OPTIMAL SPAN OF CONTROL IN CIM SYSTEMS

A common representation of manufacturing planning and control in CIM s ystems is in the form of a hierarchy of controllers. An important issu e 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 decision-maker or controller has considerable influence on the quantit y and quality of information exchanged. In this study, we determine th e optimal span of control based on quantitative factors that shape the multilevel coordination in the CIM hierarchy. The control scope in th e study is limited to the bottom two levels of such a hierarchical cha in of control, namely, the workstation controller and the automation m odule (or device controller). These two levels are responsible for exe cuting the production plans and schedules developed in the upper level s of the CIM hierarchy. The ability of the workstation controller to m aintain bidirectional communication with automation modules is constra ined by the capacity of the processor, the desired response time based on the characteristics of the controlled environment, and an acceptab le quality of information. We model these fundamental constraints that shape the interaction between workstation controller and automation m odules and determine the optimal span of control for workstation contr ollers, i.e. how many automation modules they can control. A queuing a pproach is used to acknowledge priorities in the action requests handl ed by the workstation controller. The modelling and analysis approach is generally applicable to all levels of the CIM hierarchy.