Optimal span of control in CIM systems

A common representation of manufacturing planning and control in CIM systems is in the form of a hierarchy of controllers. An important issue in terms of data management and communication in such systems is the quantity and quality of information exchanged between the controllers. Just as in an organizational hierarchy, the span of control of each decisionmaker or controller has considerable influence on the quantity and quality of information exchanged. In this study, we determine the optimal span of control based on quantitative factors that shape the multilevel coordination in the CIM hierarchy. The control scope in the study is limited to the bottom two levels of such a hierarchical chain of control, namely, the workstation controller and the automation module (or device controller). These two levels are responsible for executing the production plans and schedules developed in the upper levels of the CIM hierarchy. The ability of the workstation controller to maintain bidirectional communication with automation modules is constrained by the capacity of the processor, the desired response time based on the characteristics of the controlled environment, and an acceptable quality of information. We model these fundamental constraints that shape the interaction between workstation controller and automation modules and determine the optimal span of control for workstation controllers, i.e. how many automation modules they can control. A queuing approach is used to acknowledge priorities in the action requests handled by the workstation controller. The modelling and analysis approach is generally applicable to all levels of the CIM hierarchy.