G. De Maria

Calyceal microlithiasis in children: report on 196 cases

Abstract. Recognition of children at greatest risk for urolithiasis may allow early detection or prevention of stone formation. We report clinical data from 196 children aged 0.9–15.9 years in whom renal ultrasound examination revealed hyperechogenic spots in renal calyces less than 3 mm in diameter. We called this finding “calyceal microlithiasis” (CM). There was a history of urolithiasis in 70.4% of patients in at least one first- or second-degree relative. Presenting symptoms were recurrent abdominal pain, dysuria, and hematuria, occurring alone or in combination. Hematuria was the presenting symptom in 41% of patients and was the only urinary finding in more than one-third. Hypercalciuria was present in about one-third and hyperuricuria in one-fifth of the patients. Of 29 patients who were followed for at least 2 years, 9 developed calculi 4–7 mm in diameter. CM possibly represents the first step in calculus formation. The finding of CM might explain a number of symptoms and signs that are often mild and non-specific, thus reducing invasive diagnostic procedures.

Experimental Comparison of Sensor Fusion Algorithms for Attitude Estimation

Abstract Inertial Measurement Unit is commonly used in various applications especially as a low-cost system for localization and attitude estimation. Some applications are: real-time motion capture system, gait analysis for rehabilitation purposes, biomedical applications, advanced robotic applications such as mobile robot localization and Unmanned Aerial Vehicles (UAV) attitude estimation. In all the mentioned applications the accuracy and the fast response are the most important requirements, thus the research is focused on the design and the implementation of highly accurate hardware systems and fast sensor data fusion algorithms, named Attitude and Heading Reference System (AHRS), aimed at estimating the orientation of a rigid body with respect to a reference frame. A large number of different solutions can be found in the literature, and an experimental comparison of the most popular is presented in this work. In particular, the algorithm based on the gradient descent method and the algorithm based on a nonlinear complementary filter are compared to a standard Extended Kalman Filter (EKF) with the aim to show that a general method can easily compete with ad-hoc solutions and even outperform them in particular conditions. In order to validate the estimation accuracy a Kuka robot is used to compute the ground truth. Moreover, in order to estimate the computational burden, the algorithms are implemented on an ARM-Cortex M4-based evaluation board.

Tactile data modeling and interpretation for stable grasping and manipulation

This paper is devoted to present the latest results on the exploitation of the force/tactile sensor developed by the authors in terms of modeling and interpretation of the data provided by the device. An analytical nonlinear model of the elastically deformable sensor is derived and validated, which allows to reconstruct the position and orientation of the surface in contact with a rigid object on the basis of the sensor signals. The reconstruction is performed via an Extended Kalman Filter able to counteract the measurement noise and to handle the nonlinearity of the model at the same time. The contact plane position and orientation information together with the contact force vector measured by the sensor are used to estimate the physical parameter most relevant to manipulation control purposes: the friction coefficient. A slippage control algorithm is presented which exploits the estimated friction and a novel slipping detection algorithm is proposed to cope with the unavoidable uncertainties of the real world and its effectiveness is experimentally proved in comparison with the existing techniques.

Modal Analysis and Vibration Control of a Fuselage Aeronautical Panel

Abstract A well-known problem in civil aeronautic engineering is the reduction of vibrations of all the parts of the fuselage, e.g. frames, skin panels, trim panels, caused by the external airflow and by the airplane engines, which affect both comfort and safety of the flight. Currently, special passive devices are adopted to reduce these vibrations, namely Dynamic Vibration Absorbers (DVA), but their performance are quite limited, especially for rejection of broadband disturbances. In this work the possibility to adopt active dynamic absorbers is explored, by resorting to an actuator based on a magnetostrictive material, with the aim of increasing the reduction of undesired vibrations. First, a mathematical model of the flexible structure, i.e. a fuselage panel of a civil airplane, is deduced by means of a new modal analysis algorithm aimed at identifying the modal parameters of the mechanical system. Then, a number of different control strategies are designed and experimentally compared in two case studies, showing the feasibility of the proposed approach.

An Advanced System for Vibration Control of Flexible Structures

Abstract The objective of the research work here presented is the rejection of a broadband disturbance in a vibrating flexible structure. From a technological point of view, the problem is tackled using an advanced lightweight magnetostrictive resonant actuator with an integrated optical strain sensor. The adopted control strategy consists of a two-levels controller. Usefully exploiting the measurement of the integrated sensor, a low-level feedback loop, aimed at linearizing the actuator behaviour, is designed by resorting to a model-following approach. An optimal control law is specifically implemented as the high-level feedback loop providing a H ∞ strongly stabilizing controller with bandpass capability for both low- and high-frequencies measurement disturbances affecting the accelerometer used as control sensor. The advanced control system has been experimentally tested on an aeronautical stiffened panel.

Vibration Control of Flexible Systems via Sliding Manifold Approach

Abstract In this paper an active vibration controller for flexible systems is developed using a sliding manifold approach. The controller is designed to “eliminate” the system’s mode whose frequency is closer to the disturbance frequency. The sliding approach ensures the robustness of the control scheme against large uncertainties generally present in flexible structure models. The sliding surface consists of a time-invarying part which “eliminates” the selected mode without affecting the other dynamics, and a time-varying part which bounds the control amplitude and its rate in the transient. If the state is not available an observer is needed to implement the control law. In particular, a time varying term is introduced in the observer in order to avoid the peaking phenomenon. The features of the controller and observer allow one to reduce the excitation of high frequency modes, hence to reduce the spillover phenomenon.