Fault Tolerance Control of an Underwater Swimming Manipulator

The underwater swimming manipulator (USM) is a new type of underwater vehicle manipulator composed of an underwater snake robot and several thrusters. A USM system has many actuators, so it is more likely to break down, for example, a single joint swinging freely. In this paper, a fault tolerance controller is designed for the USM system to deal with the free-swinging fault of a single joint. Specifically, we derive a kinematic model and a dynamic model of the USM with single joint free-swinging fault and analyze the impact of this kind of fault. The actuator configuration of the USM with single joint free-swinging fault is closer to the singular point, which can reduce the controllability. Therefore, we introduce the actuator singular point avoidance task as a hard constraint into the controller in operational space to ensure the controllability. We also impose the joint constraint task and the trajectory tracking task to the controller and these three tasks should be executed according to priority order. To manage multiple tasks, we adopt a task priority strategy to design the fault tolerance controller. Finally, the effectiveness of the proposed controller is verified with simulation.