Petri Net Representation for the Process Specification Language - Part 1: Manufacture Process Planning D. Kiritsis, P. Xirouchakis and C. Gunther CAD/CAM Laboratory (LICP), Department of Mechanical Engineering, Swiss Federal Institute of Technology at Lausanne (EPFL), CH-1015 Lausanne, Switzerland Abstract In this paper we propose Petri nets as a representation technique for modelling and analysing process planning activities as they are specified in the Process Specification Language (PSL) project of NIST. The goal of this project is to identify or create a process specification language (PSL) that can be common to all manufacturing applications, generic enough to be decoupled from any given application, and robust enough to be able to represent the necessary process information for any given application. The model discussed in this paper allows the modeling of tasks, their precedence constraints and the required resources (machines, setup and tools) and the corresponding costs within a compact Petri net, named Compact Process Planning net (CPP-net). This model can be easily extended and incorporate time. This part will be discussed in a next paper. 1. INTRODUCTION Process planning and production planning for manufacturing processes are still most times two distinct sequential off-line activities. Process plans are ordered sequences of tasks able to transform raw material to a final part or product. Tasks are chosen taking into account available or potential production means. Production planners receive process plans as their input and their task is to schedule the tasks on the machines while respecting the precedence relations given in the process plans. However, decisions made at the process planning stage, e.g., selection of machines, selection of task sequence, constrain the available choices for optimization on the subsequent production planning phase. On the other hand, process planning and scheduling may have conflicting objectives, such as required technology versus resource usage [Chryssolouris and Chan 1985]. Petri nets have been extensively used for modeling Discrete Event systems and FMS. For a review of Petri net applications in process planning and a complete list of related references see the papers of (Cecil et.al., 1992], [Srihari and Emerson, 1990], [Kiritsis and Porchet, 1995] and [Kiritsis and Xirouchakis 1996]. Various aspects related to the use of Petri nets for the Modeling of manufacturing systems can be found in [Ham and Lu, 1988], [Kruth and Detand,1992], and [Tönshoff et.al. 1991 and 1993]. In the present paper our attention is concentrated into the process planning problem and a new structure of a Petri net model for dynamic process planning is proposed. This model is generic in the sense that its construction is based on a set of standard generic rules and its graphic representation is similar for any part to be processed. With the proposed method two tools are used for model analysis and solutions finding: 1) the simulation tool can show