Reactive online scheduling of mobile resources for adaptive layout evolution in line-less assembly system

Assembly systems are required to be more flexible due to unpredictable resource and demand fluctuations. Line-less assembly systems (LAS) implement flexible job routes through multi-purpose resources and flexible transportation systems. Moreover, a completely reactive layout through (re-)arrangement of stations with mobile resources enables reconfigurations without interrupting production. A scheduling that can handle the complexity of dynamic events is necessary to plan job routes and control transportation in such an assembly system. Since the system layout and the job scheduling influence each other, only an integrated view of layout planning and scheduling implements a reactive system behaviour. Existing pre-planning methods with fixed cycle times are not designed for reactive layout optimization during line-less assembly operations with mobile resources. Therefore, the contribution of this paper is an integrated online optimization architecture for layout evolution using mobile resources and simultaneous job scheduling to increase the efficiency of LAS. The optimization is implemented using modular matching and scheduling algorithms considering temporary station setup states and parallel processing based on zone restrictions. The proposed algorithms are connected to a modular discrete-event simulation and scenario analysis tool of LAS. The simulation and control architecture is validated by applying an industry-based use case. The reactive layout evolution, including station exchanges and mobile resource repositioning are benchmarked with nonflexible control methods. Results show that the developed control system allows for shorter average lead-time and increased throughput and utilization of (mobile) resources.