Automated synthesis of Ladder automation circuits based on state-diagrams S. Manesis * , K. Akantziotis University of Patras, Electrical and Computer Engineering Department, Patras 26500, Greece Received 26 March 2004; received in revised form 3 November 2004; accepted 5 November 2004 Available online 29 January 2005 Abstract One area where discrete event systems are currently used is the design of control systems based on programmable logic controllers (PLCs). As the PLC technology is evolving into a family of control functions of many types at many different levels of complexity, there is an increasing need for software tools providing the systematic development of real industrial applications including modeling and control of discrete event systems. This paper describes the use of a state-diagram method in the computer aided logical synthesis and design of automation circuits. It also presents the corresponding software package developed for control logic creation. The developed software generates control logic in the form of Ladder electric circuits since they present descriptive simplicity and are widely known in the PLCs’ world. The developed software package is also suitable for both industrial practice and teaching purposes. q 2004 Elsevier Ltd. All rights reserved. Keywords: Industrial automation; Discrete event systems; State diagrams; Ladder logic diagram; Programmable logic controllers 1. Introduction The industrial production lines are dynamic systems whose states evolve according to the occurrence of abrupt physical events thus exhibiting the characteristics of a discrete event system (DES). Automata and Petri nets are the most basic theoretic tools for modelling and analysis of DESs [1–3]. Furthermore, supervisory control methodologies for manufacturing workcells use DES-based implementation in order to generate step-by-step control strategies in an on-line and automatic manner [4,5]. In general, an industrial automation system includes various levels of control and monitoring as we are going up from the field controllers to the supervising layers. There is intensive research on theoretical subjects of the higher levels of this hierarchical scheme and consequently various software tools have been developed for modelling, simulation, execution and translation purposes. For example, a rule-based method has been presented by Jafari et al. [6] to derive a Ladder-logic program from a high- level system model. At lower levels of the above mentioned hierarchical scheme there is need to develop user friendly tools with nice graphical interfaces, more powerful and with more emphasis on computational efficiency in order to allow industry to adopt real applications of DES theory. For many academic researchers, the implementation of control logic and algorithms is an afterthought, compared to the process of solving a problem mathematically. The gap between the finite automata or Petri nets describing an industrial system and the physical realization of them must be covered. Many researchers have been working on the improvement of industrial logic creation and design. The problem that many are trying to solve is the perceived inefficiency of the current methods, which use primitive, low-level design languages, with practically no logic reuse, and are very time- consuming [7]. In searching for a solution, researchers have focused on methods that can be automatically generated from a specification. Companies such as Rockwell and Siemens have already started to develop software tools for this purpose, e.g. VALID software from Siemens [8]. The various machines operating simultaneously in an industrial manufacturing system are usually controlled with programmable logic controllers (PLCs), which are currently the most suitable and widely employed industrial control 0965-9978/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.advengsoft.2004.11.002 Advances in Engineering Software 36 (2005) 225–233 www.elsevier.com/locate/advengsoft * Corresponding author. Tel.: C30 2610 997335; fax: C30 2610 991812. E-mail address: stam.manesis@ee.upatras.gr (S. Manesis).