Temperature measuring device and temperature measuring method

Abstract

To measure temperature distribution in the width direction of a GA steel sheet during transfer at high speed without having the influence of emissivity much changed in the process of alloying.SOLUTION: A temperature measurement device for measuring the temperature of a steel sheet having wavelength dependency in emissivity includes: an imaging part capable of acquiring a first radiance EA being the radiance of the steel sheet at a first wavelength λA and a second radiance EB being the radiance of the steel sheet at a second wavelength λB different from the first wavelength λA; and an arithmetic processing part 14 capable of calculating an apparent temperature Te using λA and λB, calculating an apparent emissivity εe using EA, λA and Te and using a radiance Lb (λA and Te) calculated from the formula of a black body radiation previously obtained, calculating an emissivity εA approximately derived using εe at the λA of the steel sheet by the formula and calculating the temperature of the steel sheet using εA.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a temperature measurement device and a temperature measurement method, and more particularly to a temperature measurement device and a temperature measurement method that utilize radiance detected from an object. [Background technology]

[0002] Galvannealed steel sheets (hereinafter referred to as "GA steel sheets"), which are produced by heat-treating hot-dip galvanized steel sheets to form an iron-zinc alloy on the surface, have excellent corrosion resistance, paintability, and press formability. They are used, for example, for automobile exterior panels. One of the manufacturing processes for GA steel sheets involves an alloying process, in which the steel sheet is immersed in molten zinc and then heated in an alloying furnace to form a zinc-iron plating alloy layer on the steel sheet surface. The iron content in the plating alloy layer is called the alloying degree. Because this alloying degree significantly affects the properties of GA steel sheets, such as press formability and durability, it is important to control the alloying degree within an appropriate range. The alloying degree is correlated with the heating temperature and heating time during the alloying process. Therefore, to produce GA steel sheets with a uniform, high-quality plating alloy layer, it is important to uniformly control the temperature distribution in the width direction during the alloying process within an appropriate temperature range. Therefore, a technology for measuring the temperature distribution in the width direction during the alloying process is needed.

[0003] Radiation thermometry is a remote temperature measurement method that can measure the temperature of an object quickly and without contact. Radiation thermometry uses a photodetector to detect the thermal radiation emitted by a high-temperature object according to its temperature, and measures the temperature based on its intensity. Accurate temperature measurement requires understanding the emissivity, which varies depending on the object and its surface condition. However, during the manufacturing process of GA steel sheets, the roughness of the steel sheet surface changes as molten zinc reacts with iron to form an alloy, causing the emissivity of the steel sheet to change significantly from approximately 0.2 before alloying to approximately 0.8 after alloying. This makes it difficult to measure the surface temperature of GA steel sheets during the alloying process using a conventional radiation thermometer.

[0004] Two-color radiation thermometry is a method for measuring the temperature of an object with varying emissivity. The radiance of the radiation emitted from the object to be measured (temperature T [K]) is measured at two wavelengths λ. A and λ B Radiance E at A and E B is the wavelength of the two A and λ B The emissivity at ε A and ε B Then, it can be expressed by equations (101) and (102). Here, L b (λ, T) is the radiance at temperature T and wavelength λ of blackbody radiation according to Planck's law, and can be expressed as in equation (103). Note that c1 is the first constant of radiation in Planck's law, and c2 is the second constant of radiation in Planck's law.

[0005]

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[0006] ε A =ε B When this occurs, it is called a gray body, and is a condition commonly used in two-color radiation thermometry. In two-color radiation thermometry, the temperature T can be calculated without the influence of emissivity by taking the ratio of the radiance of the two wavelengths (two-color ratio R) as in equation (104). Furthermore, emissivity can also be calculated from the calculated temperature T and radiance using equation (101). The greater the difference between the two wavelengths, the greater the advantage in that sensitivity improves, but in that case it generally becomes difficult to meet the gray body condition.

[0007]

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[0008] As mentioned above, when a GA steel sheet coated with molten zinc is heated to grow an alloy layer, the emissivity changes from approximately 0.2 (before alloying) to approximately 0.8 (after alloying) as the alloying progresses. This corresponds to the fact that molten zinc has a metallic luster, whereas after alloying, it solidifies and develops a rough surface as FeZn compounds are formed. The wavelength λ of molten zinc and zinc after alloying is i Emissivity ε in [μm] i has a wavelength-dependent term as in equation (105), and it is empirically known that the wavelength-dependent coefficient A1 = 0.1. A and λ B Since the emissivity at different wavelengths is not equal, as shown in equation (106), the temperature cannot be calculated by a typical two-color radiation thermometer. For this reason, as shown in Patent Documents 1 and 2, conventional radiation thermometers for GA steel sheets in the alloying process measure the radiance at two wavelengths and calculate the temperature and emissivity by simultaneously solving equations (101), (102), and equation (106), which is the relational equation between the emissivities at the two wavelengths, through numerical analysis.

[0009]

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[0010] Patent Document 1 discloses a method for determining the temperature of a target material through repeated convergence calculations using the radiance, apparent temperature, and apparent emissivity of two wavelengths, and an experimentally determined emissivity characteristic function between the two wavelengths. Patent Documents 2 and 3 disclose a method for determining the temperature of a target material by repeatedly calculating the apparent temperature and apparent emissivity from the radiance of three or more wavelengths, utilizing the fact that the spectral emissivity of a zinc-alloy plated steel sheet is proportional to the reciprocal of the wavelength. Patent Document 4 discloses a method for determining the true emissivity from the radiance, apparent temperature, and apparent emissivity of two wavelengths, and a previously calculated equation relating the apparent emissivity and true emissivity, and then determining the temperature of the target material. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2-85730 [Patent Document 2] Patent Publication No. 5-231944 [Patent Document 3] Patent Publication No. 5-231945 [Patent Document 4] JP 5-240711 Summary of the Invention [Problem to be solved by the invention]

[0012] However, the methods described in Patent Documents 1 and 2 calculate temperature by convergence calculation, which requires a long calculation time. Therefore, they are unsuitable for measuring the temperature distribution in the width direction of a GA steel sheet, which requires calculating temperatures at many measurement points. Furthermore, Patent Document 3 discloses a method of approximating the radiance of three different wavelengths using an experimentally determined relational expression between each wavelength and emissivity, and calculating the temperature of the GA steel sheet from simultaneous equations. However, the specific calculation method is not clearly stated, making the calculation difficult. The method described in Patent Document 4 requires that the relational expression between the true emissivity and apparent emissivity of each wavelength be determined in advance, but determining this relational expression is not easy.

[0013] Therefore, an object of the present invention is to provide a temperature measuring device and a temperature measuring method that can quickly measure the temperature distribution in the width direction of a GA steel plate being transported without being affected by the emissivity, which changes significantly during the alloying process. [Means for solving the problem]

[0014] The temperature measuring device according to the first aspect of the present invention measures a temperature at an arbitrary wavelength λ i Emissivity ε at i A temperature measuring device for measuring the temperature of a steel plate having the relationship of formula (1), A The first radiance E is the radiance of the steel plate at A , and the first wavelength λ AA second wavelength λ different from B The second radiance E is the radiance of the steel plate at B and a calculation processing unit that calculates the temperature of the steel sheet, A and the second wavelength λ B Using the above, the apparent temperature T is calculated based on equations (2) and (3). e Calculate the first radiance E A and the first wavelength λ A and the apparent temperature T e Using the previously calculated radiance of blackbody radiation L b (λ A ,T e ) and the apparent emissivity ε based on equation (4) e and the apparent emissivity ε e Using the above, the first wavelength λ of the steel sheet is calculated based on the formulas (5) to (7). A Emissivity ε at A is calculated, and the emissivity ε A The temperature of the steel plate is calculated based on equation (8) using the above formula. Note that A0 is an unknown constant determined by the steel plate, A1 is a known constant determined by the steel plate, c2 is the second constant of radiation in Planck's radiation law, and the function L b (λ i ,T i ) at any temperature T i Any wavelength λ at i shows the radiance of blackbody radiation at

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[0015] A temperature measurement method according to a second aspect of the present invention is a method of measuring a temperature at an arbitrary wavelength λ i Emissivity ε at i A temperature measurement method for measuring the temperature of a steel plate having a relationship of formula (1), A The first radiance E is the radiance of the steel plate at A , and the first wavelength λ A A second wavelength λ different from BThe second radiance E is the radiance of the steel plate at B a radiance acquisition step of acquiring the first wavelength λ A and the second wavelength λ B Using the above, the apparent temperature T is calculated based on equations (2) and (3). e an apparent temperature calculation step of calculating the first radiance E A and the first wavelength λ A and the apparent temperature T e Using the previously calculated radiance of blackbody radiation L b (λ A ,T e ) and the apparent emissivity ε based on equation (4) e an apparent emissivity calculation step of calculating the apparent emissivity ε e Using the above, the first wavelength λ of the steel sheet is calculated based on the formulas (5) to (7). A Emissivity ε at A an emissivity calculation step of calculating the emissivity ε A and a temperature calculation step of calculating the temperature of the steel plate based on equation (8) using the above formula, where A0 is an unknown constant determined by the steel plate, A1 is a known constant determined by the steel plate, c2 is the second constant of radiation in Planck's radiation law, and is a function L b (λ i ,T i ) at any temperature T i Any wavelength λ at i shows the radiance of blackbody radiation at

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[0016] The present invention provides a temperature measuring device and a temperature measuring method that can quickly measure the temperature distribution in the width direction of a GA steel plate being transported without being affected by the emissivity, which changes significantly during the alloying process. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing the configuration of a continuous hot-dip galvanizing treatment facility in which a temperature measurement device according to an embodiment of the present invention is installed. [Figure 2] FIG. 2 is a functional block diagram of a calculation processing unit. [Figure 3] FIG. 2 is a block diagram showing the hardware configuration of a calculation processing unit. [Figure 4] 10 is a flowchart showing the flow of a temperature measurement process. [Figure 5] 1 is a graph showing the relationship between wavelength and blackbody oven measured luminance. [Figure 6] 1 is a graph showing the relationship between blackbody furnace temperature and radiance. [Figure 7] 1 is a graph showing the relationship between the inverse of temperature and radiance. [Figure 8] FIG. 1 is a diagram showing a configuration of a test device in an example. [Figure 9] 1 is a graph showing changes in luminance value and radiance over time. [Figure 10] 10 is a graph showing an example of a calculation result of temperature. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings.

[0019] (Explanation of the temperature measurement device configuration) FIG. 1 shows the configuration of continuous hot-dip galvanizing treatment equipment in which a temperature measuring device 10 according to this embodiment is installed. A steel sheet to be galvanized is subjected to continuous annealing (not shown) and then introduced into a hot-dip galvanizing bath containing molten zinc. The steel sheet introduced into the hot-dip galvanizing bath is turned upward by an in-bath roll and drawn out of the hot-dip galvanizing bath. Wiping gas is sprayed from a wiping nozzle onto both sides of the steel sheet with molten zinc attached, and the amount of molten zinc attached is adjusted. The steel sheet with the adjusted coating weight is then passed through an alloying furnace. The alloying furnace uses induction heating to heat the steel sheet to an alloying temperature of approximately 500°C to 550°C. The heated steel sheet is completely alloyed by the time it reaches the upper roll (not shown).

[0020] The temperature measuring device 10 according to this embodiment is a steel plate having wavelength-dependent emissivity, specifically, a steel plate having an emissivity of an arbitrary wavelength λ i Emissivity ε at i The temperature measuring device 10 is an apparatus for measuring the temperature of a steel sheet having the relationship of equation (105). In equation (105), A0 is an unknown coefficient determined by the GA steel sheet. Also, A1 is a wavelength-dependent coefficient as described above, and is a known constant determined by the GA steel sheet. The temperature measuring device 10 includes an imaging unit 12 and an arithmetic processing unit 14.

[0021] The imaging unit 12 is a camera alone or a device including a camera that can acquire radiance at a plurality of different wavelengths at least at a predetermined position on the GA steel sheet shown in Fig. 1, and can be realized by appropriately combining known cameras. For example, the imaging unit 12 may be a hyperspectral camera that acquires the radiance of the GA steel sheet for each of a plurality of wavelengths at a plurality of positions within the field of view, with a range including the entire width in a direction perpendicular to the conveying direction of the GA steel sheet shown in Fig. 1 (hereinafter also referred to as the "sheet width direction"). The plurality of wavelengths may include an arbitrary first wavelength λ A and the first wavelength λ A A second wavelength λ different from B This includes:

[0022] A hyperspectral camera that can be used as the imaging unit 12 is a camera that can capture spectral information obtained by dispersing light into wavelengths, along with spatial information. This allows for the acquisition of more information than can be obtained visually or with an RGB camera, and research into this technology is advancing in fields such as engineering, biology, and medicine. Furthermore, in recent years, devices have become cheaper, leading to their widespread adoption in factory lines and their use in fields such as foreign object detection, quality control, and component inspection.

[0023] A typical hyperspectral camera is a line-scan type. It has a linear field of view and captures an image of the target, acquiring detailed spectral information for each pixel that makes up the line. To achieve this function, a hyperspectral camera is composed of a lens, a slit, a spectrometer, and a 2D image sensor. First, the lens forms an image of the target on the slit. The light formed on the slit is then transmitted to the spectrometer as one-dimensional information (line). The spectrometer then splits the light into multiple wavelengths using a diffraction grating or prism, and the 2D image sensor captures the split light. As a result, the 2D image sensor of the hyperspectral camera captures the detected light intensity for each wavelength at each position in the linear field of view as a two-dimensional hyperspectral image (spatial channel × wavelength channel). The number of spatial channels is typically 320 or 640, and the number of wavelength channels is typically 100 or 200. The wavelength band of the spectral spectrum is determined by the spectrometer specifications, the size of the 2D image sensor, the detection wavelength band, and the number of channels. The detected intensity of light at each position is acquired as a brightness value of, for example, 4096 gradations (12 bits) in the hyperspectral image.

[0024] By using a hyperspectral camera with these characteristics, it is possible to quickly acquire the spectral radiation spectrum across the width of the plate in a single image, realizing a high-speed temperature measurement device 10. By measuring the GA steel plate as it is threaded in the rolling (longitudinal) direction, it is possible to measure the entire length. Furthermore, by using two-color radiation thermometry for temperature measurement, the two wavelengths used in two-color radiation thermometry can be freely selected from the wavelengths of the spectral spectrum.

[0025] Specifically, the imaging unit 12 captures one hyperspectral image for each line of view in the width direction of the GA steel sheet. A The radiance E of GA steel sheet at A , and a second wavelength λ B The radiance E of GA steel sheet at B A hyperspectral image including the above is captured.

[0026] The calculation processing unit 14 is a functional unit that calculates the temperature of the GA steel plate based on the hyperspectral image captured by the imaging unit 12, and is realized by a computer with a hardware configuration described below. As shown in FIG. 2, the calculation processing unit 14 functionally includes an apparent temperature calculation unit 22, an apparent emissivity calculation unit 24, an emissivity calculation unit 26, and a temperature calculation unit 28. Below, the calculation of the temperature at any one point on the GA steel plate will be described as an explanation of each functional unit. Each functional unit executes the processing described below for each point of the measurement target.

[0027] The apparent temperature calculation unit 22 calculates the first wavelength λ A and the second wavelength λ B and emissivity ε A and ε B The apparent temperature T when e Specifically, the apparent temperature calculation unit 22 calculates the wavelength λ A and λ B The radiance E at each A and E B and wavelength λ A and λ B and the extracted radiance E A and E B Using equations (107) and (108), the apparent temperature T is calculated via the dichromatic ratio R. e Calculate.

[0028]

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[0029] The apparent emissivity calculation unit 24 calculates the radiance E A , wavelength λ A , and the apparent temperature T e Using the above, the emissivity ε A and ε B Apparent emissivity ε when e Specifically, the apparent emissivity calculation unit 24 calculates the apparent emissivity using a relational expression L that indicates the radiance at a temperature T and a wavelength λ that are previously calculated for blackbody radiation. b From (λ,T), the wavelength λ A and the apparent temperature T calculated by the apparent temperature calculation unit 22 e radiance L at b (λ A ,T e The apparent emissivity calculation unit 24 then calculates the radiance E extracted by the apparent temperature calculation unit 22. A and the calculated radiance L b (λ A ,T e ) and the apparent emissivity ε e Calculate.

[0030]

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[0031] The emissivity calculation unit 26 calculates the apparent emissivity ε calculated by the apparent emissivity calculation unit 24. e Using this, the wavelength λ of the GA steel sheet A Emissivity ε at A Specifically, the emissivity calculation unit 26 calculates the wavelength-dependent coefficient A1 and the wavelength λ A and λ B Using these, calculate a and b in equations (111) and (112), and use the calculated a and b and the apparent emissivity ε e Using Equation (110), the emissivity ε A The equation (110) is an approximately derived equation. The derivation of this approximate equation will be described in detail later.

[0032]

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[0033] The temperature calculation unit 28 calculates the emissivity ε A Using the temperature T of the GA steel sheet i Specifically, the temperature calculation unit 28 calculates the relational expression L b wavelength λ in (λ,T) A Applying the relation L b (λ A ,T i ) is found by the relation L b (λ A ,T i ) is the wavelength λ of blackbody radiation A and temperature T i The temperature calculation unit 28 calculates the radiance at b (λ A ,T i ) and the emissivity ε calculated by the emissivity calculation unit 26 A and the radiance E extracted by the apparent temperature calculation unit 22. A Using the temperature T i Calculate.

[0034]

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[0035] Fig. 3 is a block diagram showing the hardware configuration of the arithmetic processing unit 14. As shown in Fig. 3, the arithmetic processing unit 14 has a CPU (Central Processing Unit) 32, a memory 34, a storage device 36, an input device 38, an output device 40, a storage medium reader 42, and a communication I / F (Interface) 44. Each component is connected to each other via a bus 46 so as to be able to communicate with each other.

[0036] The storage device 36 stores a program for executing a temperature measurement process, which will be described later. The CPU 32 is a central processing unit that executes various programs and controls each component. That is, the CPU 32 reads the program from the storage device 36 and executes the program using the memory 34 as a work area. The CPU 32 controls each component and performs various arithmetic operations in accordance with the program stored in the storage device 36.

[0037] The memory 34 is made up of RAM (Random Access Memory) and serves as a working area to temporarily store programs and data. The storage device 36 is made up of ROM (Read Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), etc., and stores various programs including the operating system and various data.

[0038] The input device 38 is a device for performing various inputs, such as a keyboard or a mouse. The output device 40 is a device for outputting various information, such as a display or a printer. A touch panel display may be used as the output device 40 to function as the input device 38.

[0039] The storage medium reader 42 reads data stored in various storage media such as CD (Compact Disc)-ROM, DVD (Digital Versatile Disc)-ROM, Blu-ray Disc, USB (Universal Serial Bus) memory, etc., and writes data to the storage media. The communication I / F 44 is an interface for communicating with other devices, and uses standards such as Ethernet (registered trademark), FDDI, or Wi-Fi (registered trademark).

[0040] (Derivation of an approximate formula for calculating emissivity) In the dual-wavelength thermometry described above, the relationship between temperature and spectral radiance is nonlinear, making it impossible to analytically determine temperature and emissivity. Instead, temperature and emissivity must be calculated through time-consuming convergence calculations during the short time it takes for the line-shaped field of view (the inspection position) to pass through. Therefore, applying this method to width-direction temperature distribution, which requires several hundred temperature calculations, requires excessively long calculation times, making it impractical. Therefore, for processes like hot-dip galvanizing, which involve alloying processes like this, we decided to utilize the relatively small wavelength-dependent coefficient A1 to develop and use an approximate formula that can quickly calculate emissivity and temperature. The process of deriving the approximate formula is explained below.

[0041] First, when considering calculating the radiance ratio of two wavelengths, the radiance ratio of two wavelengths (dichromatic ratio) R is expressed by equation (114), which can be transformed into equation (115).

[0042]

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[0043] Here, the emissivity of the two wavelengths is the same, ε e (apparent emissivity), the apparent temperature T e If the correlation between temperature and radiance at two wavelengths in blackbody radiation is calculated in advance, that is, if temperature calibration is performed, ε can be calculated from equation (117). e It is possible to calculate

[0044]

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[0045] Here, when equation (117) is substituted into equation (115), equation (118) is derived.

[0046]

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[0047] On the other hand, the apparent emissivity ε e For , equation (119) holds.

[0048]

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[0049] Using equations (118) and (119), T and T e By eliminating A and ε B and apparent emissivity ε e The relational expression (120) is derived.

[0050]

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[0051] Substituting equation (106) into equation (120) and rearranging it, we obtain the apparent emissivity ε e can be expressed as in equation (121).

[0052]

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[0053] a / ε A When ∇<<1, the right-hand side of equation (121) can be approximated to a linear expression by Maclaurin series expansion as shown in equation (122). When up to two terms of the series are used so that it can be calculated analytically (i.e., so that convergence calculations are not required), equation (123) is derived.

[0054]

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[0055] where b=λ B / (λ B -λ A ) and convert it as in equation (124), and use the formula for solving the quadratic equation, the apparent emissivity εe From the actual emissivity ε A The emissivity ε is calculated as follows: A and radiance E A Using this, the temperature can be calculated by monochromatic calculation. Also, the emissivity ε B It is also possible to calculate the temperature using two-color calculations by calculating the above.

[0056]

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[0057] In this way, the emissivity ε A By calculating the emissivity ε A can be calculated, so the emissivity ε A Calculate the temperature T i can be calculated.

[0058] (Temperature measurement method explanation) Fig. 4 is a flowchart showing the flow of the temperature measurement process executed by the CPU 32 of the arithmetic processing unit 14. The CPU 32 reads a program for executing the temperature measurement process from the storage device 36, loads it into the memory 34, and executes it, causing the CPU 32 to function as each functional unit of the arithmetic processing unit 14 and execute the temperature measurement process shown in Fig. 4. In this way, the temperature measurement method is executed in the temperature measuring device 10.

[0059] In step S10, the apparent temperature calculation unit 22 acquires a hyperspectral image captured by the imaging unit 12. Next, in step S12, the apparent temperature calculation unit 22 calculates the wavelength λ A and λ B The radiance E at each A and E B Next, in step S14, the apparent temperature calculation unit 22 extracts the wavelength λ A and λ B and the extracted radiance E A and E BUsing equations (107) and (108), the apparent temperature T e Calculate.

[0060] Next, in step S16, the apparent emissivity calculation unit 24 calculates the apparent emissivity by using the relational expression L, which indicates the radiance at the temperature T and wavelength λ that has been previously calculated for blackbody radiation. b From (λ,T), the wavelength λ A and apparent temperature T e radiance L at b (λ A ,T e ) is calculated. Then, the apparent emissivity calculation unit 24 calculates the radiance E A and the calculated radiance L b (λ A ,T e ) and the apparent emissivity ε e Calculate.

[0061] Next, in step S18, the emissivity calculation unit 26 calculates the wavelength-dependent coefficient A1 and the wavelength λ A and λ B Then, the emissivity calculation unit 26 calculates a and b in the equations (111) and (112) using the above equations. e Using the above, the emissivity ε is calculated from the equation (110) which is an approximate calculation formula for the emissivity. A Calculate.

[0062] Next, in step S20, the temperature calculation unit 28 calculates the relational expression L b wavelength λ in (λ,T) A Applying the relation L b (λ A ,T i ) and the calculated emissivity ε A and radiance E A Using the temperature T i Calculate.

[0063] Next, in step S22, the temperature calculation unit 28 determines whether or not to end the measurement. For example, the temperature calculation unit 28 may determine that the measurement has ended when it detects that the imaging field of view of the imaging unit 12 has reached the end of the GA steel sheet. If the measurement has not ended, the process returns to step S10. If the measurement has ended, the temperature measurement process ends.

[0064] (Effect of temperature measurement device) As described above, when measuring the temperature of a steel sheet whose emissivity has a strong wavelength dependency, such as hot-dip galvanizing during the alloying process, the temperature measuring device according to this embodiment calculates the emissivity using an approximate formula derived by taking advantage of the fact that the wavelength-dependent coefficient is a relatively small value. This allows for high-speed calculation of the emissivity without requiring convergence calculation. Therefore, it is possible to quickly measure the temperature distribution in the width direction of a moving GA steel sheet without being affected by the emissivity, which changes significantly during the alloying process.

[0065] Furthermore, by using the temperature measured by the temperature measuring device according to this embodiment to uniformly control the temperature distribution in the width direction of the GA steel sheet within an appropriate temperature range, it becomes possible to produce a GA steel sheet with a uniform, high-quality plating alloy layer. That is, it becomes possible to measure the temperature distribution and radiance distribution in the width direction of the GA steel sheet during the iron-zinc alloying treatment within a time that is sufficient for the production speed (conveyance speed) of the GA steel sheet. Furthermore, it becomes possible to appropriately change and control the conditions of the iron-zinc alloying treatment of the GA steel sheet, which makes it possible to produce a uniform, high-quality GA steel sheet, as described above.

[0066] <Example> An example will be described that targets a GA steel sheet in the alloying process.

[0067] (Sensor specifications and hyperspectral camera used) Table 1 shows the required specifications for the temperature measurement device. The temperature of the GA steel sheet during the alloying process is between 400°C and 600°C, and the emissivity changes from approximately 0.2 (before alloying) to approximately 0.8 (after alloying) due to alloying. This corresponds to the fact that molten zinc has a metallic luster, whereas after alloying, the surface becomes rough as FeZn compounds solidify. To enable understanding of the relationship between plating quality and each part of the steel sheet as it is alloyed while being passed through, the distribution of temperature measurement points in the sheet width direction (width direction resolution) was set to 5 mm or less, the temperature measurement cycle in the sheet width direction (response speed) to 20 Hz, and the measurement accuracy was targeted to be within ±10°C of the actual measured value.

[0068] [Table 1]

[0069] Table 2 lists the specifications of the hyperspectral camera used as the imaging unit 12. To ensure sufficient sensitivity for detecting radiation even at a target temperature of 400°C and an emissivity of 0.2, a hyperspectral camera with an InGaAs photodetector sensitive to wavelengths from 900 nm to 1650 nm was selected as the 2D imaging element. The spatial channel count was 640. With a lens with a spatial angle of view of 65° and a distance of 1670 mm from the measurement point, the field of view in the strip width direction was 2000 mm, resulting in a resolution of approximately 3 mm. Meanwhile, the wavelength channel count was approximately 200, enabling the acquisition of spectral spectra in the range from 900 nm to 1700 nm at 3.5 nm intervals. The maximum frame rate was 50 fps, and sensitivity could be controlled by adjusting the exposure time.

[0070] [Table 2]

[0071] The hyperspectral image output from the hyperspectral camera is output as an image of 640 pixels (spatial direction CH) x 200 pixels (wavelength CH) and 4096 gradations (12 bits), and is input to the arithmetic processing unit 14. The arithmetic processing unit 14 calculates the radiance Ei is calculated and used to measure the temperature.

[0072] In the following embodiment, an example is shown in which two wavelengths are selected from four wavelengths to perform temperature measurement, but the number of wavelengths is not limited to four in order to widen the temperature measurement range. As long as the number of wavelengths is significant within the wavelength range of the hyperspectral camera, for example, six wavelengths may be used, with three wavelength combinations.

[0073] (Wavelength selection) Figure 5 shows the spectral spectra (measured luminance of the blackbody furnace at each wavelength) of the blackbody radiation from the high-temperature section of the blackbody furnace measured using a hyperspectral camera at temperatures of approximately 400°C, 500°C, and 600°C, which are included in the measurement temperature range for GA steel sheets. Figure 5 shows the values ​​after background correction (detected luminance values ​​in a completely dark environment, resulting from the dark current of the 2D image sensor). The exposure time of the blackbody furnace was set so that the radiated light intensity (measured luminance of the blackbody furnace) was approximately the same at each temperature. A temperature increase of approximately 100°C corresponds to 1 / 4 the exposure time. The radiated light intensity increases with wavelength, reaching a maximum around 1600 nm due to the sensitivity characteristics of the detector (InGaAs) used. The detection wavelengths were λ1 = 1300 nm, λ2 = 1400 nm, λ3 = 1500 nm, and λ4 = 1600 nm. In two-color radiation pyrometry, sensitivity decreases when the wavelength spacing is narrow. In order to ensure sufficient sensitivity to meet the required accuracy, a wavelength interval of 100 nm was set. The alloying temperature was around 500°C, and L b (1600nm, 500℃) / L b (1300 nm, 500°C) = 5.18. This value is greater than the magnification factor of 4 (= 0.8 / 0.2) of the change in emissivity before and after alloying, and temperature measurement is possible using either wavelength even if there is uneven alloying within the field of view. Note that when extracting brightness values ​​(radiant light intensity) from hyperspectral images, the average value of multiple channels (e.g., 5 channels) in the wavelength direction can be used to stabilize the brightness value.

[0074] (Temperature calibration using a blackbody furnace) Figure 6 shows the results of taking images of a blackbody furnace (T [℃] = 300-600) at set exposure times, extracting the radiance of each wavelength from the hyperspectral image, and plotting the relationship with temperature. d [μs] is t d [μs] = 1000, 1600, 2560, 4096, 6553, 10485, 16777, 26489, and the detection wavelengths are λ1 = 1300 nm, λ2 = 1400 nm, λ3 = 1500 nm, and λ4 = 1600 nm. In Figure 6, the background is shown as a subtracted value. Since the background may differ depending on the exposure time, measurements were taken by closing the shutter for each exposure time so that no light entered the two-dimensional image sensor. If the exposure time differs, the sensitivity of the hyperspectral camera will differ, making it impossible to obtain a correlation with temperature. Therefore, the brightness value I extracted from the hyperspectral image i (125) to obtain the reference exposure time t dst = 4096μs equivalent radiance E i I BG is the background. Figure 7 shows the radiance E i The results are shown below (equivalent to an exposure time of 4096 μs).

[0075]

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[0076] Next, the blackbody furnace temperature T and the radiance E for each wavelength i The relationship between these factors was investigated, and the temperature calibration coefficient α in Eq. (126) was calculated by curve regression. i and β i The results are shown in Table 3. By using this temperature calibration coefficient, it is possible to convert radiance and temperature using one calibration curve for each wavelength, without having to use a calibration curve for each exposure time.

[0077]

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[0078] [Table 3]

[0079] (Verification of temperature measurement accuracy) To verify the accuracy of the temperature measurements in the examples, the plated base sheet was electrically heated to alloy it with the Fe base material, and the thermal radiation spectrum during this process was measured using a hyperspectral camera to evaluate the temperature measurement performance during the alloying process. The plated base sheet was a 0.4 mm thick mild steel sheet that was coated with molten zinc and allowed to solidify. Figure 8 shows the configuration of the test equipment. The plated base sheet was heated to the alloying temperature (approximately 500°C) using electrical heating, maintained at a constant temperature, and alloyed. The radiation intensity during alloying was measured using a hyperspectral camera. The area directly behind the measurement point was painted with black paint, and the actual temperature was measured using a radiation thermometer. This was compared with the temperature measured by the hyperspectral camera.

[0080] (Temperature calculation method) A method for calculating the temperature at a certain position in the sheet width direction of the GA steel sheet in this embodiment will be described.

[0081] First, the radiance E of the temperature measurement area i is obtained from the hyperspectral image. Specifically, the wavelength λ at the temperature measurement position is obtained from the obtained two-dimensional hyperspectral image. i Brightness value I of (i=1,2,3,4) i Then, the brightness value I i The reference exposure time t dst = 4096μs, the radiance E i Get.

[0082] Next, the apparent temperature T when the emissivity of the wavelength is equal e and apparent emissivity ε e Specifically, the calculated radiance E i Of these, two wavelengths λ A and λ B The radiance E A and E Bis selected, and the temperature and emissivity are calculated assuming that the emissivity at both wavelengths is equal. More specifically, the apparent temperature T e and the dichromatic ratio R(=E A / E B ) is expressed as equation (127), so the apparent temperature T e Furthermore, the calculated apparent temperature T e Using Eq. (129), the apparent emissivity ε e Calculate.

[0083]

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[0084] Next, the actual emissivity ε is calculated by the approximation of Eq. (110). A Specifically, a = A1(1 / λ A -1 / λ B ), b=λ B / (λ B -λ A ), then ε e Using Eq. (110), ε A Here, A1 is a value determined in advance through an experiment. In the case of GA steel sheet, A1 = 0.10.

[0085] And finally, the calculated emissivity ε A The actual temperature T is calculated using the temperature calibration coefficient α i and β i and the calculated emissivity ε A and radiance E A Using the above, the temperature T is calculated using equation (131) which is a conversion of equation (130).

[0086]

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[0087] (Effect of calculation using approximate formula) Figure 9 shows the results of measuring the brightness values ​​at wavelengths λ1 to λ4, with the temperature fixed at 530°C and the exposure time adjusted so that wavelength λ4, which has the maximum intensity, does not saturate during the alloying process. Figure 9(a) shows the brightness values ​​extracted from the hyperspectral image, and Figure 9(b) shows the radiance after background correction and conversion to the standard exposure time (4096 μs). Figure 9(a) shows that the brightness values ​​increased during the alloying process, so the exposure time was changed from 4096 μs to 2560 μs to prevent saturation.

[0088] Figure 10 shows the calculated results for temperature and emissivity. It can be seen that the emissivity changed from approximately 0.2 before alloying to approximately 0.8 after alloying. In the case of A1 = 0.00, which does not take into account the wavelength dependence of emissivity as shown in Figure 10(a), the calculated temperature before alloying is output as approximately 30°C higher than the measured value. On the other hand, in the case of using the wavelength dependence coefficient A1 = 0.10 for the GA steel sheet as shown in Figure 10(b), it can be seen that the calculated temperature is within ±10°C of the measured value from before to after alloying.

[0089] In this way, it can be seen that calculating the temperature using the wavelength-dependent coefficient makes it possible to measure the temperature of the plating surface from before alloying to after alloying with high precision. Furthermore, because it is an approximate calculation, repeated numerical calculations such as convergence calculations are not required, and the temperature can be calculated quickly.

[0090] Although one example of the present invention has been described above, the present invention is not limited to the above, and it goes without saying that the present invention can be implemented in various modified forms within the scope of the gist of the present invention. [Explanation of symbols]

[0091] 10 Temperature measuring device 12 Imaging unit 14 Processing unit 22 Apparent temperature calculation section 24 Apparent emissivity calculation section 26 Emissivity calculation section 28 Temperature calculation section 32 CPU 34 memory 36 Storage device 38 Input Devices 40 Output Devices 42 Storage media reader 44 Communication I / F 46 Bus

Claims

1. Any wavelength λ ｉ Emissivity ε at ｉ A temperature measuring device for measuring the temperature of a steel plate having a relationship of formula (1), First wavelength λ Ａ The first radiance E is the radiance of the steel plate at Ａ , and the first wavelength λ Ａ a second wavelength λ different from Ｂ The second radiance E is the radiance of the steel plate at Ｂ an imaging unit for acquiring the a calculation processing unit that calculates the temperature of the steel plate; and The arithmetic processing unit The first wavelength λ Ａ and the second wavelength λ Ｂ Using the above, the apparent temperature T is calculated based on the equations (2) and (3). ｅ Calculate The first radiance E Ａ and the first wavelength λ Ａ and the apparent temperature T ｅ The radiance L of blackbody radiation, which was previously calculated using ｂ (λ Ａ , T ｅ ) and the apparent emissivity ε based on equation (4) ｅ Calculate The apparent emissivity ε ｅ Using the above, the first wavelength λ of the steel sheet is calculated based on the formulas (5) to (7). Ａ Emissivity ε at Ａ Calculate The emissivity ε Ａ A temperature measuring device that calculates the temperature of the steel plate based on equation (8) using the above. In addition, A ０ is an unknown constant determined by the steel plate, and A １ is a known constant determined by the steel plate, and c ２ is the second constant of radiation in Planck's radiation law, and the function L ｂ (λ ｉ , T ｉ ) at any temperature T ｉ Any wavelength λ at ｉ shows the radiance of blackbody radiation at [Equation 1]

2. The imaging unit has a field of view that includes the entire width of the steel plate, and captures the first wavelength λ at a plurality of positions within the field of view. Ａ and the second wavelength λ Ｂ The temperature measuring device according to claim 1 , further comprising a hyperspectral camera that acquires radiance of the steel plate for each of a plurality of wavelengths including

3. 3. The temperature measuring device according to claim 1, wherein the steel plate is a galvannealed steel plate.

4. Any wavelength λ ｉ Emissivity ε at ｉ A temperature measurement method for measuring the temperature of a steel plate having a relationship of formula (1), Using the imaging unit, a first wavelength λ Ａ The first radiance E is the radiance of the steel plate at Ａ , and the first wavelength λ Ａ a second wavelength λ different from Ｂ The second radiance E is the radiance of the steel plate at Ｂ a radiance acquisition step of acquiring Using a calculation processing unit, The first wavelength λ Ａ and the second wavelength λ Ｂ Using the above, the apparent temperature T is calculated based on the equations (2) and (3). ｅ an apparent temperature calculation step of calculating The first radiance E Ａ and the first wavelength λ Ａ and the apparent temperature T ｅ The radiance L of the blackbody radiation that was previously calculated using ｂ (λ Ａ , T ｅ ) and the apparent emissivity ε based on equation (4) ｅ An apparent emissivity calculation step of calculating The apparent emissivity ε ｅ Using the above, the first wavelength λ of the steel sheet is calculated based on the formulas (5) to (7). Ａ Emissivity ε at Ａ an emissivity calculation step of calculating The emissivity ε Ａ a temperature calculation step of calculating the temperature of the steel plate based on equation (8) using A temperature measurement method comprising: In addition, A ０ is an unknown constant determined by the steel plate, and A １ is a known constant determined by the steel plate, and c ２ is the second constant of radiation in Planck's radiation law, and the function L ｂ (λ ｉ , T ｉ ) at any temperature T ｉ Any wavelength λ at ｉ shows the radiance of blackbody radiation at [Equation 2]

5. The imaging unit has a field of view that includes the entire width of the steel plate, and captures the first wavelength λ at a plurality of positions within the field of view. Ａ and the second wavelength λ Ｂ The temperature measuring method according to claim 4, further comprising a hyperspectral camera that acquires radiance of the steel plate for each of a plurality of wavelengths including

6. 6. The temperature measuring method according to claim 4, wherein the steel sheet is a galvannealed steel sheet.

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