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Inverse Kinematic Control of a Free-Floating Underwater Manipulator Using the Generalized Jacobian Matrix

Traditional control of robot manipulators assume that the base of the manipulator is fixed in the environment. However, underwater vehicle-manipulator systems are usually floating freely. Using traditional fixed-base manipulator control for floating systems requires thruster actuation and a stationkeeping algorithm capable of stabilizing the manipulator base. This paper describes a method for underwater manipulation that needs no stationkeeping, and therefore no thrusters. For vehicles with thrusters, the method presented can reduce the energy that the thrusters use on vehicle stabilization. The method is based on inverse kinematics using the generalized Jacobian matrix, a generalization of the traditional fixed-base manipulator Jacobian, formerly used for spacecraft manipulators. The generalized Jacobian matrix makes it possible to control the manipulator end-effector in inertial coordinates while the base remains passive and unactuated. The proposed control method is verified through simulations of an underwater swimming manipulator, using the Vortex Studio software. We compare the performance of the method in open-loop and with position feedback in closed-loop. The simulations show that underwater manipulation without base actuation is possible and that accuracy improves with access to position estimates.