Drives & Controls April 2022

36 n MACHINE VISION April 2022 www.drivesncontrols.com Camera detects flaws in battery coatings A ustrian scientists have developed an optical inspection system to ensure that quality is maintained in a process that coats the anode and cathode foils used as building blocks for battery cells. Using a high-speed camera, the researchers from the Austrian Institute of Technology (AIT) achieved operating speeds of up to 2m/s, with a resolution of 50μm/pixel, using photometric stereo surface reconstruction. Their system can detect flaws in batteries as they are being manufactured, thus improving battery performance and safety, cutting production waste, and minimising the risk of shipping faulty products. Electrode materials for batteries are produced using a coating process in which an electrochemically active material is applied onto a metal substrate foil. A slurry of active materials, binders, conductive additives and solvents is placed into an funnel and then applied onto the substrate with a defined thickness. The coated electrodes are then dried and stored for a subsequent calendaring process, where they are compressed. The quality of the applied coating is an important factor that affects the electrical characteristics of the battery cells. Ideally, the coating should be finely grained and should cover the substrate evenly. However, coatings can sometimes deviate from these ideal conditions, especially when new mixes are being developed. Using defective electrodes in cells degrades their electrical capabilities, and can lead to undesirable exothermic reactions which could injure people. The system developed by the AIT scientists consists of: n a high-speed industrial camera that views the electrode material from above; n four linear light sources that illuminate the material from four directions; n FPGA-based trigger hardware that synchronises the strobing of the four lights with the camera acquiring the images; and n a PC that coordinates the image data acquisition and computes a representation of the foil surface. The FPGA-based controller synchronises control of the lighting and the camera’s image acquisition with the movement of the material. First, it splits pulses from an optical encoder with 5μm increments to frame trigger pulses with 50μm increments, thus defining the resolution in transport direction as 50μm per pixel. Then, for each frame trigger pulse, the controller switches on a different light while the other lights are off, and triggers an image acquisition by the camera. To be able to acquire each object point under four different illumination conditions, four rows of the camera’s pixel matrix are read out per frame trigger. The camera that the Austrian researchers chose for the application is a Mikrotron EoSens 4CXP CoaXPress monochrome area-scan camera with a 2,336 × 1,728 pixel resolution and 7μm pitch. It achieved an optical resolution of 50μm/pixel, which is equal to the resolution in the direction of transport. This configuration achieved a field-of-view of about 116mm perpendicular to the transport direction, and 200μm in the transport direction. An industrial PC running Windows 10 was used to configure the acquisition subsystem and to process the image data, which is acquired via a CoaXPress frame grabber. The PC is located in the machine and its user interface can be accessed remotely via an Ethernet network. Tests using deliberately defective anode and cathode foils provided an overview of real-world defects that can occur in foil coating, such as missing or uneven coatings, pinholes, agglomerations, cavities and cracks. The scientists obtained results that show that common defects occurring in the coating process of battery electrodes can be visualised clearly. While the researchers focused on electrodes for their study, they believe that their system can could also be used to detect defects in other materials, such as steel surfaces. n Austrian researchers have used a vision system to inspect the quality of coatings on battery anodes and cathodes. They believe the technology will improve battery performance and safety, cut production waste, and reduce the risk of shipping faulty products The area-scan camera attached to a roll simulator in the prototype battery coating inspection system