Halmstad University Post-Print
An Implementation of a 3-tier
Hierarchical Wireless Sensor Network
Urban Bilstrup and Per-Arne Wiberg
N.B.: When citing this work, cite the original article.
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Bilstrup U, Wiberg P. An Implementation of a 3-tier Hierarchical Wireless Sensor Network. In: 2006 IEEE International Conference on industrial Informatics. IEEE;
2006. p. 138-143.
DOI: http://dx.doi.org/10.1109/INDIN.2006.275749 Copyright: IEEE
Post-Print available at: Halmstad University DiVA
http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-2107
Research
onData Transformation in Integrated
Virtual Assembly
Environment
Wen-hua ZHUl, Deng-zhe MA 2
1 CIMSand Robot Research Center, ShanghaiUniversity, 200072, China 2. CIMResearchInstitute, ShanghaiJiao TongUniversity, 200030, China
Abstract- This paper presents a new method of data transformation inanintegrated virtual assembly environment.
Information extraction and model conversion method is put forward. In this method the process of assembly model transformation is divided into two processes; information extraction and model conversion. Model data information is transferred intoan integrated virtual assembly environment by application development of CAD systems and model conversion. Treating the feed device ofa conecrusher as a virtual assemblyobject, the result of data transformation has beenverifiedaninintegrated virtual assembly environment.
This concludes that the method is accurate and the effect of datatransformation has been validated.
I. INTRODUCTION
W ITH the globalization and networking of the manufacturing industry, the virtual manufacturing technique ofaproduct becomes increasingly important, and virtual assembly is one of the key techniques of virtual manufacturing. It is universally acknowledged that product assembly is to assemble the scattered parts and subassembliestobeanintegrated product. Itis the last step of a product manufacturing process. Generally the traditional assembly ofaproduct is completed with the real models, any small change will bring the result that a real model has to berebuilt, so it is a process to spend more time and more work, which leads to the waste ofcapital and material. With the development of the virtual assembly technique, a newlowcostandrapidmethod isprovidedto solve thequestion. Virtualassemblyisakind oftechnique that combines CAD techniques, visualization techniques, simulationtechniques, manufacturing techniques,assembly techniques and virtual reality andso on[l].
Nowadays manyresearch institutes andenterpriseshave Foundation item: Project supported by the Grand Science
&Technology Program, Shanghai,China. (No.025115007) Wen-hua ZHU is with CIMS and Robot ResearchCenter, Shanghai University, 200072, Shanghai, China. (e-mail:
Deng-zheMAis withComputer Integrated Manufacturing Institute, ShanghaiJiaoTongUniversity, 200030, Shanghai, China.(e-mail: mdz(cimssitu.edu.cn).
studied the virtualassembly technique and have gained a lot of progress. VADE [2,3] (Virtual Assembly Development Environment) which was developed by Washington University and the America Research Institute of Standard Technology. CODY [4] (Concept Dynamics) virtual assembly systemwasdeveloped by Bielefeld University in Germany. VDVAS [5] (Virtual Design and Virtual Assembly System) which is based on disassembly was developed by ZheJiang University in China. TsingHua University put forward and realized an assembly system ASMLS[6](Assembly SiMuLation System) in a concurrent environment. NorthwestIndustry University put forwardan assembly simulation based on operation models [7]. These above-mentioned researches on virtual assembly have received progress respectively, but they are not mature.
Virtual assembly technique is still developing. Integrated Virtual Assembly Environment (IVAE) is developed by Shanghai Jiao Tong University, in the environment an operatorcan usevirtualreality communication apparatusto interact the assembly operation. It supports scene navigating based on position tracker, and realizes real-time collision detection and optimum path plan in the environment, so that we can ensure the actual assembly process, increase theassembly efficiency and decrease the assemblycost.
Tobuildaflexibleassembly model is the first assignment in an integrated virtual assembly environment (IVAE).
Althoughcurrentvirtualreality software hassomeability of building models, ifwe want to create acomplex shape part or alarge assembly model, itcannot meettherequirement of modeling. Atpresentthe virtual model ismainly generated by 3D CAD system (e.g. UniGraphics and Pro/Engineer etc.),butIVAE cannotdirectlymakeuseofthe solid model which come from 3D CAD software. The model mustbe converted and besent toIVAE. How to convertthe model data into IVAE is the first step of virtual assembly, and is also thekeystepthat will affect thedisplay effect, assembly validation andrequired precision. This paper will focuson data transformation inIVAE.
II. INFORMATIONEXTRACTION AND MODEL CONVERSION METHOD[8]
Owingtothe virtualrealitydoesnothaveastrongability tobuildmodels,manyresearchers have studiedonthe data
conversion techniques from CAD systems to a virtual assembly environment. Their researches can be mainly classified into two kinds. One is that data exchange is depended on a neutral file, e.g. IGES (Initial Graphics Exchange Specification);STEP(STandard for the Exchange of Product model data); STL (STereo Lithography) and VRML (Virtual Reality Modeling Language); etc..
Although this method isverysimpleand direct, it has some obvious disadvantages. First, sometimes the model is simplified and approximated in the neutral file, and informationcanbe easily lost. Moreover, sometimes there is much redundant information inthe neutral file, and the data conversionefficiency is lower. Inparticular, there isa lack of required information of virtual assembly in the neutral file. The other kind is thatthey directly develop a newCAD systemby themselves, and combineCADdesign systemand virtual assemblysystem to share thesame data structure basis. This method can realize modeling and assemblingin a system, and doesnotneed dataconversion, but it is difficult tointegrate with the mainCAD software systems.
Each above-mentioned method has its advantages and disadvantages, in order to translate model from CAD systems to avirtual assembly environment better andmore effectively, this paper put forward information extraction and model conversionmethod, asFig.1 shown, the method is divided into two processes, which are information extraction and model conversion, and then take thesetwo processes data intoIVAE. This methodnotonly keeps the advantages of neutral file, but also compensates the disadvantages and can integrate with the main CAD systems. This method is characterized with datareliability and informationintegrality.
CADsystem
t IVAE environment c
Fig. 1 Diagram of informationextraction and model conversion method
A. Informationextractionprocess
Bytheapplication development ofCAD systems, we can directlyaccessthe inside data ofaCADmodel and transmit outthehierarchystructure, partsinformation and constraints information of the assembly model. As Fig.2 shows, traversing assemblytree canobtain allpartsinformation and
hierarchy structure, traversing assembly tree again can obtain mated constrains information and fill reference information ofgeometry item to the related parts model.
According to the model data rule in IVAE, information conversion is carried on, and is written to the initial file of assembly information, it fits the complicated assemblytree to adopt recursive transversal. The functionality ofthe information extraction is to transfer the assembly information of CAD model to virtual environment, and make the model data which is taken into the IVAE environment more accurate, more credible and with overall information.
I3DCAD Assembly model
F pEnd Fig.2 Flow chart of information extraction program
B. Modelconversionprocess
In the IVAE environment the assembly model can be renderedrapidly and checkanyconflict, therefore the model should have precise topology and geometry information, andassembly constraints information is also definedonthe precise model. In the IVAE environment we adopt two kinds of models to represent the same part; one is facet model to display, and the other is convex modelto detect collision. The functionality of model conversion is to display the product model and render it rapidly. Virtual reality apparatus can interact with the model to detect collision in real-time, allocate the parts position by constraint andoptimize the assembly path.
The conversion of the facet modelexports aSTLmodel through the model interface of CAD software. The parameterized solid model which is faceted can be taken into a virtual environment directly. The conversion ofa collision model isindirectly generated by facet model, with thehelpofgraphicalsystemaSTLmodelcanbe transferred to aneutral geometryPOLY (POLYgon face) model, then carry on the convex decomposition and generate a DCP (DeComPoser) modelto detectcollision,aDCPmodelcan take into theIVAEenvironmentdirectly.
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III. DETAILED REALIZATIONAND APPLICATION EXAMPLE
A. Software and Hardware Environment
In order to realize the information extraction and model conversion method, software environment we use UniGraphics NX as a CAD system to build a assembly model. We use Visual C++6.0 and UG/OPEN API as a development platform, using OpenGL Performer 3.0 and VR Flier developed by our project group as a graphical platform, using IVAE developed by our group as a application platform. For the hardware environmentwe use thePower Wall system. Itmainly includes an arc screen projection system, a SGI Onyx 3200 work station and VR peripheral apparatus e.g. data glove(pinch glove), 3D position trackerFOB(Flock of Birds),etc.. The data glove is shown in Fig.3(a), there are 10 touching sensors in the finger tips, and the FOB position tracker is bound on the backs ofthehand,asshown inFig.3(b).
(a) Pinch Glove (b) 3D position tracker FOB Fig.3 Data glove and Position tracker
B. Information extraction
Through the UG/OPEN API application program interface, UG NX is application developed by Visual C++6.0 to accessthe model databasis, the model assembly tree is traversedtwice, and obtain the hierarchy structure, parts information, constraints information and referenced geometryitems. Accordingtothe model data rule ofIVAE, information conversion is carried on, and is written to the initial file of theassembly information.
InUG NXsoftware theassembly model is expressed with a treelike datastructurewhich is calledanassemblytree. Its assembling process istobuild the hierarchical connections among the components. This connection relationship includes theassembly sequence implicitly. The component models are referred to assembly and the actual geometry data isnotstored in thecorresponding component in stead of assembly [9]. The assemblymust be traversed in orderto extract the assembly hierarchical structure and parts information. There is only one assembly tree for an assembly model, that means there is only one root, obviouslythe assemblyroot is veryimportto traverse the parts,it is thestarting positionof traversal.
UG/OPENAPI isaUserFunction toolkit that allows programshaveaccess toobject models in the database. In addition itprovides acompatible wayto compile and link programswith theUGenvironment. Itsupportsthe C/C++
language, the customer accesses the object model with
UF_initialize( and returns through UF terminate(. In UG/OPENAPI we cangetthe identifier ofanassemblyroot with the function UF ASSEM ask root_part occ, and get the identifiers of the children component ofrootwith the
function UF ASSEM ask_part occ children. For every child component we make use of seek children identifier function again, such circulation is going on until the componentis constitutedby a part only, then the traversal is complete. Based on this theory sub-program void CycleAssemblytree(tag_t child tag, tag_t parent tag, ivae appdata* appd) is designed with Visual C++ to traversetheassembly by using a recursion method, we can obtain the parts information with the function UF_ASSEM_ask_part_data, sub-program void AssemblyMembers(tag_t tag, ivae assembly* pa, ivae appdata* appd) is used to record the component member and part to get the hierarchy structure.
InUG NX software constraints relationship is expressed by mate condition. When mate conditions between two componentsaredefined, the systemcansolve the constraint automatically and parts positions are allocated. Thereare several constraints in mate condition, each constraint describes the mate type between the component features.
Generally thereareeightmatetypes whicharemate, align, angle, parallel, distance, tangent, perpendicular, and center.
Matecondition has different degrees of freedom based on the number of constraints. The mate information which should be extracted include such information as: mate component name, mate type, referred geometry item, and geometry item information etc.. Since mate condition is always stored in the component, we must traverse the assemblytreeagaintogetthemateconstraints information by using function UF ASSEM ask mc data of compnt.
Howeverthese mate constraints information is not available in IVAE,they should be restructured, TableIis themapping relationship between UG NX and IVAE.
TABLE I
MAPPING RELATIONSHIPFROMUG NXTOIVAE
Mate Type Mate Type
Constraint Value Constraint Value
TypeinUG inUG Typein in Remark
NX NX IVAE IVAE
Mate 3 Mate 0
Align 4 Aligninsertor 2or 8 Ifcylinder then 8
Angle 5 Angle 4
Mate Offset Ifthe directionof Distance 6 orAlign Ior3 mate face is
Distance 6 orAlign 1 or 3 coincident then3, is oppositethenI Ifthe direction of Parallel 7 Angle 4 mate facecoincidentisthen0,
isopposite thenPI
Perpen 8 Angle 4 AngleisPI/2
dicular
Center 9 Align 2 Transform
Tangent 10 Tangent 7
Accordingtorelationshipasshown inTABLEI,wemake use of sub-program UGconstrainttolVAE (UF_ASSEM_constraint_s constraint, ivae_constraint&
pcdata)totransfer the constraintsinformation, makeuseof sub-program void PartSelectAddltem(ivae appdata&
appdata) to get referred geometry item information, and utilizesub-program PartAddltem(inttag, inttag2, inttype,
ivae_part*part)toaddgeometryitemtocorrespondingparts information.
C. Modelconversion
Theassembly modelbuiltin UG NXisexportedanSTL model through the rapid prototyping interface. The STL model ismainly appliedinrapidprototype,herewe useitto facet the solid models. In a STL file all geometry are dispersed as a set of triangle facet, every triangle are described by the coordinate of three vertex and anormal vector. Theprecision oftriangle facetcanbe controlledby distance deviation andangle deviation. ASTLfile has less modelinformation, and itcanbeputintoavirtualassembly environment directly, to display the model and rapidly render. Onthe basis ofaSTL model we extractthe facet information of referenced geometry items through applicationdevelopment of UG/OPEN API, and write itto the initialassembly information filetosupplement the facet information.
The collision detect model of a virtual assembly is indirectly generated by facet model, with thehelp of the graphical system Open GL Performer, the STL model is convertedto aneutralgeometryPOLYmodelbyGsettopoly program, then the POLY model is converted a collision detect model DCP by convex decompose program Decomposer, and theDCPModel canbe taken intoIVAE directly, Fig.4 is flow chart of model conversion fromUG NXmodeltotheIVAEenvironment.
UGNX1
Assemblymodel
IUG/OPEN API ControldeviationI
| eeencegeometry Exporti Gsettopoly_,|Neutral geometry
item facet model STL model |
Decomposer
Initialassemblyinfo Convexdecomposer
TXTfile DCPmodell
| nironmen|
Fig.4Flow chart of model conversion
D. ApplicationExample
Treating the feed device ofa cone crusher as a virtual assembly object, webuild the assemblymodel in UG NX environment,usethe method of information extraction and modelconversion, and realize the data conversion fromUG
NX system toIVAE. ClickUGtoIVAE menucustomizedin UG NX to run the Export UGtoIVAE File, convert the assembly model information, export the initial assembly information file inthe IVAE environment, click Display IVAE File menu and it can show the initial assembly information converted, then carry on the conversion of modeltogetthecorrespondingSTLmodel andDCPmodel.
Theinitial assembly information file is readintheIVAE environment, and theassemblysceneispresentedinFig.5.
Accordingtohierarchicalstructureandassemblysequences we cancarry on theassemblyprocess, snap the part with pinchglove, thenmoveitto someposition thataconstraint can be highlighted to some extent. At the same time a constraint is recognized and confirmed. Inthe assembly process collision is detected automatically and the movementofpartswill form theassemblypath. Finally the assembly of feed device iscompleted.
Fig.5Assemblysceneof the feed device ofconecrusher IV. CONCLUSION
This paper study on the data transformation in IVAE, information extraction and modelcornversionmethod isput forward,and detailed realized the process ofthe method. By the application development of a CAD system, we can
directlyaccessthe inside data ofaCADmodel and transmit the hierarchical structure, parts information, constraints information and referenced geometry item of assembly
model. Facet model of STLstyleisexported throughmodel interface of CAD software. With thehelp ofa graphical system the STL model can be transferred to a neutral geometry POLY model, then carry on the convex
decomposition and generate a DCP model to detect collision. This methodcanbeapplied inmulti main CAD systems, probably there are some distinction among the differentapplication development. Treatingthe feed device ofa conecrusher as avirtualassembly object, the result of data transformation has been verified in the integrated
virtual assembly environment. This concludes that the method isaccurateand the effect of data transformation has been validated.
2006IEEEInternationalConferenceonIndustrialInformatics 291
ACKNOWLEDGEMENT
The authors gratefully acknowledge the contributions of Prof. Xiu-min FAN, PhD. Yang-xing OU, Dian-liang WU, andRun-dang YANG, etal.
REFERENCES
[1] Jun-qi YAN, Xiu-minFAN, Deng-zhe MA, et al. Theory, technicalfoundation andpractice of virtual manufacturing.
Shanghai Jiao Tong University Press, Shanghai: 2003 (in Chinese).
[2] S. JAYARAM, U. JAYARAM, Y. WANG, et al. "VADE: a virtual assembly design environment." IEEE Computer Graphics andApplications, vol. 19, no.6, 1999,pp.44-50.
[3] S.JAYARAAM, H. Connacher,K. Lyons. "Virtual assembly using virtual reality techniques." Computer-Aided Design, vol.29, no.8, 1997,pp.575-584.
[4] B. JUNG, M. HOFFHENKE, I. WACHSMUTH. "Virtual Assembly with Construction Kits." In Proceedings of DETC'97, ASME Design for Engineering Technical Conferences, September 14-17, 1997, Sacramento, California. (DETC97/DFM4363).
[5] Hua-gen WAN, Shu-ming GAO, Qun-sheng PENG.
"VDVAS: anintegrated virtual design and virtual assembly environment." Chinese Journal of Computer & Graphics, vol.7, no.1, 2002,pp.27-35(in Chinese).
[6] Lin-xuan ZHANG,Bing-shu TONG, Tian-yuan XIAO,etal.
"Realization andapplication ofassembly simulationsystemin the CE environment." Computer Applications, vol.2, no.8, 2000,pp. 194-197(in Chinese).
[7] Yuan LI, Tao ZHANG, Jian-feng YU, Hai-chang YANG.
"Research on assembly simulation based on operation models." MechanicalScienceandTechnology. vol.19, no.3, 2000,pp.503-505(in Chinese).
[8] Wen-hua Zhu. Research on Virtual Product Rapid Development andData Transformation in VirtualAssembly Environment. PostdoctoralWorking Thesis of Shanghai Jiao TongUniversity. 2005(in Chinese).
[9] Zhong-wei DONG, Li-zhong TIAN, Yi-li FU. Program foundation of UGIOPENAPI. Tsinghua University Press,
Beijing:2002(in Chinese)
logical rulesareconfigured by theoperator.
General issuesconcerning the design of wireless sensor networks are of course the problem of proving the correctness of a distributed system. It is very hard to actually pinpoint errors, especially when it comes to transient errors. The complexity of a distributed system, such as a wireless sensor network, is high even if the functionality may seem to be very limited. Non-coherent system state is a general problem and has atendency to generate system errors if not properly implemented. One example is that a device thinks that a wireless communication link is lost caused by retransmission timeoutevenifthelinkisnotlost,e.g.,problemwith local clocks' drift. As aconcluding remarkone cansaythat the 3-tier architecture reflects thestructureofawirelesssensor network on a holistic level but it lacks the inherent structure to distribute functionality over several devices.
This isnecessary inordertofulfilresourcerestrictionsin a heterogeneous wirelesssensornetwork.
IX.REFERENCES
[1] Theodore S. Rappaport, "Indoor Radio Communications for Factories in the Future", IEEE Commun. Mag., Vol. 27. Issue 5, May 1989,pp. 15- [2] 24.P-A. Wiberg andU.Bilstrup, "Wireless technologyin industry - Applications and user scenarios", in Proceeding of the 8thIEEEConference onEmerging Technologies and FactoryAutomation, Antibes-Juan lesPins,FranceOctober 2001,pp. 123-133.
[3] A. Willig K. Matheus and A. Wolisz, "Wireless Technology in Industrial Networks," in Proceedings ofthe IEEE, Vol. 93,No.6,June2005 pp. 1130-1151.
[4] R. Zurawski edi., The Industrial Information Handbook,CRC press,U.S.,2005.
[5] K. Koumpis, L. Hanna, M. Andersson and M.
Johansson, "A review and roadmap of wireless industrial control," available at:
protocol stack, available at: www.bluez.org,(060215).
[12] E. Morrogh, Information Architecture: An Emerging 21]t Century Profession, Prentice Hall, U.S., November 2002.
[13] Free2move Embedded Linux System - F2MO5, information available at www.free2move.se/
prod emb.shtml (060215).
[14]Bluetooth serial port plug - F2M01, information available at www.free2move.se/prod_spp.shtml, (060515).
[15]Bluetooth SIG,Specification of the Bluetooth system -Profilesv. 1.1,February,2001.
[16] Free2move AB, Wireless UART protocol v. xx, information available from www.free2move.se (060515).
[17]Bluetooth Class 1 module - F2M03C1, information available at www.free2move.se/prod_mod.shtml, (060515).
[18] Nordic VLSI, "Single chip 2.4GHz Transceiver nRF2401", available at: http:Hwww.nvlsi.no (060215).
[19] MICROCHIP, "PIC16F87/88 Data sheet", available athttp:Hwww.microchip.com (050215).
[20]D. Baum, M. Gasperi, R Hempel and L.Villa, Extreme Mindstorms -Anadvanced guide toLEGO Mindstorms, Apress, U.S.,2000.
[21]LabView, information available at http:Hwww.ni.com/labview/ (060515)
[22]Tiny OS, available at: http:Hwww.tinyos.net/
(060215)
(060215).
[6] D.Estrinet.al.. Embedded,Everywhere -Aresearch Agenda for Networked Systems of Embedded Computers, Committee on Networked Systems of Embedded computers, Computer Science and Telecommunication Board and National Research Council, National Academy Press, Washington DC, 2001.
[7] IEEE Computer Society LAN MAN standards Committee. IEEE Std 802.15.4-2003 Wireless MediumAccess Control (MAC) and Physical Layer (PHY) Specifications forLow-Rate Wireless Personal Area Networks (LR-WPANs). The institute of Electrical and ElectronicsEngineers, NewYork, NY, May2003.
[8] ZigBee Alliance, ZigBee standardv 1.0,2005.
[9] Free2moveAB, www.Free2move.se, (060215).
[10] Linux kernel 2.6.11 for ETRAX available at:
http:Hdeveloper.axis.com/download/software.html (060215).
[11] Sourceforge, BlueZ - Official Linux Bluetooth
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