The objective of this paper is to propose an innovative visual servoing method in order to improve the 3D reconstruction of objects for quantitative measurements. The method uses a Stereovision system that allows us to obtain several shots of an object, at regular intervals according to a predefined trajectory. In our case, the stereo rig is equipped with two different cameras, consequently the intrinsic parameters are not the same. The first one is fixed while the other one is mounted on a pan and tilt. Simulation and preliminary experiments in laboratory conditions shows the validity of our approach

We present a vision-based method to control the displacement of robot arm mounted on an underwater remotely operated vehicle (ROV). A closed-loop system based on an eye-to-hand visual servoing approach has been designed to achieve this task. We show that, using such an approach, the measuring of the manipulator motion with proprioceptive sensors is not required to precisely control the end-effector motion. To maintain the end effector in the field of view, the camera orientation is also controlled. The results presented show the validity of the approach.

The paper is devoted to the problem of nonlinear robust control design for underwater vehicle/manipulator (UVM) systems composed of a freefloating platform equipped with a robot manipulator. The different bandwidth characteristics of the composite vehicle/arm dynamics are used as a basis for the control design via singular perturbation theory. The main contribution of this paper is that a robust nonlinear control is only required in the slow-subsystem (vehicle dynamics). Thus, this control is only used to compensate the coupling effects from the arm to the base. The paper also presents a comparative study between simple PD, a partial linearized control and the nonlinear robust feedback.

Underwater robotic systems require a control architecture that handles automatic control aspects and discrete-event management while considering real-time issues within a formalized framework in order to achieve a high degree of autonomy and robustness while performing missions. To extract generic characteristics of working implementations, we examine two methodologies developed independently by French and American research organizations to control their underwater robots. In particular, we study how a specific reactive and complex mission is encoded under the two different methodologies. Details of the methodologies along with mission programs created by each team to accomplish the evaluation mission are presented.

This paper investigates the benefits of applying simple PID+nonlinear controller to subsea robot. This control structure has the advantage of only adding a supplementary nonlinear feedback loop to the existing linear PID-regulator and at the same time improving both the transient and stability margins. Several simulations and experiments have been performed on the experimental subsea robot (VORTEX) and have demonstrated the improvements of the PID+nonlinear controller over the simple PID.>