| Assembly sequence planning is the basis of assembly process planning,the changes of assembly sequence would lead to the changes of assembly process and assembly line,further influence the quality of assembly.It is a combinatorial optimization problem with characteristics of strong constrains,multi-objectives and massive calculation.The complexity of solving the problem can be increased exponentially when the number of parts grows.It will be much harder to generate feasible solutions.To solve these problems,this thesis proposes a generation method of feasible sequence based on disassembly hierarchy and then puts forward an efficient modified harmony search algorithm.Here are the specific research contents:Firstly,it generates feasible sequences base on the thought of disassembly guiding assembly.In order to improve the efficiency of generating feasible sequences,a classification method of building a disassembly hierarchy,and a method of reverse outputting feasible assembly sequence by disassembly hierarchy are proposed.Meanwhile,it is proved by experiments that the disassembly hierarchy method can absolutely generate feasible sequences,and the results are of better quality and more centralized in distribution compared with usually random method.Secondly,a modified harmony search algorithm for the assembly sequence planning problem is brought up.The disassembly hierarchy method is utilized to initialize the harmony memory,thus the complex process of searching feasible sequences by algorithm is avoided.Then,a new strategy of improvising harmony is proposed,which includes a local search operator and a precedence preservative crossover operator.The modified harmony search algorithm is compared with four popular algorithms in the case study.In terms of problem-solving,this method can obtain optimal solutions with maximum probability,especially in the examples of stop valve.As to speed of solving,it can reduce 84% iterations and save 71% computing time at most.Thirdly,after applying the proposed methods to an all-direction propeller’s assembly sequence planning of a domestic shipbuilding enterprise,the feasibility of the proposed methods is confirmed by solving the assembly sequence of two key parts.Finally,the studies in this thesis have been concluded with further improvements discussed and following work listed. |
