Determination of the thickness of a workpiece with non-uniform resistivity

Abstract

This invention provides a method and system for determining the thickness of a metal plate with non-uniform resistivity, while improving the accuracy of measurement. [Solution] The method for determining the thickness of a workpiece (metal plate) comprises controlling a magnetic field generating device 106 that applies magnetic field pulses to the workpiece, obtaining a data signal S that reflects the time dependence of the decay of eddy currents in the workpiece due to the magnetic field pulses, calculating a first thickness tj0 of the workpiece from a set of data samples comprising multiple consecutive data samples, calculating a first resistivity res(Rs) from the first set of data samples Rs, calculating a second resistivity res(tj2) from a subsequent second set of data samples tj2, determining a resistivity gradient compensation coefficient from the difference between the second resistivity and the first resistivity, calculating a thickness tj with a compensated resistivity gradient from the first thickness tj0, the relationship between the first thickness and the first resistivity, and the resistivity gradient compensation coefficient, and providing an output of the thickness tj.

Description

Technical Field

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

Background Art

[0002] Metal rolling generally involves manufacturing a metal workpiece with a reduced and uniform thickness by stretching the metal workpiece between two rotating work rolls.

[0003] To ensure high product quality, the thickness of the workpiece is accurately monitored and controlled. It is particularly important to monitor rapid thickness variations of workpieces such as metal sheets, even for very thin metal sheets. The operation of the rolling mill can be controlled based on the measured thickness. Specifically, to ensure the quality of the final product, the rolling mill at the last stand, i.e., at the end of the processing line of the rolling mill, can be controlled based on the thickness measured upstream of the last stand.

[0004] Conventionally used pulsed eddy current measurement technology is based on measuring the eddy current induced in a metal sheet by a rapidly changing magnetic field applied to the metal sheet. Based on the measured eddy current, the resistivity and thickness of the metal sheet are obtained.

[0005] However, for sheets with non-uniform resistivity across the sheet, the conventional method is not accurate enough, thereby limiting its application.

[0006] Therefore, it is desirable to improve the accuracy of thickness measurement in a rolling mill, especially for metal sheets with non-uniform resistivity.

Summary of the Invention

[0007] In view of the above and other drawbacks of the prior art, an object of the present invention is to provide a method for determining the thickness of a workpiece having a non-uniform resistivity with improved accuracy.

[0008] According to a first aspect of the present invention, a computer-implemented method is provided for determining the thickness of a workpiece while it is being processed in a rolling mill, the method comprising: controlling a magnetic field generating device to apply magnetic field pulses to a workpiece; obtaining a data signal that reflects the time dependence of the decay of eddy currents in the workpiece caused by the applied magnetic field pulses; calculating a first thickness of the workpiece based on a set of data samples in the data signal, wherein the data signal comprises a plurality of consecutive data samples; calculating a first resistivity of the workpiece based on the first set of data samples; calculating a second resistivity of the workpiece based on a second set of data samples in the data signal, wherein the data signal comprises a plurality of consecutive data samples; calculating a resistivity gradient compensation coefficient based on the difference between the second resistivity and the first resistivity; calculating a resistivity gradient compensated thickness of the workpiece based on the first thickness, the relationship between the first thickness and the first resistivity, and the resistivity gradient compensation coefficient; and providing an output of the resistivity gradient compensated thickness of the workpiece.

[0009] The present invention is at least in part based on an embodiment for measuring the response of a pulsed magnetic field at different depths in a workpiece. Thus, samples of the response from different depths in the workpiece can be used to determine the resistivity at different depths, which can then be used to determine a compensation factor used to account for the resistivity that varies throughout the workpiece.

[0010] The proposed method allows for improved accuracy in measuring the thickness of workpieces with non-uniform resistivity. As a result, this enables improved control over the thickness of workpieces being rolled in a rolling mill, leading to higher production speeds and higher quality of the final processed workpieces.

[0011] The data signal is sampled after a sufficiently long time delay so that any large initial signal transients caused by the pulsed magnetic field are avoided in the sampled data signal. Since the time delay is sufficiently long, the time dependence of the eddy current decay in the workpiece depends primarily on the ratio of thickness to resistivity, but also on the distance between the workpiece and a measuring device, often provided as a receiver coil, which detects the magnetic field generated by the eddy currents to determine the decay. Therefore, the thickness can be calculated based on the time dependence of the eddy current decay.

[0012] More precisely, the thickness is preferably determined from the time derivative of the magnetic flux produced by eddy currents in the workpiece after a predetermined delay, and the distance between the workpiece and the measuring device. For example, if the distance is constant, the thickness can be determined by detecting the time dependence of the decay of the eddy currents and then using a model that relates the time dependence of the decay of the eddy currents to a thickness value, i.e., the ratio of the thickness to the resistivity of the workpiece. This model may be theoretically established, or it may be based on large-scale prior measurements.

[0013] As mentioned above, eddy currents can be detected by a receiver coil placed at a distance from the workpiece. In such a case, a voltage signal is induced in the receiver coil by the time derivative of the magnetic field produced by the eddy currents in the workpiece. The voltage signal is preferably amplified and integrated to produce the acquired signal.

[0014] Preferably, the first set of data samples is a sample in the data signal that follows the distance sample. The distance sample av1 is used to calculate the distance between the receiver coil and the workpiece.

[0015] In an embodiment, a second set of data samples may reflect the time dependence of eddy current decay as the eddy currents penetrate further into the workpiece compared to the case in the first set of data samples. That is, the second set of data samples follows the first set of data samples in the data signal, but there may be overlap between parts of the samples. In other words, the last sample of the first set of data samples may still overlap with the first sample of the second set of data samples. The fact that the second set of data samples may reflect the time dependence of eddy current decay as the eddy currents penetrate further into the workpiece enables determining the resistivity to a greater depth in the workpiece compared to using the first set of samples.

[0016] In an embodiment, the relationship between the first thickness and the first resistivity may be a predetermined function based on empirical data. This function may follow a polynomial dependence between thickness and resistivity. Using an empirical model provides an accurate method for calculating the thickness with a compensated resistivity gradient.

[0017] In the embodiment, a second set of data samples may include the data samples used to calculate the first resistivity.

[0018] In one embodiment, a first set of data samples (Rs) may reflect the time dependence of eddy current decay when the eddy currents penetrate only partially through the workpiece. This advantageously enables the determination of resistivity assuming a uniform resistivity that will be compensated for by subsequent steps of the method.

[0019] In some embodiments, the resistivity gradient compensation coefficient can be dynamically updated during the processing of the workpiece in the rolling mill. This is advantageous as it allows for the consideration of changes in the resistivity of the workpiece due to variations in temperature, composition, or processing speed.

[0020] In embodiments, the output of the thickness with a resistivity gradient compensated may be used to control one or more operating parameters of the rolling mill. For example, the operating parameters may include rolling force or rolling speed to ensure that the workpiece achieves a desired final thickness.

[0021] In embodiments, the method may further include storing the calculated resistivity, thickness, and resistivity gradient compensation coefficient in a database for the purpose of later analysis or quality control. That is, the collected data may be used to make later improvements to the method and / or rolling mill.

[0022] In embodiments, the method may comprise determining that the resistivity gradient compensated thickness deviates from a predetermined acceptable range and generating a warning signal indicating the deviation. This deviation may, advantageously, indicate a potential defect or inconsistency in the workpiece. By generating a warning when the resistivity gradient compensated thickness deviates from an acceptable range, the system enables real-time monitoring of the workpiece thickness. This prompts immediate corrective action, minimizes defective production, and ensures the consistency of the final product.

[0023] In embodiments, the method may comprise calculating a further resistivity of a workpiece based on a further set of data samples in a data signal, including data samples following at least one sample in a first set of data samples, and storing the further resistivity data in data storage. Advantageously, the stored data of the further resistivity can be used to analyze the workpiece to obtain a more detailed picture of the resistivity gradient. This can yield more detailed insights into defects, composition, or other inconsistencies in the workpiece.

[0024] The workpiece may be a metal plate or a metal piece.

[0025] A control unit is further provided, configured to perform any of the steps of the first embodiment.

[0026] According to a second aspect of the present invention, there is provided a system comprising a controllable magnetic field generating device, a receiver device for acquiring a data signal reflecting the time dependence of the decay of eddy currents in a workpiece, and a control unit configured to perform any of the steps of the embodiments of the first aspect.

[0027] The magnetic field generating device is preferably a coil capable of generating magnetic field pulses using a pulsed power supply.

[0028] The receiver device is preferably a receiver coil for detecting a magnetic field generated by eddy currents in the workpiece caused by the pulses applied by the magnetic field generating device.

[0029] Further effects and features of the second aspect of the present invention are very similar to those described above in relation to the first aspect of the present invention.

[0030] According to a third aspect of the present invention, there is provided a rolling mill comprising a set of work rolls configured to process a workpiece between the work rolls to a predetermined workpiece thickness, and a system according to the second aspect.

[0031] Further effects and features of the third aspect of the present invention are very similar to those described above in relation to the first and second aspects of the present invention.

[0032] Further features and advantages of the present invention will become apparent upon consideration of the appended claims and the following description. Those skilled in the art will recognize that, without departing from the scope of the present invention, different features of the present invention may be combined to produce embodiments other than those described below.

[0033] Here, these and other features of the present invention will be described in more detail with reference to the accompanying drawings showing exemplary embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] [Figure 1] A diagram conceptually showing a workpiece being processed in a rolling mill according to one embodiment of the present invention. [Figure 2] A box diagram illustrating an embodiment of the present invention. [Figure 3] A flowchart of the method steps according to an embodiment of the present invention. [Figure 4] A flowchart of the method steps according to an embodiment of the present invention. [Modes for carrying out the invention]

[0035] In embodiments for carrying out this invention, various embodiments of the invention are described herein with reference to specific implementations. Certain terminology is used in describing embodiments for clarity. However, the invention is not intended to be limited to such selected terminology. Certain exemplary embodiments are discussed, but it should be understood that this is for illustrative purposes only. Those skilled in the art will recognize that other components and configurations may be used without departing from the scope of the invention.

[0036] Figure 1 conceptually shows a rolling mill 110 having a set of work rolls 102a and 102b adapted for processing a workpiece 104. The work rolls 102a-b rotate while the workpiece 104, for example, a metal sheet, is fed between the work rolls 102a-b. As will be understood by those skilled in the art, the work rolls 102a-b reduce the thickness of the workpiece. The workpiece 104 is a metal sheet or metal piece.

[0037] It is desirable to accurately control the thickness of the workpiece 104 output downstream of the work rolls 102a-b. For this purpose, a pulsed eddy current technology device 106, which is based on applying a pulsed magnetic field to the workpiece 104, is often used. The pulsed eddy current technology device 106 detects eddy currents induced in the workpiece 104 to estimate the thickness of the workpiece portion before it reaches the work rolls 102a-b. The present invention relates to improving this thickness estimation. More specifically, for workpieces 104 having non-uniform resistivity across their thickness, the conventional technique is not satisfactoryly accurate.

[0038] A control unit 108, configured to generate an output signal indicating the thickness of a workpiece 104 while it is being processed in a rolling mill, is conceptually shown here.

[0039] The control unit 108 is configured to acquire a data signal S that reflects the time dependence of the decay of eddy currents in the workpiece caused by the applied pulsed magnetic field. In other words, the control unit 108 is communicably connected to the pulsed eddy current technology device 106, either wirelessly or hardwired, so that it can receive data signals from the pulsed eddy current technology device 106. The time dependence of the decay of eddy currents reflects the derivative of the decay of eddy currents in the workpiece 102. The data signal S comprises a plurality of consecutive data samples.

[0040] The pulsed eddy current technology device 106 includes a controllable magnetic field generating device 106a, such as a coil, and a receiver device in the form of a receiver coil 106b, which induces a voltage signal by the magnetic field generated by eddy currents in the workpiece 104. The pulsed eddy current technology device 106 includes an electronic device for amplifying and integrating the voltage signal and provides the resulting signal S to a control unit 108.

[0041] Figure 2 is a box diagram schematically illustrating an embodiment of the present invention. Figure 3 is a flowchart of the method steps according to an embodiment of the present invention, which will be described in relation to Figure 2.

[0042] In step S102, the control unit 108 controls the magnetic field generating device 106 so that it applies magnetic field pulses to the workpiece 104 using a control signal Cr provided to the magnetic field generating device 106, causing the coil 106a to generate magnetic field pulses for the workpiece 104.

[0043] In step S104, the control unit 108 acquires a data signal S that reflects the time dependence of the decay of eddy currents in the workpiece caused by the applied magnetic field pulse, and the data signal S comprises a plurality of consecutive data samples.

[0044] The acquired data signal S includes a set of data samples, the first of which, also called distance sample av1, is provided from the data sampling module 202, which includes appropriate data acquisition electronic devices, to the software module 204, which can calculate the distance d from the receiver coil 106b to the workpiece 104. Furthermore, at least a subset S' of data points is provided to the thickness calculation module 206. The entire acquired data signal S may be provided to the thickness calculation module 206, but only selected data points are sufficient. The data points S' should reflect the time dependence of the decay of eddy currents in the workpiece 104.

[0045] Based on the acquired signal S, the control unit 108 can determine the thickness value (E) and resistivity value (R) of the workpiece. The thickness value (E) and resistivity value (R) are determined from the sample in the acquired signal. The thickness value E depends on the ratio of the workpiece thickness (tj) to the workpiece resistivity (Res). In other words, E ~ tj / res.

[0046] The thickness value E can be determined using Model 208a, which calculates the thickness value E by processing the time decay of the determined eddy current, such as the time derivative of the decay of the eddy current. Similarly, the resistivity value can be determined from Model 208b, which calculates the resistivity value R by processing the time decay of the determined eddy current. Models 208a and 208b may be empirically determined models that relate the time dependence of the decay of the eddy current to the thickness and resistivity of the workpiece 104.

[0047] In addition, the thickness value E can be further determined based on the determined distance d. Thus, the distance d can be input as a parameter in Model 208a. The distance (d) between the receiver coil 106a and the workpiece affects the strength of the detected magnetic flux. Thus, this distance is a parameter that can be included in the determination of the thickness value E. The distance d is calculated based on the distance sample av1. That is, the distance d is determined from a sample in the data signal S during the initial stage of eddy current decay. As is known, magnetic field strength decays with distance to the source. Instead of measuring the distance using separate measuring means such as an optical measuring device or a capacitive measuring device, the above knowledge can be used to calculate the distance from the receiver coil 106b to the workpiece 104.

[0048] The control unit 108 uses models 208a and 208b to calculate the first and second thicknesses, as well as the first and second resistivity values, which are collectively referred to above as thickness value E and resistivity value R.

[0049] The thickness value reflects the ratio of the workpiece's thickness to its resistivity, but directly obtaining the thickness from the thickness parameter value is not straightforward because it requires knowledge of the workpiece's resistivity. Embodiments of the present invention particularly address cases where the resistivity is non-uniform.

[0050] In step S106, the control unit 108 calculates a first thickness (tj0) of the workpiece based on a set of data samples in the data signal. This first thickness (tj0) is the estimated total thickness of the workpiece, assuming a uniform resistivity throughout the workpiece.

[0051] In step S108, the first resistivity res(Rs) of the workpiece 104 is calculated based on a first set of data samples Rs. The first set of data samples (Rs) reflects the time dependence of the decay of eddy currents when they penetrate only partially through the workpiece 104. In other words, the first set of data samples Rs is a sample in the data signal following the first distance sample av1. Sample av1 is included in the complete signal S.

[0052] In step S110, the control unit 108 calculates the second resistivity res(tj2) of the workpiece 104 based on the second set of data samples tj2 in the data signal S', which includes data samples that follow at least one sample in the first set of data samples (Rs), and based on the first thickness tj0. The second set of data samples (tj2) is contiguous with the first set of data samples (Rs). This means that the second set of data samples (tj2) reflects the time dependence of the decay of eddy currents as they penetrate further into the workpiece compared to the case in the first set of data samples (Rs). The thickness value E, here the first thickness (tj0), reflects the relationship, or ratio, between the thickness and resistivity of the workpiece. Therefore, the first thickness tj0 is used when calculating the second resistivity (res(tj2)) because the data signal tj2 depends on both thickness and resistivity.

[0053] In step S112, the control unit 108 determines the resistivity gradient compensation coefficient rescomp based on the difference between the second resistivity and the first resistivity. The resistivity gradient compensation coefficient rescomp is Rescomp=Res(tj2)-Res(tj1) It can be given by.

[0054] The resistivity gradient compensation coefficient (rescomp) is preferably dynamically updated during the processing of the workpiece 104 in the rolling mill 100 to account for changes in the resistivity of the workpiece due to variations in temperature, composition, or processing speed.

[0055] In step S114, the control unit 108 calculates the thickness tj of the workpiece 104 with the resistivity gradient compensated, based on the first thickness (tj0), the relationship f between the first thickness and the first resistivity, and the resistivity gradient compensation coefficient. The relationship f between the first thickness and the first resistivity is a predetermined function f based on empirical data. The function f is typically a polynomial function.

[0056] For example, the relationship f between a first thickness (tj0) and a first resistivity (Res(rs)) can be empirically determined by measuring the resistivity and resistivity gradient compensation coefficient for multiple workpieces using an instrument (e.g., a BoxGauge). The actual thickness of the workpiece is measured using a mechanical thickness measuring device. Using the measured resistivity, resistivity gradient compensation coefficient, and measured thickness, the variation of the relationship f can be empirically determined.

[0057] In step S116, the control unit 108 provides an output C of the thickness (tj) of the workpiece 104 with the resistivity gradient compensated.

[0058] To ensure that the workpiece 104 achieves the desired final thickness, the output C of the thickness (tj) with a resistivity gradient compensated may be used to control one or more operating parameters of the rolling mill 100, such as rolling force or rolling speed.

[0059] The control unit 108 may store the calculated resistivity (Res(Rs), Res(tj2)), thickness (tj0, tj), and resistivity gradient compensation coefficient (rescomp) in the database 220 for later analysis or quality control purposes.

[0060] Now, let's look at the flowchart in Figure 4. In some embodiments, the control unit 108 determines that the resistivity gradient compensated thickness (tj) deviates from a predetermined tolerance range. A deviation from the predetermined tolerance range indicates a potential defect or inconsistency in the workpiece. For example, the thickness may be too small or too large compared to the predetermined tolerance range, i.e., the resistivity gradient compensated thickness may be above or below the predetermined tolerance range. The predetermined tolerance range may include a target thickness value and a limit on the acceptable deviation. The predetermined tolerance range depends on the acceptable manufacturing tolerance for the immediate machining.

[0061] In response to detecting a deviation, the control unit 108 generates a warning signal A in step S120 to indicate the deviation to the user or operator of the rolling mill on a user interface 222, such as a display or speaker. In this way, human intervention may occur. In other possible implementations, automatic intervention may occur. The intervention or correction may include adjusting the rolling force, speed, or other processing parameters to correct the problem.

[0062] The data signal S' may be split into further datasets, i.e., S'=[Rs tj1...tjx...] That is the case.

[0063] In this way, the control unit 108 can calculate the additional resistivity (res(tjX)) of the workpiece 104 based on each of the additional sets (tjX) of data samples in the data signal. The additional sets of data samples include data samples that follow at least one sample in the first set of data samples (Rs). The data of the additional resistivity (res(tjX)), such as the resistivity properties of the workpiece, can be analyzed and stored in the data storage 220.

[0064] It should be understood that the above process for determining the resistivity gradient-compensated thickness of the workpiece is performed while the workpiece 104 is being processed in the rolling mill 100. This accurate determination of the resistivity gradient-compensated thickness enables improved control of the thickness of the workpiece 104, even when the processing speed in the rolling mill 100, i.e., the supply speed of the workpiece 104, is increased. Therefore, the control unit 108 operates to determine this resistivity gradient-compensated thickness online while the workpiece 104 is being supplied through the rolling mill.

[0065] The control unit may include a microprocessor, microcontroller, programmable digital signal processor, or other programmable device. The control unit may also, or instead, include an application-specific integrated circuit, programmable gate array or programmable array logic, programmable logic device, or digital signal processor. If the control unit includes a programmable device such as a microprocessor, microcontroller, or programmable digital signal processor as mentioned above, the processor may further include computer executable code that controls the operation of the programmable device.

[0066] Communication between devices, control units, or other modules described herein may be wireless or hardwired where appropriate, and protocols appropriate to the particular case may be implemented.

[0067] Although the present invention has been described with reference to certain exemplary embodiments, many different modifications and alterations will become apparent to those skilled in the art.

[0068] In addition, modifications to the disclosed embodiments can be understood and achieved by those skilled in the art in practicing the claimed invention, based on a review of the drawings, this disclosure, and the appended claims. In the claims, the word “equips” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude the plural. The mere fact that certain measures are described in different dependent claims does not imply that combinations of these measures cannot be used for benefit.

Claims

1. A computer-based method for determining the thickness of a workpiece (104) while it is being processed in a rolling mill (100), Controlling the magnetic field generating device (106) to apply a magnetic field pulse to the workpiece (104) (S102), Obtaining a data signal (S) that reflects the time dependence of the decay of eddy currents in the workpiece caused by the applied magnetic field pulse (S104), wherein the data signal comprises a plurality of consecutive data samples, The first thickness (tj0) of the workpiece is calculated based on the set of data samples in the data signal (S106), Calculating the first resistivity (res(Rs)) of the workpiece based on a first set of data samples (Rs) (S108), S110: Calculating the second resistivity (res(tj2)) of the workpiece based on a second set of data samples (tj2) in the data signal, which includes a data sample that follows at least one sample in the first set of data samples (Rs), Determining the resistivity gradient compensation coefficient based on the difference between the second resistivity and the first resistivity (S112), Based on the first thickness (tj0), the relationship between the first thickness and the first resistivity (f), and the resistivity gradient compensation coefficient, the thickness of the workpiece with the resistivity gradient compensated (tj) is calculated (S114), (S116) To provide an output of the thickness (tj) of the workpiece with the resistivity gradient compensated. A method that includes [a certain feature].

2. The method according to claim 1, wherein the second set of data samples (tj2) reflects the time dependence of the decay of the eddy currents as the eddy currents penetrate further into the workpiece (104) compared to the case in the first set of data samples (Rs).

3. The method according to any one of claims 1 to 2, wherein the relationship between the first thickness and the first resistivity is a predetermined function based on empirical data.

4. The method according to any one of claims 1 to 3, wherein the second set of data samples is included in the data samples used to calculate the first resistivity.

5. The method according to any one of claims 1 to 4, wherein the first set of data samples reflects the time dependence of the decay of the eddy current when the eddy current penetrates only partially through the workpiece (104).

6. The method according to any one of claims 1 to 5, wherein the resistivity gradient compensation coefficient is dynamically updated during the processing of the workpiece (104) in the rolling mill (100).

7. The method according to any one of claims 1 to 6, wherein the output of the thickness with the resistivity gradient compensated is used to control one or more operating parameters of the rolling mill.

8. The method according to any one of claims 1 to 7, further comprising storing the calculated resistivity, thickness, and resistivity gradient compensation coefficient in a database for the purpose of later analysis or quality control.

9. The resistivity gradient is determined to be in a state where the compensated thickness (tj) deviates from a predetermined acceptable range (S118), To generate a warning signal indicating the aforementioned deviation (S120) The method according to any one of claims 1 to 8, further comprising:

10. Calculating a further resistivity (res(tjX)) of the workpiece based on a further set (tjX) of data samples in the data signal, which includes a data sample that follows at least one sample in the first set (Rs) of data samples, The method according to any one of claims 1 to 9, further comprising storing the data of the further resistivity (res(tjX)) in data storage.

11. The method according to any one of claims 1 to 10, wherein the first set of data samples (Rs) is a sample in the data signal that follows a distance sample (av1) used to calculate the distance between a receiver coil configured to measure the attenuation of the eddy current and the workpiece.

12. The method according to any one of claims 1 to 11, wherein the workpiece is a metal plate or a metal piece.

13. A control unit (108) configured to perform the method according to any one of claims 1 to 12.

14. A controllable magnetic field generating device (106), A receiver device (106a) for acquiring a data signal that reflects the time dependence of the decay of eddy currents in a workpiece (104), The control unit (108) according to claim 13 and A system that includes these features.

15. A set of work rolls (102a, b) configured to process a workpiece (104) between the work rolls to a predetermined thickness, The system according to claim 14 and A rolling mill (100) equipped with the following.

Images