Machine Scheduling and Job Shop Scheduling
This chapter focuses on job shops. There are n jobs and each job visits a number of machines following a predetermined route. In some models a job may visit any given machine at most once and in other models a job may visit each machine more than once. In the latter case it is said that the job shop is subject to recirculation. A generalization of the basic job shop is a so-called flexible job shop. A flexible job shop consists of a collection of workcenters and each workcenter consists of a number of identical machines in parallel. Each job follows a predetermined route visiting a number of workcenters; when a job visits a workcenter, it may be processed on any one of the machines at that workcenter.
Job shops are prevalent in industries where each customer order is unique and has its own parameters. Wafer fabs in the semiconductor industry often function as job shops; an order usually implies a batch of a certain type of item and the batch has to go through the facility following a certain route with given processing times. Another classical example of a job shop is a hospital. The patients in a hospital are the jobs. Each patient has to follow a given route and has to be treated at a number of different stations while going through the system.
KeywordsSingle Machine Precedence Constraint Total Weighted Tardiness Longe Processing Time Disjunctive Graph
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