Object oriented modelling and development of a dispatching algorithm for automated guided vehicles

The main problem for an automated guided vehicle (AGV) dispatching system is to assign vehicles to transport demands which optimise some predetermined objectives of a manufacturing shop. This paper presents a framework for an AGV dispatching system based on an object oriented approach using the unified modelling language (UML), and the development of a dispatching algorithm to facilitate a human controller to dispatch efficiently a fleet of AGVs in response to calls from any shop floor (or machine) operator. The main reason for this work is to model an AGV dispatching system as well as to develop a dispatching algorithm which can record details of the AGV position and movement and ensure their allocation of new orders. The provision of both immediate and pre-booked orders for an AGV is also incorporated in the proposed AGVs dispatching system. The underlying AGV dispatching system and algorithm are capable of dispatching a vehicle automatically to handle a call at the required time. In order to overcome difficulties associated with tackling immediate orders, pre-booked orders, and processing of information related to AGVs, a comprehensive dispatching algorithm is developed which aims to minimise lateness, traveling time and distance of empty vehicles in a simulated job-shop scenario. The effectiveness of the proposed framework for an AGV dispatching system is shown through a test problem.     

Vehicle requirements model for automated guided vehicle systems

A simulation-based cost model is presented for determining the number of automated guided vehicles (AGVs) needed to meet the material handling requirements in a manufacturing system. The estimation of the number of vehicles is based on the sum of the idle-time costs of vehicles and machines, and the cost of waiting time of parts. While an increase in the number of vehicles reduces the waiting time of parts and the idle time of machines, it increases the idle time of vehicles. The application is illustrated using a hypothetical manufacturing system.     

A Schema for Flexile Equipment Control in Manufacturing Systems

In this work a methodology is proposed for increasing the flexibility of the control software of Flexible Manufacturing Systems (FMSs). This greater flexibility is required due to factors such as uncertain product demand, uneven distribution of shop load, and machine or cutting tool unavailability. In the proposed framework the following modules were developed: (a) an automated process planning module which generates non-linear process plans for a given part, considering the shop floor resource availability; the non-linear plans include both material handling and material processing information; (b) a planning module that linearises the process plan aiming at minimising the total manufacturing time of the parts; (c) a NC program generation module, which generates the NC program for the chosen CNC machine(s). In order to increase the flexibility of the control software even more, a resource model was devised and implemented, which provides the necessary resource information for the above modules. Each of these modules is described within this paper, and details about the part and process plan representation necessary for this implementation are also given. A case study is presented in order to show the capability of the methodology.     

A mathematical programming approach to simultaneous unit-load and fleet-size optimisation in material handling systems design

This paper develops a model for simultaneously determining the optimal performance-based unit-load and fleet sizes for material handling vehicles serving work stations in a manufacturing system. The mathematical programming model maximises the number of units transported by the material handling vehicle during a given production cycle. The optimisation model simultaneously specifies the unit-load and fleet sizes, based on material transportation requirements and system characteristics.     

New hybrid vision-based control approach for automated guided vehicles

Automated guided vehicles (AGVs) are a common choice made by many companies for material handling (MH) in manufacturing systems. AGV-based internal transport of raw materials, goods, and parts is becoming improved with advances in technology. Demands for fast, efficient, and reliable transport imply the usage of the flexible AGVs with onboard sensing and special kinds of algorithms needed for daily operations. So far, the majority of these transport solutions have not considered the modern techniques for visual servoing, monocular SLAM, and consequently, the usage of camera as onboard sensor for AGVs. In this research, a new hybrid control of AGV is proposed. The main control algorithm consists of two independent control loops: position-based control (PBC) for global navigation and image based visual seroving (IBVS) for fine motions needed for accurate steering towards loading/unloading point. By separating the initial transportation task into two parts (global navigation towards the goal pose near the loading/unloading point and fine motion from the goal pose to the loading/unloading point), the proposed hybrid control bypasses the need for artificial landmarks or accurate map of the environment. The state estimation of the robot pose is determined in terms of monocular SLAM, via extended Kalman filter coupled with feedforward neural network—the neural extended Kalman filter (NEKF). NEKF is used to model unknown disturbances and to improve the robot state transition model. The integration of the new hybrid control and NEKF has been tested in laboratory with the mobile robot and simple camera. Experimental results present the effectiveness of the proposed hybrid control approach.     

A guidance technique for an automated guided vehicle

Automated Guidance Vehicles' guidance techniques, make use, in most vehicles, of a painted strip or a cable buried in the floor. Free ranging vehicles are now also available in limited types but at prohibitive cost. This work presents a type of guidance technique whereby the vehicle follows a path created by the light emitted from suspended fluorescent lights. The method has been tested on a multi-directional vehicle. The results are encouraging when compared with other available guidance techniques. The possible integration of this guidance method with a navigation method could make AGVs more attractive to most of the manufacturing environments. The design, implementation and experimental results are outlined and described.     

跨单元调度及其车辆路径集成优化

为了提高跨单元调度中车辆利用率,降低运输成本和缩短完工时间,综合考虑调度方案中零件的加工顺序和异常件运输路径之间的相互影响,建立了一个以最小化最大完成时间和总成本为优化目标的跨单元调度及其车辆路径集成优化模型.提出了一种包含工序编码、机器编码、单元编码、车辆编码和车辆路径编码的五段式编码方法;设计了基于分解的多目标进化...     

A Multi-Agent-Based Agile Shop Floor Control System

The ability of an enterprise to deliver new products quickly and efficiently to market is often the chief determinant of competitive success. The shop floor control system must be an open dynamic system with the capability of adapting and accepting radical unpredictable changes in its structures and industrial practices. This paper presents a new architecture for an agile shop floor control system. The architecture is based on the methodology of multi-agent systems in distributed artificial intelligence (DAI). The multi-agent system has some common characteristics such as: distribution, autonomy, interaction, and openness, which are helpful for transferring traditional architecture to a distributed, cooperative architecture for a shop floor control system. A bidding method based on the required production cost and processing time is also proposed. Using a distributed object-oriented technique, a CORBA-based multi-agent framework for an agile shop floor control system is constructed to integrate all the activity of the shop floor into a distributed intelligent open environment. To implement the framework, a coordination model between agents and behavioural models of some representative agents are established.     

Hybrid shop floor control system for Computer Integrated Manufacturing (CIM)

A shop floor can be considered as an important level to develop Computer Integrated Manufacturing system (CIMs). However, a shop floor is a dynamic environment where unexpected events continuously occur, and impose changes to the planned activities. To deal with this problem, a shop floor should adopt an appropriate control system that is responsible for the coordination and control of the manufacturing physical flow and information flow. In this paper, a hybrid control system is described with a shop floor activity methodology called Multi-Layered Task Initiation Diagram (MTD). The architecture of the control model contains three levels: i.e., the shop floor controller (SFC), the intelligent agent controller (IAC) and the equipment controller (EC). The methodology behind the development of the control system is an intelligent multi-agent paradigm that enables the shop floor control system to be an independent, an autonomous, and distributed system, and to achieve an adaptability to change of the manufacturing environment.     

Modeling and solving a one-supplier multi-vehicle production-inventory-distribution problem with clustered retailers

This paper considers a supply chain management problem which integrates production, inventory, and distribution decisions. The supply chain is composed of one supplier production facility and several retailers located in a given geographic region. The supplier is responsible for the production and the replenishment of the inventory of retailers, in a vendor managed inventory (VMI) context. The distance between retailers is negligible compared to the distance between the supplier and the retailers’ region. Thus, for each vehicle, there is a major fixed cost for traveling to the cluster of retailers and a minor fixed cost for visiting each individual retailer. The problem consists of determining quantities to be produced, quantities to be delivered to retailers, vehicles to be used, and retailers to be serviced by each vehicle. This problem is an extension of the one warehouse multi-retailer problem with the consideration of production planning and storage and vehicle capacity limitations in addition to fixed vehicle utilization costs and retailer servicing costs. The objective is to minimize a total cost composed of production, transportation, and inventory holding costs at the supplier and at the retailers. Two mixed integer linear programming formulations are proposed and six families of valid inequalities are added to strengthen these formulations. Two of these families are new and the others are adapted from the literature. The numerical results show that the valid inequalities considerably improve the quality of the formulations. Moreover, the parameters that influence the most computational times are analyzed.     

低地板公共汽车的开发技术

低地板公共汽车是一种新型的运输工具，代表着公共交通未来的发展趋势。低地板车辆是各种新技术，新设计的综合体现。本文详细介绍了低地板车辆的设计原则，分析了各种新技术的特点和发展趋势。     

Vehicle dispatching for highly loaded semiconductor production considering bottleneck machines first

Semiconductor wafer fabrication lines can be characterized by re-entrant product flow, long production lead-time, large variety of production processes, and large capital investment. These distinctive characteristics make the flow control in the fab very complicated. Throughput rate and lead-time are among the most important performance measures. The throughput rate is usually determined by a bottleneck resource, and the lead-time depends on the machine utilization level and the amount of variability in the system. Due to the high efficiency of material handling and reduced particles, automated material handling systems such as automatic guided vehicles (AGVs), overhead hoist transporters (OHTs), and overhead shuttles (OHSs) are being widely used in wafer fabrication lines (wafer fabs) instead of human operators. Although a material handling system itself is seldom a bottleneck of production in a fab, it is important for that to effectively support the bottleneck machines to maximize the throughput and reduce production lead-time. This paper presents a vehicle dispatching procedure based on the concept of theory of constraints, in which vehicle dispatching decisions are made to utilize the bottleneck machines at the maximum level. Simulation experiments have been performed to compare the proposed vehicle dispatching procedure with existing ones under different levels of machine utilization, vehicle utilization, and local buffer capacity.     

基于虚拟现实的汽车操纵稳定性试验技术

汽车操纵稳定性试验对汽车的主动安全性有着重要影响。随着汽车工业的发展，汽车的行驶速度不断提高，因而对汽车操纵稳定性的试验和评价方法也提出了更高的要求。车辆道路试验的巨大成本和对汽车工作原理日益深入的了解使得在计算机上仿真汽车操纵稳定性试验成为必要和可能。本文介绍了将先进的计算机仿真技术-虚拟现实技术应用于汽车操纵稳定性试验的现状，并对其应用前景做了展望。     

Estimation of Part Waiting Time and Fleet Sizing in AGV Systems

As manufacturing systems have grown in size and complexity, material flow control has become one of the key issues for system efficiency, and determination of the number of vehicles required is an important issue in the design of the AGV (automatic guided vehicle) systems for automated material flow control. In an AGV system, a part issues a delivery request for its transportation, and then an empty vehicle is assigned based on a pre-determined vehicle selection rule and provides delivery service. This research presents a fleet sizing procedure for an AGV system with multiple pickup and delivery stations. A queueing model is used to estimate part waiting times. The fleet sizing procedure estimates the minimum number of vehicles needed to ensure a predefined part waiting time limit. While most stochastic models assume first-come-first-served or random vehicle selection rules for the selection of an empty vehicle, this model considers such additional rules as the nearest vehicle selection rule, which is the most popular among all vehicle selection rules. The performance of the proposed model is examined through computational experiments. This work was supported by Korea Research Foundation Grant (KRF-2003-042-D20136).     

基于双单元制造模式的车间调度控制系统

基于敏捷制造思想研究了离散生产类型的先进制造车间的调度控制系统。在研究双单元制造模式运行和组织特点的基础上，给出了单元重组方法。研究了先进制造车间生产任务管理、生产计划、车间调度、生产运行控制、生产信息管理等问题，提出了以单元动态重组技术为基础的车间生产调度控制系统。     

基于多Agent的网络化车间制造系统调度问题研究

提出一种基于多Agent的网络化车间调度方法，给出任务驱动的网络化车间多Agent调度模型，提出了车间调度的综合指标，分析了模型中各Agent的主要功能和调度过程的算法流程。在此基础上，针对不同的动态事件，讨论了相应的调度策略，以实现网络化车间任务的分配和再调度。     

Multi-items ordering model considering transportation constraint on the inventory management

Ordering multi-items from a vendor is a standard business practice. It is also common for a purchaser to have some constraints such as a budgetary limitation, warehouse capacity restriction or transportation problems. As a result, the problem of making ordering decisions for multi-items with various constraints is regarded as an important issue on the inventory management. In this paper, we propose a new ordering model for multi-items with the mixed parts transportation problem based on the warehouse system. Order range is especially introduced and used as decision parameters instead of order point to order multi-items. Finally, a numerical example and computational results are given to illustrate the proposed model.     

自动化分拣仓库中多AGV调度与路径规划算法

自动化分拣仓库由多自动导引小车(AGV)同时作业,对大量包裹进行快速分拣。如何为AGV确定搬运包裹序列并规划无冲突的路径,是分拣作业的关键所在。为提高分拣效率,以最小化最大搬运完成时间为目标,定义了冲突AGV的优先级,提出一种生成无路径冲突的路径规划算法;进而,综合考虑AGV调度和路径规划,提出一种改进差分进化算法,算法采用反学习方法生成初始种群,运用自适应的变异和交叉概率进行进化操作,设计动态差分进化策略来提高收敛速度,并设计交换邻域和基于关键AGV的插入邻域进行局部搜索。通过数据实验验证了算法的有效性,并对关键问题参数进行了分析。     

Operation of AGVs using information derived from encoded tiles

Flexible manufacturing systems technology requires a versatile means of moving parts and components from one point to another within the production process, a function which is increasingly being performed by means of Automatic Guided Vehicle (AGV) systems. Conventionally, such systems have operated by following a buried cable or a line marker on the floor of the building. More recently, Free Ranging Automatic Guided Vehicles (FRAGV) using laser based triangulation and other techniques have made an appearance, while navigation systems based on the use of binocular or trinocular vision are under development. However, the bulk of the AGVs currently deployed or likely to be deployed in the near future will almost certainly be of the conventional, line following type. This paper discusses a means by which the operational flexibility of such AGVs can be enhanced by introducing a navigation system based on the use of a series of encoded ‘tiles’. These ‘tiles’ can be rapidly positioned on a floor, and operate in association with a vehicle mounted sensor array as detector to provide information on the current position and heading of the AGV, enabling it to manoeuvre ‘off-wire’ in situations such as docking or at complex junctions. The construction of the ‘tiles’ and the operation of the sensor array are presented, together with the software structures required for navigation.     

An new approach for the automatic analysis and control of material handling systems: integrated layout flow analysis (ILFA)

In the majority of small and medium sized enterprises (SEMs), the direct costs of material handling cannot be clearly measured. There are several reasons for this, including the large number of product types, complexity of their production cycle, and continuous change in markets. Therefore, production managers require flexible tools to create a suitable material handling system model which explicitly and rapidly calculates the indices required as these are traditionally neglected or laboriously approximated, (i.e., time and cost in material flow inside the factory, storage area requirements, and MH utilization percentage). This paper proposes an integrated approach to analyzing and controlling material handling operations in an industrial manufacturing plant from a “full quantitative” point of view. The model presented unites quite different fields of research into a unique methodology. This material handling model rapidly and automatically provides production managers with extensive and significant information. As a result, integrated layout flow analysis interrelates systematic layout planning with operational research algorithms and visual interactive simulation, using a complete software platform to implement them. This integrated layout flow analysis approach focuses on determining the space requirement for manufacturing department buffers, the transportation system requirements, the performance indices, and the time and cost of material flows spent in the layout and in MH traffic jams.