  This paper addresses the problem of cooperative object transportation for
multiple Underwater Vehicle Manipulator Systems (UVMSs) in a constrained
workspace with static obstacles, where the coordination relies solely on
implicit communication arising from the physical interaction of the robots with
the commonly grasped object. We propose a novel distributed leader-follower
architecture, where the leading UVMS, which has knowledge of the object's
desired trajectory, tries to achieve the desired tracking behavior via an
impedance control law, navigating in this way, the overall formation towards
the goal configuration while avoiding collisions with the obstacles. On the
other hand, the following UVMSs estimate the object's desired trajectory via a
novel prescribed performance estimation law and implement a similar impedance
control law. The feedback relies on each UVMS's force/torque measurements and
no explicit data is exchanged online among the robots. Moreover, the control
scheme adopts load sharing among the UVMSs according to their specific payload
capabilities. Finally, various simulation studies clarify the proposed method
and verify its efficiency.
