CART-I: Design and Development of Collision Avoidance Robotic Tether for Underwater Nuclear Inspection Vehicles

摘要

In Underwater exploration, umbilical cord or tether cables are used to provide data transfer, electrical power and control commands to underwater robots and surface vessels. Umbilicals are also useful for anchoring, mooring, and for the deployment of underwater sensors. In general, tethers are naturally buoyant and are designed to work under rough sea conditions and is managed via the Tether Management Systems(TMS). In a limited-size environment such as nuclear environment inspection, multiple ROVs may be deployed and due to the density of various objects underwater, tangles and loops tend to form in low-tension zones due to residual torsion and flexure. The formation of tangles could hinder the operation of the ROV, and attenuate signal transmission in fibre-optic cables due to formed knots and kinks on the cables. Moreover, the risk of collection and entanglements is even increased if the ROV is equipped with manipulators that may tangle with the tether. In this paper, a novel robotics tether system is developed that is capable of navigating in the water to prevent loops and tangles and avoid obstacles. The developments of the system is a bio-inspired design that mimics the motion of a snake in the water. The design of the system single unit consists of a double $\mu$thrust system that is designed to be fitted on the tether. The developed system is distributed in the form of sections on the tether cable. The $\mu$thruster implement a specific pulse thrust according to the distance from an object to prevent collection and entanglement. To effectively simulate the proposed system, a tether cable is simulated for three types of cases, traditional tether, constant thrust tether and constant thrust with wave pattern. Moreover, the initial experiments in the hydrodynamics lab tank showed efficient locomotion of the tether cable away from obstacles.