A formal functional characterization of shop floor control

Abstract

Shop-floor control systems for discrete part manufacturing have been widely described by many researchers. These descriptions have led to several proposed frameworks to solve the overall shop floor control problem. Some terms commonly used to describe these frameworks include: centralized control, hierarchical control, heterarchical control, and hybrid control. However, these frameworks have not provided a formal generic vision of shop floor control. Rather, they have concentrated on specific implementations of the problem, or small classes of similar implementations. As a result, the frameworks which have been developed are applicable only to a subset of the problem domain. By contrast, a solution to the general shop floor control problem is highly desirable. It is only after the general shop floor problem is understood that such a general solution can be developed. In response to this need, this paper presents a formal functional characterization of the general shop floor control problem. Key to our functional characterization of the controller is the use of process plans as part of the control. We use a process plan representation model compatible with the ISO TC184/SC4/WG3/P11 proposed standard as part of the control input. The ISO process plan model is converted to a digraph which provide the task representation for control. In this paper, we illustrate how these digraphs provide the essential requirements for input to and for a functional characterization of shop floor control.