Conclusion

In this chpater, the design, implementation and test results of a small AUV named ISiMI are presented. The AUV, ISiMI, developed in KORDI is a test-bed for the validation of the algorithms and instruments of the AUV. For fast experimental feedback on new algorithms, ISiMI was designed to be able to cruise in the Ocean Engineering Basin environment at KORDI. The zigzag test and the turning test were carried out to check ISiMI's maneuvering properties. The depth control and waypoint tracking tests were carried out to validate the feedback controller of ISiMI. The experiment results were compared with those of the simulation. The research works were fed back to the design and implementation of a 100m-class AUV named ISiMI100. ISiMI100 is equipped with additional sensors such as a doppler velocity log, an acoustic telemetry modem, an obstacle avoidance sonar, a range sonar, and a GPS module. A photo of ISiMI100 is shown in Fig. 28. The mission test of ISiMI and the sea trial of ISiMI100 remain to be performed in future works.

Acoustic telemetry modem GPS

Acoustic telemetry modem GPS

Doppler velocity log Obstacle avoidance sonar Figure 28. Sea-trial version of ISiMI AUV named ISiMI100

A final approach algorithm based on vision guidance for the underwater docking of an AUV was developed and introduced. The algorithm allowed the tested AUV to identify dock lights, eliminate interfering luminary noises and successfully estimate both the center of the dock and the distance to it during the first stage of the docking sequence despite the fact that the AUV was unable to detect the dock lights when close to the dock. The final approach algorithm based on vision guidance did guide the AUV to the dock successfully. The area where the lights were out of the camera viewing range occasioned confusion, as expected, but the attitude keeping control was able to keep the AUV on the way to the dock. Underwater docking experiments showed the necessity of the attitude keeping control. The use of the attitude keeping control as well as the vision-guidance control improved the precision of docking performance. The fixed references guided the AUV more precisely and safely. Although the docking experiments were conducted under controlled conditions, the results of the experiments showed the utility and potential of the vision-based guidance algorithm for docking.

Future problems include successfully docking when (1) the dock is moving, (2) the dock is placed out of the camera viewing range at the beginning of a return process, and (3) currents and waves are present. Generation of the optimized path from any initial start point to the dock is also a subject for future study.

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