Modeling operator/workstation interference in asynchronous automatic assembly systems

Abstract

In several instances ofdiscrete event dynamic systems (DEDS), jobs sometimes require service from two or more resources at the same time. When queueing network models are used to study DEDS, this feature ofsimultaneous resource possession is often ignored because it is difficult for the models to handle. In some DEDS, this feature of a job demanding several resources simultaneously can have a significant effect on system performance, especially if there is a limited amount of one or more of these resources. For example, in an asynchronous automatic assembly system, an assembly at a workstation needs an operator when it experiences a jam (a random phenomenon) in order to clear the jam. Due to the presence of a limited (small) number of operators, an assembly may have to wait for an operator. This waiting orinterference time has a significant effect on the system production rate. This paper develops an analytical approximation method that can be used to determine the steady-state performance of automatic assembly systems for a given assignment of operators. The analytical method involves the simultaneous solution of two “coupled” queueing models; one of the models calculates the waiting time for an operator resource, while the other computes the waiting time for a workstation resource. The solution technique developed can be adapted to study instances of simultaneous resource possession in other DEDS, such as flexible manufacturing systems and computer/communication networks.