Sauro Longhi

Development and experimental validation of an adaptive extended Kalman filter for the localization of mobile robots

A basic requirement for an autonomous mobile robot is its capability to elaborate the sensor measures to localize itself with respect to a coordinate system. To this purpose, the data provided by odometric and sonar sensors are here fused together by means of an extended Kalman filter. The performance of the filter is improved by an online adjustment of the input and measurement noise covariances obtained by a suitably defined estimation algorithm.

A Quasi-Sliding Mode Approach for Robust Control and Speed Estimation of PM Synchronous Motors

This paper presents a discrete-time variable-structure-based control and a speed estimator designed for a permanent-magnet synchronous motor (PMSM). A cascade control scheme is proposed which provides accurate speed tracking performance. In this control scheme the speed estimator is a robust digital differentiator that provides the first derivative of the encoder position measurement. The analysis of the control stability is given and the ultimate boundedness of the speed tracking error is proved. The control scheme is experimentally tested on a commercial PMSM drive. Reported experimental evidence shows that the proposed solution produces good speed trajectory tracking performance and it is robust in the presence of disturbances affecting the system.

A Vision-Based Guidance System for UAV Navigation and Safe Landing using Natural Landmarks

In this paper a vision-based approach for guidance and safe landing of an Unmanned Aerial Vehicle (UAV) is proposed. The UAV is required to navigate from an initial to a final position in a partially known environment. The guidance system allows a remote user to define target areas from a high resolution aerial or satellite image to determine either the waypoints of the navigation trajectory or the landing area. A feature-based image-matching algorithm finds the natural landmarks and gives feedbacks to an onboard, hierarchical, behaviour-based control system for autonomous navigation and landing. Two algorithms for safe landing area detection are also proposed, based on a feature optical flow analysis. The main novelty is in the vision-based architecture, extensively tested on a helicopter, which, in particular, does not require any artificial landmark (e.g., helipad). Results show the appropriateness of the vision-based approach, which is robust to occlusions and light variations.

Zeros and poles of linear periodic multivariable discrete-time systems

In this paper the notions of transmission zero, invariant zero, and structural zero (that is the geometric notion of zero) are extended to linear periodic discrete-time systems, as well as the notion of pole. Their meaning is clarified and their relationships stressed, thus extending the time-invariant theory. In particular, the invariant zeros and the structural zeros are shown to coincide, together with their multiplicities, and the former are shown to be independent of a linear state feedback. Moreover, the nonzero transmission zeros, the nonzero invariant zeros, and the nonzero poles are shown to be independent of time, together with their multiplicities. Some of these results are obtained with the help of the notions of reachability subspace and inner controllable subspace, which constitute a further development of the geometric theory for this class of systems.

Finite zero structure of linear periodic discrete-time systems

Periodic ordered sets of structural indices and a new and simpler characterization of the notions of invariant zero, transmission zero, pole and eigenvalue are introduced for a linear periodic discrete-time system. Also the notions of input and output decoupling zeros (together with their ordered sets of structural indices) are extended to this type of system and are shown to have a meaning and relations with the structural properties of the system, wholly similar to the time-invariant ones. The ordered sets of structural indices of non-zero poles, eigenvalues and zeros of any type are independent of time, while those (and even the existence) of the null invariant zero, transmission zero, input and output decoupling zero and pole can depend on time, as well as those of the null eigenvalue (although its algebraic multiplicity is independent of time). The ordered sets of structural indices of invariant zeros are not altered by a linear periodic state feedback (as well as those of input decoupling zeros) and...

Structural properties of multirate sampled-data systems

A complete analysis of the structural properties of multirate sampled-data systems is considered in this paper. Necessary and sufficient conditions for the reachability, controllability and stabilizability and for the dual notions are given in terms of simple rank tests. These results obtained by the structural theory of periodic systems, generalize to the multirate case the well-known conditions of the single-rate case. >

A Feedback Linearization Approach to Fault Tolerance in Quadrotor Vehicles

Abstract In this paper the control problem of a quadrotor vehicle experiencing a rotor failure is investigated. First we derive a nonlinear mathematical model for the quadrotor including both translational and rotational drag terms. Then we use a feedback linearization approach to design a controller whose task is to make the vehicle enter a constant angular velocity spin around its vertical axis, while retaining zero angular velocities around the other axis. These conditions can be exploited to design a second control loop, which is used to perform trajectory following. The proposed double control loop architecture allows the vehicle to perform both trajectory and roll/pitch control when a rotor failure is present.

The geometric approach for linear periodic discrete-time systems☆

Abstract Recently, the disturbance localization problem and the problems of designing disturbance decoupled observers and of giving a geometric characterization of invariant zeros were solved for linear periodic discrete-time systems through an extension of the geometric approach, based on the notions of controlled invariant and conditionally invariant subspaces, to periodic ones. Here the existing periodic geometric theory is supplemented with the notions of outer reachable subspace and controllability subspace, and with some further results on the previously introduced notions of inner reachable (controllable) subspace and outer controllable subspace. In addition, it is shown that any such periodic geometric theory can be restated in an equivalent time-invariant form, which is just the same theory written for a suitable time-invariant system having an extended state space.

A navigation system for increasing the autonomy and the security of powered wheelchairs

Assistive technology is an emerging area where some robotic devices can be used to strengthen the residual abilities of individuals with motor disabilities or to substitute their missing function thus helping them to gain a level of independence at least in the activities of daily living. This paper presents the design of a navigation system and its integration with a commercial powered wheelchair. The navigation system provides the commercial wheelchair with a set of functions which increase the autonomy of elderly and people with motor disabilities. In general, a robot device must be adapted to assistive applications in such a way as to be easily managed by the user. Users, especially young ones, prefer to directly control the robotic device and this aspect of usability has to be managed without affecting the security and efficiency of the navigation module. These aspects have been considered as specifications for the navigation module of powered wheelchairs. Different autonomy levels of the navigation module and proper user interfaces have been developed. Two autonomy levels have been designed. Simple collision avoidance is also implemented in order to stop the mobile base when an obstacle is detected. The preliminary technical tests performed on the navigation system have shown satisfactory results in terms of security and response time. A modular solution for the navigation module was considered in order to simplify the adaptation of the module to different powered wheelchairs.

Disturbance localization by measurement feedback for linear periodic discrete-time systems

Abstract The recent notions of inner controllable, outer controllable and outer reconstructible subspaces, together with the extension of the notion of ( C , A , B )-pair of subspaces to the class of linear periodic discrete-time systems, are the main tools used in this paper in order to study the disturbance localization problem by measurement feedback for the same class of systems. By means of these concepts the necessary and sufficient solvability conditions of such a problem and synthesis procedures of the solutions are found for three different cases, i.e. with and without an additional requirement of output or state dead-beat control.