Determination of optimum unit load size of the AGV in an electronics assembly production system

This paper deals with the problem of determining an optimum unit load size of automated guided vehicle (AGV) in an electronics assembly production line. It is assumed that an AGV delivers assembly parts to each workstation from a miniload automated storage/retrieval system and a conveyor line transports subassemblies between workstations. Two types of operating policies for the AGV system are proposed. For each policy, a nonlinear mathematical model is formulated. Based on the characteristics of the objective function and feasible region, a solution algorithm is developed, which finds an optimum unit load size. To illustrate the models, problems are chosen and solved.     

Analytical model to estimate performances of autonomous vehicle storage and retrieval systems for product totes

In today's competitive scenario of increasingly faster deliveries and smaller order sizes, material-handling providers are progressively developing new solutions. A recent, automated material-handling technology for unit load storage and retrieval consists of an autonomous vehicle storage and retrieval system (AVS/RS). The present paper presents an analytical model to estimate the performances (the transaction cycle time and waiting times) of AVS/RS for product tote movement. The model is based on an open queuing network approach. The model effectiveness in performance estimation is validated through simulation.     

Design of material transportation system for tandem automated guided vehicle systems

A new design concept of materialtransportation system is proposed on the basis of tandem automated guided vehicle (AGV) systems. The first design stage is to find the one and only one optimal transfer point for each traffic zone. All in-process parts to be moved into and out of a zone must go through the specified transfer point and parts can be moved directly to their destinations. The second design stage is to link all transfer points as a 'transportation centre' by several bidirectional tracks. This design concept can simplify material transportation system and provides accurate estimation of traffic load in a zone.     

Analysis of automated guided vehicle configurations in flexible manufacturing systems

Automated guided vehicle (AGV) systems complement the operation of flexible manufacturing systems (FMS) by providing integrated automated material handling that capitalizes on the system's flexibility. Previous research considering AGV systems for use in FMS installations has focused on complex control strategies to reduce the congestion problem often encountered in these systems. Recently, attention has been given to tandem system configurations that reduce congestion and simplify system control. The present study uses the simulation methodology to compare the performance of three AGV configurations under a variety of experimental conditions. The results indicate that system size, load/unload time, and machine failure rate factors have significant impacts on the operation of the systems considered. In general, with respect to due date performance, it is recommended to use the traditional configuration in small systems while using the tandem/loop configuration in larger systems. Furthermore, it is shown that the addition of the loop to the tandem configuration mitigates the sensitivity of the tandem configuration to the load/unload time factor as well as significantly improving its performance under high load/unload times. Thus, if tandem configuration is desired to reduce congestion and simplify system control, investments must be made to directly reduce the load/unload times or to construct a loop to avoid the load/unload time penalty.     

求解带AGV柔性作业车间调度问题的改进灰狼算法

针对带AGV的柔性作业车间调度问题,以最小化完工时间为目标,考虑AGV在装载站、机器、卸载站之间的有效负载时间和空载时间,构建了数学规划模型。其次,提出一种有效的灰狼算法进行求解,基于该问题特征,设计机器选择、工序排序和AGV搬运的3段编码,有效地保证每个个体均可产生可行解;灰狼算法中改进了关键参数a和E设定方式,有效平衡了算法的勘探能力和局部搜索能力;为进一步提升算法跳出局部最优解的能力,该算法融合了领域搜索等方法。最后,案例测试结果表明,改进灰狼算法在求解带AGV柔性作业车间调度问题中具有优越的性能。     

Comparison of dynamic routeing techniques for automated guided vehicle system

An automated Guided Vehicle (AGV) System with a limited number of vehicles cannot perform all of the transportation requests on demand. When a capacitated AGV system is used, then it is possible for the material handling system to become the bottleneck. There are many factors that affect the efficiency of an AGV system including how vehicles are routed and schedules. This paper presents a new dynamic approach to AGV routing. Simulation is used to study the effectiveness of this approach.     

Dynamic relative positioning of AGVs in a loop layout to minimize mean system response time

One of the control decisions in the operation of an automated guided vehicle (AGV) system is to determine the home locations of idle vehicles. In this paper, the problems of selecting home location of a vehicle when idle in a single loop AGV network is presented. As the number of unit loads to be picked up at each workstation dynamically changes over time, the optimum home location of vehicles may also change. Based on the objective of minimizing the expected response time of a vehicle, models are constructed. Example problems are given to illustrate the use of the solution algorithms. The results of the system response times obtained using the dynamic dwell point models are compared with those of other dwell point rules.     

Performance evaluation of tandem and conventional AGV systems using generalized stochastic Petri nets

This paper investigates the different policies and concepts followed in the traffic management of automated guided vehicle (AGV) systems, and develops the controls for automatically eliminating potential vehicle conflicts in an AGV system. The planning of the AGV system is performed in such a way that there are no conflicts or deadlocks for the vehicles using stochastic Petri nets (SPNs). The major effort is devoted to determining the benefits of the tandem AGV control in comparison with the conventional AGV control method. SPNs have been used to model the different designs of flexible manufacturing systems (FMSs) and with different policies for the movement of material, vehicle path control, inventory planning and tool control. The SPN model is solved and the performance of the system can be evaluated. In this study, the effort is directed to model an FMS with two different types of AGV traffic management methods, namely the conventional and tandem AGV control. A SPN program is used which takes the FMS Petri net model as the input and evaluates the different properties of the Petri net. Finally the performance measures are obtained, which helps in evaluating and comparing the two different AGV traffic management methods.     

Deadlock avoidance in an automated guidance vehicle system using a coloured Petri net model

This paper addresses the problem of deadlock control in automated guided vehicle (AGV) systems for automated manufacturing systems with unidirectinal guided paths. First, a Petri net (PN) model was developed for the problem. Then, by using the PN model developed, the condition for deadlock-free operation in AGV system and a control law are presented. To avoid deadlocks in AGV systems by this law, one needs only to observe the state of the system and check the number of free spaces available in some of the circuits. It is estimated that the proposed control law is simple enough to be used in the real-time control of contemporary system configuration. Three examples are used to show the application and efficiency of the proposed control law.     

Scheduling of Automated Guided Vehicles in a Decision Making Hierarchy

Scheduling efforts made without considering the special limitations of the material handling system might lead to infeasible results. An analytical model is proposed, first, to incorporate the automated guided vehicle (AGV) system into the overall decision making hierarchy. A mathematical formulation is developed to include interaction between the AGV module and other modules in the system by considering the restrictions of the material handling system. A micro-opportunistic approach is then proposed to solve the AGV scheduling problem. Finally, the proposed method is compared with a number of dispatching rules.     

A beam search-based algorithm and evaluation of scheduling approaches for flexible manufacturing systems

This paper presents a new algorithm for the flexible manufacturing system (FMS) scheduling problem. The proposed algorithm is a heuristic based on filtered beam search. It considers finite buffer capacity, routing and sequence flexibilities and generates machine and automated guided vehicle (AGV) schedules for a given scheduling period. A new deadlock resolution mechanism is also developed as an integral part of the proposed algorithm. The performance of the algorithm is compared with several machine and AGV dispatching rules using mean flow time, mean tardiness and makespan criteria. It is also used to examine the effects of scheduling factors (i.e., machine and AGV load levels, routing and sequence flexibilities, etc.) on the system performance. The results indicate that the proposed scheduling algorithm yields considerable improvements in system performance over dispatching rules under a wide variety of experimental conditions.     

基于IGPS和麦克纳姆轮的AGV导航控制系统设计

目前常规使用的舵轮和差速轮自动导引车（automated guided vehicle,AGV）的精度和灵活性低,无法满足在大型高端产品装配过程中精确定位和导航的要求。为了进一步提高AGV的导航精度和柔性,提出了一种基于IGPS （indoor global positioning system,室内全球定位系统）和麦克纳姆轮的AGV高精度导航控制系统。首先通过IGPS高精度定位和坐标计算获取IGPS接收器的位置坐标,其次采用车体中心提取算法和坐标转换矩阵实现接收器坐标位置到车体中心坐标的转换,最后通过对全向移动AGV的建模,采用模糊PI控制方法对AGV的路径偏差进行纠正,实现AGV的精确定位和循迹导航。利用Simulink对模糊PI控制和传统PI控制进行仿真分析,结果表明,相对于传统PI控制,模糊PI控制响应速度快,调整曲线更平滑。同时,在基于IGPS的AGV试验平台进行试验,采用激光跟踪仪对AGV重复定位位置进行测量,结果显示定位精度达到±0.2 mm。研究结果对提高AGV的高精度定位能力具有借鉴意义,也为后续可移动机器人加工模式的研究提供参考。     

Kanban number optimisation in a supermarket warehouse feeding a mixed-model assembly system

Following just-in-time principles, a growing number of manufacturers are adopting the so-called supermarket concept. Supermarkets are decentralised storage areas scattered throughout the shopfloor that serve as an intermediate store for parts required by nearby assembly lines. From these stores, a certain number of handling operators deliver parts from the supermarket to, and collect empty bins from, assembly stations. Finally, they return to the supermarket and are refilled for their next tours. The assembly stations are typically refilled from the supermarket through the constant replacement of the consumed parts pulled by the kanban system. Considering a mixed model assembly system composed of different assembly lines, feeding problems can occur as an effect of the replenishment lead time, of the production mix variation, of the commonality between the different models assembled. The aims of this paper are (i) to highlight how the supermarket/multi-mixed assembly-line system presents specific attributes that prohibit the simple application of well-known kanban dimensioning formulations and (ii) to provide an innovative procedure to optimally set all decision variables related to such a feeding system.     

Change management in modular assembly systems to correspond to product geometry change

Modular assembly systems are a category of changeable manufacturing systems, which can handle the rapid change in customer demands, product design change and market fluctuations. On the operational level, jigs and fixtures are fundamental elements of assembly systems. They are used to hold parts and subassemblies in place, and directly affect assembly cost, quality and time. Therefore, modular fixtures that can adapt to different geometries are becoming a very important enabler for changeable manufacturing. In this paper, two mathematical models are presented to optimise the use of a passive modular assembly fixture plan in an automated assembly system by considering different production scenarios and constraints. These models optimise the changeability plan of the modular fixture by minimising the number of dowel replacements between different part geometries assuming that the candidate dowels locations for each part have been determined using existing methods in the literature by considering different assembly requirements. The first model, LRTE, considers all possible part rotations and translations on the fixture to minimise setup time. In addition, the second model, SLRTE, enables the system to simultaneously optimise job sequence. This paper presents various examples in different sizes, and the results show that the model can effectively reduce the fixture setup time up to %50.     

Automated Two-machine Flowshop Scheduling: A Solvable Case

This paper considers new flowshop scheduling problems related to automated manufacturing systems in which n jobs are processed on two machines M_a and M_b in this order. The job transportation between two machines is done by a single automated guided vehicle (AGV), and is crucial because no machine has buffer storage for work-in-process (WIP) and hence a machine cannot release a finished job until the empty AGV becomes available at that machine, while the AGV cannot transfer an unfinished job to a machine until the machine is empty. O(n³) algorithms are given in this paper to find optimal sequences of n jobs that minimize their maximum completion time (i.e., makespan). Some numerical results are also given to evaluate the effect of computing optimal sequences.     

Modelling of an automated guided vehicle system (AG VS) in a just-in-time (JIT) environment

Like other production systems, just-in-time (JIT) systems need to address the issue of material transport between workstations such as those served by automated guided vehicles (AGVs). Unlike other production systems, however, the JIT philosophy imposes strict requirements on inventory levels and supply-demand protocols which render conventional AGV delivery strategies ineffective and counter-productive. This paper describes the modelling of an AGV system (AGVS) in a JIT environment in a way that is consistent with JIT principles. The influence of a ‘JIT perspective’ is emphasized throughout the model by introducing threshold values for both input and output queues, performance measures that emphasize lower inventories in addition to transport efficiency, and a new dispatching rule that implements better inventory and transport control. The dispatching rule is shown to perform better in a JIT environment than previously developed AGV dispatching rules in both transport and logistic criteria.     

A neural algorithm for finding the shortest flow path for an automated guided vehicle system

The automated guided vehicle (AGV)system is emerging as the dominant technology to maximize the flexibility of material handling, while increasing the overall productivity of manufacturing operations. This paper presents a new way of finding the shortest flow path for an AGV system on a specific routing structure. An optimal solution of the system is determined by using an approach based on the Hopfield neural network with the simulated annealing (SA) procedure. In other words, the proposed approach reduces the total cost of an AGV delivery path from one workstation to another on the shop floor. By changing the temperature of the two-stage SA, a solution can be found that avoids potential collisions between AGVs. Both the flow path and the potential collision, which are major problems in AGV systems, may be solved simultaneously by the proposed neural network approach. Other advantages offered by the proposed method are its simplicity compared with operations research (OR)methods and a decreased number of needed AGVs. The performance of the approach is also investigated.     

精密微小装配系统柔性化技术

随着产品的微小型化, 人工装配作业的难度增大, 无法满足高性能微小器件装配的要求, 研制微小装配自动化设备是解决装配难题的有效途径。由于装配任务的多样化, 同时伴随着器件的改进或产品的升级, 以及缩短研发周期等诸多因素, 要求研制的微小装配设备能够对产品的快速变化做出响应。因此, 柔性化微小装配设备的研发是应对这一挑战的关键。本文重点介绍提升微小自动化装配系统柔性化的主要技术和方法, 即设备模块化方法和微小零件操作工具的自动换接, 并总结了研究进展, 在此基础上, 面向某一类微小器件的精密装配,提出了柔性微小装配设备的系统架构, 并简要介绍了基于这些系统架构所研制的精密微自动化装配设备。论文旨在为柔性化微小装配设备的研制提供一定的参考。     

Heuristic,storage space minimization methods for facility layouts served by looped AGV systems

An analytical method for predicting work-in-process storage requirements resulting from a fixed number of looping, automated guided vehicles (AGVs) serving a line layout is described. The method is based on a model of storage queue dynamics that predicts material flow rates and vehicle response times resulting from vehicle dispatching within a single loop system. The method is applied in the development of two heuristic, random number driven procedures designed to perform sequential search for WIP storage minimizing line layouts over alternative AGV fleet sizes. The first algorithm is a greedy, ‘CRAFT like’ procedure based on local improvement in storage requirements using random, pairwise exchanges of workcentre locations. The second algorithm is a modification to the greedy procedure using simulated annealing methods designed to avoid trapping at local minima. Limited computational studies using the methods are reported.     

基于eM-Plant软件的液压支架装配线物流仿真与优化

以eM-Plant软件为平台,对混流装配线进行仿真建模.在某液压支架项目建成之前,对订单所包含的产品种类、型号规格、需求数量、交货期及物流配送情况进行仿真,并合理优化小车数量、速度和装载量等参数.认为AGV小车为5台,运行速度为1.2m/s,运载量为20件的方案较优.