JP2009008439A - Method and device for measuring temperature distribution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a temperature distribution of the surface of a measuring object having a wide temperature range with higher-temperature resolution and higher resolution than ever. <P>SOLUTION: This device is equipped with a two-dimensional camera 1 having a shutter having a changeable exposure time and a two-dimensional solid imaging element, for outputting a brightness image of the measuring object; an imaging condition setting part 6 for outputting a plurality of brightness images to which an exposure time is linked by imaging with a plurality of exposure times by controlling the two-dimensional camera 1; an A/D conversion part 9 for taking each brightness image to which the exposure time is linked as gradation data; a temperature conversion data recording part 11 for storing data of a calibration curve showing a relation between a temperature and a gradation set in each exposure time; and a temperature distribution operation part 12 for deriving a temperature distribution in an effective temperature range corresponding to each exposure time based on the calibration curve relative to gradation data acquired in each of the plurality of exposure times, and deriving the temperature distribution of the surface of the measuring object. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for capturing a two-dimensional luminance image of a measurement object and measuring the temperature distribution on the surface of the measurement object.

  In general, there is an infrared thermography as a device for measuring the temperature distribution of an object to be inspected (object to be measured) in a non-contact manner. According to the latest catalogs of manufacturers of infrared thermography, those using a microbolometer (detection wavelength range 8-14 μm) as an infrared detector can operate at room temperature because it is an uncooled detector, and is relatively small and lightweight. It can be used for industrial purposes. The detection temperature range is from room temperature to about 500 ° C. at the maximum, and an ND filter is inserted in front of the infrared detector to attenuate incident light so that it can be measured to a high temperature of about 2000 ° C.

  However, the temperature measuring device has a problem that the temperature resolution is poor because the change in the received light energy of the infrared detector with respect to the temperature change amount of the inspection object is small. Further, the number of pixels of the microbolometer two-dimensional image sensor is as small as about 320 × 240, and the spatial resolution may be insufficient depending on the application. Furthermore, there is a limit to the downsizing of the image sensor unit, and there are cases where it is subject to space restrictions on the installation location compared to a CCD camera or the like.

  One means for solving this problem is to use a two-dimensional camera having a solid-state imaging device such as a CCD or CMOS having a sensitivity peak in the visible light wavelength range of 0.4 to 0.8 μm. One example is described in Patent Document 1, but there is a problem that the measurement temperature range is narrow at a high temperature of 1450 to 1600 ° C.

  Further, Patent Document 2 proposes a method for accurately measuring temperature in a wider temperature range. However, a two-dimensional image sensor having a logarithmic amplification function with respect to the amount of incident light is used as a detection unit, and is desired to be installed. There were many targets that could not be applied due to camera size restrictions, lack of resolution, processing speed restrictions, etc.

JP 2006-119110 A JP 2006-3081 A

  Therefore, there has been a demand for a technique that can measure the temperature distribution of an object to be inspected using a general two-dimensional camera having a solid-state imaging device such as a CCD or CMOS.

  In view of the above situation, the present invention provides a temperature distribution on the surface of an object to be measured having a wide temperature range (for example, about 500 ° C. or more and about 1500 ° C. or less) with a higher temperature resolution (for example, about 1 ° C. or less). ) And to provide a technique for measuring at high resolution.

The temperature distribution measuring method of the present invention is a temperature distribution measuring method for measuring the temperature distribution of the surface of a measured object by taking a luminance image of the measured object with a two-dimensional camera, and using the two-dimensional camera. A procedure for capturing an object to be measured for each of a plurality of exposure times, converting a luminance image obtained by the imaging to obtain gradation data, and exposing the gradation data obtained for each of the plurality of exposure times in advance. A procedure for deriving a temperature distribution of an effective temperature range corresponding to each exposure time based on a calibration curve indicating a relationship between temperature and gradation set for each time, and a temperature of the effective temperature range corresponding to the plurality of exposure times And a procedure for deriving a temperature distribution of the surface of the object to be measured using the distribution.
Another feature of the temperature distribution measuring method according to the present invention is that, prior to imaging by the two-dimensional camera, a procedure for inputting temperature measurement information for temperature measurement related to the object to be measured, and the input. And determining a plurality of exposure times by estimating a temperature range of the object to be measured by a predetermined process based on the measured temperature information.
A temperature distribution measuring apparatus according to the present invention is a temperature distribution measuring apparatus that measures a temperature distribution of a surface of a measurement object by taking a two-dimensional luminance image of the measurement object, and includes a shutter having a variable exposure time and An imaging unit having a two-dimensional solid-state imaging device and outputting a luminance image of the object to be measured; and controlling the imaging unit to capture images with a plurality of exposure times, and outputting a plurality of luminance images associated with the exposure times Imaging condition setting means to be performed, fetching means for capturing each luminance image associated with the exposure time as gradation data, and temperature storing calibration curve data indicating the relationship between the temperature and gradation set for each exposure time For the gradation data obtained for each of the plurality of exposure times with the conversion data recording means, a temperature distribution in an effective temperature range corresponding to each exposure time is derived based on the calibration curve, and a table of the object to be measured is obtained. Characterized in that it comprises a temperature distribution computing means for deriving a temperature distribution.
Further, another feature of the temperature distribution measuring apparatus according to the present invention is that the temperature measurement information input by the input means is input to temperature measuring information for temperature measurement related to the object to be measured. An exposure time setting unit that estimates the temperature range of the object to be measured and determines the plurality of exposure times, and the imaging condition setting unit sets the plurality of exposure times determined by the exposure time setting unit. Based on this, the imaging means is controlled.

  According to the present invention, since a luminance image of the object to be measured is captured for each of a plurality of exposure times using a two-dimensional camera and a temperature distribution is derived for each of the luminance images, the object to be measured having a wide temperature range. It becomes possible to measure the temperature distribution of the surface of the object with high temperature resolution and high resolution.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of a temperature distribution measuring apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining the processing operation of the temperature distribution measuring apparatus according to the embodiment of the present invention.

  The main components of the temperature distribution measuring apparatus according to the present embodiment are a two-dimensional camera 1 having a solid-state image sensor and a signal processing unit 2. In this case, the two-dimensional camera 1 and the signal processing unit 2 may be configured integrally, or for example, the two-dimensional camera 1 and the signal processing unit 2 may be configured separately.

  The two-dimensional camera 1 corresponds to the imaging means in the present invention, and includes a CCD or CMOS type two-dimensional solid-state imaging device 8 and an electronic shutter 7 whose shutter speed can be flexibly changed from a low speed to a high speed. The image data captured at the set shutter speed is output.

  The signal processing unit 2 includes an A / D conversion unit 9 (corresponding to a capturing unit in the present invention) that captures image data output from the two-dimensional camera 1 as gradation data that is digital data, and a gradation data storage unit 10. And a temperature distribution calculation unit 12 and a temperature conversion data recording unit 11 to perform data processing. In addition, the signal processing unit 2 includes an input unit 4, an exposure time setting unit 5, and an imaging condition setting unit 6 so that the two-dimensional camera 1 can capture an image under a desired appropriate condition. The signal processing unit 2 includes an output unit 13 and displays or records the temperature distribution measurement result.

  The imaging condition setting unit 6 controls the two-dimensional camera 1 to capture images with a plurality of exposure times, and outputs a plurality of luminance images associated with the exposure times. The A / D conversion unit 9 corresponds to the capturing means referred to in the present invention, and captures each luminance image associated with the exposure time as gradation data. The temperature conversion data recording unit 11 stores calibration curve data indicating the relationship between temperature and gradation set for each exposure time. The temperature distribution calculation unit 12 derives the temperature distribution of the effective temperature range corresponding to each exposure time based on the calibration curve for the gradation data obtained for each of a plurality of exposure times, and the surface of the object to be measured The temperature distribution of is derived. The input unit 4 inputs temperature measurement information for temperature measurement and a measurement start command regarding the object to be measured. The exposure time setting unit 5 estimates a temperature range of the object to be measured based on the temperature measurement information input by the input unit 4 and determines a plurality of exposure times.

  The temperature conversion data recording unit 11 of the signal processing unit 2 stores calibration curve data of the two-dimensional camera 1 (see FIG. 3). The calibration curve is measured in advance using the black body furnace as the object to be measured by the two-dimensional camera 1 while changing the temperature, and the exposure time of the two-dimensional camera 1 (reciprocal of shutter speed: ti (where i = 1, 2, ...)) is used as a parameter to image the inside of the black body furnace, and the relationship between the brightness level of the captured image and the temperature of the surface of the object to be measured is obtained using the emissivity of the object to be measured. It is. In the present embodiment, the output level after A / D conversion is represented by 8 bits, that is, 0 to 255 levels (hereinafter referred to as “gradation”).

The gradation that has no saturation of the luminance signal or the like and has a good one-to-one correspondence accuracy with the temperature is in the range of 40 to 210. Therefore, in the range of 1000 ° C. ≧ T> T ₁ , the gradation P can be uniquely converted into temperature by the curve l ₁ calibrated at the exposure time t ₁ . Similarly, T ₁ ≧ T> T curve l ₂ in ₂ ranges, T ₂ ≧ T> T ₃ in the range curve _{l 3, T 3 ≧ T>} T curve l ₄ in the range of _4, T ₄ ≧ T> In the range of 500 ° C., the gradation P can be uniquely converted into temperature by the curve l ₅ .

  As described above, by increasing the shutter speed of the two-dimensional camera 1 in accordance with the input light amount (incident light amount) and shortening the exposure time (t1 <t2 <t3 <t4), the object to be measured has a higher temperature. However, the calibration curve can be derived as long as the temperature can be measured in the experiment.

  Temperature measurement information for temperature measurement related to the object to be measured imaged by the two-dimensional camera 1 is input to the input unit 4 of the signal processing unit 2. The input unit 4 may be manually input with a keyboard or the like, or may be configured with, for example, a network I / O device in a factory. The temperature measurement information is a material to be measured (depending on the emissivity of synchrotron radiation for temperature measurement) and operation conditions (heating information in the furnace, welding information, heating cutting information, etc.). For example, when measuring the surface temperature of the metal strip in the heating furnace, the material of the metal strip and the operating conditions of the heating furnace are applicable, and when measuring the surface temperature of the welded portion of the steel plate, the steel type and welding conditions of the steel plate are Applicable.

In the exposure time setting unit 5, a reference table or an estimation that roughly estimates the temperature region and the emitted light intensity of the object to be measured from the knowledge accumulated based on the results of measuring many objects to be measured and the emissivity of each material. The formula is held in advance as an estimation database. And based on the said estimation database, although the effective temperature range (maximum temperature-minimum temperature) of a to-be-measured object is estimated by the exposure time setting part 5 about the said temperature measurement information, from the effective temperature range, the above-mentioned calibration curve ( The exposure time used in the two-dimensional camera 1 is obtained by referring to FIG. In the example of FIG. 3, when the temperature range is determined to be 800 to 950 ° C., the exposure times t ₁ and t ₂ are selected. When the temperature range is determined to be 600 to 850 ° C., the exposure times t ₂ , t ₃ and t ₄ are selected.

In FIG. 3, the temperature ranges of adjacent curves l _i are set so as not to overlap each other, but may be overlapped by about 1/5, for example. Then, an exposure time that is, for example, within 1/10 from the end of the temperature range of the curve l _i is not adopted. In this way, even when the effective temperature range is the boundary region between the temperature ranges of the two curves l _i , measurement can be performed with an appropriate exposure time with little measurement error.

  The exposure time of one set (one or more) selected as described above is read out by the imaging condition setting unit 6 of the image processing unit 3, and window setting parameters (parameters for specifying the range of images to be extracted) or It is sent to the two-dimensional camera 1 together with other set values such as a shutter mode (step S101 in FIG. 2). Setting values other than the exposure time are sent to the two-dimensional camera 1 in advance.

  When a measurement start command is input to the input unit 4, the imaging condition setting unit 6 sends an initial exposure time to the two-dimensional camera 1 and exposes and captures an image for the exposure time set by the electronic shutter 7. Light energy accumulated in each pixel of the two-dimensional solid-state imaging device 8 of the two-dimensional camera 1 is converted into a signal and output as luminance image data. This luminance image data is sent to the A / D conversion unit 9 of the image processing unit 3 of the signal processing unit 2, where it is converted into gradation data which is digital data of a predetermined number of bits, and the gradation data storage unit 10 (Step S102 in FIG. 2).

Further, similar imaging is performed for all the plurality of exposure times set by the exposure time setting unit 5 under the instruction of the imaging condition setting unit 6, and each gradation data is stored in the gradation data storage unit 10 according to the exposure time. Are stored in association with each other. For example, when the exposure time t ₂ and t ₃ and t ₄ have been selected will be carried out continuously three measurements. What is important here is that a plurality of measurements, that is, a plurality of imaging operations and storage of gradation data are performed without any delay, and no other processing is performed during the measurement, and the imaging processing is performed at high speed. Thus, a plurality of measurements are completed in a short time, and a plurality of gradation data having different exposure times are accumulated in the data storage unit 10 while there is almost no temperature change with the passage of time.

  Note that the measurement start command may be configured by manually or continuously measuring the input unit 4 with a keyboard or switch, or configured with an I / O port or network port with an external device, It may be synchronized with the phenomenon so that it is output according to the purpose of temperature measurement.

Next, the temperature distribution calculation unit 12 performs temperature conversion for each pixel using the calibration curve stored in the temperature conversion data recording unit 11 for the gradation data stored in the gradation data storage unit 10. For example, when exposure times t ₂ , t ₃ and t ₄ are selected, first, the temperature T is obtained by applying the gradation obtained by imaging at the exposure time t ₂ to the curve l ₂ , and T ₁ ≧ If T> T ₂ , the temperature is adopted. In this case, if T ₂ ≧ T, the temperature T is obtained by applying the gradation obtained by imaging at the exposure time t ₃ to the curve l ₃ , and if T ₂ ≧ T> T ₃ , Adopt that temperature. In this case, if T ₃ ≧ T, the temperature T is obtained by applying the gradation obtained by imaging at the exposure time t ₄ to the curve l ₄ , and if T ₃ ≧ T> T ₄ , If that temperature is adopted and T ₄ ≧ T, the temperature is T ₄ or less. By performing such processing in each pixel, the temperature distribution can be output (step S103 in FIG. 2). Here, the portion outside T ₄ ≧ T and the effective temperature range may be, for example, a portion where an object around the object to be measured is measured, which is not a portion to be measured, and may be a result of T ₄ or less. . Although it has been described that the temperature conversion is performed for each pixel, the temperature conversion may be performed after averaging a plurality of adjacent pixels.

  Thereafter, the temperature distribution calculation unit 12 displays the gradation conversion result for each pixel of the gradation data (or for each of a plurality of pixels) on the output unit 13 constituted by a computer display, color-coded according to the temperature, or displays the contour lines. (Step S104). Further, the temperature conversion result and the display image on the computer display may be recorded in a recording device constituted by a hard disk drive or the like having a built-in function.

  With the temperature distribution measurement method described above, a wide temperature distribution of about 500 ° C. to 1000 ° C. can be obtained with a high resolution of about 1 ° C. or less using a general two-dimensional camera having a CCD or CMOS type two-dimensional solid-state imaging device. It becomes possible to measure with.

  In the above processing, as an example, the method of measuring using the calibration curve in the range of 500 to 1000 ° C. shown in FIG. 3 has been described, but this range can be changed according to the purpose. Since the light energy becomes weak, the measurement for an object of 500 ° C. or lower is difficult because the radiation intensity in the visible light region is extremely small and difficult, but it can be sufficiently applied to an object of about 500 ° C. or higher. By determining the calibration curve range according to the measurement purpose, selecting the camera while considering the measurement conditions, and selecting the exposure time appropriately, if a calibration curve in the desired range is created, measurement in a wider range is possible It is.

In the processing described so far, the temperature measurement information is received by the input unit 4, the exposure time is selected by the exposure time setting unit 5, and the subsequent processing is performed only for the selected exposure time. However, there is also a method of performing subsequent processing for all exposure times. Specifically, if calibration curve data of the two-dimensional camera 1 as shown in FIG. 3 is used, all exposure times from t ₁ to t ₅ are selected and the subsequent processing is performed. . In this method, in order to determine the effective temperature range, it is not necessary to measure a large number of objects in advance and obtain knowledge, and this saves time, but it takes time to measure one temperature distribution, so time elapses. It is unsuitable for a measurement object having a large temperature change due to. Therefore, it is necessary to select an optimum method according to the object to be measured and the measurement purpose.

Further, only the exposure time as a parameter t _i in order to adjust the amount of light incident on the two-dimensional camera 1. From the viewpoint of capturing a luminance image at high speed, it is preferable to perform high-speed imaging with the aperture of the two-dimensional camera 1 fully opened. However, when the temperature change with time is not so fast, the exposure time and field of view are only adjusted by adjusting the amount of incident light. An aperture may be used together as an exposure parameter. At this time, the exposure time in the above description may be read as the exposure time and the field stop.

  In the temperature distribution measuring apparatus of the present invention, the signal processing unit 2 includes a keyboard, a mouse, an I / O board, or a network card as the input unit 4, a memory for storing and recording each data and database, an HDD, or a DVD-RAM. Further, it can be constituted by a recording device such as a computer and a computer having a computer display for displaying the measurement result. What is necessary is just to create a computer program for executing each procedure of the above-described imaging control of the two-dimensional camera 1 and signal processing over temperature conversion from imaging data, and load and execute it in a built-in memory.

(Example)
For the purpose of measuring the temperature distribution of the welded portion in flash butt welding for joining steel plates, the temperature distribution measuring device to which the present invention is applied is input to the image processing unit 3 and the signal processing unit 2 as an A / D conversion unit 9. It was constructed and applied using a personal computer with a board. FIG. 4 shows an example of the resulting gradation data and the temperature distribution of the temperature conversion result.

  From the process computer of the line including the welder, the material information and welding conditions of the preceding steel plate and the succeeding steel plate are transmitted to the input unit 4 via the network before the start of welding, and are selected by the exposure time setting unit 5 from the information. The three exposure times are (1) 0.72 ms, (2) 3.0 ms, and (3) 15.0 ms.

  Immediately after welding, a measurement start command is issued from the process computer to the input unit 4 and the exposure time is changed by the electronic shutter 7 of the two-dimensional camera 1 (using a 2000 × 2000 pixel CMOS camera). Went. A signal of 2000 × 500 pixels including a welded portion is read from the two-dimensional imaging device 8, converted into 8-bit gradation data by the A / D conversion unit 9, and stored in the gradation data storage unit 10. The Examples of images corresponding to exposure times of 0.72 ms, 3.0 ms, and 15.0 ms are P1, P2, and P3 in FIG. Using the gradation data of the three images, the temperature of each pixel was converted by the method described above to obtain the temperature distribution.

  The obtained result is a set (distribution) of temperature values with a resolution of about 1 ° C. or less, and it is effectively used for various applications such as applying to the logic for judging the soundness of the welding state. Even if the numerical data that is the result of is enumerated or re-imaged, it cannot be evaluated. Therefore, in order to show the validity of the results in an easy-to-understand manner, I used a graph. Regarding the images of P1 to P3, G1 to G3 represent the temperatures of the portions corresponding to the weld lines at the same position, respectively, and the graph output from the temperature distribution measurement result by this method is G4. is there. In the measurement with a single exposure time setting, a measurement result (G1 to G3) in which a sufficient temperature range cannot be obtained is obtained. According to the method of the present invention, a wide temperature distribution can be measured (G4). It can be seen that

It is a figure which shows schematic structure of the temperature distribution measuring apparatus which concerns on embodiment of this invention. It is a flowchart for demonstrating the processing operation of the temperature distribution measuring apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the calibration curve of the camera used for temperature conversion. It is a figure which shows the result of applying this invention to the temperature distribution measurement of the welding part in flash butt welding.

Explanation of symbols

1: two-dimensional camera 2: signal processing unit 3: image processing unit 4: input unit 5: exposure time setting unit 6: imaging condition setting unit 7: electronic shutter 8: two-dimensional solid-state imaging device 9: A / D conversion unit 10 : Gradation data storage unit 11: temperature conversion data recording unit 12: temperature distribution calculation unit 13: output unit

Claims (4)

A temperature distribution measuring method for measuring a temperature distribution of a surface of a measurement object by taking a luminance image of the measurement object with a two-dimensional camera,
A procedure for capturing an object to be measured for each of a plurality of exposure times using the two-dimensional camera, converting a luminance image obtained by the imaging, and obtaining gradation data;
With respect to the gradation data obtained for each of the plurality of exposure times, a temperature distribution of an effective temperature range corresponding to each exposure time is derived based on a calibration curve indicating a relationship between a temperature and a gradation set for each exposure time in advance. And the steps to
And a procedure for deriving the temperature distribution of the surface of the object to be measured using the temperature distribution in the effective temperature range corresponding to the plurality of exposure times. Prior to imaging by the two-dimensional camera, a procedure for inputting temperature measurement information for temperature measurement related to the object to be measured;
2. The temperature distribution according to claim 1, further comprising: a step of estimating a temperature range of an object to be measured by a predetermined process based on the input temperature measurement information and determining the plurality of exposure times. Measuring method. A temperature distribution measuring device that takes a two-dimensional luminance image of a measurement object and measures the temperature distribution of the surface of the measurement object,
An imaging means having a shutter and a two-dimensional solid-state imaging device with variable exposure time, and outputting a luminance image of the object to be measured;
Imaging condition setting means for controlling the imaging means to take images at a plurality of exposure times and outputting a plurality of luminance images associated with the exposure times;
Capture means for capturing each luminance image associated with the exposure time as gradation data;
Temperature conversion data recording means storing calibration curve data indicating the relationship between temperature and gradation set for each exposure time;
For the gradation data obtained for each of the plurality of exposure times, a temperature distribution in the effective temperature range corresponding to each exposure time is derived based on the calibration curve, and a temperature distribution on the surface of the object to be measured is derived. A temperature distribution measuring device comprising temperature distribution calculating means. Input means for inputting temperature measurement information for temperature measurement related to the object to be measured;
An exposure time setting means for estimating the temperature range of the object to be measured based on the temperature measurement information input by the input means and determining the plurality of exposure times;
The temperature distribution measuring apparatus according to claim 3, wherein the imaging condition setting unit controls the imaging unit based on a plurality of exposure times determined by the exposure time setting unit.

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