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Continuous low-latency 3D measurements using efficient freeform GOBO pattern projection and close-to-sensor image rectification

: Munkelt, C.; Speck, H.; Bösel, C.; Junger, C.; Töpfer, S.; Notni, G.


Harding, K.G. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Dimensional Optical Metrology and Inspection for Practical Applications IX : 27 April - 8 May 2020, Online Only, United States
Bellingham, WA: SPIE, 2020 (Proceedings of SPIE 11397)
ISBN: 978-1-5106-3571-5
ISBN: 978-1-5106-3572-2
Paper 1139705, 8 S.
Conference "Dimensional Optical Metrology and Inspection for Practical Applications" <9, 2020>
Fraunhofer IOF ()

Optical 3D measurement using active pattern projection is well known for its high precision and high 3D point density. Recently, increasing the reconstruction frame rate and the number of active sensors in a simultaneous and continuous operation regime used for sensor networks has become more important. Traditionally, light modulators such as LCoS, DMD, or GOBO (GOes Before Optics) have been used, which generate the projected pattern by blocking the light at dark areas of the pattern. In order to further increase the measurement speed and/or the number of time-sequential continuously active sensors, brighter light sources must be chosen to achieve sufficient short exposure times. Alternatively, as we show in this paper, a more efficient pattern modulator can be used. By applying an optical freeform element to generate an aperiodic sinusoidal fringe pattern, up to 100 % of the available light can be utilized. In our prototype, we show how to employ a freeform element moved in a linear bearing to create a compact low-cost, high-speed projection unit. Furthermore, to reduce the computational burden in processing numerous simultaneous image streams, we have implemented the rectification step of the 3D reconstruction pipeline into the field programmable gate array (FPGA) sensor module. Both approaches enable us to use structured light sensors for continuous high-speed 3D measurement tasks for industrial quality control. The presented prototype utilizes a single irritation-free near-infrared (NIR) LED to illuminate and reconstruct within a measurement field of approximately 300 mm × 300 mm at a measurement distance of 500 mm.