Abstract
Automated manufacturing systems (AMSs) consist of computer-controlled interconnected manufacturing components (MCs) that are used to transport and process different product types. Each product type requires a certain sequence of processing steps in different MCs. Hereby, multiple product types can share processing steps on the same MC and the paths of different products types can overlap. In this paper we consider the modeling of AMSs in the scope of supervisory control for discrete event systems (DES). On the one hand, a suitable AMS model must allow the representation of sequential and concurrent processing steps in MCs. On the other hand, such model must be able to track different product types traveling through the AMS so as to process the products correctly. While previous work is commonly concerned with the first requirement, this paper identifies that the existing literature lacks a general treatment of the second requirement. Accordingly, we first introduce order-preserving (OP) languages that preserve the order of different product types in MCs and we propose a suitable finite state automaton model for OP languages. Then, we show that the composition of OP languages again leads to an OP language. That is, modeling MCs by OP languages, an OP model of a complete AMS that is suitable for supervisory control is obtained. In addition, it is possible to use both OP models and non-OP models for general AMSs, where MCs have different properties. We demonstrate the applicability of the proposed modeling technique by a flexible manufacturing system example.
Highlights
Discrete event system (DES) models are suitable for representing sequential and concurrent processes in technical systems such as automated manufacturing systems (AMSs) [1]–[8]
We demonstrate the practicability of the proposed modeling method by an flexible manufacturing systems (FMSs) example with multiple products, OP and non-OP manufacturing components (MCs) and overlapping product paths
The subject of this paper is the development of discrete event system (DES) models for a particular property of automated manufacturing systems (AMSs)
Summary
Discrete event system (DES) models are suitable for representing sequential and concurrent processes in technical systems such as automated manufacturing systems (AMSs) [1]–[8]. The main focus of this paper is the modeling and supervisory control of AMSs with different product types and overlapping product paths. There is existing work that incorporates the product order in the system model These works either use example systems where different product types follow independent paths through the AMS [11], [16], [44] or they define the product paths such that it is not necessary to remember the product order for MCs that can hold more than one product [9], [14], [15], [34], [35], [45], [46]. We use a particular model of MCs with input events and output events that characterize the arrival and departure of products, respectively We note that such model is used in existing work such as [47] but in a different context.
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