AUTOMATED STORAGE/RETRIEVAL SYSTEMS USING PETRINETS
Automated storage/retrieval systems (AS/RSs) are of great current interest due to many attractive benefits, e.g. lower cost of building and land, saving of labour, reduction of inventory levels, improvement of material tracking and higher system throughput. Once the system is installed and operated, the measurable benefit of an AS/RS is predominantly dependent on the control policies used. The control policy of an AS/RS is usually application-dependent and dynamic. To effectively operate an AS/RS, system simulations are often required to determine the best control policies. Thus, various ways to efficiently build simulation models for AS/RSs are illustrated. PN theory is a widely used tool for modeling complex systems of interacting concurrent components. The net theory allows a system to be represented by a mathematical model. Important information of the system concerning basic structures and dynamic behaviors is well characterized by the net model. Thus, the model can be used for structural analysis and/or performance evaluation. In this project, a PN based AS/RS is proposed to focus on modeling the unit operation module using a modular concept and to establish a unit operation module for use in a general AS/RS model. With this unit operation module structure, the AS/RS model of any unit-load type can easily be obtained by assembling these modules. PNs are adopted as the modeling tool and to ensure the proposed model is robust, structural properties are analyzed.