Ground Irregularities Research Articles

Comparison of finite element analysis results with strain gauge measurements of a front axle housing

Abstract. The strength of the front axle of tractors used on rough terrain is crucial in countries in which agriculture is widespread. Rough agricultural fields, rugged village roads, and ground irregularities cause unexpected reaction forces on the axles. Thus, it is important to analyze the front axle of a tractor with respect to stress, which eventually leads to cracks and premature failure. In this study, ANSYS 13.0 finite element analysis (FEA) software (ANSYS, 2010) was used to predict the strength of a design under loading conditions. ANSYS 13.0 allows products to be tested in a virtual environment and helps to prevent problems that may arise later and accordingly improve them. This study aims to investigate the stresses that occur on the housing of the front axle of a tractor. The reaction forces acting on the front axle housing can cause cracks near the middle of the housing. The study applies a static load of 30 000 N to both hubs at the end of the front axle housing and uses the FEA method to predict and evaluate the maximum stress areas on the housing. Strain gauges are bonded to these locations to measure the real-life stresses on the axle housing in these areas. The results of the FEA and strain gauge measurements were compared, and a correlation was found with 98 % accuracy.

Investigating the performance of soft robotic adaptive feet with longitudinal and transverse arches.

Biped robots usually adopt feet with a rigid structure that simplifies walking on flat grounds and yet hinders ground adaptation in unstructured environments, thus jeopardizing stability. We recently explored in the SoftFoot the idea of adapting a robotic foot to ground irregularities along the sagittal plane. Building on the previous results, we propose in this paper a novel robotic foot able to adapt both in the sagittal and frontal planes, similarly to the human foot. It features five parallel modules with intrinsic longitudinal adaptability that can be combined in many possible designs through optional rigid or elastic connections. By following a methodological design approach, we narrow down the design space to five candidate foot designs and implement them on a modular system. Prototypes are tested experimentally via controlled application of force, through a robotic arm, onto a sensorized plate endowed with different obstacles. Their performance is compared, using also a rigid foot and the previous SoftFoot as a baseline. Analysis of footprint stability shows that the introduction of the transverse arch, by elastically connecting the five parallel modules, is advantageous for obstacle negotiation, especially when obstacles are located under the forefoot. In addition to biped robots' locomotion, this finding might also benefit lower-limb prostheses design.

Development and implementation of a new approach for posture control of a hexapod robot to walk in irregular terrains

AbstractThe adaptability of hexapods for various locomotion tasks, especially in rescue and exploration missions, drives their application. Unlike controlled environments, these robots need to navigate ever-changing terrains, where ground irregularities impact foothold positions and origin shifts in contact forces. This dynamic interaction leads to varying hexapod postures, affecting overall system stability. This study introduces a posture control approach that adjusts the hexapod’s main body orientation and height based on terrain topology. The strategy estimates ground slope using limb positions, thereby calculating novel limb trajectories to modify the hexapod’s angular position. Adjusting the hexapod’s height, based on the calculated slope, further enhances main body stability. The proposed methodology is implemented and evaluated on the ATHENA hexapod (All-Terrain Hexapod for Environment Adaptability). Control feasibility is assessed through dynamic analysis of the hexapod’s multibody model on irregular surfaces, using computational simulations in Gazebo software. Environmental complexity’s impact on hexapod stability is tested on both a ramp and uneven terrain. Independent analyses for each scenario evaluate the controller’s effect on roll and pitch angular velocities, as well as height variations. Results demonstrate the strategy’s suitability for both environments, significantly enhancing posture stability.

Hierarchical generative modelling for autonomous robots

Humans generate intricate whole-body motions by planning, executing and combining individual limb movements. We investigated this fundamental aspect of motor control and approached the problem of autonomous task completion by hierarchical generative modelling with multi-level planning, emulating the deep temporal architecture of human motor control. We explored the temporal depth of nested timescales, where successive levels of a forward or generative model unfold, for example, object delivery requires both global planning and local coordination of limb movements. This separation of temporal scales suggests the advantage of hierarchically organizing the global planning and local control of individual limbs. We validated our proposed formulation extensively through physics simulation. Using a hierarchical generative model, we showcase that an embodied artificial intelligence system, a humanoid robot, can autonomously complete a complex task requiring a holistic use of locomotion, manipulation and grasping: the robot adeptly retrieves and transports a box, opens and walks through a door, kicks a football and exhibits robust performance even in the presence of body damage and ground irregularities. Our findings demonstrated the efficacy and feasibility of human-inspired motor control for an embodied artificial intelligence robot, highlighting the viability of the formulized hierarchical architecture for achieving autonomous completion of challenging goal-directed tasks.

ROBUST CONTROL H∞ OVER AN ACTIVE DAMPING SYSTEM OF A VEHICLE ROOM

This paper aims to show and analyze the different types of suspensions: passive, semi-active, and active in a vehicle room. It presents a robust H∞ controller for an active suspension system of the quarter vehicle. Implementing this controller and estimating the weight functions are to minimize vibrations in the vertical axis. This paper compares three control systems corresponding to high comfort, balanced, and highly maneuverable systems. This comparison from the active suspension will allow us to observe that these systems reduce the deflection of the suspension and the acceleration of the sprung mass below the rattle space frequency. A time-domain simulation used a path disturbance signal representing ground irregularities to evaluate the three designs as an essential contribution to this paper. This paper shows that it is possible to develop a control strategy H∞ with robust performance to control a complex analysis system through state feedback. Keywords: Types of Suspension, Robust Controller, Damping, Frequency, Weight Functions DOI： https://doi.org/10.35741/issn.0258-2724.58.1.68

Method for Determining the Susceptibility of the Track

This paper discusses real-world experiments in which selected ground imperfections were dynamically analysed in terms of track susceptibility for a linear and non-linear system. The imperfections included wheel pressure on local ground irregularities within the railway turnout. In this study, susceptibility was assumed as an element between two points (two masses)—most often susceptibility is assumed as a Voigt model (parallel combination of stiffness and damping). The tests were carried out for two configurations of train passage through a railway turnout on straight and diverging track. The track stiffness parameters of the railway turnout were determined from deflection measurements measured by sensors positioned at different points of the turnout. The components of the railway turnout were loaded with different forces. The damping parameter was determined from bench measurements of the actual track component. The function describing this damping is dry friction and such a function was determined. The second part of the study was concerned with measurements of stiffness and moments of inertia in a railway switchyard. The analysis carried out indicated the significance of the adverse effects of selected factors on the operation of the railway track (e.g., increasing the length of non-contact of the track with the ground or additional deflections of the railway track rail arising). The paper points out that such imperfections, in addition to the calculated additional deflections, cause, among other things, disturbances in the progressive movement of the rolling stock.

SIDEWALK DETECTION AND PAVEMENT CHARACTERISATION IN HISTORIC URBAN ENVIRONMENTS FROM POINT CLOUDS: PRELIMINARY RESULTS

Abstract. The definition of physical accessibility in urban environments is a topic of recognized importance by policy makers and by international organizations. A first step to address the accessibility topic is the definition and characterisation of urban elements, like sidewalks, roads, and ramps. Sidewalk inventory plays a crucial role in this phase. In literature there are several ways to extract sidewalks from a point cloud, but they are all tailored on modern and standardized situations. For example the presence of a curb is assumed as the normality and the roads are supposed to have the same width along the path. When dealing with an Urban Heritage, some difficulties arise. In fact, in an historic urban environment ground irregularities should be taken in consideration: the paving is composed by different materials, curbs are not always present, and a Z difference between road and sidewalks is not so sure. In such cases existing methodologies cannot be applied. This paper present a method to semantically segment a point cloud, labelling sidewalks and roads. Sidewalks are also characterized by detecting their pavings. The method is tested on an Urban Heritage: the Unesco site of Sabbioneta, in northern Italy. The results are promising, sidewalks are detected with a precision of 80%, main errors are in corner areas. Paving characterisation is based on thresholds derived from some samples, and the method shows an high precision (more than 90%) in all the pavings considered.

Design of a Mechanism with Embedded Suspension to Reconfigure the Agri_q Locomotion Layout

The Agri_q is an electric unmanned ground vehicle specifically designed for precision agriculture applications. Since it is expected to traverse on unstructured terrain, especially uneven terrain, or to climb obstacles or slopes, an eight-wheeled locomotion layout, with each pair of wheels supported by a bogie, has been chosen. The wide contact surface between the vehicle and the ground ensures a convenient weight distribution; furthermore, the bogie acts like a filter with respect to ground irregularities, reducing the transmissibility of the oscillations. Nevertheless, this locomotion layout entails a substantial lateral slithering along curved trajectories, which results in an increase of the needed driving torque. Therefore, reducing the number of ground contact points to compare the torque adsorption in different configurations, namely four, six, or eight wheels, could be of interest. This paper presents a reconfiguration mechanism able to modify the Agri_q locomotion layout by lifting one of the two wheels carried by the bogie and to activate, at the same time, a suspension device. The kinematic synthesis of the mechanism and the dynamic characteristics of the Agri_q suspended front module are presented.

Virtual Testing of Counterbalance Forklift Trucks: Implementation and Experimental Validation of a Numerical Multibody Model

This study investigates the dynamic behavior of a recently developed counterbalance forklift truck. The final objective is creating virtual testing tools based on numerical multibody models to evaluate the dynamic stresses experienced by the forklift family of interest during a reference operating cycle, defined by the manufacturer’s testing protocols. This work aims at defining sufficiently accurate and easy-to-implement modelling approaches and validation procedures. It focuses on a specific test, namely the passage of a speed-bump-like obstacle at high velocity, which represents one of the most severe conditions within the reference cycle. Indeed, unlike most of the other wheeled vehicles, forklifts typically do not have advanced suspension systems and their dynamic response is significantly affected by ground irregularities. To this end, a preliminary model of the complete forklift, featuring rigid bodies and a simplified tire–ground contact model, is implemented with a commercial software. Experimental tests are conducted on the forklift to measure the vehicle vibrations when running on the obstacle, for model validation purposes. After model updating, the results provided by the numerical simulations match the experimental data satisfactorily. Hence, the modelling and validation strategies are proven viable and effective.

Mutual Coupling Reduction of MIMO Antenna for Satellite Services and Radio Altimeter Applications

Ground irregularities also known as defected ground structures (DGS) is a freshly presented innovatory way in designing of patch antennas to boost up the performance of antenna constraints. This study presents a novel proposal of ground irregularities or defected ground structure is proposed for suppression of mutual coupling effects among 2x1 multiple input multiple output patch array designed on Roggers Duroid 5880. The two adjacent M shape structures surrounding Dumbbell Shaped structure and sandwiched between Dumbbell shape patterns showed the significant level of surface wave suppression up to -42dB while maintaining the gain of 4.7dB and 5.6dBi of directivity. The patch array operates at 4 to 4.3GHz for Fixed and Radio satellite services (FSS) and (RSS) and radio altimeter application systems.

Stiffness and damping real-time control algorithms for adjustable suspensions : A strategy to reduce dynamical effects on vehicles in off-road conditions

In this paper, the problem of dynamical effects of ground irregularity or stability of vehicles in off-road conditions is addressed thanks to a dynamic analysis of the vehicle. In particular, the choice of suitable real-time values for the stiffness and the damping of adjustable suspensions, in order to reduce dynamical effects, is investigated thanks to the analysis of a Laplace transfer function describing the mechanical behaviour of the vehicle. Moreover, a decoupled load transfer computation to identify the suspended masses on each suspension is used and a way to modify in real time suspension parameters by modifying the settling time value in order to drive over obstacles is proposed. This new point of view may permit to use effectively adjustable suspensions in off-road context. Previous approaches indeed only focus on the control of adjustable suspensions on road or by using an actuator in parallel of the suspension and are often dedicated to the driver comfort.

A Novel Design of Patch Antenna using U-Slot and Defected Ground Structure

A novel design of patch antenna is presented with double U slot structure on patch with ground irregularities. As a result tri-band response is achieved with gain reaching 0.785 to 3.75dB respectively and directivity of 5.5 to 5.6dBi. Coaxial cable is mounted with patch as medium of power. The antenna has shown minimum mismatch loss with 0 to 5% with high bandwidth response of 37 to 1200MHZ. The proposed antenna can be used for GSM, W-LAN, GPRS and other radio communication services systems.

The Analysis of Regional Scale Topographic Effect Using MM5-A2C Coupling Modeling

The terrain features and surface characteristics are the most important elements not only in meteorological modeling but also in air quality modeling. The diurnal evolution of local climate over complex terrain may be significantly controlled by the ground irregularities. Such topographic features can affect a thermally driven flow, either directly by causing changes in the wind direction or indirectly, by inducing significant variations in the ground temperature. Over a complex terrain, these variations are due to the nonuniform distribution of solar radiation, which is highly determined by the ground geometrical characteristics, i.e. slope and orientation. Therefore, the accuracy of prediction of regional scale circulation is strong associated with the accuracy of land-use and topographic information in meso-scale circulation assessment. The objective of this work is a numerical simulation using MM5-A2C model with the detailed topography and land-use information as the surface boundary conditions of the air flow field in mountain regions. Meteorological conditions estimated by MM5-A2C command a great influence on the dispersion of mountain areas with the reasonable feature of topography where there is an important difference in orographic forcing.

Hexapod Robot Energy Consumption Dependence on Body Elevation and Step Height

Walking robots are well known for being able to walk over rough terrain and adapt to various environments. Hexapod robots are chosen because of their better stability and higher number of different gaits. However, having to hold the whole weight of the body and a large number of actuators makes all walking robots less energetically efficient than wheeled machines. Special methods for energy consumption optimization must be found. In this paper, hexapod robot energy consumption dependence on body elevation and step height is presented. Three main hexapod gaits are used: tripod, tetrapod and wave. Experimental results show that energy consumption does not depend on body elevation or gait. Although, higher steps increases the power consumption. Therefore, when walking over even terrain, lower step heights along with higher body elevation must be selected for tripod or tetrapod gait in order to surpass ground irregularities but still maintain maximum energetic efficiency. DOI: http://dx.doi.org/10.5755/j01.eee.20.7.8017

The effect of space charge produced by corona at ground level on lightning attachment to high objects

Abstract The influence of the corona space charge layer created at ground level on lightning attachment to high (20–100 m) slender objects is numerically studied. The shielding effect of corona space charge produced near the object tip on the electric field at ground level is considered. The behavior of a non-stationary streamer-free corona developed from ground irregularities in a time-varying thundercloud electric field is discussed. The initiation of an upward leader from the tip of a high grounded object is simulated in the electric field created by a storm-cloud, approaching downward leader and space charge produced by corona at ground level and near the object tip. The corona space charge produced on the ground surface is shown to affect only slightly the inception of an upward connecting leader from the object when the local electric field near the object tip rises rapidly due to an approaching downward leader. The effect of neutral aerosol particles on lightning attachment to high grounded slender objects is also small.

Quadruped robot trotting over irregular terrain assisted by stereo-vision

Legged robots have the potential to navigate in challenging terrain, and thus to exceed the mobility of wheeled vehicles. However, their control is more difficult as legged robots need to deal with foothold computation, leg trajectories and posture control in order to achieve successful navigation. In this paper, we present a new framework for the hydraulic quadruped robot HyQ, which performs goal-oriented navigation on unknown rough terrain using inertial measurement data and stereo-vision. This work uses our previously presented reactive controller framework with balancing control and extends it with visual feedback to enable closed-loop gait adjustment. On one hand, the camera images are used to keep the robot walking towards a visual target by correcting its heading angle if the robot deviates from it. On the other hand, the stereo camera is used to estimate the size of the obstacles on the ground plane and thus the terrain roughness. The locomotion controller then adjusts the step height and the velocity according to the size of the obstacles. This results in a robust and autonomous goal-oriented navigation over difficult terrain while subject to disturbances from the ground irregularities or external forces. Indoor and outdoor experiments with our quadruped robot show the effectiveness of this framework.

Potential dry slab avalanche trigger zones on wind-affected slopes in central Svalbard

Experience suggests that shallow, steep zones on slopes are potential dry slab avalanche trigger points. However, a scientific understanding of this common knowledge is not well quantified due to the spatial variability of snowpack stability, which is governed by various internal and external processes. Currently, the best way to investigate these processes is through point stability testing on small slopes. We thus performed Compression and Extended Column Tests (CTs and ECTs) on three small, wind-affected alpine slopes in central Svalbard. While one study slope (Gangskaret) had smooth ground topography, the other two (Fardalen and Larsbreen) exhibited irregular, rugged ground topography. Our results show that weak layer reactivity was largely influenced by the ground topography, as snow depth is a function of terrain on wind-affected slopes. Slab thickness determines weak layer sensitivity where the ground topography is rugged. Thus, the most unstable spots on these slopes coincided with the shallower zones characteristic of steeper ground surfaces inclinations where the snowpack is thin and the weak layers are close to the surface. This was not as pronounced on slopes with smooth ground topography. However, as snowpack develops and thickens to a “snow depth threshold X”, the ground irregularities are leveled out and their influence diminishes. Thus, knowing the terrain is crucial. Moreover, it is crucial to follow the seasonal snowpack development and extreme weather events that influence it. We found inverse relationships between stability and slab thickness for weak layers that developed early in the season. These early instabilities displayed discontinuity due to melt out over topographic highs during rain-on-snow events, but were left in a preserved state in topographic lows that became overlain by shielding refrozen meltform layers.

Water quality and risk assessment of dug wells: a case study for a poor community in the city of São Paulo, Brazil

Sparsely populated areas, or peripheral communities commonly lack access to a public water supply and sewerage systems. The inhabitants of these areas must make use of excavated wells to provide their water needs, and cesspits for domestic wastewater disposal. These on-site sanitation systems can release pathogens and nutrients into shallow groundwater. These poor communities urgently require cheap and efficient techniques for the detection of sanitary conditions, in order to prevent contamination of the water resources supplied by dug wells. The sanitary risk assessment methodology, applied in an irregular settlement south of the city of Sao Paulo, was based on a questionnaire with yes/no questions (risk factors), which allowed the identification of problems related to the well construction and operation, and the presence of potential contamination sources in its vicinity. These risk factors were compared against nitrate and bacterial analysis using the clustering statistical method, to verify the relationship between contamination and certain aspects surveyed in the questionnaire. Questions that were more related to contaminated wells were those concerning the presence of cover and its integrity; gaps between mouth and cover; the surrounding pavement and presence of ground irregularities; infiltration in the well casing; water-suspended materials; and proximity to contamination sources. Contamination models based on variograms allowed to observe that bacterial contamination presented a strong localized component, which was associated frequently with the way residents handled the wells, whereas nitrate contamination was related more to a regional (spatial) component; that is, the distance between wells and cesspits.

Is “Circling” Behavior in Humans Related to Postural Asymmetry?

In attempting to walk rectilinearly in the absence of visual landmarks, persons will gradually turn in a circle to eventually become lost. The aim of the present study was to provide insights into the possible underlying mechanisms of this behavior. For each subject (N = 15) six trajectories were monitored during blindfolded walking in a large enclosed area to suppress external cues, and ground irregularities that may elicit unexpected changes in direction. There was a substantial variability from trial to trial for a given subject and between subjects who could either veer very early or relatively late. Of the total number of trials, 50% trajectories terminated on the left side, 39% on the right side and 11% were defined as “straight”. For each subject, we established a “turning score” that reflected his/her preferential side of veering. The turning score was found to be unrelated to any evident biomechanical asymmetry or functional dominance (eye, hand…). Posturographic analysis, used to assess if there was a relationship between functional postural asymmetry and veering revealed that the mean position of the center of foot pressure during balance tests was correlated with the turning score. Finally, we established that the mean position of the center of pressure was correlated with perceived verticality assessed by a subjective verticality test. Together, our results suggest that veering is related to a “sense of straight ahead” that could be shaped by vestibular inputs.

Dynamic modeling of wheeled planetary rovers: A model based on the pseudo-coordiates approach

The paper deals with the dynamic modeling of wheeled planetary rovers operating on rough terrain. The dedicated model here presented, although kept as simple as possible, includes the effect of nonlinearities and models the suspensions in a realistic, albeit simplified, way. It can be interfaced with a model of the control system so that different control strategies can be studied in detail and, in case of teleoperated rovers, it can be used as a simulator for training the operators. Different implementations, with different degrees of complexity, are presented and compared with each other so that the user can simulate the dynamics of the rover making a tradeoff between simulation accuracy and computer time. The model allows to study the effects of the terrain characteristics, of the ground irregularities and the operating speed on the behavior of the rover. Some examples dealing with rovers with different configurations conclude the paper.