Gianfranco Fenu

Approximate model predictive control laws for constrained nonlinear discrete-time systems: analysis and offline design

The objective of this work consists in the offline approximation of possibly discontinuous model predictive control laws for nonlinear discrete-time systems, while enforcing hard constraints on state and input variables. Obtaining an offline approximation of the receding horizon control law may lead to a very significant reduction of the online computational burden with respect to algorithms based on iterated optimization, thus allowing the application to fast dynamics plants. The proposed approximation scheme allows to cope with discontinuous control laws, such as those arising from constrained nonlinear finite horizon optimal control problems. A detailed stability analysis of the closed-loop system driven by the approximated state-feedback controller shows that the devised technique guarantees the input-to-state practical stability with respect to the (non-fading) approximation-induced errors. Two examples are provided to show the effectiveness of the method when the approximator is chosen either as a discontinuous nearest point function or as a smooth neural network.

Image processing issues in a social assistive system for the blind

We systematically analyse the design of the low-level vision components of a real-time system able to help a blind person in his/her social interactions. We focus on the acquisition and processing of the video sequences that are acquired by a wearable sensor (a smartphone camera or a Webcam) for the detection of faces in the scene. We review some classical and some very recent techniques that seem appropriate to the requirements of our goal.

Towards More Natural Social Interactions of Visually Impaired Persons

We review recent computer vision techniques with reference to the specific goal of assisting the social interactions of a person affected by very severe visual impairment or by total blindness. We consider a scenario in which a sequence of images is acquired and processed by a wearable device, and we focus on the basic tasks of detecting and recognizing people and their facial expression. We review some methodologies of Visual Domain Adaptation that could be employed to adapt existing classification strategies to the specific scenario. We also consider other sources of information that could be exploited to improve the performance of the system.

Technical Communique: A note on nonparametric kernel smoothing for model-free fault symptom generation

This paper describes some new developments to a recently proposed approach to the generation of fault symptoms in dynamic systems. The method is model-free, in the sense that no analytical model of the plant is needed. The kernel-smoother makes it possible to detect changes in the plant dynamics, possibly due to some malfunction. A simple sufficient condition for fault detectability is presented and an application example is given, showing the effectiveness of the proposed method.

Trajectory clustering by means of Earth Mover's Distance

Abstract We propose a method for trajectory classification based on a general cluster-based methodology, that can be used both off-line in an unsupervised fashion, both on-line, classifying new trajectories or part of them. We use the Earth Movers Distance (EMD) and we adapt it in order to employ it as a tool for trajectory clustering. We propose a novel effective method to identify the clusters’ representatives by means of the p —median location problem. This methodology is able to manage different length and noisy trajectories and takes velocity profiles and stops into account. We discuss the experimental results and we compare our approach with other trajectory clustering methods.

Model-Free Plant Tuning

Given a static plant described by a differentiable input-output function, which is completely unknown, but whose Jacobian takes values in a known polytope in the matrix space, this paper considers the problem of tuning (i.e., driving to a desired value) the output, by suitably choosing the input. It is shown that, if the polytope is robustly nonsingular (or has full rank, in the nonsquare case), then a suitable tuning scheme drives the output to the desired point. The proof exploits a Lyapunov-like function and applies a well-known game-theoretic result, concerning the existence of a saddle point for a min-max zero-sum game. When the plant output is represented in an implicit form, it is shown that the same result can be obtained, resorting to a different Lyapunov-like function. The case in which proper input or output constraints must be enforced during the transient is considered as well. Some application examples are proposed to show the effectiveness of the approach.

Safety critical supervision for steel industry robotic applications

In the past years within the steel industry a growing emphasis has been put on fully automatic production lines with a high degree of reliability. The main challenge in designing of these systems is to foster the production process efficiency while improving operators working condition and maintaining the same proper safety level. The CESAR project aims at elaborating a Reference Technology Platform for the cost effective development and validation of safety related embedded systems. In the CESAR project Danieli Automation SpA, in collaboration with the University of Bologna and University of Trieste, has put focus on the development process of a safety system for steel industry robotic applications. In this paper the achieved results related to the exploiteness and usability of the RTP during the development process are reported.

Fault detection on a real three-phase induction motor: simulation and experimental results on residual generation

AC machines have become the industrial standard not only in high power-constant speed applications, but also in the medium and low power range. While most of the problems related to the feedback control of AC motors have been successfully solved, another crucial point emerged with the diffusion of induction motors: the condition monitoring and the detection of their most common faults. In this work, a novel approach to fault diagnosis of AC motors is introduced. Specifically, the architecture of a nonlinear tracking controller made of an observer and a feedback-linearizing module is exploited in order to generate residual signals to be used for fault diagnosis purposes. In the paper, both simulation and experimental results on a real AC motor are provided showing the effectiveness of the proposed approach.

On the Assessment of Segmentation Methods for Images of Mosaics

The present paper deals with automatic segmentation of mosaics, whose aim is obtaining a digital representation of the mosaic where the shape of each tile is recovered. This is an important step, for instance, for preserving ancient mosaics. By using a ground-truth consisting of a set of manually annotated mosaics, we objectively compare the performance of some existing recent segmentation methods, based on a simple error metric taking into account precision, recall and the error on the number of tiles. Moreover, we introduce some mosaic-specific hardness estimators (namely some indexes of how difficult is the task of segmenting a particular mosaic image). The results show that the only segmentation algorithm specifically designed for mosaics performs better than the general purpose algorithms. However, the problem of segmentation of mosaics appears still partially unresolved and further work is needed for exploiting the specificity of mosaics in designing new segmentation algorithms.

Plant tuning: A robust Lyapunov approach

We consider the problem of tuning the output of a static plant whose model is unknown, under the only information that the input-output function is monotonic in each component or, more in general, that its Jacobian belongs to a known polytope of matrices. As a main result, we show that, if the polytope is robustly non-singular (or has full rank, in the non-square case), then a suitable tuning scheme drives the output to a desired point. The proof is based on the application of a well known theorem concerning the existence of a saddle point for a min-max zero-sum game. Some application examples are suggested.