International journal of computer integrated manufacturing , tập 24, số 5, 2011

International Journal of Computer Integrated Manufacturing Vol 24, No 5, May 2011, 375–377 EDITORIAL Special issue on ‘6th CIRP-Sponsored International Conference of Digital Enterprise Technology (DET2009) – Enterprise Informatics’ The CIRP-Sponsored International Conference of Digital Enterprise Technology (DET2009) was held on 14–16 December 2009 at The University of Hong Kong This international conference series of Digital Enterprise Technology aims to provide a forum for academia and industrialists to disseminate, to all branches industries and businesses, information and knowledge on the most recent and relevant innovations, theories and practices in electronic business and digital enterprise technology This special issue is based on contributions carefully reviewed and extended from the Proceedings of DET2009 on the topic of Enterprise Informatics Enterprise Informatics deals with the optimal use of enterprise-level information and knowledge to support decision-making processes and/or dayto-day operations Eleven papers were eventually selected out of over 130 DET2009 contributions They cover a set of issues concerning some important research and application developments of enterprise informatics technologies, forming the broad basis of research agenda to identify and explore the ways in which users and their actions can be facilitated The issue begins with a paper entitled ‘Planning towards enhanced adaptability in digital manufacturing’ by Wang The paper presents an integrated approach for developing a web-based system with enhanced adaptability, including distributed process planning, real-time monitoring and remote machining This approach is enabled by a Wise-ShopFloor (Web-based integrated sensor-driven e-ShopFloor) framework targeting distributed yet collaborative manufacturing environments It allows end-users to plan and control distant manufacturing operations based on runtime information from shop floors An example of distributed process planning for remote machining is chosen to demonstrate the effectiveness of the approach towards web-based digital manufacturing Bottlenecks, as the key ingredients for improving the performances of the production networks, have been profoundly studied However, the major definitions of bottlenecks are derived in terms of the throughput and based on the Theory of Constraints (TOC) In the paper ‘Modelling dynamic bottlenecks in production networks’, Scholz-Reiter et al develop a systematic and comprehensive definition of dynamic bottlenecks of the production networks based on both ISSN 0951-192X print/ISSN 1362-3052 online Ó 2011 Taylor & Francis DOI: 10.1080/0951192X.2011.568841 http://www.informaworld.com the TOC and the Bottleneck Oriented Logistic Analysis (BOLA) Distinguishing from the traditional view at the bottlenecks, the defined dynamic bottlenecks are modelled by means of discrete simulation using practical data, aimed at visualising them in the production network By applying the logistic operating curves (LOCs), the practical application of the proposed research and its procedures is discussed in detail Multi-material products are getting increasingly popular in recent years However, no systems have been developed to support the design of such products In the paper ‘A haptic-based part decomposition method for multi-material product design’, Chen et al propose a haptic-based method for designing multi-material products This approach consists of three main parts: haptic painting/marking, boundary smoothing/fitting and volume decomposition The haptic device provides an intuitive user interface for quick volume mark up in a multimaterial product by direct mesh painting Based on the boundaries of painted regions, volume decomposition can be done automatically when needed The numerous iterations of volume mark up and decomposition in the early stage of multi-material product design can now be made easy and effective with the proposed method The paper ‘Optimal service selection and composition for service-oriented manufacturing network’, by Huang et al presents the service management of service-oriented manufacturing network (SOMN) It considers the key problem, the optimisation of service selection and composition, to realise the integration and optimisation of services in an open environment which contains large amounts randomicity and uncertainty The integrated performance evaluation metrics for SOMN is described, which combines the key performance indicators of services from business, service and implementation level The performance evaluation model is brought forward to analyse the local and global performance An uncertainty and genetic algorithm-based method is developed to realise the optimisation of service selection and composition in an effective and efficient way Zhang et al introduce ‘Real-time work-in-progress management for smart object enabled ubiquitous shop 376 Editorial floor environment’ This paper proposes a work-inprogress (WIP) management framework for a ubiquitous manufacturing (UM) environment Under the framework, two types of services and a WIPA (workin-progress agent) are designed and developed To implement the integration of heterogeneous Enterprise Information Systems (EISs), the wipML (work-inprogress markup language) is established based on some important standards such as ISA 95 and B2MML During production execution, real-time visibility explorers are provided for operators and supervisors to reflect the real-time situation of current manufacturing environment The presented framework is studied and demonstrated using a near real-life simplified shop floor that consists of typical manufacturing objects In view of the seamless integration of products, production systems and business processes, the paper ‘Framework for extended digital manufacturing systems’ by Nylund et al deals with their work on building up a framework of EDMS – Extended Digital Manufacturing Systems A reference model of EDMS is presented that consists of manufacturing entities with different roles and similar structures EDMS provides an integrated environment for products, production systems and business processes The theoretical application areas of the past, present and future and the process from ideas to innovative solutions are described A real-life example of an intelligent manufacturing environment is introduced to demonstrate manufacturing development, operation, performance monitoring and measurement, etc of the EDMS framework Production service system (PnSS) is a new business mode where a manufacturer obtains manufacturing resources in the form of continuous production services instead of resource entities In the paper ‘Analytical target cascading enabled optimal configuration platform for production service systems’, Qu et al focus on the configuration platform of the PnSS business mode A systematic PnSS configuration methodology and the enabling platform are developed based on a newly extended Analytical Target Cascading (ATC) method As ATC accommodates heterogeneous sub-system integration and multi-level problem solving, the methodology is able to address the typical challenges that a practical component service PnSS configuration process normally faces, such as distributed decision rights, uncertain decision structure and short decision period In the paper ‘A hierarchical deployment of distributed PLM system in collaborative product development’, Chu et al propose a novel methodology of distributed Product Lifecycle Management (PLM) platform deployment It incorporates information technologies to support collaborative product development in a global enterprise with multiple distributed sites The operational guidelines are provided for determining the hardware configuration integrated from the analysis of the organisational, data, content and application views of the requirements of the enterprise A customised deployment plan that reflects the actual user needs is then generated to construct a cost-effective collaborative PLM platform Finally, a case study is included to demonstrate the feasibility of the proposed methodology One of the most difficult problems in mobile robot navigation is the acurate estimation of the robot’s position and orientation In the paper entitled ‘High accuracy mobile robot positioning using external large volume metrology instruments’, Wang et al present a method of accurately controlling the position of a mobile robot using an external Large Volume Metrology (LVM) instrument such as the laser tracker, a navigation algorithm, and a low cost robot, a repeatability of mm could be achieved over a volume of 30 m radius In addition, a surface digitisation scan of a wind turbine blade section is also demonstrated, illustrating possible applications of the proposed method for manufacturing processes The ‘near-zero inventory production’ and ‘realtime delivery’ is becoming a powerful solution to reduce the inventory cost and improve the production efficiency and benefits for enterprises The paper ‘A RFID-based optimal material delivery for digital plant production’ by Zhou et al uses Radio Frequency Identification (RFID) technology to develop a realtime optimal material delivery method A mathematical model for dynamically obtaining the optimal routes for forklifts is established by taking the minimal travel distance as the objective Then, an Ant Colony Optimisation (ACO)-based real-time optimum route planning algorithm is designed to solve the material delivery problem The feasibility of presented model and algorithm is validated by a case study Evolvable systems has been developed and tested as a next-generation production system paradigm since its inception in 2002 The paper entitled ‘Evolvable systems: an approach to self-X production’ by Onori et al presents current developments and applications of Evolvable Product Systems (EPS) It has been pointed out that the essence of evoluability resides not only in the ability of system components to adapt to the changing operational conditions, but also in the evolution of these components over time such that processes may become self-X, where X stands for one International Journal of Computer Integrated Manufacturing or more desirable system properties such as self evolvable, self reconfigurable, self-tuning, self-diagnosing etc The core approaches and techniques of EPS have been discussed in detail The guest editors would like to thank all the authors for the time and effort in contributing their papers and in incorporating the referees’ comments in revising their manuscripts Thanks are especially extended to the referees in giving their valuable comments to the papers The guest editors are grateful to Springer, the publisher of DET2009 Proceedings, for giving permission to extend the papers for this special issue Finally, the guest editors would like to express their thanks to Professor Stephen Newman (Editor-in-Chief) and the Journal Office for their advice and support that made this special issue project a success Professor George Q Huang Department of Industrial and Manufacturing Systems Engineering, The University of Hong Kong, Hong Kong, PR China gqhuang@hku.hk 377 Professor Yingfeng Zhang Key Laboratory of Contemporary Design and Integrated Manufacturing Technology, Ministry of Education, Northwestern Polytechnical University, PR China zhangyf@nwpu.edu.cn Professor T Qu Faculty of Electromechanical Engineering, Guangdong University of Technology, Guangdong, PR China quting@gdut.edu.cn Professor Paul G Maropoulos Department of Mechanical Engineering University of Bath, UK P.G.Maropoulos@bath.ac.uk International Journal of Computer Integrated Manufacturing Vol 24, No 5, May 2011, 378–390 Planning towards enhanced adaptability in digital manufacturing Lihui Wang* Virtual Systems Research Centre, University of Sko¨vde, Sweden (Received 25 March 2010; final version received July 2010) This paper presents an integrated approach for developing a web-based system with enhanced adaptability, including distributed process planning, real-time monitoring and remote machining The objective is to develop a new methodology and relevant processing algorithms for enhancing adaptability in digital manufacturing This approach is enabled by a Wise-ShopFloor (Web-based integrated sensor-driven e-ShopFloor) framework targeting distributed yet collaborative manufacturing environments Utilising the latest Java technologies (Java 3D and Java Servlet) for system implementation, it allows end-users to plan and control distant manufacturing operations based on runtime information from shop floors Details on the principle of the Wise-ShopFloor framework, system architecture, and a prototype system are reported in this paper An example of distributed process planning for remote machining is chosen as a case study to demonstrate the effectiveness of this approach toward web-based digital manufacturing Keywords: process planning; web-based monitoring; remote machining; digital manufacturing Introduction In the last decade, digital manufacturing has emerged as the norm of manufacturing in a computer- and/or web-based environment This is largely due to the global business decentralisation and outsourcing, where the large-scale operations are better tested digitally than physically To stay competitive in the global market, companies with distributed operations are demanding a new way of effective collaborations between themselves and service providers Among many factors, flexibility, timeliness and adaptability are identified as the major characteristics in this research to bring dynamism to manufacturing Targeting the manufacturing dynamism in a distributed environment, this research introduces a Wise-ShopFloor (Web-based integrated sensor-driven e-ShopFloor) framework for distributed process planning, dynamic scheduling, real-time monitoring, and remote control This approach is supported by sensors, function blocks, as well as Java and Web technologies The Wise-ShopFloor is designed to use the popular B/S (browser/server) architecture, as well as VCM (view-control-model) and publish-subscribe design patterns for effective information sharing during decentralised planning and control The rest of the paper is organised as follows In Section 2, enabling technologies including Web, Internet, Java 3D and Java servlets are introduced based on a brief literature review It is followed by a description *Email: lihui.wang@his.se ISSN 0951-192X print/ISSN 1362-3052 online Ó 2011 Taylor & Francis DOI: 10.1080/0951192X.2010.506657 http://www.informaworld.com of the Wise-ShopFloor framework in Section Details on adaptive and distributed process planning are presented in Section 4, which leads to web-based real-time monitoring and control documented in Section A case study using planning results for web-based remote machining are described in Section Finally, contributions are summarised in Section Enabling technologies With the growing manufacturing decentralisation, products and services are distributed everywhere and sourced anywhere along supply chains Product design and fabrication have shifted rapidly from intracorporation to global networks How to coordinate manufacturing activities and keep them under control is a challenging issue Flexibility, timeliness and adaptability of manufacturing operations are the essential requirements for digital manufacturing in such a dynamic environment Fortunately, the Web infrastructure today is mature enough to form a distributed manufacturing network through browserserver inter-connections In addition to the Web technology, Java has brought about a fundamental change in the way that applications are designed and deployed With Java, the browser paradigm has emerged as a compelling way to produce collaborative applications over the Web Examples include WebCADET (Caldwell and Rodgers 1998) for collaborative International Journal of Computer Integrated Manufacturing design, CyberCut (Smith and Wright 1996) for rapid machining and other efforts (Deek et al 2003, Azevedo et al 2004) In terms of technologies used in the existing systems, HTML, Java applets, ActiveX, and VRML are widely adopted for developing client-side user interfaces At the server side, technologies including JSP (JavaServer Pages), Java Servlets, and XML are obtaining attentions for new system development To facilitate a viable collaborative system, its application server must engage users in a 3D graphical interaction in addition to the dialogue-like data sharing, because remote users need visual aids to coordinate their efforts in a digital environment Today, digital manufacturing tops the wish list for many manufacturers Unfortunately, most of the manufacturing equipment of today does not have the built-in capability to transmit and receive data Few of the available Web-based systems are designed for shopfloor monitoring and control or for advanced factory automation Some related systems listed below are limited in their functionality and platform requirements The latest Cimplicity (GE Fanuc 2008) allows users to view a factory’s operational processes through an XMLbased WebView screen, including all alerts on every Cimplicity system The FactoryFlow of Unigraphics Solutions (USA) can provide off-line factory layout planning, material handling, and simulation (Waurzyniak 2001) By most estimates, the number of CNC machines capable of linking to the Internet is less than 10% of the installed base, according to Waurzyniak (2001) Seeking the opportunity in linking CNC machines with the Internet, MDSI (USA) uses OpenCNC (MDSI 2008) to automatically collect and publish machine and process data on a network In 1999, Hitachi Seiki (Japan) introduced FlexLink to its turning/machining centres (http://www.flexlink.com) Since 1998, Mazak has operated its high-tech Cyber Factory concept (Mazak 1998) in Japan The fully networkable Mazatrol Fusion control allows Mazak machines to communicate over wireless factory networks for real-time machine tool monitoring and diagnostics In addition, Japanbased Mori Seiki introduced a CAPS-NET system that polls machine tools on Ethernet at settable increments, usually five-second or longer, for engineers to get updates on machine tools’ run-time status in production (Mori Seiki 2009) To bring legacy machine tools with serial ports on-line, e-Manufacturing Networks Inc (now Memex Automation, Canada) introduced its ION Universal Interface and CORTEX Gateway (Memex 2009) to help the old systems go online Despite various accomplishments, the available systems mentioned above are either for off-line simulation or for monitoring only Most systems require a specific application to be installed instead of using a standard user interface such as a web 379 browser, which reduces a system’s portability Remote shop-floor monitoring and control remain impractical as web-based applications owing to real-time constraints Reducing network traffic, increasing system performance, and overcoming security barriers are the major concerns in web-based system developments To bridge the gap, a sensor-driven approach is proposed in this research for real-time monitoring so as to facilitate web-based planning and control for digital manufacturing Web and Java technologies are also adopted as enabling technologies for system implementation Details on how the two technologies can work together are explained below Wise-ShopFloor framework The Wise-ShopFloor framework has been designed to provide users with a web-based and sensor-driven intuitive environment where distributed process planning, dynamic scheduling, real-time monitoring and remote control are undertaken Within the framework, each machine should become an information node and be a valuable resource in the information network A direct connection to sensors and machine controllers is used to continuously monitor, track, compare, and analyse production parameters Instead of camera images (usually large in data size), a physical device of interest (e.g a milling machine) can be represented by a Java 3D model with behavioural control nodes embedded Once downloaded from its application server, the 3D model is rendered by the local CPU and can work on behalf of its remote counterpart showing real behaviour for visualisation at a client side It remains alive by connecting with the physical device through low-volume message passing (sensor data) In addition to motion data, other sensor data including temperature, vibration and force can also be transmitted via network and shown in colours or contour lines on the 3D model for machine condition monitoring As the 3D model is driven by the sensors and rendered locally for visualisation, there is no need for transmitting camera images over the Internet The largely reduced network traffic makes real-time monitoring and remote control practical for dispersed users It also enables users to make accurate decisions in a timely manner, and to ensure that machines are operating within defined expectations Being able to plan and control shop-floor operations from anywhere yet at any time, collaboratively, is what this research is aiming at Figure illustrates the architecture of the Wise-ShopFloor framework The framework is designed in B/S architecture using VCM design pattern with built-in secure session control The mid-tier application server handles major security concerns, such as session control, session 380 Figure L Wang Wise-ShopFloor framework registration, sensor data collection and distribution, planning and scheduling, as well as real device manipulation A central Session Manager is to look after the issues of user authentication, session synchronisation, and sensitive data logging All initial transactions need to go through the Session Manager for access authorisation In a multi-client environment, different users may require different sets of data or logic for different tasks For example, in the case of monitoring, it is not efficient to have multiple users who share the same model talking with the same device at the same time Publish-subscribe design pattern is adopted to collect and distribute sensor data at the right time to the right user, efficiently As a server-side module, the Signal Collector is responsible for sensor data collection from networked physical devices The collected data are then passed to another server-side module Signal Publisher who in turn multicasts the sensor data to the registered subscribers (clients) through applet-servlet communication A Registrar is designed to maintain a list of subscribers with the requested sensor data when the subscribers have selected appropriate machines for monitoring, including IP address and port number of each subscriber, along with the chosen machine A Java 3D model can thus communicate indirectly with sensors no matter where the client is HTTP streaming is chosen as the communication protocol between server and clients Although the global behaviours of a Java 3D model are controlled by the server based on real-time sensor signals, users still have the flexibility of viewing the model from different perspectives at a client side In order to control a device, an authorised user can send control commands to the application server which in turn manipulates the physical device The Wise-ShopFloor framework provides an alternative of camera-based monitoring through Java 3D models Nevertheless, an off-the-shelf web-ready camera can easily be switched on remotely to capture an unpredictable (un-modelled) scene for diagnostic purposes Distributed process planning 4.1 Architecture design Figure shows the detailed architecture of a new CAPP (computer-aided process planning) module In the current Wise-ShopFloor, the process planning is dedicated to machining operations and is realised by a two-layer structure of shop-level Supervisory Planning and machine-level Operation Planning A process plan generally consists of two parts: generic data (machining method, machining sequence, and machining strategy) and machine-specific data (tool data, cutting parameters, and tool paths) Such a two-layer structure can separate generic data from machine-specific ones Since resources, knowledge, and decisions are both logically and geographically distributed, such a process planning approach is also named Distributed Process Planning (DPP) (Wang et al 2003) 381 International Journal of Computer Integrated Manufacturing Figure Architecture of distributed process planning The supervisory planning focuses on product data analysis, machining feature (m-feature) parsing, setup planning, machining process sequencing, and machine selection, while the operation planning considers jig/ fixture selection and detailed working steps for every machining operations, including cutter selection, cutting parameters assignment, tool path planning, and control code generation At the supervisory planning stage, the decisions made are generic and applicable to all machines Process optimisation is performed at the operation planning stage when specific resources (machine, tool and fixture) are known and within a relatively small search space for better adaptability Job assignment and dispatching to the best available machines are dealt with by a separate dynamic scheduling module 4.2 Process sequencing One critical task in process planning is machining sequence generation Since a part design can be decomposed into basic m-features (such as hole, slot, pocket, etc.), the task of machining process sequencing is literally treated as the task of putting m-features into proper setups and in the right sequence, which is called m-sequencing in DPP A generic process plan, as a result of m-sequencing, only consists of machineneutral information in the form of machining sequence, including both critical (with datum references and other manufacturing constraints) and non-critical machining operations Some of the non-critical sequences are presented in parallel whose specific sequence will be determined by a CNC controller during operation planning Before an m-feature can be machined, it must be grouped into a setup for the ease of fixturing The basic idea of feature grouping is to determine a primary locating direction of a setup, and group the appropriate m-features into the setup according to their pre-defined tool access directions This process is repeated for a secondary locating direction and so on until all the m-features are properly grouped Here,* a primary locating direction is the surface normal V of the primary locating surface (LS) It can be determined by the following equations: Aà Tà fðAÃ; TÃÞ International Journal of Computer Integrated Manufacturing Figure 15 Mini-omniMove control station A MatLab script was used to create the 10waypoint grid for the robot The position of the SMR is measured every mm the robot travels The raw data from two trials are plotted in Figure 12 The robot took slightly different paths in the two trials, especially in the beginning, because the starting positions of the robot were different The scanned data can then be imported into CAD software, such as Catia V5, as shown in Figure 13, in which a surface can be fitted to the data cloud The fitted surface is then offset in the surface normal direction, by a distance equal to the radius of the SMR, taking into account that the measurement data corresponds to the centre of the SMR and not the surface measured Since the data is acquired at laser tracker accuracies (20–30 mm), it can be used for operations such as reverse engineering, metrology-assisted assembly, or quality control Further work on the indoor global positioning system guidance of the KUKA omniMove The KUKA omniMove platform is a scalable omnidirectional vehicle that is designed primarily for material handling, replacing lift trucks, trolleys and overhead cranes The omni-directional drive mechanism allows the vehicle to travel in any direction and orientation The omniMove platforms come in sizes ranging from less than half a metre long with a few kilograms capacity to over tens of meters long and with over tens of tons of load capacity All current omniMove vehicles are driven manually by a trained operator KUKA Robotics UK is interested in developing the omniMove into an AGV to increase production line automation.Preliminary trials showed that the iGPS is a very suitable system for providing the position and orientation data to drive an omniMove-type AGV Only a small amount of 491 Figure 16 Full-scale omniMove moving to waypoint under iGPS guidance additional work was needed to adapt the Lego robot control software to control an omni-directional vehicle The working mini-omniMove (Figures 14 and 15) was demonstrated at the Airbus ALCAS (Advanced Low Cost Aircraft Structures) open day on 20–22 October 2009 Work is currently being carried out to trial the system on a full size omniMove (Figure 16) in a simulated production environment Conclusions In this paper, the possibility of using an external LVM instrument such as the laser tracker in mobile robot navigation was investigated The repeatability of the robot was experimentally determined to be mm and there exists room for improvement in the robot navigation algorithm A surface scanning of a wind turbine blade section was also demonstrated, illustrating possible applications of the method for manufacturing processes.Metrology guidance simplifies many of the most difficult problems in mobile robot navigation, and the accurate metrology information allows the robot to perform tasks such as measuring the shape of an irregular surface, which would have been very difficult to automate A number of improvements can be made in the robot hardware and navigation algorithm For example, a proper digital filter may be used to calculate better estimates of the robot course at any given time, rather than the mm distance limit used in the experiments described in this paper Other onboard sensors such as an inertial navigation system may also be used in conjunction with the laser tracker, to improve navigation and achieve DOF measurements 492 Z Wang et al Given the reliability and accuracy of the LVM position data and reduced complexity in integration, the methods described in the paper are currently being applied to develop an industrial AGV prototype Acknowledgements This research has been carried out as part of the IdMRC at the Department of Mechanical Engineering of the University of Bath, under EPSRC Grant Nos EP/E002617/1 and EP/ E00184X/1 The funding of EPSRC and the support of our industrial partners is gratefully acknowledged This article has been presented in the DET2009 conference held at the University of Hong Kong during 14–16 December 2009 and included in the conference proceedings published by 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environments Robotics and Computer-Integrated Manufacturing, 26, 296–311 Moore, P., et al., 1999 Intelligent semi-autonomous vehicles in materials handling Mechatronics, 9, 881–892 Surmann, H., et al., 2001 A 3D laser range finder for autonomous mobile robots Proceedings of the 32nd ISR (International Symposium on Robotics), April 2001, Seoul, Korea, 153–158, 19–21 Wang, Z., et al., 2009 Experimental testing of the dynamic tracking performance of iGPS and laser tracker Laser Metrology and Machine Performance, IX, 305–314 International Journal of Computer Integrated Manufacturing Vol 24, No 5, May 2011, 493–505 A radio frequency identification based optimal material delivery method for digital plant production Guanghui Zhoua,b, Zhongdong Xiaoc,d*, Pingyu Jianga,b and Yingfeng Zhanga,b a State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, China; bSchool of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049, China; cSchool of Management, Xi’an Jiaotong University, Xi’an 710049, China; dThe Key Lab of Ministry of Education for Process Control and Efficiency Engineering, Xi’an Jiaotong University, Xi’an 710049, China (Received May 2010; final version received January 2011) Currently, Just-in-Time (JIT) is becoming one of the increasingly important manufacturing modes applied by enterprises for surviving in drastic market competition As a key function of JIT manufacturing, the material delivery characterised by real time, accuracy and optimisation can make sure of JIT’s implementation in enterprises effectively and efficiently In the study, we present a new kind of real-time optimal material delivery method for plant production by utilising radio frequency identification (RFID) technology In the method, the precise and visual layouts for the whole physical plant and all kinds of its inner manufacturing resources such as machines, RFID devices, forklifts and inventories are realised Later, the mathematical model for dynamically obtaining the optimal routes for forklifts is established by taking the minimal travel distance as the objective Particularly, to solve the problem, a real-time optimum route planning method based on the ant colony optimisation (ACO) algorithm is developed In order to monitor and navigate the forklifts in real time during material distribution in the plant for material delivery planners and operators, a position locating scheme for forklifts and materials is proposed Finally, a case study is carried out to demonstrate the feasibility of the presented method, which establishes the base for implementing JIT manufacturing in plant production Keywords: material delivery; RFID; plant production; route planning; monitoring; navigation Introduction Currently, with the progress of market globalisation, customisation and agility, the manufacturing enterprises are changing their production modes from the uniform variety and volume-produce to the batch and variety and small amount for sustaining competitive advantage Especially, along with the Just-in-Time (JIT) manufacturing mode being introduced and adopted by more and more enterprises, the material delivery in plant production characterised by ‘nearzero inventory production’ and ‘real-time delivery’ is becoming the much powerful solution to reduce the inventory cost and improve the production efficiency and benefits for enterprises (Jiang et al 2007, Huang et al 2009) Nevertheless, the growing importance of material delivery as well as the increasing complexity of material delivery networks and the service requirement of plant production has become a challenge to material delivery planners and operators, who are now expected to deliver optimal material services The major concern of material delivery planners and operators is the strategic use of material capabilities *Corresponding author Email: xzd@mail.xjtu.edu.cn ISSN 0951-192X print/ISSN 1362-3052 online Ó 2011 Taylor & Francis DOI: 10.1080/0951192X.2011.554870 http://www.informaworld.com and distinctive competencies to achieve competitive advantage for plant production It makes the material delivery become more complicated and difficult than ever Therefore, the crucial problem to be resolved for implementing material delivery in plant production is to ensure that all kinds of materials required in plant production process are planned and delivered by the right number to the right places at the right time Though more and more manufacturing enterprises realise the importance of material delivery in production and strive for developing effective methods and reliable techniques to reduce material-related cost and enhance production efficiency, material delivery in most manufacturing enterprises still rests on the laggard stage which mainly depends on the traditional experiences of material delivery planners and operators The key issues including intelligent planning and monitoring of material delivery tasks, real-time locating and tracing of the position of forklifts used to deliver the materials, and dynamic route optimisation and navigation of delivery tasks while being delivered cannot be completely fulfilled It unavoidably leads to 494 G Zhou et al the disgusting problems of improper-time delivery or wrong delivery every now and then It not only makes the production process wait behind or break off as well as the delivery delay, but moreover possibly disorganises the whole operation scheduling of plant production, which heavily hinders the JIT manufacturing mode to be taken effect in manufacturing enterprises (Liu and Mei 2009) One of the key issues leading to the above problems is that the capture and collection of realtime information of shop-floor becomes a bottleneck while data processing is no longer an issue of concern with the rapid improvement in computational and communication power in plant production Because the traditional manual data collection and capture systems are time consuming, prone to errors and tedious, and because manual identification sheets are frequently damaged, lost or misplaced, the information does not accurately and promptly reflect the materials/forklifts situations and even the changes of these situations due to disturbances Without up-todate information, it is impossible to make accurate material delivery decisions, no matter how advanced enterprise resource planning (ERP) systems and manufacturing resources are (Huang et al 2009) Therefore, online collection of real-time information of shop-floor is becoming the all-important problem to be resolved for precise material delivery in plant production Because the limitation of using barcoding based technology for automatic object identification (Auto ID) and ‘tracing and tracking’ in manufacturing plant was recognised and discussed as early as in early 1990s (Udoka 1991, 1992), radio frequency identification (RFID) technology (tags and readers) has motivated worldwide sporadic piloting efforts across different product sectors ranging from garment, electronic, mechanical, aerospace and automotive products Johnson (2002) presented an RFID application in a car production line Chow et al (2006, 2007) proposed a real-time knowledge support framework for the development of an RFID-multiagent based process system which has the ability to solve the problems about dynamic logistics process management Poon et al (2009) developed an RFID case-based management system for logistics resource to handle warehouse resources and monitor warehouse operations in supply chain In the manufacturing area, the study of Kohn et al (2005) was an early piece of precious work in addressing repair control of manufacturing systems by using real-time RFID information Then, Huang et al (2007, 2008a,b) paid much attention to applying RFID technology in a typical product assembly flow line and a typical shop-floor with a functional layout for part fabrication Another key issue resulting in the above problems in traditional material delivery is that most existing methods and models for material delivery tasks decision, forklifts route planning, and navigation are not capable of dealing with such real-time information Till now, many researches have focused on solving the routing planning problem for vehicles or forklifts in supply chain or material delivery in which a lot of constructive methods and models have been developed The typical ones include the following: Al-Hasan and Vachtsevanos (2002) presented a 2D route planning model to support operations for an autonomous vehicle conducting missions at high speed in a large natural terrain In this model, an intelligent learning support engine was used to decide the optimal route scheme for vehicles Regarding the logistic decisions towards JIT and agile manufacturing, Shimizu and Wada (2003) developed a non-linear integer model to simultaneously obtain optimal site locations and routes from plants and customers practically and efficiently with the aid of the hybrid Tabu search method Zachariadis et al (2009) developed a hybrid meta-heuristic algorithm to deal with the vehicle routing problem, and the optimal set of routes to satisfy both the delivery and pick-up demand of customer population were obtained Nishi and Maeno (2010) proposed a Perti Net (PN) decomposition approach for the optimisation of route planning of automated guided vehicles (AGVs) in semiconductor fabrication bays Due to classical vehicle routing problems typically not considering the impact of delivery price on the demand for delivery services, Geunes et al (2007) proposed approximation models to plan vehicle route which sought after to maximise profit from delivery service and served as useful tools in the planning phase for delivery providers Huang et al (2009) presented a route planning method for container cranes to minimise the cycle time by calculating the most efficient combination of horizontal and vertical motions of container loading/unloading, and an optimum route solution scheme based on genetic algorithm was developed to obtain the optimal routes for correspondent unmanned cranes Though the developed methods and models are unable to cope with the real-time information, they provide the references for our study on solving the route planning and control in material delivery in plant production Considering the limitations of traditional material delivery methods as well as new material delivery characteristics and requirements derived from current digital plant production, this paper investigates and proposes a new kind of RFID-based optimal method for material delivery in digital plant production With the help of this approach, first of all, the whole physical plant and its inner manufacturing resources including International Journal of Computer Integrated Manufacturing machines, inventories, forklifts and RFID devices are configured and mapped precisely and visually in a computer which establishes the base for implementing the real-time optimal material delivery And then, the mathematical model for obtaining the optimal routes in real time for forklifts is established by taking the minimal travel distance as the objective Particularly, in order to solve the problem, an optimum route planning method based on an ant colony optimisation (ACO) algorithm is developed Thirdly, for facilitating the monitoring and navigation of forklifts in real time during material distribution for material delivery planners and operators, a real-time position locating scheme based on ultra wideband (UWB) technology for forklifts and materials tracking is proposed Finally, a prototype system of RFID-based optimal material delivery in digital plant production is developed and the corresponding case study is carried out to demonstrate the feasibility of the proposed method The presented method and developed software system establish the foundation for implementing JIT manufacturing in digital plant production The rest of this paper is organised as follows Section presents an overall architecture for RFIDbased optimal material delivery in a digital plant and briefly describes the main functional modules In Section 3, we propose the layout schemes for the whole plant and all kinds of its inner manufacturing resources Section formulates a mathematical model and its resolving solution algorithm to obtain the most suitable forklifts with optimal material delivery route solutions in real-time for related material delivery tasks Section develops a position locating method for navigating and tracking the forklifts and delivery tasks in real-time while delivering We devote Section Figure 495 to report and analyse the case study of the presented method and discuss the implications of these results Finally, some conclusions are drawn and future work is discussed in Section Radio frequency identification based optimal material delivery model The RFID-based optimal model for material delivery in digital plant production proposed in this paper is utilised for both material delivery planners and operators to enhance the precise and efficiency of material delivery operations by means of monitoring, tracking and optimising material utilisation Figure shows the overall architecture of the model which involved two functional modules: 1) digital plant layout and; 2) real-time material delivery The digital plant layout module is used to deal with the digital planning and mapping of the whole physical plant and its inner manufacturing resources to makes them visibility and traceability It establishes the foundation to compose the real-time material delivery module The digital plant layout module is divided into five sub-functional modules, which are plant layout, machines layout, RFID devices layout, inventories layout and forklifts layout In order to implement the plant layout well, we take advantage of systematic layout planning (SLP) method as the layout solution whose detailed theory and mechanism is described in Section Supported by the digital plant layout module, the real-time material delivery module is responsible for optimal delivery route planning as well as forklifts and material delivery tasks navigating and monitoring during material delivery, which has three basic tasks Overall architecture of RFID-based optimal material delivery model 496 G Zhou et al The first task is to apply the RFID technology to collect the information about the concrete content and real-time status related to delivery tasks, and current positions and destinations of forklifts; the second one is to propose a mathematical method to effectively obtain the optimal material delivery routes for related forklifts in real time while carrying out the delivery tasks by taking the minimal travel distance as the decision objective; the third one is to realise the realtime monitoring, tracking and navigating of material delivery tasks and forklifts during the material distribution in digital plant Methodology of digital plant layout As mentioned above, digital plant layout is the primary issue for real-time optimal material delivery in digital plant production Therefore, in order to implement the digital plant layout effectively and efficiently, two key problems such as basic layout of the digital plant and the RFID devices selection and layout should be dealt with, whose concrete solutions are addressed in particular as follows 3.1 Basic layout of digital plant The function of the basic layout of the digital plant mainly deals with the overall arrangement and Figure Layout for the digital plant geographical layout of the whole physical plant and its inner manufacturing resources The manufacturing resources in a digital plant mainly contains all kinds of machines, inventories, such as raw material inventory, tool inventory, out-sourcing inventory, and finished product inventory, and forklifts Because the whole physical plant and its inner correspondent manufacturing resources are static and whose dimensions and positions are generally fixed, we introduce the SLP method (Wang and Wang 2005) to implement the basic layout of the digital plant The overall physical plant, machines, inventories, and aisles are simplified as the correspondent proportional rectangles in the light of their actual sizes by means of the SLP method In this way, the whole digital plant is simplified as a large rectangle and its inner static manufacturing resources are simplified as some kinds of small rectangles which are located at the fixed positions according to their relative positions in the digital plant Hereby, the positions of the manufacturing resources are identified by the x and y coordinates in the computer As for forklifts, though their positions are always variable in the digital plant, we can also simplify them as the rectangles whose current positions can be indicated by their x and y coordinates derived from the real-time information acquired by RFID devices Figure illustrates the basic layout of the digital plant International Journal of Computer Integrated Manufacturing 3.2 Radio frequency identification devices selection and layout RFID devices are utilised to accurately indentify materials for delivery, locate the forklifts and monitor the execution of material delivery tasks in real time Since ultra-wideband (UWB) technology can provide very fine range resolution and precision distance and/ or positioning measuring capabilities (Giuliano et al 2004, Hahnel et al 2004, Liu et al 2008), UWB RFID devices are adopted to transfer, define and process position data between the reader, and tags are adopted to accurately locate the forklifts The configuration, as shown in Figure 2, includes a set of four UWB RFID readers located on the vertices of the digital plant square, and the active tags are mounted at forklifts The UWB active tags consist of an internal battery and a short pulse transmitter to provide a much longer reading range and a shorter pulse radio frequency to the readers The tag emits the short pulse signal several times every second With the triangulation logic setup as read by the various readers, the exact x, y coordinates of the active tag can be calculated In doing so, the coordinates of the forklifts in the digital plant are then accurately calculated, and their positions are located and tracked in real time In order to obtain the exact x, y coordinates of the active tag, we propose a hybrid locating solution algorithm combining the angle of arrival (AOA) locating method and the time difference of arrival (TDOA) locating method, whose detailed working mechanism will be described in Section Unlike the real-time location of forklifts, the monitoring and tracking on delivery tasks adopts low-power RFID devices to exchange data wirelessly between passive tags and readers As shown in Figure 2, the passive tag is attached on items such as materials or pallets for loading the materials to record the item identity The tag reader, on the other hand, is integrated to a fixed positioned antenna that is mounted on inventory entrances/exits, machine entrances/exits and forklifts Each reader contains one or more antennas which can recognise and read hundreds of tags within its reading range 497 solution for planning the optimal delivery route is then formulated dynamically by the real-time material delivery module In order to acquire the optimal routes for delivery tasks and forklifts, the mathematical model and solution algorithm should be studied 4.1 Problem description The problem of optimal route planning for real-time material delivery in digital plant production is described as follows (1) There exist m forklifts and n machines or fixed inventories consisting of raw material inventory, tool inventory, work-in-process (WIP) inventory and finished product inventory (2) A delivery task contains q(q ! 1) delivery destinations such as machines or inventories (3) A delivery task can be implemented by several candidate forklifts (4) The objective of material delivery route planning is to obtain the minimal travel distance and related optimal forklift for the delivery task in real time As a matter of fact, in line with the above definition and assumptions, planning the optimal material delivery route of a forklift can be transformed into achieving its weighted-based Hamilton path Accordingly, how to obtain the weighted-based Hamilton path of a forklift becomes a challenge before we calculate the optimal material delivery route As shown in Figure 3, suppose there exist m candidate forklifts locating at different starting positions of the digital Mathematical model and solution algorithm for optimal delivery route planning As one of the focal tasks in the real-time material delivery module mentioned in Figure 1, the optimal route planning for material delivery tasks and forklifts plays an important role in implementing real-time material delivery in the digital plant Based on the realtime information collected and retrieved from passive/ active tags and material delivery task attributes, the Figure delivery Weight-based Hamilton path for material 498 G Zhou et al plant, each forklift can implement the same delivery task which contains q(1 q n) delivery destinations The Hamilton path of forklift p(1 p m) locating at the starting point i for the delivery task is defined as the path which is formed by visiting every vertex once and only once along the edge of a graph that is composed by starting point i and destination 1, 2, , q The shortest distance between two consecutive vertices along an edge is defined as the edge weight Consequently, we further define the weight-based Hamilton path as a special Hamilton path which has the edge weights In this way, through calculating the Hamilton aths of all candidate forklifts and comparing each other, we can obtain the optimal Hamilton path which has the minimal travel distance, and finally, we can select the related optimal forklift to be utilised to carry out the delivery task 4.2 Mathematical model Concerning the above-described problem, the mathematical model for optimal route planning of material delivery is formulated and the objective function is presented in the following equation R ¼ ðR1 ; R2 ; ; Rm Þ ð1Þ where Rp (1 p m) represents the minimal travel distance of forklift p while carrying out a material delivery task It is calculated by the following equation q X q X B C Rp ¼ @ dse zse A Constraint set (3) ensures that the picked starting point is definitely only one before forklift p goes to destination point e; constraint set (4) ensures that a unique destination point e in the case of the starting point had been determined As the initial starting point must be visited first, it is redundant to include (s) and/or e 6¼ in constraint set (3) In this paper, we calculate dse by the following two equations If Xs ¼ Xe, dse ¼ jYs À Ye j ð5Þ If Xs 6¼ Xe, jYs À Yy1 j þ jYy1 À Ye j > > > > = < jYs À Yy2 j þ jYy2 À Ye j dst ¼ jXs À Xe j þ ÁÁÁ > > > > ; : jYs À Yy1 j þ jYy1 À Ye j ð6Þ where (Xs, Ys) is the coordinate of the starting point of the forklift (s ¼ 0, 1, 2, , q); (Xe, Ye) is the coordinate of the destination point of the forklift (e ¼ 1, 2, , q); x1, x2, , xn are the numbers of aisles that are parallel with the Y-axis; y1, y2, , yl are the numbers of aisles that are parallel with the X-axis; fXðx1 ;x2 ; ;xn Þ ; Yðy1 ;y2 ; ;yl Þ gare coordinates of the aisles ð2Þ s¼0 e¼1 s6¼e where s(s ¼ 0, 1, 2, , n) represents the number of the starting point of forklift p before carrying out a delivery task Here, s ¼ denotes the initial position of forklift p, or else it represents the current position where forklift p locates corresponding to the machine or inventory number in the digital plant e(e ¼ 1, 2, , q) represents the number of delivery destination points corresponding to the machine or inventory number where forklift p is to travel dse represents the distance between s and e zse is a decision variable If forklift p goes from s to e, zse ¼ 1; if not, zse ¼ Meanwhile, Equation (2) is subjected by Equations (3) and (4) q X s¼0 q X zse ¼ 1; zse ¼ 1; e¼0 for e ¼ 1; 2; ; q; s 6¼ e ð3Þ for s ¼ 0; 1; 2; ; q; s 6¼ e ð4Þ 4.3 Solution algorithm design In order to effectively resolve the above mathematical model, we adopt an ACO algorithm and design an ACO-based solution algorithm to achieve the optimal routes for delivery tasks and forklifts The principle of the presented ACO-based solution algorithm is similar to an ACO algorithm called Ant System Travelling Salesperson Problem (AS-TSP) (Dorigo et al 1996, Dorigo and Gambardella 1997) Before designing the ACO-based solution algorithm, we define some notations and assumptions listed in the following (1) For forklift p, suppose there exist u ants on the starting point s and be(t) ants on the delivery node e at time t; (2) Denote the tij(t) as the pheromone information on the path between the delivery nodes i and j at time t; (3) Suppose that if Xi ¼ Xj, the distance between the delivery nodes i and j is calculated by Equation (5), if not, it is calculated by Equation (6); (4) Tabu table tabuk is utilised to record the visited nodes of ant k, which is a dynamic growing vector; International Journal of Computer Integrated Manufacturing (5) The moving direction of ant k is decided by tij(t); the transition probability from delivery nodes i to j of ant k at time t is calculated by the following equation: pkij ðtÞ ¼ a b < P½tij ðtފ ýZaij ðtފ j2 = tabuk : k=2tabuk j tabuk ½tik ðtފ ýZik ðtފb ð7Þ where a is the influence of the residual pheromone information on the path between delivery nodes i and j; b is the influence of the heuristic information for path selection; Zij(t) is the heuristic information and is define as  Zij ðtÞ ¼ dij : (6) The update of pheromone information on the path between the delivery nodes i and j is calculated by the following equation: tðt þ q þ 1Þ ¼ rtij ðtÞ þ Dtij ð8Þ where r is the reservation rate of pheromone information; Dtij is the increased residual pheromone information on P the path between delivery nodes i and j,Dtij ¼ uk¼1 Dtkij ; Dtkij is the increased residual pheromone information on the path between delivery nodes i and j of ant k which is calculated by the following formula:  < Q Lk if ant k travel from delivery Dtkij ¼ node i to j; : otherwise where Q is a constant and Lk represents the visiting path length of ant k in a visiting loop On the basis of above-defined notations and assumptions, we design the ACO-based solution algorithm going after the optimal routes for delivery tasks and forklifts The flowchart of the solution algorithm is illustrated in Figure and its working mechanism is described step by step in the following section Real-time position locating scheme for forklifts Locating the real-time position of forklifts plays an important role in optimal material delivery, which acts as the base for real-time monitoring, tracking and navigating the material delivery tasks and forklifts Therefore, the challenge we face is how to propose the suitable real-time position locating scheme for forklifts As described in Section 3, we intend to adopt the 499 UWB RFID technology and design the layout scheme of UWB RFID devices to fulfil the objective The detailed real-time position locating scheme as well as its solution algorithm is specified The real-time position locating framework is illustrated in Figure in which two functional modules are included, namely UWB devices configuration and position locating data acquiring UWB devices configuration module is responsible for the selection and layout of UWB devices including UWB readers and active tags The number of UWB devices mainly relies on the plant dimension and their wave bandwidth The position locating data acquiring module is mainly responsible for calculating the exact coordinates of forklifts attached on active tags which provides the real-time information for delivery tasks and forklifts monitoring, tracking and navigating As shown in Figure 5, four UWB readers and one active tag are selected The active tag sends out the UWB pulses which are received by the fixed UWB readers The fixed UWB readers then send the received pulse signals to the second functional modules – position locating data acquiring module by means of wireless network technology to calculate the exact x, y coordinates of active tag with the aid of the correspondent position locating solution algorithm In this way, the suitable position locating solution algorithm plays an important role As for the position locating solution algorithm, angle of arrival (AOA) and time difference of arrival (TDOA) are two common algorithms which have been widely applied to solve the locating problems of mobile entities whose working mechanisms can be consulted in the literature (Yu et al 2006, Dogancay and Hmam 2008, Boushaba et al 2009) Because solely adopting AOA or TDOA always leads to a poor position locating accuracy, we adopt a hybrid position locating solution algorithm in this paper, which combines the advantages of AOA and TDOA The detailed mechanism is described as follows As shown in Figure 6, assume there exists three UWB devices and one active tag, the transferring time of pulse signals from active tag to UWB and UWB are t1 and t2, respectively, and the incident angle from the active tag to UWB is y; therefore, the x, y coordinates of the active tag can be calculated by the following equations, in which the position of the active tag can be located accurately qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi > 2 2 > < ðx2 À xÞ þ ðy2 À yÞ À ðx1 À xÞ þ ðy1 À yÞ [...]... 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Relative proportion of throughput time (%) 77 14.1552 78 3.3212 79 3.6503 81 1.6918 International Journal of Computer Integrated Manufacturing Figure 11 401 Practical application of modelling dynamic bottlenecks at, on one hand, making money as much as possible, on the other hand, saving the production costs (removing production waste) to increase the value of end products, both of the goals must be... and Science, Jacobs University, Campus Ring 1, 28759 Bremen, Germany; c International Graduate School for Dynamics in Logistics (IGS ), Hochschulring 2 0, 28359 Bremen, Germany (Received 3 March 2010; final version received 21 June 2010) Bottlenecks, as the key ingredients for improving the performances of the production networks, have been profoundly studied However, the major definitions of bottlenecks... operating curve, the both types of costs can be depicted by decomposing the total costs according to Jainczyk (1994 ), Großklaus (1996) and Kerner (2002) Because the total costs, as the function of output rate and WIP, 402 B Scholz-Reiter et al are determined by the sum of production cost, processing cost, WIP cost and setup cost, each of the four type of costs can be descript as the function of WIP after... run-time by an event switch FB (ES-FB) For instance, if a sequence of ‘342’ is given, the ES-FB will fire events accordingly to the appropriate MF-FBs for feature fabrications in the order of 3!4!2 It thus adds International Journal of Computer Integrated Manufacturing flexibility to the composite FB Figure 4(b) illustrates the graphical definition of the ES-FB, where ROUTE is the only data input to the FB... Pushlet event, and thus will not be a client of the Pushlet Another Pushlet adapter, the Machine Adaptor, is required to take information from the Postlet (i.e from the client ), and send it to a device controller in the International Journal of Computer Integrated Manufacturing Figure 7 Event/data flow between clients and machines required format As the Pushlet does not provide this functionality, the Wise-ShopFloor