Methods and systems for inspecting laser welds connecting battery cells to a current collector

Abstract

A system and a method of inspecting laser welds of a stack of battery cells comprising steps of: forming laser welds connecting pole regions to corresponding poles and performing real-time weld conformity measurements of the laser welds; performing a corresponding deferred weld conformity measurement of the welds; using a controller, determining grades of the laser welds based on said real-time weld conformity measurements and said deferred weld conformity measurements; determining confirmatory grades for the weld locations using the deferred weld conformity measurements; outputting confirmatory fail grade weld locations to a laser welder controller; and using the laser welder reworking said fail grade welds to conforming welds.

Description

METHODS AND SYSTEMS FOR INSPECTING LASER WELDS CONNECTING BATTERY CELLS TO A CURRENT COLLECTOR FIELD

[0001] The improvements generally relate to energy storing devices including module(s) of battery cells and more specifically to laser-welding current collectors onto such module(s).BACKGROUND

[0002] Typically, energy storing devices include one or more packs of multiple modules, with each module containing a number of battery cells stacked together (hereinafter “battery module”). Among the existing various types of cells, cylindrical cells are widely used today for their ease of manufacturing, handling and stacking. An example of such a cylindrical battery cell includes, but is not limited to, the standardized battery cells “size 21700,” “size 18650” or “4680” to name only a few examples.

[0003] To interconnect the electric poles of the battery cells of a module to one another, a current collector is generally used. The current collector is part of the energy storing device and is provided in the form of a sheet-like element having independent conductive circuits which is first deposited on the top of the module(s) of battery cells in a manner aligning all the pole regions of the current collector to corresponding electrical poles of the battery cells. When suitably positioned, a pressure is applied proximate a pole region of the current collector to force it against the underlying electrical pole while it is welded thereto. Such a pressure-and-weld technique is typically applied sequentially to all the pole regions of the current collector, until all of the pole regions are solidly welded to corresponding electrical poles of the battery module.

[0004] It is apparent that as society is migrating an increasing portion of its energy consumption from fossil fuel energy towards electrical energy, manufacturing energy storing devices as efficiently as possible is desirable. As an energy storage unit can include well over a hundred individual battery cells, with each battery cell can require two weld lines, i.e. , one weld line for the positive pole and one weld line for the negative pole, the overall number of weld lines required for a single energy storage unit can be significant. Accordingly, any improvement in the process of performing one or two of these weld lines can be highlybeneficial over the course of the manufacturing of a whole energy storing device, which can require hundreds of weld lines. Such improvements are currently highly sought after, especially considering the ever-increasing number of energy storing devices which are expected to be manufactured in the next decade.

[0005] It is known to use laser-welding systems to perform such weld lines, as laser-welding can provide, in a remote manner, weld lines which are clean and resistant at a fast pace. Although systems and methods for laser-welding current collectors to battery modules are satisfactory to a certain degree, there remains room for improvement, especially in monitoring whether the laser welds are satisfactory.SUMMARY

[0006] Monitoring the quality of a laser-weld can be performed in real-time or quasi realtime using a laser welding monitor (LWM). More specifically, a laser welding monitor is a device used for the continuous monitoring of a laser welding process to ensure quality and reliability. As a non-destructive testing (NDT) technique, the laser welding monitor receives return signals returning from a laser weld location and measures parameters such as returning laser power, temperature, plasma radiations, and / or weld penetration depth to detect potential defects as welding is being performed. As such, once a battery module has been processed at a laser welding station incorporating a laser-welder and a laser welding monitor, an output indicating which ones of the laser welds have a pass or fail grade can be produced. In these instances, it is known to bring the battery module to a separate processing station of the production line where the unsatisfactory laser weld(s) can be further tested and corrected, if necessary.

[0007] However, these tests revealed that a significant portion of the laser welds deemed unsatisfactory by the laser welding monitor, or other real time weld conformity measurement devices, were in fact satisfactory. In other words, the laser welding monitor has a tendency of producing false negatives and laser welds identified as a fail grade are in fact flawless, requiring no correction whatsoever. Even though no correction is required at the separate processing station for these wrongly graded laser welds, investigating the false negatives require both time and resources which are detrimental to the optimization of the whole laserwelding process. There is thus a need in the industry for laser-welding systems and methods which can omit or at least minimize the use of such a separate processing station downstream from the laser welding station.

[0008] To circumvent at least some of the above-identified drawbacks, the instant disclosure presents systems and methods which perform the testing of presumably faulty laser welds prior to the exit of the battery module from the laser welding station. In fact, the testing for false negatives can be performed without any physical interference with the laser-welding process, and can be performed even while the laser-welder is laser-welding some other spaced-apart pole regions, or during down times of the laser-welder. For instance, these testing step can be performed while the laser-head is being moved from a working area to another, and / or while safety door(s) are being opened at the end of the laser welding process. In these latter embodiments, a deferred weld conformity measurement device may be mounted to a pressure application module which can be moved, during periods of down times of the laser-welder, towards the laser welds having fail grades to perform measurements thereon including, measuring resistivity, acquiring images of the laser weld, to name only a few examples. Performing the additional tests measures either while the laser-welder is working elsewhere or when it is deactivated allows time savings that may appear as negligible when appreciated individually. However, in practice, these time savings add up to one another over the course of a lifetime of the production line and are crucial in efficiently producing battery modules according to the highest standards of the industry. The correction of true negatives, i.e., laser welds that have been identified as a fail grade by both the laser welding monitor and the deferred weld conformity measurement device, can be performed within the laser welding station ordownstream thereto, depending on the embodiment.

[0009] In accordance with a first aspect of the present disclosure, there is provided a method of inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, the current collector and battery cells received at a given welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles, the method comprising: while forming laser welds connecting pole regions to corresponding poles using a laser-welder, performing real-time weld conformity measurements of the laser welds; using a processor of a computing device, determining grades of the laser welds basedon said real-time weld conformity measurements, and outputting one or more pole region locations corresponding to one or more given laser welds which grade correspond to a fail grade; performing one or more deferred weld conformity measurements of the given laser welds; and using the processor of the computing device, determining one or more confirmatory grades of the given laser welds based on the deferred weld conformity measurements, and when the confirmatory grade of one of the given laser welds is a pass grade, registering the confirmatory grade as an updated grade for the corresponding given laser weld.

[0010] Further in accordance with the first aspect of the present disclosure, said one or more deferred weld conformity measurements can for example be performed during a deactivation moment of the laser-welder.

[0011] Still further in accordance with the first aspect of the present disclosure, said deactivation moment can for example occur when the laser-welder moves from a given working area to another working area.

[0012] Still further in accordance with the first aspect of the present disclosure, said deactivation moment can for example occur when the laser-welder processes battery cells of another working area different from the given working area.

[0013] Still further in accordance with the first aspect of the present disclosure, said deactivation moment can for example occur when safety conditions are not met.

[0014] Still further in accordance with the first aspect of the present disclosure, at least some of said one or more deferred weld conformity measurements can for example be performed while the laser-welder is processing battery cells of another working area.

[0015] Still further in accordance with the first aspect of the present disclosure, said realtime weld conformity measurements can for example involve measuring one or more return signals returning from the pole regions during said forming.

[0016] Still further in accordance with the first aspect of the present disclosure, the one or more return signals can for example be one of: optical signals and acoustic signals.

[0017] Still further in accordance with the first aspect of the present disclosure, when the one or more return signals are acoustic signals, the acoustic signals can for example form a first set of acoustic signals, the method can for example further comprise: performing a Fourier transform on the first set of acoustic signals and outputting a second set of acoustic signals.

[0018] Still further in accordance with the first aspect of the present disclosure, said realtime weld conformity measurements can for example be based on at least one of: the first set of acoustic signals and the second set of acoustic signals.

[0019] Still further in accordance with the first aspect of the present disclosure, said performing the real-time weld conformity measurements can for example involve executing at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine said grades from the one or more return signals.

[0020] Still further in accordance with the first aspect of the present disclosure, said performing the real-time weld conformity measurements can for example factor in the one or more pole region locations of the corresponding laser welds.

[0021] Still further in accordance with the first aspect of the present disclosure, said performing the real-time weld conformity measurements can for example factor in force sensor readings measured by one or more force sensors during said forming.

[0022] Still further in accordance with the first aspect of the present disclosure, said one or more deferred weld conformity measurements can for example involve capturing one or more images of the laser welds and analyzing the one or more images using a classification module.

[0023] Still further in accordance with the first aspect of the present disclosure, said classification module can for example execute at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine the confirmatory grades from the one or more images.

[0024] Still further in accordance with the first aspect of the present disclosure, said one or more deferred weld conformity measurements can for example be performed using a deferredweld conformity measurement device mounted to a robot movable within a given working area, said robot can for example remain out of interference with the laser-welder during a moment of activation of the laser-welder.

[0025] Still further in accordance with the first aspect of the present disclosure, the one or more deferred weld conformity measurements can for example be a first set of deferred weld conformity measurements directed to the given laser welds, the method can for example further include performing a second set of deferred weld conformity measurements directed to remaining ones of the laser welds, the remaining ones of the laser welds can for example correspond to a pass grade.

[0026] Still further in accordance with the first aspect of the present disclosure, the second set of deferred weld conformity measurements can for example be performed after said first set of deferred weld conformity measurements.

[0027] Still further in accordance with the first aspect of the present disclosure, the second set of deferred weld conformity measurements can for example be performed at least one of: during a deactivation moment of the laser-welder and while the laser-welder is processing pole regions of another working area.

[0028] In accordance with a second aspect of the present disclosure, there is provided a system for inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, the current collector and battery cells received at a given welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles, the system comprising: a laser-welder forming laser welds connecting pole regions to corresponding poles; a laser welding monitor performing real-time weld conformity measurements of the laser welds during said forming of the laser welds; a controller having a processor and a non-transitory memory having stored thereon instructions that when executed by the processor perform the steps of: determining grades of the laser welds based on said real-time weld conformity measurements, and outputting one or more pole region locations corresponding to one or more given laser welds which grade correspond to a fail grade; a deferred weld conformity measurement device performing one or more deferred weld conformity measurements of the given laser welds at the one or more pole region locations;and wherein the controller determines one or more confirmatory grades of the given laser welds based on the deferred weld conformity measurements, and when the confirmatory grade of one of the given laser welds is a pass grade, registers the confirmatory grade as an updated grade for the corresponding given laser weld.

[0029] Further in accordance with the second aspect of the present disclosure, the system can for example further comprise a robot movable within a given working area, the robot having mounted thereto: a pressure application module applying a pressure around the pole regions during said forming the laser welds, and the deferred weld conformity measurement device.

[0030] Still further in accordance with the second aspect of the present disclosure, the deferred weld conformity measurement device can for example include a camera capturing one or more images of the laser welds.

[0031] Still further in accordance with the second aspect of the present disclosure, the controller can for example have a classification module executable to determine the confirmatory grades from the images.

[0032] Still further in accordance with the second aspect of the present disclosure, said deferred weld conformity measurements can for example be performed during a deactivation moment of the laser-welder.

[0033] Still further in accordance with the second aspect of the present disclosure, said one or more deferred weld conformity measurements can for example be performed while the laser-welder is processing pole regions of another working area spaced apart from the given working area.

[0034] In another aspect of the present disclosure, it was found that both a real-time weld conformity measurement and a deferred weld conformity measurement can be performed for each laser weld. More specifically, a real-time weld conformity measurement can be performed as a given laser weld is being formed by a laser-welder, after which the freshly formed laser weld can be assessed using a deferred weld conformity measurement. This pair of measurements can be associated with the given laser weld for further analysis or correctivemeasures. In these embodiments, the grade of each laser weld can be determined based on both the real-time weld conformity measurement and the deferred weld conformity measurement, or at least one thereof. In some embodiments, the deferred weld conformity measurement is given more weight in the determination of the corresponding grade than the real-time weld conformity measurement, or vice versa. Accordingly, an asymmetric weight can be attributed to the real-time and deferred weld conformity measurements, depending on the embodiment. In any event, when a grade is identified to be a fail grade, a corresponding pole location region can be outputted for use in correcting the faulty laser weld and / or ensuring that the corresponding pole region and electrical pole are satisfactorily welded to one another. Indeed, the laser-weld can be operated to form an additional laser weld at the corresponding pole location region corresponding to laser welds having a fail grade. The additional laser weld is generally laterally spaced apart from the original laser weld. It was found that performing the two measurements for each laser weld can help reach maximal laser welding performance which is highly sought after by the industry.

[0035] In accordance with a third aspect of the present disclosure, there is provided a method of inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, the current collector and battery cells received at a given welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles, the method comprising: while forming laser welds connecting pole regions to corresponding poles using a laser-welder, performing real-time weld conformity measurements of the laser welds, and after each real-time weld conformity measurement, performing a corresponding deferred weld conformity measurement; using a processorof a computing device, determining grades of the laser welds based on said real-time weld conformity measurements and said deferred weld conformity measurements, and outputting one or more pole region locations corresponding to each laser weld which grade corresponds to a fail grade; and forming one or more additional laser welds at said one or more pole region locations based on said outputting.

[0036] Further in accordance with the third aspect of the present disclosure, for each pole region location, the additional laser weld can for example be laterally spaced apart from the laser weld which grade corresponds to a fail grade.

[0037] Still further in accordance with the third aspect of the present disclosure, the realtime weld conformity measurement of a given laser weld can for example be given a first weight value, and the corresponding deferred weld conformity measurement is given a second weight value different from the first weight value, said determining the grade of the given laser weld can for example be based on the first and second weight values.

[0038] Still further in accordance with the third aspect of the present disclosure, each deferred weld conformity measurement can for example be performed within 100 ms, and preferably within 10 ms, of a preceding real-time weld conformity measurement.

[0039] Still further in accordance with the third aspect of the present disclosure, said deferred weld conformity measurements can for example be performed during a deactivation moment of the laser-welder.

[0040] Still further in accordance with the third aspect of the present disclosure, said deactivation moment can for example occur immediately after said forming.

[0041] Still further in accordance with the third aspect of the present disclosure, said realtime weld conformity measurements can for example involve measuring one or more return signals returning from the pole regions during said forming.

[0042] Still further in accordance with the third aspect of the present disclosure, the one or more return signals can for example be one of: optical signals and acoustic signals.

[0043] Still further in accordance with the third aspect of the present disclosure, said performing the real-time weld conformity measurements can for example involve executing at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine said grades from the one or more return signals.

[0044] Still further in accordance with the third aspect of the present disclosure, said performing the real-time weld conformity measurements can for example factor in force sensor readings measured by one or more force sensors during said forming.

[0045] Still further in accordance with the third aspect of the present disclosure, said one or more deferred weld conformity measurements can for example involve capturing one or more images of the laser welds and analyzing the one or more images using a classification module.

[0046] Still further in accordance with the third aspect of the present disclosure, said classification module can for example execute at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine the grades from the one or more images.

[0047] Still further in accordance with the third aspect of the present disclosure, said one or more deferred weld conformity measurements can for example be performed using a deferred weld conformity measurement device mounted to a robot movable within a given working area, said robot can for example remain out of interference with the laser-welder during a moment of activation of the laser-welder.

[0048] Still further in accordance with the third aspect of the present disclosure, the robot can for example have an end effector applying pressure to an area surrounding a corresponding one of the pole regions during the real-time weld conformity measurements and said deferred weld conformity measurements.

[0049] In accordance with a fourth aspect of the present disclosure, there is provided a system for inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, the current collector and battery cells received at a given welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles, the system comprising: a laser-welder forming laser welds connecting pole regions to corresponding poles; a laser welding monitor performing real-time weld conformity measurements of the laser welds during said forming of the laser welds; a deferred weld conformity measurement device performing deferred weld conformity measurements of the laser welds after said forming; a controller having a processor and a non-transitory memory having stored thereon instructions that when executed by the processor perform the steps of: determining grades of the laser welds based on said real-time weld conformity measurements and said deferred weld conformity measurements, and outputting one or more pole region locations corresponding to each laser weld which grade corresponds to a fail grade; whereinthe laser-welder is configured for forming one or more additional laser welds at said one or more pole region locations.

[0050] Further in accordance with the fourth aspect of the present disclosure, the system can for example further comprise a robot movable within a given working area, the robot having mounted thereto the deferred weld conformity measurement device.

[0051] Still further in accordance with the fourth aspect of the present disclosure, the deferred weld conformity measurement device can for example include a camera capturing one or more images of the laser welds.

[0052] Still further in accordance with the fourth aspect of the present disclosure, the controller can for example have a classification module executable to determine the grades from the one or more images.

[0053] Still further in accordance with the fourth aspect of the present disclosure, said deferred weld conformity measurements can for example be performed during a deactivation moment of the laser-welder.

[0054] Still further in accordance with the fourth aspect of the present disclosure, the laserwelder can for example include an enclosure inside which the laser welds are formed and inside which the real-time weld conformity measurements and the deferred weld conformity measurements are performed.

[0055] All technical implementation details and advantages described with respect to a particular aspect of the present invention are self-evidently mutatis mutandis applicable for all other aspects of the present invention.

[0056] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.DESCRIPTION OF THE FIGURES

[0057] In the figures,

[0058] Fig. 1 is an oblique view of an example of a current collector, in accordance with the prior art;

[0059] Fig. 1 A is a sectional view of the current collector of Fig. 1 , taken along section 1 A-1A, showing underlying battery cells, in accordance with the prior art;

[0060] Fig. 1B is a top view of a portion of the current collector of Fig. 1, showing the underlying battery cells and welds, in accordance with the prior art;

[0061] Fig. 2 is a schematic view of an example of a laser welding system incorporating a laser-welder, robots applying pressure at pole region locations, a laser welding monitor, deferred weld conformity measurement devices movable by the robots, and a controller, in accordance with one or more embodiments;

[0062] Fig. 3 is a graph showing an exemplary return signal produced by the laser welding monitor of Fig. 2 during the welding of the battery cells to the current collector, in accordance with one or more embodiments;

[0063] Fig. 4 is a flow chart of an exemplary method of inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, in accordance with one or more embodiments;

[0064] Fig. 5 is a top plan view of an example battery module being laser processed by the laser welding system of Fig. 2, showing pass or fail grade annotations overlaid to each of the battery cells inspected using the laser welding monitor, in accordance with one or more embodiments;

[0065] Fig. 6A is a top plan view of the laser welding system of Fig. 2, showing deferred weld conformity measurements being made within a first working area while the laser-welder moves to a second welding area, in accordance with one or more embodiments;

[0066] Fig. 6B is a top plan view of the laser welding system of Fig. 2, showing deferred weld conformity measurements being made within the first working area while the laser-welder measures positions of the battery cells of the second welding area, in accordance with one or more embodiments;

[0067] Fig. 6C is a top plan view of the laser welding system of Fig. 2, showing deferred weld conformity measurements being made within the first and second working areas using a first pair of robots while the laser-welder is working on a third working using a second pair of robots, in accordance with one or more embodiments;

[0068] Fig. 7 is a graph showing exemplary states for the robots, the laser-welder and the deferred weld conformity measurement device during the method of Fig. 4, in accordance with one or more embodiments;

[0069] Fig. 8 is a top plan view of an example battery module which first working area is being tested using a deferred weld conformity measurement device while a second working area is being processed by a laser-welder separate and independent from the deferred weld conformity measurement device, showing pass or fail grade annotations overlaid to each of the battery cells within a first working area, in accordance with one or more embodiments;

[0070] Fig. 9 is a graph showing states for a safety door of the laser-welding system, the laser-welder, and the deferred weld conformity measurement device during the processing of the battery module of Fig. 8, in accordance with one or more embodiments;

[0071] Fig. 10A is a post-welding image showing welds performed on a battery module, in accordance with one or more embodiments;

[0072] Fig. 10B is an enlarged view of a first weld of the welds of Fig. 10A, in accordance with one or more embodiments;

[0073] Fig. 10C includes processed views of the first weld of Fig. 10B, showing a weld classification module classifying the first weld as a pass grade, in accordance with one or more embodiments;

[0074] Fig. 10D is an enlarged view of a second weld of the welds of Fig. 10A, in accordance with one or more embodiments;

[0075] Fig. 10E includes processed views of the second weld of Fig. 10E, showing a weld classification module classifying the second weld as a fail grade, in accordance with one or more embodiments;

[0076] Fig. 11 is a flow chart of another method of inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, in accordance with one or more embodiments; and

[0077] Fig. 12 is a schematic view of an example of a computing device of the controller of Fig. 2, in accordance with one or more embodiments.DETAILED DESCRIPTION

[0078] Figs. 1 and 1A show an example of an energy storing device 10 having a current collector 12 which is to be welded to battery cells 14 to form a battery module 16. In this example, the current collector 12 is provided in the form of a sheet-like element having sets of pole regions 18 interconnected via conductive paths. Typically, such a current collector 12 can have a plurality of negative pole regions interconnected to one another via a negative conductive path, and a plurality of positive pole regions interconnected to one another via a positive conductive path, for example. The current collector 12 can be deposited onto the arrayed battery cells in a manner aligning all the pole regions of the current collector to corresponding electrical poles of the 14 battery cells (see Fig. 1A). The battery module 16 includes a number of battery cells 14 which are, in this example, of cylindrical shape. However, in some other embodiments, the battery cells can have a prismatic shape. As depicted, the battery cells 14 can have both electrical poles 20 accessible at a same, upper end. In this specific example, each battery cell 14 has an upper end with a first electric pole 20a, which is provided here in the form of a protrusion located on the centre of one of the disk-shaped endface of the cell, and a second electric pole 20b, provided here as an end of a peripheral wall extending between a first, upper end of the battery cell 14 to an opposite second, lower end. In this example, the first electric pole 20a is a positive pole, and the second electric pole 20b is a negative pole.

[0079] As shown, the current collector 12 has at least a pair of positive and negative pole regions 18 positioned over a corresponding pair of electrical poles 20a and 20b of the battery module 16 when the current collector 12 is suitably positioned over the battery module 16. The poles can be reversed, and their respective shape, form or size changed depending on the embodiment. The battery cells 14 showed in this example are standardized cylindricalbattery cell “size 21700,” however any other battery cell type can be used in other embodiments such as standardized cylindrical battery cell “size 18650” or “size 4680,” to name a few other examples. Also, the methods and systems described herein can be used to inspect other types of battery cells such as pouch cells or prismatic battery cells. Fig. 1 B shows a top view of the current collector 12 showing the underlying battery cell 14 in dashed lines. As shown, exemplary first and second weld lines 22a and 22b for the positive and negative poles 20a and 20b are also shown in dashed lines. Although two weld lines are required for such battery cells, it is intended that for other types of battery cells, only one, or more than two weld lines may be performed at either one or both ends of each battery cell.

[0080] Fig. 2 shows an example of a system 100 for inspecting laser welds connecting pole regions of the current collector 12 to poles of a stack of battery cells 14. As described in more details in the following paragraphs, the system 100 has a laser-welding monitor 102 which gives instant or quasi-instant feedback as to whether the laser welds made using a laserwelder 104 are satisfactory. For some battery module manufacturers, the laser-welding monitor 102 is calibrated in a way that is adapted for the type (e.g., cylindrical cells, prismatic cells, pouch cells) or size of battery cells to be laser welded, for the type of laser-welder used, etc.

[0081] As shown, the system 100 incorporates the laser-welder 104, the laser welding monitor 102, but also includes deferred weld conformity measurement devices 106 and a controller 108 which is communicatively coupled to the laser-welder 104, the laser welding monitor 102, the deferred weld conformity measurement devices 106 and any other suitable components of the system 100. During use, the laser-welder 104 is operable for sequentially laser-welding pole regions of the current collector 12 to corresponding electrical poles of the set of battery cells 14 thereby forming welds at spaced apart locations. During the laserwelding, the laser welding monitor 102 receives return signals returning from the spaced apart locations. Weld data sets indicative of the return signals returned from corresponding ones of the spaced apart locations are generated by the laser welding monitor 102 and transmitted to the controller 108 in real time or quasi real time. The return signals can be examined to determine whether each laser weld has a pass grade or a fail grade. Accordingly, the controller can output a map of grades which identifies the locations of the laser welds having a passgrade and the locations of the laser welds having a fail grade, the latter of which may require further tests before corrections are actually made.

[0082] Fig. 3 shows a plot of some exemplary data sets showing the return signals returned to the laser welding monitor 102 as the laser welds are being formed at different locations of the battery module. As shown, some return signals are well within predetermined upper and lower boundaries, which indicate that the corresponding signals are associated to weld lines having a pass grade. However, some other return signals step outside the predetermined boundaries, thereby indicating that the corresponding signals are associated to weld lines having a fail grade. The controller receiving the data sets from the laser welding monitor 102 can thus compare the corresponding data to pass grade data including predetermined boundaries, criterions or requirements useful in the determination of the corresponding grade. Experimental tests revealed that the typical laser welding monitor 102 may show data stepping outside the predetermined boundaries even if the corresponding laser weld is perfectly fine. In these instances, the laser welds having a fail grade have to be tested and, only infrequently, corrected further down the production line.

[0083] The methods and systems presented herein can prevent or at least minimize the need from having a separate processing station downstream from the laser-welding system 100. Indeed, the system 100 performs the testing of laser welds identified as having a fail grade prior while the battery module remains within the laser welding station. As such, the testing for false negatives can be performed during down times of the laser-welder 104 or while the laser-welder 104 is laser-welding some other pole regions. These down times occurring while the laser-head is being moved from a working area to another, while the laserwelder performs location measurements, or while safety door(s) are being opened at the end of the laser welding process. These parallel deferred testing steps are performed using the deferred weld conformity measurement device 106, examples of which will be described below. Performing these additional tests either while the laser-welder 104 is working elsewhere or when it is deactivated allows time savings that may appear as negligible when taken individually. However, in practice, these time savings add up to one another over the course of a lifetime of the production line and are crucial in efficiently producing battery modules according to the highest standards of the industry.

[0084] It is intended that the correction of true negatives, if any, may be performed while the stack of battery cells still remains within a working area of the laser-welder, before its removal from the laser welding station. This may thus add processing time to the overall process. To circumvent such undesired delays, having two or more laser-welders can be envisaged to correct the true negatives using one of the laser-welders while another one of the laser-welders is working elsewhere on the stack of battery cells. However, since the occurrence of a true negative requiring correction is infrequent (e.g., it may happen only once in fifty stacks of battery cells), only one laser-welder may suffice in most intended embodiments.

[0085] The determination of these predetermined boundaries can have an impact on the proportion of laser welds identified as having a pass grade compared to those identified as having a fail grade. For instance, if the predetermined boundaries are too tight, then a greater proportion of the laser welds may be deemed to have the fail grade. In contrast, if the predetermined boundaries are too loose, then a greater proportion of the laser welds may be deemed to have a pass grade. Such predetermined boundaries can be automatically set by the laser welding monitor based on artificial intelligence teaching procedures involving a set of return signals known to be associated with satisfactory welds. In some certain circumstances, the laser welding monitor can be further tuned to allow signals to come out of the predetermined boundaries for a certain time, or at a specific position / timeframe, and still output a pass grade. Indeed, although the predetermined boundaries shown in Fig. 3 have been shown for understanding purposes, it is appreciated that a classification module determining whether the laser weld has a pass grade or a fail grade may not involve such actual boundaries, but rather involve artificial intelligence training. For instance, the training of such a classification module can involve the inputting of a significant number of optical returns signals, each annotated to the corresponding pass or fail grade as would have been determined using for instance destructive weld conformity determination techniques.

[0086] It was found that about one fail grade in a few thousands can be a true negative. In these infrequent cases, the correction can be performed by the laser-welder as the stack of battery cells lies within the laser welding station, thereby rending any additional further processing station obsolete. In some other embodiments, the further processing station maystill be used, but less frequently. In these situations, the number of laser welds having the fail grade enables the possibility of testing them all using one or more of the deferred weld conformity measurement devices 106 while not impeding the remainder of the laser-welding process. In some embodiments, for instance when time allows, all of the laser welds, even the ones identified with the pass grade, can be tested using the deferred weld conformity measurements.

[0087] Typically, the laser-welding is not performed in an arbitrary manner. Rather, the laser welds are performed in a sequence which tends to minimize the amplitude or time of movements of the robots moving a pressure application module which applies a localized pressure forcing the pole region of the current collector against the corresponding electrical poles of the battery cell. For instance, the laser welds can be performed within a first working area, then within a second working area, and so forth, until all the working areas are suitably laser-welded. Such a technique has the advantage of clearing at least a non-negligible portion of the stack of battery cells, thereby allowing the deferred weld conformity measurement device(s) 106 to performs tests on already welded laser welds, as explained in further detail below. Moreover, this technique has also the advantage of allowing the deferred weld conformity measurement devices 106 to perform the testing while the laser-welder is being moved from one working area to another, thereby maximizing the use of the down times of the laser-welder. In some embodiments, the working area can be a 400 mm by 400 mm square region, a 300 mm by 300 mm square region, a 250 mm by 250 mm square region, or any other suitably shaped region. Different ways of dividing the stack of battery cells, or other ways of preventing physical overlapping of the real-time and deferred weld conformity measurement devices 106, may be used in other embodiments.

[0088] Fig. 4 is a method 400 of inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells. The method 400 can be initiated when the current collector and the battery cells are received at a welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles. The method 400 can be performed by the system 100 described with reference to Fig. 2, or any other suitable laser welding system.

[0089] At step 402, while laser welds connecting pole regions to corresponding poles are formed using a laser-welder, real-time weld conformity measurements of the laser welds are simultaneously performed. These real-time weld conformity measurements can be performed using an optical-based laser welding monitor, an acoustic-based laser welding monitor, or both, examples of which are described in further detail below. In some embodiments, the realtime weld conformity measurements can factor in the x and y locations of the welds. Indeed, some return optical or acoustic return signals monitored by the optical-based laser welding monitor or the acoustic-based laser welding monitor can vary based on the individual location of the welds in the battery module. In certain embodiments, the real-time weld conformity measurements can also involve readings from one or more force sensors measurement a force applied around each pole region during the corresponding laser welding.

[0090] At step 404, grades of the laser welds are determined on the basis of the real-time weld conformity measurements performed at step 402. The step 404 also includes outputting one or more pole region locations corresponding to one or more given laser welds which grade correspond to a fail grade. The step 404 of determining the grade of the first laser weld can be performed by a controller which receives output(s) from the laser welding monitor and produces corresponding grades. In the embodiment described above, the grades can be either a pass grade, indicative that a laser weld has been satisfactorily formed at a pole region, or a fail grade, indicative that the laser weld is unsatisfactory. The types of weld defects leading to a fail grade can differ from one embodiment to another. Examples of such defects can include, but are not limited to, the laser weld is too shallow, fails mechanical strength or electrical conductivity requirements, the laser weld bears a wrong shape, form or size, and the like.

[0091] In some embodiments, the step 404 can include a step of executing at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine the grades from one or more return signals measured by the optical and / or acoustic laser welding monitor.

[0092] At step 406, one or more deferred weld conformity measurements of the given laser welds are performed. The deferred weld conformity measurements can either be performed during a deactivation moment of the laser-welder or while the laser-welder is working, depending on the embodiment. For instance, in some embodiments, the deferred weldconformity measurement(s) are performed as the laser-welder is momentarily moved from a first welding area to a second welding area spaced apart from the first welding area. This step can also be performed while the laser-welder measures (e.g., using camera(s) and computer vision) the locations of the battery cells of the adjacent working area to be processed next. Alternately or additionally, the deferred weld conformity measurement(s) are performed when safety doors of the laser-welder have been momentarily opened. As will be discussed below, the step 406 can also be performed as other laser welds are being formed elsewhere on the stack of battery cells. In any case, the step 406 is performed using a deferred weld conformity measurement device which is physically out of interference with the laser-welder. Preferably, the step 406 of performing the deferred weld conformity measurement is made at no additional expense in terms of processing time.

[0093] At step 408, one or more confirmatory grades of the given laser welds are determined based on the deferred weld conformity measurements. In some embodiments, the deferred weld conformity measurements involves a step of capturing images of the laser welds and a further step of analyzing the images using a classification module. In some embodiments, the classification module can execute at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsulebased networks to determine the confirmatory grades from the images. Additionally or alternately, the deferred weld conformity measurement made on a given weld can factor in information gathered during the real-time weld conformity measurement previously made on the same given weld. In other words, the deferred weld conformity measurements can be further based on readings produced by the optical-based laser welding monitor, the acousticbased laser welding monitor, or a combination of both, during the initial real-time weld conformity measurements.

[0094] At step 410, when the confirmatory grade of one of the given laser welds is a pass grade, the confirmatory grade is registered as an updated grade for the corresponding given laser weld. This is also done for each of the other laser welds that have been inspected using the deferred weld conformity measurements. This registration process implies that a register associating grades to each one of the laser welds is updated to reflect that a previously erroneous identified fail grade is now updated to a pass grade which requires no furthercorrection. The register can be stored on a memory of the controller or any other accessible memory, depending on the example.

[0095] In some embodiments, the step 402 can include a step of moving, using a robot, the pressure application module from one pole region to another, in order to apply a satisfactory amount of pressure forcing the current collector around the corresponding electrical pole for the laser-welding beam. In embodiments where a deferred weld conformity measurement device is also mounted to the same robot, the step 406 can also involve a step of moving, using the same robot, the deferred weld conformity measurement device between one laser weld and another.

[0096] Referring back to Fig. 2, the laser-welder 104 is configured to laser weld pole regions of a current collector to corresponding electrical poles of battery cells of any type or size including, but not limited to, the size 21700 battery cells, the size 18650 battery cells or the size 4680 battery cells. The number of welds (e.g., weld lines) performed at each laser weld location can differ from one embodiment to another. In the case of the aforementioned battery cells 14, two weld lines are performed, one for the positive electrical pole and the other for the negative electrical pole. The weld lines can be linear or arcuate, and can form open-ended or closed shape. The one or more weld lines are collectively referred to herein as “weld” (or “laser weld,” equivalently).

[0097] As depicted, the laser-welder 104 is preferably mounted to a frame 110 maintaining the laser-welder 104 in position above a first working area. When all of the required laser welds are made within the first working area W, the laser-welder 104 can be moved to another, adjacent working area where other battery cells may be welded to the current collector. In some embodiments, the frame 110 includes a gantry system 112 to which is mounted the laser-welder 104 thereby enabling movement in the x and y plane as desired. The laser-welder 104 has a field of view 114 encompassing some or all of the battery cells 14 of a battery module 16 disposed in the first working area W. In some embodiments, the field of view 114 of the laser-welder 104 is such that only a portion of the battery cells 14 of a battery module 16 lies within the first working area W of the laser-welder 104. For instance, for a given distance d, the first working area W has dimensions of 400 mm by 400 mm whereas the battery module 16 has dimensions of 230 mm by 1000 mm. In these embodiments, movement of thelaser-welder 104 and a few laser-welding passes may be required to laser-weld all of the battery cells 14 of the battery module 16 to corresponding pole regions of the current collector 12. In some other embodiments, the field of view 114 of the laser-welder 104 encompasses the full battery module 16.

[0098] The laser-welder 104 includes a laser source 116 emitting a laser-welding beam 118 along a beam path 120. In some embodiments, the laser source is pulsed and the beam is a pulsed laser-welding beam. In some other embodiments, the laser source is continuous wave (CW) so the laser-welding beam a CW laser-welding beam. A source collimating lens 122 can be optically coupled to the laser source 116 to collimate the laser-welding beam 118 along the beam path 120 as it exits the laser source 116. In this example, the laser-welder 104 has a scanning head 126 including a pair of reflective surfaces which can redirect the laser-welding beam 118 in the x and y plane as desired. The pair of reflective surfaces can be provided in the form of galvo scan mirrors in some embodiments. The scanning head 126 generally defines the first working area W and corresponding field of view 114 of the laser-welder 104 as the first working area W is generally circumscribed by the maximal x and y movements of the laser-welding beam 118 in the x and y plane. The size of the first working area W generally further depends on the distance d separating the scanning head 126 and the current collector 12. Accordingly, for similar x and y movements of the laser-welding beam 118, a greater distance d results in a larger working area W, or vice versa.

[0099] In this specific configuration, the laser-welder 104 has a pre-focusing configuration. Accordingly, a pre-focusing module 128 including at least two lenses 130, including at least one movable along the beam path 120, is provided between the laser source 116 and the scanning head 126 to adjust the focusing of the laser-welding beam 118 by moving a focal point of the laser-welding beam 118 along the beam path 120. In the f-theta lens configuration, the pre-focusing module 128 can be omitted as an f-theta lens is instead positioned downstream of the scanning head 126 to perform a similar focusing function.

[0100] As discussed in greater detail below, the laser-welder 104 is operable for laserwelding pole regions of the current collector 12 to corresponding electrical poles of the battery cells 14 lying within the field of view 114 of the laser-welder 104. By doing so, a series of welds 22 are formed at spaced apart locations. The laser welding can be performed in a sequentialmanner within the first working area W. For instance, the laser-welder 104 may perform a first weld at location p1, then a second weld at location p2, then a third weld at location p3, then an ith weld at location pi (with i an arbitrary integer), and so forth, until all of the battery cells 14 encompassed within the field of view 114 of the laser-welder 104 are suitably laser-welded to corresponding pole regions of the current collector 12. In the depicted embodiment, the locations p1 , p2 and p3 share same z and y positions, but differ in their respective x positions. For instance, the coordinates of the first location p1 can be (0, 0, 0), the coordinates of the second location p2 can be (100 mm, 0, 0) and the coordinates of the third location p3 can be (200 mm, 0, 0). In embodiments where more than one laser-welder 104 is used, laser welding may occur simultaneously at different locations. However, only one laser-welder 104 has been found to be satisfactory in most embodiments.

[0101] It is noted that for each weld 22, a pressure is preferably applied proximate to the pole region of the current collector 12 to force it against the underlying electrical pole while it is welded thereto. Such a pressure-and-weld technique is typically applied serially to all the pole regions of the current collector 12, until all of the pole regions are solidly welded to corresponding electrical poles of the battery module 16. Such a pressure can be applied using a pressure application module 132. The pressure application module 132 can include a movable arm having an end fixed to a base and an opposite free arm having an end effector applying the pressure where desired. An example of such a pressure-and-weld system and method is described in International Patent Application filing no. PCT / CA2023 / 050492, the contents of which are hereby incorporated by reference. However, other pressure-and-weld systems and methods can be used in some other embodiments.

[0102] As illustrated in this specific embodiment, the laser welding monitor 102 is optically coupled to the beam path 120 of the laser-welder 104. For instance, in this embodiment, the laser welding monitor 102 taps into the beam path 120 of the laser-welder 104 using a first beam splitter 134 located between the pre-focusing module 128 and the scanning head 126. In a laser-welding direction, the first beam splitter 134 redirects the laser-welding beam 118 from the pre-focusing module 128, extending in the vertical orientation, to the scanning head 126, which input lies along the horizontal orientation. The scanning head 126 then redirects the laser-welding beam 118 along the vertical orientation. In the opposite return direction, anyreturning signal is propagated from the field of view 114 of the scanning head 126 through the first beam splitter 134 towards the laser welding monitor 102. It is noted that by using a laserwelding monitor 102 in the pre-focused configuration, the return signals do not pass into the focusing module 128 before reaching the laser welding monitor 102. In this way, chromatic aberrations can be avoided, which is not necessarily the case for laser-welding monitors of the f-theta lens configuration which would refocus the return signals, thereby adding chromatic aberrations thereto, prior to reaching the laser welding monitor 102.

[0103] During use, the laser welding monitor 102 is operable for receiving return signals returning from the spaced apart locations, e.g., from locations p1, p2, p3 and pi, during their corresponding laser-welding. Depending on the laser welding monitor 102, one or more different return signals can be simultaneously monitored by the laser welding monitor 102. In the illustrated embodiment, the laser welding monitor 102 includes a back reflection detector 136 monitoring a back reflection signal 138 resulting from a reflection of the laser-welding beam 118 at the laser weld location, a temperature detector 140 (e.g., a pyrometer) monitoring an infrared (IR) radiation signal 142 (from which the temperature can be inferred) from the laser weld location during the laser welding process, and / or a plasma detector 144 monitoring an ultraviolet (LIV) radiation signal 146 from a plasma plume appearing at the laser weld location during the laser welding process. An example of such a laser welding monitor 102 is the Laser Welding Monitor LWM 4.0 manufactured by Precitec. However, other laser welding monitors can be used.

[0104] In the depicted embodiment, dichroic beam splitters 148 and 150 are optically coupled into the returning beam path 152 to deflect a portion of the return signals towards respective ones of the detectors 140 and 144. More specifically, in this embodiment, a first dichroic beam splitter 148 redirects the ultraviolet radiation 146 towards the plasma detector 144, a second dichroic beam splitter 150 redirects the infrared radiation 142 towards the temperature detector 140 while the back reflection signal 138 is propagated through both the first and second dichroic beams 148 and 150 towards the back reflection detector 136. However, other types of laser welding monitors can be used. Fewer than three different detectors, or more than three different detectors, can be used in some other variants of the laser welding monitor 102. For instance, the laser welding monitor 102 can also include acamera 154 acquiring images of the laser weld locations during or shortly after the laserwelding process. In some embodiments, the deferred weld conformity measurement, and corresponding image capture, is performed as soon as the freshly formed laser weld becomes cleanly visible by the corresponding deferred weld conformity measurement device, e.g., camera 154 and / or cameras 162. The visibility of the freshly formed laser weld increases as laser-welding fumes or ablated particles passively or forcingly evacuate from the corresponding pole region. Depending on the embodiment, the deferred weld conformity measurement can be performed within 100 ms, and preferably within 10 ms, of the forming of the laser weld.

[0105] The real-time weld conformity measurements involve measuring one or more return signals returning from the first pole region during its laser welding. In some embodiments, the return signal(s) can be optical return signal(s) as would be monitored by the laser welding monitor 102 such as the one disclosed above. However, in some other embodiments, the return signal(s) can be acoustic signals signal (e.g., auditory signals) measured by one or more microphones (not shown) located proximate to the working area. For instance, the microphone(s) may be mounted on the pressure application module 132 or robot 109 moving the pressure application module 132. In these embodiments, the acoustic signals can be amplitude signals varying over time. Additionally or alternately, these so-recorded timedomain acoustic signals can be transformed into frequency-domain signals using Fourier transforms (e.g., fast Fourier transforms), which can also be used for the grade determination. In these instances, both the time-domain signals and the frequency-domain signals can be inputted into a classification module determining whether the laser weld has a pass grade or a fail grade.

[0106] Regardless of whether the return signals are optical and / or acoustic, the classification module can compare the return signal(s) to predetermined pass or fail grade data. For instance, the predetermined grade data can specify upper and lower boundaries which when compared to the return signal(s) associated to a laser weld can indicate whether the laser weld has a pass grade or a fail grade. It is understood that such a classification module may also involve artificial intelligence in its training. The training of such a classification module can involve the inputting of a significant number of optical signals, time-domainacoustic signals and / or frequency-domain acoustic signals, each annotated to the corresponding pass or fail grade as would have been determined using for instance destructive weld conformity determination techniques. In certain embodiments, the real-time weld conformity measurements can involve a first measurement based on optical return signals (using an optical laser welding monitor) and on a second measurement based on acoustic signals (using microphone(s)). In these cases, the first and second measurements are made simultaneously to one another during the laser-welding of each laser weld. In these instances, a fail grade can be registered for the laser weld when either one or both of the first and second measurements are indicative of a fail grade. Some other type of majority voting algorithms can be used in some other embodiments. It was found that such redundancy in the real-time weld conformity measurements can improve the odds of timely and accurately identifying unsatisfactory laser welds in practice.

[0107] The specific nature of the measurements performed by the deferred weld conformity measurement device 106 may vary among embodiments. In the embodiment illustrated in Fig.2, the deferred weld conformity measurement device 106 includes one or more dedicated cameras 160 configured to acquire image(s) of the laser welds. In this example, each camera 160 is mounted on a corresponding robot 162. The robots 162 serve to reposition the pressure application modules 132 and the cameras 160 in unison from one pole-region location to another. The image(s) of the laser welds can be acquired using the camera 154 of the laser welding monitor 102, from the dedicated cameras 160 of the deferred weld conformity measurement device 106, or both, depending on the embodiment.

[0108] Additionally or alternatively, each deferred weld conformity measurement operation may employ at least one illuminator 164 to illuminate the laser welds as the camera(s) 160 capture the corresponding image(s). In certain embodiments, the illuminators 164 are configured to provide constant and uniform lighting conditions to support reliable execution of computer-vision algorithms or trained machine-learning engines used to analyze the acquired image data. In the depicted embodiment, each illuminator 164 is integrated with a corresponding pressure application module 132. For example, each pressure application module 132 may define a laser aperture through which the laser beam passes to create the weld, and the illuminator 164 may take the form of a lighting ring, such as a ring of light-emittingdiodes (LEDs), disposed around the laser aperture. In this manner, the illuminators 164 can provide full and consistent illumination of a newly formed laser weld through the laser aperture, enabling the cameras 160 to capture images under stable and uniform lighting conditions..

[0109] In some other embodiments, the deferred weld conformity measurement can involve a step of performing an electrical measurement using the first laser weld as part of a test electrical circuit involving the battery cell bearing the laser weld and / or other proximate battery cells, has an electrical measurement device which is suited to measure an electrical resistance of any given laser weld. In preferred embodiments, the electrical measurement device is configured for performing an electrical resistance measurement such as the four-wires probing technique which uses two different pairs of current-carrying and voltage-sensing electrodes to make the resistivity measurements. In some other embodiments, the two-terminal (2T) sensing technique can also be used, but has been shown to be less reliable at least in some circumstances. In yet some other embodiments, the electrical measurement device includes electrodes which are positioned to measure a voltage drop occurring across a weld 22 identified as having a fail grade (by the laser welding monitor 102). Typically, a voltage drop is indicative that the current flows satisfactorily between the two battery cells. If, however, the voltage does not drop when a current is injected, the resistance is deemed to be high so the fail grade of the laser weld 22 may be confirmed. This can trigger the correction of the actually faulty laser weld, if necessary.

[0110] Whether the deferred weld conformity measurement device 106 performs electrical measurements or image captures, it is generally operated so as to remain out of interference from the laser beam emitted by the laser-welder 104 at all times. For instance, if the laserwelder is working within a given working area, then the deferred weld conformity measurement device 106 may work within any of the other working areas of the stack of battery cells, thereby limiting any possible physical interference with the laser-welding operation.

[0111] Depending on the embodiment, the deferred weld conformity measurement can include, but are not limited to, electrical measurements, optical measurements (e.g., imagebased measurements), radio measurements, X-ray radiography measurements, thermography measurements, any other suitable non-destructive testing technology, or a combination thereof. Each of these deferred weld conformity measurements is non-destructivein nature. As will be described further below, the deferred weld conformity measurement device can include a camera and a software application configured for analyzing images captured by the camera in order to determine whether a laser weld is satisfactory. For instance, the grades can indicate whether a laser weld has a pass grade for satisfactory welds or a fail grade for unsatisfactory welds. In some specific embodiments, the fail grade can include an indication as to why the weld has been rejected. For instance, the fail grade can further indicate whether a defect of the weld includes spatter, top porosity, undercut, top crack, overlap, burn through or a combination thereof.

[0112] Fig. 5 shows a top plan view of an example stack of battery cells having a first working area W1 and a second working area W2, in accordance with an embodiment. As shown, a robot moving a pressure application module 132 has moved from one battery cell to another to apply a pressure against the current collector (not shown) overlaid on the battery cells. At each laser-welding operation, return signals were detected and analyzed by a laser welding monitor to determine if each laser weld has a pass grade or a fail grade. This first preliminary laser weld conformity measurement is somewhat instantaneous (i.e., real time or quasi real time), which means that either a pass grade or a fail grade can be swiftly associated to each laser weld performed by the laser-welder. As discussed above, as the laser-welder works through the battery cells of the first working area W1 , a map or register of grades can be updated. For instance, this map of grades can associate pass or fail grades to corresponding battery cells or pole region locations. An example of which has been overlaid to the battery cells. As depicted, most laser welds are deemed to possess a pass grade, whereas a minority of laser welds are deemed to possess a fail grade. As discussed above, such fail grades may be false negatives, in the sense that they may be associated with laser welds that are flawless.

[0113] In response to the determination of a fail grade, a deferred weld conformity measurement can be performed on each laser weld deemed faulty. Such deferred weld conformity measurements may be performed using a deferred weld conformity measurement device 106. In the illustrated embodiment, the deferred weld conformity measurement device 106 incorporates a camera which is mounted on the same robot which moved the pressure application module 132 used in the preceding laser-welding step. Indeed, in this embodiment,the laser-welder is deactivated because it is either being moved towards another spaced apart working area (using a gantry system, for instance), performing location measurements, or when safety conditions are not met. For instance, safety doors enclosing the laser-welder may be open for some reasons.

[0114] During these deactivation moments, the pressure application module 132 is not used by the laser-welder. Accordingly, it can be used for the purpose of performing deferred weld conformity measurements to confirm or infirm whether some of the laser welds identified with a fail grade are actual faulty welds. In this embodiment, the pressure application module 132 has just terminated a laser weld on a last battery cell of the first working area W1, which initiates the moving of the laser-welder to another working area adjacent to the first working area using the gantry system, after which the pressure application module 132 is swiftly moved to a laser weld having a fail grade to perform one or more deferred weld conformity measurements. As shown, a first deferred weld conformity measurement revokes the previous fail grade of the first laser weld, which is then modified to a pass grade in the register. As such, the deferred weld conformity measurement device 106 can be moved proximate to all of the laser welds having a fail grade to take deferred weld conformity measurements, until all of the laser welds associated with fail grades are re-examined.

[0115] The camera can be communicatively coupled to the controller which can execute a classification module on the basis of the image captured by the camera. The camera used to take the image(s) required for the deferred weld conformity measurements can include one or more cameras. These camera(s) can be mounted to the pressure application module, to the frame of the laser-welder, or to both, depending on the embodiment. The camera can be two-dimensional camera(s), three-dimensional camera(s), high-resolution camera(s), infrared camera(s), and the like. Two or more two-dimensional cameras can be used in conjunction to perform stereoscopic measurements leading to an image having a depth perception. Other types of camera assemblies may be used to provide three-dimensional images.

[0116] Not shown in this figure, but the deferred weld conformity measurement device performs deferred weld conformity measurements in the first working area W1 while the laserwelder is deactivated, either because the laser-welder is moving to a second working area W2, because it is performing location measurements in a subsequent working area, orbecause safety requirements require the shutting down of the laser-welder. These steps can help ensuring that the laser-welder is not interrupted due to these deferred weld conformity measurements, which overall improves the overall welding process.

[0117] In this embodiment, the deferred weld conformity measurements can be made using the robot while the laser-welder is being moved to the second welding area W2, such as shown in Fig. 6A. Fig. 6B shows an embodiment where the deferred laser weld conformity measurements are performed while the laser-welder is measuring locations of the battery cells of the second working area W2. Deferred laser weld conformity measurements can also be performed during any other moment of deactivation of the laser-welder, such as when safety doors are opened. Moreover, in some embodiments, the deferred laser weld conformity measurements can be performed as the laser-welder is working elsewhere. For instance, as shown in Fig. 6C, deferred laser weld conformity measurements are performed within the first and second working areas W1 and W2 using a first pair of robots while the laser-welder is performing laser welds within a third working area using a second pair of robots. In any case, the deferred laser weld conformity measurement device 106 is moved from one laser weld deemed faulty to another, until all of the laser welds associated with fail grades are reexamined using the deferred weld conformity measurement device 106. As shown in these figures, deferred weld conformity measurements can be performed in a manner which does not interfere or interrupt the laser-welding process.

[0118] Fig. 7 shows a graph 700 of the states of different components of a laser-welding system while the method 400 of Fig. 4 is performed. As depicted in this example, the safety doors of the laser-welder’s enclosure open to allow the stack of battery cells to enter. Then, the safety doors are closed to prevent laser security incidents from happening. After laserwelding within a first working area W1, the laser-welder may be moved from the first working area W1 to a second working area W2 to perform yet another series of laser welds in each of the working area. However, once moved into position over the second working area W2, the laser-welder has to perform measurements (e.g., 2D or 3D image-based measurements) to determine the position of the battery cells within the second welding area W2. During these location measurements, the robots are not utilized, which make them available for deferred weld conformity measurements within the first working area W1 during a longer period of time.During those down times of the laser-welder, some or all of the deferred weld conformity measurements can be performed. This can be repeated until all of the working areas have been laser-welder and inspected accordingly. Then, the safety doors may be opened to enable the stack of battery cells to exit the laser-welder. During the opening of the safety doors, an additional window for deferred weld conformity measurements is available for instance to test the laser welds identified as having a fail grade during the last working area in which laserwelding has been performed.

[0119] Fig. 8 shows a top plan view of an example stack of battery cells, in accordance with an embodiment. As shown, a robot moving a pressure application module 132 has moved from one battery cell to another to apply a pressure against the current collector (not shown) overlaid on the battery cells within the entirety of a first working area W1. At each laser-welding operation, return signals were detected and analyzed by a laser welding monitor to determine if the laser weld has a pass grade or a fail grade. These first preliminary laser weld conformity measurements are somewhat instantaneous (i.e. , real time or quasi real time), which means that either a pass grade or a fail grade can be swiftly associated to each laser weld performed by the laser-welder. As discussed, above, Fig. 8 shows an example of a map or register of grades which is updated in real time or quasi real time as the real-time weld conformity measurements are being performed. In contrast to the embodiment of Fig. 5, in which the deferred weld conformity measurement device is mounted to the same robot as the pressure application module, the deferred weld conformity measurements are performed using a dedicated deferred weld conformity measurement device separate from the pressure application module 132.

[0120] Fig. 9 shows a graph of the states of different components of a laser-welding system having a dedicated deferred weld conformity measurement device such as shown in Fig. 8. As depicted in this example, the laser-welding system includes four robots moving a corresponding pressure application module. Each of the four robots moves a corresponding pressure application module at a given location where a next laser weld is to be performed. Once the laser-welder ends a previous welding operation, it can be swiftly directed towards the given location where pressure is being applied, to complete the laser weld. While this laser weld is being completed, the other robots are in movement or already positioned in a laser-welding position. As can be seen, the use of four robots can reduce the amount of down during which the laser-beam is deactivated, thereby increasing the number of laser welds per unit of time. Now, in this specific example, instantaneous weld conformity measurements are made during each laser welding operation. The results of such measurements are shown in the graph where the laser weld #1 and the laser weld #3 are identified as having fail grades. Now, while the laser-welder works on laser welds #4 through #8, deferred weld conformity measurements using a dedicated measurement device are made on the laser welds #1 and #3 to confirm or infirm the preliminary grades. In some cases, these are false negatives and the fail grades which were preliminary associated with laser weld #1 and laser weld #3 are registered as pass grades on the go, while the laser-welder is working on other, remote laser welds. Such a dedicated deferred weld conformity measurement device allows such measurements to be performed while the laser-welder is working elsewhere.

[0121] In some embodiments, a camera, such as the camera 154 of the system 100 of Fig.1, is configured to capture one or more images of the battery module. In certain situations, the image can be captured prior to the welding of the pole regions. This pre-welding image can help identify the coordinates of the poles regions to be welded and thereby guide the welding process. In some other situations, the image can be captured after the welding of the pole regions. Fig. 10A shows an example of such a post-welding image. As depicted, the battery module has a number of pole regions being welded to corresponding electrical poles, thereby showing a plurality of welds. This post-welding image can be used to perform one or more deferred weld conformity measurements. To do so, an image processing module generally processes the post-welding image to generate a plurality of sub-images each showing an individual weld from a similar point of view. The image processing module can perform different image processing steps including, but not limited to, cropping, rotating, translating, filter application on the post-welding image to produce the sub-images. Preferably, the individual welds of the sub-images are processed in a similar way, which can help reduce the discrepancies between the sub-images thereby removing noise and / or artifacts which could be otherwise identified as relevant by a weld classification module. For instance, each individual weld may be centered in the corresponding sub-image with a dark surrounding background, such as shown in Figs. 10B and 10D. As shown, a weld classification module is applied on the sub-images to output a corresponding pass or fail grade, such as shown inFigs. 10C and 10E, respectively. In this example, the weld of Fig. 10B is identified as a pass grade whereas the weld of Fig. 10D is identified as a fail grade by the weld classification module. It is noted that the image processing module and / or the weld classification module can be conventional algorithms in some embodiments whereas they can involve machine learning and / or artificial intelligence aspects in some other embodiments.

[0122] Fig. 11 shows another example of a method 1100 of inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells. The method 1100 can be initiated when the current collector and the battery cells are received at a welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles. The method 1100 can be performed by the system 100 described with reference to Fig.2, or any other suitable laser welding system.

[0123] At 1102, while laser welds connecting pole regions to corresponding poles are formed using a laser-welder, real-time weld conformity measurements of the laser welds are performed using a real-weld conformity measurement device. After each real-time weld conformity measurement, a corresponding deferred weld conformity measurement is performed by a deferred weld conformity measurement device. Examples for the real-weld conformity measurement device and the deferred weld conformity measurement device are provided above. In some embodiments, each deferred weld conformity measurement is performed within 100 ms, and preferably within 10 ms, of a preceding real-time weld conformity measurement. As such, the two measurements are performed shortly one after the other, preferably as the robot or pressure application module are still in position over the corresponding pole region.

[0124] At 1104, grades of the laser welds are determined based on the real-time weld conformity measurements and the deferred weld conformity measurements. This step can be performed using a processor of a computing device which may or may not be part of the corresponding laser welding system. In some embodiments, the real-time weld conformity measurement of a given laser weld is given a first weight value, and the corresponding deferred weld conformity measurement is given a second weight value different from the first weight value. Preferably, the second weight value is greater than the first weight value. This can be explained by the real-time weld conformity measurement devices often generatingfalse negatives, or by the deferred weld conformity measurements being generally more reliable than the real-time weld conformity measurements. In these instances, the determination of the grades can factor in the first and second weight values associated to the real-time and deferred weld conformity measurements, respectively. Examples for the first weight value can range between 20% and 80%, whereas the second weight value can range between 80% and 20%, depending on the embodiment.

[0125] At 1106, once the grades have been determined, the processor of the computing device outputs one or more pole region locations which correspond to each laser weld which grade corresponds to a fail grade.

[0126] At 1108, one or more additional laser welds are formed at the one or more pole region locations based on the step 1106 of outputting. It is intended that, for each pole region location, the additional laser weld is preferably laterally spaced apart from the laser weld which grade corresponds to a fail grade. In other words, the additional laser welds do not overlap with the fail laser weld, but is formed besides it. In some embodiments, each pole region has two spaced-apart zones, one of which being reserved for a first laser weld, and the other one being dedicated to any additional laser weld, if necessary.

[0127] Referring now to Fig. 12, the controller of the system 100 of Fig. 2 can be provided as a combination of hardware and software components. The hardware components can be implemented in the form of a computing device 1200, an example of which is described with reference to Fig. 9. The computing device 1200 can have a processor 1202, a memory 1204, and I / O interface 1206. Instructions 1208 for controlling some or all of the components of the laser-welding system 100 can be stored on the memory 1204 and accessible by the processor 1202.

[0128] The processor 1202 can be, for example, a general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field-programmable gate array (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), a programmable logic controller (PLC), a central processing unit (CPU), a graphics processing unit (GPU), a tensor processing unit (TPU), or any combination thereof.

[0129] The memory 1204 can include a suitable combination of any type of computer-readable memory that is located either internally or externally such as, for example, randomaccess memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable readonly memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

[0130] Each I / O interface 1206 enables the computing device 1200 to interconnect with one or more input devices, such as the laser welding monitor, the deferred weld conformity measurement device, a camera, a pressure sensor, or any other sensor, or with one or more output devices such as robot arm(s), the gantry system(s), the laser-welder(s), an accessible memory and the like.

[0131] Each I / O interface 1206 enables the controller to communicate with other components, to exchange data with other components, to access and connect to network resources, to server applications, and perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fibre optics, satellite, mobile, wireless (e.g., Wi-Fi, WiMAX), SS7 signalling network, fixed line, local area network, wide area network, and others, including any combination of these.

[0132] The computing device 1200 and any software application that can be run by the computing device 1200 are meant to be examples only. Other suitable embodiments of the controller can also be provided, as it will be apparent to the skilled reader.

[0133] As can be understood, the examples described above and illustrated are intended to be exemplary only. For some battery module manufacturers, the calibration of the laserwelding system can be performed only once for any given laser-welding system. However, in some other embodiments, the calibration can be performed at any given frequency (e.g., twice per year, once per year) depending on the embodiment. Performing the calibration at a given frequency can help reduce the impact of small variations or drifts imparted over time by any component of the laser-welding system. In some embodiments, the calibration of the laser-welding system is repeated when the battery cells or current collector have a minor or major change in geometry, size, thickness or material. It is intended that sometimes some robots can have completed their jobs in the laser-welding process. In some instances, these robots may not reach the latest working areas where other robots are currently assisting the laser-welding. In these situations, the former robots become available for the deferred weld conformity measurements. In some embodiments, the given laser welds, i.e., the laser welds identified as a fail grade by the real-time weld conformity measurements, are a first set of deferred weld conformity measurements. In these embodiments, the methods and systems can include a further step of performing a second set of deferred weld conformity measurements directed, not to given laser welds having a fail grade, but to the remaining ones of the laser welds having a pass grade. Performing the second set of deferred weld conformity measurements is only optional, as it can be omitted in some embodiments. However, in embodiments that allows them, the second set of deferred weld conformity measurements is generally performed after the first set of deferred weld conformity measurements. For instance, during a deactivation moment of the laser-welder or while the laser-welder is processing pole regions of another working area. The scope is indicated by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method of inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, the current collector and battery cells received at a given welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles, the method comprising:while forming laser welds connecting pole regions to corresponding poles using a laser-welder, performing real-time weld conformity measurements of the laser welds, and after each real-time weld conformity measurement, performing a corresponding deferred weld conformity measurement;using a processor of a computing device, determining grades of the laser welds based on said real-time weld conformity measurements and said deferred weld conformity measurements, and outputting one or more pole region locations corresponding to each laser weld which grade corresponds to a fail grade; andforming one or more additional laser welds at said one or more pole region locations based on said outputting.

2. The method of claim 1 wherein, for each pole region location, the additional laser weld is laterally spaced apart from the laser weld which grade corresponds to a fail grade.

3. The method of claim 1 or 2 wherein the real-time weld conformity measurement of a given laser weld is given a first weight value, and the corresponding deferred weld conformity measurement is given a second weight value different from the first weight value, said determining the grade of the given laser weld based on the first and second weight values.

4. The method of any one of claims 1 to 3 wherein each deferred weld conformity measurement is performed within 100 ms, and preferably within 10 ms, of a preceding real-time weld conformity measurement.

5. The method of any one of claims 1 to 4 wherein said deferred weld conformity measurements are performed during a deactivation moment of the laser-welder.

6. The method of claim 5 wherein said deactivation moment occurs immediately after said forming.

7. The method of any one of claims 1 to 6 wherein said real-time weld conformity measurements involve measuring one or more return signals returning from the pole regions during said forming.

8. The method of claim 7 wherein the one or more return signals are one of: optical signals and acoustic signals.

9. The method of claim 7 wherein said performing the real-time weld conformity measurements involves executing at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine said grades from the one or more return signals.

10. The method of any one of claims 1 to 9 wherein said performing the real-time weld conformity measurements factors in force sensor readings measured by one or more force sensors during said forming.

11. The method of any one of claims 1 to 10 wherein said one or more deferred weld conformity measurements involve capturing one or more images of the laser welds and analyzing the one or more images using a classification module.

12. The method of claim 11 wherein said classification module executes at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine the grades from the one or more images.

13. The method of any one of claims 1 to 12 wherein said one or more deferred weld conformity measurements are performed using a deferred weld conformity measurement device mounted to a robot movable within a given working area, said robot remainingout of interference with the laser-welder during a moment of activation of the laserwelder.

14. The method of claim 13 wherein the robot has an end effector applying pressure to an area surrounding a corresponding one of the pole regions during the real-time weld conformity measurements and said deferred weld conformity measurements.

15. A system for inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, the current collector and battery cells received at a given welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles, the system comprising:a laser-welder forming laser welds connecting pole regions to corresponding poles;a laser welding monitor performing real-time weld conformity measurements of the laser welds during said forming of the laser welds;a deferred weld conformity measurement device performing deferred weld conformity measurements of the laser welds after said forming;a controller having a processor and a non-transitory memory having stored thereon instructions that when executed by the processor perform the steps of: determining grades of the laser welds based on said real-time weld conformity measurements and said deferred weld conformity measurements, and outputting one or more pole region locations corresponding to each laser weld which grade corresponds to a fail grade;wherein the laser-welder is configured for forming one or more additional laser welds at said one or more pole region locations.

16. The system of claim 15 further comprising a robot movable within a given working area, the robot having mounted thereto the deferred weld conformity measurement device.

17. The system of claim 15 or 16 wherein the deferred weld conformity measurement device includes a camera capturing one or more images of the laser welds.

18. The system of claim 17 wherein the controller has a classification module executable to determine the grades from the one or more images.

19. The system of any one of claims 15 to 18 wherein said deferred weld conformity measurements are performed during a deactivation moment of the laser-welder.

20. The system of any one of claims 15 to 19 wherein the laser-welder includes an enclosure inside which the laser welds are formed and inside which the real-time weld conformity measurements and the deferred weld conformity measurements are performed.

21. A method of inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, the current collector and battery cells received at a given welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles, the method comprising:while forming laser welds connecting pole regions to corresponding poles using a laser-welder, performing real-time weld conformity measurements of the laser welds;using a processor of a computing device, determining grades of the laser welds based on said real-time weld conformity measurements, and outputting one or more pole region locations corresponding to one or more given laser welds which grade correspond to a fail grade;performing one or more deferred weld conformity measurements of the given laser welds; andusing the processor of the computing device, determining one or more confirmatory grades of the given laser welds based on the deferred weld conformity measurements, and when the confirmatory grade of one of thegiven laser welds is a pass grade, registering the confirmatory grade as an updated grade for the corresponding given laser weld.

22. The method of claim 21 wherein said one or more deferred weld conformity measurements are performed during a deactivation moment of the laser-welder.

23. The method of claim 21 or 22 wherein said deactivation moment occurs when the laser-welder moves from a given working area to another working area.

24. The method of claim 23 wherein said deactivation moment occurs when the laserwelder processes battery cells of another working area different from the given working area.

25. The method of claim 22 wherein said deactivation moment occurs when safety conditions are not met.

26. The method of any one of claims 21 to 25 wherein at least some of said one or more deferred weld conformity measurements are performed while the laser-welder is processing battery cells of another working area.

27. The method of any one of claims 21 to 26 wherein said real-time weld conformity measurements involve measuring one or more return signals returning from the pole regions during said forming.

28. The method of claim 27 wherein the one or more return signals are one of: optical signals and acoustic signals.

29. The method of claim 28 wherein when the one or more return signals are acoustic signals, the acoustic signals form a first set of acoustic signals, the method further comprising: performing a Fourier transform on the first set of acoustic signals and outputting a second set of acoustic signals.

30. The method of claim 29 wherein said real-time weld conformity measurements are based on at least one of: the first set of acoustic signals and the second set of acoustic signals.

31. The method of claim 27 wherein said performing the real-time weld conformity measurements involves executing at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine said grades from the one or more return signals.

32. The method of any one of claims 21 to 31 wherein said performing the real-time weld conformity measurements factors in the one or more pole region locations of the corresponding laser welds.

33. The method of any one of claims 21 to 32 wherein said performing the real-time weld conformity measurements factors in force sensor readings measured by one or more force sensors during said forming.

34. The method of any one of claims 21 to 33 wherein said one or more deferred weld conformity measurements involve capturing one or more images of the laser welds and analyzing the one or more images using a classification module.

35. The method of claim 34 wherein said classification module executes at least one of: one or more trained artificial neural networks, one or more support vector machines, and one or more capsule-based networks to determine the confirmatory grades from the one or more images.

36. The method of any one of claims 21 to 35 wherein said one or more deferred weld conformity measurements are performed using a deferred weld conformity measurement device mounted to a robot movable within a given working area, said robot remaining out of interference with the laser-welder during a moment of activation of the laserwelder.

37. The method of any one of claims 21 to 36 wherein the one or more deferred weld conformity measurements is a first set of deferred weld conformity measurements directed to the given laser welds, the method further including performing a second set of deferred weld conformity measurements directed to remaining ones of the laser welds, the remaining ones of the laser welds corresponding to a pass grade.

38. The method of claim 37 wherein the second set of deferred weld conformity measurements is performed after said first set of deferred weld conformity measurements.

39. The method of claim 38 wherein the second set of deferred weld conformity measurements is performed at least one of: during a deactivation moment of the laserwelder and while the laser-welder is processing pole regions of another working area.

40. A system for inspecting laser welds connecting pole regions of a current collector to poles of a stack of battery cells, the current collector and battery cells received at a given welding area with the pole regions located adjacent to and aligned with corresponding ones of the poles, the system comprising:a laser-welder forming laser welds connecting pole regions to corresponding poles;a laser welding monitor performing real-time weld conformity measurements of the laser welds during said forming of the laser welds;a controller having a processor and a non-transitory memory having stored thereon instructions that when executed by the processor perform the steps of: determining grades of the laser welds based on said real-time weld conformity measurements, and outputting one or more pole region locations corresponding to one or more given laser welds which grade correspond to a fail grade;a deferred weld conformity measurement device performing one or more deferred weld conformity measurements of the given laser welds at the one or more pole region locations; andwherein the controller determines one or more confirmatory grades of the given laser welds based on the deferred weld conformity measurements, and when the confirmatory grade of one of the given laser welds is a pass grade,registers the confirmatory grade as an updated grade for the corresponding given laser weld.

41. The system of claim 40 further comprising a robot movable within a given working area, the robot having mounted thereto: a pressure application module applying a pressure around the pole regions during said forming the laser welds, and the deferred weld conformity measurement device.

42. The system of claim 40 or 41 wherein the deferred weld conformity measurement device includes a camera capturing one or more images of the laser welds.

43. The system of claim 42 wherein the controller has a classification module executable to determine the confirmatory grades from the images.

44. The system of any one of claims 40 to 43 wherein said deferred weld conformity measurements are performed during a deactivation moment of the laser-welder.

45. The system of any one of claims 40 to 44 wherein said one or more deferred weld conformity measurements are performed while the laser-welder is processing pole regions of another working area spaced apart from the given working area.

Images