| Lunar rover is an important part in lunar investigation project, and it is also an essential tool to realize the lunar investigation objective. Lunar rover evolves on natural and challenging terrain to finish complex missions. To develop a lunar rover involves many scientific branch, including AI, automatically controlling, mechanism, information technology and computer technology. As a complicated system, the development of the hardware and software on lunar rover involves a large amount of validation works in realistic operational conditions, including its mechanical subsystem and on-board software. Real tests require equipped rover platform and a realistic terrain. It is very time consuming and high cost. Obviously, using the simulation technology is a good way to lower the cost and improve the designing efficiency. Before manufacturing a physical model, designer can use software to construct a virtual model on computer, and simulate the real working condition of lunar rover in order to test and maturate the rover technology. But the traditional software is not enough to simulate the virtual machine interact with its environment. Since Lunar rover works on a very special environment and the environment plays critical role to rover's locomotive performance, so another tool which allowing for lunar environment is needed. With the development of computer technology and the emergency of Virtual Reality technology, simulating becomes a more powerful tool for designing. This dissertation based on the project named"Virtual lunar surface modeling"and"The simulation of lunar rover evolving on lunar surface"under contract with the Aerospace System Engineering, Shanghai, focused on the development of the virtual simulating environment for lunar rover called RSVE. And it is also supported by Science and Technology Commission of Shanghai Municipality, PRC's project (08DZ1110303).After the framework and components of RSVE is described in detail, the function and designing of the geometry modeling module, the dynamic module and the visualization module is introduced. Then we focused on the key technologies of this dissertation include: realistic virtual lunar surface constructing technology, lunar rover dynamic modeling and solving technology, module integrating technology in the VR environment.Firstly, in order to ensure that lunar rover can be simulated in a high fidelity environment, a realistic lunar surface simulation method is proposed. It uses the fractal technology to form the base of lunar terrain, gets lunar crater modeling method according to former researcher's statistic information and calculating result, creates fractal stone through extending the fractal approach from 2D to 3D, adds lunar craters and stones to the terrain according to the real statistic information. Especially, the relationship between new crater and old crater, the relationship between crater and the terrain are dealt based on two hypotheses. At last, the realistic virtual lunar surface is created through setting lighting, material attribute, texture and shadow. The proposed method above satisfied the real statistic information, satisfied the physical law, it can create virtual lunar surface with high fidelity. Adjusting the parameters, different virtual lunar surface can be created to provide convenient and ideal testing environment for lunar rover.Secondly, as a high fidelity simulation, a whole rover dynamic model is needed. So kinematic and dynamic modeling of lunar rover on uneven terrain is studied, how to solving these dynamic formulations is also studied. Allowing for that the geometry shape and physical attribute of lunar surface are the main factor influencing the lunar rover's traversability, accurate contact dynamics model between rover and terrain is essential. Generally the equations of motion of rovers are very complicated. This complication arises from three factors: complicated mechanism, uneven terrain they are moving on and non-holonomic constraints. Base on analyzing the physical model of lunar rover, constraints dynamic is used to create the dynamic model of lunar rover. Introduce the constraint modeling of lunar rover in detail, and formulate the lunar rover dynamics as a linear complementary problem (LCP). Due to the friction between rover's wheels and the terrain, the formulations have problem to find a solution, so we solve the formulations based on time steps method and Projected Gauss-Seidel algorithm. In order to validate the dynamic model, Matlab and ASSTM are used to the same simulation under several specific working conditions. The dynamic model proposed in this dissertation is validated by compared the simulation results from two different system. And it also validated by real test.Thirdly, RSVE is a complicated system, in order to save the developing cost and efficiency, different tools/API are used in different module. For example, OpenGL performer is used to develop the visualization module, Open Flight is used to create the geometry model. RSVE is developed based on the researching work about the compatibility of different tool/API. To improve the visualization effect, soil brought by wheels, wheel sinkage and wheel track are simulated. Stereo viewing is realized base on the SGI graphic working station, which increases reality and immersion during the simulating process.At last, MR-2 and MR-3 rover prototypes from aerospace engineering, Shanghai are tested in RSVE. The system also has left interface for future extension.The dissertation presented a detailed study of the key technologies which used to develop RSVE, including realistic virtual lunar surface constructing technology, lunar rover dynamic modeling and solving technology, module integrating technology in the VR environment, which bring the reality and immersion to the bicycle simulator system.
|
PDF Full Text Request