【作者】 郎跃东；

【导师】 姚英学；

【作者基本信息】 哈尔滨工业大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 虚拟装配是虚拟现实技术在工业领域的重要应用之一,为解决复杂产品的装配工艺设计问题提供了经济有效的解决途径。虚拟装配的沉浸性能直接影响其实际应用效果。然而,传统虚拟装配系统的沉浸感不足,难以反映实际装配过程中的问题。随着科学技术的发展,人们开发出具有高度沉浸式虚拟装配环境,但是由于系统的构建耗资巨大,且多种关键技术尚不完善,无法满足装配设计的实际需求。因此,迫切需要引入新的方法和手段,建立具有高度沉浸感的、低成本的虚拟装配环境系统,以获得具有实际指导意义的装配方案。本文建立了一个新型的具有高度沉浸感的虚拟装配系统,设计了系统的总体硬件结构,并对相关功能模块的关键技术进行研究。该系统通过多个投影机和所研制的大型球面屏幕组成的投影系统为操作者提供360°全景展示画面,具有高度的沉浸感和广阔的操作空间,能够满足产品虚拟装配设计的要求。研制出一种低成本的立体图像分配器,通过基于低端硬件的立体投影显示系统,实现了球面屏幕的立体投影显示。在该系统中,首先建立立体像对生成的数学模型,并采用Off-axis算法实现立体场景源图像的获取,经过立体图像分配器的处理后生成满足投影显示的立体视对图像,以增强虚拟装配系统的沉浸感。针对平面图像投影到球面屏幕上发生变形的情况,提出了一种非线性几何拼接校正方法。该方法建立球面投影的数学模型,求解投影机在球幕上的最大显示区域,并利用相机获取最大区域内的标准网格图案,确定投影机与显示屏幕之间的几何关系,由双向曲线法逆运算求解双三次NURBS曲面的控制点阵,初步获得满足多投影显示的几何校正图像,再通过NURBS曲面的局部可修改特性进行图像重叠部分的拼接校正,实现了高精度、无缝的球面多投影显示。在分析球面屏幕多投影显示图像之间颜色差异原因的基础上,提出了一种适用于球面多投影显示的全局颜色校正方法。该方法采用基于相机的HDR图像处理技术重建所有投影机显示图像的亮度响应值,并针对球面背投显示模式的特点,从人对颜色视觉感知的角度出发,进行三个方面的全局颜色校正处理,包括全局的亮度均匀化、边缘亮度融合和色彩度的公共ITF匹配,实现了在视觉感知上统一的球面多投影显示效果。研究了球面投影图像的场景显示技术,在并行绘制环境下建立球面图像分割模型,根据球面多投影空间的实际布局情况,设计出满足球面多投影拼接显示的分割方案,通过球面投影图像的区域划分设计,使得经过几何拼接校正后的显示图像具有良好的连续性。基于sort-first并行绘制系统实现场景的并行渲染,并实现系统视觉显示各功能模块的集成处理,考虑到三维交互操作和场景漫游的同步显示要求,采用有效的同步控制技术实现场景动态显示的逻辑统一。最后开发了卫星虚拟装配系统,将本文所研究的关键技术用于系统的场景显示中,通过实际的投影验证了所提出理论方法的合理性和有效性。实验结果表明所建立的球面虚拟装配系统具有高度的沉浸性能,可用于产品的虚拟装配设计。更多还原

【Abstract】 Virtual assembly(VA), as one of the important applications for virtual reality(VR) applied in industrial area, provides an economical way to solve the issues of product assembly process design. Immersive performance of VA influences the effectiveness of its application directly. However, traditional VA system does not provide enough high degree of immersion, and the assembly operations of designer’s simulation lack sense of reality, thus it is difficult to predict problem that occurs during actual assembly process. With gradual improvement of technology, immersive VA environment is developed, but constructing such a system incurs substantial expenditures, and several key technologies are still not perfect to meet the actual needs of assembly design. Therefore, it is urgent to construct a low-cost, high-immersive VA system by introducing new mehods and means, to obtain a simulation result with pratical guidance.In this thesis, a new highly immersive VA system was constructed, the whole hardware architecture of the system was designed, and various functional modules were developed and integrated in the system. The system could provide 360°panoramic display for the operator through a projection system consisting of projectors and a large spherical screen developed independently. Simutaniously, it had a high degree of immersion and broad operation space that could meet the requirements of VA product design.A low-cost 3D image distributor was developed, and a method based on ordinary hardware was used to achieve 3D projection display that could meet the spherical screen. In the system, a 3D image generation model was established firstly, and Off-axis algorithm was applied to acquire 3D scene source images, then the distributor deal with that images information to create 3D images for projection display, therefore it can enhance the immersive effect of VA system.As a planar image deformed when projected on the irregular spherical screen, a correction method based on NURBS surface model was proposed for nonlinear geometric mosaic, a camera was used to obtain standard grid pattern on the screen, then the geometric relationship between projector and display screen was seted up, and control points of bicubic NURBS surface lattice were calculated by a two-directional curves inversed solving method. A geometric correction image was obtained initially so that met the multi-projection display, and local modify characteristics of NURBS surface was used to perform mosaic correction of overlapped images. Therefore, it can realize high precision, seamless spherical multi-projection display.Based on analysing color difference between images, a global sphere color correction method that considers color visual perception of humankinds was proposed for spherical screen multi-projection display. HDR image processing technique with a camera was applied to modify brightness response value of display images for all of the projectors. According to characteristics of spherical rear projection display mode, there were three aspects of the global color correction as following, including the overall brightness uniformity, edge brightness blending and color common ITF match, to achieve visual perception unification on the spherical multi-projection display.Scene dynamic display technology was studied for spherical projection real-time display. Spherical segmentation model was established under a parallel rendering environment. According to the actual layout of pherical multi-projection space, spherical partition scheme was designed to fulfill multi-projector display. Through region division design of spherical projection image, it made the display images well continuity after geometric mosaic correction. A sort-first parallel rendering system is used in VA system to achieve parallel scenes rendering, and realize visual display of the system and integration processes of each functional module, to meet the requirements of synchronization display for 3D interaction operation and scene roaming. Therefore, an efficient synchronization technology was adopted for the logical unity of scene dynamic display.Finally, a virtual environment was designed and developed for satellite assembly, the key technologies studied in this paper were used for scene display, and their validity and reasonability of theoretical approach proposed were verified by some actual projection tests. The experimental results demonstrated that immersive performance of the established VA system with spherical screen is excellent, and it could be used for VA design of products.更多还原