Task assignment and subassembly scheduling in flexible assembly

This paper deals with models for flow management problems in flexible assembly systems (FAS’s). The system consists of a set of machines that must perform the assembly of a number of parts, possibly of different types. Each part type requires a set of operations; the precedence relations among the operations are specified by an assembly tree. Machines are provided with limited-capacity tool magazines and a finite buffer for holding parts. Each machine can be tooled to perform only a particular subset of the operations required by the whole process. One problem is that of finding a feasible assignment of operations to machines and a feasible schedule of the subassemblies in order to minimize the completion time of all of the parts. In this paper, the problem is analysed as a case of pipelined assembly, i.e., when the FAS is characterized by a serial transportation system (flow line) and there exists a dominating path in the assembly tree. Typically, this happens when there is a main pallet and all of the other components are assembled directly on it in a given sequence. The authors present a polynomial-time dynamic programming algorithms for solving the problem for both single-type and multitype production. The approach is more general than typical ALB algorithms.