Integrated conflict free routing of AGVs and workcenter scheduling in a just-in-time production environment

This paper addresses the integrated problem of scheduling machines and conflict-free routing of Automated Guided Vehicles (AGVs) in a manufacturing environment which produces complex assemblies. Given the due-dates of the end items, the objective is to minimize the cumulative lead time of the production schedule (total makespan) and reduce material handling and Work-in-Process (WIP) costs. A JIT production strategy is adopted in which all operations are scheduled as late as possible (to reduce WIP costs), but without backlogging end items. The transportation integrated scheduling problem within such an environment has been formulated and is NP-hard. An effective heuristic is developed that simultaneously schedules production and material handling operations by exploiting the critical path of an operations network to minimize the makespan as well as material handling and WIP costs, while routing AGVs in a non-conflicting manner on bidirectional travel paths.