An efficient and reliable onboard perception system is critical for a mobile robot to increase its degree of autonomy toward the accomplishment of the assigned task. In this regard, laser range sensors represent a feasible and promising solution that is rapidly gaining interest in the robotics community. This paper describes recent work of the authors in hardware and algorithm development of a 3-D laser scanner for mobile robot applications, which features low-cost, lightweight, compactness, and low power consumption. The sensor allows a vehicle to autonomously scan its environment and to generate an internal hazard representation of the world in the form of digital elevation maps. This suggests a general approach to terrain analysis in structured and unstructured environments for a safe and collision-free path planning. The proposed sensor system along with the algorithms for mapping and planning is validated in indoor laboratory experiments as well as in tests on natural terrain using an all-terrain rover.

This paper presents a novel approach to detect traversable and non-traversable regions of the environment from a depth image that could enhance mobility and safety of mobile robots through integration with localization, control and planning methods. The proposed system is based on Principal Component Analysis (PCA). PCA theory provides a powerful means to analyze 3D surfaces widely used in computer vision. It can be successfully applied, as well, to increase the degree of perception in autonomous vehicles, as new generations of 3D imaging sensors, including stereo and RGB-D-cameras, are increasingly introduced. The approach described in this paper is based on the estimation of the normal vector to a local surface leading to the definition of a novel, so-called, Unevenness Point Descriptor. Experimental results, obtained from indoor and outdoor environments, are presented to validate the system. It is demonstrated that the proposed approach can be effectively used for scene segmentation and it can efficiently handle difficult scenarios, including the presence of terrain slopes.

This paper describes recent efforts by the authors in the development of a robotic hand, referred to as the Adam’s hand. The end-effector is underactuated through a multiple bevel-gear differential system that is used to operate all five fingers, resulting in 15 degrees of freedom actuated by just 1 degree of actuation. Special focus is devoted to the transmission ratios and gear dimensions of the system to maintain the kinematic behaviour and the dimensions of the prototype as close as possible to that of human hand.

This work presents the dynamic modeling and active vibration control of planar multilink manipulators having flexible links. Since the eigenvalue problem of such continuous structures is strongly dependent on the posture configuration, at first an efficient matrix formulation is provided in order to derive exact natural frequencies and mode shapes of a robot in its general posture. The analytical modal data are used to develop the forced vibration model; this is accomplished through the analytical decoupling of the modal coordinates of the manipulator; to this latter end, orthogonality conditions of modal shapes sets of planar multilink manipulators are demonstrated. The suppression of vibrations is challenged through a full-state linear quadratic regulator controller by optimally placing collocated sensor/actuator pairs. An optimal stochastic observer is designed in line with the noise-corrupted truncated model, i.e. the continuous Kalman-Bucy filter. The simulation results demonstrate that the presented matrix formulation for deriving exact modal data is effective, and the designed control method, along with the forced vibration solving strategy, is feasible and efficient.

This paper analyses the influence of different sets of edge-boundary conditions on the dynamics of freely vibrating isotropic and cross-ply multilayer laminated rectangular plates. The analysis is carried out within the frame of the full three-dimensional theory of elasticity through a formulation which is based on assumed displacements only; this formulation presents its relevant objectives in a unified manner, regardless of the nature of the stacking patterns of the laminated plates (isotropic, single layers or multi-layers). The analytical and/or numerical performance of the formulation is compared to those few results achievable through the exact three-dimensional theory and/or to those few existing results achieved by other researchers through alternative formulations. Convergence analyses are carried out on eigenvalues, displacement and stress fields in order to describe the capability of the formulation when compared to the exact three-dimensional results. The analysis reveals an interesting dependence on the edge-boundary conditions and highlights the need to carry out deeper investigations even though certain classical boundary conditions are taken into account through the most modern electronic computers.This paper analyses the influence of different sets of edge-boundary conditions on the dynamics of freely vibrating isotropic and cross-ply multilayer laminated rectangular plates. The analysis is carried out within the frame of the full three-dimensional theory of elasticity through a formulation which is based on assumed displacements only; this formulation presents its relevant objectives in a unified manner, regardless of the nature of the stacking patterns of the laminated plates (isotropic, single layers or multi-layers). The analytical and/or numerical performance of the formulation is compared to those few results achievable through the exact three-dimensional theory and/or to those few existing results achieved by other researchers through alternative formulations. Convergence analyses are carried out on eigenvalues, displacement and stress fields in order to describe the capability of the formulation when compared to the exact three-dimensional results. The analysis reveals an interesting dependence on the edge-boundary conditions and highlights the need to carry out deeper investigations even though certain classical boundary conditions are taken into account through the most modern electronic computers.

Future mobile robots will have to explore larger and larger areas, performing difficult tasks, while preserving, at the same time, their safety. This will primarily require advanced sensing and perception capabilities. In this respect, laser range sensors represent a feasible and promising solution that is rapidly gaining interest in the robotics community. This paper describes recent work of the authors in hardware and algorithm development of a 3-D laser scanner for mobile robot applications, which features cost effectiveness, lightweight, compactness, and low power consumption. The sensor allows an autonomous vehicle to scan its environment and to generate an internal hazard representation of the world in the form of digital elevation map. Details of the device are presented along with a thorough performance analysis as function of the relevant operational parameters, such as elevation and nodding angular rate. The generation of elevation models is also investigated, addressing the issues connected with the presence of overhanging objects and occluded areas.

Surface irregularity acts as a major excitation source in off-road driving that induces vibration of the vehicle body through the tire assembly and the suspension system. When adding ground deformability, this excitation is modulated by the soil properties and operating conditions. The underlying mechanisms that govern ground behavior can be explained and modeled drawing on Terramechanics. Based on this theory, a comprehensive quarter-car model of off-road vehicle is presented that takes into account tire/soil interaction. The model can handle the general case of compliant wheel rolling on compliant ground and it allows ride and road holding performance to be evaluated in the time and frequency domain. An extensive set of simulation tests is included to assess the impact of various surface roughness and ground deformability through a parameter study, showing the potential of the proposed model to describe the behavior of off-road vehicles for design and performance optimization purposes.

This manuscript deals with a novel approach aimed at identifying multiple damaged sites in structural components through finite frequency changes. Natural frequencies, meant as a privileged set of modal data, are adopted along with a numerical model of the system. The adoption of finite changes efficiently allows challenging characteristic problems encountered in damage detection techniques such as unexpected comparison of possible shifted modes and the significance of modal data changes very often affected by experimental/environmental noise. The new procedure extends MDLAC and exploits parallel computing on modern multicore processors. Smart filters, aimed at reducing the potential damaged sites, are implemented in order to reduce the computational effort. Several use cases are presented in order to illustrate the potentiality of the new damage detection procedure.

This work analyzes the influence of edge-boundary conditions on the static and dynamic behavior of isotropic and cross-ply plates in cylindrical bending conditions. The main concern of the analysis is addressed to dynamic problems (free vibrations) along with certain boundary conditions that seem to be mainly responsible for a low convergence of the eigenvalues to the exact values. The interest on the static behavior comes from the inherent sensitivity of related quantities, which can both be compared with previous studies and can better elucidate such a low convergence. The analysis is carried out within the frame of the three-dimensional theory by using different variational formulations based both on assumed displacements and/or stresses along with the attempt to unify the comparison of the different formulations. The numerical results/performance of such formulations are also compared to those achieved through alternative models.

In this article, freely vibrating multilayered piezoelectric plates are analyzed through a set of adaptive global piecewise- smooth functions along with governing differential equations and associated boundary conditions, which are consistently derived from the classical theorem of virtual displacements. The analysis demonstrates the capability of the adaptive glo- bal piecewise-smooth functions to treat any multilayered plate as if it were made up of a single layer even in the presence of multiphysics analyses such as piezoelectric layers. The relevant model is essentially two-dimensional because it is based on an expansion through the thickness of the plate aimed at modeling a three-dimensional dynamical behavior. In order to demonstrate the effectiveness of the model, all the results are compared to exact three-dimensional results; these latter are extracted through a three-dimensional model based on a transfer matrix technique whose numerical sta- bility is achieved using scaled electric potentials. The exact graphical results are herein illustrated, thus showing both the effectiveness of using weighted electric potentials and the capability of adaptive global piecewise-smooth functions to converge at exact results through a minimum computational effort.

This article presents two models that have the aim of analysing three-dimensional freely vibrating plates made of an arbi- trary combination of structural and/or piezoelectric layers. The first model is derived from a displacement-based varia- tional statement, and it investigates the possibility of approaching exact three-dimensional results at any degree of accuracy. This model has been developed as if the plates were virtually made of a single layer, and it is herein referred to as the approximate analysis model. The second model is based on solving the set of three-dimensional linear equations coupling the relevant mechanical and electric quantities, and it therefore provides exact results. The latter model is derived from the transfer-matrix technique which, having shown numerical instability in the multiphysics problem being dealt with, was then successfully modified to provide exact and reliable results. Excellent agreement has been obtained between the models, and this shows how the exact approach here designed is stably able to overcome ill conditioning problems, while the first model, having been validated by the exact results, could be applied to effectively investigate mul- tiphysics problems for general boundary conditions, and for cross- and/or angle-ply laminates, at any level of required accuracy.

Mobile robots are increasingly being employed in challenging outdoor applications including search and rescue for disaster recovery, construction, mining, agriculture, military and planetary exploration. In this kind of robotic applications, the accuracy and robustness of the motion control system is greatly affected by the occurrence of undesired dynamics effects such as wheel slippage. In this paper a cross-coupled controller is presented that can be integrated with 4-wheeldrive/ 4-wheel-steer robots to optimize the wheel motors’ control algorithm and reduce synchronization errors that would otherwise result in wheel slip with conventional controllers. Experimental results, obtained with an all-terrain rover operating outdoor, are presented to validate this approach showing its effectiveness in reducing slippage and vehicle posture errors.

The modelling and the control of web handling systems have been studied for a long time; correct modelling is necessary in order to design a better control system or to identify the plant parameters experimentally. On the web dynamics itself, lumped parameters expressions may be used to designate a web section between two adjacent drive rolls, and there is the necessity of incorporating the property of viscoelasticity to the web. In this paper the lumped model of a new web tension experimental system is updated; the model is based on the conservation mass, torque balance and viscoelasticity (Voigt approach). The experimental system consists of four sections each of which is driven by a servomotor; the speed and tension feedback, by using encoders and tension sensors, drives simultaneously the four servomotors through a real time C programmed D/A board. Usually, as described in the literature, these kinds of models are developed in the Laplace domain and the block scheme gives a graphical interpretation of the interaction between different sections. The transformation of the block scheme in a differential equation system in the time domain is fully described in this paper; it is not a simple step and it requires the introduction of not null initial condition for the derivative of physical variables. Moreover, the problem of validation has been dealt with in detail in this paper, considering simultaneously 2 different combinations of input data in open loop and a multivariable optimization method in order to estimate a certain number of unknown parameters. The results will show the accuracy of this kind of lumped parameters model for the complex experimental systems and useful information for successively designing an efficient control strategy.