In: International Journal of Advanced Manufacturing Technology 18 (6), pages 434-447. September 2001.
Abstract: A system theory approach is used to design rule-based discrete-event controllers for the sequencing of jobs in manufacturing systems. The controller is described in terms of matrix equations that are easy to implement on a personal computer. Industrial engineering (IE) techniques and the concepts of Petri nets (PN) are included. A standard bill of materials (BOM) is used in the first design step to make a "task sequencing matrix". Then a resource requirement matrix is constructed to add non-shared resources and shared resources (e.g. pallets, transport robots, and material handling machines). Non-shared resources are controlled using inner decision loops. However, shared resources require outer decision loops for dispatching and routeing that resolve conflicts, taking into account the specified performance measures to be optimised (e.g. percentage of idle time, throughput, etc.). Failures are simply represented as disturbance inputs, allowing design for failure recovery. The rule-based controller design algorithm is a step-by-step procedure with repeatability and guaranteed conflict/deadlock resolution. It shows that the closed-loop system, once designed, is equivalent to a Petri net (PN); this gives, as a by-product, an algorithm for PN design. Furthermore, the matrix formulation allows a rigorous analysis of deadlocks in terms of circular wait and blocking, and the resources available.
Keywords: Bill of materials; Manufacturing dispatching; Petri nets; Rule-based controller; Task sequencing.