【作者】 马志艳；

【导师】 陈幼平； 周祖德；

【作者基本信息】 华中科技大学 ， 机械电子工程， 2007， 博士

【摘要】 以虚拟现实为主要技术基础的虚拟数控加工系统是实现加工过程仿真并进行产品可加工性评估的有效手段,但是其实现的结果却是将用户与真实加工场景进行了完全隔离,用户完全处于一个由计算机生成的虚拟世界中。利用增强现实技术实现的数控加工仿真是解决这一问题的有效途径。本文从增强现实技术和数控加工仿真技术两方面着手,主要在加工仿真虚拟场景的三维实时注册、虚拟场景的快速生成、合成场景的显示与交互以及整体计算策略等方面展开研究。首先,在分析虚拟数控技术和增强现实技术的基础上,提出了通过增强现实实现数控加工仿真的技术方案,进一步提出了面向数控加工仿真的增强现实系统的体系结构。在利用增强现实技术将数控加工仿真场景与真实加工场景进行融合时,系统对三维注册算法和数控加工仿真场景的生成提出了更高的要求。本文针对真实加工场景的特点,提出一种基于实体特征的实时三维注册方法。为解决真实场景中的目标与3D模型之间的点配对问题,提出了借助于训练图像实现匹配点对替换的方法来快速计算加工仿真虚拟场景的投影变换矩阵,从而实现虚实场景之间的实时配准。其次,针对不同的加工条件,在均匀三角片分裂法的基础上提出了两种数控加工仿真算法。如果加工目标模型已知且加工面形状较为简单,可采用自下而上的非均匀三角片分裂法;如果加工目标形状未知或加工面较为复杂,可采用自上而下的自适应三角片分裂法。这两种方法的原理都是利用局部加大网格划分密度来保证加工的精度,在提高仿真显示质量的同时,也较大限度地减少了仿真计算负担,并且从机理上保证了虚拟加工系统实时几何变换的实现。另外,研究了虚拟场景和真实场景之间的光照一致性实现技术,并实现了用户与系统的交互问题。通过在OpenGL环境中交互设置虚拟光源的方式来模拟真实加工车间中的环境光、日光灯和机床的聚光灯光照效果,实现真实感场景的输出;人机交互方面以用户与虚拟场景的交互为研究的重点,实现了对虚拟对象或控制按钮的选择,从而完成在虚实合成场景中对虚拟加工系统的初始设置和运行过程控制。针对系统中各主体计算模块的沉重计算负担给合成场景的实时动态显示和恒定帧频率输出带来了严重障碍,从模块内部计算优化和整体计算均衡的角度提出了一系列的策略,如运动图像分析、预计算技术、层次细节渲染控制等,从而实现虚实合成场景的稳定显示输出。最后,应用本文研究成果,实现了面向数控加工仿真的增强现实系统的原型系统。以真实加工环境中机床夹具为参考目标,实现了以工件和刀具为组成的虚拟数控3轴铣削加工场景在真实加工环境中实时注册并进行加工仿真的实例。更多还原

【Abstract】 It is an effective way to perform the NC machining simulation and evaluate the machinability of product by using Virtual NC system (VNC) which based on Virtual Reality (VR). However the result of that separates users from the real machining environments. Users are immersed in the virtual world. Using the technology of NC machining simulation that based on Augmented Reality (AR) can solve the problem effectively. Starting with the theories of augmented reality and NC machining simulation, this paper discusses the 3D real-time registration and rapid generating of virtual machining scenes, and on the other hand, the display and interactive operations of synthetic scenes and system computational strategies are also studied.Firstly, the technology scheme and architecture of augmented reality system for NC machining simulation are presented on the basis of analyzing the virtual NC and augmented reality. When the NC machining simulation scenes are merged into the real machining environment by augmented reality, the system puts forward a more strict condition for the 3D registration and virtual machining scene generating. Against the characteristics of real machining environment, a new method for real-time 3D registration based on markerless image is proposed. To obtain the correspondence point pairs between the target in real scene and its 3D model, a new method is put forward that rapidly calculate the projection matrix of virtual machining scene by replacing the correspondence point pairs with the help of training image.Secondly, on the basis of the method of uniform triangulation, another two methods of NC machining simulation are proposed. If the machining target is known and its finished surface is simple, the method of down-top non-uniform triangulation is more efficient. If the machining target is unknown or the mathematic representation of the finished surface is complex, the method of top-down adaptive triangulation is attractive. Both the methods are quite similar in principle as ensuring the machining precision by increasing the local density of triangulation. In the premise of improving the quality of simulation display, the algorithms have a good performance in reducing the computation burden, and guarantee the implementation of geometrical transformation of virtual machining scenes in principle.Furthermore, the implementation of illumination consistency between the real environment and the virtual scenes is researched. The system implements the output of the realistic scenes in OpenGL by interactively installing virtual light source to simulate the illumination effect in the real workshop, such as ambient illumination, lamp and spotlight on the machine. In interactive system, the paper puts much emphasis on the interaction between the user and the virtual scene. It provides some functions such as the selection of virtual object or command button to implement the initial settings and the operational control of the virtual machining system in the synthetic scenes.Because the heavy computational burden of each subsystem brings severe obstacle to the real-time dynamic display and the constant output of synthetic scene, some computing strategies are proposed to optimize those subsystem and balance global computation, such as the analysis of image motion, pre-calculate, LOD rendering control. Through those ways, the implementation of the real-time dynamic display and the constant frame rate output of synthetic scene is accessible.Finally, a prototype of augmented reality system for NC machining simulation is investigated and developed by use of the above theories and technologies. Taking a clamp in the real environment as the reference target, the instance implements 3D registration and machining simulation of the virtual NC 3-axis milling system that composed of workpiece and cutter in real environment.更多还原