Many operations performed by work class Remotely Operated Vehicles (ROVs) require the manipulation of heavy loads. An example is the manipulation and grouting of armour stones. A way to increase the working capabilities of the ROV is to introduce cables among the set of actuators. The cable lengths and tensions are controlled by winches placed on the vehicle. Being similar to a cable-driven parallel robot (CDPR), the resultant system inherits some advantages such as the possibility to generate large forces over a large workspace and the possibility to use CDPR techniques to estimate the pose of the ROV. This paper proposes a complete control architecture for the Hybrid Cable-Thruster actuated ROV (HCT-ROV) and analyzes, in computer simulations, the performances of such a system while it performs real world operations, such as heavy lifting and hovering in presence of water current.

The paper proposes a robust estimation method which implements, in cascade, two algorithms: (i) a Random Sample and Consensus (RANSAC) algorithm and (ii) a novel nonlinear prediction error estimator minimizing a cost function inspired by the mathematical definition of Gibbs entropy. The minimization of the nonlinear cost function allows to refine the Consensus Set found with standard RANSAC in order to reach optimal estimates of geometric transformation parameters under image stitching context. The method has been experimentally tested and compared with a standard RANSAC-MSAC algorithm where noticeable improvements are recorded in terms of computational complexity and quality of the stitching process, namely of the mean squared symmetric re-projection error.

This article proposes a novel solution to the Pose Estimation problem for Ego-Motion from stereo camera images. The approach uses a nonlinear function, derived from the concept of Gibbs' Entropy, which is robust by nature to the presence of noise and outliers in the visual features. The SIFT algorithm is used to collect and match the features from stereo images. The 3-vectors quaternion parameterization is used to parameterize the rotation matrix, in order to avoid the unit norm constraint in the minimization computation. Simulations and experimental results are presented and compared with the results obtained via the classical Iterative Closest Point approach.

This paper presents the application of the Null-Space based Behavioral (NSB) approach to the motion control of a non-holonomic mobile robot with velocity saturated actuators. In particular, the proposed solution aims at managing actuator velocity saturations by dynamically scaling task velocity commands so that the hierarchy of task priorities is preserved in spite of actuator velocity saturations. The approach is tested on a specific case study where the NSB approach elaborates the motion directives for a mobile robot that has to reach a target while avoiding a punctual obstacle. The approach is validated by numerical simulations and by experimental results with a non-holonomic mobile robot.

Standard kinematics prioritized task based motion control solutions do not take into account the physical limitations in terms of maximum actuator speed of robots. In this paper, a prioritized task based kinematics control solution is presented that, under given conditions on the kind of concurrent tasks to be pursued, guarantees task error stability and convergence. Moreover the joint velocities are guaranteed to be bounded by a desired threshold. As for other a null-space projection techniques known in the literature, joint speed commands are computed in such a way that lower priority tasks do not interfere with higher priority ones in the assumption that joint speeds can be arbitrarily large: in addition, if joint speeds are to be bounded by a desired value, joint velocity commands are limited by dynamically chosen values depending on the task priority. As a result, joint velocities are always bounded such that, if necessary, higher priority tasks are executed first.

This paper presents the application of the null-space based behavioral (NSB) approach to the motion control of a team of mobile robots with velocity saturated actuators. In particular, the proposed solution aims at managing actuator velocity saturations by dynamically scaling task velocity commands so that the hierarchy of task priorities is preserved in spite of actuator velocity saturations. The approach is tested on a specific case study where the NSB elaborates the motion directives for a team of six mobile robots that has to entrap and to escort a target. The approach is validated by numerical simulations and by experimental results.

Swedish wheeled robots have received growing attention over the last few years. Their kinematic models have interesting properties in terms of mobility and possible singularities. This paper addresses the issue of kinematic modeling, singularity analysis, and motion control for a generic vehicle equipped with${\bm N}$Swedish wheels.

A line following guidance solution for underactuated marine systems is presented. The approach differs from other ones known in the literature in the definition of the error variables to be stabilized to zero. The proposed guidance technique has been applied to the Charlie USV (Unmanned Surface Vehicle), developed by CNR-ISSIA Autonomous robotic systems and control group, and experimental results are presented.

The great majority of path following control laws for either kinematical or dynamical mobile robot models are designed assuming ideal actuators, i.e. assuming that any commanded velocity or torque (in the kinematical and dynamical cases respectively) will be instantly implemented regardless of its value. Real actuators are far from being ideal. In particular, only bounded velocities and torques can be realized for any given command. With reference to the kinematical model of a differential drive mobile robot, a known path following control law is modified to account for actuator velocity saturation. The proposed solution is experimentally shown to be particularly useful for high speed applications where accounting for actuator velocity saturation may have a large influence on performance.

Swedish wheeled mobile robots have remarkable mobility properties allowing them to rotate and translate at the same time. Being holonomic systems, their kinematics model results in the possibility of designing separate and independent position and heading trajectory tracking control laws. Nevertheless, if these control laws should be implemented in the presence of unaccounted actuator peak velocity limits, the resulting saturated linear and angular velocity commands could interfere with each other thus dramatically affecting the overall expected performance. Based on Lyapunov's direct method, a position and heading trajectory tracking control law for Swedish wheeled robots is developed. It explicitly accounts for actuator velocity saturation by using ideas from a prioritized task based control framework.

A novel strategy to design time invariant motion controllers for underactuated mobile systems is applied to the position and attitude control of an underactuated 3D vehicle. The idea consists in defining a velocity vector field such that an ideal, fully actuated system would exponentially achieve the control objective by simply following such field. Then a steering law for the given underactuated system is designed such that it is exponentially stabilized parallel to the above mentioned velocity vector field. For the particular problem here addressed, due to the use of polar like coordinates, this method yields a discontinuous control law. Both the design process and the resulting solution have a most clear physical interpretation. Important practical requirements as approaching the target on a null curvature path, avoiding cusps in the whole path and moving in only one given forward direction are easily satisfied within this framework.

An underwater planar vehicle, actuated by rear thrusters and equipped with longitudinal control surfaces which allow the drag coefficient modulation in the sway direction, is considered in a dynamic setting. The maneuvring controls for the vehicle, in order to reach the required final position and attitude are devised by exploiting both the rear thrusters actuation and the capability offered by the admitted presence of the longitudinal, modulable, control surfaces.

We present a robotic software development framework for rapid simulation and programming of mobile robot teams. The framework uses a specification-centred generative approach. A robot control program is specified in an intuitive graphical representation of a hyper-graph of typed data processing elements. This specification is automatically refined to all design artifacts required in a robotic software development environment: simulation models, robot control programs, team communication infrastructure, documentation, and real-time monitoring. Although our framework was originally intended to design behavior-based robot control programs using the dual dynamics architecture, we demonstrate the flexibility of the environment by an example which integrates a "classical" control schema into a dual dynamics behavior system. Experimental validation was done on GMD-Robots, our team of mid-size league RoboCup robots.