Approximate decomposition for closed queueing network models of FMSs with a block-and-wait and state-dependent routing mechanism

Closed queueing networks with a central server configuration are used to analyse the performance of Flexible Manufacturing Systems. The blocking phenomenon of cart-type Material Handling Systems (MHS) due to the finite capacity of local buffers is addressed and a state-dependent routing scheme is introduced to assure that the MHS does not send parts to workstations where blocking events have already occurred. Under the assumptions of exponential service time distribution and the FCFS discipline at workstations, an efficient approximate decomposition approach is developed to evaluate the performance measures of the resulting non product-form queueing networks with a block-and-wait mechanism. The accuracy of the proposed method is established by comparison with the results of simulation experiments.