Approximations for the mean and variance of the throughput of flexible manufacturing cells

A large complex flexible manufacturing system consisting of a number of manufacturing cells can be modeled as a composite of open and closed sequencing networks. The entire manufacturing system is modeled as an open queueing network, and individual manufacturing cells arel modeled as closed queueing networks. The means and variances of the cells throughput are needed so that the overall system performance can be estimated. The analysis provided in this paper focuses on the distribution of the interdeparture time of the loading/unloading station in the cell. The distribution is formulated as a phase-type function. Three cell structures are investigated: stations in series, stations in parallel, and stations with feedback. Numerical results are given to illustrate the effect of the cell structure on the means and variances of the cell throughput.