Optimal Schedule And Control Method Of Batch Production Process Via Composing Petri Nets

For a typical sequence of actions of a batch plant,the materials are transferred from tanks to a reactive vessel,operated according to the required conditions,and discharged from this vessel to another one.Further,such sequence of actions occur periodically.Therefore,a batch production process is featured as multiple batches.Two operations may be in conflict and,consequently cannot be executed concurrently since they shared some resources.Otherwise,they are asynchronous or concurrent.The production market is becoming to be of small and personal orders,and multiple batches.Hence,a production system needs to flexibly and quickly respond to market changes to maintain its competitiveness.The optimal schedule and control of batch production processes has naturally become a hot research area,and considerable achievements have been made.How to quickly compute an optimal schedule and its control codes is a challenge.1?A method is presented for modeling a batch production process via Petri nets(PN).As a graphic and mathematical tool,PN is a good tool for modeling and synthesis of discrete event systems.A multitask and multiple-batches production process model is ingeniously constructed based on the composing PNs.The global Petri net is modeled step by step,considering the time-dependent process flow,valve switching state,operation constraints and so on.Each subnet modeling algorithm is given.This model overcomes the disadvantages of too many nodes and too much complex representation of PNs,and provides a unified environment for subsequent research on schedule and control of a batch system.2?The optimal schedule is to achieve the shortest batch processing time.Based on the constructed global PN,a mathematical model for the optimal schedule of batch production process is established.Meeting the constraints of the production process,materials delivery and resource conflict avoidance,an optimal schedule strategy with the shortest processing time is solved by the heuristic search.A strategy net based on the optimal schedule strategy is constructed using PN,and the corresponding modeling algorithm is given.A strategy net is prepared for the design of control codes.3?The method is presented to compute the control codes for the optimal schedule.The optimal schedule strategy is depicted as a strategy net,and the strategy net vividly describes the optimal process sequence of the batch production process.The Boolean expressions satisfying the firing conditions are written out for each place of the strategy net,and all of the variables are in the one-to-one mapping relationship with the contacts or coils in the ladder diagram.This results in a ladder diagram for the batch production process,and the algorithm for automatic design of control codes is given.4?The Kingview and programmable logic controllers are used for a joint simulation to verify this work.A typical batch production process is taken as an example to illustrate and demonstrate the methods proposed in the thesis.