a component-based distributed control system for assembly automation

7/28/2019 A Component-based Distributed Control System for Assembly Automation

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A Component-based Distributed Control Systemfor Assembly AutomationSzer-Ming Lee,Robert Hamisonand And rew A. West3%er-Ming Lee, Robert Harrison and Andrew A. Wesl, MSI Research Institute,Loughborough University, United Kingdom, LEI 13TU,e-mail : (s.m.lee, r.harris

Abslracr-This pnprr describes the implementation o f anovel distributed network-based indutri al control system fo rPO assembly automation system. The control system iscomposed of autonomous, intelligent components which haveIh e capability 9f participating in I h i Putomtion ranlmlwi thon1 the need for a master controller. It is rnvisaged thatassembly automation system that adopt this contrel approachcan lead to greater agility. reusability and reduction indevelopment cost.

Index Teerms-Componmt-based. distributed cootro1.assembly automation1. INTRODUCTlON

In 6.6 0 0 6.4 18greate tN that
mailto:a.a.west)@lbaro.ac.uk


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191 have proposed a peer-to-peer sequential contmlapproach to achieve simple sequential contml operationwithout the need o f a central controller. However, thiswncept have not been taken further to investigate theirapplicability in a practical industrial context, i.e.. enorrecovcry, fault diagnostic, human-machine interface etc.

111. BENEFITSF COMPONENT-BASED DEVELOPMENTComponent-based development ( CBD) appmach has

been regarded as the answer for organisations to managecomplexities and adapt lo changes rapidly [lO-l2]. Insteado f building a system from scratch, the C BD approachfacilitates system development using previously developedsystem elements. It encourages and enables systemdevelopment by building on and reusing past experiencesand knowledge. CBD is based on the assumption that thereissufficient commonality inmany large software systems tojusti* developing reusable components to exploit andsatisfy that wmmonality [13]. Developing systems out ofexisting components offers many benefits to developen andusers. namely. increased functionality. usability, efficiency,improve maintainability, reliability and decreasedevelopment cost [14-16].

With the emerging trend for distribution o f controlintelligence to field device, there i s a need for a component-based paradigmIOuppon the composition and deploymento f distributed components in an industrial controlenvironment. However, current component models is notsuitable for distributed control in indus trial automation dueto the following reasons:Industrial contrd systems have to meet real-time

requirements, such as predictability, quality-of-service,reliability, and timeliness. However, wmmoncomponent models such as COMiDCOM andC O M A ,does not address such issues (171.The component technologies are inherently wmplexand require large overheads an physical resources(processing power, memory, communicationbandwidth) [17, 181. This is not feasible in industrialautomation where the controllers and field devices havevery limited resources.

W. OTN AT ION FOR DlSTRlBUTED CONTROL SYSTEMFOR ASSEMBLYAUTOMATION

The need for a distributed control methodology and thebenefits o f component-based development concept hasmotivated researches into ways o f mplementing distributedwntml strategies for network-based industrial controlsystems. Based on this objective. the authors haveconceivedadistributed control approach that ca n be appliedinto the contcxt of distributed network-based industrialconVol systems [IS]. The approach has been investigatedand developed by MS I Research Institute under acollaborative research pmject invo lving F ord Motor UKand their partners [ ZO] . The project has resulted in theimplementation and evaluation of reeyn.5 5999 Tc -0.02ho9 308.6 21Tm 199.1e

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components during commissioning time. Communicationchannels are setup to connect the components logically sothat they can mgnitor the slate of one another and reactaccordingly. This component-based approach eliminates theneed for the system integrators to develop control programs,instead, they configure and logically couple componentstogether to enable them to operate in a coordinated way toachieve common system goals.VI]. IMPLEMENTATIONN ASSEMBL Y UTOMATION

peer-to-peer fashion. In addition to the main automationdevice, sensors are included with the component whenevernecessary to provide local close-loop control. T heinterfacing electronics are used to condition and translatethe output control signals from the controller to theautomation device and the input signals from the device tothe controller. Therefore, a component is a self-containedunit that is ready to be deployed immediately to anautomation svstem.

A. OverviewThe component-based approach was implemented on anevaluation assembly machine in Krause MachinenfabrikGmbH (K rause) in Bremen, Germany. T he machineconsists of a transport system and an assembly station. Thetransport system moves pallets into the assembly stationwhere pick-and-place operations were performed on thepallet. After the operation, pallets exit the station and weresorted by a track diverter to two lanes. The pallets werebuffered for a short period of time before released andtransported again into the assembly station for the next

the pallet and result of the assembly-operation.K Developmenr ojrhe componenr-basedconrrol sysrem

It isobserved that the assembly machine ismade up of anumber of common control elements that provides standardcontrol finctionalities to the system. In fact, Krause'scommissioning engineers have expressed that about70%ofthe controls and equipments for assembly are standard andefforts can be saved if the design, development andimplementation efforts for such control elements can beencapsulated and reused. Examples of these commonelementsareconveyor drives, stops, diverters, fixing units,indexing tables and pick-and-place gantries.Eleven different types of components were developed -namely, ConveyorDrives, Paller Sensor, Slop. Diverrer, RF/radio freouencvi ideenrilicorion unfr. Indexexim Unit.

has only a finite, constant number of SIUI IS . Each state hasflon.silionrIOne or more states. The transition Eom onestate to another is governed by condirions or rules. ThcFSMs provide an abstract description o f the component'sembedded contro l behavior. The states of the component(FSMs) arc available through the component's logicalinterface. V ia the interface, componentscan be interlockedtogether - associating the conditions for the transition as alogical combination of the states of other components.System application is defined t hrough the process ofcomponent interlocking.This paradigm allows a component to be developed andthen configured (interlocked) later to parlicular controlsystem requirements.

VI. DEVELOPINGOMPONENT-BASED SV SmM ~ . ,_ ~crrpper. z-axis "erricol gmrry Y-ans h"rb0nral gunnyPower supply unit and HMI connol pond Thesecomponents were used to compose the entire assemblysystem consisting of 22 components.

The component-based paradigm effectively decouplescomponent development with system development.Component development is primarily concerned withdefining the abstrad control behavior of the component(what to do) and implementing the control functionalities(how to do). On the other hand, the main objective ofsystcm devclopmcnt to define the situation or condition atwhich thc component can invoke its control function (whento do) based an thc abstract description of the component(what to do).System integrators can specify and develop the systemapplication by interlocking the components togetherwithout knowing the intemal implementation of thecomponenl. This enables them to focus on thedevelopmentof thc application without having to worry about lhe Iow-leve implementation detail s.The intcrlack definitions are downloaded into the

Fig. 2 shows the control behaviorsI - -]---- ir conveyor drive35


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stops. diverterr and fixing units. The wmponents weredeveloped according to the control behaviors described bythe respeclive FSMs. Law-level IiO , unctions wereimplemented to provide the control output actuation andwntrol feedback. Extemal conditions for transition werenot defined during component development time and couldbe specified afler the component has been developed. It isimportant to realize that component wntml behavior isgeneric and is not developed for any parlicular systemimplementation. The same wmponent can be reusedinstantly for any assembly system implementation.Afler the components have been developed, the nextstage concerns the development ofthe system by integratingthe pre-fabricated components. Appl ication behavior for thesystemwas specif ied by interlocking the external conditionswith other components' states.Fig. 3 shows an example of the application definitionfor a pan of the transport system. The task herewas to sortincoming pallets into two lanes using a STOP actuator, aPALLET SENSOR, a DIVERTER actuator and a TAGREADER (not shown in the figure). The pallet sensor woulddetect pallet arriving at the location. The pallet was stoppedand the program number was read off a RF data tag by theTAG READER. Pallets with program number I were sonedto lane I while pallets with program number 2 were sortedto lane 2. The STOP would wait far the DIVERTER toswitch to the correct lane before releasing the pallet.C.lmplrmrnlalfono/dislribuleed conrrol network usingLonWorkr M conlrol nehvork

Thc assembly system is implemented using L onW or kPwntrol network. LonWorks was developed by EchelonCorporation [Z] . Unlike mast fieldbuses which arefundamentally based on a masterlslave wntrol andwmmunication relationship, L onWorks provides a trulydistributed, heterarchical architecture which allows devicesfull autonomy to communicate with one another thmugh adistributed control network.Using LonWorks, the component control applicationdevelopment process can be decoupled from systemapplication configuration through the use of nerworkvarfublc fnrerf occes and conJ igurarion parameters.Components can communicate with one another using inputand output network variables by sending uni-directionalevent messages through the output network var iableinterfaces and receiving incoming messages through theinput network variable interfaces. Component developers

can create applications to response to changes in the inputnetwork variables and publish updates to the network viaoutput network variables without knowing who will be thesender and receiver of network messages duringdevelopment. This mmmunication relationship is definedafler the wmponent has heen developed. Configuration ofthe component is achieved with the use of configurationparameters, which can be accessed and modified afler thewntml application hasbeen developed.4 shows the network interface of a componentdeveloped for the assembly automation. Componentreceives operation commands from the operator console viathe oper,eruoonmode and operalion command input networkinterface. The component publishes its state through the

m l e and error output network interfaces. These can bebound to exrernal condi t i ons input network interface ofother components to interlock the wmponents together. Theinterlocks (external wnditions) far the components. as wellas other operational parameters are defined through theconfiguration parameters.Using this methodology, generic wntrol for thewmponents can he developed and implementedindependently without any prior knowledge of the targetapplication that they will be deployed. System application isdeveloped on top of such component by defining externalconditions to interlock the components together to providethe required system behavior.Fig. 6 shows a picture of the assembly system and thelayout of the transport system. The components that wereimplemented for the system are labeled in the diagrams.The components were packaged into small boxes andinstalled near the pi nt of control. They were networked toa 78 kbps (kilobitrisec) L onWorks free topl ogy network.A fl er the components application were separatelydeveloped and installed, a Process Definition Tooldeveloped for the research was used to dcfinethe interlocksfor the components [22]. The system is then installed andcommissioned.The assembly system had been successfully evaluated byK rause's commissioning engineer and demonstrated tocollaborating panners.

Fig.

vII1. ANALYSISND DlSCllSSlONIt is observed from the implementation that thebandwidth utilization of the component-based assemblyautomation system is less than 6% (Typically, the controlnetwork would be able to perf om effectively at bandwidth

0-

( comwonm JFig 4 Network interrace of r component

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Fig 6 tmplementmon ofcomponent-based aiiembly automation systemutilization below 40% before it starts to degrade). 7he lowutilization can he attributed to the use of event basedmessage propagation, where messages are sent via thecomponents in the network in an "as need basis.Application of the wmpanent-based approach toassembly automation can offeen imponant benefits. Thesystem is highly adaptable to change. I t is inherentlyscaleable, simply by adding or removing individualcomponents as required. Modifications to the systembehaviors can be achieved by simply altering the interlocksof the components. Therefore, the approach can offergreater agility to the system. It has been obsened that thewmponent-based approach can reduce th e time a e n forthedevelopment and implementation of thewntrol systemby as much as 40% [23]. This is mainly achieved throughthe ability to reuse wmmon componenu and the ease ofdeveloping t he system from components by merelyconfiguring the component interlocks instead of developinglow-level programs, for example, ladder logic.One critical phase in contemporary wmponent-basedsobar e engineering involves the mapping of logicalsoftware wmponents to physical resources. i.e., processingand data storage. Non-functional issueshas to be laken intoconsideration, e.g. how long does it lakes to execute thesolhvare components and how much memoly it consumes,in order to ensure the system can deliver the requiredperformance at runtime [ I X ] . In the wmponent-basedapproach proposed in this research, thewmponenl has pre-defined physical resources within the wmpanent boundaryand it isnot accessible across wmponents (Fig. 5 ) . Hence,the runtime perf omance of the component is independentof that of the other components. This enables larger systemto be constructed from components without violating theprinciple of wmposabili ty ~ i.e., propenies that have beenestablished at the component level will also hold as thesystem level 1241.

I t has been determined that by distributing the wntrdfunctionalities to nctworked components instead of wiringthe scnsarslaclualors o a central controller. significant costcan be saved. Moreover, sinw a number ofcontrol elementsused for assembly automalion are wmmon. they can be

embedded into standard wmponents. Researchen in K rausehave also foreseen the need to transfer the responsibility ofprogramming low-level automation wntrol devices to theequipment suppliers so that they can focus ondesigning anddeveloping assembly system without worrying about thelow-level programming details. The component-baseddistributed wntml approach proposed in this paper istherefore able to offer a practical way to achieve thisobjective.

1X.CONCLUSI ONIn this paper the concept of a campanent-baseddistributed wntrd system has been discussed. The controlsystem is able to operate without the need for a central

control ler. The component-based concept has beenimplemented in an assembly automation system. I t has beenestablished that the companent-based distributed wntmlapproach can offer greater agility, reusabili ty and ws tsaving for the development and implementation of assemblyautomation system. The implementation demonstrated thepracticality of distributing control to local wmponents inactuatodsensar leve ina network industrial wnml system.

X. REFERENCES[ I ] K . Ryu. Y . Son, and M. Jung, "Modeling andspecif ication of dynamic agents in fractalmanufacturing systems," Compuiers in Indusrry, vol.52, pp. 161- I 82.2003.

D K o a, S. Wu. M . Fleetwood, and H. Tamoto,"Agent-based holonic design and operationsenvironment for distributed manufacturing,"Compwers in I ndwq,v o l . 52.pp. 95-108,2003.121

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P. L eitao and F. Restivo. "A Framework forDistributed Manufacluring Applications." presentedat Advanced Summer Institute InternationalConference, AS1 2000, Bordeaux, France, 2000.A . Tbarumarajah, A. I. Wells, and L. Nemes,"Comparison of Ih e Bionic. Fractal and HolonicManufacturing systems concepts," IntC" rono1J ownul oJ iComputer ntegurrd Munufudurmy. vol.9, pp. 211-226, 19Y6.Anon., "PABADIS - Plant automation based ondistributed systems. White paper," PABA DISConsortium. URL :l lhtt~:llwwn. badis.arg 200 .D M . Dil ts, N. P. Boyd, and H. H. Whorms, "Theevolution of control architectures for automatedmanufacturing systems," ./ournu/ .fMunu/octwingSy.vtems.vol. I O pp. 79-93. 1991.V . Vyatkin and H.-M . Hanisch, "Component designand validation of decentralized reconfigumblecontrol systems with IEC61499," presented atProceeding of International Symposium onAdvanced Convol of Industrial Processes,Kumamoto, J apan, June 2002.C. M. Chew, G. S. Hong, and Y . S. Wong,"Distributed sequential control implementation usingpeer-to-peer approach," J ournol017he1nslitd;on sfEngi neers ,Singopore,vol.42, pp. 29-37,2002.S. M. Lee. G. S. Hong, Y. S. Wang, and C. M.Chew, "Directed Graph Model for DistributedSeauential Control." Intemot#onul Journal olCompurer Apphcatrons m Technologv, voI IO . pp.337-347, 1997K. Mclnnis, "Component-based Development - TheConcepts. Technology and Methodology," CastekSoftware Factory Inc. 2000.A. W. Brawn and K . C. Wallnau, "The current stateof Component-Based Sohare Engineering," IEEESoJ iioreSeptemher/October, 1998.C. Sryperski, Component s @ w r e :beyond objecr-orrenred propxm"m: New Y ork : ACM Press ;Harlow :Addison-Wesley, 1997.P. C. Clemena, "Fmm Subroutines to Subsystems:Component-Based Software Development," TheAmerican Programmer,vol. 8, 1995.1. Cmkovic and M. Larsson, "A case sNdy:Demands on camponent-based development."presented at Proceedings of 22th InternationalConference of Software Engineering, Limeric,

I. Cmkovic. M. L arsson, and F. L aden, "State ofthepractice: Component-based software engineeringcourse.." presented at Proceedings of 3rdInternational Workshop of Component-BasedSaflware Engineering, IEEE Computer Society,2000.W. Fleisch, "Applying Use Cases for theRequirements Validation of Component-Based Real-Time Solhare," presented at Proceedings of 2ndIEEE International Symposium on Object-OrientedReal-Time Distributed Computing (ISORC'99),,Saint-M alo, France, 1999.ARTIST, "Roadmap - Component-based Design andIntegration Platforms," Project IST-2001-34820.Advanced Real-Time Systems. httv:llwww.anist-embedddorg! 2003.U. Rastofer and F. Bellosa, "An Appmach toComponent-Bascd S o h a r e Engineering forDistributed Embedded Real-Time Systems."presented at World Multiconference on Systemics,Cybernetics and I nformatics (SCI 2000), Orlando,Florida, USA ., July 2000.S . M. Lee, "A Component-based Distributed ControlSystem for M anufacturing Automation. To besubmitted as Doctoral Dissertation," in MSIResearch Insrirute. Wolfson School o/ Mechanicaland Munu/acruring Engineering.: LoughboroughUniversity, 2004.Anon., "Assessment and Implementation of aComponent-based Paradigm for Agile Automation.GRlM 43586," MSI Research Instilute,Loughborough University 1998.Echelon, "Introduction 10 Ih e LanWorks System,"Echelon Corporation 1999.D. W. Thomas, A. A. West. R. Harrison, and C. S.McLead, " A Process Definition Envimnment forComponent Based Manufacturing Machine ControlSystems dcvcloped under th e Fonight VehiclePmgrmme," presented at S.A .E. Conference, 2001.M. H. Ong, "Evaluating the implementation ofCompoent-based A pproach in the domain ofAutomotive M anufacturing. To be submitted asDoctoral Dissertation.," in MSI Research Institute.WolfFon School oJ Mechanical and Mcmu/ocIruri ngEngineering. Loughborough University, 2004.H. Kopetz, "Component-based design of largedistributed real-time systems." Comtrol EngmeeringIreland, 2000 Proctrse, voI 6, pp. 53-60, 1997

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a component-based distributed control system for assembly automation

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