OBTAINING OPTIMAL CONTROL PARAMETERS-ACCELERATION BASED WHEEL TRACTION CONTROL

This project deals with a detailed dynamic model of a two independent wheel drives and a traction control system. By applying external force it is possible to have a path plan in each wheel drive that enables the implementation of a traction control algorithm. This control level improves the stability and the safety of the vehicle. Analysis, design and simulation results of this system will be presented. The wheel traction control method for path tracking of the two independent wheel drives is the function of velocity and acceleration of the mobile robots. The traction control algorithm which can be independently implemented to each wheel without extra sensors and devices compared with standard speed control. Simulations are performed to verify the validity of the algorithm. The proposed traction control algorithm to improve the tracking control efficiency. This project work aims to analyze the fixed acceleration path for two independent wheel drives system by using analyzing software (Adams 12.0) and also this project work is mainly focused on the increase stability and the safety of the two independent wheel drives by planning the fixed acceleration path

Trajectory tracking and traction coordinating controller design for lunar rover based on dynamics and kinematics analysis

Trajectory tracking control is a necessary part for autonomous navigation of planetary rover and traction coordinating control can reduce the forces consumption during navigation. As a result, a trajectory tracking and traction coordinating controller for wheeled lunar rover with Rocker Bogie is proposed in the paper. Firstly, the longitudinal dynamics model and the kinematics model of six-wheeled rover are established. Secondly, the traction coordinating control algorithm is studied based on sliding mode theory with improved exponential approach law. Thirdly, based on kinematics analysis and traction system identification, the trajectory tracking controller is designed using optimal theory. Then, co-simulations between ADAMS and MATLAB/Simulink are carried out to validate the proposed algorithm, and the simulation results have confirmed the effectiveness of path tracking and traction mobility improving

Coordinated Control of Slip Ratio for Wheeled Mobile Robots Climbing Loose Sloped Terrain

A challenging problem faced by wheeled mobile robots (WMRs) such as planetary rovers traversing loose sloped terrain is the inevitable longitudinal slip suffered by the wheels, which often leads to their deviation from the predetermined trajectory, reduced drive efficiency, and possible failures. This study investigates this problem using terramechanics analysis of the wheel-soil interaction. First, a slope-based wheel-soil interaction terramechanics model is built, and an online slip coordinated algorithm is designed based on the goal of optimal drive efficiency. An equation of state is established using the coordinated slip as the desired input and the actual slip as a state variable. To improve the robustness and adaptability of the control system, an adaptive neural network is designed. Analytical results and those of a simulation using Vortex demonstrate the significantly improved mobile performance of the WMR using the proposed control system

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

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

A Mars-back approach to lunar surface operations

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005."The code for the Activities Model and the Habitat Model can be found on the CD accompanying this thesis"--Appendix C, p. 113.Includes bibliographical references (p. 104-116).The Vision for Space Exploration initiated a new space exploration program and called for a long term national commitment to space exploration starting with a return to the Moon and continuing with the exploration of Mars and beyond. The development and operation of the new space exploration system needs to occur within the confines of NASA's current funding. This funding restriction prevents the development of separate space exploration systems for both the Moon and Mars. Therefore, in order to explore both locations, it is necessary to adopt a "Mars-back" approach to lunar exploration, wherein a Martian system is designed and then applied to the Moon. The lunar missions will not require the entire suite of hardware that will be needed on Mars. This thesis describes the reasoning behind using a Mars-back approach and its application to surface operations, using a baseline surface architecture consisting of 5 crew staying on the surface of Mars for 600 days. The surface mobility system will consist of 5 all-terrain vehicles and two towable pressurized volumes, termed campers. The power and habitation requirements are discussed. The Martian surface architecture is then applied to the Moon, where the performance of the same equipment on the lunar surface is evaluated. A campaign of lunar missions is designed to take advantage of the staged development of equipment for the exploration system. While the entire suite of equipment will be needed on Mars, the lunar missions can accomplish useful work and perform real exploration using only a subset of the equipment, such as only the mobility equipment and not the habitat. The main goal of the lunar missions is to prepare for Martian exploration.(cont.) The progress of the lunar missions towards accomplishing this goal is measured using the Mars Exploration Readiness Level (MERL).by Howard Neil Kleinwaks.S.M

Reconfigurability in space systems : architecting framework and case studies

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006.Includes bibliographical references (p. 247-257).Reconfigurability in engineered systems is of increasing interest particularly in Aerospace Systems since it allows for resource efficiency, evolvability, and enhanced survivability. Although it is often regarded as a desirable quality for a system, it has traditionally been difficult to quantitatively analyze its effects on various system properties in the early design stage. In order to allow for gaining an in-depth understanding of the various aspects of reconfigurability and its relationship with a system's architecture, a framework encompassing a set of definitions, metrics, and methods has been proposed. Two different modeling schemes, based on Markov models and controls theory, are first developed to show how the states and time aspects of reconfigurable systems can be naturally modeled and studied. An analytical model for quantifying the effect of reconfigurability on mission logistics, specifically spare parts demands, is formulated and it is shown through one specific example that reconfigurable parts can allow for 33-50% mass reduction. The system availability, however, becomes very sensitive to the reliability of the parts. Two case studies are then used for detailed illustration of the application of the developed framework.(cont.) In the first case study, the effect of reconfigurability on a fleet of planetary surface vehicles for a surface exploration mission are analyzed. It is found that a fleet of reconfigurable vehicles can allow for a mass savings of up to 27% and their expected transport capability degradation is almost three times lower as compared to a fleet of non-reconfigurable vehicles. In the second case-study, the reconfiguration of low earth-orbit communication satellite constellations is considered for evolving to higher capacity levels. It is found that reconfiguring a previously deployed constellation can be a viable option only for certain capacity levels and multi-payload launch capability scenarios. In addition to the high level 'ility' perspectives, a lower level design assessment is also carried out through a survey of 33 representative reconfigurable systems. It is found that on average, for commercial items the cost of reconfigurability is 35%, and the average useful state occupancy time is always at least 10 times the reconfiguration time of the system. Based on the illustrative results of the case studies, and generalization of empirical data, a few principles and guidelines for design for reconfigurability are proposed.by Afreen Siddiqi.Ph.D