【作者】 杨艳春；

【导师】 金烨；

【作者基本信息】 上海交通大学 ， 机械制造及自动化， 2009， 博士

【摘要】 月球车是月球探测工程的重要组成部分,也是实现月球探测目标不可缺少的重要媒介。月球车是用于复杂地形探测的移动机器人,它的研制涉及到多个学科领域,它是人工智能、自动控制、机构学、信息技术及计算机技术等高新技术的结晶。作为一个复杂的系统,月球车软硬件的研究、开发和验证都需要大量的试验,这是一个高时耗并且高成本的过程。借助仿真技术无疑是一种降低成本,提高效率的方式。在建造物理样机之前,研究人员利用软件技术建立机械系统计算机实体模型,进行仿真分析并以图形显示该系统在真实工况下的运动特性,从而修改并优化设计方案。但是传统虚拟样机分析软件在考虑环境对样机的影响方面做得不够,而月球车的工作环境是非常特殊的,并且环境是影响月球车运动性能的一个主要因素,所以需要一个融合月面环境的仿真工具来满足需求。近年来,随着计算机技术的发展,虚拟现实技术的不断成熟,仿真技术有了更有效的手段。本文基于与上海宇航系统工程研究所合作的“嫦娥工程”月球车预研项目《月面可视化建模》、《月球车月面巡视视景仿真》为研究背景,对在虚拟现实环境下开发月球车仿真试验系统RSVE进行了深入的研究。同时,得到了上海市科学技术委员会的支持(课题号:08DZ1110303)。在详细分析了月球车仿真试验系统RSVE的总体构架、模块构成以及模块与模块之间关系的基础上,重点介绍了系统中的几何建模模块、动力学模块和可视化模块的功能及其设计,从而聚焦到本文的关键技术:真实感虚拟月面生成技术,月球车动力学建模与求解技术,虚拟现实环境下的系统集成与实现技术。首先,针对月球车仿真过程月面环境建模的准确性问题,为了实现月球车仿真环境的真实性,在分析月球表面特征地形的基础上,提出了一种真实感虚拟月面的建模方法。该方法基于分形算法生成月面基础地形;根据前人对月面陨石坑的统计和计算的经验,得出了陨石坑近似建模的原理和方法;将二维分形算法扩展到三维生成分形石块,根据统计信息,确定陨石坑和石块的分布情况;同时将陨石坑、石块与基础月面地形合理地叠加在一起,其中陨石坑的添加基于对陨石坑形成的两点假设处理新、老陨石坑之间关系、陨石坑与基础地形之间的关系;最后通过添加光照、设置材质属性、纹理映射和阴影处理生成用于月球车运动仿真、动力学计算等多种用途的真实感数字月面。该方法符合实际统计规律,也符合陨石坑形成过程的物理规律,可以在虚拟现实环境下生成真实感和沉浸感较好的数字月面模型。调整各个参数可以生成各式各样的月面数字模型,为月球车提供了一个相当方便和理想的试验场所。其次,要保真地仿真月球车在月面上的运行就需要一个准确的月球车动力学模型,并能给出求解的方法。月球车行驶在凹凸不平的松软月面之上,考虑到月面几何结构和物理属性对于月球车的运行性能是有至关重要影响作用的,所以要建立一个融合月面环境的月球车动力学模型,这就需要在建立月球车运动学、动力学方程时考虑月球车车轮与月面之间的作用关系,这为月球车动力学模型的建立和求解带来了极大的难度。文章在研究了多刚体运动学、动力学基础上,分析了月球车物理模型的特点,采用基于约束的多体动力学方法对月球车进行动力学建模,并详细介绍了月球车的约束建模。考虑到月球车车轮与地面之间的非完全约束关系,将月球车动力学模型看作是一个线形互补问题(Linear Complementary Problem简称LCP)。然后在研究了车轮与地面作用力关系的基础上,将车轮-地面作用力模型集成到月球车LCP方程。由于模型的复杂性,导致了求解的难度,本文基于时间步长方法对月球车LCP方程进行了处理,并利用PGS和Lemke算法对月球车LCP方程进行了求解。为了验证动力学求解的准确性,利用Matlab+ASSTM就几个特殊工况进行了月球车动力学仿真,通过对比两者的仿真结果来验证RSVE仿真系统所采用的月球车动力学模型的正确性。并进行了真实试验来验证月球车动力学模型的正确性。第三,基于虚拟现实环境开发月球车仿真试验系统RSVE。月球车仿真试验系统是一个复杂系统,为了节省开发成本和开发效率,不同的模块采用了一些不同的工具集,包括可视化模块基于OpenGL Performer进行开发,几何模型的生成基于Open Flight数据格式。在研究了这些工具集兼容性问题的基础上开发了仿真系统RSVE。为了增强仿真过程中的可视化效果,还研究了由软质月面引起的车轮卷起沙土、车轮沉陷及车辙等特效的实现方法,并结合SGI图形工作站的硬件条件实现了立体显示,增强了仿真平台仿真过程中的沉浸感。最后,上海宇航系统工程研究所研发的MR-2和MR-3月球试验车在RSVE系统中进行了仿真。从应用角度展示了仿真试验系统的有效性和可扩展性。论文对在虚拟现实环境下开发月球车仿真试验系统的关键技术:真实感虚拟月面生成技术,月球车动力学建模与求解技术,虚拟现实环境下的系统集成与实现技术进行了深入研究。并将它们成功应用到了月球车仿真试验系统中,实现了月球车仿真的真实感与沉浸感,为月球车软、硬件的研发和验证提供了系统层面的仿真工具。更多还原

【Abstract】 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.更多还原