Development of a coordinated controller for underwater vehicle-manipulator systems

In this work, the motions of an underwater remotely operated vehicle (ROV) and a spatial manipulator are coordinated using a consolidated controller. The controller translates a single pilot command, the desired position and orientation of the end effector, into a coordinated set of ROV and manipulator joint motions that satisfy the pilot intent in addition to a series of secondary objectives. The controller relies on a unified dynamic model of the system. The quasi-Lagrange method is used to derive the equations of motion in terms of the ROV body-fixed frame. For the control problem, a novel sliding-mode based controller is proposed. The controller contains two layers of adaptivity. The first layer is for adjusting PID gains, whereas the second layer is for estimating the bound on a lumped uncertainty vector. The second level of adaptation is shown to relax the Lyapunov stability requirements leading to a more robust controller. To generate reference state values, a redundancy resolution technique is utilized that is based on the gradient projection method merged with a fuzzy determination of the hierarchy of the secondary objectives. The redundancy resolution method distributes the pilot´s end-effector command over the ROV and the manipulator in an optimal manner using the redundant degrees of freedom. The results illustrate that detailed subsea tasks can be completed with a small, low-cost ROVM system using the proposed unified control scheme.