L'Fraunhofer Institute for Applied Optics and Precision Engineering in Jena, Germany, conducts application-oriented research in the field of photonics and develops innovative optical systems for the control of light, from generation and manipulation to applications. The institute's range of services covers the entire photonic process chain, from the design of opto-mechanical and opto-electronic systems to the production of customer-specific solutions and prototypes. From 2019, the programme will also include a high-speed 3D thermography system with a scientific thermal imaging camera from FLIR Teledyne: the FLIR X6901sc SLS LWIR model that operates up to a speed of 1000 Hz, with a resolution of 640 × 512 pixels. The aim of the system is to combine highly dynamic 3D spatial data and thermal data in extremely fast processes: a moving athlete, a crash test or the deployment of an airbag. Martin Landmann of the IOF research team is confident: the possible applications for a combination of high-resolution 3D data and fast thermal images are numerous. "You can gain valuable information, for example, by observing crash tests, studying deformation and friction processes, or extremely fast and thermally relevant events, such as explosions when an airbag is deployed or in an electrical panel," he explains.
How the system works
The system is based on two monochrome cameras that are sensitive in the visible spectrum (VIS). They operate at frame rates in excess of 12,000 Hz and at a resolution of one megapixel - although it is possible to have higher frame rates at a lower resolution. However, the two cameras are not yet capable of producing meaningful 3D data in the desired quality. In addition, a sophisticated lighting system is required to project an ultra-fast sequence of striped patterns. These patterns are similar to conventional sinusoidal stripes, but the widths of these stripes vary aperiodically. To achieve the desired effect, a sheet of glass was vaporised with metallic chrome strips. This plate then rotates in a projector placed in front of the optical unit, providing the striped pattern necessary for the specific pixel assignment of both cameras. This principle is called GOBO projection(GOes Before Optics). The 3D information is recorded by the monochrome cameras using the striped projections of the GOBO projector. The 2D infrared data from the LWIR camera can then be merged with the 3D data to form a 3D thermal image in a subsequent step by calibrating all 3 cameras.
Fields of application
The system was tested in various scenarios: a basketball player dribbling a ball (which not only deforms the ball, but also causes thermal heating). Another possible application is the measurement of temperature trends and spatial representation in the case of an airbag deployment: the system recorded the process at high speed from a distance of 3 m for half a second. By combining the three-dimensional data with the thermal image information, it became clear not only how hot the airbag had become as a result of deployment, but also at what point in time and with what exact spatial coordinates. Such information can help reduce and prevent the risk of driver injury related to airbag deployment.
