Sliding Mode Control of an Underwater Robotic Manipulator

This paper deals with the application of the sliding mode control theory to the specific case of a manipulator for which mono-directional control actions only have to be considered. In particular the control of an underwater gripper is presented. Many even complex robotic structures, can be actuated by mono-directional control actions, for example the so called tendon-arms, the jet-actuated vehicles, underwater vehicles with mono-directional thrusters, etc.. The robotic system which is considered in the paper belongs to the above class, since it is actuated by voice coil motors which, acting on a hydraulic circuit, are able to generate mono-directional forces. In practical realizations actuators often show imprecise relationships between the electrical input signals and the mechanical outputs, that is joint forces or torques. Such a situation constitutes a source of uncertainties we have to deal with. A sliding mode control methodology based on the use of a simplex of constant control vectors is presented, which has revealed to be general enough to work with different applications too.