A new concept of job shop scheduling system-Hierarchical decision model

The function of scheduling is to determine when the product is to be completed, i.e. to make the schedule of the order and to manufacture the product on schedule. In job shop environment, productive activities are started when the customer order arrives at the shop and are finished when the product is completed. Consequently, job shop scheduling system has to cover the time period between the arrival of the customer order and the completion of the product. Examined the accuracy of informations essential to scheduling, they are rough when the customer order arrived, and it becomes accurate step by step. Due to the range scheduling system must cover and to the accuracy of informations, decisions should be made hierarchically in job shop scheduling. Looking over research on job shop scheduling, almost all researches have focused on dispatching problem. Dispatching problem is a decision made in job shop scheduling system, to be sure, but models of those researches have defects in basic structure of the system. It is out of bounds of the possibility that order is put into object of dispatching directly after it arrived at the shop. Scheduling is a set of decisions to be made hierarchically by its very nature. Therefore, in this paper, a new concept of job shop scheduling system which consists of five decision systems such as order entry, master scheduling, job scheduling, operation scheduling and dispatching is proposed.