Research On The Assembly Process Planning Of Products Mixed With Rigid And Flexible Parts And Its Application

Assembly process planning (APP) plays a very crucial role in product design and manufacturing. An effective and optimized assembly scheme can significantly shorten the life cycle of product development, improve the assembly quality, and reduce assembly costs. With the progress of science and technology, more and more modern electromechanical products, such as aerospace, aviation, automobile, electrical and mechanical products, not only contain a lot of rigid parts, but also consist of many different slender flexible parts (SFP). In these products, the slender flexible parts include cable, hose, wire, rope and etc. How to solve the assembly process planning of these products mixed with rigid and flexible parts is becoming one of the most difficult problems in the mechanical and electronic industry, especially in the aerospace. In order to deal with the existing assembly problems in these electromechanical products, this paper discusses these aspects as follows:A novel discrete Cosserat method is proposed to efficiently build the physical model of slender flexible parts. First, the Cosserat model is used to describe the configuration of SFP according to its shape and physical property. Based on the finite element theory, the discrete Cosserat model of SFP is presented, and the dynamics equation of this model is derived from dynamical theory at the same time. Then, the formulations of the external forces and constraint forces are derived for the discrete model of SFP. Finally, the dynamic equations of the SFP are solved by using a semi-implicit iterative Euler’s method. The proposed model can realistically simulate the bending deformation and torsion deformation of SFP at very low computational cost, which is also very well suited for interactive operation in the virtual or augmented reality environment.To reduce the amount of calculation for collision detection, a real-time collision detection scheme based on Hierarchical Bounding Volumes (BVHs) is designed in this thesis. Considering the difference between the rigid parts and SFP, a referential partitioning plane method is proposed to construct BVHs of rigid parts, while a discrete masses-based approach is realized to construct BVHs of SFP. Based on the analysis of the contact characteristics between various objects, a novel contact processing mechanism is presented to handle collision problems between SFP and the outside objects, so as to prevent SFP penetrating the outside objects or itself.In order to reduce the difficulty of assembly sequence planning (ASP), this thesis presents a new hierarchical classification approach to adjust the assembly relationship of products. First, two hierarchical-classification principles are presented based on the key assembly constraint (KAC) of parts. Based on the two hierarchical-classification principles, the implementation process of hierarchical classification algorithm is explained. The initial assembly relationship of the product could be readjusted to a new hierarchical structure which is more suitable for assembly planning according to the novel hierarchical-classification algorithm.Since triangle mesh model lost a lot of topology information, the location and operation means between tools and parts in virtual environment are difficult. This thesis presents a feasible and effective approach for modeling and locating of assembly or disassembly tools in the virtual reality environment. A universal point-vector model for tool is presented by means of abstracting the locating constraints of tools, which greatly simplify the expression of tool’s locating information. With the effective and reasonable creation of tools modeling, a so-called best matching constraints algorithm is implemented to calculate the locating constraints on the triangle model of part that is installed or demolished through tools.On the basis of the new hierarchy of product, an intelligent disassembly-based approach is presented to obtain an optimized and feasible assembly process. An improved ant colony algorithm is first established for searching and constructing an initial assembly sequence that can be used as a very useful guidance for the following interactive disassembly planning. Then, the human experience bring into play to achieve an optimized assembly process with necessary information about assembly fixtures and tools under a simulation environment. The proposed method can take full advantage of the intelligent algorithm and the expert knowledge to get more practical assembly plan.In order to deal with the problems of laying and assembly planning of slender flexible parts in electromechanical products, a novel approach to operate the physically-based slender flexible parts in an augmented reality environment is presented in this thesis. Considering characters of the physical and virtual parts, a mixed model is used to uniformly manage all the physical and virtual parts. With a reasonable construction of augmented reality environment, a real-time interactive algorithm based on the operating panel is proposed to enable users to interact with the virtual slender flexible parts in the mixed reality-based scene, where the user may more easily perceive the relationship between SFP and physical parts than in the virtual environment.Aiming at solving the existing assembly problems in these electromechanical products, an assembly prototype system is developed, which integrates the presented methods in this thesis. Finally, A aerospace product is validated by this prototype system.