“Researchers at the Fraunhofer Institute for Applied Optics and Precision Engineering (Fraunhofer IOF) in Jena, Germany have developed an imaging system that uses two high-speed, high-resolution monochromatic imagers and a GOBO projector to perform imaging on objects. Three-dimensional inspection. In typical dynamic applications such as crash testing and airbag deployment, in addition to rapid spatial changes, temperature changes also play an important role.
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Researchers at the Fraunhofer Institute for Applied Optics and Precision Engineering (Fraunhofer IOF) in Jena, Germany have developed an imaging system that uses two high-speed, high-resolution monochromatic imagers and a GOBO projector to perform imaging on objects. Three-dimensional inspection. In typical dynamic applications such as crash testing and airbag deployment, in addition to rapid spatial changes, temperature changes also play an important role.
Researchers use their GOBO system to project the necessary non-periodic stripe patterns
The working principle of high-speed 3D thermal imaging system
The Fraunhofer Institute for Applied Optics and Precision Engineering in Jena, Germany (“IOF”) is mainly engaged in applied research in the field of photonics. As early as 2016, it developed a high-speed 3D imaging system. The system consists of two stereo-arranged high-speed stereo black and white imagers and a self-developed active lighting GOBO projector. Since 2019, it has also introduced the FLIR scientific imager (FLIR X6900sc superlattice long-wave thermal imager, which supports a frame rate of up to 1000 Hz and a resolution of 640×512 pixels), and launched a high-speed 3D Thermal imaging system.
The high-speed 3D imaging system is based on two monochromatic imagers that are sensitive to the visible spectral range (VIS). Both operate at a frame rate of 12,000 Hz and a resolution of 1 megapixel-higher frame rates can also be achieved at lower resolutions. However, the two imagers have not yet been able to produce meaningful 3D data with the required quality standards. In addition, a sophisticated lighting system is needed to project a sequence of fringe patterns ultra-fast. These patterns are similar to regular sinusoidal fringes, except that their width will vary irregularly.
The 2D infrared data from the LWIR thermal imager can be combined with the 3D data to form a 3D infrared image subsequently, and all 3 imagers have been calibrated
Combine the reconstructed 3D data with the 2D data from the FLIR X6900sc SLS high-speed thermal imager to generate a three-dimensional high-speed infrared image. The FLIR X6900sc superlattice detector operates in the long-wave infrared range, so it is not sensitive in the visible and near-infrared wavelength range of the radiation emitted by the GOBO projector light source. Since the projected non-periodic sinusoidal pattern does not matter to the heating of the object, the GOBO projector will not affect the infrared imaging.
FLIR X6900sc SLS丨LWIR high-speed thermal imaging camera
FLIR X6900sc SLS is an ultra-fast, high-sensitivity thermal imaging camera for scientists, researchers and engineers. This thermal imager has an advanced shutter release function. With an additional SSD hard disk, its built-in memory can play a super recording capacity. Whether in the laboratory or the test site, it can capture high-speed events with superb quality. Freeze the image. It can be said that everything is worry-free with one machine in hand.
The FLIR X6900sc superlattice long-wave infrared thermal imaging camera has a recording rate of up to 1,004 frames per second in a full-size format of 640×512 pixels, and a recording rate of up to 29 kHz in the smallest partial image format. Using these thermal imaging cameras, you can record up to 26 seconds of full-frame format data in the built-in memory without any damage to the image. With the strained superlattice (SLS) long-wave infrared detector, FLIR X6900sc SLS can achieve approximately 12 times shorter integration time and larger dynamic range than other X6900s models.
Measurement and calculation of new systems
During the measurement, the three imagers simultaneously record image data. The data from the black-and-white imager is combined with the non-periodic fringe projection of the GOBO projector to produce the actual 3D image, and then a set of 10 image sequences are calculated to form the 3D image. This “3D reconstruction” will form a spatial shape, and then superimpose the infrared image data of the FLIR long-wave thermal imager on the spatial shape, so that the temperature values can be assigned to the spatial coordinates during the mapping process.
3D thermal imaging system: visible light imager (green) uses GOBO projector (green) to record 3D information. The infrared data from the long-wave thermal imager (red) is combined with the reconstructed 3D shape to form a 3D thermal image.
Of course, before the measurement, the system composed of the visible light imager and the long-wave thermal imager needs to be calibrated. For this, the IOF team used a calibration board with regular open-loop and closed-loop grids. To ensure that these structures can be detected in the visible spectrum and long-wave infrared even under the condition of uniform temperature distribution, materials with different reflectance (visible light) emissivity (long-wave infrared) are selected for the circle and background. Researchers in Jena found a solution to this problem through printed circuit boards. To this end, they developed an unusual circuit board that consists of regular open-loop and closed-loop grids, rather than electrical connections between electrical components.
Calibration: It can easily identify regular open loop and closed loop on the circuit board in the visible light and long-wave infrared range
Practical application of high-speed 3D thermal imaging system
IOF’s new high-speed 3D thermal imaging measurement system is designed to combine high dynamic spatial 3D with infrared data. Ultra-fast processes such as sports athletes, crash tests, and airbag deployment not only have rapid changes in surface shape, but also local temperature changes. In the past, these changes could not be captured at the same time. This system has achieved this goal for the first time.
At present, the system has been tested in various scenarios, including basketball players dribbling (not only deforms the ball, but also causes heat):
Take basketball as an example to measure: After 258 milliseconds, the player’s handprints can be seen on the basketball, which is a kind of hot mark
It is also used to measure the temperature change and space representation when the airbag is deployed. The system records the high-speed process for half a second at a distance of 3 meters. After combining the three-dimensional data with the thermal imaging information, not only the temperature of the airbag after deployment can be clearly seen, but also the time point and spatial coordinate information can be obtained. With the help of this information, the risk of injury to the driver caused by the deployment of the airbag can be reduced and prevented.
Take airbag measurement as an example: just above the visual information and below the calculated 3D thermal image sequence example, the airbag deploys at a speed of up to 50 meters per second, which takes only 20 milliseconds
Martin Landmann of the IOF research team is convinced that the application scenarios of the combination of high-resolution 3D data and fast thermal imaging images are very wide. Martin Landmann explained: “For example, by observing crash tests, studying deformation and friction processes, or studying ultra-fast heat-related events, such as an explosion when an airbag is triggered or an explosion in a switch cabinet, we can get very useful Information.” He emphasized that they are constantly developing and optimizing the system. It can be seen that in the future we are expected to see more innovative research results of the Fraunhofer Institute of Applied Optics and Precision Engineering team.
FLIR X6900sc thermal imaging camera provides faster snapshot speed, wider temperature band and better uniformity for current long-wave infrared or mid-wave infrared detectors, strained layer superlattice (SLS) detectors. This thermal imager has advanced trigger function and built-in RAM/SSD recording function. It is equipped with a four-slot motorized filter wheel, which can realize the screen freeze function for high-speed events in the laboratory environment and within the test range.
The Links: SKM195GB126DN SKKT92-12E
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