PSI - Issue 17

Behzad V. Farahani et al. / Procedia Structural Integrity 17 (2019) 712–717 Behzad V. Farahani et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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mW circular laser module possessing an output wavelength of 520 nm. The optical instruments were assembled on a 20-by-20-mm 2 Bosch profile (1000 mm long). A general view of the optical components related to the deployed 3D LSS is shown in Fig. 2. It has been designed to mount on the welding robot’s arm moving inside the tower with an adjustable altitude. The camera was calibrated based on Zhang’s formulations (Zhang 2005). The laser calibration followed the formulations extensively described in (Farahani et al. 2019). An 8×9 calibration pattern with a square size of 80 mm was used for the calibration procedure. A series of images of the calibration pattern with the laser projection being reflected inside the pattern was captured. Fig. 3 depicts the calibration, laser and camera positions.

(a) (b) Fig. 2: (a) Adopted 3D LSS for the tower experiment and ( b) the system mounted on the welding robot’s arm.

(a) (b) Fig. 3: (a) A 9-by-8-square calibration pattern and laser projection on and (b) laser and camera positions.

3. Experiments, analyses and results T he adopted LSS was mounted on the welding robot’s arm and the whole system was moving thro ugh the tower with a constant velocity of = 32 mm⁄s . Due to the camera ’s field of view (FOV), it was not possible to acquire the complete profile with a single acquisition; therefore, to tackle this disturbance, the experiment was carried out in two stages. After the first image acquisition the tower was rotated through 180  by means of rollers holding the exterior wall. The experiment related to the original and rotated states of the tower were identified as Half_one and Half_two , respectively. Prior to the test performance, two hand switch magnetic bases were attached on the interior wall where the second part of the tower section initiates. They played a role of auxiliary marks contributing to merge the two point clouds acquired in the original and rotated states. Experimental activities were carried out following the configurations reported in Table 1. Due to the limited travelling distance of the welding robot, only 2561 mm of the middle part has been captured.