A FORMAL FUNCTIONAL-CHARACTERIZATION OF SHOP-FLOOR CONTROL

Shop-floor control systems for discrete part manufacturing have been w idely described by many researchers. These descriptions have led to se veral proposed frameworks to solve the overall shop floor control prob lem. Some terms commonly used to describe these frameworks include: ce ntralized control, hierarchical control, heterarchical control, and hy brid control. However, these frameworks have not provided a formal gen eric vision of shop floor control. Rather, they have concentrated on s pecific implementations of the problem, or small classes of similar im plementations. As a result, the frameworks which have been developed a re applicable only to a subset of the problem domain. By contrast, a s olution to the general shop floor control problem is highly desirable. It is only after the general shop floor problem is understood that su ch a general solution can be developed. In response to this need, this paper presents a formal functional characterization of the general sh op floor control problem. Key to our functional characterization of th e controller is the use of process plans as part of the control. We us e a process plan representation model compatible with the ISO TC184/SC 4/WG3/P11 proposed standard as part of the control input. The ISO proc ess plan model is converted to a digraph which provide the task repres entation for control. In this paper, we illustrate how these digraphs provide the essential requirements for input to and for a functional c haracterization of shop floor control.