Research On Virtual Assembly Process Planning Technology And Its Application For Aerospace Products

Traditional assembly process planning for aerospace products requires plenty of physical mock-up trials to verify designs because of their complicated structures and large number of components. Meanwhile papery process files are difficult to express complex assembly process clearly. As is stated above, the problem leads to long assembly cycle and high cost, so traditional assembly process planning can't satisfy the agile manufacturing requirement of enterprise. Virtual assembly technology is a new approach to solve the problem. This research task has a background of enterprise application to research the virtual assembly process planning technology and its application for aerospace products, which has important practical significance and values for realizing the rapid assembly process planning and improving enterprise's emergency mobilization productive capacity.The main work is illustrated in the following aspects:First, the desktop virtual assembly process planning system is designed. Virtual assembly systems are classified and functional requirements of virtual assembly process planning system are analyzed. Based on them the research contents and characters of the system are expressed. The system's hierarchical architecture is established which is divided into four layers: interaction layer, function layer, core services layer and database layer. And the workflow includes data preprocessing phase, assembly process planning phase and process files output phase.Second, the virtual assembly modeling technology for aerospace products is studied. The demands of aerospace products assembly models are analyzed. The model representation and information description are researched according to the classification of models in the virtual assembly scene, which consists of rigid parts, cable harness parts and other parts. The dendritic liaison model of mixed assembly of rigid and flexible parts is introduced based on the hierarchical model and graph model. The content and workflow of assembly modeling in the virtual environment are proposed. And methods of model data transformation and storage are presented.Third, the interactive aid technology for virtual assembly manipulation is researched. The flow of virtual assembly manipulation with interaction aid is presented. A novel assembly intention capturing algorithm based on constraint element bounding box and its efficiency evaluation is proposed. And the precise positioning solving algorithm of constraint based on pose transform of elements decomposition is presented, in which pose transform is classified into three cases as follows: placing a point onto a line, placing a point onto a plane and paralleling a line to a line. Parts assembly motion navigation is realized by solving parts degree of freedom and mapping the motion component to the target constraint direction. The interactive aid technology can easily eliminate error and escaped constraint realization and can improve the validity and efficiency of assembly intention capturing. The assembly constraint dynamic remove method and fastener assembly tools'manipulation and its effective space estimation technique are also studied in virtual environment. The virtual assembly technology of cable harness parts is researched based on mass-spring system whose dynamic characteristics in cable harness model are analyzed. The dynamic differential equations are solved by Verlet integration method. Aiming to improve the reality of simulation, the spring dynamic deforming constraint algorithm and cable harness mesh deformation update algorithm are proposed.Four, assembly path and sequence planning for virtual assembly process are studied. With favorable interaction of virtual assembly system a man-machine cooperation method to solve the assembly sequence planning for aerospace products is presented based on particle swarm optimization and genetic algorithm (PSO-GA). The assembly precedence constraint relationship model is studied which is described by assembly precedence relations and liaisons matrix. The code representation of genomes, chromosomes and particles is also studied. Then the fitness function with engineering significance is presented by comprehensive consideration of assembly continuity, assembly resource and influence of instrument and equipment. The geometric feasible assembly sequences are initialized and optimized based on PSO-GA in which the GA's crossover operator is reconstructed by PSO. An application case is discussed to demonstrate good convergence and stability of the proposed algorithm. Meanwhile, the assembly path generation and storage are presented. Assembly BOM and animation generations and process data extraction strategy are proposed for assembly process files.Finally, a prototype of desktop virtual assembly process planning system is developed and realized. The system is divided to four modules: Assembly modeling, virtual assembly simulation, assembly sequence planning and assembly process files design and guiding. The data flows among these modules are described, and the development frame and environment are introduced. A complete virtual assembly process planning workflow case of an aerospace products component is studied to verify each module's function by introducing functional interfaces in the flow. And the system has been applied preliminarily for the aerospace products.