Aldo Balestrino

Path tracking control for Dubin's cars

The problem of driving a Dubins car (1957) along a given path is considered. In order to model a realistic road-following problem, the car is supposed to move forward only and to have bounds on the turning radius (Dubins car). We propose a discontinuous control scheme on the angular velocity of the vehicle, based on the theory of sliding modes, that achieves the goal of tracking an unknown path relying on measurements of the current distance from the path and of the heading angle error.

Cuk converter global control via fuzzy logic and scaling factors

A successful implementation of a low-cost PI-fuzzy controller for a Cuk converter is presented in this paper. Properties of the proposed controller are robustness around the operating point, good performance of transient responses in changing load conditions and/or input voltage, and invariant dynamic performance in the face of varying output operating points. Simulations and experimental results have been obtained via a suitable variation of the scaling factors related to the input variables of the fuzzy controller.

Automatic nonlinear auto-tuning method for Hammerstein modeling of electrical drives

Accurate modeling of electrical drives for online testing is a relevant problem, because of their nonlinear behavior. Efficient modeling for simulation, performance evaluation, and testing must consider accurate as well as simple models. This paper proposes the application of auto-tune methods to identify equivalent Hammerstein models, where the nonlinear process is approximated by a static nonlinear element followed by a linear dynamic second or third-order model. The effectiveness of the presented procedure is first verified by simulation results, showing that Hammerstein models overcome the limitations inherent to small-signal linearizations. A standard implementation of such technique considers a relay adjustment for attempts in a heuristic way. In this paper, two innovations are proposed: the relay adjustment is automatically shifted and the method is applied for complex electric drives. Experimental results are shown in the case of a drive constituted by a DC/AC inverter supplying a single-phase induction motor and of a step-down chopper.

Innovative Solutions for Overhead Catenary-Pantograph System: Wire Actuated Control and Observed Contact Force

In this paper an innovative active pantograph for high-speed trains is proposed. The results presented are based on extensive simulation tests. The parameters used in the simulation are those of a real pantograph for high-speed trains: the pantograph model is modified by adding a wire actuation, in order to exert a constant contact force between the moving pantograph and the overhead contact wire. A wire-actuated control and contact force observers are proposed as effective solutions in the case of a possible implementation.

Closed loop smooth steering of unicycle-like vehicles

Within this paper it is shown that, provided a special choice for the system state equations is a priori made, the use of the simplest quadratic form as candidate Lyapunov function, directly leads to the definition of smooth and effective closed loop control laws for unicycle-like vehicles, suitable to be used for steering, path following, and navigation among assigned points. Some considerations about the curvature of the corresponding manoeuvres are also reported.<<ETX>>

Breaking the lab's walls. Tele-laboratories at the University of Pisa

In this paper we describe work being done at our Department to make the Robotics laboratory accessible to students and colleagues, to execute and watch real-time experiments at any time and from anywhere. We describe few different installations, and highlight the underlying philosophy, which is aimed at enlarging the lab in all the dimensions of space, time, and available resources, through the use of Internet technologies.

From Remote Experiments to Web-Based Learning Objects: An Advanced Telelaboratory for Robotics and Control Systems

This paper describes the current evolution of the telelaboratory facilities at the University of Pisa. In particular, starting from a standard environment providing remote access to a set of experiments, the telelaboratory is now organized as a collection of learning objects, i.e., modular didactic units designed following specific learning objectives within control systems and robotic fields. The telelaboratory has a remote Web-based access which can be used both as a simulation environment and as a remote way of performing real physical experiments. The developed telelaboratory is based on free open-source software such as Scilab/Scicos, Comedi, and real-time application interface patch for Linux kernels. In-house software tools, such as a Java Web hyper modular interface system, graphic environment tools, and a virtual laboratory interface based on Java applets, have been developed as a support for the learning process.

Closed-loop steering for unicycle-like vehicles: A simple lyapunov like approach

Abstract In this paper it is shown that a special choice of the variables representing the position of a unycicle-like vehicle allows the determination of a smooth and globally stabilizing closed loop steering law. The analysis is carried out by means of a Lyapunov-like approach which directly leads to the steering strategy. An extension related with the use of “multiple objective function” is introduced an and the analysis of the limiting behaviour of the path’s curvature is reported.

Circle-Based Criteria for Performance Evaluation of Controlled DC–DC Switching Converters

An experimental method is proposed to estimate all design specifications represented by circles in the Nyquist plane (e.g., phase margin, sensitivity, and closed-loop bandwidth) in case of closed-loop dc/dc switching converters. The method is based on the complete root contour (CRC) analysis in the root locus plane. All typical specifications for controller design are experimentally checked in case of a boost converter, using only input/output data. The main innovation of this paper is the automatic and systematic application of the CRC method to controlled dc-dc converters. The classic relay-based structure for an experimental estimation of the critical parameters (autotune variation) is compared with a different technique, called sinusoidal autotune variation, more efficient in the case of nonlow-pass systems

Observability and Nonlinear Observers for Mobile Robot Localization 1

Abstract In this paper, the problem of localizing a nonholonomic vehicle moving in an unstructured environment is addressed by the design of a novel nonlinear observer, based on suitably processed optical information. The localization problem has been shown to be intrinsically nonlinear, indeed the linear approximation of the system has different structural properties than the original model. The proposed nonlinear observer allows the localization of nonholonomic mobile robots by using an estimated expression of the extended output Jacobian, local practical stabilization of the observation error dynamics is also ensured. A singularity-avoidance exploration strategy is also included to deal with the output Jacobian singularities crossing.