Modelling of AS/RS Using Hierarchical and Timed Coloured Petri nets Erik Kučera, Branislav Hrúz Faculty of Electrical Engineering and Information Technology Slovak University of Technology in Bratislava Bratislava, Slovakia erik.kucera@stuba.sk Abstract —Presently, discrete-event dynamic systems represent a significant group of varied systems e.g. computer networks, manufacturing systems, communication systems, database systems etc. An important class of discrete-event systems are automated storage and retrieval systems (AS/RS). These systems are equipped by robots and other automation technology. The article deals with Hierarchical Coloured Petri nets applied in modelling of these systems. Main results of the article include brief description of the method and hierarchical model of storage system implemented by Hierarchical and Timed Coloured Petri net in CPN Tools software. We also discuss the possible application of the model and modelling method in practice. Keywords—Petri net; colour; hierarchical; CPN; storage; system; AS/RS; robotics; informatics, warehouse; model; modelling I. INTRODUCTION Development of varied systems is a complex discipline that includes many activities, e.g. system design, specification of required properties, implementation, testing and further development of the system [1]. As these operations are challenging and important for the final product, it is appropriate and necessary to create a model of the system. One of the modelling tools are Coloured Petri nets. They are used for modelling of concurrent Discrete Event Systems. Activation of such systems is event-based, not time-based; discrete time is just an information value. Hierarchical Coloured Petri nets are very useful extension of conventional Coloured Petri nets. Automated storage systems are an important part of logistics. Presently, economic activity across continents is gaining unprecedented dimensions. The consumer lifestyle of a majority of population requires production of large quantities of goods for a short time. The advantage of automated storage systems consists especially in saving the human capital, and higher reliability. Such systems are widely called as AS / RS systems (automated storage and retrieval systems). Buying a AS/RS system, however, requires significant acquisition costs but also development of the control and monitoring software. The presented article outlines the possibilities for the development of such software using innovative methods - Hierarchical and Timed Coloured Petri nets. Presented paper briefly describes new ways and insights to modelling of automated storage systems. They are many papers that deals with this particular topic. We can mention the work of Italian authors Mariagrazia Dotoli and Maria Pia Fanti from Politecnico di Bari, Italy [2], [3]. Our view of modelling method is little different. In our case we consider that there are goods to be stored on the input station of the warehouse system. The information about locations, where the goods should be stored, are known. Correct cooperation (without conflicts) of the components of AS/RS system is provided by operational control which is modelled by Coloured Petri net using conditional constructions (i.e. guards, arcs, etc.). In the work of Italian authors there is considered that a fictional scheduler assigns an exact plan to pallets of goods how they should move throughout the storage systems. A description of the activity of the scheduler is not mentioned in the Italian authors' paper. However, in referenced paper there is a very good state analysis of the storage system using Matlab- Stateflow. An advantage of our models is also that they were implemented in CPN Tool software so these ones are not presented only in their mathematical form. There is also a paper published by Chinese authors Cai Wenxue and Wu Zhongming from technical university in Guangzhou [4]. Their conception and modelling method is closer to our solution than the first one. However, the paper is a bit disarranged. The model of Chinese authors is relatively simple and there are not solved some of the conflict situations. II. STORAGE SYSTEMS An automated storage system (AS/ RS) usually consists of the following parts: Racks - they are mostly metal structures where pallets with items are placed; Aisles - they are created by empty space between racks; Cranes - they are fully automated devices for storing and retrieving pallets from racks of storage system. Input and output points - are points where items are transferred by a crane from storage to vehicles or conveyor or the crane receives items from these devices.