An improved genetic algorithm based on NSGA-Ⅱnon-dominated sorting is proposed to solve flexible job-shop scheduling problem. Makespan and machine maximum load are chosen as objective function to establish multi-objective optimization model. Real encoding and plug-in decoding are used to transform chromosomes and scheduling schemes. NSGA-Ⅱnon-dominated sorting with elite reserved strategy is designed to improve search efficiency, and different strategies for selection, cross and mutation are adopted. The feasibility and effectiveness of the algorithm are verified by simulation and results from comparison with other algorithms.
In view of application requirements, control axes, the development cycle and other factors of open CNC machine tools, we consider the modular as the guiding ideology and propose a design method of three-dimensional engraving and milling machine based on open CNC system. In this paper we make a detailed design for mechanism structure and control system. Experiments show that this machine has milling and engraving capabilities, can process metal and non-metallic parts, which is a high efficiency, multi-function numerical control equipment.
A Two-level method is proposed to solve the one-dimensional cutting-stock problem during the production process in this paper. First, nested layer cycle is designed to enumerate all the feasible cutting patterns, then a integer linear programming model is established with quantity demands as the constraint. The best cutting scheme is obtained finally according to the branch and bound method. The effectiveness of the proposed method is proved through a real world example, the calculations demonstrate that scheme obviously improves the utilization rate of stock
In this paper, the pre-tightening force on piezoelectric multi-dimensional force sensor is researched. Structure of multi-dimensional force sensor and piezoelectric quartz crystals are introduced and analyzed. The relationship between pre-tightening force and measuring range of force sensor is researched. Structural model of multi-dimensional force sensor is built and analyzed by FEM. Horizontal linearity in horizontal direction with different preloads is obtained. In order to verify FEM analysis, a reduced prototype of piezoelectric multi-dimensional force sensor is fabricated. Verification test is designed and made. The research will provide certain reference value for development of piezoelectric multi-dimensional force sensor.
Current scheduling approach for multiple objective flexible job shop problem (FJSP) cannot construct a precise scheduling model and obtain a satisfactory scheduling result at the same time. To deal with this problem, a simulation optimization scheduling approach was presented which was composed of two basic modules: the Fast non-dominated Sorting Genetic Algorithm (NSGA-II) module and Witness simulation module. Firstly, a multi-objective mathematical model was found for FJSP and NSGA-II was applied to solve. Then, a set of Pareto optimal solution was obtained by NSGA-II module. In order to select the final solution from the Pareto optimal solution for FJSP, the simulation model was set up by Witness, every Pareto solution was as input for simulation model. Finally, the final solution can be selected according other performance indicators.
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