Research On Job-shop Scheduling Problem Based On Petri Nets

Job-shop production scheduling is the core of manufacturing enterprises' production, operation and management. Facing fierce market competition, every enterprise is trying to seek the program to improve the efficiency of production, operation and management. Therefore, to establish a reasonable, close to the actual scheduling model and to formulate an effective optimizing algorithm is the basis and also the key to solve the problem. In the actual production scheduling process, uncertainties brought from the market and technology can't be avoided, resulting in the research findings of classical scheduling problems and deterministic scheduling problems are unable to be applied to the actual job-shop production scheduling. Under this background, for the job-shop scheduling problem, how to establish a more realistic scheduling model and formulate the corresponding optimizing algorithm will bring more profound significances theoretically and practically.In this paper, the research objective is Petri Net-based job shop scheduling problem. First, deep study was made to the model and algorithm of static scheduling, and then analysis was carried on to the flaw of the result. Further, take the uncertainties existing in the process of production scheduling in job shop as a breakthrough and perform the research on manufacturing enterprise's dynamic scheduling method under those uncertainties.First of all, detailed description was made to the production scheduling problem and through in-depth analysis of the problem research situation at home and abroad, main issues and development trends were summed up.Secondly, the Petri net was established with regard to the static scheduling problem, with its own unique characters, which has been one of the most effective and widely used methods for the discrete event system's description, analysis and control. On this basis, while applying the Petri net to establish the production scheduling module, this paper developed the algorithm of L1 which is applicable for the Petri net to achieve optimal solution and with regard to the defect that the L1 algorithm is easy to lose the most optimized solution put forward the improved L1 algorithm. With the MATLAB as the tool to realize the algorithm, through real cases, the effectiveness of the algorithm was verified.However, static scheduling neglected the uncertainty in the actual schedule, so there is a big flaw in its result and can't be applied to the actual job-shop scheduling. Therefore, this paper made a systematic analysis of the uncertainties generated in job shop as well as the cause, classified them and made qualitative and quantitative analysis with regard to the uncertainties of personnel, equipment, and production orders.Finally, based on Petri net model, with regard to job-shop orders intermittent arrival and uncertainty events occurrence, this paper put forward the dynamic scheduling strategy of event-driven and cyclical-driven rolling window technique. Besides, specific research was performed to the production scheduling method under the uncertain conditions of machine failures, workers departure, emergent orders and cancellations, and also made verification with production scheduling methods research and examples. For multi-objective job shop scheduling and equipments'load balance issue, the paper introduced the corresponding control elements into the Petri net model to achieve optimal scheduling algorithm;In conclusion, it summed up the content of the work and analyzed the shortcomings of this work and further research.