Introduction
For decades, lithium-ion batteries (LIBs) have provided a reliable power source for laptops, smartphones, cameras, headphones, and many other portable consumer electronics. More recently, LIBs have seen significant growth in interest and demand due to widespread adoption of hybrid and fully electric vehicles (EVs) and the stationary energy storage sectors.
Demand is surging as LIB technology revolutionizes these markets and redefines the world of technology as we know it. The next major hurdle in integrating renewable energy sources into the grid and clean transportation is energy storage, likely in the form of advanced LIBs. Over the next decade, the battery industry is expected to grow almost exponentially, presenting a real challenge for LIB manufacturers.
The main elements of EV electric powertrains, namely batteries and electric motors, are not recent innovations. However, their current widespread use and the shift toward mass production have led to the adoption of process control methods and the implementation of strict quality standards similar to those in the automotive industry.
Safety Is Paramount
A lot is at stake when it comes to safety and LIBs. Battery fires and explosions lead not only to massive recalls and lawsuits but also significant reputational damage. The moment a car manufacturer develops a reputation for failures, signs start warning people not to park those EVs in garages. When mobile devices are known to fail frequently, airlines ban these phones from planes, even publishing lists and sometimes announcing the brands over the public address system before flights.
Intense Competition
In addition to increased safety requirements, large-size LIB applications require batteries with higher power and energy densities, and longer life spans. As researchers examine a variety of solutions to meet these requirements, they must test new active materials, additives, higher electrode area loadings, and other variations in electrode composition and structure in pilot tests. The highly customized and continuously evolving pilot tests that are successful are then scaled up for production.
As competition stiffens in the LIB market, one key for battery manufacturers is to maintain an edge by improving process efficiency. To improve process and quality control, many battery manufactures rely on machine vision systems. While machine vision inspection can minimize production scrap and increase yields, reducing the cost of LIB production, it’s crucial to understand that proper illumination is essential for defects to be identified and analyzed accurately.
Advanced Illumination (Ai) offers a wide range of off-the-shelf and custom lighting solutions that meet the needs of the LIB manufacturing process at every stage. Ai has a wealth of experience working with EV battery manufacturers and related applications from R&D and design to process ramp-up and production so that the machine vision applications deployed achieve better results, improving efficiency and maximizing ROI by reducing waste from failed inspections.
Cell Component Inspection
LIB production involves several extremely delicate phases that require sophisticated control systems to ensure the highest quality and efficiency of the line. The manufacturing process for batteries begins with the creation of electrodes (anodes and cathodes), which requires roll-to-roll (R2R) machinery that integrates systems for controlling key dimensional parameters and ensuring defect-free manufacturing.
The field is highly competitive with ongoing innovation and a focus on finding the fastest and most effective solutions. The main goal right now is to quickly find the best solution for a challenging range of applications, amidst that intense competition. As a result, battery manufacturers must continuously innovate and update these processes. Because it’s all about who can analyze more material in a day fastest and most cost-effectively, these battery electrode producing machines are constantly being improved for speed, cost, and efficiency.
Large Electrode Challenges
Compared with smaller electrodes and cells, larger electrodes and cells require less periphery, reducing the relative mass of inactive components. Larger electrodes, however, demand higher production quality when it comes to coating uniformity and defect density.
Larger electrodes usually have a higher waste ratio because excluding defects from the final electrode is more complex. For the scrap rate of large electrodes to decrease, it is essential to understand why and how defects occur, which helps differentiate critical from noncritical defects and prevent as many critical defects as possible.
The R2R processes required for high-volume production of electrodes include rolling, coating, drying, calendaring (compression of the electrode materials), slitting, separation, and winding. To control the amount of active material deposited during coating operations, which is known as basis weight measurement, manufacturers use ultrasonic technology. The thickness of electrode materials after calendaring is measured precisely using confocal chromatic sensors.
DF198 Series
MicroBrite™ Diffuse Ring Light Series
Our MicroBrite™ DF198 Series provides diffuse illumination at a low angle to cast shadows used to identify surface defects, embossed text, etc.
LL330 Series
Sealed High Intensity Line Lights
Engineered to withstand harsh conditions, these line lights are completely protected from dust and debris, ensuring reliable performance where other lights fail.
In addition to these dimensional checks, critical surface defects are identified at different stages of production using automated visual inspection by machine vision systems with line scan or area array cameras. Optimal illumination is critical to the success of these machine vision inspection systems to accurately identify and analyze surface defects such as bends, folds, tears, rips, and discoloration.
Electrodes Significantly Contribute to Overall LIB Cost
It is estimated that cathodes, anodes, and separators account for a significant portion of the overall cost of LIBs. As a result, machine vision systems have become increasingly popular in LIB cell component inspection to achieve better process and quality control while reducing cost.
Primarily used for inspecting film and battery materials in R2R coating equipment for defect, foreign object, and debris detection, machine vision is a key enabling technology during this critical early production phase as electrode components are progressively coated with various layers of material.
The high-speed calendaring processes used to produce these electrode components also make visual inspection extremely challenging due to increased reflectivity of the materials after compression, and the continuous process improvements often require different camera and illumination system mounting and positioning to properly identify coating crack, cut, contamination, micro-compression, pinhole, slip, stripe, and other defects.
High-Intensity Light Required
Ai has extensive experience in its applications lab that includes analyzing raw materials and determining appropriate lighting. Our expertise in battery manufacturing and inspection applications expedites the problem-solving process, reducing the need for extensive preliminary testing.
With our rapid prototyping capability, Ai can quickly develop machine vision illumination prototypes for LIB manufacturers testing new pilot lines and developing highly customized machines for cell component inspection and then leverage our in-house manufacturing capacity to deliver unique lighting solutions at scale. All this helps battery manufacturers meet the need for increased speed and quality while reducing waste and cost.
For example, Ai recently developed a custom high-intensity, oblique, linear line light that helps detect defects on various shades of dark material moving at speeds up to several meters per second. These anode and cathode material inspection processes require high-speed cameras and high-intensity illumination. Ai’s high-intensity low-angle line light reflects off defects by creating shadows that help identify the defects more reliably.
Direct Part Marking Code Reading
Direct part marking (DPM) 2D codes on the electrode components before they are wound or assembled into a stack is common practice. In addition to tracking each individual component through the winding or stacking process, 2D codes allow battery manufacturers to track each lot of components, cells, and modules through the entire production process.
Lighting conditions play a vital role in ensuring that DPM codes are clearly visible against varying backgrounds, since factors such as surface reflectivity and texture can adversely affect image quality. To read DPM codes effectively, it is necessary to achieve a clear contrast between light and dark elements within the code.
DF241
Small Low Angle Dark Field
The DF241 is characterized as a Small Low Angle Dark Field ring light. A scratch on a sheet of glass is a good example of a defect that can be detected with a low-angle dark field illuminator.
Ai specializes in specific illumination techniques, such as dark-field illumination, that enhance the visibility of DPM codes. Our DF198 ring light, for example, can be used as a low-angle dark field illuminator that allows the codes to appear darker or lighter relative to the surrounding area. Such techniques improve reading accuracy by enhancing contrast and reducing glare to optimize the visibility of codes marked on challenging surfaces.
Winding/Stacking
Cylindrical, pouch, and prismatic LIB cells have distinct design and assembly differences. For cylindrical cells, winding is the predominant technique. For pouch cells, stacking is the primary technique. For prismatic cells, either stacking or winding can be applied depending on the design. Prior to winding or stacking, multiple rounds of web inspection ensure that anode, cathode, and separator layers are defect free.
For machine vision systems to be effective during the winding or stacking of lithium-ion battery cells, proper illumination is imperative. Optimal lighting enhances visibility, improves defect detection, and ensures precision in measuring battery anode overhang, which plays a crucial role in the overall performance and safety of the battery.
Cell Inspection
While battery cells are less intensive to inspect than cell components, they are no less demanding in terms of defect tolerance, quality control, or speed. Maintaining yields, performance, and safety requires fast, high-resolution machine vision systems with optimal illumination.
This step in the production process involves placing wound or stacked electrode components inside the cell housing before adding electrolyte and welding the cell closed. A poor weld or seal puts the integrity of the cell at risk. Consequently, it is essential that each cell’s surface and welds have no flaws, foreign particles, holes, or voids that might compromise the integrity of the housing, as such problems could pose a fire hazard.
As cells are transported along a conveyor belt, they are inspected in-line. Battery cells often contain metallic materials that can make proper illumination more challenging because light reflecting off them can reduce image contrast and obscure other vital information. Additionally, tabs and connectors must be inspected for burrs, edge deviations, dents, and other defects to prevent downstream assembly problems.
The Importance of Lighting Angles
Machine vision systems that utilize various lighting techniques inspect welded and soldered tabs in LIB cells. In addition to enhancing visibility and accuracy, these techniques ensure battery quality and reliability by effectively highlighting defects for detection.
For optimal defect detection, imaging systems often use multiple independently controllable lighting sources. In this approach, lighting conditions can be tailored to the surface of the battery weld and the defect. By increasing the contrast between the tab material and the background, this technique detects various defects, including porosity, burn marks, splatter, and misaligned welding.
Lighting with acute incidence angles enables even tiny defects to cast shadows, significantly increasing their visibility during inspection. With computational imaging capabilities, multiple shots can be captured preventing hotspots caused by highly reflective surfaces and improving the clarity of images and the accuracy of defect detection.
For soldered tabs, Ai offers the DF198 ring light that improves contrast and minimizes reflections. Using this low-angle illumination makes it possible to avoid reflections while highlighting the electrode tab’s contours and joints. Depending on use case requirements and the intensity of specular reflections, coaxial diffuse illumination technique may be useful for some applications.
A coaxial light generates diffuse illumination from an internal source. Using a 50% beamsplitter, the light is deflected downward onto the imaging plane, enabling the camera above to collect light from the object. A coaxial light is ideal for imaging highly reflective objects or when shadows from the surrounding area obscure the inspection area because it applies a sheet of light to an object from above and the results are collected based on how the light is reflected, scattered, or absorbed.
LL158 Series
Oblique Line Lights
When oriented across a moving web or conveyor line, unlike standard line lights, this linear light’s unique geometry highlights engraved or raised lines that run parallel to the material travel.
Battery Module Assembly
To ensure lot tracking and quality control, high-speed cameras are used to read and verify each cell’s barcode before it is assembled and interconnected with others to form modules. As in earlier production steps, such processes must be completed as rapidly as possible without impairing code-reading accuracy. During assembly, proper illumination is crucial.
Assembling battery modules essentially involves joining battery cells into a module housing and inspecting their interconnections before closing the housing. Vision-guided robotics (VGR) can speed up the automation of this process.
Lighting Techniques Enhance Visibility When Placing Battery Cells into Modules
When picking and placing battery cells to form battery modules, machine vision illumination techniques play a crucial role in ensuring VGR accuracy and efficiency. To enhance visibility and facilitate accurate object recognition, a variety of lighting methods are used, including structured light, line lighting, and diffuse lighting.
Structured light imaging projects patterns of light onto battery cells, which are distorted by the surface of the object being inspected, providing high-resolution data for three-dimensional (3D) reconstruction. By providing a 3D topography of the cells, structured light imaging techniques enhance the robot’s ability to accurately identify the position and orientation of battery cells.
The purpose of diffuse lighting is to reduce reflections and glare, especially on reflective surfaces such as battery cells. With this technique, the surface of an object is illuminated from multiple angles, enabling critical features to be seen more clearly. In addition to aiding the vision system in accurately identifying the cells, diffuse lighting also improves the overall quality of any required inspections.
Color lighting can also help identify different types of battery cells during the pick-and-place process in some applications. Using specific wavelengths of light can assist in distinguishing various materials, enhancing quality control and ensuring the correct handling of components.
By combining these techniques, VGR can complete their tasks efficiently and with high precision, ultimately improving battery module quality and reliability by not only aiding the pick-and-place procedure but also performing other tasks such as cell interconnection inspection, battery module surface inspection, and final battery module assembly verification.
Battery Pack Assembly
To protect cells from external shock, thermal shock, and vibration, an EV battery module encloses them in a frame. These modules are then assembled into a battery pack. While battery pack assembly is still often done manually, vision-enabled automation such as VGR will not only enhance the speed and precision of this process but also reduce the risk of repetitive strain injuries to assemblers.
VGR can quickly and precisely place completed modules into a battery pack mounted on an autonomous mobile robot (AMR). The same machine vision system that guides the robot can also locate bolting holes and facilitate robotic installation of interconnects for busbars, which is a large part of the manual process today.
As modules and busbars are installed, the AMR can transport the assembled pack through one or more inspection tunnels on its way to the next stage. At each inspection station, the machine vision system acquires an image or images of the assembled pack moving through the inspection tunnels, which employ extensive use of 2D and 3D imaging tools and line lighting or structured lighting. During each inspection, software tools such as pattern matching, measurement, edge, and blob analysis are used for assembly verification. As the pack moves between production stations, the machine vision systems capture detailed images of its components.
Frequently, 3D laser displacement sensors or line scan cameras are used for detailed inspections of specific components, such as cable clips and coolant connections. Systems such as these are capable of providing high-resolution images, detecting defects in weld seams, and checking parts for uniform application characteristics. Due to the precision offered by these cameras, defects such as edge deviations, cracks, and disconnections are detected early. Additionally, the continuous scanning they provide enhances inspection efficiency.
SL256
High Intensity Pattern Projecting Spot Light
A structured LED light projector featuring a large cluster of high-intensity LEDs in a focused, homogeneous Spot Light.
For maximum results, each inspection requires selecting the right illumination technique to assess the structural integrity of the battery packs, ensuring there are no defects such as misalignments or weak joints and that various components — such as cable clips, electrical connections, coolant connections, and cables — are properly aligned.
Ai provides numerous line lights for line scan imaging in different sizes and wavelengths as well as structured lighting options. Backlights from Ai are useful for contrast enhancement to visualize edge defects more clearly. Ai’s many diffuse lighting options help minimize glare and provide even illumination across the wide variety of components inside the battery pack. The company also provides other machine vision illumination products essential to the final inspection of assembled EV battery packs.
Cover-to-Tray Assembly
During the final phase of EV battery manufacture, the cover is mounted and fastened onto the battery tray. This step may appear deceptively simple, but it serves as the last opportunity to inspect internal components and detect any final issues.
Before the external cover is placed and fastened precisely within a very short cycle time, machine vision inspection systems verify that battery pack assemblies meet the manufacturer’s specification. This is accomplished by ensuring that the final assembly is free of problematic items, contaminants, or debris that might compromise its safety or functionality.
Automating the final placement of the cover using VGR is possible, and the same vision system can simultaneously be used to inspect the fastener placement and security. These machine vision tasks require several lighting techniques, such as diffuse lighting, structured light, and laser scanning, which play essential roles in enhancing visibility and accuracy.
By reducing glare and reflections, diffuse lighting techniques improve component visualization. By using this type of lighting, it is possible to see any underlying issues such as misalignment, scratches, or dirt on the battery pack’s sealing surface. Diffuse lighting allows thorough examination of each part of the battery assembly without getting over-exposed by harsh light reflections, which obscure critical details.
Using structured light techniques, predefined patterns are projected onto the surface of the EV battery pack, enabling 3D reconstruction. Inspection systems utilize this lighting technique to identify gaps, misalignments, and other problematic items. Projected patterns demonstrate distortions that help determine the integrity of the assembly, ensuring all components are aligned correctly and that harmful contaminants are not present.
FD2 Series
High Intensity Back-lit Flat Diffuse Lights
The FD2 Series provides a highly diffuse and high intensity source of illumination that is offered in 5 wavelength options.
Machine Vision Illumination Check List For LIB Manufacturing
Described within this guide are the six production segments that define the LIB manufacturing environment. In every segment, machine vision systems rely on proper illumination techniques to ensure the efficiency, reliability, safety, and traceability of finished battery products. Each category in this check list details and highlights the potential applications for machine vision inspection, followed by a list of illumination techniques and Ai products designed to deliver inspection results that will help today’s battery manufacturers, integrators, Tier 1 suppliers, and automakers innovate, compete, and optimize yields.
Cell Component Inspection
Comprises accurate defect detection for high-speed web production of electrode components, as well as track and trace and evaluation of electrical component compliance early in the production process.
Machine Vision Tasks: Defect detection for components and coatings; checking anode/cathode stack alignment; gauging anode overhang; inspecting manufactured cells; identifying surface defects such as bends, folds, tears, rips, and discoloration; detecting coating crack, cut, contamination, micro-compression, pinhole, slip, stripe, and other defects; reading/validating DPM barcodes.
Lighting Solutions: Custom high-intensity, oblique, linear line light; DF198 dark-field illumination
Cell Inspection
Includes precise detection of defects or imperfections on highly reflective surfaces and materials.
Machine Vision Tasks: Defect detection in battery cells; inspecting size/integrity of tab and connectors; weld inspection, surface flaw and foreign particle detection; identifying holes or voids that might compromise housing integrity; inspecting tabs and connectors for burrs, edge deviations, dents, and other defects.
Lighting Solutions: Low-angle ring lights (dark field) DF198; LL330 or LL158 line lights, AL295 bar light, SL164 spot light
Cell Stack Assembly
Encompasses fast, accurate reading and verification of barcodes on cells prior to assembly as well as measurement and validation of bead thickness, dimension, and position.
Machine Vision Tasks: 2D barcode reading; adhesive/thermal bead inspection; checking cell alignment; ensuring that anode, cathode, and separator layers are defect free.
Lighting Solutions: BL2 Backlight; FD2 diffuse light, DF198 dark-field illumination
Battery Module Assembly
Consists of ensuring precise alignment of cell components in assembled modules and verifying the quality of solder beads or outside welds to enhance safety and avoid costly rework downstream.
Machine Vision Tasks: Surface inspection, vision-guided pick-and-place
Lighting Solutions: BL2 backlight; FD2 diffuse light, DF198 dark-field illumination, SL256 structured lighting
Battery Pack Assembly
Integrating 2D and 3D software tools and smart cameras with robots streamlines quality inspection of assembled EV batteries; 3D imaging techniques can further aid inspection where contrast or lighting is challenging; high-resolution imaging ensures no problematic contaminants compromise the safety or functionality of final assemblies
Machine Vision Tasks: Accurate and efficient VGR assembly when picking and placing battery cells to form battery modules; accurate identification of battery cell position and orientation; quality assessment of assembled packs; cell inspection and identification of edge defects such as burrs, deviations, and dents.
Lighting Solutions: LL330 or LL158 line lights; BL2 backlight; FD2 diffuse light; lighting of various wavelengths.
Cover-to-Tray Assembly
Includes accurate defect detection on highly reflective surfaces and materials at final stage of production
Machine Vision Tasks: Detection of misaligned components; identification of foreign objects; scratches, or dirt on the battery pack’s sealing surface
Lighting Solutions: LL330 or LL158 line lights; FD2 diffuse light
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