Control of an underwater reconfigurable robot: spatial maneuver with planar eel-like configuration

USS is a novel underwater self-reconfigurable robot, which consists of modules of the same type. By the modules´ connecting and disconnecting, USS can change its configuration in real-time. A feature of USS is that it can execute underwater spatial maneuver with only the planar eel-like configuration, which is due to the module´s capability of buoyancy regulation and one degree metamorphosing. This article focuses on control of the type of maneuver. We built the nonlinear 6-DOF dynamics model firstly, and then perturb it around the nominal state of straight forward motion with constant speed, which gives two uncoupled linear models for the horizontal maneuver and the perpendicular motion. The perpendicular controller is designed based on the robust control technique of mix sensitivity, while the horizontal controller is designed based on Masashi Saito´s method, in which maneuver is achieved by serpentine gait, and the speed and heading are stabilized by feeding back the metamorphosing frequency and the average joint angles respectively. The control strategy is then verified by digital simulation, which shows that the expected maneuver is achieved well by the suggested method.