Welding Inspection Device Comprising Thermal Imaging Camera

Abstract

The present invention relates to a welding inspection device comprising a base portion on which a battery module to be inspected is placed, a positive electrode connector and a negative electrode connector connected for charging and discharging the battery module, a thermal imaging camera for photographing a welded portion of the battery module, and a driving portion for moving the thermal imaging camera, thereby enabling the determination of defects in the welded portion by a non-destructive inspection method.

Description

Technology Field

[0001] The present invention relates to a welding inspection device using a thermal imaging camera. Specifically, it relates to a welding inspection device comprising a thermal imaging camera that can determine whether there are welding defects in battery cells constituting a battery module using a non-destructive inspection method. Background Technology

[0002] As the safety and capacity of rechargeable lithium secondary batteries are rapidly improving, the types of devices using the aforementioned lithium secondary batteries as an energy source are increasing.

[0003] For example, the above-mentioned lithium secondary battery is not only widely used as an energy source for wireless mobile devices or wearable devices worn on the body, which are multifunctional small products, but is also used as an energy source or energy storage system (ESS) for electric vehicles and hybrid electric vehicles, which are presented as alternatives to conventional gasoline and diesel vehicles that cause air pollution.

[0004] The above-mentioned lithium secondary batteries are classified according to the shape of the battery case into cylindrical and prismatic secondary batteries, in which the electrode assembly is embedded in a cylindrical or prismatic metal can, and pouch-type secondary batteries, in which the electrode assembly is embedded in a pouch-type case made of an aluminum laminate sheet. Among these, cylindrical secondary batteries have the advantage of relatively high capacity and structural stability.

[0005] In order to manufacture the above medium-to-large battery pack, a process of electrically connecting a plurality of cylindrical battery cells is required; for example, the positive terminals and negative terminals of the cylindrical battery cells can be connected by wire bonding.

[0006] When using the above wire bonding, if weak welding occurs on the wires connected to the positive and negative terminals, the bonding strength of the wires is weak, so they can easily detach even with a small force.

[0007] In this way, it is necessary to check the welding condition of the wire-bonded weld in advance to prevent the above-mentioned problem from occurring.

[0008] In this regard, Patent Document 1 discloses a contact failure detection device comprising: a total voltage acquisition unit for acquiring the total voltage of a secondary battery module, an individual voltage acquisition unit for acquiring the voltage of each of a plurality of battery cells provided by the secondary battery module, and a contact failure determination unit for determining whether a contact failure has occurred in the connection portion of a battery cell by considering the difference between the total sum of the voltages acquired by the individual voltage acquisition unit and the voltage acquired by the total voltage acquisition unit.

[0009] Patent Document 1 uses a thermistor, which is a temperature sensor, to determine whether an arc discharge has occurred in a battery cell inside a battery module, and presents a method for checking for contact failure between the electrode terminal and the busbar connection part. Therefore, Patent Document 1 does not provide a method for determining contact failure when the electrode terminals are joined by wire bonding.

[0010] Patent Document 2 relates to a method for determining the quality of a micro-diameter wire bonding based on the bonding area of ​​the bonding portion, comprising: a heating process of heating the micro-diameter wire with a laser of a micro-spot diameter; a temperature measurement process of measuring a temperature variation at high speed by correcting the emissivity of a minute amount of infrared radiation emitted from the heated portion of the micro-diameter wire bonding portion; a correction process of correcting the measurement result in the temperature measurement process with respect to the absorption rate of the laser; and a quality determination process of determining the quality of the bonding by comparing and selecting a value that is correlated with the temperature variation after correction or the bonding area obtained from the temperature variation based on the measurement temperature corrected in the correction process.

[0011] Patent Document 2 includes a process of heating a micro-diameter wire with a laser of a micro-spot diameter to measure the temperature of a joint joined by wire bonding, and includes a process of correcting the results measured in the temperature measurement process with respect to the absorption rate of the laser and a process of comparing and selecting values ​​that are correlated with the bonding area of ​​the joint, etc., which requires additional equipment such as a laser and has the problem of a complex method for determining the quality of wire bonding.

[0012] Therefore, there is a need for a technology that can easily check for contact failures at the electrode terminal welds in battery modules where battery cells are electrically connected by wire bonding. Prior art literature

[0013] Japanese Published Patent Application No. 2015-109148 (June 11, 2015) Japanese Published Patent Application No. 2011-191232 (September 29, 2011) The problem to be solved

[0014] The present invention aims to provide a welding inspection device using a thermal imaging camera to easily check for defects in the portion where a wire is connected to an electrode terminal in a battery module in which battery cells are connected by wire bonding, in order to solve the above-mentioned problem. means of solving the problem

[0015] A welding inspection device according to the present invention for achieving such an objective may include a base portion on which a battery module to be inspected is placed, a positive electrode connector and a negative electrode connector connected for charging and discharging the battery module, a thermal imaging camera for photographing the welded portion of the battery module, and a driving portion for moving the thermal imaging camera.

[0016] The above battery module may include cylindrical battery cells.

[0017] The above cylindrical battery cells are electrically connected by wire bonding, and the thermal imaging camera can measure the temperature of the welded portions of the positive and negative terminals of the cylindrical battery cells.

[0018] The charging and discharging of the above battery module can be performed two or more times.

[0019] The above thermal imaging cameras may be arranged in a configuration where two or more are placed adjacently.

[0020] The thermal imaging camera may be in a form capable of moving in three axes, x-axis, y-axis, and z-axis by the driving unit.

[0021] With the battery module positioned on the base, the thermal imaging camera can photograph the welded portion while moving over the upper part of the battery module.

[0022] A difference image algorithm can be used to determine whether the temperature of the weld measured by the above thermal imaging camera is within the normal range.

[0023] The normal temperature range can be derived based on the temperature difference that occurs between a frame in which there is no temperature increase and a specific frame among the frames measured by the above thermal imaging camera.

[0024] The aforementioned specific frame may be a frame among all frames where a rapid change in temperature occurs.

[0025] As the above normal temperature range, a normal charging range and a normal discharge range can be derived for each of the anode weldment and the cathode weldment.

[0026] The present invention can also be provided in a form that combines various means for solving the above problem. Effects of the invention

[0027] As described above, the welding inspection device according to the present invention can determine whether there are defects in the welded part by observing the external appearance of the battery module with a thermal imaging camera, thereby providing a non-destructive inspection method that does not damage the welded part like conventional inspection methods. Brief explanation of the drawing

[0028] FIG. 1 is a perspective view illustrating a schematic form of a welding inspection device according to one embodiment. FIG. 2 is a perspective view schematically showing the structure of a thermal imaging camera in a welding inspection device according to another embodiment. Figure 3 is a graph showing the temperature change of the cathode captured in a specific pattern of a specific area. Figure 4 shows the graph and numerical range of the charging 3σ specification and the discharging 3σ specification for the positive and negative electrodes, respectively. Figure 5 is a table showing the ΔT obtained from the difference image between frame 0 and frame 40 by measuring the temperature of the wire welds welded to the negative electrodes of the battery cells in a specific area partitioned by the battery module for 10 patterns. Figure 6 is a table showing the ΔT obtained from the difference image between frame 0 and frame 40 by measuring the temperature of the wire welds welded to the positive electrodes of the battery cells in a specific area partitioned by the battery module for 10 patterns. Specific details for implementing the invention

[0029] Embodiments that enable a person skilled in the art to easily practice the present invention are described in detail below with reference to the attached drawings. However, in describing the operating principles of preferred embodiments of the present invention in detail, if it is determined that a specific description of related known functions or configurations may unnecessarily obscure the essence of the present invention, such detailed description is omitted.

[0030] In addition, the same reference numerals are used for parts having similar functions and operations throughout the drawings. Throughout the specification, when a part is described as being connected to another part, this includes not only cases where they are directly connected, but also cases where they are indirectly connected with other elements in between. Furthermore, unless specifically stated otherwise, the inclusion of a certain component does not exclude other components but implies that additional components may be included.

[0031] Furthermore, descriptions that specify components by limiting or adding them may be applied to all inventions unless specifically limited, and are not limited to descriptions of specific inventions.

[0032] In addition, throughout the description of the invention and claims of this application, items indicated in the singular include cases where they are plural unless otherwise noted.

[0033] In addition, throughout the description of the invention and the claims of the present invention, "or" includes "and" unless otherwise noted. Therefore, "comprising A or B" means all three of the above cases: including A, including B, or including both A and B.

[0034] The present invention is described in detail with reference to the drawings and embodiments.

[0035] FIG. 1 is a perspective view illustrating a schematic form of a welding inspection device according to one embodiment.

[0036] Referring to FIG. 1, the welding inspection device according to the present invention includes a base part (200) on which a battery module (100) to be inspected is placed, 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) for photographing the welded part of the battery module (100), and a driving part (500) for moving the thermal imaging camera (400).

[0037] The battery module (100) includes cylindrical battery cells (101). The top cap of the cylindrical battery cell (101) functions as a positive terminal (110), and the crimping portion functions as a negative terminal (120). A wire (150) made of an electrically conductive material can be joined to the positive terminal (110) and the negative terminal (120) by wire bonding to form an electrical connection.

[0038] For the wire (150), a material having excellent electrical conductivity can be used, for example, gold, silver, copper, etc.

[0039] A conductive plate (140) may be used as needed to connect multiple cylindrical battery cells in series or in parallel, and electrical connection of multiple cylindrical battery cells may be achieved by first bonding one end of a wire (150) to an electrode terminal and connecting the other end to a conductive plate.

[0040] The arrangement of cylindrical battery cells can be configured in various ways depending on the shape of the conductive plate, and as shown in FIG. 1, all cylindrical battery cells can be arranged so that their top caps face upward. Alternatively, unlike as shown in FIG. 1, some cylindrical battery cells can be arranged so that their top caps face upward and the remaining cylindrical battery cells can be arranged so that their top caps face downward.

[0041] Alternatively, all cylindrical battery cells can be arranged with the top caps facing upward, and all top caps can be wire-bonded from the top to form a positive parallel connection, and all cylindrical battery cells can be wire-bonded from the bottom to form a negative parallel connection.

[0042] The above conductive plate can be used in various forms without any limitations on shape and is generally an electrically conductive material, and can be made of metals such as aluminum, copper, nickel, iron, and alloys thereof.

[0043] The base portion (200) may have a flat upper surface and a planar surface area larger than the area of ​​the battery module (100) so that the battery module (100) can be fixed in position without shaking when the battery module (100) is placed on the upper surface of the base portion (200). Optionally, a structure such as an upwardly protruding side wall may be formed on the outer periphery of the upper surface of the base portion to guide the position where the battery module is placed.

[0044] Additionally, the thermal imaging camera (400) that photographs the battery module (100) measures the temperature of the welded portion where the wire is joined while moving over the upper part of the battery module, and the thermal imaging camera (400) may be in a form that allows movement in three axes, x-axis, y-axis, and z-axis while connected to the driving unit (500). The driving unit (500) may be mounted on the base unit (100), or it may be a separate structure separated from the base unit (100).

[0045] The thermal imaging camera (400) can measure the temperature of the welded portion of the positive terminal (110) and the negative terminal (120), and continuously measures the temperature of the welded portion during the process of charging and discharging the battery module with the positive connector (310) and the negative connector (320) combined with the battery module.

[0046] Battery modules tend to show a gradual increase in temperature as charging and discharging are repeated, and the difference between the maximum and minimum temperatures may vary depending on the charge / discharge cycle, and rapid temperature changes may occur during charging and discharging.

[0047] Therefore, the normality of the weld can be determined by considering such temperature changes.

[0048] In one specific example, when the number of cylindrical battery cells accommodated in a battery module is large and it is difficult to capture all the cylindrical battery cells within the frame of a thermal imaging camera, the battery module can be divided into multiple zones, and the thermal imaging camera can measure the weld temperatures of the cylindrical battery cells while moving sequentially through each zone.

[0049] For example, the detection logic using the thermal imaging camera in one area can have 'Rest-Charge-Rest-Discharge' as a pattern, the Rest time is 1 second, and the Charging time and Discharge time can each be 2 seconds.

[0050] Specifically, with a thermal imaging camera positioned in a specific area of ​​the battery module, the temperature of the weld can be measured as, for example, the above pattern is performed 10 times. That is, the temperature of the weld can be measured while performing 10 charging cycles and 10 discharging cycles, including a rest. After the measurement of 10 patterns in the above specific area is completed and a certain amount of time has elapsed, the position of the thermal imaging camera is moved to the next area, and the temperature is measured for 10 patterns while performing charging and discharging again in the same manner.

[0051] Because charging and discharging are stopped for a certain period of time before moving the thermal imaging camera to the next zone, the temperature of the battery cells, which had increased in the previous zone, can be lowered to the level before charging and discharging.

[0052] By moving through all zones partitioned according to the size of the battery module and the number of battery cells, and repeating the above process to measure the temperature of the welds of all battery cells, it is possible to check for defects in the welds.

[0053] However, since the temperature increase of the weldment is not large in the first 1st and 2nd patterns, the temperature is not measured, and the temperature measured from the 3rd pattern onwards can be used to determine the normal temperature range.

[0054] A difference image algorithm can be used to determine whether the temperature of the weld measured by the above thermal imaging camera is within the normal range. The difference image algorithm is a method for finding and comparing differences between two images. In this specification, the image before the temperature change begins is referred to as the comparison image, and the image in which the temperature increase is measured is referred to as the target image.

[0055] Specifically, the thermal imaging camera can capture 50 frames per second and can capture 100 frames each during charging and discharging, which take place for 2 seconds each. Hereinafter, the image captured before charging and discharging is designated as frame 0, and the nth frame among the 100 frames captured during 2 seconds is designated as frame n.

[0056] During charging and discharging, the temperature tends to increase rapidly in the initial stage and then decrease in the rate of temperature increase after the initial stage. When the frame where the slope decreases in the graph showing the temperature of each frame is set as the n-frame, the 0-frame becomes the comparison image and the n-frame becomes the target image, and the location of the maximum temperature pixel can be derived from the difference image between them.

[0057] Therefore, it is possible to check the temperature change of specific parts of the outer surface of the battery cell, such as the positive weld and the negative weld, and by analyzing the temperature deviation ΔT of specific parts between the 0 frame and the n frame obtained in this way at the 3σ level, the normal temperature range of the positive weld and the negative weld can be derived.

[0058] The above normal temperature range can be derived based on ΔT, which is the temperature deviation of a specific part between frame 0 and frame n in all patterns in which charging and discharging are performed, and if the ΔT of frame n of a specific part measured in all patterns deviates from the above normal temperature range, it can be determined as a welding defect.

[0059] In addition, since the temperature changes of the anode and cathode welds may appear differently during charging and discharging, respectively, the normal charging range and normal discharging range can be determined for the anode and cathode, respectively.

[0060] As described above, when ΔT is calculated based on a frame where a rapid temperature change occurs, there is an advantage of a low probability of mismeasurement within the temperature measurement range.

[0061] Alternatively, if the maximum temperature is measured across the entire range from frame 0 to frame 100, the temperature at frame 100 may be the maximum temperature, so there is an advantage in being able to analyze and utilize the maximum temperature change data.

[0062] When the distance between the thermal imaging camera (400) and the wire (150) increases, the number of pixels measuring one wire decreases, and thus the detection capability is significantly reduced. Therefore, it is necessary to adjust the working distance of the thermal imaging camera so that at least 2 pixels can be included per wire.

[0063] For example, when using a wire with a thickness of 0.5 mm, the distance between the thermal imaging camera and the wire can be set to 250 mm so that 3 pixels fit into one wire.

[0064] Figure 1 illustrates a thermal imaging camera being moved using a drive unit in the form of a multi-joint robot arm.

[0065] Since two or more thermal imaging cameras may be arranged adjacently, if each thermal imaging camera captures the outer surface of the battery module without overlapping, a wide area can be captured at once, thereby increasing the inspection speed.

[0066] Meanwhile, if multiple thermal imaging cameras are provided—corresponding to the number of partitions on the upper surface of the battery module—enough to simultaneously capture the entire area, the temperature of the welds can be measured in multiple patterns while stationary without moving the thermal imaging cameras. In other words, since the time required to stop charging and discharging when the thermal imaging cameras move through the partitioned areas can be eliminated, defect inspection of all welds can be performed quickly.

[0067] In one specific example, the welding inspection device according to the present invention may further include a display unit that displays the temperature change of the weld part measured by a thermal imaging camera as a graph over time.

[0068] In this way, since it includes a display unit that visually indicates temperature changes in the weld area, defects in the weld area can be easily and quickly recognized.

[0069] FIG. 2 is a perspective view schematically showing the structure of a thermal imaging camera in a welding inspection device according to another embodiment.

[0070] Referring to FIG. 2, a frame (501) is installed on the upper part of the base part (210). A battery module (not shown) may be placed inside the frame (501), and a driving part (510) is mounted on the frame (501) and is movable in the x-axis direction.

[0071] The drive unit (510) is equipped with two thermal imaging cameras (410, 420), and the thermal imaging cameras (410, 420) may be capable of moving independently or simultaneously in the z-axis direction within the drive unit (510).

[0072] The thermal imaging cameras (410, 420) may be shaped such that their length can be increased or decreased in the y-axis direction, and they may be able to move freely in the three axes of the x-axis, y-axis, and z-axis depending on the position of the welded portions of the cylindrical battery cells included in the battery module.

[0073] The description of the detection logic using the thermal imaging camera (410, 420) and other components constituting the welding inspection device can be applied in the same way to the description of the welding inspection device shown in FIG. 2 as described in FIG. 1.

[0074] The thermal imaging camera according to the present invention can extract the temperature of a specific part from a screen capturing the temperature of the upper surface of a battery module, and thus can measure the temperatures of multiple specific parts in a single frame.

[0075] The following description refers to embodiments of the present invention, but this is for the sake of easier understanding of the present invention and does not limit the scope of the present invention.

[0076] <Example>

[0077] A battery module accommodating cylindrical battery cells, in which electrode terminals are electrically connected by wire welding, is placed on the base, and the battery module is connected to the positive and negative connectors.

[0078] Two thermal imaging cameras were prepared and fixed to the drive unit to photograph the electrode terminals from the top of the battery module. The two thermal imaging cameras were set so that the resolution of each wire was displayed in at least 2 pixels.

[0079] The thermal imaging camera used was the Fire A655sc.

[0080] The temperatures of 32 battery cells were measured simultaneously using two thermal imaging cameras, with 16 battery cells being measured by one thermal imaging camera.

[0081] Although the same number of battery cells may not be measured in all areas depending on the number of battery cells arranged along the width and length directions of the battery module, a thermal imaging camera was positioned to measure the temperature of all battery cells, and the temperature of all battery cells was measured while moving.

[0082] In the first zone, the temperature of the weld was measured by performing charging and discharging, including rest periods, up to 10 patterns using the thermal imaging camera's 'Rest-Charge-Rest-Discharge' as one pattern.

[0083] The above Rest was performed for 1 second, and the above Charging and Discharging were performed for 2 seconds each.

[0084] The thermal imaging camera took 50 frames for 1 second and 100 frames for 2 seconds.

[0085] In this way, the temperature changes of the battery cells were measured while performing charge and discharge for 10 patterns in each zone.

[0086] Figure 3 illustrates a graph showing the temperature change of the cathode captured in a specific pattern of a specific area. Referring to Figure 3, the horizontal axis represents the number of frames and the vertical axis represents the temperature; it can be seen that the temperature increases rapidly up to 40 frames and then the slope of the temperature graph decreases.

[0087] For all battery cells in all areas of the battery module, video was captured while performing charge and discharge in 10 patterns for each area, and among the videos of all patterns, a difference image was obtained by using frame 0 as the comparison image and frame 40 as the target image to calculate the temperature deviation ΔT, and the said ΔT was analyzed at the 3σ level to derive the normal temperature range of the wire welds welded to all battery cells.

[0088] Figure 4 shows the graph and numerical range of the charging 3σ specification and the discharging 3σ specification for the positive and negative electrodes, respectively.

[0089] That is, the range of ΔT determined as normal welding is 0.44 ℃ to 1.62 ℃ during anode charging, 0.81 ℃ to 2.44 ℃ during anode discharge, 1.22 ℃ to 4.41 ℃ during cathode charging, and 0.64 ℃ to 3.16 ℃ during cathode discharge. Therefore, if the ΔT obtained from the above difference image falls outside the above range, the weld is determined to be defective.

[0090] Figure 5 is a table showing the ΔT obtained from the difference image between frame 0 and frame 40 by measuring the temperature of the wire weld joint welded to the negative electrode of the battery cells in a specific area partitioned by the battery module for 10 patterns, and Figure 6 is a table showing the ΔT obtained from the difference image between frame 0 and frame 40 by measuring the temperature of the wire weld joint welded to the positive electrode of the battery cells in a specific area partitioned by the battery module for 10 patterns.

[0091] Referring to Fig. 5, it can be seen that when following the criteria for negative charging and negative discharging, temperatures outside the normal temperature range were measured in Cell 12 and Cell 13 of Camera 2.

[0092] Referring to Fig. 6, according to the criteria for positive charging and positive discharging, cell 1 of camera 1 shows a temperature that exceeds the upper limit of the normal temperature range when charging 10 patterns, and cell 15 of camera 2 shows a temperature that exceeds the normal temperature range during charging and / or discharging after 5 patterns and 7 patterns.

[0093] In this way, battery cells exhibiting temperatures outside the normal temperature range are determined to be defective and removed, thereby preventing problems in finished products containing defective battery cells in advance.

[0094] In addition, when using the welding inspection device according to the present invention, the defect status of the weld can be determined in real time using a non-destructive method.

[0095] A person skilled in the art to which the present invention pertains would be able to perform various applications and modifications within the scope of the present invention based on the above content. Explanation of the symbols

[0096] 100: Battery module 101: Cylindrical battery cell 110: Positive terminal 120: Negative terminal 140: Conductive plate 150: Wire 200, 210: Base section 310: Positive connector 320: Negative connector 400, 410, 420: Thermal imaging camera 500, 510: Drive unit 501: Frame

Claims

Claim 1 A welding inspection device comprising: a base portion on which a battery module to be inspected is placed; a positive connector and a negative connector connected for charging and discharging the battery module; a thermal imaging camera for photographing a welded portion of the battery module; and a driving portion for moving the thermal imaging camera; wherein a difference image algorithm is used as a method to determine whether the temperature of the welded portion measured by the thermal imaging camera is within a normal range, and a normal temperature range is derived based on the temperature difference that occurs between a frame in which there is no temperature increase and a specific frame among the frames measured by the thermal imaging camera, and the charging and discharging of the battery module are performed two or more times. Claim 2 In claim 1, the battery module is a welding inspection device comprising cylindrical battery cells. Claim 3 In paragraph 2, the cylindrical battery cells are electrically connected by wire bonding, and the thermal imaging camera is a welding inspection device that measures the temperature of the welded portion of the positive and negative terminals of the cylindrical battery cells. Claim 4 delete Claim 5 In claim 1, the welding inspection device is configured such that two or more thermal imaging cameras are arranged adjacently. Claim 6 In claim 1, the thermal imaging camera is a welding inspection device capable of moving in three axes, x-axis, y-axis, and z-axis by the driving unit. Claim 7 A welding inspection device according to claim 1, wherein, while the battery module is positioned on the base part, the thermal imaging camera moves over the upper part of the battery module to photograph the weld. Claim 8 delete Claim 9 delete Claim 10 In claim 1, the specific frame is a welding inspection device in which a rapid temperature change occurs among all frames. Claim 11 A welding inspection device according to claim 1, which derives a normal charging range and a normal discharge range in each of the anode weld and cathode weld as the normal temperature range.

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