Filippo Arrichiello

Experiments of Formation Control With Multirobot Systems Using the Null-Space-Based Behavioral Control

In this paper, the experimental validation of a behavior-based technique for multirobot systems (MRSs), namely, the Null-Space-based Behavioral (NSB) control, is presented. The NSB strategy, inherited from the singularity-robust task-priority inverse kinematics for industrial manipulators, has been recently proposed for the execution of different formation-control missions with MRSs. In this paper, focusing on the experimental details, the validation of the approach is achieved by performing different experimental missions, in presence of static and dynamic obstacles, with a team of grounded mobile robots available at the Laboratorio di Automazione Industriale of the Universita degli Studi di Cassino.

Decentralized time-varying formation control for multi-robot systems

In this paper, a distributed controller–observer schema for tracking control of the centroid and of the relative formation of a multi-robot system with first-order dynamics is presented. Each robot of the team uses a distributed observer to estimate the overall system state and a motion control strategy for tracking control of time-varying centroid and formation. Proof of the overall convergence of the controller–observer schema for different kinds of connection topologies, as well as for the cases of unsaturated and saturated control inputs is presented. In particular, the solution is proven to work in the case of strongly connected non-switching topologies and in the case of balanced strongly connected switching topologies. In order to complete the work, the approach is validated by experimental tests with a team of five wheeled mobile robots.

Formation control of marine surface vessels using the null-space-based behavioral control

In this paper the application of the Null-Space-Based behavioral control (NSB) to a fleet of marine surface vessels is presented. From a marine applications point of view, the NSB can be considered as a guidance system that dynamically selects the motion reference commands for each vessel of the fleet. These motion commands are aimed at guiding the fleet in complex environments simultaneously performing multiple tasks, i.e., obstacle avoidance or keeping a formation. In order to apply the guidance system to a fleet of surface vessels through the entire speed envelope (fully-actuated at low velocities, under-actuated at high velocities), the NSB works in combination with a low-level maneuvering control that, taking care of the dynamic models of the vessels, elaborates the motion commands to obtain the generalized forces at the actuators. The guidance system has been simulated while successfully performing complex missions in realistic scenarios.

Formation Control of Underactuated Surface Vessels using the Null-Space-Based Behavioral Control

In this paper the application of a behavior-based control approach, namely the null-space-based behavioral control, to coordinate a fleet of autonomous surface vessels is presented. The NSB can be considered as a centralized guidance system aimed at driving the fleet in complex environments while simultaneously performing multiple tasks, i.e., obstacle avoidance or keeping a formation. In order to apply the guidance system to a fleet of underactuated surface vessels, the NSB works in combination with a low-level maneuvering control that, taking care of the dynamics of the vessels, elaborates the motion commands to generate the generalized forces at the actuators. The guidance system has been simulated in the accomplishment of a mission in presence of obstacles and sea current in the environment

Flocking for multi-robot systems via the Null-Space-based Behavioral control

Flocking is the way in which populations of animals like birds, fishes, and insects move together. In such cases, the global behavior of the team emerges as a consequence of local interactions among the neighboring members. This paper approaches the problem of letting a group of robots flock by resorting to a behavior-based control architecture, namely Null-Space-based Behavioral (NSB) control. Following such a control architecture, very simple behaviors for each robot are defined and properly arranged in priority in order to achieve the assigned mission. In particular, flocking is performed in a decentralized manner, that is, the behaviors of each robot only depend on local information concerning the robot’s neighbors. In this paper, the flocking behavior is analyzed in a variety of conditions: with or without a moving rendez-vous point, in a two- or three-dimensional space and in presence of obstacles. Extensive simulations and experiments performed with a team of differential-drive mobile robots show the effectiveness of the proposed algorithm.

Observer-Based Decentralized Fault Detection and Isolation Strategy for Networked Multirobot Systems

In this paper, we present a distributed fault detection and isolation (FDI) strategy for a team of networked robots that builds on a distributed controller-observer schema. Remarkably different from other works in literature, the proposed FDI approach makes each robot of the team able to detect and isolate faults occurring on other robots, even if they are not direct neighbors. By means of a local observer, each robot can estimate the overall state of the team and it can use such an estimate to compute its local control input to achieve global tasks. The same information used by the local observers is also used to compute residual vectors, whose aim is to allow the detection and the isolation of actuator faults occurring on any robot of the team. Adaptive thresholds are derived based on the dynamics of the residual vectors by considering the presence of nonzero initial observer estimation errors, and noise terms affecting state measurement and model dynamics. The approach is validated via both numerical simulations and experiments involving four Khepera III mobile robots.

Observability analysis of relative localization for AUVs based on ranging and depth measurements

The paper studies the observability properties of the relative localization of two Autonomous Underwater Vehicles (AUVs) equipped with depth sensors, linear/angular velocity sensors, and communication devices with range measurement. The conditions that ensure observability of the linearized model and locally weak observability of the nonlinear system are derived. An Extended Kalman Filter is then designed aimed at estimating the relative position between two AUVs. Simulations in 3D and reconstruction from experimental data in 2D provide a numerical validation of the analysis.

Observability metric for the relative localization of AUVs based on range and depth measurements: Theory and experiments

This paper addresses the problem of observability of the relative motion of two AUVs equipped with velocity and depth sensors, and inter-vehicle ranging devices. We start by exploiting nonlinear observability concepts to analyze, using observability rank conditions, some types of relative AUV motions. Because rank conditions only provide binary information regarding observability, we then derive a specific observability index (metric) and study its dependence on the types of relative motions executed by the vehicles. In particular, it is shown that the degradation of observability depends on the range and angle between the relative velocity and position vectors. The problem addressed bears affinity with that of single beacon localization. For this reason, the results derived are validated experimentally in a equivalent, single beacon navigation scenario.

The Null-Space-based Behavioral Control for Mobile Robots with Velocity Actuator Saturations

In this paper we present the application of the Null-Space-based Behavioral (NSB) approach to the motion control of mobile robots with velocity saturated actuators. The NSB is a behavior-based robot control approach that uses a hierarchical organization of the tasks to guarantee that they are executed according to a desired priority: it uses a projection technique to avoid that, in the absence of actuator saturations, low-priority tasks could influence higher-priority tasks. The main contribution of this paper is the extension of the NSB approach to the case where actuator velocity saturation bounds are explicitly taken into account. The proposed solution dynamically scales task velocity commands so that the hierarchy of task priorities is preserved in spite of actuator velocity saturations. The approach has been validated on two specific case studies. In the first case, the NSB elaborates the motion directives for a single mobile robot that has to reach a target while avoiding a point obstacle1 in this case, the mission is composed of two tasks. In the second case, the NSB elaborates the motion directives for a team of six mobile robots that has orates the motion directives for a team of six mobile robots that has to entrap and escort a target1 in this case the mission is composed of four tasks. The approach is validated by numerical simulations and by experiments with real mobile robots.

Adaptive trajectory tracking for quadrotor MAVs in presence of parameter uncertainties and external disturbances

The paper presents an adaptive trajectory tracking control strategy for quadrotor Micro Aerial Vehicles. The proposed approach, while keeping the typical assumption of an orientation dynamics faster than the translational one, removes that of absence of external disturbances and of perfect symmetry of the vehicle. In particular, the trajectory tracking control law is made adaptive with respect to the presence of external forces and moments, and to the uncertainty of dynamic parameters as the position of the center of mass of the vehicle. A stability analysis as well as numerical simulations are provided to support the control design.