To avoid safety risks, quality assurance is essential in the production of parts made from carbon fiber reinforced polymers (CFRP). These components exhibit particularly high tensile strength in the direction of the fibers, so manufacturersmust pay close attention to the direction in which the various plies are formed together during the production process. To inspect carbon fiber components, researchers from the Fraunhofer Institute for Integrated Circuits IIS have deployed a polarization camera.
Initially, the team developed a proprietary polarization camera called POLKA, which captures the orientation and position of the carbon fiber bundle in real-time. The camera features a custom 640 x 480-pixel CMOS image sensor with on-chip polarizers that also features a frame rate of up to 25 fps, a pixel size of 6 µm, and Polka imaging software, which is used to calculate the degree of linear polarization.
Recently, however, Fraunhofer Institute for Integrated Circuits IIS showcased a carbon fiber inspection demonstration at Control 2018 in Stuttgart using an off-the-shelf polarization camera from LUCID Vision Labs, the LUCID Phoenix polarization camera.
The PHX050S-P camera features Sony’s IMX250MZR CMOS polarized image sensor, which is a 5 MPixel global shutter sensor with a 3.45 μm pixel and a frame rate of up to 24 fps. The sensor is based on the IMX250 Sony Pregius CMOS monochrome sensor with a polarizing filter added to the pixel. The sensor has four different directional polarizing filters (0°, 90°, 45°, and 135°) on every four pixels. Lucid Vision’s GigE Vision camera, the company said, performs on-camera processing using the four directional filters and outputs both the intensity and polarized angle of each image pixel.
One of the unique properties of carbon fibers is that they polarize incidental unpolarized light parallel to the direction of the fiber, so the Phoenix camera was used to capture the orientation and position of the carbon fiber bundle in real time to determine which way the fiber runs. The demonstration again used the Fraunhofer IIS Polka imaging software, which performs the required computation for calculating the degree of linear polarization, which directly indicates the direction of the fibers for each pixel. This, according to LUCID Vision Labs, is the only way to ensure the required stability of the component.
Pictured: The right image shows the measured intensity, the left image shows the false color polarization information, with color depicting of the measured angles of the fibers.