Underwater Robots - Gianluca Antonelli.pdf

8. Interaction Control of UVMSs
8.1 Introduction to Interaction Control of Robots
In view of the development ofanunderwater vehicle able to perform acompletely
autonomous mission the capability ofthe vehicle to interact with
the environment by the use of amanipulator isofgreatest interest. To this
aim, control of the force exchanged with the environment must be properly
investigated.
Underwater Vehicle-Manipulator Systems are complex systems characterized
by several strong constraints that must be taken into account when
designing aforce control scheme:
• Uncertainty in the model knowledge, mainly due tothe poor description
of the hydrodynamic effects;
• Complexity ofthe mathematical model;
• Structural redundancy of the system;
• Difficulty tocontrol the vehicle in hovering, mainly due to the poor thrusters
performance;
• Dynamic coupling between vehicle and manipulator;
• Low sensors’ bandwidth.
Limiting our attention to elastically compliant, frictionless environments
several control schemes have been proposed in the literature. An overview of
interaction control schemes can befound, e.g., in [70, 303].
Stiffness control is obtained by adopting a suitable position control
scheme when in contact with the environment [248]. In this case, it is not
possible to give areference force value; instead, adesired stiffness attitude
of the tip of the manipulator isassigned. Force and position at steady state
depend on the relative compliance between the environment and the manipulator.
Impedance control allows toachieve the behavior of agiven mechanical
impedance at the end effector rather than asimple compliance attitude [149].
In this case, while it is not possible to give areference force value, the force
measure at the end effector is required to achieve adecoupled behavior.
To allow the implementation ofacontrol scheme that fulfills contact force
regulation one should rather consider direct force control [302]. This can be
G. Antonelli: Underwater Robots, 2nd Edition, STAR 2, pp. 201–223, 2006.
© Springer-Verlag Berlin Heidelberg 2006