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cloud manufacturingthe manufacturing version of cloud computing. Cloud computing has been in

some of key areas of manufacturing such as IT, pay-as-you-go business models, production scaling up

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Contents lists available at ScienceDirect

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Robotics and Computer-In

Robotics and Computer-Integrated Manufacturing 28 (2012) 7586sectors, e.g. inline commerce [6], conference origination [7], andE-mail address: x.xu@auckland.ac.nzfundamental computing resources are dened as standardized form Solutions play an important role in transforming enterprisesystems, contributing to cost reduction, agile deployment ofservices, expanded exibility and improved productivity [5].Cloud computing is also being used in other business and science

0736-5845/$ - see front matter & 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.rcim.2011.07.002

n Tel.: 64(9)3737599; fax: 64(9)3737479.Service) and IaaS (Infrastructure as a Service). These servicesdene a layered system structure for cloud computing (Fig. 1). At

ities to enterprises and customers.More and more businesses are taking advantage of cloudprovider interaction.In Cloud computing, everything is treated as a service (i.e.

XaaS), e.g. SaaS (Software as a Service), PaaS (Platform as a

cloud computing means a paradigm shift of business aninfrastructure, where computing power, data storage and serare outsourced to third-parties and made available as comand Technology (NIST) [2] dened cloud computing as a modelfor enabling ubiquitous, convenient, on-demand network access to ashared pool of congurable computing resources (e.g., networks,servers, storage, applications, and services) that can be rapidlyprovisioned and released with minimal management effort or service

several computing trends such as Internet delivery, pay-as-you-go/use utility computing, elasticity, virtualization, distributedcomputing, storage, content outsourcing, Web 2.0 and gridcomputing. In fact, cloud computing can be considered thebusiness-oriented evolution of grid computing [4]. Implementing1. Introduction

Collaboration, Internet of thingsed as key business technology treprises worldwide [1]. The manufactumajor transformation enabled by ITgies. Cloud computing is one of smain thrust of Cloud computing isputing services with high reliabilitya distributed environment. The Nadistributed resources are encapsulated into cloud services and managed in a centralized way. Clients

can use cloud services according to their requirements. Cloud users can request services ranging from

product design, manufacturing, testing, management, and all other stages of a product life cycle.

& 2011 Elsevier Ltd. All rights reserved.

loud have been identi-at will reshape enter-dustry is undergoing aelated smart technolo-art technologies. Thevide on-demand com-ility and availability inInstitute of Standards

services over the network. Cloud providers clients can deploy andrun operating systems and software for their underlying infra-structures. The middle layer, i.e. PaaS provides abstractions andservices for developing, testing, deploying, hosting, and maintain-ing applications in the integrated development environment. Theapplication layer provides a complete application set of SaaS. Theuser interface layer at the top enables seamless interaction withall the underlying XaaS layers [3].

Sometimes, cloud computing is considered as a multidisciplin-ary research eld as a result of evolution and convergence ofFrom cloud computing to cloud manufa

Xun Xu n

Department of Mechanical Engineering, University of Auckland, Auckland 1142, New Z

a r t i c l e i n f o

Article history:

Received 14 May 2011

Received in revised form

1 July 2011

Accepted 15 July 2011Available online 9 August 2011

Keywords:

Cloud computing

Cloud manufacturing

Service-oriented business model

a b s t r a c t

Cloud computing is cha

dynamically scalable and

creates a brand new oppo

computing are briey dis

platform, and cloud provi

for the manufacturing ind

to align product innovat

encourage effective colla

sector have been suggeste

journal homepage: wwwturing

nd

g the way industries and enterprises do their businesses in that

ualized resources are provided as a service over the Internet. This model

ity for enterprises. In this paper, some of the essential features of cloud

sed with regard to the end-users, enterprises that use the cloud as a

themselves. Cloud computing is emerging as one of the major enablers

y; it can transform the traditional manufacturing business model, help it

with business strategy, and create intelligent factory networks that

tion. Two types of cloud computing adoptions in the manufacturing

anufacturing with direct adoption of cloud computing technologies and

lsevier.com/locate/rcim

tegrated Manufacturing

Nomenclature

AaaS Application as a ServiceAP Application ProtocolAPI Application Programming InterfaceASP Application Service ProviderB2B Business-to-businessBOL Beginning-Of-LifeBPM Business Process ManagementCAD Computer-Aided DesignCAE Computer-Aided EngineeringCAM Computer-Aided ManufacturingCAPP Computer-Aided Process PlanningCIO Chief Information OfcerCMM Coordinate-Measuring MachineCNC Computer Numerical ControlCRM Customer Relationship Management

XaaS everything is treated as a Service

X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 758676biomedical information sharing [8]. There are valid reasons andperhaps requirement for manufacturing businesses to embracecloud computing and to borrow the concept of cloud computing

CRM Customer Relationships ManagementDAMA Design Anywhere, Manufacture AnywhereDAML DARPA Agent Markup LanguageDARPA Defense Advanced Research Projects Agency, USADIMP Distributed Interoperable Manufacturing PlatformEDM Electrical Discharge MachiningEOL End-Of-LifeERP Enterprise Resource PlanningGPS Global Positioning SystemHaaS Hardware as a Serviceto give rise to cloud manufacturing, i.e. the manufacturingversion of cloud computing. Such a lateral thinking is consideredlogical and natural as manufacturing businesses in the newmillennium become increasingly IT-reliant, globalized, distribu-ted and agile-demanding.

In the rst-half of this paper, the essential requirements of acloud computing system are briey discussed. These considera-tions are useful for software architects and developers to designcloud-based applications. They also preface the main focus of thispaper, i.e. cloud manufacturing, which forms the second-half ofthe paper. The rest of this paper is organized as follows. Section 2describes the key requirements of cloud computing systems.

Ever

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s a

serv

ice

(Xaa

S)

User Front-end

Applications

Run time/middleware

Computingpower

Software as a Service (SaaS)Target: User/business

Platform as a Service (PaaS)

Infrastucture as a Service (IaaS)

Target: Developer

Target: Administrator

Fig. 1. Cloud computing: everything is a service.Section 3 discusses cloud computing in the context of manufac-turing businesses. In particular, Section 3.1 discusses utilization ofcloud computing in manufacturing businesses and Section 3.2IaaS Infrastructure as a ServiceIT Information TechnologyLAN Local Area NetworkMGrid Manufacturing GridMOL Middle-Of-LifeNIST National Institute of Standards and Technology, USAopenCBM open Computer-Based ManufacturingOWL Web Ontology LanguagePaaS Platform as a ServiceQoS Quality of ServiceREST REpresentational State TransferRFID Radio-Frequency IDenticationSaaS Software as a ServiceSHOE Simple HTML Ontology ExtensionSLA Service Level AgreementSOA Service-Oriented ArchitectureSTEP Standard for Exchange of Product dataSTEP-NC STEP for Numerical ControlSTRL STEP Resource LocatorUbiDM Ubiquitous Design and ManufactureUPLS Ubiquitous Product Life cycle SupportURL Universal Resource LocatorUX User ExperienceVMM Virtual Machine ManagerWPM Workforce Performance ManagementWSN Wireless Sensor Networkspresents the manufacturing version of cloud computingcloudmanufacturing. Section 4 concludes the paper.

2. Cloud computing systems

This section provides an abridged version of general architec-tural requirements for cloud computing as presented in [9]. Rimalet al. [9] classied architectural requirements into cloud providers,the enterprises that use the cloud, and cloud users.

2.1. Provider requirements

From the service providers perspective, highly efcient servicearchitecture to support infrastructure and services is needed inorder to provide virtualized and dynamic services. This sectionexplains the requirements of a provider service delivery modeland other key requirements.

2.1.1. Service delivery models

Software as a Service, Platform as a Service, and Infrastructureas a Service are three common types of service delivery models.These services are usually delivered through industry standardinterfaces, such as Web services, service-oriented architecture(SOA) [10] or REpresentational State Transfer (REST) [11] services.

Software-as-a-Service is sometimes referred to as Applicationas a Service (AaaS). It offers a multi-tenant platform wherebycommon resources and a single instance of both the object code ofan application and the underlying database are used to supportmultiple customers simultaneously. To this end, SaaS is alsoreferred to as the Application Service Provider (ASP) model.Examples of the key providers are the Salesforce Customer

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X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 7586 77 Quality of Service (QoS)Like many services on offer, QoS provides a guarantee ofperformance, availability, security, reliability and dependabil-ity. QoS requirements are associated with service providersand end-users. Service Level Agreements (SLAs) are an effec-tive means for assuring QoS between service providers andend-users. QoS may entail systematic monitoring of resources,storage, network, virtual machine, service migration and fault-tolerance. In the context of a Cloud service provider, QoSshould emphasize the performance of virtualization andmonitoring tools.

InteroperabilityInteroperability is about creation of an agreed-upon frame-work/ontology, open data format or open protocols/APIs thatenable easy migration and integration of applications and databetween different cloud service providers. It is an essentialrequirement for both service providers and enterprises. Ser-vices with interoperability allow applications to be portedbetween clouds, or to use multiple cloud infrastructures beforebusiness applications are delivered from the cloud.

Fault-toleranceFault-tolerance presents the ability of a system to continue tooperate in the event of the failure of some of its components.Application-specic, self-healing, and self-diagnosis mechan-isms are for example enabling tools for cloud providers todetect failure. Once detected, fault is isolated and revisionCloud architecture needs to have a unied service-centricapproach. The cloud services should have the ability todynamically adapt to changes with minimum human assis-tance. Services need to be self-describing so that they cannotify the client exactly how they should be called and what.2. Other essential requirements

Other essential requirements are to do with service-centricues, quality of service, interoperability, fault-tolerance, loadancing and virtualization management [9].

Service-centric issuesport multiple applications on the same platform.Infrastructure-as-a-Service is sometimes called Hardware as avice (HaaS). IaaS promotes a usage-based payment scheme,aning that customers pay as they use. This service is extremelyful for enterprise users as it eliminates the need for investingbuilding and managing their own IT systems. Another impor-t advantage is the ability of having access to, or using, theest technology as it emerges. On-demand, self-sustaining orf-healing, multi-tenant, customer segregation are the keyuirements of IaaS [9]. GoGrid, Mosso/Rackspace, MSP On-mand, and masterIT are some of the pioneer IaaS providers.supsiderations.As the name implies, Platform-as-a-Service provides developersth a platform including all the systems and environmentsprising the life cycle of development, testing, deploymenthosting of sophisticated web applications as a service

ivered by a cloud-based platform. Commonly found PaaSludes Facebook F8, Salesforge App Exchange, Google Appgine, Bunzee connect and Amazon EC2. PaaS may offer amber of readily available services, which means that PaaS canconationships Management (CRM) system, NetSuite, and Googlece Productivity application. A major consideration in SaaS isective integration with other applications. At the applicationel, the important aspects of scalability, performance, multi-ancy, congurability, and fault-tolerance are primarymode is activated. buand Hocenski [14] discussed security issues and challenges inail. The above discussed service models (i.e. SaaS, PaaS andS) place different levels of security requirements in the Cloudironment. IaaS is the foundation of all cloud services, withS built upon it and SaaS in turn built upon PaaS. Just asabilities are inherited, so are the information security issuesrisks [15].

.3. Business Process Management (BPM)

Typically, a business process management system provides aem Load balancingLoad balancing represents the mechanism of self-regulatingthe workloads within the clouds entities (e.g. servers, harddrives, network and IT resources). Load balancing is often usedto implement failover in that the service components aremonitored continually and when one becomes non-respon-sive, the load balancer stops sending trafc, de-provisions itand provisions a new service component. A load balancer isanother key requirement to build dynamic and stable cloudarchitecture.

Virtualization managementVirtualization refers to abstraction of logical resources fromtheir underlying physical characteristics in order to improveagility, enhance exibility and reduce cost [12]. Virtualizationin the cloud may concern servers, client/desktop/applications,storage (e.g. Storage Area Network), network, and service/application infrastructure. Quality of virtualization determinesthe robustness of a cloud infrastructure. Good virtualizationcan effectively assist sharing of cloud facilities, managing ofcomplex systems, and isolation of data/application.

2.2. Enterprise requirements

Enterprises are being constantly reminded about the servicesthey are paying in terms of the service quality, service levels,privacy matters, compliances, data ownership, and data mobility.This section describes some of the cloud deployment require-ments for enterprises.

2.2.1. Cloud deployment for enterprises

There are four types of cloud deployment models, public,private, community and hybrid clouds. These cloud services areubiquitous as a single point of access. Different types of deploy-ment models suit different situations. Public cloud realizes thekey concept of sharing the services and infrastructure provided byan off-site, third-party service provider in a multi-tenant envir-onment [13]. Private cloud entails sharing services and infra-structure provided by an organization or its specied serviceprovider in a single-tenant environment. Enterprises mission-critical and core-business applications are often kept in a privatecloud. Community cloud is shared by several organizations and issupported by a specic community that has shared interests andconcerns [2]. Hybrid cloud consists of multiple internal (private)or external (public) clouds. Added complexity of determining howto distribute applications across both private and public cloudscan be challenging. Clearly, enterprises need to strategicallyleverage all four cloud deployment models.

2.2.2. Security

The notion of entrusting data to information systems that aremanaged by external entities on remote servers in the cloudcauses varying levels of anxiety [7]. This is because corporateinformation often contains data of customers, consumers and

ployees, business know-how and intellectual properties. Popo-siness structure, security and consistent rules across business

resource planning (ERP) and e-commerce portals. Cloud-based

X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 758678BPM (e.g. combining SaaS with a BPM application) enhancesexibility, deploy-ability and affordability for complex enterpriseapplications [9].

2.3. User requirements

Users requirements are the third key factor for a willing andsuccessful adoption of any cloud system in an enterprise. Forusers, trust is often a major concern. Trust-based cloud is there-fore an essential and must-have feature [7]. This section describesuser consumption-based billing and metering requirements, user-centric privacy requirements, service level agreements and userexperience requirements.

2.3.1. User consumption-based billing and metering

When it comes to individual end-users and consumption-based billing and metering in a cloud system, an analogy can bedrawn with the consumption measurement and allocation ofwater, gas or electricity on a consumption unit basis. Costmanagement is important for making planning and controllingdecisions. Cost breakdown analysis, tracing the utilized activity,adaptive cost management, transparency of consumption andbillings are also important considerations.

2.3.2. User-centric privacy

In cloud computing, some of the users data (regarded as his/her personal intellectual property) are stored at mega-datacenters located in the cyber space. In such an environment,privacy becomes a major issue [7,16]. There is strong resistanceand reluctance of an enterprise storing any sensitive data on thecloud. Thankfully, there are various technologies that can enhancedata integrity, condentiality, and security in the clouds, e.g. datacompressing and encrypting at the storage level, virtual LANs andnetwork middle-boxes (e.g., rewalls and packet lters).

2.3.3. Service Level Agreements (SLAs)

Service level agreements are mutual contracts between provi-ders and users for the assurance of a cloud provider to deliver theservices that are agreed-upon. Currently, many cloud providersoffer SLAs, but they are rather weak on user compensations onoutages. Some of the important architectural issues are measure-ment of service delivery, method of monitoring performance, andamendment of SLA over time.

2.3.4. User Experience (UX)

The notion of UX is to provide an insight into the needs andbehaviors of an end-user so as to maximize the usability, desir-ability and productivity of the applications. UX-driven design anddeployment is the next logical step in the evolution of CloudComputing. Cloud-based application/systems should be easy touse, capable of providing faster and reliable services, easilyscalable, and customizable to meet the goal of localization andstandardization. Human-Computer Interaction, ergonomics andusability engineering are some of the key technologies that can beused for designing UX-based Cloud applications [9].

3. Cloud computing in the context of manufacturing

In recent years, the philosophy of Design Anywhere, Manu-processes, users, organization and territory. Some of the examplesof BPM applications include customer relationship management(CRM), workforce performance management (WPM), enterprisefacture Anywhere (DAMA) has emerged [1719]. The DAMAapproach demands the ability to exchange design and manufac-turing data across multiple sites. DAMA also helps establish linksbetween manufacturing resource planning, enterprise resourceplanning, engineering resource planning and customer relation-ship management. It is believed that cloud computing may play acritical role in the realization of DAMA. In general, there are twotypes of cloud computing adoptions in the manufacturing sector,manufacturing with direct adoption of some cloud computingtechnologies and cloud manufacturingthe manufacturing ver-sion of cloud computing.

3.1. Smart manufacturing with cloud computing

Cloud computing is rapidly moving from early adopters tomainstream organizations. It has become one of the top prioritiesof many CIOs in terms of strategic business considerations. Somemanufacturing industry starts reaping the benets of cloudadoption today, moving into an era of smart manufacturing withthe new agile, scalable and efcient business practices, replacingtraditional manufacturing business models.

In terms of cloud computing adoption in the manufacturingsector, the key areas are around IT and new business models thatthe cloud computing can readily support, such as pay-as-you-go,the convenience of scaling up and down per demand, andexibility in deploying and customizing solutions. The adoptionis typically centered on the BPM applications such as HR, CRM,and ERP functions with Salesforce and Model Metrics being two ofthe popular PaaS providers (refer to Section 2.2.3).

The cost benet of adopting clouds in a typical manufacturingenterprise can be multiple. The savings obtained from theelimination of some of the functions that were essential intraditional IT can be signicant. With cloud-based solutions, someapplication customizations and tweaks that the company needs atthe process level may be dealt with by the companys IT sectoralong with some of the smart cloud computing technologies.When a different way of executing a process is initiated, the ITstaff can make the change happen seamlessly and in less time[20]. Elkay Manufacturing Company, a world leader in stainlesssteel sinks, water coolers and kitchen cabinets, is one of themanufacturing companies that have successfully adopted andbeneted from cloud computing technologies [20].

When it comes to supporting smart business processes, cloudcomputing can be effective in offering Business-to-business (B2B)solutions for commerce transactions between businesses, such asbetween a manufacturer and a wholesaler, or between a whole-saler and a retailer. Cloud-based solutions enable better-inte-grated and more efcient processes.

Cloud computing can also be used to enhance many other aspectsof manufacturing businesses by moving a traditional process to thecloud for improved operational efciency. For example, cloud com-puting can assist the development of an application for customer on-boarding process that is more efcient than the traditional process ofcompany on-boarding customers. The procedure for a company toon-board customers may involve a salesperson visiting a prospectivecustomer, the customer lling in a form, company credit checkingetc. A Cloud-based customer on-boarding process may do all of theseautomatically via cloud resources on the Internet.

Collaboration at scale using cloud technology is an emergingbusiness trend according to McKinsey [1]. Adopting cloud tech-nologies, enterprise collaboration can happen at a much broaderscale. Within the organization, demand planning and supply chainorganization can be tied into a cloud-based system, allowingdifferent parts of the organization to take a peek into theopportunities that their sales teams are working on. In a moretraditional environment, that would involve a few sit-down meet-

ings, several face-to-face discussions, or phone conversations.

adopting manufacturing enterprise also requires is a smart

functions for a cloud manufacturing application.

be virtualized in similar ways as are the general Cloud computingresources. Manufacturing hardware is usually mapped to becomevirtual machines that are system-independent. Virtualization man-agers (e.g. Virtual Machine Monitor and Virtual Machine Manager(VMM)) are responsible for communicating with the lower leveldevices, and coordinating and allocating virtual machines.

Agent can be an effective tool for virtualization. Take MTCon-nect [2628] as an example. MTConnect is a standard based on anopen protocol for data integration. Although it is for enhancingdata acquisition capabilities of machine tools, the use of agenttechnology provides a plug-and-play environment for manufac-turing facilities, which has the potential to support cloud manu-facturing. Fig. 3 shows a schematic of a factory system with threemachine tools that are virtualized and integrated via MTConnectagents. It needs to be pointed out though that MTConnect mainlysupports monitoring processes.

The next step is to package the virtualized manufacturingresources to become cloud manufacturing services. To do this,resource description protocols and service description languages can

X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 7586 79mechanism to deal with integration. Solutions such as Cast Ironare addressing some aspects of such integration; vendors such asModel Metrics are pitching in as well.

3.2. Cloud manufacturing

With cloud manufacturing, what comes into ones mind rst isthe existing networked manufacturing concept, or sometimescalled Internet-based manufacturing or distributed manufacturing.However, todays networked manufacturing mainly refers to inte-gration of distributed resources for undertaking a single manufac-turing task [21,22]. What is lacking in this type of manufacturingregime are the centralized operation management of the services,choice of different operation modes and embedded access ofmanufacturing equipment and resources, without which a seam-less, stable and high quality transaction of manufacturing resourceservices cannot be guaranteed. In a typical distributed manufactur-ing environment, the resource service provider and resource servicedemander have little coordination. Thus, adoption of the networkedmanufacturing concept has been slow and less effective.

Moving from production-oriented manufacturing to service-oriented manufacturing and inspired by cloud computing, cloudmanufacturing seems to offer an attractive and natural solution.cloud computing is viewed as the evolution and convergence ofseveral independent computing trends such as Internet delivery,pay-as-you-go utility computing, elasticity, virtualization, gridcomputing, distributed computing, content outsourcing and Web2.0 [3]. Likewise, cloud manufacturing is also considered as a newmultidisciplinary domain that encompasses technologies such asnetworked manufacturing, manufacturing grid (MGrid), virtualmanufacturing, agile manufacturing, Internet of things, and ofcourse cloud computing. Cloud manufacturing reects both theconcept of integration of distributed resources and the conceptof distribution of integrated resources. Mirroring NISTs deni-tion of cloud computing, cloud manufacturing may be dened asa model for enabling ubiquitous, convenient, on-demand networkaccess to a shared pool of congurable manufacturing resources (e.g.,manufacturing software tools, manufacturing equipment, and man-ufacturing capabilities) that can be rapidly provisioned and releasedwith minimal management effort or service provider interaction.

In Cloud manufacturing, distributed resources are encapsulatedinto cloud services and managed in a centralized way. Clients canuse the cloud services according to their requirements. Cloudusers can request services ranging from product design, manu-facturing, testing, management and all other stages of a productlife cycle. A cloud manufacturing service platform performs search,intelligent mapping, recommendation and execution of a service.Fig. 2 illustrates a cloud manufacturing system framework, whichconsists of four layers, manufacturing resource layer, virtualservice layer, global service layer and application layer.

3.2.1. Manufacturing resource layer

The manufacturing resource layer encompasses the resourcesthat are required during the product development life cycle.These manufacturing resources may take two forms, manufactur-ing physical resources and manufacturing capabilities. Manufac-turing physical resources can exist in the hardware or softwareThe cloud in this case provides a collaborative environment thatcan give people agility, more transparency, and empowermentthrough more effective collaborations.

Typically, there are some parts of the manufacturing rm thatcan quickly and easily adopt cloud-based solutions, whereas otherareas are better to remain traditional. Hence, what a cloud-form. The former includes equipment, computers, servers, rawA number of technologies can be used for identifying (ortagging) manufacturing resources [2325], e.g. RFID, computa-tional RFID, wireless sensor networks (WSN), Internet of things,Cyber Physical Systems, GPS, sensor data classication, clusteringand analysis, and adapter technologies.

Manufacturing resource virtualization refers to abstraction oflogical resources from their underlying physical resources. Qualityof virtualization determines the robustness of a cloud infrastruc-ture. Different manufacturing resources are virtualized in differentways. Computational resources and manufacturing knowledge canmaterials, etc. The latter includes for example simulation soft-ware, analysis tools, know-hows, data, standards, employees,etc. Manufacturing capabilities are intangible and dynamicrecourses representing the capability of an organization under-taking a particular task with competence. These may includeproduct design capability, simulation capability, experimentation,production capability, management capability, and maintenancecapability. The types of service delivery models that may exist atthis layer are IaaSs and SaaSs.

3.2.2. Manufacturing virtual service layer

The key functions of this layer are to (a) identify manufactur-ing resources, (b) virtualized them, and (c) package them as cloudmanufacturing services. Comparing with a typical cloud comput-ing environment, it is much more challenging to realize these

Fig. 2. Layered architecture of a cloud manufacturing system.be used. The latter may include different kinds of ontology languages,

to the client as one manufacturing service. It is up to the resource

Agent 3

X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 758680Internal TCP/IP Network

Monitoring/visualization/

analysissoftware

InternetRemote

Web-basedmonitoring

MTConnectAgent 1 MTConnect

Agent 2

Fig. 3. Cloud manufacturing resources enabled by MTConnect.MTConnecte.g. Simple HTML Ontology Extension (SHOE), DARPA Agent MarkupLanguage (DAML), and Web Ontology Language (OWL).

In a STEP-enabled, networked manufacturing process planningenvironment [2932], a STEP resource locator (STRL for short)represents a simplest form of cloud manufacturing service. STRLconsists of a URL, an Action and a Query (Fig. 4). STRL is similar tothe concept of giving a URL address through the Web. The URLgives the name (location) of the system and data identication. Itcan therefore be used as a link to a particular manufacturingresource, e.g. a data le, workingstep (machining step), program,etc. For example, if an STRL as shown in Fig. 4 is activated, we willknow that the client has requested the job (as described by lemanifold.238) to be machined (run) from the rst line until theend for all the three workingsteps.1

To describe manufacturing capability, Zhang et al. [34] used afour-dimension array: (Task, Resource, Participator, Knowledge).Task denotes a manufacturing job; Resource denotes the manu-facturing resources that are needed to do the task; Participatorrepresents human resources needed for the job; and Knowledgerepresents all the knowledge required to do the job.

3.2.3. Encapsulating manufacturing resources with mapping

The process of virtualizing a manufacturing resource can alsobe viewed as an encapsulating process, which can be carried out

Fig. 4. A STEP resource locator for STEP-enabled manufacturing.

1 The workingsteps represent technology-independent actions in STEP-NC

such as rapid movements or probing operations, and machining workingsteps that

relate to the different technologies like milling, drilling, turning, etc.provider to seek a way of delivering the service and guarantee thequality. Manufacturing of complex mechanical components, e.g.car engine block and alloy wheel, may call upon multiple resources,e.g. casting equipment, machine tools and heat treatment facilities.

The one-to-many mapping concerns with a single resourcethat appears to a client as a multiple resource. The clientinterfaces with the virtualized resources as though he/she is theonly consumer. In fact, the client is sharing the resource withother users. For example, ANSYS software can provide structureanalysis, thermal analysis, magnetic analysis, and computationaluid dynamics analysis. Therefore, ANSYS software can be encap-sulated by many different services.

3.2.4. Enterprise requirementsGlobal Service Layer

The Global Service Layer relies on a suite of cloud deploymenttechnologies (i.e. PaaS). Internet of things has advanced to a newlevel with RFID, intelligent sensors, and nano-technology as thesupporting technologies. Interconnections between physical devicesor products are made easier because of Internet of things. Havingsaid this, a centralized and effective management regime needs tobe in place to provide manufacturing enterprises with agile anddynamic cloud services. Based on the nature of the provided cloudresources and the users specic requirements, two types of cloudmanufacturing operation modes can take place at the Global ServiceLayer, complete service mode and partial service mode.

In a complete service mode, the Global Service Layer takes fullresponsibility of the entire cloud operational activities. The typeof cloud service that suits this mode is virtualized computingresources, e.g. CPU, RAM, and network. These cloud services canbe dynamically monitored, managed and load-balanced withease. Application software is also suitable for the complete servicemode in that running and execution of software can take place ina distributed computing environment taking advantage of gridcomputing and parallel computing. Knowledge, human resources,and manufacturing capabilities may also be managed at theGlobal Service Layer in a complete service mode.

It is possible and sometimes necessary to partially hand overan activity to the cloud manufacturing servicehence a partialusing three different mapping methods, one-to-one, many-to-one,and one-to-many.

One-to-one mapping is the simplest situation, which applies tomanufacturing resources that can only provide a single function andcan therefore directly be encapsulated into one service. The CAD andCAE data format exchange service is one of the common types of suchresource. For example, Creo Elements/Pro can save a n.iv le that is to,and can only, be read by Autodesks Inventor. Vice versa, Inventor cansave a n.prt le only for Creo Elements/Pro to read in. An EDM tool isanother example that can only carry out the EDM process.

In a many-to-one mapping, multiple resources (each providinga specic function) may be combined to create a more powerful orfunctional resource form. For example, the ADINA software canprovide mesh function, and SOLIDCast software can simulate acasting process. When combined, these two resources can providea generic simulation service. At the user end, such combination ofmultiple resources is invisible. In cloud manufacturing, whenmultiple manufacturing resources are combined, more compre-hensive manufacturing resource services called resource servicecomposition can be provided to users to enable value-addedservices. Zhang et al. [34] and Guo et al. [35] discussed theexibility issues of resource service compositions. For example,use of a particular machine tool for a manufacturing job may leadto generation of a specic CAM program for machining and aspecic CMM program for inspection. All of these will only appearservice mode. In such a mode, the service provider provides

Although the concept of cloud manufacturing is new, virtualenterprise and distributed manufacturing concepts have been

where applications are not realised as monolithic programs, butas a set of services that are loosely connected to each other,

for engineering simulations, van der Velde [45] reported a plug-and-play framework for the construction of modular simulationsoftware. In this framework (Fig. 6), the user (at the Application

X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 7586 81A rigorous Service Level Agreements for cloud manufacturingis a must to win any end-users trust and condence over theservices. When manufacturing hardware is involved, SLAs areparticularly important as hardware failure is more difcult torecover from.

Data portability at the Application Layer is another importantmatter. Open data format and open APIs have been suggested [9].Industry vendors and users have been seeking a common lan-guage to be used for the entire product development life cyclethat can describe design, manufacturing, and other data pertain-ing to a product. Many solutions were proposed, the mostsuccessful being the Standard for Exchange of Product data (STEP)[32,37]. STEP provides a mechanism that is capable of describingproduct data, independent of any particular system. The nature ofthis description makes it suitable not only for neutral leexchange, but also as a basis for implementing, sharing andconstruct a manufacturing application through the virtualizedresources. Such a manufacturing application often involves morecomprehensive manufacturing resource services that provideusers with a value-added service [34,35].

Similar to cloud computing, end-user consumption-based bill-ing and metering in cloud manufacturing resembles the con-sumption measurement and allocation of costs of water, gas, andelectricity. Users often have a demand for transparency of con-sumption and billings. Activity-Based Costing [36] can be a usefulproler that the user can use to understand how much theirimplementation will cost in terms of cloud manufacturingcharges, hence enhance cost transparency.

The issue of user-centric privacy is a thorny one. The mainconcern with cloud manufacturing for end-users is related to thestorage of personal/enterprise sensitive data. This data includesnot only product information but also information of some of thehigh-end manufacturing resources. There are some technologiesthat can enhance data integrity, condentiality and security overcloud Manufacturing [9]. They are

data compressing and encrypting at the storage level, virtual LANs, that can offer secure remote communications,

and network middle-boxes (e.g., rewalls, packet lters), for fail-

safe communications.areandarccomplex system modeling tools, generic simulation terminals,new product development utilities. The user can dene andter

manufacturing cloud resources. This layer provides client

minals and computer terminals. Some examples of interfaces

andadditional input and operational activities. Typically, manufactur-ing hardware (e.g. machine tools and experiment devices) is thistype of cloud services. The Global Service Layer is mainlyresponsible for locating, allocating, fee-calculating and remotemonitoring the manufacturing resources. The hardware providersare still responsible for executing the manufacturing tasks andensuring the quality of the manufacturing job.

In order to meet the above enterprise requirements, somecritical technologies are needed. For example, optimal resourceselection and allocation methods are needed to guarantee aneffective cloud manufacturing service. Theories such as Intuitio-nistic Fuzzy Set, Partial Swarm Optimization, and QuantumMulti-agent Evolutionary Algorithm can be handy when developing anenabling technology. Evaluation and management of QoS isanother important exercise at this layer [22,33].

3.2.5. User requirementsApplication Layer

The Application Layer serves as an interface between the userhiving product data over a cloud manufacturing system. ISOLayer as in a cloud manufacturing system) is allowed to select atarget of simulation and assign the performer of the simulationcalled component before running the selected components.These components are effectively software entities (or otherwiseknown as SaaS as in cloud computing/manufacturing). They aremodulised, self-contained, mobile and pluggable. After the simu-lation, the output is post-processed through the components. Insuch architecture, software modules are detected, loaded andused at run-time with the framework (i.e. the Global ServiceLayer) needing no prior knowledge of the type and availability ofguaranteeing the modularity and reusability of a system. Themodule providers as shown in the gure form the ManufacturingVirtual Service Layer and the module database forms a GlobalService Layer.

4.2. SaaS for engineering simulations

To achieve a run-time conguration integration environmentaround for awhile and some of the proposed systems and frame-works bear visible traces of cloud manufacturing or make con-tributions to a cloud manufacturing system. This section discussessome of these research outcomes.

4.1. Service-oriented manufacturing environment

Brecher, et al. [42] recognized that applications in an informa-tion-intensive manufacturing environment can be organized in aservice-oriented manner. They proposed a module-based, cong-urable platform for interoperable CAD-CAM-CNC planning. Thegoal is to combat the problems of software inhomogeneity alongthe CAD-CAM-NC chain. The approach is called open Computer-Based Manufacturing (openCBM) in support of co-operativeprocess planning (Fig. 5). To implement the architecture andintegrate inspection tasks into a sequence of machining opera-tions, STEP standard is utilized to preserve the results of manu-facturing processes that are fed back to the process planning stage[43]. The openCBM platform is organized through a service-orientarchitecture providing the abstractions and tools to model theinformation and connect the models [45]. It is much like thePlatform as a Service concept and resembles an Application Layer,10303-AP203 [38] is the rst and perhaps the most successful AP(Application Protocol) developed to exchange design databetween different CAD systems. Going from geometric data (asin AP203) to features (as in AP224) represents an important steptowards having the right type of data in a STEP-based CAD/CAMsystem. Of particular signicance is the publication of STEP-NC[3941], as an extension of STEP to NC, utilizing feature-basedconcepts for CNC machining purposes. STEP and STEP-NC cantherefore provide a common information ground for cloud man-ufacturing at the Application Layer.

4. Research contributions to the concept of cloudmanufacturingcomponents, thus providing true plug-and-play capabilities.

M(D

ers

X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 758682User interface controller

User interface

Component library

Plug-in system

User I

User II

openCBMFramework

of Provider A

openCBMFramework

of Provider B

Fig. 5. Module users and provid4.3. Some embryonic cloud manufacturing systems

This section presents a few embryonic or quasi-cloud manu-facturing systems that are developed in the recent years.Although these systems vary in their structures and applicationdomains, the philosophy and underpinning concepts are conver-ging toward those of cloud manufacturing.

Nessehi et al. proposed a framework to comeback the incom-patibility problem among CAx systems [46]. Much like an IaaS,the platform provides individual interfaces for different CAD/CAM/CNC systems. A comprehensive data warehouse is utilized tostore CNC manufacturing information with STEP-NC data modelutilized as the basis for representing manufacturing knowledgethat is augmented with XML schema. Such knowledge informa-tion is categorized into product information, process informationand resource information. The platform is further explained in[46], where the system consists of manufacturing data ware-house, manufacturing knowledgebase, intercommunication bus,and various CAx interfaces as the main structure (Fig. 7). Mobileagent technology is used to support the intercommunication busand CAx interfaces. In the system, different components of theCAD/CAM/CNC chain can exchange information with one anotherregardless of their native standards.

More recently, Mokhtar and Houshmand [48] studied a similarmanufacturing platform, using the axiomatic design theory torealize interoperability among the CAx chain. The methodology ofaxiomatic design is proposed to generate a systematic roadmap ofan optimum combination of data exchange via direct (using STEP

Simulation

Simulation system

Project

Project system

Fig. 6. Main elements of the plug-and-play framework.neutral format) or indirect (using bidirectional interfaces) solu-tion in the CAx environment (Fig. 8). This approach providedsome insight into how a design and manufacturing resource maybe encapsulated and how Global Service Layer may be developedfor cloud manufacturing.

UbiDM, a concept of design and manufacture via ubiquitouscomputing technology, is proposed by the researchers in POST-ECH, Korea [49]. The key aspect of UbiDM is the utilization of theentire product life cycle information obtained via ubiquitouscomputing technology for product design and manufacture(Fig. 9). To support the concept, a Ubiquitous Product Life CycleSupport (UPLS) system is presented as well [50]. Module andagent concepts are mentioned in the function of the request-nd-provide chain. A unied product life cycle data model, which iscompliant with international standards, is utilized for dataexchanges. The model represents the input and output informa-tion used in the life cycle activity, in the stages of Beginning-Of-Life (BOL), Middle-Of-Life (MOL), and End-Of-Life (EOL).

Wang and Xu [51,52] proposed a Distributed InteroperableManufacturing Platform (DIMP) as an integrative environmentamong existing and future CAD/CAM/CNC applications. It is amodule-based structure. In order to integrate the software suitesbased on the requests and tasks from a user, service-orientedarchitecture is used. In DIMP, users requests are collected andorganized as a serial of software services. From the service point

odule Databaseirectory Service)

Module Provider 1

Module Provider 2

Module Provider 3

Module Provider n

(Sub-)Moduleof another provider

of the openCBM approach [42].of view, heterogeneous software tools are integrated as VirtualService Combinations and provided to the user. In this way,software suites are embedded into operational processes.

Both STEP and STEP-NC data models are utilized as the centraldata schema. With coupling technologies, STEP and STEP-NCdata models can be connected to commercial CAD/CAM softwaresuites, giving the system much needed portability. DIMP aims tointegrate software applications (i.e. SaaS) based on the requestfrom users. The platform is capable of handling requests fromusers such as task objects, software functionality and input/output requirements, and then organizing a serial of softwareservices, which forms a request-nd-combine-provide loop. Asdepicted in Fig. 10, DIMP has a User Domain and a PlatformDomain. The User Domain is effectively the Application Layer asin Cloud Manufacturing. The Platform Domain contains theResource Layer and Provider Layer. An important feature of thesystem is its service-oriented supervision mechanism. Consistingof an interface agent, broker agent and supervision agent, theSupervisory Module is connected with the other modules directly,e.g. Database Module and Application Warehouse Module. Thelatter represents the cloud manufacturing resources.

factu

X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 7586 83Fig. 7. Universal manuThe Supervision Module is a decision maker and core super-visor for the platform. The Interface agent collects requirementsfrom a user. After proposing a set of tasks to the user, the Interfaceagent gives the user access to a list of available applicationmodules and translates the result into a service description in apredened format before passing it to the Broker agent. TheBroker agent searches for available modules in the ApplicationWarehouse and chooses the best composition of the CloudManufacturing resources. As an approach to scenario generation,an optimized list of tasks and events is generated and passed tothe Supervision agent. Based on this list, selected software toolswill be packaged and provided to the user.

So far, there has been no report on a developed cloudmanufacturing system. However, the above-mentioned systemsand concepts echo the spirit of cloud manufacturing and providesome essential technological support.

5. Conclusions

Cloud computing is changing the way industries and enter-prises do their businesses. With wider cloud adoption, access tobusiness-critical data and analytics will not just help enterprises

Fig. 8. Data exchange in a typical productring architecture [47].stay ahead, it will also be crucial to their existence. There arethree architectural features of cloud computing in terms of therequirements of end-users, enterprises that use the cloud as aplatform, and cloud providers themselves. These architecturalfeatures play a major role in the adoption of the cloud computingparadigm as a mainstream commodity in the enterprise world.

Cloud computing is emerging as one of the major enablers forthe manufacturing industry, transforming its business models,helping it align product innovation with business strategy, andcreating intelligent factory networks that encourage effectivecollaboration. This pay-by-use scenario will revolutionize manu-facturing in the same way that the Internet has already revolu-tionized our everyday and business lives. Manufacturing shopsare starting to take advantage of cloud computing because itsimply makes good economic sense. Two types of cloud comput-ing adoptions in the manufacturing sector have been suggested,manufacturing with direct adoption of cloud computing technol-ogies and cloud manufacturingthe manufacturing version ofcloud computing.

In terms of direct adoption of cloud computing in the manu-facturing sector, the key areas are around IT and new businessmodels, e.g. pay-as-you-go, production scaling up and down perdemand, and exibility in deploying and customizing solutions.

ion echelon, the shop oor level [48].

X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 758684The HR, CRM, and ERP functions may benet from using someemerging PaaS. Cloud computing can be effective in offeringBusiness-to-Business solutions for commerce transactionsbetween businesses, such as between a manufacturer and awholesaler, or between a wholesaler and a retailer.

Moving from production-oriented manufacturing to service-oriented manufacturing, cloud manufacturing seems to offer anattractive and natural solution. In cloud manufacturing, distribu-ted resources are encapsulated into cloud services and managed ina centralized way. Clients can use cloud services according to theirrequirements. Cloud users can request services ranging from

Fig. 10. Service-oriented

Fig. 9. System spectrumproduct design, manufacturing, testing, management and all otherstages of a product life cycle. The cloud manufacturing serviceplatform performs search, mapping, recommendation, and execu-tion of a service. Two main types of manufacturing resources canbe considered at the manufacturing resource layer, manufacturingphysical resources, and manufacturing capabilities.

Although the concept of cloud manufacturing is relatively new,virtual enterprise, and distributed manufacturing concepts havebeen around for a while and some of the proposed systems andframeworks bear the trace of cloud manufacturing, e.g. develop-ment of a service-oriented manufacturing environment and

DIMP architecture.

of the UbiDM [50].

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Acknowledgments

The author would like to thank the researchers at the Intelli-gent and Interoperable Manufacturing Systems group, TheUniversity of Auckland, for their valuable input and comments.

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X. Xu / Robotics and Computer-Integrated Manufacturing 28 (2012) 758686

From cloud computing to cloud manufacturingIntroductionCloud computing systemsProvider requirementsService delivery modelsOther essential requirements

Enterprise requirementsCloud deployment for enterprisesSecurityBusiness Process Management (BPM)

User requirementsUser consumption-based billing and meteringUser-centric privacyService Level Agreements (SLAs)User Experience (UX)

Cloud computing in the context of manufacturingSmart manufacturing with cloud computingCloud manufacturingManufacturing resource layerManufacturing virtual service layerEncapsulating manufacturing resources with mappingEnterprise requirements--Global Service LayerUser requirements-Application Layer

Research contributions to the concept of cloud manufacturingService-oriented manufacturing environmentSaaS for engineering simulationsSome embryonic cloud manufacturing systems

ConclusionsAcknowledgmentsReferences