Motion Coordination of AGV's in FMS using Petri Nets

This paper presents a motion coordination strategy based on a hierarchical control architecture for a flexible manufacturing cell equipped with automated guided vehicles (AGVs). The AGV's transport raw material among different workstations and automated warehouses. The hierarchical control architecture is divided into two levels. The high level includes a Discrete-Event plant model using the Finite-State Automata formalism and two supervisors are synthesized to enable concurrent tasks obeying process restrictions, and the product sequences, respectively. In the low level, the transportation tasks are translated to each AGV using motion coordination control laws based on artificial vector fields to guarantee convergence to the goals. Repulsive vector fields are also employed to avoid inter-robot collisions. The approach was tested in both virtual reality environment and a experimental setup with two AGV's for a specific product sequence.

International Journal of Production Research, 2004

Automated Guided Vehicle Systems (AGVSs) are material handling devices representing an efficient and flexible option for products management in Automated Manufacturing Systems. In AGVSs vehicles follow a guide-path while controlled by a computer that assigns route, tasks, velocity, etc. Moreover, the design of AGVSs has to take into account some management problems such as collisions and deadlocks. This paper presents a novel control strategy to avoid deadlock and collisions in zone controlled AGVSs. In particular, the control scheme manages the assignments of new paths to vehicles and their acquisition of the next zone. Moreover, we propose the use of Coloured Petri Nets (CPNs) to model the dynamics of AGVSs and implement the control strategy stemming from the knowledge of the system state. Additionally, extending the CPN model with a time concept allows investigation of the 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 to an alternative policy previously presented by one of the authors.

This paper describes the planning process in flexible manufacturing systems. Flexible manufacturing system consisting of machines, computers, robots and automated guided vehicle. The skeleton and the functionality of a Petri Net Toolbox, embedded in the MATLAB environment, are briefly presented, as offering a collection of instruments devoted to simulation, analysis and synthesis of discrete event systems. The integration with the MATLAB [1] philosophy responds to the general interest manifested by educators for enlarging the compatibility between the traditional background of Control Engineering applications and the novelty of discrete-event-systems scenarios. It explains a scheme of labelling and firing which makes modelling convenient for complex systems whose constraints are difficult to express only in terms of firing duration. The system manufacture choose is from the undertake S.C. APULUM S.A. Alba Iulia. Timed Petri nets are used to model operational and routing flexibility ...

Manufacturing systems are undergoing a noticeable evolution due to an intense technological progress in industrial robotics. Serial production has evolved into the concept of Flexible Manufacturing Systems (FMS), which encapsulate processes in automatic equipment that are capable of executing different operations, that before be performed in several stages and diverse equipments. Automated Guided Vehicle (AGV) systems have been frequently used as material handling equipment in manufacturing systems since the last two decades. Particularly, AGV´s with trailers are, and will continue to be, the backbone of the material transport industry. The use of these systems has taken the attention of experts and researchers. They are numerous studies concerning AGV with trailers systems in literature; few of them deal with the adaptation of these systems into FMS. In this paper, a study of the trajectories and a simulation model of a hypothetical system, which included a FMS environment, were developed. In addition, a potential field's method was explored in order to improve the ability of detecting obstacles in AGV´s with trailers moving through stations.

IFAC Proceedings Volumes, 2000

A software tool for modeling and simulation of Flexible Manufacturing Systems is proposed in this paper. Variety of robots, conveyers and working machines can be used in building of the FMS. Control program for the whole system is written through Petri net model. Transformation from Petri net into control program is automated. Programming language is derived from real language for robot control. Simulation is done in 3D environment with full real-time animation. Used technique of 3D animations allows using different views to system with full zooming and change of angle and position.

2004

Automated Guided Vehicle Systems (AGVSs) are material handling devices representing an efficient and flexible option for products management in Automated Manufacturing Systems. In AGVSs vehicles follow a guide-path while controlled by a computer that assigns route, tasks, velocity, etc. Moreover, the design of AGVSs has to take into account some management problems such as collisions and deadlocks. This paper presents a novel control strategy to avoid deadlock and collisions in zone controlled AGVSs.

Iranian Journal of Science and Technology Transaction B Engineering, 2012

Automated Guided Vehicles (AGV) have been a conventional solution and choice made by many manufacturing enterprises as means for Flexible Material Handling Systems (FMHS). In recent years, a considerable number of these vehicles have been installed on shop floors worldwide, effectively proving the usefulness of material handling systems. However, the increasing complexity of demand as well as a need for "make to order" rather than "make to stock" policy implies usage of more intelligent material handling solutions. This paper discusses the usage of an intelligent AGV as means for FMHS which should have Intelligent Material Handling System (IMHS) as the final outcome. This paper presents the experimental results of hybrid robotic control architecture. To evaluate the performance of the architecture, a mobile robot built on LEGO ® Mindstorms NXT technology was used. Some of the architectural modules are based on the implementation of Artificial Neural Networks in order to achieve the needed robustness in exploitation. Then, through simulation using AnyLogic ® 6 software, the performance in terms of manufacturing system effectiveness and workstation utilization is analyzed. Based on the experimental results, the proposed IMHS can have significant advantages over conventional material handling systems.

1994

A PETRI-NET BASED METHODOLOGY FOR MODELING, SIMULATION, AND CONTROL OF FLEXIBLE MANUFACTURING SYSTEMS by Venkatesh Kurapati Global competition has made it necessary for manufacturers to introduce such advanced technologies as flexible and agile manufacturing, intelligent automation, and computer-integrated manufacturing. However, the application extent of these technologies varies from industry to industry and has met various degrees of success. One critical barrier leading to successful implementation of advanced manufacturing systems is the ever-increasing complexity in their modeling, analysis, simulation, and control. The purpose of this work is to introduce a set of Petri net-based tools and methods to address a variety of problems associated with the design and implementation of flexible manufacturing systems (FMSs). More specifically, this work proposes Petri nets as an integrated tool for modeling, simulation, and control of flexible manufacturing systems (FMSs). The contrib...

IJST, 2012

Automated Guided Vehicles (AGV) have been a conventional solution and choice made by many manufacturing enterprises as means for Flexible Material Handling Systems (FMHS). In recent years, a considerable number of these vehicles have been installed on shop floors worldwide, effectively proving the usefulness of material handling systems. However, the increasing complexity of demand as well as a need for "make to order" rather than "make to stock" policy implies usage of more intelligent material handling solutions. This paper discusses the usage of an intelligent AGV as means for FMHS which should have Intelligent Material Handling System (IMHS) as the final outcome. This paper presents the experimental results of hybrid robotic control architecture. To evaluate the performance of the architecture, a mobile robot built on LEGO ® Mindstorms NXT technology was used. Some of the architectural modules are based on the implementation of Artificial Neural Networks in order to achieve the needed robustness in exploitation. Then, through simulation using AnyLogic ® 6 software, the performance in terms of manufacturing system effectiveness and workstation utilization is analyzed. Based on the experimental results, the proposed IMHS can have significant advantages over conventional material handling systems.

IEEE Transactions on Industrial Informatics, 2000

In the context of automated manufacturing systems (AMS), Petri nets are widely adopted to solve the modeling, analysis, and control problems. So far, nearly all wellknown Petri net approaches study AMS with either flexible routes or assembly operations, whereas few work investigates their combination. In this paper, we propose a novel class of nets, which can well deal with both features. We also derive a supervisory controller for on-line ratio enforcement among all processes. Using structural analysis, we show that liveness of such systems can be attributed to the absence of undermarked siphons. We also reveal the design separability between ratioenforcing and liveness-enforcing supervisors.