Coloured timed Petri net for real-time control of automated guided vehicle systems

Automated guided vehicle systems (AGVS) are material-handling devices representing an efficient and flexible option for products management in automated manufacturing systems. In AGVS, vehicles follow a guide-path while controlled by a computer that assigns the route, tasks, velocity, etc. Moreover, the design of AGVS has to take into account some management problems such as collisions and deadlocks. The paper presents a novel control strategy to avoid deadlock and collisions in zone-controlled AGVS. In particular, the control scheme manages the assignments of new paths to vehicles and their acquisition of the next zone. Moreover, the use of coloured Petri nets is proposed to model the dynamics of AGVS and implement the control strategy stemming from the knowledge of the system state. Additionally, extending the coloured Petri net model with a time concept allows investigation of system performance. Several simulations of an AGVS with varying fleet size while measuring appropriate performance indices show the effectiveness of the proposed control strategy compared with an alternative policy previously presented.