Research On Vr-Based Assembly Process Design Method And Its Application For Satellite

The assembly process of complicated product is a difficult work, which consumes a great deal of manpower, material and finance, and affects production quality, cost and cycle. Virtual reality technology provides a new and low-cost way to solve these problems. This paper studies VR-based assembly process design method and its key technologies oriented to satellite etc, which has important theorical and pratical values.The contents and features of virtual assembly process design are expatiated, the existing problems in assembly process design for satellite are analysised, and the objectives of virtual assembly process design for satellite are pointed out. Then the architecture and workflow of virtual assembly process design system orieted to satellite is proposed. According to function decomposion the system can be divided into CAD modeling subsystem, virtual assembly process planning subsystem, process document generation and assembly training subsystem, and two interfaces between them. The workflow of the system includes model data obtaining phase, virtual operation phase, assembly sequence planning and path planning phase, and application and training phase.Product assembly modeling in virtual environment is studied. Analyzing the basic requirements of virtual assembly model, a hierarchically constraints-based virtual assembly model is proposed, which includes product layer, subassembly layer, part layer, feature layer, surface layer and polygon layer, and the constraint relationships in these layers. Data transformation from CAD to virtual reality is realized, which divides the CAD information into geomtry information, topology information, structure hiberarchy information and assembly constraint information, and transformed them into virtual environment by different ways. The virtual assembly scenegraph is erected according to virtual assembly model, which can be support interative assembly operation in virtual environment.Geometry constraint based virtual assembly position technology is studied. A hierarchically collision detection algorithm oriented to virtual assembly is proposed, which includes bounding box layer, space division cell layer, surface layer and polygon layer. The algorithm can improve accuracy and efficiency on one hand, on the other hand the algorithm can return colliding surface pairs for constraint recognization. Surface based constraint solving method is proposed, which can be used for rapid and accurate part positioning in virtuan environment. Dynamic constraint recognization and management method is proposed. According to collision detection, part matching, surface matching and priority selection, the accuracy and efficiency of constraint recognization can be improved. A geometry constraint manager is designed, and motion navigation based on geometry constraint is realized.Virtual assembly sequence planning and path planning is studied. Aimed at the limitations of automated assembly sequence planning and interative assembly sequence planning, a combined approach based on intelligent assembly sequece reasoning and interactive assembly evaluation is proposed. After the precedence constraint relationships between parts are generated and represented by defining a precedence constraint table, the ant colony optimization algorithm is applied to generate initial optimized assembly sequence. This sequence can be interactively simulated, evaluated and optimized by virtual assembly. During the assembly process new precedence constraints and evaluation rules will be recognized, and assembly tool positioning and operation space verification is realized, a more practical and optimal assembly sequence is then replaned, and once again evaluated by virtual assembly simulation. This is an iterative process until the best assembly sequence is obtained.The method of generating assembly process documents and assembly training are studied. A process-orieted assembly process model is erected to represent assembly process information during virtual assembly, this assembly process model can be transformed into working procedures and steps, and then the assembly process tree is obtained, based on which the user can perform assembly process editing. A method based on XML technology is applied to design, generate and output assembly process card, and web-based assembly training system is realized for assembly traning and guiding.An integrated virtual assembly process design system oriented to satellite is developed, and has been applied in China Academy of Space Technology.