|An article by reseachers from Fraunhofer IOF on a technique for high-speed 3D shape measurement has been awarded the 2014 Rudolf Kingslake Medal and Prize. Above, Fig. 15: Snapshot during the measurement of a collapsing wooden toy wall: (a) camera image and (b) point cloud (doi:10.1117/1.OE.53.11.112208); below, the paper's authors.
BELLINGHAM, Washington, USA, and CARDIFF, UK -- Five researchers from Fraunhofer Institute for Applied Optics and Precision Engineering (Fraunhofer IOF) are recipients of the 2014 Rudolf Kingslake Medal and Prize. This annual prize is awarded to authors of the most noteworthy original paper on theoretical or experimental aspects of optical engineering published in Optical Engineering, the flagship journal of SPIE, the international society for optics and photonics. The award will be presented at SPIE Optical Systems Design 2015, 7-10 September in Jena.
Stefan Heist, Andreas Mann, Peter Kühmstedt, Peter Schreiber, and Gunther Notni wrote the winning paper, "Array projection of aperiodic sinusoidal fringes for high-speed three-dimensional shape measurement," published in the journal's November 2014 issue.
The paper introduces a new array projector for high-speed 3D shape measurement. This alternative method uses aperiodic sinusoidal fringes instead of the well-known phase-shifted sinusoidal fringes and Gray code patterns. The LED-based multi-aperture projection system is suitable for high-speed measurement of object topographies since it enables pattern projection with frame rates of several 10 kHz.
The authors note that in their previous work, they used the phase-shifting fringe projection in conjunction with Gray code. Since the phase difference between the sinusoidal patterns varied strongly with the projection distance, measuring ability was restricted.
The new setup features "nine aperiodic sinusoidal fringe patterns with spatially varying offset, amplitude, period length, and phase shift, consecutively projected onto the object to be measured, which is observed by two calibrated cameras," the authors write. The stereo correspondence problem is solved with the help of the temporal correlation technique.
After verifying the accuracy of the array projector, its capability for high-speed 3D shape measurement needed to be proven, the authors continue. Their first measurements at 3-kHz projection frame rate resulted in a 3D frame rate of >330 Hz, proving the applicability of the array projector for accurate high-speed 3D shape measurements. The measurement of a test plane (a flat piece of granite painted white) showed the standard deviation as ~100 μm. The high-speed capability of the setup was verified by taking measurements of a collapsing wall made of wooden toy blocks.
SPIE Fellow Tomasz Tkaczyk, chair of the Kingslake Award committee said the array projector demonstrates a new paradigm in that the proposed method "enables higher projection frame rates and the ability accurately measure the variable topography of 3D objects at high speeds."
At Fraunhofer IOF, Heist works with 3D scanning systems R&D in the Optical System Department; Kühmstedt is group manager of the 3D Measurement Group; Schreiber heads the Illumination and Projection Group; and Notni heads the Optical Systems Department. Mann is currently working in Esslingen.
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