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Modeling Simulation and Experimental Research on Six-wheeled Rocker Lunar Rover

Author: MaoNing
Tutor: CaoGuoHua
School: Changchun University of Science and Technology
Course: Mechanical and Electronic Engineering
Keywords: Six-wheeled rocker lunar rover kinematic model wheel-soil model slip rate low gravity lunar soil simulation virtual simulation system
CLC: V476.3
Type: PhD thesis
Year: 2014
Downloads: 13
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Abstract

Lunar rover is an important carrier to detect lunar by carrying a variety of instruments. It’s direct-detecting tool by lunar landing. We must improve the trafficability of lunar rover and ensure the stability and reliability of the system by building virtual environment to improve the machine and control system. In this paper, the prototype of six-wheeled rocker rover multi-body kinematics model, dynamic model and control model under unstructured environment were studied, and the rover moving characteristics and wheel-soil impact were simulated, and the virtual lunar surface environment of six-wheeled rocker lunar rover simulation system was built, which provide the verification platform for predicting design, performance test and prototype preview.Firstly, the kinematic equations of six-wheeled rocker lunar rover were deduced in accordance with the engineering prototype of the definition of the motor polarity in this paper. In kinematics modeling analysis, this paper fully considered the influences on the mobile systems from the sliding, rolling slippage and steering wheel slip. And all of these are helpful for providing analytical foundation for wheel-soil dynamics. Two methods were put forward which can solve efficiently the inverse kinematics analytical solution in this paper. On this basis, the simulation test was carried out on the rover configuration, and the configuration possesses strong adaptability to the ground and high capacity. And the solving method is simple, small amount of calculate, high precision. It is verified by simulation, and the steering angle error is below0.4%, and the drive wheel speed accuracy is at2.5%, which can meet the needs of controller design, and provide the theoretical basis for analysis of terramechanics, dynamics and statics.To improve the efficiency of the rover trafficability and drive efficiency, the relationship of wheel-soil mechanics must be analyzed. With deep analysis of Beeker and Reece model, and based on the wheel teeth effect and static and dynamic sinkage, the rigid wheel-soil dynamics model was established. For experimental verification, low gravity simulated lunar soil and the light-small rigid mesh wheel and low-gravity test device were designed, and then the wheel-soil dynamics model was amended by the simulation comparing with experiment, and the overall error is3%. This will lay the foundation of dynamics modeling, statics modeling, controller design and virtual environment simulation system building. Power coefficient and drive efficiency were analyzed through the test data, which can be found that drive efficiency is the highest when slip rate is0.2. Accordingly, the optimal control area of the slip rate control model is obtained.Based on kinematics and wheel-soil dynamics model, the statics model of lunar rover was derived. Under the condition of optimal energy consumption, simulation analysis is proceeding for the climb over complex terrain. The optimal traction and the slip rate were got which can be used for evaluating the rover motion performance and designing slip rate control system. In the process of rover dynamics modeling, with space position, each joint angle and the six dimensional forces as generalized coordinates. Newton-Euler recursive equation was deduced. This method has the characteristics of modular modeling, which is facilitate for other payload dynamic modeling on this rover. Finally, virtual environment of six-wheeled rocker rover dynamics simulation system were realized, the effect is good, which provides a good test platform for the simulation of control system and trafficability of six-wheeled rocker lunar rover.In the end, the control model was studied based on the kinetic model and dynamic model of six-wheeled rocker lunar rover. For parameters uncertain nonlinear system of dynamic model, slip rate control model based on sliding mode variable structure was established. It has strong robust performance, and can effectively improve the traction performance of mobile system. The traction control model based on wheel slip model was put forward based on the kinematic model of six-wheeled rocker rover, and can be solved by the linear quadratic optimal control method. On this basis, a variety of complex topography simulation test has been carried on, and each wheel slip rate can be efficiently controlled. The ability of climbing, cross obstacle and ravines have been strengthened effectively. And the model is suitable for engineering application.In conclusion, the research can provide engineering support for structure optimization, controller design and quasi real-time/high fidelity virtual simulation theory and experiment foundation of six-wheeled rocker lunar rover.

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