Coordinated Vehicle/Manipulator Design and Control Issues for Underwater Telemanipulation

Abstract

Control of underwater vehicle/manipulator systems described by highly nonlinear and coupled dynamics can be improved through careful vehicle and manipulator design, while novel controller structures can improve system performance and simplify the man/machine interface requirements. Understanding and overcoming sensor limitations present in underwater vehicle navigation is one of the basic requirements for high fidelity control and trajectory planning of the manipulators’ endeffector attached to its mobile base. Modelling and control of ducted propellers used as actuators becomes crucial for fine control and the avoidance of limit-cycling during hovering maneuvers. The ability to model the pitch/roll-translation coupling for such systems is necessary to increase the performance and fidelity of trajectory following and force/impedance control. Neglecting such coupling effects not only results in poor tracking performance but can also cause instabilities due to excitation of unmodelled ‘pendulum’ modes and the operation near venicle/manipulator singularities. The necessity to coordinate vehicle ana manipulator control for unconstrained motions and contact tasks requires the development of a coordinated controller structure. The use of a dual impedance structure can insure stability during contact tasks with a wide variety of environments, while the use of a coupling impedance is used to shape the relative behavior between vehicle and manipulator endpoint. The operational use of such a dual/coupled controller structure extends the maneuvering and manipulation capabilities of mobile manipulation platforms by reducing the number of variable controller parameters and thus operator burden while increasing system flexibility and userfriendliness of the man/machine interface. This paper presents preliminary simulation and experimental results.