Welding inspection device including a thermal imaging camera

Abstract

The present invention relates to a weld inspection device comprising: a base unit housing a battery module for inspection; a positive electrode connector and a negative electrode connector for charging and discharging the battery module; a thermal imaging camera for photographing the welded area of ​​the battery module; and a drive unit for moving the thermal imaging camera. In this way, defects in the welded area can be identified using a non-destructive inspection method.

Description

Welding inspection device including a thermal imaging camera Technical field This application claims the benefit of priority based on Korean Patent Application No. 2021-0051665, filed on April 21, 2021. The present invention relates to a weld inspection apparatus using a thermal imaging camera. More particularly, the present invention relates to a weld inspection apparatus that includes a thermal imaging camera capable of determining whether there are weld defects in the battery cells that constitute a battery module using a non-destructive inspection method. Previous technique Improvements in safety and increased capacity of a secondary lithium battery, which is capable of being charged and discharged, have been achieved rapidly, and the types of devices that use the secondary lithium battery as a power source have increased. For example, the secondary lithium battery has been widely used as a power source for wireless mobile devices, which are small, multifunctional products, or wearable devices, which are carried on the body, and has also been used as a power source for electric vehicles and hybrid electric vehicles presented as alternatives to existing gasoline and diesel vehicles, which cause air pollution, or as an energy storage system (ESS). Based on the shape of the battery casing, lithium-ion batteries are classified as cylindrical batteries, which have an electrode array mounted in a cylindrical metal can; prismatic batteries, which have an electrode array mounted in a prismatic metal can; or pouch batteries, which have an electrode array mounted in a pouch-shaped casing made of rolled aluminum sheet. Among these, the cylindrical battery offers advantages such as relatively large capacity and structural stability. To manufacture medium and large battery packs, an electrical connection process is required for a plurality of cylindrical battery cells. For example, the positive and negative electrode terminals of the cylindrical battery cells can be connected together by a wire bond. If the conductor wires are coupled to the positive electrode terminals and the negative electrode terminals by weak soldering when using conductor wire joining, the conductor wires can be easily separated from the positive electrode terminals and the negative electrode terminals even with a small force, since the coupling force of the conductor wires is weak. Therefore, it is necessary to check the welding condition of the wire-jointed weld portions beforehand to prevent such a problem from occurring. In connection therewith, Patent Document 1 discloses a poor contact detection apparatus utilizing the fact that the output voltage of a secondary battery module is reduced or defects occur, such as heat generation, due to arc discharge or increased contact resistance when poor contact occurs between the electrode terminals of the battery cells and the bus bars, wherein the poor contact detection apparatus includes a total voltage acquisition unit configured to acquire the total voltage of the secondary battery module, an individual voltage acquisition unit configured to acquire the voltage of each of a plurality of battery cells constituting the secondary battery module,and a poor contact determination unit configured to determine whether poor contact has occurred in the connection portions of the battery cells based on the difference between the sum of the voltages acquired by the individual voltage acquisition unit and the voltage acquired by the total voltage acquisition unit. Patent Document 1 uses a thermistor, a temperature sensor, to determine whether an arc discharge has occurred in the battery cell of the battery module, and proposes a method for determining whether the contact at the connection point between the electrode terminal and the bus bar is faulty. Consequently, Patent Document 1 does not propose a method for determining faulty contact when the electrode terminals are coupled together by a wire connection. Patent Document 2 relates to a method for determining whether a microdiameter conductive wire joint is good or bad, based on the joint area of ​​a joint. The method includes a heating process of heating the microdiameter conductive wire using a laser having a microscopic spot diameter, a temperature measurement process of correcting the emissivity of a very small amount of infrared light emitted from a heated portion of the microdiameter conductive wire joint to measure the temperature variation at high speed, and a correction process of correcting the measurement result in the temperature measurement process with respect to a laser absorption rate.and a process of determining whether a bond is good or bad by comparing and selecting values ​​related to the temperature variation after correction or the bond area obtained from the temperature variation based on the measured temperature corrected in the correction process to determine if the bond is good or bad. Patent Document 2 describes the process of heating a microdiameter conductive wire using a laser with a microscopic spot diameter to measure the temperature of the wire-bonded junction. It also includes the process of correcting the measurement result based on the laser's absorption rate, and comparing and selecting values ​​related to the junction area. As a result, an additional device, such as a laser, is required, and the method for determining whether the wire bond is good or bad is complex. Therefore, there is a need for a technology capable of easily determining whether, in a battery module that includes battery cells electrically connected to each other by a conductive wire bond, the contact of a weld portion of the electrode terminal is defective. (Patent Document 1) Japanese Patent Application Publication No. 2015-109148 (2015.06.11) (Patent Document 2) Japanese Patent Application Publication No. 2011-191232 (2011.09.29) Patent document CN 105445668 A describes the thermographic inspection of battery welds during charging and discharging, in which the welds with the highest temperature are identified, and patent document WO 2019 / 145976 A1 describes an apparatus for monitoring the health of a battery module in cell, comprising an infrared camera coupled to a frame, allowing movement of the camera in the xy plane. Divulgation Technical problem The present invention has been made in view of the foregoing problems, and it is an object of the present invention to provide a welding inspection apparatus that includes a thermal imaging camera capable of easily determining whether the portion of an electrode terminal to which a conductor wire is attached is defective in a battery module that includes battery cells connected together by a conductor wire bond. Technical solution A weld inspection apparatus according to the present invention for achieving the foregoing object includes a base unit configured to have thereon a battery module, as the object to be inspected, a positive electrode connector and a negative electrode connector connected for charging and discharging the battery module, a thermal imaging camera configured to photograph a weld portion of the battery module, a drive unit configured to move the thermal imaging camera, and detection logic using the thermal imaging camera and configured to: charge and discharge the battery module two or more times, and use a difference imaging algorithm as a method for determining whether a temperature of the weld portion measured by the thermal imaging camera is within a normal temperature range. The battery module may include cylindrical battery cells. Cylindrical battery cells can be electrically connected to each other by a wire splice, and the thermal imaging camera can measure the temperature of the solder joint at each of the positive and negative electrode terminals of each cylindrical battery cell. Two or more thermal imaging cameras can be provided to be arranged adjacent to each other. The thermal imaging camera can be moved by the drive unit in three axis directions, including an x-axis direction, a y-axis direction, and a z-axis direction. The thermal imaging camera can photograph the solder portion as it moves over the battery module in the state in which the battery module is arranged in the base unit. The normal temperature range can be derived based on the temperature difference between a frame with no temperature increase and a specific frame, among the frames measured by the thermal imaging camera. The specific frame can be one that shows a sudden temperature change, among all the frames. A normal charging interval and a normal discharging interval can each be derived from a portion of positive electrode welding and a portion of negative electrode welding as the normal temperature interval. Furthermore, the present invention can provide various combinations of the aforementioned solution means. Advantageous Effects As is evident from the above description, a weld inspection apparatus according to the present invention is capable of determining whether a weld portion is defective by a method of observing the external appearance of a battery module using a thermal imaging camera, i.e., a non-destructive inspection method, which does not damage the weld portion, unlike a conventional inspection method. Description of the Drawings Figure 1 is a perspective view showing the schematic shape of a welding inspection apparatus according to one embodiment. Figure 2 is a perspective view schematically showing the structure of a thermal imaging camera in a welding inspection apparatus according to another embodiment. Figure 3 is a graph showing the change in temperature of a photographed negative electrode terminal in a specific area during the execution of a specific pattern. Figure 4 is a graph showing the charge specifications 3 and discharge specifications 3 of each of a positive electrode and a negative electrode along with a numerical range. Figure 5 is a table showing T obtained from difference images at frames 0 and 50 after the temperatures of wire-soldered portions welded to the negative electrodes of battery cells in specific partitioned areas in a battery module were measured during the running of 10 patterns. Figure 6 is a table showing T obtained from difference images at frames 0 and 50 after the temperatures of the wire-welded portions soldered to the positive electrodes of the battery cells in the specific partitioned areas on the battery module were measured during the running of 10 patterns. Best Mode Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that the preferred embodiments of the present invention can be readily implemented by a person of ordinary skill in the art to which the present invention belongs. In describing the operating principle of the preferred embodiments of the present invention in detail, however, a detailed description of known functions and configurations incorporated herein will be omitted where such a description might obscure the subject matter of the present invention. Furthermore, the same reference numbers will be used throughout the drawings to refer to parts that perform similar functions or operations. When a part is described as being connected to another part in the specification, it may be directly connected or indirectly connected through an additional component. Additionally, the inclusion of a particular element does not exclude other elements; such elements may be included unless otherwise specified. Furthermore, a description for incorporating elements by limitation or addition may apply to all inventions, unless particularly restricted, and does not limit a specific invention. Furthermore, in the description of the invention and the claims of this application, singular forms are intended to include plural forms unless otherwise stated. Furthermore, in the description of the invention and the claims of this application, "or" includes "and" unless otherwise stated. Therefore, "including A or B" means three cases, namely, the case including A, the case including B, and the case including both A and B. The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Figure 1 is a perspective view showing the schematic shape of a welding inspection apparatus according to one embodiment. Referring to Figure 1, the welding inspection apparatus according to the present invention includes a base unit 200 configured to have on it a battery module 100, which is an object to be inspected, a positive electrode connector 310 and a negative electrode connector 320 connected to the battery module 100 for charging and discharging the battery module 100, a thermal imaging camera 400 configured to photograph a weld portion of the battery module 100, and a drive unit 500 configured to move the thermal imaging camera 400. The battery module 100 includes cylindrical battery cells 101. A top cap of each cylindrical battery cell 101 functions as a positive electrode terminal 110, and a crimp portion thereof functions as a negative electrode terminal 120. A conductive wire 150 made of an electrically conductive material is coupled to the positive electrode terminal 110 and the negative electrode terminal 120 by conductive wire bonding, thereby achieving electrical connection. A material that has excellent electrical conductivity can be used as the conductive wire 150. For example, gold, silver, or copper can be used. To connect the plurality of cylindrical battery cells 101 together in series or in parallel, a conductive plate 140 can be used as required. One end of the conductive wire 150 can be primarily attached to the electrode terminal, and the other end of the same can be coupled to the conductive plate 140, thereby achieving the electrical connection between the plurality of cylindrical battery cells 101. Cylindrical battery cells can be arranged in various ways depending on the shape of the conductive plate. As shown in Figure 1, the top caps of all the cylindrical battery cells can be arranged so that they face upwards. Alternatively, contrary to what is shown in Figure 1, the top caps of some of the cylindrical battery cells can be arranged so that they face upwards, and the top caps of the other cylindrical battery cells can be arranged so that they face downwards. Alternatively, the top caps of all cylindrical battery cells can be arranged so that they face upwards, the parallel connection between the positive electrodes can be achieved by connecting the top caps with a conductive wire, and the parallel connection between the negative electrodes can be achieved by connecting the bottoms with a conductive wire. The conductive plate can be used in various forms without any limitation on shape. In general, the conductive plate can be made of an electrically conductive material, for example, a metal such as aluminum, copper, nickel, iron, or an alloy thereof. The base unit 200 may have a flat top surface with a larger flat area than the battery module 100, such that the position of the battery module 100 is fixed without wobbling when it is placed on the top surface of the base unit 200. Optionally, an upward-protruding structure, such as a side wall, may be formed on the outer edge of the top surface of the base unit to guide the position of the battery module. In addition, the thermal imaging camera 400, configured to photograph the battery module 100, measures the temperature of the solder portion to which the conductive wire 150 is attached as it moves over the battery module 100. The thermal imaging camera 400 can move in three axis directions—an x-axis direction, a y-axis direction, and a z-axis direction—while attached to the drive unit 500. The drive unit 500 can be mounted on the base unit 200 or can be a separate structure detached from the base unit 200. The 400 thermal imaging camera can measure the temperature of the weld area at each of the positive electrode terminal 110 and the negative electrode terminal 120. The thermal imaging camera continuously measures the temperature of the weld area during the charging and discharging of the battery module when the positive electrode connector 310 and the negative electrode connector 320 are connected to the battery module. As the battery module is repeatedly charged and discharged, its temperature tends to gradually increase. Furthermore, the difference between the maximum and minimum temperatures can change depending on the charge and discharge cycles, and a sudden temperature change can occur during the charging and discharging of the battery module. Consequently, it is possible to determine if the weld portion is normal by taking into account this temperature variation. In a specific example, when the number of cylindrical battery cells received in the battery module is large and therefore it is difficult to place all the cylindrical battery cells on the screen of the thermal imaging camera, the battery module can be divided into a plurality of zones, and the thermal imaging camera can measure the temperature of the solder portion on each of the cylindrical battery cells while moving sequentially to the respective zones. For example, the detection logic in an area using the thermal imaging camera may have "rest-charge-rest-discharge" as a pattern, where the rest time may be 1 second, and each of the charge and discharge times may be 2 seconds. Specifically, when the thermal imaging camera is positioned over a specific area of ​​the battery module, the temperature of the solder portion can be measured, for example, while the pattern is executed 10 times. That is, the temperature of the solder portion can be measured during 10 charge cycles and 10 discharge cycles, including breaks. After a predetermined time elapses following the completion of the 10 pattern measurements in the specific area, the thermal imaging camera moves to the next area, and the temperature of the solder portion is measured during the execution of 10 patterns while the charging and discharging cycles are performed in the same manner. Since charging and discharging are paused for a predetermined time before the thermal imaging camera moves to the next zone, the increased battery cell temperatures in the previous zone can be reduced to the level prior to charging and discharging. The above process can be repeated to measure the temperature of the solder portion on each of the battery cells while the thermal imaging camera moves to all partitioned areas depending on the size of the battery module and the number of battery cells, so it is possible to determine if the solder portion is defective. However, since the temperature rise interval of the weld portion during the first and second patterns is not large, the temperature may not be measured during the first and second patterns, and the temperature measured during the third and subsequent patterns can be used to calculate a normal temperature interval. A difference image algorithm is used to determine whether the temperature of the weld portion measured by the thermal imaging camera is within a normal temperature range. The difference image algorithm compares two images to identify differences between them. In this specification, the reference image is an image taken before the temperature change begins, and the image with the measured temperature increase is called the target image. Specifically, the thermal imaging camera can photograph 50 frames per second and, therefore, can photograph 100 frames during each of the charging and discharging cycles performed over 2 seconds. Hereafter, an image photographed before the charging and discharging cycles will be referred to as frame 0, and a frame n photographed, among 100 frames photographed over 2 seconds, will be referred to as frame n. There is a trend where, during charging and discharging, there is a sudden temperature increase in the initial stage, and the interval of temperature increase decreases after the initial stage. Assuming that, in a graph showing the temperature of each frame, a frame with a reduced slope is the nth frame, the 0th frame becomes a comparative image, and the nth frame becomes a target image, the position of the pixel with the maximum temperature can be derived from the difference between these two frames. Consequently, it is possible to verify the temperature change of a specific portion of the battery cell's outer surface, such as a positive electrode weld portion or a negative electrode weld portion. The temperature deviation T of this specific portion in frames 0 and n, obtained as described above, can be analyzed at a level of 3, allowing for the derivation of a normal temperature range for the positive or negative electrode weld portion. This normal temperature range can be derived based on T, which is the temperature deviation of the specific portion in frames 0 and n, during all charging and discharging patterns.When T of the nth frame of the specific portion measured during the execution of all patterns deviates from the normal temperature range, it can be determined that the weld is defective. Furthermore, the temperature change of the welding portion of the positive electrode or the welding portion of the negative electrode during charging and the temperature change of the welding portion of the positive electrode or the welding portion of the negative electrode during discharging can differ, and a normal charging interval and a normal discharging interval can be calculated for each of the positive and negative electrodes. When T is calculated based on the frame in which a sudden temperature change occurs, as described above, there is an advantage in that the probability of incorrect measurement within a measurement temperature range is low. Alternatively, when the maximum temperature is measured in all periods from frame 0 to frame 100, the temperature at frame 100 may be the maximum temperature, and therefore there is an advantage in that the maximum temperature variation data can be analyzed and used. When the distance between the thermal imaging camera 400 and the conductive wire 150 is increased, the number of pixels measuring a conductive wire decreases, thus significantly reducing the detection power. Therefore, the working distance of the thermal imaging camera must be adjusted so that at least two pixels are allocated to each conductive wire. For example, when using conductive wires each with a thickness of 0.5 mm, the distance between the thermal imaging camera and each conductive wire can be set to 250 mm so that three pixels are allocated to each conductive wire. Figure 1 shows that the thermal imaging camera is moved using the drive unit implemented by an articulated robotic arm. Two or more thermal imaging cameras can be arranged adjacent to each other. When the thermal imaging cameras photograph the outer surface of the battery module without overlapping each other, it is possible to photograph a wide area, and therefore increase the inspection speed. Meanwhile, when thermal imaging cameras are positioned in the corresponding number across the partitioned areas of the battery module's top surface to photograph the entire surface area at once, it is possible to measure the temperature of the solder joints during multiple scans while the cameras are stationary. This eliminates the time lost during the charging and discharging process when the cameras move to the partitioned areas, allowing for rapid inspection of defects across all solder joints. In a specific example, the welding inspection apparatus according to the present invention may further include a display unit configured to show the change in temperature of the weld portion measured by the thermal imaging camera over time in the form of a graph. Since the display unit configured to visually show the change in temperature of the soldering portion is included, as described above, it is possible to easily and quickly determine if the soldering portion is defective. Figure 2 is a perspective view schematically showing the structure of a thermal imaging camera in a welding inspection apparatus according to another embodiment. Referring to Figure 2, a 501 frame is installed on a 210 base unit. A battery module (not shown) can be arranged on the 501 frame, and a 510 drive unit is mounted on the 501 frame so that it is movable in the x-axis direction. Two thermal imaging cameras 410 and 420 are mounted on the drive unit 510, and the thermal imaging cameras 410 and 420 can be moved independently or simultaneously along the drive unit 510 in the z-axis direction. Each of the thermal imaging cameras 410 and 420 can be configured so that its length increases or decreases along the y-axis, and the thermal imaging cameras can move freely in all three axes—the x-axis, y-axis, and z-axis—depending on the position of the solder portions of the cylindrical battery cells within the battery module. The detection logic using the thermal imaging cameras 410 and 420 and the other structural elements of the solder inspection apparatus, described with reference to Figure 1, can be applied equally to the solder inspection apparatus shown in Figure 2. Thermal imaging cameras according to the present invention can extract the temperature from a specific portion of the screen that has the photographed temperature of the top surface of the battery module, and can measure the temperatures of a plurality of specific portions in a frame. The present invention will now be described with reference to the following example. The example is provided only for a better understanding of the present invention and should not be construed as limiting its scope. Example A battery module comprising cylindrical battery cells with electrode terminals electrically connected to each other by wire welding was arranged in a base unit, and then a positive electrode connector and a negative electrode connector were connected to the battery module. Two thermal imaging cameras were prepared, attached to a drive unit, and positioned over the battery module to photograph the electrode terminals. The resolution of each of the two thermal imaging cameras was adjusted so that a conductive wire would be displayed in at least two pixels. FLIR A655sc products were used as thermal imaging cameras. The setup was made so that one thermal imaging camera was able to measure 16 battery cells, and therefore the temperatures of 32 battery cells were measured simultaneously using the two thermal imaging cameras. The same number of battery cells may not be measured in all areas depending on the number of battery cells arranged along the full width and full length of the battery module. However, the thermal imaging cameras were positioned to measure the temperatures of all battery cells, and these measurements were taken while the thermal imaging cameras were being moved. In the first zone, the temperatures of the welding portions were measured using thermal imaging cameras while loading and unloading were performed during the execution of 10 patterns, each of which consisted of "rest-load-rest-unload", including rest periods. The rest period lasted 1 second, and each charging and discharging period lasted 2 seconds. Each thermal imaging camera captured 50 frames per second, thus capturing 100 frames in 2 seconds. For all zones, the temperature variation of the battery cells was measured while charging and discharging during the execution of 10 patterns. Figure 3 is a graph showing the temperature change of a negative electrode terminal photographed in a specific area during the execution of a specific pattern. Referring to Figure 3, the horizontal axis indicates the frame number, and the vertical axis indicates the temperature change. It can be seen that the temperature increases sharply up to the 50th frame, and the slope of the temperature graph is smooth thereafter. For all battery cells in all partitioned areas of the battery module, images were captured while charging and discharging were performed during the execution of 10 patterns in each area. Difference images were calculated at the 0th frames, as comparative images, and at the 50th frames, as target images, between the images during the execution of all patterns. The temperature deviation T was calculated, and T was analyzed at a level of 3, thus deriving a normal temperature range of the wire-soldered portions of the battery cells. Figure 4 is a graph showing the charge specifications 3 and discharge specifications 3 of each of a positive electrode and a negative electrode along with a numerical range. In other words, the temperature range (T) within which a weld is considered normal is 0.44 °C to 1.62 °C when the positive electrode is charged, 0.81 °C to 2.44 °C when the positive electrode is discharged, 1.22 °C to 4.41 °C when the negative electrode is charged, and 0.64 °C to 3.16 °C when the negative electrode is discharged. When the temperature (T) obtained from the difference images deviates from this range, the weld portion is considered defective. Figure 5 is a table showing T obtained from difference images at frames 0 and 50 after the temperatures of the wire-soldered portions welded to the negative electrodes of the battery cells in specific partitioned areas on the battery module were measured during the execution of 10 patterns, and Figure 6 is a table showing T obtained from difference images at frames 0 and 50 after the temperatures of the wire-soldered portions welded to the positive electrodes of the battery cells in specific partitioned areas on the battery module were measured during the execution of 10 patterns.Referring to Figure 5, it can be seen that, according to the criteria corresponding to the charging of the negative electrode and the criteria corresponding to the discharging of the negative electrode shown in Figure 4, temperatures were measured that deviated from the normal temperature range in cell 12 and cell 13 by the second chamber, excluding the values ​​of the first pattern and the second pattern. Referring to Figure 6, according to the criteria corresponding to the charging of the positive electrode and the criteria corresponding to the discharging of the positive electrode shown in Figure 4, the temperature of cell 1 measured by the first chamber deviates from the upper limit of the normal temperature range during the charging of 10 patterns, and the temperature of cell 15 measured by the second chamber deviates from the normal temperature range during the charging and / or discharging after 5 patterns, excluding the values ​​of the first pattern and the second pattern. The battery cell that has a temperature that deviates from the normal temperature range, as described above, is determined to be defective, and the battery cell is removed, so that it is possible to prevent a problem arising from a finished product that includes a defective battery cell. Furthermore, when using the weld inspection apparatus according to the present invention, it is possible to determine whether the weld portion is defective using a non-destructive inspection method. Description of reference numbers 100: Battery module 101: Cylindrical battery cell 110: Positive electrode terminal 120: Negative electrode terminal 140: Conductive plate 150: Conducting thread 200, 210: Base units 310: Positive electrode connector 320: Negative electrode connector 400, 410, 420: Thermal imaging cameras 500, 510: Drive units 501: Frame

Claims

1. A weld inspection apparatus for a battery module (100), comprising: a base unit (200, 210) configured to accommodate the battery module (100) as an object to be inspected; a positive electrode connector (310) and a negative electrode connector (320) connected for charging and discharging the battery module (100); a thermal imaging camera (400, 410, 420) configured to photograph a weld portion of the battery module (100); A drive unit (500, 510) configured to move the thermal imaging camera (400, 410, 420), and detection logic using the thermal imaging camera (400, 410, 420) and configured to: charge and discharge the battery module (100) two or more times, and use a difference imaging algorithm as a method to determine whether a temperature of the solder portion measured by the thermal imaging camera (400, 410, 420) is within a normal temperature range. 2.The weld inspection apparatus according to claim 1, which is configured to inspect a battery module (100) comprising cylindrical battery cells (101).

3. The weld inspection apparatus according to claim 2, wherein the cylindrical battery cells (101) are electrically connected to each other by a conductive wire junction, and the thermal imaging camera (400, 410, 420) is configured to measure a temperature of the weld portion at each of a positive electrode terminal (110) and a negative electrode terminal (120) of each of the cylindrical battery cells (101).

4. The weld inspection apparatus according to claim 1, wherein the thermal imaging camera (400, 410, 420) is provided in two or more configurations to be arranged adjacent to each other. 5.The welding inspection apparatus according to claim 1, wherein the thermal imaging camera (400, 410, 420) is movable by the drive unit (500, 510) in three axis directions comprising an x-axis direction, a y-axis direction, and a z-axis direction.

6. The welding inspection apparatus according to claim 1, wherein the thermal imaging camera (400, 410, 420) photographs the weld portion while moving over the battery module (100) in a state where the battery module (100) is disposed on the base unit (200, 210).

7. The welding inspection apparatus according to claim 1, wherein the detection logic is configured to derive the normal temperature range based on a temperature difference between a frame (501) that has no temperature increase and a specific frame (501), among the frames (501) measured by the thermal imaging camera (400, 410, 420). 8.The welding inspection apparatus according to claim 7, wherein the specified frame (501) is a frame (501) having a sudden temperature change, among all frames (501).

9. The welding inspection apparatus according to claim 7, wherein a normal charging interval and a normal discharging interval are derived from each of a positive electrode welding portion and a negative electrode welding portion as the normal temperature interval.

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