Modeling of Wheel-Soil Interaction for Small Ground Vehicles Operating on Granular Soil.

Unmanned ground vehicles continue to increase in importance for many industries, from planetary exploration to military defense. These vehicles require significantly fewer resources compared to manned vehicles while reducing risks to human life. Terramechanics can aid in the design and operation of small vehicles to help ensure they do not become immobilized due to limited traction or energy depletion. In this dissertation methods to improve terramechanics modeling for vehicle design and control of small unmanned ground vehicles (SUGVs) on granular soil are studied. Various techniques are developed to improve the computational speed and modeling capability for two terramechanics methods. In addition, a new terramechanics method is developed that incorporates both computational efficiency and modeling capability. First, two techniques for improving the computation performance of the semi-empirical Bekker terramechanics method are developed. The first technique stores Bekker calculations offline in lookup tables. The second technique approximates the stress distributions along the wheel-soil interface. These techniques drastically improve computation speed but do not address its empirical nature or assumption of steady-state operation. Next, the discrete element method (DEM) is modified and tuned to match soil test data, evaluated against the Bekker method, and used to determine the influence of rough terrain on SUGV performance. A velocity-dependent rolling resistance term is developed that reduced DEM simulation error for soil tests. DEM simulation shows that surface roughness can potentially have a significant impact on SUGV performance. DEM has many advantages compared to the Bekker method, including better locomotion prediction, however large computation costs limit its applicability for design and control. Finally, a surrogate DEM model (S-DEM) is developed to maintain the simulation accuracy and capabilities of DEM with reduced computation costs. This marks one of the first surrogate models developed for DEM, and the first known model developed for terramechanics. S-DEM stores wheel-soil interaction forces and soil velocities extracted from DEM simulations. S-DEM reproduces drawbar pull and driving torque for wheel locomotion on flat and rough terrain, though wheel sinkage error can be significant. Computational costs are reduced by three orders of magnitude, bringing the benefits of DEM modeling to vehicle design and control.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/108811/1/wsmithw_1.pd

Adaptive motion planning for a mobile robot

Historically, trapezoidal velocity profiles have been widely used to control engines. Nevertheless, the evolution of robots and their uses has led to the need of using smoother profiles, due to the demand of high precision and delicate movements. It has been shown that this can be achieved by minimizing the change of acceleration and using s-curve profiles. Moreover, to provide a good control of the movement of a robot, it is necessary to ensure that it will meet the desired velocity profile. Therefore, a way to prevent how the wheels will react on the soil becomes highly useful, in order to adapt the supplied torque. This thesis suggests a model to define an appropriate s-curve velocity profile given the desired starting and ending kinematic states for a mobile robot. The study is then focused on a one-wheel system to define the interaction between the soil and a wheel. This interaction is modelled and extended in order to calculate the required torque, drawbar pull and power needed to fulfil the desired s-curve velocity profile. Finally, an introduction to unicycle robots is given as an example of how the proposed models could be applied in the motion planning of a mobile robot. Key words: terramechanics, s-curve, jerk, velocity profileOutgoin

DEVELOPMENT OF A FINITE ELEMENT MODEL TO PREDICT THE BEHAVIOR OF A PROTOTYPE WHEEL ON LUNAR SOIL

The All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) is a mobile lunar lander under development by the National Aeronautics and Space Administration\u27s Lunar Architecture Team. While previous lunar missions have lasted only a few days, the ATHLETE is designed to last for 10 years, which will enable a sustained U.S. presence on the moon and exploration of the more treacherous regions which are not suitable for landing. Because the ATHLETE will carry entire astronaut habitats, its six wheels must be carefully designed to support a large load on soft lunar soil efficiently. The purpose of this thesis is to develop a finite element model that will allow designers to examine how the tractive performance of the lunar wheel is affected by changes in the wheel geometry through numerical analysis. It has been shown in the literature that a wheel rolling on soil is not suited to a plane strain analysis. Two different three-dimensional deformable wheel models are explored, a single-part shell model and a multi-part solid-shell model. For the purposes of this research, the shell model offers sufficient detail with less computational expense. The key to obtaining a smooth pressure distribution is in careful selection of the contact stiffness. For the soil model, a set of parameters to represent a pressure-dependent elasto-plastic cap hardening lunar soil was assembled. Two different methods of selecting an appropriate soil bed size are compared. A holistic method that determines all dimensions at once was found to be quick and reliable. Finally, the wheel and soil models were integrated into one finite element model in the commercial code, AbaqusTM, and three small studies were conducted to demonstrate the utility of the model in predicting changes in traction dues to change in wheel design and operation. For example, the model can help determine how quickly the wheel can accelerate without significant slippage. The model can also inform design decisions. The pilot tests suggested that softening the cylinders and/or the spokes could improve traction, but softening the cylinders too much can lead to structural failure

A Volumetric Contact Model for Planetary Rover Wheel/Soil Interaction

The main objective of this research is the development of a volumetric wheel-soil ground contact model that is suitable for mobile robotics applications with a focus on efficient simulations of planetary rover wheels operating on compliant and irregular terrains. To model the interaction between a rover wheel and soft soil for use in multibody dynamic simualtions, the terrain material is commonly represented by a soil continuum that deforms substantially when in contact with the locomotion system of the rover. Due to this extensive deformation and the large size of the contact patch, a distributed representation of the contact forces is necessary. This requires time-consuming integration processes to solve for the contact forces and moments during simulation. In this work, a novel approach is used to represent these contact reactions based on the properties of the hypervolume of penetration, which is defined by the intersection of the wheel and the terrain. This approach is based on a foundation of springs for which the normal contact force can be calculated by integrating the spring deflections over the contact patch. In the case of an elastic foundation, this integration results in a linear relationship between the normal force and the penetration volume, with the foundation stiffness as the proportionality factor. However, due to the highly nonlinear material properties of the soft terrain, a hyperelastic foundation has to be considered and the normal contact force becomes proportional to a volume with a fractional dimension --- a hypervolume. The continuous soil models commonly used in terramechanics simulations can be used in the derivation of the hypervolumetric contact forces. The result is a closed-form solution for the contact forces between a planetary rover wheel and the soft soil, where all the information provided by a distributed load is stored in the hypervolume of interpenetration. The proposed approach is applied to simulations of rigid and flexible planetary rover wheels. In both cases, the plastic behaviour of the terrain material is the main source of energy loss during the operation of planetary rovers. For the rigid wheel model, a penetration geometry is proposed to capture the nonlinear dissipative properties of the soil. The centroid of the hypervolume based on this geometry then allows for the calculation of the contact normal that defines the compaction resistance of the soil. For the flexible wheel model, the deformed state of the tire has to be determined before applying the hypervolumetric contact model. The tire deformation is represented by a distributed parameter model based on the Euler-Bernoulli beam equations. There are several geometric and soil parameters that are required to fully define the normal contact force. While the geometric parameters can be measured, the soil parameters have to be obtained experimentally. The results of a drawbar pull experiment with the Juno rover from the Canadian Space Agency were used to identify the soil parameters. These parameters were then used in a forward dynamics simulation of the rover on an irregular 3-dimensional terrain. Comparison of the simulation results with the experimental data validated the planetary rover wheel model developed in this work

Advanced Testing and Characterization of Bituminous Materials, Two Volume Set

Bituminous materials are used to build durable roads that sustain diverse environmental conditions. However, due to their complexity and a global shortage of these materials, their design and technical development present several challenges. Advanced Testing and Characterisation of Bituminous Materials focuses on fundamental and performance testin

Agricultural Structures and Mechanization

In our globalized world, the need to produce quality and safe food has increased exponentially in recent decades to meet the growing demands of the world population. This expectation is being met by acting at multiple levels, but mainly through the introduction of new technologies in the agricultural and agri-food sectors. In this context, agricultural, livestock, agro-industrial buildings, and agrarian infrastructure are being built on the basis of a sophisticated design that integrates environmental, landscape, and occupational safety, new construction materials, new facilities, and mechanization with state-of-the-art automatic systems, using calculation models and computer programs. It is necessary to promote research and dissemination of results in the field of mechanization and agricultural structures, specifically with regard to farm building and rural landscape, land and water use and environment, power and machinery, information systems and precision farming, processing and post-harvest technology and logistics, energy and non-food production technology, systems engineering and management, and fruit and vegetable cultivation systems. This Special Issue focuses on the role that mechanization and agricultural structures play in the production of high-quality food and continuously over time. For this reason, it publishes highly interdisciplinary quality studies from disparate research fields including agriculture, engineering design, calculation and modeling, landscaping, environmentalism, and even ergonomics and occupational risk prevention

Advanced Testing and Characterization of Bituminous Materials, Two Volume Set

Bituminous materials are used to build durable roads that sustain diverse environmental conditions. However, due to their complexity and a global shortage of these materials, their design and technical development present several challenges. Advanced Testing and Characterisation of Bituminous Materials focuses on fundamental and performance testin

Desarrollo de un robot móvil con inteligencia artificial para recolectar botellas de plástico

La robótica en la actualidad busca incrementar los lazos entre robots y seres humanos, de forma que realizar las tareas en conjunto sea más amigable y no se requiera de un extenso periodo de adaptación. Ello, en ocasiones se ve perjudicado por la operación manual constante que requiere un robot debido a que un individuo emplea su tiempo para manipular el robot y no se genera la independencia anhelada en este campo. Por lo descrito, surge como alternativa de solución los robots autónomos que emplean visión artificial y algoritmos de Inteligencia Artificial (IA) para el cumplimiento de tareas. Este trabajo de tesis, se centra en el diseño y desarrollo de un robot móvil utilizando visión artificial para identificar botellas de plástico en las playas del litoral limeño. Se emplea una RCNN para el procesamiento de imágenes y esta red es entrenada por imágenes de autoría propia, las cuales se realizaron en las playas mencionadas, hasta obtener un óptimo reconocimiento de las botellas y las personas. Asimismo, se generaron propuestas de diseño de los dominios mecánico, electrónico y de control, de tal forma que el proyecto resultante abarque de forma integral el funcionamiento esperado. Se realizaron pruebas de simulación al sistema de control y visión artificial y se obtuvo que, efectivamente consta de una alternativa de solución robusta, pues reconoce las botellas de plástico y se acerca hacia ellas, esquivando obstáculos y consiguiendo su objetivo. Se realizaron simulaciones donde se obtuvieron parámetros que confirman lo designado en el diseño. Esta tesis, también tiene un impacto significativo en el medio ambiente, pues se trata de un robot eco amigable que trabaja para el beneficio de las playas, de tal forma que se inspiren futuros trabajos de investigación que tengan por consigna impulsar la sostenibilidad

Space Exploration Robotic Systems ¿ Sample Chain Analysis and Development for Enceladus Surface Acquisition

L'abstract è presente nell'allegato / the abstract is in the attachmen