Research On The Key Technologies Of Assembly-oriented Virtual Environment With Spherical Screen

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.