Research On Scheduling Method And System For The Machine Shop Based On Bottleneck Machines Identification

The production volatility and processing dependency of production systems, as well as limited manufacturing resources, inevitably lead to bottlenecks that restrict the maximization of system throughput. Bottleneck machines are the practical problems that often occur to restrict the maximization of system throughput in machining workshop. According to theory of constraints(TOC), bottlenecks control the circulation of the entire system. It not only limits the output speed of the whole process, but also restricts the good use of the abilities of other production processes. Bottleneck identification is a prerequisite to bottleneck management and a fundamental key to production management and process control. Therefore, identifying system bottlenecks rapidly and accurately before the overall system circulation is significant and instructive to optimize production process and improve production performance.Scheduling is one of the core processes of the whole production management and is vital to determine the production performance of production system. As a typical combinatorial optimization problem, scheduling problems have been shown to be NP-hard in the strong sense. How to solve them quickly and accurately and obtain the optimal scheduling scheme has been one of the hot topics in academic and industrial research.In recent years, bottlene ck information in production system has attracted wide attention from many researchers and has been regarded as important characteristic information that might utilized for solving the problem. Based on the prior-to-run bottleneck identification, to explore how the use of bottleneck information to the solving process of job shop scheduling problems could accelerate the convergence of the optimal scheduling scheme has great academic and engineering significance to achieve rational resource al ocation and maximum production benefits.Research status of bottleneck identification is first introduced. Based on this, a new prior-to-run bottleneck detection method based on theory of constrains and sensitivity analysis is presented to overcome the disadvantages of existing bottleneck identification methods for a job shop including complex recognition algorithms, and poor guidance caused by posterior-to-run recognition. The designed identification approach, as a prior-to-run method, can identify bottleneck machine clusters under different hierarchies before the overall system circulation, thereby providing considerable valuable information for subsequent production process control and optimization to better improve the overall system performance.On the foundation of the definition to bottleneck machines in a job shop based on the basic principle of TOC, a bottleneck index matrix of machines is first obtained by measuring the sensitivity of system performance to the capacity of each machine. TOPSIS is then employed to calculate the comprehensive bottleneck index. Based on the calculation results, bottleneck clusters under different hierarchies are obtained through hierarchical cluster analysis. Finally, benchmarks of job shop scheduling problems with different scales are selected to compare the proposed approach with several existing approaches, i.e., Shifting Bottleneck Detection Method and Bottleneck Cluster Detection Method to illustrate the effectiveness and performance of the designed method.Then a scheduling method for machining shop based on bottleneck machines identification is proposed by taking bottleneck information as characteristic information of scheduling problems. The mathematical model of machining shop scheduling problem based on bottleneck machines identification is first established. Then the business process to solve the model based on genetic algorithm, as well as several key technologies including hybrid coding method based on bottleneck machines, decoding method, improved two-stage POX crossover operator and two-stage mutation operator are introduced. Finally simple genetic algorithm without the use of bottleneck information are selected to verify the effectiveness of the proposed method by separately solving JSP benchmarks and practical production case.Lastly, the machine shop scheduling system that include two functions, scheduling data management and operations scheduling, is designed and developed based on the above techniques and methods, and the effectiveness and performance of this system is validated by comparing with the results of manual scheduling to a practical scheduling case in a mechanical processing enterprise.