S-graph

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S-graph is a framework for batch process scheduling problems.

S-graph is especially developed for the problems with NIS (Non Intermediate Storage) Policy, which often appears in chemical productions, but it is also capable to solve problems with UIS (Unlimited Intermediate Storage) policy.

In this model there are products, and a set of task, which have to be performed to produce a product. There are dependences between the tasks, and every task has a set of Equipments, that can perform the task. Also we can set different processing times for the same task in different Equipments. It is also possible to have more Equipment units from the same type, or define changeover times between two task in one equipment.

There are two types of the scheduling problems:

  1. The number of batches to produce is set, and we try to minimize the makespan (processing time)
  2. 2nd problem: Every product has a revenue, and a time horizon is set. The objective is to maximize the revenue in this fixed time horizon.

S-graph framework also contains combinatoric algorithms to solve both of these problems.

There is a graph representation of S-graph:

Image:s-graph.gif

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