One important problem in autonomous robot navigation is the effective following of an unknown path traced in the environment in compliance with the kinematic limits of the vehicle, i.e., bounded linear and angular velocities and accelerations. In this case, the motion planning must be implemented in real-time and must be robust with respect to the geometric characteristics of the unknown path, namely curvature and sharpness. To achieve good tracking capability, this paper proposes a path following approach based on a fuzzy-logic set of rules which emulates the human driving behavior. The input to the fuzzy system is represented by approximate information concerning the next bend ahead the vehicle; the corresponding output is the cruise velocity that the vehicle needs to attain in order to safely drive on the path. To validate the proposed algorithm two completely different experiments have been run: in the first experiment, the vehicle has to perform a lane-following task acquiring lane information in real-time using an onboard camera; in the second, the motion of the vehicle is obtained assigning in real-time a given time law. The obtained results show the effectiveness of the proposed method

This paper proposes an approach to the design of control laws for underwater vehicles that takes into account the hydrodynamic effects affecting the tracking performance. To this aim, a suitable adaptive action based on appropriate kinematic transformations between the earth-fixed frame and the vehicle-fixed frame is developed. The proposed control law adopts quaternions to represent attitude errors, thus avoiding representation singularities that occur when using instead Euler angles. The stability of the designed control law is demonstrated by means of a Lyapunov-based argument. In view of practical implementation, a simplified version of the developed control law is also proposed that compensates only the persistent hydrodynamic terms, namely, the restoring generalized forces and the ocean current. Finally, the tracking performance of the proposed control law is analyzed in comparison to that of other existing control laws available in the literature. The obtained simulation results confirm the effectiveness of the proposed technique.

For a mobile robot, odometry calibration consists of the identification of a set of kinematic parameters that allow reconstructing the vehicle's absolute position and orientation starting from the wheels' encoder measurements. This paper develops a systematic method for odometry calibration of differential-drive mobile robots. As a first step, the kinematic equations are written so as to underline linearity in a suitable set of unknown parameters; thus, the least-squares method can be applied to estimate them. A major advantage of the adopted formulation is that it provides a quantitative measure of the optimality of a test motion; this can be exploited to drive guidelines on the choice of the test trajectories and to evaluate accuracy of a solution. The proposed technique has been experimentally validated on two different mobile robots and, in one case, compared with other existing approaches; the obtained results confirm the effectiveness of the proposed calibration method.

The presence of joint velocity and acceleration limits must be taken into account by the inverse kinematics of robot manipulators, so as to avoid incorrect task execution when these are violated. To solve this problem, a novel algorithmic approach to kinematic control is presented in this paper, which guarantees that the joint variables do not overtake their limits. The proposed technique is based on a new second-order inverse kinematics algorithm, which enables the handling of velocity and acceleration constraints while tracking the desired end-effector path. The goal is achieved by suitably slowing down the task-space trajectory via a time warp when joints limits are encountered. The proposed method is designed for online applications, i.e., the desired trajectory is not known in advance, and requires a light computational burden. The application of the proposed approach is finally illustrated in experiments implemented on a six-degree-of-freedom industrial robot manipulator.

Distributed generation, which is installed to exploit renewable energy sources, can also be used as a reactive power resource and contribute to tackle the voltage regulation problem in smart distribution grids. Adopting a decentralized approach with off-line coordination, the paper proposes an optimal set-point design for the voltage/reactive power control scheme of distributed generation. The objective is to improve the voltage profile along the feeders of a distribution system. Using only local measurements, the actual operating conditions of the feeder are firstly estimated; then, the set-point is evaluated by solving an optimal voltage profile problem. The off-line coordination avoids any modification to the architecture of existing control systems and requires communication only in the case of significant changes of the distribution system topology. The results of numerical simulations are presented for MV feeders with wind and photovoltaic generations. A comparison with standard control schemes is reported, as well as considerations about the off-line coordination among the distributed generations and the tap-changer of the HV/MV transformer.

The design of a decentralized control scheme is presented which is capable of counteracting voltage variations and offering the ancillary service of voltage regulation to the Distribution Network (DN) by acting on reactive and active power injections of Distributed Energy Resources (DERs). The design is based on a complete dynamic Multi-Input Multi-Output (MIMO) model of the distribution system with different types of DERs interfaced to the DN by inverters. Each DER is equipped with a state-feedback controller and two standard regulators of type PI and I, which realize the dynamic voltage adjustment, ensure null regulation error of voltage and active power at the Point of Common Coupling (PCC) and guarantee robust stability. This control objective is achieved without communication links among the local controllers and in presence of parameters uncertainty affecting the MIMO model. Finally, the proposed approach is validated by dynamic simulations on the IEEE 123 node test feeder with 15 additional DERs of three different types in presence of different scenarios of the distribution system, inaccuracy of the DN line parameters and voltage sags.