Quasi on-line scheduling procedures for flexible manufacturing systems

This paper presents three quasi on-line scheduling procedures for FMSs consisting oi work stations, transport devices, and operators. In the scheduling different types of decisions are taken to perform a particular operation, i.e. the selection of (1) a work station, (2) a transport device and (3) an operator. Further, (4) the scheduling sequence of the operations has to be determined. The three developed procedures differ in the way these four decision problems are solved hierarchically. Several dispatching rules (SPT, SPT.TOT, SPT/TOT and EFTA) are available to solve the last mentioned decision problem. Limited buffer capacities in an FMS may cause deadlock in the procedures as well as in practice. The scheduling procedures involve a buffer handling method to avoid deadlock. A case study is presented to demonstrate the three procedures and to show some properties. Based on simulation tests, some conclusions are drawn about the performance of the scheduling procedures and the various dispatching rule.