Solution Of Assembly Sequence Planning Problem Based On Symmetry Destruction By CSP

It is an important research content in the assembly sequence planning to find out the reasonable and optimal sequence in the assembly sequence space,and it is also the difficulty of the current research.(CSP)model of assembly sequence problem is proposed,and the method of symmetry damage is proposed,and the symbol solving technique of ordered binary decision graph(OBDD)is combined.Firstly,the symbol representation in the assembly model is given,and the CSP model of the assembly sequence planning problem is established.The assembly sequence problem is transformed into the CSP model.Then,using the Lex-Leader constraint and the value-first constraint to destroy the symmetric solution of CSP,the symbol OBDD is solved by combining the backtracking algorithm to get all feasible assembly sequences.Finally,the correctness and feasibility of using CSP model and OBDD technology are proved by experiments.At the same time,the symmetry solution in CSP has a significant improvement in the efficiency of all feasible assembly sequences.Because the backtracking algorithm of ordered binary decision graph(OBDD)is used to solve the problem of assembly sequence,it is inevitable to repeat the search of symmetric variables and values,which is not conducive to the improvement of algorithm efficiency.For the constraint problem In this paper,the symmetry is destroyed by adding static constraints and constructing the GE tree two methods respectively.The main contents are as follows:(1)The CSP model is constructed based on the assembly sequence planning problem.A new constraint set is added.In the symbol OBDD algorithm,the variables and values in the CSP are symmetrically destroyed by adding static variables.It avoids searching the symmetric solution path repeatedly when performing the backtracking algorithm,so as to eliminate the symmetric solution in the backtracking algorithm and get all the feasible solutions quickly and efficiently.(2)to the actual constraint to meet the problem of all the different value distribution,through the construction of the GE tree to destroy the value of symmetry.In this paper,the complexity of the GE tree is studied,and the complexity of the GE tree is constructed.The complexity of the GE tree search program is higher than that in the polynomial level,and the CSP efficiency is improved at the exponential level.(3)Develop a CUDD package that provides basic functions for OBDD,ADD,and ZDD operations using Fabio et al.Given the input variable and then perform the symbol operation to output the corresponding OBDD plot.