Temperature measurement device and temperature measurement method

Abstract

A temperature measurement device 100 according to the present disclosure comprises a first camera 12 which continuously images a surface of an object 16 to generate a plurality of surface images IMGv, and a second camera 14 which images the surface of the object 16 to generate an infrared image IMGi. The phase state of the surface of the object 16 is determined on the basis of changes over time occurring in the plurality of surface images IMGv, and emissivity corresponding to the phase state determination result is used to create surface temperature data IMGc from the infrared image IMGi.

Description

Thermometer and Temperature Measurement Method

[0001] The present disclosure relates to a thermometer and a temperature measurement method.

[0002] Conventionally, a technique for joining two members by laser welding is known.

[0003] Patent Document 1 discloses non-contact measurement of the surface temperature of a welded portion using an infrared camera in order to evaluate the quality of the welded portion by laser welding.

[0004] In order to accurately measure the temperature of an object with an infrared camera, it is desirable to set an emissivity according to the object. Patent Document 2 describes determining an object from an image generated by a visible light camera and setting the emissivity of the infrared camera according to the object.

[0005] Japanese Patent Application Laid-Open No. 2001-191186, Japanese Patent Application Laid-Open No. 2022-85673

[0006] The present disclosure provides a technique for improving the accuracy of non-contact temperature measurement.

[0007] The present disclosure provides a thermometer comprising: a first camera that continuously photographs the surface of an object to generate a plurality of surface images; and a second camera that photographs the surface of the object to generate an infrared image. Based on changes over time in the plurality of surface images, the phase state of the surface of the object is determined, and temperature data of the surface is created from the infrared image using an emissivity corresponding to the determination result of the phase state.

[0008] According to the technique of the present disclosure, the accuracy of non-contact temperature measurement can be improved.

[0009] FIG. 1 is a configuration diagram of a thermometer according to an embodiment of the present disclosure. FIG. 2 is a conceptual diagram of a table storing the correspondence between the material of an object, the emissivity in the solid state, and the emissivity in the liquid state. FIG. 3 is a flowchart showing processing related to a temperature measurement method according to an embodiment of the present disclosure. FIG. 4 is a schematic diagram showing a method for determining a phase state from a plurality of surface images of an object.

[0010] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0011] (Embodiment) Figure 1 is a configuration diagram of a temperature measuring device according to an embodiment of the present disclosure. The temperature measuring device 100 is a device for measuring the surface temperature of an object 16 in a non-contact manner, and comprises a first camera 12, a second camera 14, and a computer 20.

[0012] The first camera 12 continuously captures images of the surface of the object 16 to generate multiple surface images IMGv. In other words, the first camera 12 can capture a video of the surface of the object 16 at a predetermined frame rate (fps). The first camera 12 is a visible light camera equipped with an image sensor that is sensitive to visible light. The surface images IMGv generated by the first camera 12 may be visible light images. Visible light images may be color images or monochrome images.

[0013] The first camera 12 can, for example, photograph the surface of the object 16 at a frame rate of 12,000 fps or higher.

[0014] The second camera 14 captures the surface of the object 16 and generates one or more infrared images IMGi. The second camera 14 may be an infrared camera equipped with an image sensor sensitive to infrared light. The infrared images IMGi may be two-dimensional heatmaps.

[0015] The second camera 14 may continuously capture images of the surface of the object 16 to generate multiple infrared images IMGi. In other words, the second camera 14 can also capture a video of the surface of the object 16 at a predetermined frame rate. The frame rate of the second camera 14 may match or differ from the frame rate of the first camera 12. However, it is not essential that the second camera 14 can capture video.

[0016] The second camera 14 generates an infrared image IMGi of the object 16 using a preset emissivity. When using the second camera 14, the operator inputs an appropriate emissivity corresponding to the object 16 to the second camera 14. The emissivity corresponding to the object 16 may be provided to the second camera 14 from the computer 20. The second camera 14 generates an infrared image IMGi from the signal intensity of each pixel, for example, using the emissivity of a blackbody (=1).

[0017] The object 16 is, for example, a workpiece to be laser-welded. The precise temperature of the workpiece and its change over time can be valuable information when setting various parameters related to laser welding, such as the laser light intensity, laser light irradiation time, and laser light spot diameter. The workpiece may be made of metal or resin. The first camera 12 and the second camera 14 capture images not only of the welding area but also of the surrounding area.

[0018] The physical phenomena involved in laser welding are largely unknown. Therefore, setting various parameters for laser welding relies on human trial and error. The precise temperature of the weld area and its time evolution can provide clues when setting these parameters. Furthermore, accurate information on the temperature of the weld area and its time evolution is necessary to elucidate the physical phenomena of laser welding using computer simulations. This information can improve the accuracy of simulations and, consequently, enable the deriving of optimal parameters for laser welding.

[0019] The computer 20 acquires multiple surface images IMGv generated by the first camera 12 and one or more infrared images IMGi generated by the second camera 14. The computer 20 includes a processor, memory, storage, input / output interfaces, etc., and operates according to a predetermined program.

[0020] The memory or storage of the computer 20 stores the emissivity of various objects 16 in their solid and liquid states. Figure 2 is a conceptual diagram of a table that stores the correspondence between the material of the object 16, its emissivity in the solid state, and its emissivity in the liquid state. The computer 20 may have such a table. Such a table contributes to the rapid measurement of the temperature of various types of objects 16.

[0021] Figure 3 is a flowchart illustrating the process of the temperature measurement method according to this embodiment. Each process shown in Figure 3 can be executed by the computer 20.

[0022] In step S1, while processing (laser welding) the object 16, multiple surface images IMGv of the object 16 are acquired from the first camera 12, and one or more infrared images IMGi of the object 16 are acquired from the second camera 14. The multiple surface images IMGv are time-series images. The multiple infrared images IMGi are also time-series images.

[0023] In step S2, the phase state of the surface of the object 16 is determined based on the changes over time in multiple surface images IMGv. More specifically, the phase state is determined by whether or not there are changes between multiple surface images IMGv.

[0024] Figure 4 is a schematic diagram showing a method for determining the phase state of an object 16 from multiple surface images IMGv. When the surface of the object 16 changes from a solid state to a liquid state, this change is reflected in the surface images IMGv. In this embodiment, the phase state of the surface of the object 16 is determined by comparing multiple surface images IMGv with each other. Compared to a method for determining the phase state from a single visible light image, the method of this embodiment is suitable for capturing changes in the phase state.

[0025] At time t0 shown in Figure 4, laser light irradiation of the object 16 is started. No change is observed between the surface image IMGv at time t0 and the surface image IMGv at time t1. Specifically, the difference between the signal intensity of each pixel in the surface image IMGv at time t0 and the signal intensity of each pixel in the surface image IMGv at time t1 is calculated. Based on the difference in signal intensity of the corresponding pixels, the presence or absence of a change is determined. In other words, the change over time in multiple surface images IMGv is calculated in the form of the change in signal intensity at each pixel of the first camera 12. The presence or absence of a change in phase state is determined from the calculated change. For example, if the change in signal intensity exceeds a predetermined threshold, it is determined that there is a change in phase state. If the change in signal intensity is less than or equal to the predetermined threshold, it is determined that there is no change in phase state. Using this method, it is possible to determine the change in phase state for each pixel.

[0026] The computer 20 determines the phase state of the object 16 for each pixel of the surface image IMGv. In other words, in the process executed by the computer 20, the surface of the object 16 is divided into multiple parts corresponding to each pixel, and the phase state is determined for each divided part.

[0027] The change in signal intensity may be calculated using multiple pixels as a single unit. For example, the presence or absence of a phase state change may be determined from the change in the total signal intensity of nine pixels (3 pixels vertically x 3 pixels horizontally). If the change in the total value exceeds a predetermined threshold, it is determined that there is a change in the phase state for the corresponding nine pixels. In this case, the phase state determination only needs to be performed once for each of the nine pixels.

[0028] In step S3 of Figure 3, surface temperature data IMGc is created from the infrared image IMGi using the emissivity corresponding to the phase state determination result. This allows for accurate temperature measurement results corresponding to the phase state.

[0029] As shown in the example in Figure 4, the solid-state emissivity is applied to the entire range of the infrared image IMGi at time t1 to create the final temperature data IMGc. Specifically, the temperature data IMGc is created by multiplying the signal intensity of each pixel in the infrared image IMGi by the solid-state emissivity. The temperature data IMGc can be a two-dimensional heatmap similar to the infrared image IMGi. In other words, the temperature data IMGc can be a corrected infrared image.

[0030] As shown in Figure 4, at time t2, a welded portion L appears on the surface of the object 16. Therefore, the extent of the welded portion L can be determined from the difference between the surface image IMGv at time t1 and the surface image IMGv at time t2. Before welding, the surface of the object 16 is in a solid state. When laser light is irradiated onto the object 16, the surface of the irradiated portion melts and changes to a liquid state. Therefore, the welded portion L is in a liquid phase state. The emissivity of the liquid state is applied to the pixels corresponding to the welded portion L, and the emissivity of the solid state is applied to the other pixels, and temperature data IMGc is created from the infrared image IMGi at time t2.

[0031] As shown in Figure 4, the size of the welded area L expands from time t2 to time t3. Therefore, the emissivity of the liquid state is applied to the pixels corresponding to the expanded welded area L, and the emissivity of the solid state is applied to the other pixels, and temperature data IMGc is created from the infrared image IMGi at time t3.

[0032] According to the above method, surface temperature data IMGc is created from the infrared image IMGi using the emissivity corresponding to the phase state determination result. By comparing multiple surface images IMGv with each other, changes in the surface of object 15 can be captured. Changes in the surface of object 16 represent changes in the phase state. By applying the emissivity corresponding to the phase state to the infrared image IMGi, the accurate surface temperature can be measured.

[0033] According to the method of this embodiment, temperature data IMGc is created in a time series in synchronization with the infrared image IMGi.

[0034] At time t3, when laser irradiation is stopped, the welded portion L solidifies rapidly. Similar to the change from a solid state to a liquid state, the change from a liquid state to a solid state can be captured from a time-series surface image IMGv, and the final temperature data IMGc can be created using the emissivity corresponding to the phase state.

[0035] In this embodiment, when determining whether or not there is a change in the surface of the object 16, the surface image IMGv at time t1 is compared with the surface image IMGv at time t2. However, the surface image IMGv at time t0 may be compared with the surface image IMGv at time t1, or the surface image IMGv at time t1 may be compared with the surface image IMGv at time t3. The surface images IMGv being compared do not have to be adjacent to each other on the time axis.

[0036] The pixel size of the first camera 12 may or may not match the pixel size of the second camera 14. The pixel size of the first camera 12 may be smaller than the pixel size of the second camera 14. In this case, the final temperature data IMGc can be created to match the pixel size of the infrared image IMGi generated by the second camera 14. For example, if the pixel size of the first camera 12 is 8.33 μm / pixel and the pixel size of the second camera 14 is 25 μm / pixel, the phase state determination result based on nine pixels (e.g., the average value of the difference in signal intensity of multiple (nine) pixels) in the surface image IMGv generated by the first camera 12 can be applied to one pixel in the infrared image IMGi generated by the second camera 14.

[0037] As shown in Figure 1, the positional relationship between the first camera 12 and the object 16 is different from the positional relationship between the second camera 14 and the object 16. On the other hand, the coordinates of the area captured by the first camera 12 are known. The coordinates of the area captured by the second camera 14 are also known. Therefore, the correspondence between each pixel in the surface image IMGv generated by the first camera 12 and each pixel in the infrared image IMGi generated by the second camera 14 is also known.

[0038] For example, the correspondence between each pixel of the surface image IMGv generated by the first camera 12 and each pixel of the infrared image IMGi generated by the second camera 14 is predetermined and stored in the computer 20. The computer 20 also sets an emissivity for each pixel of the infrared image IMGi based on the correspondence between each pixel of the surface image IMGv and each pixel of the infrared image IMGi, according to the phase state determined from multiple surface images IMGv. The computer 20 uses the emissivity set for each pixel to convert the infrared intensity of each pixel of the infrared image IMGi into a temperature value.

[0039] As shown in Figure 1, the final temperature data IMGc may be fed back to a processing device 22 (e.g., a laser processing machine) for processing the object 16. This configuration can improve the processing accuracy in the processing device 22. For example, the processing conditions in the laser processing machine may be adjusted using the temperature data IMGc. For example, the laser processing machine adjusts processing conditions such as the laser beam intensity, laser beam irradiation time, and laser beam spot diameter so that the temperature of the welded portion L falls within a specified range.

[0040] (Modification) The first camera 12 and the second camera 14 may be integrated. For example, with an image sensor having a structure in which a photoelectric conversion film sensitive to visible light and a photoelectric conversion film sensitive to infrared light are stacked, the number of pixels and shooting range of the first camera 12 will match the number of pixels and shooting range of the second camera 14. In this case, image processing to match the number of pixels and shooting range of the first camera 12 to the number of pixels and shooting range of the second camera 14 can be omitted.

[0041] The computer 20 may be located at a distance from the object 16. The computer 20 may be, for example, a cloud computer. In this case, image data is transmitted from the first camera 12 and the second camera 14 to the computer 20 via a communication network such as the internet.

[0042] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0043] (Technology 1) A temperature measurement device comprising: a first camera that continuously photographs the surface of an object to generate a plurality of surface images; and a second camera that photographs the surface of the object to generate an infrared image. Based on the temporal changes in the plurality of surface images, the phase state of the surface of the object is determined, and temperature data of the surface is created from the infrared image using an emissivity corresponding to the determination result of the phase state.

[0044] According to the technology of the present disclosure, the accuracy of non-contact temperature measurement can be improved.

[0045] (Technology 2) The temperature measurement device according to Technology 1, wherein the phase state is determined by the presence or absence of changes between the plurality of surface images. According to such a configuration, the accuracy of non-contact temperature measurement can be improved.

[0046] (Technology 3) The temperature measurement device according to Technology 1, wherein the temporal change in the plurality of surface images is calculated in the form of a change amount of signal intensity in one or more pixels of the first camera, and the presence or absence of a change in the phase state is determined from the change amount. According to such a method, the change in the phase state can be determined for each pixel.

[0047] (Technology 4) The temperature measurement device according to any one of Technologies 1 to 3, wherein the temperature data is fed back to a processing device for processing the object. According to such a configuration, the processing accuracy in the processing device can be improved.

[0048] (Technology 5) The temperature measurement device according to any one of Technologies 1 to 4, wherein the object includes a workpiece to be laser welded. The accurate temperature of the workpiece to be laser welded can be useful information when setting various parameters related to laser welding, such as the intensity of the laser beam, the irradiation time of the laser beam, and the spot diameter of the laser beam.

[0049] (Technical 6) A method for measuring temperature, comprising: continuously photographing the surface of an object to acquire multiple surface images; photographing the surface of the object to acquire an infrared image; determining the phase state of the surface of the object based on the changes over time in the multiple surface images; and creating temperature data of the surface from the infrared image using the emissivity corresponding to the determination result of the phase state.

[0050] The technology disclosed herein is useful for non-contact temperature measurement, and is particularly useful for laser welding and its simulation.

Claims

1. A temperature measuring device comprising: a first camera that continuously photographs the surface of an object to generate multiple surface images; and a second camera that photographs the surface of the object to generate an infrared image, wherein the phase state of the surface of the object is determined based on the temporal changes in the multiple surface images, and temperature data of the surface is created from the infrared image using the emissivity corresponding to the determination result of the phase state.

2. The temperature measuring device according to claim 1, wherein the phase state is determined by whether or not there is a change between the plurality of surface images.

3. The temperature measuring device according to claim 1, wherein the changes over time in the plurality of surface images are calculated in the form of a change in signal intensity in one or more pixels of the first camera, and the presence or absence of a change in the phase state is determined from the amount of change.

4. The temperature measuring device according to claim 1, wherein the temperature data is fed back to a processing device for processing the object.

5. The temperature measuring device according to claim 1, comprising a workpiece on which the object is laser-welded.

6. A temperature measurement method comprising: continuously photographing the surface of an object to acquire multiple surface images; photographing the surface of the object to acquire an infrared image; determining the phase state of the surface of the object based on the changes over time in the multiple surface images; and creating surface temperature data from the infrared image using the emissivity corresponding to the determination result of the phase state.

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