An integrated, hierarchical framework for planning, scheduling and controlling job shops

In this paper an explanation is proposed for the fact that job shop scheduling in real-life environments is so complicated. A typical job shop has a large variety of machines mostly organised as a functional layout. The demand for a large variety of products is irregular, both in timing and in quantities. Each product type is manufactured in batches which flow through the shop, each one following its own routing. At each machine multiple operations for various products can take place with a setup in between batches requiring two different types of operations. The objective is to satisfy as good as possible customer demands: meeting due-dates while trying to control lead-times and work-in-process and securing smooth operations on the aggregate level as well as on the day-to-day execution level. We show how a new integrated, hierarchical framework for planning, scheduling and control tries to cope with the job shop realities. Guaranteeing the practicality of the approach is anything but simple.