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A 3D measuring endoscope for hand-guided operation

Optical measuring devices are widely used in industrial production and maintenance processes. With increasing integration, the accessibility of functional elements inside machines is limited for measuring devices. In order to provide a new measurement tool for these applications, the design of an endoscopic 3D sensor based on the structured light principle is presented. Application specific sensor heads are introduced, with diameters down to 8 mm attached to endoscopes with a length of 1 m. The sensor features a flexible pattern generator and a camera, allowing for dynamic reconfiguration of structured illumination patterns. Based on a brief comparison of existing light coding approaches, two different measuring modes for the sensor are described. The first measuring mode uses conventional phase-shift sequences in order to achieve highly accurate measurements under controlled conditions. The second measuring mode uses a new interleaved encoding approach for phase-shift patterns, which enables robust measurements even in the presence of relative motion between object and sensor. An example for this type of motion is the movement of the endoscope tip by hand. Using the proposed sequence design, the 3D acquisition rate is identical to the capture rate of the camera, which amounts to a maximum of 180 Hz in the current hardware configuration of the measuring endoscope. In combination with a registration and merging algorithm, consecutive measurements are automatically combined, enabling the measurement of large surfaces. Moreover, the approach is capable of estimating the relative location and orientation of the endoscope tip using odometry based on depth data. The performance of the sensor in both measuring modes is evaluated on the basis of measurements of reference objects. Furthermore, the results of a hand-held measurement of a reference standard are shown.