A Comparison Between Two Definitions of Idle Time in Offline Scheduling of Flexible Job Shop Problem

Calculating idle time (IDT) based on different definitions for solving flexible job shop scheduling problems (FJSSPs), may lead to dissimilar results. This is valid for both offline and online scheduling. Therefore, it is important to clarify the description of IDT. In this study, the differences between offline and online scheduling concepts are first explained. The advantages and disadvantages of these two approaches are analyzed in detail. The details of an offline scheduling method are illustrated through a step-by-step example, which is solved manually to be elucidative. Two definitions for IDT are then given over the waiting of the operations and machines, and an FJSSP is solved offline with a priority rule defined based on them. The differences in the results of the two definitions are demonstrated through the illustrative example. In addition, a source code is written in MATLAB for offline scheduling, with which some benchmarks are solved. Details of benchmarks are presented and the results are discussed.