Automated Guided Vehicle System Research Articles

Modelling and performance maximization of an integrated automated guided vehicle system using coloured Petri net and response surface methods

The objective of this study is to model and maximize performance of an integrated Automated Guided Vehicle System (AGVS), which is embedded in a pull type multi-product, multi-stage and multi-line flexible manufacturing system (FMS). This study examines the impact of guide-path flexibility on system performance through the development of three different guide-path configurations which range from dedicated to flexible relationships between automated guided vehicles (AGVs) and machine/assembly station resources. The system is modelled using coloured Petri net method (CPN) and the simulation results lead to identify the resource redundancy which can be rectified to achieve lower overall cost of the system through the development of flexible guide-path configurations. The study is extended to seek global near-optimal conditions for each guide-path configuration using response surface method, which yields improvements in system throughput and cycle time along with a decrease in the numbers of AGVs.

A new memetic algorithm for optimizing the partitioning problem of tandem AGV systems

In tandem automated guided vehicle (AGV) systems, all the work stations (processing centers) are partitioned into non-overlapping zones, where each zone is served by a dedicated vehicle. Beside the system input/output stations, additional pickup/drop-off (P/D) points are installed to link these zones as transfer points. In this paper, a new memetic algorithm (MA) is proposed to optimize the partitioning problem of tandem AGV systems. MAs are hybrid evolutionary algorithms (EAs) that combine the global and local search by using a genetic algorithm (GA) to perform exploration and a local search method to perform exploitation. Hence, a local search method has been designed and combined with a GA to refine the individuals of the population (i.e. improve their fitness). The objective is to minimize the maximum AGVs’ workload in order to balance the workload among all the zones and hence avoid the presence of bottlenecks. The MA performance is evaluated by comparing the obtained results with the reported results in the literature as well as the pure GA. Furthermore, some newly designed test cases are proposed and solved using both, MA and GA. The results show that, overall, the developed MA outperforms both pure GA and the other reported methods in the literature.

A simulation model for parts selection and routing in manufacturing systems

The current article proposes a modeling and simulation framework for parts selection and routing in automated guided vehicle systems. The proposed model has been built in Arena and employs several rule-based procedures. Design of experiments is conducted to identify the best sequence of rules to follow to parts selection and routing in order to improve system performance. An application of the model is illustrated using a hypothetical automated guided vehicle system (AGVS) layout.

自動搬送システムの運行制御とその解析手法

It is important to discuss the behavior of traffic at merging sections for the design and realization of an automated guided vehicle system (AGVS). In this study, we deal with a merging section of the AGVS by considering a time limit for the merging of vehicles. Near the merging section, traffic flowing in one direction must form a queue to avoid collisions between vehicles. We propose an improvement in the control strategy proposed in the previous research. However, it is difficult to analyze the mathematical model of the merging section. Analysis can be performed only for the case in which the time limit is one unit. We also propose a method for analyzing the model for an arbitrary time limit using a linear recurrence relation. We quantitatively discuss the influence of the time limit on the average queue length and the detour rate.

Stochastic Elements in Transportation System Simulation - Unnecessary?

Abstract Discrete event system simulation is often seen as a genuine tool to investigate the performance of transportation systems. The complexity of real-world systems often prevents us from accurately describing these by a mathematical model that can be evaluated analytically, thus, simulation is often the only realistic alternative. Another advantage of the simulation is the ability to include statistical analysis for different simulation scenarios. Well-known approaches of incorporating uncertainty into models include trace driven simulations and sampling directly from gathered data. Another aspect to be taken into account is the economics of simulation modelling; a more detailed model requires additional building time, and proper treatment of stochastic models requires statistical analysis, which again usually implies several simulation runs. From this outset the following question arises: Should stochastic behaviour be included in transportation simulation models in the first place? We present real case examples including evaluation of the internal logistics of a beverage manufacturer, capacity analysis of an automatic guided vehicle system, cost benefit analysis (CBA) of a railway network investment and evaluation of different multipurpose railway wagons, where stochastic behaviour is dealt with in different ways. Based on the cases we make an initial attempt to formulate framework for deciding how to include stochastic behaviour in the simulation model. For further research topics we suggest formulating explicit guidelines to deal with stochastics to increase the efficiency of model building.

Optimal location of dwell points in a single loop AGV system with time restrictions on vehicle availability

Since the workload of a manufacturing system changes over time, the material handling equipment used in the facility will be idle at certain time intervals to avoid system overload. In this context, a relevant control problem in operating an automated guided vehicle (AGV) system is where to locate idle vehicles. These locations, called dwell points, establish the response times for AVG requests. In this article, a dynamic programming algorithm to solve idle vehicle positioning problems in unidirectional single loop systems is developed to minimize the maximum response time considering restrictions on vehicle time available to travel and load/unload requests. This polynomial time algorithm finds optimal dwell points when all requests from a given pick-up station are handled by a single AGV. The proposed algorithm is used to study the change in maximum response time as a function of the number of vehicles in the system.

A zones formation algorithm for tandem AGV systems

Abstract This article presents a zone formation algorithm for tandem AGV systems. The goal of the algorithm is to partition a given layout into a set of non overlapping zones in order to minimize the part flows between zones (or inter-zone part flows). The proposed algorithm is based on the principle of clustering. At the start of the algorithm, we allocate each station to a zone. Later, we merge zones at various runs of the algorithm to form new zones using inter-zone parts flow and distance criteria. The restriction on the size and the parts flow in the zones is obtained by comparison against user-defined values. The algorithm terminates when all the zones satisfy the desired size and parts flow limits. We demonstrate the applicability of our approach using a numerical illustration.

Zone design and control for vehicle collision prevention and load balancing in a zone control AGV system

Because of their routing flexibility, automated guided vehicles (AGVs) have been used in many manufacturing systems, especially those in which parts with diverse and complex processing routes are made. In recent years, there have been many studies on AGV-related problems. One of them is preventing the collision of vehicles. Some traditional vehicle collision prevention strategies are zone strategies that divide guide paths into several non-overlapping zones and restrict the presence of only one vehicle in any zone at any time. Traditional zone strategies are fixed zone strategies in which the area of a zone is fixed and vehicles are not allowed to help each other. Because of these restrictions, fixed zone strategies cannot always satisfy the system’s transportation demand if there is a load imbalance between vehicles of different zones. In this paper, a new zone strategy is proposed for a zone control AGV system with a network guide path. The proposed strategy is a dynamic zone strategy, which is different from a fixed zone strategy. It relies on two methods – zone partition design and dynamic zone control – to prevent the collision of vehicles and to maintain the load balance between the vehicles of different zones. The zone partition design defines a relationship coefficient, which measures both the distance relationship and the flow relationship between workstations, and uses it to find an initial zone partition design. We then improve this initial design by an SA (Simulated Annealing) based improvement procedure to achieve a better load balance result. The dynamic zone control uses two methods – zone repartition and load sharing – to ensure that vehicle collision can be prevented and the system’s load balance can be maintained when the system is in operation. Simulation experiments were conducted to understand the performance of the proposed strategy. The simulation results show that the proposed strategy outperform the fixed zone strategy in throughput, WIP inventory, and flow time. The results also show that the proposed strategy is able to adapt to any changes (in the system) that cause the load imbalance problem between zones.

Stochastic Modeling of an Automated Guided Vehicle System With One Vehicle and a Closed-Loop Path

The use of automated guided vehicles (AGVs) in material-handling processes of manufacturing facilities and warehouses is becoming increasingly common. A critical drawback of an AGV is its prohibitively high cost. Cost considerations dictate an economic design of AGV systems. This paper presents an analytical model that uses a Markov chain approximation approach to evaluate the performance of the system with respect to costs and the risk associated with it. This model also allows the analytic optimization of the capacity of an AGV in a closed-loop multimachine stochastic system. We present numerical results with the Markov chain model which indicate that our model produces results comparable to a simulation model, but does so in a fraction of the computational time needed by the latter. This advantage of the analytical model becomes more pronounced in the context of optimization of the AGV's capacity which without an analytical approach would require numerous simulation runs at each point in the capacity space.

컨테이너터미널 운영효율성을 위한 RTLS 기반 YT Dynamic Operation 모델

최근 컨테이너선의 대형화 추세와 항만간의 경쟁 가속화로 인해 컨테이너터미널의 효율적 운영과 생산성 향상에 대한 관심과 노력이 증대되고 있다. 특히 YT를 이용한 이송방식을 채택하고 있는 터미널의 경우 AGV(Automated Guided Vehicle)를 이용하고 있는 자동화터미널에 비해 상대적으로 경제성 및 운용효율성 측면에서 불리한 것이 사실이다. 최근 10여 년간 이와 같은 YT운용의 비효율성을 보완하기 위해 YT Pooling Operation 도입과 같은 노력이 계속되어 왔으나 개별 YT의 위치인식기능부재로 인한 제약으로 실질적인 효과는 미미한 수준이었다. 본 연구에서는 최근 주목받고 있는 RTLS(Real Time Location System) 기술을 활용하여 기존 YT Pooling Operation의 제약사항을 해결하는 새로운 개념의 YT Dynamic Operation 모델을 세안한다. Interest in high productivity and streamlined operation is growing amid a heated competition between ports and mega size vessel oriented operation. It becomes clear that terminals that operate YT(Yard Tractor) for transportation in container yard have less efficiency in operation and cost comparing terminals functioning AGV(Automated Guided Vehicle) system. To offset disadvantages arising out of YT operations, continual efforts (e,g YT pooling operation) were taken place for the last decade, but the result has not been fruitful; YT pooling operation still has a problem in that it cannot read individual YT's actual location. This study suggests 'YT dynamic operation model'- a practical application of RTLS(Real Time Location System) technology which will solve YT pooling operation problems.

Dual track and segmented single track bidirectional loop guidepath layout for AGV systems

In this study, we develop integer programming models for simultaneous design of the guidepath track and location of the pickup and dropoff stations for automated guided vehicle systems. Two alternative bidirectional topologies are compared: a dual track loop, and a single track loop partitioned into non-overlapping segments, each served by a single vehicle. We show that the empty vehicle trips have a significant impact on the quality of design in both topologies. More importantly, we identify the difference between empty flow node balancing for a dual track loop with the empty flow edge balancing on a single track loop subject to segmentation. Our work presents an economic decision making model for the trade-off analysis between the costs associated with the additional shop floor space of a dual track loop and the increased vehicle fleet size of a segmented single track loop.

Evaluation of automatic guided vehicle systems

This paper presents a methodology for detailed evaluation of autonomous automated guided vehicles systems (AGVS) used for material handling. The methodology includes: stand-alone sub-module evaluation, including comprehensive simulations and statistical analysis of the system's sub-modules, along with hardware validation; quantitative system evaluation for integrated system performance investigation; and structured qualitative analyses for identifying strengths and weaknesses not readily apparent. The defined performance measures include aspects from both multi-robot and AGV fields. The developed methodology provides a systematic way to model, experiment with, analyze, and compare different AGVS control methods. To demonstrate the methodology, it was applied to evaluate a recently developed decentralized AGVS control method.

Design and analysis of an automated container handling system in seaports

This article presents the design and analysis of an automated container handling system which integrates Automated Storage and Retrieval System (ASRS) and Automated Guided Vehicle Systems (AGVS) for use at seaport terminals. Current practices in seaport container terminals are discussed first, and then, the main components of the proposed automated configuration are introduced. A computer simulation model is developed to examine the key measures of effectiveness such as throughput and space/equipment utilisation. The performance of the proposed configuration shows nearly four times improvement in throughput/acre over the commonly practised block stacking approach. Implications for future automated systems of this type have been described.

Simulation of Automatic Guided Vehicle systems in manufacturing environment. Case: Volvo's Crankshaft Unit in Skovde

Competing in global markets creates pressure for manufacturers to rigidly use automation, and advanced manufacturing techniques to improve manufacturing plant productivity. Among productivity, manufacturers are also interested about other performance dimensions, namely time, flexibility and quality. With the wise use of automation, we could directly improve all of the other indicators, and indirectly quality. In this paper it is shown, how implementation and use of Automatic Guided Vehicles (AGVs) could benefit from the use of manufacturing simulation. AGVs have been available for practical use since the 1970s, but still in the investment and use processes it is rarely seen justified to a high detail, what eventually determines the number of vehicles used in the system. Our paper is able to show with two simulation cases (a hypothetical example and a real case study) that the number of AGVs is very sensitive with respect to production system output. Furthermore, some assumptions that are often made can overly simplify the problem (e.g. no recharging of batteries and constant speed). Therefore, in this paper, we propose that more research should be addressed to the AGV system simulation, and in practice tools for decisions makers should be developed further. Our research also shows that empty travelling and low utilisation is a norm in current AGV systems in order to assure production system functionality, and there is a need and potential for performance improvement here, as well.

Developing exact and Tabu search algorithms for simultaneously determining AGV loop and P/D stations in single loop systems

There are some issues which have to be addressed when designing an automated guided vehicles system (AGVS) such as flow-path layout, traffic management, the number and the location of pick up and delivery points, vehicle routing and so on. One of the AGVS guide path configurations discussed in the previous researches includes a single-loop which is the subject of this paper. In unidirectional single loop systems, determining the loop for the motion of an AGV, and the location of pick up and delivery (P/D) stations in the cells, are prominent points which, when considered simultaneously, lead to better results than determining each one independently. However, in the literature it is proved that the problem of separately determining the shortest feasible loop is a NP-complete problem. In this paper, by considering a from-to chart and a block layout as the input of problem, we try to determine: (1) a single loop, with at least one shared edge with each cell, (2) the direction of the flow and (3) the location of P/D stations on the loop, all at the same time, in a way that the total travel distance on the loop be minimised. In this regard, first a new exact algorithm is presented and then three heuristic algorithms are developed utilising a Tabu search (TS) method. Solving randomly generated test problems shows that our exact algorithm is capable of solving small size problems; also all three TS algorithms work efficiently in solving problems that could not be solved by exact algorithms.

작업환경 모델 기반 AGV의 최단 경로 탐색 알고리즘

본 논문에서는 AGVS(Automated Guided Vehicle System)가 여러 복잡한 작업 환경 또는 작업 환경 변경 시 좀 더 유연하게 운용될 수 있도록 작업환경 내에서 AGVS에 필요한 작업공간요소를 분류하고 이들을 모델링하는 방법을 제안한다. 또한, 그래프 탐색 방법인 A* 알고리즘을 이용하여 AGV의 최단 경로 탐색 알고리즘을 본 논문의 작업환경 요소로서 재 표현한다. 생성된 최단 경로와 본 논문에서 가정한 AGV의 속도 테이블을 이용하여 운행 중인 AGV의 경로 점유 시간 알고리즘을 제안한다. 마지막으로 간단한 시뮬레이션을 통하여 제안한 방법의 적용 가능성을 증명한다. This paper proposes the effective method for classifying the working spates and modelling the environments, when complex working environments of AGVS(Automated Guided Vehicle System) ate changed. And, we propose the shortest path searching algorithm using the A* algorithm of graph search method. Also, we propose the methods for finding each AGV's travel time of shortest path. Finally, a simple example is included for visualizing the feasibility of the proposed methods.

KUKA Robotics to supply robotics for automatic guided vehicle systems

KUKA Robotics to supply robotics for automatic guided vehicle systems

The Impact of Guide Path Configurations on Performance of an Integrated Automated Guided Vehicle System Using Coloured Petri Net

The objective of this study is to analyse an integrated Automated Guided Vehicle System (AGVS) which is embedded in a pull type multi-product, multi-stage and multi-line flexible manufacturing system (FMS). The analysis is carried out through the development of different guide path configurations. Three guide-path configurations are developed to add flexibility gradually in the AGVS and the impact of added flexibility is studied by examining the performance of the system. The study uses coloured Petri net methodology to model the system and the simulation results lead to decrease the number of automated guided vehicles and hence the overall cost of the system.

Building a Semantic-Rich Service-Oriented Manufacturing Environment

Service orientation has emerged as a new promising paradigm for enterprise integration in the manufacturing sector. In this article, we focus on the approach and technologies for constructing a service oriented manufacturing environment. The service orientation is achieved via virtualization in which everything, including machines, equipments, devices, various data sources, applications, and processes are virtualized as standard-based Web services. The virtualization approach is based on the emerging Web Services Resource Framework (WS-RF). A case study of virtualizing an AGV system using WS-RF is described. The use of Semantic Web Services technologies to enhance manufacturing Web services for a semantic-rich environment is discussed, focusing on OWL-S for semantic markup of manufacturing Web services and OWL for the development of ontologies in the manufacturing domain. An enterprise integration architecture enabled by Semantic Web service composition is also discussed.

Design for a tandem AGV system with two-load AGVs

Abstract The tandem AGV system is obtained by partitioning all workstations into multiple zones. Then, a single vehicle is assigned to each zone. In this paper, we present an analytical model to design a tandem AGV system with two-load AGVs. The analytical model is obtained by performing a design procedure which consists of two steps, ‘selection of feasible zones’ and ‘selection of final guide path.’ A numerical example is presented to show the design procedure.