Fig.6:Feedback Controller

7. Experimental Results

The experiments were carriedout in a 400m x 30m x 8m tank. A yellow color cable was laid on the bottom of the tank and tracking was done at a depth of 6.5m. The tracking was done for 13m along the cable at an average surging speed of about 0.lm/s.

Fig.7:Vision Based Cable Tracking

Fig.8:The Cable Parameters

Fig.9:The Targets and Vehicle State

Twin-Burger is equipped with a CCD camera having a view angle of 80 degrees, 16 T-800 transputers for parallel processing and a B429 image processing card for vision algorithms. The control system is executed on this hardware at a rate of 10Hz.

Figure 7 shows an underwater image of the yellow cable and dark dots on the cable represents the detected line by the Hough transformation technique.

The Hough parameters of the cable observed in the image are given in Figs.8(a) and 8(b): Fig.8(a) gives the perpendicular distance to the detected line from the left top corner of the image and Fig.8(b) is the angle made by this perpendicular line with the x coordinate of the image plane. Using these parameters, the targets for the control of UUV are derived as shown in Fig.9. It can be seen that the Fig.9(a) has a behaviour similar to the Fig.8(a). The state of the vehicle as it tracks the cable is shown in Fig.9(b) and in Fig.9(c). In Fig.9(c) the target surge speed is not achieved due to the fact that the Twin-Burger vehicle uses the forward thrusters for both yawing and surging. The yawing action forces the surge speed to reduce to some extent.

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