Approach for Integrating Predictive-Reactive Job Shop Scheduling with PLC-Controlled Material Flow

In a rapidly changing environment, good coordination of production and logistics at an operational level is required to handle rapidly evolving technology, frequently changing customer demand and satisfaction, and remain competitive. The job shop scheduling and the material flow control are two important factors influencing productivity and cost-controlling activities in any manufacturing system. Finding optimal solutions, however, requires an enormous computational effort, which becomes critical for large problems, particularly in situations where frequent changes in the environment occur. The material flow control system has to ensure the schedule is met. But the planned production schedules often become ineffective when being executed on the shop floor. Given the high degree of automation in material flow systems, automated control systems have to support frequent changes. Although these two problems are strongly connected and solving one significantly impacts the performance of the other, often these problems are solved independently. The complexity of the scheduling problem is increased when the material flow control is involved since not only a proper schedule must be created but an appropriate material flow needs to be provided.
Due to this challenge, this dissertation has been designed to bridge the gap by initiating an approach for integrating predictive-reactive job shop scheduling with Programmable Logics Controlled (PLC) material flow. The objective is to develop an integrated control system that supports changes of routing strategy and schedule due to unexpected events. Features offered by state of the art material flow simulation software such as Open Platform Communications (OPC) interfaces and genetic algorithms have given the opportunity to realise this approach. The integrated control system consists of a system model, a control model and a schedule generator. Through combinations of these system components, the OPC connection with the physical system enables the integrated control system to be used for generating schedules, analysing the physical system through simulation and controlling the material flow system. As verification and validation, a demonstration prototype of integrated control system has been developed and applied in an industrial environment. The exemplary implementations prove not only that the planning and operation of material flow system is systematic, but significantly rescheduling and reconfiguration of the integrated control system can be performed with minimal effort.