Research On Computer Aided Assembly Process Planning

Assembly has been playing an important role in the manufacturing process of products. With the development of digital design and manufacturing technology, assembly has become the main factor in affecting the production efficiency, manufacturing cost and product quality. So improving the automation of assembly is more important for the development of manufacturing information technology. Aiming at the characteristics and current problems of assembly process planning, the assembly sequence planning and assembly path planning have been discussed and researched based on assembly model and collision detection in this paper.The complete and accurate recording and transmission of assembly model design information is a prerequisite for the generation of assembly sequence and path planning. The assembly model which reflects the information of entity and relationship between the parts and components is analyzed. Also, the assembly information modeling technology is established based on model based definition method. Collision detection is one of the key problems of path planning, automatic assembly and other areas. Some collision geometries such as axis-aligned bounding box and sphere are analyzed in the paper. Some collision detection optimization methods are introduced in the text, such as bounding volume hierarchy and spatial data structures.In the aspect of assembly sequence planning, the disassembly path planning algorithm with correlation judgment based on the RRT method is put forward to solve the sequence planning, and then an algorithm is used for optimizing this assembly sequence. It starts with generating the initial sequence by the disassembly path based on RRT algorithm. Secondly, it analyzes relationships among the various levels of initial sequence, and then the generation technique of sequence adjacency matrix (SAM) and sequence incidence matrix (SIM) are presented in this thesis to realize the sequence planning correlation judgment, which the former shows the adjacency relationship and the later expresses the assembly precedence constraint of all those part sets. Furthermore, the effects of all kinds of factors in assembly sequence planning are analyzed. With those information, the ant colony algorithm is applied to obtain the optimal sequence. Finally, the results show that the proposed algorithm is efficient for solving assembly sequence planning problems by using some examples.In view of the problem in assembly path planning, the ant colony algorithm is applied to obtain the assembly initial path and the dichotomy interpolation method is proposed to optimize this path. By using the grid method, the planning space is divided into a series of grids, each of which corresponds to a specific number, coordinate and row-column, and then the start point as well as goal point is connected to one of the grids. The ant colony algorithm is applied to obtain an effective initial path to avoid obstacles in the three-dimensional planning space. Furthermore, the dichotomy interpolation optimization is proposed to obtain a smooth path. Finally, some example tests are carried out to verify the feasibility of the proposed assembly path planning algorithm.