Search

The paper presents an overview on the use of a behavior-based approach, namely the Null-Space-based Behavioral (NSB) approach, to control multi-robot systems in a wide application domain. The NSB approach has been recently developed to control the motion of generic robotic systems; it uses a projection mechanism to combine the multiple, prioritized, behaviors that compose the robotic mission so that the lower priority behaviors do not effect the higher priority ones. In this paper we describe how the NSB approach has been used to control different multi-robot systems (e.g., composed of wheeled and marine robots) to achieve missions such as formation control, entrapping/escorting of targets, control of mobile ad-hoc networks, flocking, border patrol and cooperative caging.

In this paper, an approach to control the motion of a platoon of autonomous vehicles is presented. The proposed technique is based on the definition of suitable task functions that are handled in the framework of singularity-robust task-priority inverse kinematics. The algorithm is implemented by a two-stage control architecture such that intervehicle communication is not required. The effectiveness of the approach is investigated by means of numerical simulation case studies. Index Terms--Closed-loop inverse kinematics, formation control, multirobot systems, platoon of vehicles.

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. Index Terms--Calibration, identification, mobile robot kinematics, mobile robots, parameter estimation.

A novel adaptive control law for the end-effector tracking problem of underwater vehicle-manipulator systems (UVMSs) is presented in this paper. By exploiting the serial-chain kinematic structure of the UVMS, the overall control problem is decomposed in a set of elementary control problems, each of them formulated with respect to a single rigid body in the system. The proposed approach results in a modular control scheme which simplifies application to UVMSs with a large number of links, reduces the required computational burden, and allows efficient implementation on distributed computing architectures. Furthermore, the occurrence of kinematic and representation singularities is overcome, respectively, by expressing the control law in body-fixed coordinates and representing the attitude via the unit quaternion. To show the effectiveness of the proposed control strategy, a simulation case study is developed for a vehicle in spatial motion carrying a six-degree-of-freedom manipulator. Index Terms--Adaptive control, control of redundant manipulators, underwater robotics, virtual decomposition control.

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 on-line 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. Index Terms--Inverse kinematics algorithms, kinematic control, path tracking.

This paper describes a systematic procedure to design [H.sub.[infinity]] position and flux-norm tracking controllers for current-fed induction motors. The designed controllers achieve convergence to zero of both position and flux-norm tracking errors while ensuring robustness with respect to unknown load torque disturbances. The proposed procedure offers the possibility of a simple development of the controllers' design; in particular, it does not require a numerical solution of the Riccati matrix equation. A case study has been set up which considers the application of the proposed control scheme to a two-link robot manipulator system actuated by two induction motors. Numerical simulation results confirm the validity, of the proposed design methodology, even in the presence of rotor resistance uncertainty.

Interaction of underwater vehicle-manipulator systems (UVMSs) with the environment is affected by several design constraints such as uncertainty in the model knowledge, presence of hydrodynamic effects, kinematic redundancy of the system, and poor performance of vehicle's actuating system. This paper presents an external force control scheme for UVMSs that does not require dynamic compensation; however, it can benefit from the knowledge of part of the dynamic model. The possible occurrence of loss of contact, due to vehicle movement during the task, is also taken into account. A numerical case study shows the application of the proposed technique in a given task. Index Terms--Force control, redundant robots, underwater robotics, underwater vehicle-manipulator systems.

The control problem for a truly cooperative manipulator system cannot be regarded as a simple extension of single manipulator control since additional complexity arises from the need for ensuring coordinated motion of the system. Recently, we have proposed a control strategy based on two stages, namely, kinematic inversion of a set of cooperative task variables and a joint space control law with kinetostatic filtering of cooperative task space errors; this strategy avoids some of the drawbacks of other approaches. In this paper, the stability analysis for the joint space control law is provided and asymptotic stability of a set of equilibrium points is demonstrated. The case of imperfect compensation of the gravity terms has been analyzed. The addition of a force loop to achieve internal force regulation is also discussed. Index Terms - Cooperative manipulators, robotics, stability.

Practical application of the task-priority redundancy resolution technique must deal with the occurrence of kinematic and algorithmic singularities. The aim of this paper is twofold. First, the application of existing singularity-robust methods to the case of kinematically redundant arms is studied. Then, a new task-priority redundancy resolution technique is developed that overcomes the effects of algorithmic singularities. Computational aspects of the solutions are also considered in view of real-time implementation of a kinematic control algorithm. The method is applied to a seven-degree-of-freedom manipulator in numerical case studies to demonstrate its effectiveness.

Stable force/position regulation of robot manipulators in contact with an elastically compliant surface is discussed in this work. The controller consists of a PD action on the position loop, a PI action on the force loop, together with gravity compensation and desired contact force feedforward. Asymptotic stability of the system in the neighborhood of the equilibrium state is proven via the classical Lyapunov method with LaSalle invariant set theorem. A modification of the Lyapunov function leads to deriving an exponential stability result. Numerical case studies are developed for an industrial manipulator.

Abstract - Force/position control strategies provide an effective framework to deal with tasks involving interaction with the environment. In this paper the parallel approach to force/position control of robotic manipulators is presented. It allows a complete use of the available sensor measurements by operating the control action in a full dimensional space without using selection matrices. Conflicting situations between the position and force tasks are managed using a priority strategy: the force control loop is designed to prevail over the position control loop. This choice ensures limited deviations from the prescribed force trajectory in every situation, guaranteeing automatic recovery from unplanned collisions. A dynamic force/position parallel control law is presented and its performance in presence of an elastic environment is analyzed; simplification of the dynamic control law is also discussed leading to a PID-type parallel controller. Two case studies are worked out that show the effectiveness of the approach in application to an industrial robot.

Byline: Gianluca Antonelli, Filippo Arrichiello, Stefano Chiaverini, Roberto Setola This paper investigates the implementation of a wireless mobile ad hoc network to guarantee that an autonomous agent (an autonomously driven mobile vehicle or a human), remains connected to a fixed base station while performing its own mission. To this purpose, the use of a platoon of mobile robots is proposed to carry a number of repeater antennas; these are suitably moved to dynamically ensure a multi hop communication link to the moving agent, hence extending and adapting the area covered by the sole base station. Self-configuration of the robots' platoon is achieved by a singularity-robust task-priority inverse kinematics algorithm via the definition of suitable task functions. The obtained simulation results show the effectiveness of the proposed approach.

This paper presents an adaptive trajectory tracking control strategy for quadrotor micro aerial vehicles (MAVs). The proposed approach, while maintaining the common assumption of an orientation dynamics faster than the translational one, removes the assumption of absence of external disturbances and of geometric center coincident with the Center of Mass (CoM). In particular, the trajectory tracking control law is made adaptive with respect to the presence of external forces and moments (e.g., due to wind) and to the uncertainty of parameters of the dynamic model, such as the position of the CoM. A stability analysis is presented to analytically support the proposed controller, while numerical simulations are provided in order to validate its performance. [ABSTRACT FROM AUTHOR]

This brief presents a decentralized coordinated strategy for multirobot patrolling missions. Patrolling is here interpreted within the framework of the sampling problem. To be applied in practice, several realistic constraints and the time/spatial variance of the information are explicitly considered. The proposed approach is well rooted in the concepts of Voronoi tessellations and Gaussian Processes. Each robot, based only on local information, computes the next point to visit according to a given performance criteria. Numerical simulations and experiments involving three autonomous marine surface robots in a harbor scenario at the Parque Expo site in Lisbon, Portugal, are presented. [ABSTRACT FROM AUTHOR]

The article reports on an entrapment/escorting or catching problem study using the multirobot system. This study consists of surrounding moving targets by decreasing its escape windows. It can have different applications, such as military robotics, entertainment robotics, or robotic surveillance security systems. Multirobot systems have garnered interest in research due to the increase in redundancy and the flexibility of mission execution and making the system resistant to robot faults. Applications, such as exploration and mapping of unknown environments and studying biological systems, are consistently being studied, but few studies address the entrapment/escorting or catching problem.

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. [ABSTRACT FROM AUTHOR]

Proposes an approach to the design of control laws for underwater vehicles that takes into account the hydrodynamic effects affecting the tracking performance. Representation of attitude errors through quaternions; Stability of the designed control law through Lyapunov-based argument.

Focuses on the problem of redundancy solution and motion coordination between the vehicle and the manipulator in underwater vehicle-manipulator systems. Tasks-priority inverse kinematics approach; Merger with a fuzzy technique; Management of vehicle-arm coordination.

Evaluates the systematic procedure to design H[sub ∞] position and flux-norm tracking controllers for current-fed induction motors. Presence of rotor resistance uncertainty; Application of the method to a robot manipulator system; Validity of the design methodology.

This paper describes a systematic procedure for designing speed and rotor flux norm tracking H∞ controllers with unknown load torque disturbances for current-fed induction motors. A new effective design tool is developed to allow selection of the control gains so as to adjust the disturbances’ rejection capability of the controllers in the face of the bandwidth requirements of the closed-loop system. Application of the proposed design procedure is demonstrated in a case study, and the results of numerical simulations illustrate the satisfactory performance achievable even in presence of rotor resistance uncertainty. [Copyright &y& Elsevier]

Describes a navigation and guidance system (NGS) with real-time path planning and obstacle avoidance capabilities that has been developed for the autonomous underwater vehicle RAIS. Description of the vehicle RAIS; Mission of the vehicle; Details on the NGS; Simulation results; Conclusions.

This article presents new closed-loop schemes for solving the inverse kinematics of constrained redundant manipulators. In order to exploit the space of redundancy, the end-effector task is suitably augmented by adding a constraint task. The success of the technique is guaranteed either by specifying the constraint task ad hoc or by resorting to a task priority strategy, instead of previous inverse kinematics schemes that use the Jacobian pseudoinverse, the schemes in this work are shown to converge using the Jacobian transpose. A number of case studies illustrate different ways of solving redundancy in the context of the proposed schemes. [ABSTRACT FROM AUTHOR]