1,720,976 research outputs found
On the vibration analysis of off-road vehicles: Influence of terrain deformation and irregularity
No full textSurface 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
A glance at the behaviour of a tracked mobile robot on different agricultural surfaces
No full textThis research work investigates the behaviour of a tracked mobile robot moving over two different types of agricultural terrain: a rigid surface, such as asphalt or concrete and a deformable clayey soil. A study on the inertial measurements and motor currents data provides an overall analysis of the robot's behaviour during classical agricultural tasks. The analysis includes ground traversability due to terrain roughness and consistency, the stress on the ground due to the vehicle movement and a rapid check of the energy consumption by looking at the motor currents. The authors emphasize that all the information obtained in the manuscript can be retrieved by direct measurements available from relatively inexpensive proprioceptive sensors without onerous calculations or expensive sensors
ON THE VERTICAL DYNAMICS MODELLING OF RIGID WHEELS ON SOFT SOIL
No full textRigid wheels or wheels much stiffer with respect to the soil are used in many applications in the field of Terramechanics, e.g., planetary exploration rovers or agricultural vehicles on ploughed terrains. In this study vertical ground forces exchanged between a rigid wheel and a soft terrain are investigated. Useful and novel information on off-road vehicles behaviour in terms of vibrations, dynamic wheel sinkage, terrain hardness and so forth are obtained. According to the derived wheel-soil interaction model, a Quarter Car (QC) system relative to off-road vehicles with rigid wheels is established and its behaviour under different scenarios (which include different terrains with different surface roughness) is investigated. The results achieved for the off-road vertical dynamics can be relevant for vehicles design. Furthermore, as an example of a real application, a model-based observer grounded on this QC system is adopted in order to estimate the terrain hardness
LEO to GEO-SAR interferences: Modelling and performance evaluation
Full text linkThis paper proposes a statistical model to evaluate the impact of the signal backscattered by low Earth orbiting (LEO) synthetic aperture radar (SAR) and received by GEO-stationary orbiting SAR. The model properly accounts for the bistatic backscatter, the number of LEO-SAR satellites and their duty cycles. The presence of many sun-synchronous, dawn-dusk satellites creates a 24 h periodic pattern in interference that should be considered in the acquisition plan of future geostationary SAR. The model, implemented by a numerical simulator, allows also the prediction of performance in future scenarios of many LEO-SAR. Examples and evaluations are made here for X band
Increasing autonomy in agricultural robots: Unevenness estimation of the terrain ahead
No full textNatural terrain traversing is playing an increasingly important role in service and field robotics to enable the achievement of several tasks in the most disparate fields of human activities, e.g. planetary explorations, nuclear site decommissioning, precision farming and so forth.In this research, a new method for terrain unevenness estimation is proposed in order to increase the ability of an agricultural bot to move autonomously in a countryside environment. By the use of exteroceptive sensors, such as stereoscopic or RGB-D cameras, soil surfaces can be acquired and then manipulated to obtain a stochastic description of their geometry by means of the Power Spectral Density (PSD)-based analysis, in order to infer soil irregularities. This automatic ground unevenness estimation is performed online during the motion, allowing safe management of robot activities
End-to-end simulator of Geosynchronous SAR data for system performance assessment
No full textThe paper describes an end-to-end simulator for Geosynchronous SAR data. The tool is composed of two modules: a raw data time domain simulator and a processor for the generation of the L1 products. The simulated raw data include the effects of atmospheric and clutter decorrelation. The end-to-end simulator is a powerful and flexible tool to be used during the system design phase for the verification of the expected performance
Kalman Supervised Network for Improved Model Predictions
No full textIn this paper, we propose a Neural Network to im-prove long-term state predictions without measurements based on Kalman filter observations. It is well known that the Kalman Fil-ter is an iterative algorithm composed of two phases: predict and update. The update corrects predictions based on measurements. Predictions rely exclusively on the embedded physical model. This research aims to learn the underlying dynamics of the system under observation from the estimates of a standard Kalman Filter that supervises a Neural Network. Then, the Kalman Supervised Net (KSN) can be used to improve predictions learning from Kalman filter corrections. Numerical results show the advantages of the proposed solution when predicting the state of a spring-mass-damper system without using acceleration measurements
Where am I heading? A robust approach for orientation estimation of autonomous agricultural robots
No full textReliable knowledge of the vehicle heading plays a significant role in the autonomous navigation of agricultural Unmanned Ground Vehicles (UGVs), especially in the context of unstructured outdoor environments such as rural and forestry scenarios. However, achieving this information with an acceptable degree of confidence is a non-trivial task and still an open field of research. Expensive solutions are available on the market, but they often discourage most farmers due to the large investments needed for the startup. This paper introduces a novel algorithmic solution for reliable evaluation of the absolute vehicle heading, grounded on adaptive Kalman filtering with input evaluation via linear regression analysis. The proposed approach provides a functional and affordable solution to the heading estimation problem that can be used in real-world applications. The system is validated through an extensive experimental campaign using an all-terrain tracked rover operating in agricultural settings, showing good accuracy compared to other approaches, such as a dual GPS method found in the literature
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
