Development of a Lightweight Underwater Manipulator for Delicate Structural Repair Operations

In recent years, underwater robots have been increasingly used in the maintenance of hydraulic structures. Underwater manipulators are essential devices that are used to carry out such maintenance tasks. For delicate repair operations such as fixing tiny cracks, most existing underwater manipulators face limitations in terms of size, accuracy, and scalability. Therefore, in this letter, we present a novel electric underwater manipulator, named SEU-4. This four-degree-of-freedom manipulator weighs 8.91 kg and has a maximum payload of 9 kg. It has a rapid-switching interface that supports convenient mechanical and electrical connections for end-effectors. To compensate for the disturbances that are present in the complex underwater environment, a trajectory-tracking control strategy based on a disturbance observer and sliding-mode control (DOB-SMC) is proposed. A prototype of the proposed underwater manipulator was created, and a flowing-water experimental platform was constructed to test its trajectory-tracking performance in fast-flowing water. The experimental results show that the manipulator achieves a trajectory-tracking error of 1.03 mm in static water and 2.91 mm in flowing water at 1.2 m/s, which satisfies the requirements of delicate repair operations.