Part and tool scheduling rules for a flexible manufacturing system

Scheduling rules for a specific general purpose Flexible Manufacturing System were investigated. The system consists of six general purpose machines with local storage at each machine, a work-in-process queue and a material handling cart. The primary purpose of this research was to investigate effects and interactions of three types of scheduling rules on the FMS performance. The rules included part scheduling on the machines and two resource allocation rules for tool scheduling and cart scheduling. In addition the part scheduling rule was modified with a tool look ahead rule to minimize tool delay. Cue to the numerous similarities in the scheduling and resource allocation problems of computer operating systems and the FMS, some techniques from operating systems were applied to the FMS tc reduce thrashing, prevent deadlocks and increase cart utilization efficiency,

A simulation model was developed to investigate the scheduling rules. SLAM was the language used to simulate this system. The main performance criteria used in this model were machine utilization, cart utilization, total time in system, number of finished parts and number of completed stages.

The most important result of this research was the discovery that individual tool allocation is superior to total tool allocation. For the system studied, the performance measurements were insensitive to the part and cart scheduling rules. However a severe reduction in cart speed caused the system to thrash. The reduction of cart speed provided the proper experimental conditions to prove that SDTF can be superior to ECFS for this system operating under thrashing conditions.

The tool look ahead feature provided a gross improvement in machine utilization and a reduction in time waiting for tools. However this improvement was not statistically significant in all cases.