpiece instead of measuring the distance using a separate measuring means such as an optical or capacitive measuring device.

[0021] According to an embodiment, the empirically determined model can relate the time dependence of eddy current decay to the ratio of workpiece thickness to workpiece resistivity for various distances between the workpiece and the magnetic field measuring device. The model can thus advantageously take into account the distance between the workpiece and the magnetic field measuring device, thereby providing a more accurate model, especially in measurement situations where the distance between the measuring device and the workpiece varies rapidly.

[0022] According to a preferred embodiment, the average resistivity value can be determined by filtering the instantaneous resistivity value. This filtering can be a low-pass time-domain filter. Thus, the instantaneous resistivity value calculated from the measured thickness parameter value is passed through a low-pass time-domain filter, and the output of this time-domain filter is the average resistivity. Since the resistivity of the workpiece can be considered to vary slowly, the instantaneous resistivity thus obtained is primarily dependent on the thickness variations of the workpiece. Therefore, by filtering the instantaneous resistivity with a time-domain filter, the actual average resistivity of the workpiece can be advantageously obtained.

[0023] The length and characteristics of the time domain filter, which may be a digital filter, are selected depending on the particular implementation at hand.

[0024] The concept of the present invention can be applied in at least three different main implementations depending on how the reference thickness value is obtained. Thus, the reference thickness value can be obtained in a variety of possible ways.

[0025] First, there is the case where the reference thickness value reflects the instantaneous thickness of the workpiece, i.e., the instantaneous thickness can be measured as the workpiece is processed in the rolling mill. This is often the case for workpieces that are thick enough for the thickness gage device to measure the workpiece thickness with some acceptable accuracy. In this case, a filter is used to reduce measurement noise from the instantaneous thickness measurement, and in this case, the filter should be as short as possible while still providing sufficient noise reduction.

[0026] Second, the reference thickness parameter value can be provided as an estimated or predetermined average thickness, i.e., nominal thickness, of the workpiece. For example, the predetermined average thickness value can be supplied or measured prior to processing of the workpiece in a rolling mill.

[0027] In this case, the ratio of the reference thickness value, provided as the nominal thickness value, to the thickness parameter value, which forms the instantaneous resistivity value, depends on the inverse of the workpiece thickness. However, if the instantaneous resistivity value is passed through a time-domain filter, the output signal will be a high-pass filtered value of the workpiece thickness, i.e., this signal will reflect the thickness variation around the average or nominal thickness. According to an embodiment, the high-pass filtered value of the thickness variation can be used for feedforward control; if so, the length of the filter and its time-domain characteristics should be selected according to the parameters and speed of the overall control loop.

[0028] Third, the reference thickness value may be provided by an inherently slow measurement, either due to a slow measurement device or a slow measurement method. Here, "slow" means that the time constant of the reference thickness value measurement is slower than the time constant of the thickness parameter value measurement. For example, in the case of a moving window filter, the time constant refers to the window length of the filter. The time constant may also refer to the overall frequency response of the measurement or filter. For example, one approach to obtaining a reference thickness value is to measure the thickness behind the next downstream processing roller in a rolling mill and estimate the thickness reduction of the workpiece using the workpiece velocity measured before and after the processing roller. These devices generally produce results inherently slowly or require long filter times. In this third case, the thickness value measured by the thickness measurement device can be filtered using a time-domain filter to provide the reference thickness value. This improves the accuracy of the thickness parameter determined for the workpiece.

[0029] Preferably, the resulting time constant for the reference thickness value filtered by the time-domain filter is matched to the time constant of the time-domain filter used to filter the thickness parameter value. In other words, the thickness parameter value can be filtered before forming a ratio with the filtered reference thickness value. By matching the time constant, the changes in each signal, i.e., the reference thickness value and the thickness parameter value, are equal, and the ratio between them does not change. In other words, in the case where the reference thickness value and the thickness parameter value are filtered by filters with equal time constants or frequency responses, the instantaneous resistivity value is equal to the average resistivity of the workpiece. This is particularly advantageous when the measurement device used to determine the reference thickness value is slow, thereby increasing the speed at which a signal representative of the current thickness of the workpiece can be determined. Thus, embodiments of the present invention can result in an increase in the measurement speed of such slow devices, which, when applied to measurements in a rolling mill, increases the resolution of the thickness information along the workpiece. The methodology provided by the embodiments herein allows updated current thickness of the workpiece to be obtained more frequently, which can improve the time between updates even with inherently slow thickness measurement devices.

[0030] According to an embodiment, the method can include providing the output signal as a feedforward control signal to a rolling mill, i.e., advantageously for controlling the operation of a set of processing rollers downstream in the rolling mill, i.e., before the workpiece reaches those processing rollers in a feedforward manner, which advantageously increases the quality of the final product, for example, resulting in improved thickness control.

[0031] Thus, according to an embodiment, the method may include controlling the operation of a rolling mill stand supporting a set of work rollers of the rolling mill based on the feedforward control signal, thereby varying the thickness of the workpiece.

[0032] According to an embodiment, the output signal may be based on a determined thickness calculated by multiplying the average resistivity of the workpiece by a thickness parameter value.

[0033] According to an embodiment, the reference thickness value is a thickness value measured by a thickness measurement device of the rolling mill, which may be, for example, an x-ray thickness measurement device, an isotope thickness measurement device, an optical-based thickness measurement device, or the like.

[0034] The embodiments described herein are advantageously applied to workpieces that are metal plates.

[0035] According to a second aspect of the present invention, there is provided a control unit configured to generate an output signal indicative of a current thickness of a workpiece while it is being processed in a rolling mill, the control unit being configured to: acquire data signals reflecting the time dependence of eddy current decay in the workpiece caused by an applied pulsed magnetic field; determine a thickness parameter value based on the acquired signals, where the thickness parameter value is determined from samples in the data signals and the thickness parameter value is dependent on a ratio of the thickness of the workpiece to a resistivity of the workpiece; calculate a ratio of a reference thickness value of the workpiece to the thickness parameter value to thereby provide an instantaneous resistivity value; determine an average resistivity value based on the instantaneous resistivity value; and provide an output signal indicative of the determined current thickness of the workpiece based on the average resistivity of the plate and the thickness parameter value.

[0036] Further advantages and features of the second aspect of the invention are largely similar to those previously described in relation to the first aspect of the invention.

[0037] According to a third aspect of the present invention, there is provided a rolling mill comprising a control unit according to an embodiment of the present invention, a set of work rollers configured to process a workpiece between the work rollers to achieve a predetermined workpiece thickness, and a rolling mill stand supporting the work rollers, wherein the rolling mill stand is controllable based on the output signal as a feedforward signal to vary the distance between the work rollers and thereby vary the thickness of the workpiece being processed in the rolling mill.

[0038] Further advantages and features of the third aspect of the invention are largely similar to those previously described in relation to the first and second aspects of the invention.

[0039] Further features of the present invention and advantages offered by the present invention will become apparent upon review of the appended claims and the following description. As will be apparent to those skilled in the art, various features of the present invention can be combined to create embodiments different from those described below without departing from the scope of the invention. [Brief explanation of the drawings]

[0040] These and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. [Figure 1] FIG. 1 conceptually illustrates a workpiece being processed in a rolling mill according to one embodiment of the present invention. [Figure 2] 1 is a block diagram illustrating the inventive concept according to an embodiment of the present invention. [Figure 3] 2 is a flowchart of method steps according to an embodiment of the present invention. [Figure 4] 2 is a flowchart of method steps according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] In this detailed description, various embodiments of the present invention will be described herein with reference to specific implementations. In describing the embodiments, specific terminology will be used for the sake of clarity. However, it is not intended that the present invention be limited to the specific terminology so selected. While specific exemplary embodiments will be described, it should be understood that this is done for illustrative purposes only. As will be apparent to those skilled in the art, other components and configurations can be used without departing from the scope of the present invention.

[0042] 1 conceptually illustrates a rolling mill 100 having a pair of work rollers 102a and 102b adapted to process a work piece 104. The work rollers 102a-b rotate while a work piece 104, e.g., a metal plate, is fed between the work rollers 102a-b. The work rollers 102a-b reduce the thickness of the work piece, as will be appreciated by those skilled in the art.

[0043] In this case, it is desirable to accurately control the thickness of the workpiece 104 delivered downstream of the processing rollers 102a-b. For this purpose, a pulsed eddy current technology device 106 is often used, which is based on applying a pulsed magnetic field to the workpiece 104. The pulsed eddy current technology device 106 detects eddy currents induced in the workpiece 104 to estimate the thickness of a portion of the workpiece before it reaches the processing rollers 102a-b. The present invention is concerned with improving this thickness estimation. For example, for thin workpieces, e.g., metal plates with a thickness of less than 1 mm, pulsed eddy current technology is noisy and not sufficiently accurate.

[0044] A control unit 108 is shown conceptually here and is configured to generate an output signal representative of the thickness of the workpiece 104 as it is being processed in the rolling mill.

[0045] The control unit 108 is configured to obtain a data signal S reflecting the time dependence of eddy current decay in the workpiece 104 caused by the applied pulsed magnetic field. In other words, the control unit 108 is communicatively connected to the pulsed eddy current technology apparatus 106, either wirelessly or via a hardwired connection, such that the control unit 108 can receive the data signal from the pulsed eddy current technology apparatus 106. The time dependence of eddy current decay reflects the derivative of the eddy current decay in the workpiece 104.

[0046] The pulsed eddy current device 106 includes a receiver coil 106a in which a voltage signal is induced by the magnetic field generated by the eddy currents in the workpiece 104. The pulsed eddy current device 106 includes electronics for amplifying and integrating this voltage signal and provides the resulting signal S to a control unit 108.

[0047] Based on the acquired signals, the control unit 108 can determine a thickness parameter value (E). The thickness parameter value (E) is determined from a sample of the acquired signals. Importantly, this thickness parameter value depends on the ratio of the thickness (t) of the workpiece to the resistivity (r) of the workpiece, in other words, E~t / r.

[0048] For thin workpieces, for example less than 1 mm thick, the thickness parameter value can be considered the inverse of the workpiece sheet resistance, ie, 1 / sheet resistance, which can be referred to as the sheet conductance.

[0049] Although the thickness parameter value reflects the ratio of the thickness and resistivity of the workpiece, it is not straightforward to extract the thickness directly from the thickness parameter value, since this requires knowledge of the resistivity of the workpiece, which is temperature dependent.

[0050] Instead, the control unit determines the reference thickness value (t r ) to the thickness parameter value E, which gives the instantaneous resistivity value r iIn other words, the instantaneous resistivity value is r i =t r / (t / r)=(t r / t)r. Therefore, the instantaneous resistivity value r i is mainly the reference thickness t r The ratio t to the thickness t, which is a part of the thickness parameter value r The resistivity r varies very slowly and therefore depends on the thickness variation in the workpiece 104, as reflected by / t. i It can be assumed that this does not affect the fluctuations of

[0051] Furthermore, the control unit 108 controls the instantaneous resistivity value r i Based on the average resistivity value r f It is configured to calculate the average resistivity value r f is advantageously obtained using a time domain filter, preferably a low pass filter, to obtain the instantaneous resistivity value r i is obtained by filtering. In this way, an accurate average resistivity of the workpiece can be obtained. If the reference thickness value comes from a noisy thickness measurement that is calculated at the same rate as the thickness parameter value, the instantaneous resistivity value is almost constant and depends only on the noise in the reference thickness value. In this case, a time domain filter is advantageously used to reduce the measurement noise.

[0052] The control unit 108 is configured to provide an output signal based on the average resistivity of the workpiece and the thickness parameter value, the output signal being indicative of the current thickness of the workpiece. The current thickness (T) is preferably determined by the average resistivity r of the workpiece. f and the thickness parameter value (E), i.e., T=r f E=r f It is calculated by (t / r)~t.

[0053] In the case where the reference thickness value is a predetermined average thickness value, the output signal is the high-pass filtered thickness of the workpiece. For example, in response to a sudden thickness fluctuation, such as 10%, the thickness parameter value (E) also increases by approximately 10%. If the time-domain filter were a low-pass filter, the average resistivity would not change instantaneously. Thus, the output signal, which is the product of the average resistivity and the thickness parameter value (E), would initially increase by approximately 10% because the average resistivity had not yet changed due to the low-pass filtering. After a certain period of time, the average resistivity would decrease by approximately 10%, and the output signal would again be equal to the reference thickness value, as it was before the sudden thickness fluctuation. In other words, the embodiments described herein are advantageously used to monitor thickness fluctuations of a workpiece.

[0054] The cutoff frequency of the high-pass filtered thickness depends on the characteristics of the time-domain filter. For example, a simple moving average with a 10 s window results in a cutoff frequency of approximately 0.024 Hz.

[0055] The time domain filter can be a moving window averaging, such as a moving average window having a window length of about 10 seconds. Moving window averaging is well known in the art and can be implemented in various forms, such as a simple moving average, a cumulative moving average, a centered moving average, a weighted moving average, a Gaussian window, etc. Other exemplary filters can be a first-order exponential filter or a binomial filter.

[0056] It should be understood that the above-described process for determining the current thickness of the workpiece is performed while the workpiece 104 is being processed in the rolling mill. Accurately determining the current thickness provides improved control of the thickness of the workpiece even if the processing speed in the rolling mill, i.e., the feed rate of the workpiece 104, is increased. Thus, the control unit operates to determine the current thickness online while the workpiece 104 is being fed through the rolling mill.

[0057] Figure 2 is a block diagram illustrating the inventive concept according to an embodiment of the present invention. Figure 3 is a flow chart of method steps according to an embodiment of the present invention, which will be described in conjunction with Figure 2.

[0058] Initially, in step S102, a data signal reflecting the time dependence of eddy current decay in the workpiece caused by the applied pulsed magnetic field is acquired. The acquired data signal S includes a series of data points, the first of which, S0, is provided from a data sampling module 202, which includes suitable data acquisition electronics, to a module 204 that can calculate the distance d from the receiver coil 106a (see FIG. 1) to the workpiece 104. Additionally, at least some of the data points, S', are provided to a thickness calculation module 206. While all of the acquired data signal S can be provided to the thickness calculation module 206, only selected data points are sufficient. The data points, S', should reflect the time dependence of eddy current decay in the workpiece 104.

[0059] In step S104, a thickness parameter value E is determined based on the acquired signal. The thickness parameter value is determined from samples in the data signal. Furthermore, the thickness parameter value depends on the ratio of the thickness of the workpiece to the resistivity of the workpiece.

[0060] The thickness parameter value can be determined from a model 208, which processes the determined time decay of the eddy currents, such as the time derivative of the eddy current decay, and calculates the thickness parameter value. The model 208 can be an empirically determined model 208, which relates the time dependence of the eddy current decay to the ratio of the workpiece thickness to the workpiece resistivity. In other words, based on the currently determined time dependence of the eddy currents, the model 208 can relate it to previous measurements and find the thickness parameter value that best fits the currently determined time dependence of the eddy currents.

[0061] Additionally, a thickness parameter value can be further determined based on the determined distance d. Thus, the distance d can be input as a parameter into the model 208. The distance between the receiver coil 106a and the workpiece affects the strength of the detected magnetic flux. Therefore, this distance is one parameter that can be included in the calculation of the thickness parameter value E. In other words, the empirically determined model 208 can relate the time dependence of the eddy current decay to the ratio of the workpiece thickness to the workpiece resistivity for various distances between the workpiece and the magnetic field measuring device 106a.

[0062] Furthermore, in step S106, the reference thickness value t r and the thickness parameter value E, and thereby obtain the instantaneous resistivity value r i supply.

[0063] The reference thickness value can be obtained in various ways. For example, the reference thickness value t r may be the thickness value measured by the thickness measurement device 212 of the rolling mill.

[0064] The thickness values ​​measured by the thickness measurement device can be filtered using a time domain filter to provide a reference thickness value. To this end, the thickness measurements made by the thickness measurement device 212 are filtered using a time domain filter, and the filtered thickness measurements are converted to the reference thickness value t r The time constant of the time domain filter used to provide the reference thickness value is preferably the same as the time constant of the time domain filter used to filter the thickness parameter value E. This results in a constant ratio between the thickness parameter value and the filtered reference thickness value, resulting in the instantaneous resistivity being equal to the average resistivity of the workpiece, and resulting in a more accurate thickness value in the output signal even if the thickness measurement device is inherently slow. However, if the reference thickness value comes from a thickness measurement that is calculated at the same rate as the thickness parameter value, it may be advantageous to calculate the average resistivity value directly from the quotient of the reference thickness value and the thickness parameter value without filtering.

[0065] The time constant can refer to the window length of the filter, for example, in the case of a moving window filter. The time constant can also refer to the measurement or the overall frequency response of the filter.

[0066] According to another embodiment, the reference thickness value is a predetermined average thickness value of the workpiece. This predetermined average thickness value can be a manual measurement of the workpiece prior to processing in a rolling mill. In this case, the ratio of the reference thickness value, provided for example as a nominal thickness value, to the thickness parameter value E depends on the inverse of the workpiece thickness. However, if this ratio, which is an instantaneous resistivity value, is passed through a time domain filter, the output signal is a high-pass filtered value of the workpiece thickness, i.e., this signal reflects thickness variations around the average or nominal thickness.

[0067] Block 212 may also represent a processing module that calculates a reference thickness value based on some algorithm.

[0068] In step S108, the average resistivity value r is calculated based on the instantaneous resistivity value. f The average resistivity value is preferably determined by filtering the instantaneous resistivity values ​​in a time domain filter 210.

[0069] In step S110, an output signal C is provided that represents a determined current thickness of the workpiece based on the average resistivity of the workpiece and the thickness parameter value, where the determined thickness is calculated using an arithmetic operation A that is the multiplication of the average resistivity of the workpiece and the thickness parameter value.

[0070] As shown in FIG. 1, the output signal can be provided as a feedforward control signal to a rolling mill.

[0071] The method may include the step of controlling the operation of a rolling mill stand supporting a set of processing rollers of the rolling mill based on the feedforward control signal C, thereby varying the thickness of the workpiece 104, as shown in the flowchart of FIG. 4, which also includes step S110 according to FIG. 3.

[0072] The control unit may include a microprocessor, a microcontroller, a programmable digital signal processor, or other programmable device. The control unit may also or alternatively include an application specific integrated circuit, a programmable gate array, or programmable array logic, a programmable logic device, or a digital signal processor. When the control unit includes a programmable device such as a microprocessor, a microcontroller, or a programmable digital signal processor as described above, the processor may further include computer executable code to control the operation of the programmable device.

[0073] Communications between devices, control units, or other modules described herein may be wireless or hardwired as appropriate, and may implement protocols appropriate for the particular case.

[0074] While the present invention has been described with reference to specific exemplary embodiments thereof, many different alterations, modifications and the like will become apparent to those skilled in the art.

[0075] In addition, those skilled in the art in practicing the claimed invention will understand and effect variations to the disclosed embodiments, by studying the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, nor does the indefinite article "a" or "an" exclude a plurality. Moreover, the mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. 1. A method for determining the current thickness of a workpiece while it is being processed in a rolling mill (100), the method comprising: acquiring (S102) a data signal reflecting the time dependence of eddy current decay in the workpiece caused by an applied pulsed magnetic field; determining (S104) a thickness parameter value based on the acquired data signal, the thickness parameter value being determined from samples in the data signal, the thickness parameter value being dependent on a ratio between the thickness of the workpiece and the resistivity of the workpiece; Calculating a ratio between the reference thickness value of the workpiece and the thickness parameter value, thereby providing an instantaneous resistivity value (S106); A step (S108) of calculating an average resistivity value based on the instantaneous resistivity value; providing an output signal representing a determined current thickness of the workpiece based on the average resistivity value and the thickness parameter value of the workpiece (S110); A method having the following.

2. determining the thickness parameter value based on an empirically derived model relating the time dependence of eddy current decay to the ratio of the thickness of the workpiece to the resistivity of the workpiece; The method of claim 1.

3. measuring the time dependence of the eddy current decay with a magnetic field measuring device positioned at a distance from the workpiece; determining the distance from samples in the data signal acquired during an initial stage of the eddy current decay, and further determining the thickness parameter value based on the determined distance.

3. The method according to claim 1 or 2.

4. the empirically derived model relates the time dependence of the eddy current decay to the ratio of the thickness of the workpiece to the resistivity of the workpiece for various distances between the workpiece and the magnetic field measuring device; The method according to claim 3, which is dependent on claim 2.

5. determining the average resistivity value by filtering the instantaneous resistivity values; 5. The method according to any one of claims 1 to 4.

6. the method comprising providing the output signal as a feedforward control signal to the rolling mill; 6. The method according to any one of claims 1 to 5.

7. the output signal is based on a current thickness of the workpiece calculated by multiplying the average resistivity value by the thickness parameter value; The method of claim 6.

8. The method includes controlling, based on the feedforward control signal, operation of a rolling mill stand supporting a set of work rollers of the rolling mill, thereby varying the thickness of the workpiece.

8. The method according to claim 6 or 7.

9. The reference thickness value is a thickness value measured by a thickness measuring device (106) of the rolling mill.

9. The method according to any one of claims 1 to 8.

10. filtering the thickness values ​​measured by the thickness measurement device with a time domain filter to provide the reference thickness values; 10. The method of claim 9.

11. the frequency response of the time domain filter used to provide the reference thickness value is matched to the frequency response of the time domain filter used to filter the thickness parameter value; The method of claim 10.

12. the reference thickness value is a predetermined average thickness value of the workpiece; 10. The method according to any one of claims 1 to 9.

13. the workpiece is a metal plate; 13. The method according to any one of claims 1 to 12.

14. A control unit (108) configured to generate an output signal representative of a current thickness of a workpiece while it is being processed in a rolling mill, said control unit (108) comprising: obtaining a data signal reflecting the time dependence of eddy current decay in the workpiece (104) caused by an applied pulsed magnetic field; determining a thickness parameter value based on the acquired data signals, the thickness parameter value being determined from a sample in the data signals, the thickness parameter value being dependent on a ratio between a thickness of the workpiece and a resistivity of the workpiece; calculating a ratio between a reference thickness value of said workpiece and said thickness parameter value, thereby providing an instantaneous resistivity value; determining an average resistivity value based on the instantaneous resistivity values; providing an output signal representative of a determined thickness of the workpiece based on the average resistivity value and the thickness parameter value of the workpiece. A control unit (108) configured to:

15. A control unit (108) according to claim 14; a set of processing rollers (102a-b) configured to process a workpiece between the processing rollers to achieve a predetermined workpiece thickness; a rolling mill stand supporting the processing roller; A rolling mill (100) having the rolling mill stand can be controlled based on the output signal as a feedforward signal to vary the distance between the work rollers and thereby vary the thickness of the workpiece being processed in the rolling mill; A rolling mill (100).

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