Efficient Sub-Optimal Inverse Kinematic Solution for Redundant Manipulators

Master'sMASTER OF ENGINEERIN

Mobility Evaluation of Wheeled Robots on Soft Terrain: Effect of Internal Force Distribution

[Abstract] Many applications of wheeled robots include operations in unstructured environments. Optimizing vehicle mobility is of key importance in these cases. Reduced mobility can limit the ability of the robot to achieve the mission goals and can even render it immobile in extreme cases. In this paper, some aspects of the effect of the wheel–ground interaction force distribution on mobility are investigated. A performance index based on the normal force distribution is used to compare different design layouts and vehicle configurations. The validity of this index was assessed using both multibody dynamics simulation and experimental results obtained with a six-wheeled rover prototype. Results confirmed that modifying the system configuration and employing active suspensions to alter the normal force distribution can lead to an increase of traction force available at the wheel–terrain interfaces, thus improving rover mobility. Finally, the study was extended to consider the change of soil properties during operation due to the multipass effect. Optimum load distributions were obtained as the solution of a constrained maximization problem.MINECO; JCI-2012-1237

A novel concept for analysis and performance evaluation of wheeled rovers

[Abstract] - The analysis, design, and operation planning of rovers are often based on predictive dynamic simulation, where the multibody model of the vehicle is combined with terramechanics relations for the representation of the wheel–ground interaction. There are, however, limitations in terramechanics models that prevent their use in parametric analysis and simulation studies. Increasing mobility is generally a primary objective for the design and operation of rovers. The models and assumptions used in the analysis phase should target this objective. In this paper we put forward a new concept for the analysis of wheeled rovers, particularly for applications in off-road environments on soft soil. We propose a novel view of the problem based on the development of models that are primarily intended to represent how parameter changes in the robot design can influence performance. These models allow for the definition of indicators, which gives information about the behavior of the system. We term such models observative. In the reported work, a set of indicators for rover performance is formulated using such models. The ability of these indicators to characterize the behavior of a rover is assessed with a series of simulation tests and experiments. The indicators defined using observative models succeeded to capture the changes in rover performance due to variations in the system parameters. Results show that the proposed models can provide a useful tool for the design and operation of planetary exploration rovers

Numerical Analysis of Transmembrane Pressure Changes in UF Systems by Changing the Geometry of the Inner Surface of Hollow Fibers

Membrane processes are one of the most important separation methods in water and wastewater treatment processes. Hollow fiber membranes are used in many separation processes due to their high surface area to volume ratio. Since porosity and permeability of porous media depend on its geometric features, a change in the geometry leads to changes in these value and the performance of the system. In this study, a mathematical modeling was made for three fiber geometry categories; including circular, square and elliptical and the geometric features were calculated based on three strategies. In order to investigate the effect of geometry, a double porosity media was considered. Results showed that the ratio of surface area to volume of hollow fiber membranes and the axial permeability in square and elliptic geometries are usually higher than circular fibers and are increased to a maximum value of 27% and 63%, respectively. Also, in a strategy, equivalence of the radius of the inspirational circle of the new geometry with the inner radius of ordinary fibers was less than the circular fiber, which was a desired result and caused a decrease in energy consumption and operation cost of the system

Effect of gravity in wheel/terrain interaction models

[Abstract] Predicting the motion of wheeled robots in unstructured environments is an important and challenging problem. The study of planetary exploration rovers on soft terrain introduces the additional need to consider the effect of non-terrestrial gravitational fields on the forces and torques developed at the wheel/terrain interface. Simply reducing the wheel load under earth gravity overestimates the travelled distance and predicts better performance than is actually observed in reduced-gravity measurements. In this paper, we study the effect of gravity on wheel/terrain interaction. Experiments were conducted to assess the effect of reduced gravity on the velocity profile of the soil under the wheel, as well as on the traction force and sinkage developed by the wheel. It was shown that in the velocity field of the soil, the decay of the tangential velocity component becomes gradual with reducing gravity, and the decay of the normal to rim velocity is slower in Lunar gravity. It was also found that wheel flexibility can have an important effect on the dynamics as the contact patch and effective radius varies periodically. These results were then used together with traditional semi-empirical terramechanics models to determine and validate the simulated drawbar pull values. The developed simulation model includes the effect of wheel flexibility, dynamic sinkage and gravity.MINECO; RYC-2016-2022

Performance evaluation and dynamics of rovers for planetary exploration

Planetary exploration and off-road applications require rovers to operate in unstructured environments, involving interaction with soft soil, non-homogeneous terrain and sloped and rocky surfaces. In this context, simulation and analysis tools can be very helpful to characterize the mobility of rovers under various terrain conditions. Modelling of rovers with the objective of predicting their behaviour requires adequate knowledge of the parameters of the system and its environment. Due to the existence of uncertainties in estimation of terrain properties, accurate prediction of wheel-soil interaction poses the main challenge in the simulation of rover manoeuvres. However, accurate prediction of a rover behaviour may not be necessary for evaluation and improvement of its design and operational strategies. To this end, an alternative approach is introduced which relies on what is termed observative models, as opposed to the predictive ones. The objective of using observative models is to develop an understanding of the way the system performance would be affected by the change of its design and operation parameters. Observative models of rovers are able to capturethe trends that are generally observed and it is shown that variations in terrain parameters do not affect the validity of the results obtained with these models. A detailed study of the wheel-soil interaction phenomena is carried out which shows that the ability of rovers in developing drawbar pull is greatly influenced by the distribution of the normal load among their wheels. The normal force dispersion isused as a performance indicator to compare the mobility of different rover configurations. Based on the type of soil and other factors such as the multipass effect, a series of design and operation guidelines are proposed in order to improve the ability of rovers to generate higher drawbar pull and climb steeper slopes and larger obstacles. These guidelines include the modification of the chassis internal force distribution via redundant actuation. The effectiveness of the proposed approaches is investigated via simulation studies and extensive sets of experiments with two rovers, the Juno and the Rover Chassis Prototype (RCP). Redundant actuation is realized by introducing some design modifications to the RCP which enables online modification of normal force dispersion. The simulation studies are carried out using a generic multibody dynamics library which is developed as a part of this research. This library can serve as a generic and rover-specific analysis tool and addresses some of the shortcomings in the available simulation packages.Les missions d'exploration planétaire comme les applications tout-terrain imposent aux véhicules d'évoluer dans des environnements nonstructurés, dans lesquels ils sont confrontés à des sols meubles, hétérogènes, irreguliers, voire rocheux. Dans un tel contexte, les simulations et les outils d'analyse se révèlent d'une aide précieuse pour caractériser la mobilité de ces véhicules sur différents types de terrains. La modélisation des robots mobiles en vue de prédire leur comportement nécessite une bonne connaissance des paramètres du système et de son environnement. Du fait des incertitudes dans l'estimation des propriétés du terrain, la restitution fidèle des interactions roues-sol constitue le défi principal de la simulation des véhicules tout-terrain. Cependant, une prédiction précise du comportement du robot n'est pas toujours nécessaire à l'évaluation et à l'amélioration de sa conception et de ses stratégies d'évolution. Aussi, une approche alternative est proposée ici, en s'appuyant sur les modèles dits observatif, par opposition aux modèles prédictifs. L'utilisation des dits modéles doit permettre de comprendre la manière dont la conception et les paramètres de fonctionnement influent sur les performances du système. Les observatif sont capables de saisir les tendances que pren globalement le robot et il a été montré que la modification des paramètres du terrain n'affectent pas la validité des résultats obtenus par de tels modèles. Une étude détaillée des phénomènes d'interaction roue-sol est réalisée. Celle-ci montre que la traction développable par un véhicule est hautement influencée par la distribution des réactions normales sur les roues. La dispersion de ces derniéres est donc utilisée comme indicateur de performance pour comparer la mobilité de différentesconfigurations de robots. À partir du type de sol et d'autres facteurs commele roulement dans les traces des roues frontales, un ensemble de directrices pour la conception et le déploiement est proposé afin de donner aux robots mobiles à roues la capacité de générer davantage de traction, gravir des pentes plus prononcée et franchir des obstacles plus importants. Ces directrices incluent la modification de la distribution des forces internes au moyen d'un actionnement redondant. L'efficacité des approches proposées est testée à l'aide de simulations et d'une gamme étendue d'essais basé sur deux exemples de robots roulants, le Juno et le Rover Chassis Prototype(RCP). La redondance d'actionnement est élaborée en introduisant quelques changements dans la conception du RCP afin de permettre la modification en ligne de la dispersion des forces normales. Les études en simulation sont réalisées en utilisant une bibliothèques dynamique générique développée dans le cadre de cette recherche. Cette bibliothèques fournitune série d'outils d'analyse aussi bien génériques que spécifiques aux systèmes roulant et permet de pallier les lacunes des logiciels de simulation existants