The 13th International Symposium on Virtual Reality Archaeology and Cultural Heritage VAST (2012)D Arnold J Kaminski F Niccolucci and A Stork (Editors)

Parametric 3D-fitted frames for packaging heritage artefacts

Asla M Saacutedagger12 Karina Rodriguez Echavarria2 Martin Griffin2 Derek Covill3 Jaime Kaminski2 and David Arnold2

1Escola de Matemaacutetica Aplicada EMAp - FGV Brazil2Cultural Informatics Research Group University of Brighton UK

3School of Computing Engineering and Mathematics University of Brighton UK

AbstractPacking fragile heritage artefacts is a challenge almost all heritage organisations have to deal with when facedwith the task of transporting or storing the artefacts The packaging solution requires fitting the artefact correctlyin order to ensure the protection and safety of the item but also to be easy and cost effective to produce Differenttechniques have been traditionally used such as double boxing padding negative spaces and cushioning bracesHowever the introduction of 3D technologies for documenting these artefacts enables innovative uses of this datafor packaging purposes Hence this paper proposes the use of the generative modelling language in order toproduce unique 3D-fitted containers for packaging heritage artefacts which fit tightly the artefact and can bemade to be reusable and more durable than traditional packaging solutions We propose to adopt an octet latticeas a low density internal structure to the proposed container By combining the parametric package design 3Dmeshes acquisition and 3D printing techniques we present a technology based solution to the traditional problemof protecting these valuable artefacts for transportation andor storing purposes

Categories and Subject Descriptors (according to ACM CCS) I33 [Computer Graphics] PictureImageGenerationmdashLine and curve generation I35 [Computer Graphics] Computational Geometry and ObjectModelingmdashGeometric algorithms languages and systems J6 [Computer Applications] Computer AidedEngineeringmdashComputer-aided design (CAD)

1 Introduction

Almost all heritage organisations are faced with the task ofplanning and designing packaging solutions when they needto store or transport artefacts to other locations Packagingheritage artefacts is a complex issue where one solution doesnot work for all situations due to the different physical char-acteristics of these artefacts However most packaging so-lutions need to address a basic set of requirements Theseinclude fitting the artefact correctly supporting its weighteffectively minimising the amount of handling an artefactrequires and simplifying the unpacking and repacking Fur-thermore more complex shapes and fragile items require ofadditional protection against the effects of temperature hu-midity and vibration as well as appropriate spacing of arte-facts if they are being grouped for transportation As suchdifferent techniques are commonly used by heritage techni-

dagger supported by CAPES - Brazil

cians as described by [Bau93] But the task is very muchstill a craft skill Automating the creation of packing arte-facts could both save money and time and additionally offera solution to smaller and less skilled users or less budgetedinstitutions of an efficient means of creating packing

The increasing popularity of 3D documentation of her-itage artefacts offers an opportunity in the packaging fieldThis is because accurate 3D models of artefacts can be usedto automatically produce packaging solutions in an easierand less time consuming manner As such this paper pro-poses the use of the generative modelling technology to au-tomatically produce unique structures which can parametri-cally adapt to the size and the shape of a specific artefactCombined with 3D printing techniques this solution repre-sents several advantages to more traditional methods suchas the automation and ease of its production as well as thereduction of material wastage

The paper will be structured as follow Section 2 will de-scribe previous work on traditional methods for packaging

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

heritage artefacts Section 3 will describe and review theconcept of low density structures and 3D printing In section4 and 5 we propose our 3D low density structure and de-scribe its implementation which takes advantage of genera-tive modelling technologies Finally in section 6 we presentour prototype followed by some conclusions and furtherwork

2 Packaging heritage artefacts

Several solutions for packing heritage artefacts have beenproposed within museum communities Proper packing tech-niques are critical to ensure artefacts are stored and trans-ported safely In contrast an artefact packed incorrectly canbe permanently damaged Another complexity is that eachartefact requires a unique packaging solution Hence tradi-tional methods for designing and producing packing mightinvolve several hours or even days depending on the spe-cific case In addition different considerations need to bemade for selecting the most suitable method for packaging afragile and valuable heritage artefact This includes the ma-terial weight stiffness and the shape of the artefact

Packing materials are diverse and can have different ef-fects on the artefacts For instance fragile artefacts madeof material such as glass charcoal or corroded metals arevulnerable to damage from abrasion polished metals var-nished woods oriental lacquer and other smooth-surfacedartefacts are vulnerable to get imprints from plastic bubblesand foams

Different shapes weight and stiffness pose specific chal-lenges to the packaging solution While the main goal is toprotect the artefact from potential damage during storageor transportation another important objective of this pro-posal is to minimize the material usage the size and the finalweight of the solution This will have a direct impact on thecost

There are a variety of techniques that are traditionallyused These rely mostly on using cushioning materials in or-der to absorb shock vibration and buffer the humidity Theyinclude materials such as foam products that can be used ina variety of cushioning techniques As described in [US99]these techniques include

bull Cavity packaging This simple technique involves plac-ing the artefact into a cut made in polyethylene foam withthe shape of the artefact This method is clean and easy touse for repacking (see Figure 1-a)

bull Sparse layered packaging This technique is similarto cavity packaging but the cushioning material is dis-tributed sparsely around the artefact (see Figure 1-b)

bull Double boxing This technique involves packing an arte-fact using two sequential boxes in order to cushion theartefact For this the artefact is cushioned inside one boxThen another box at least 5 cm larger on all sides is usedwith further cushioning in between

bull Padding negative spaces This technique involves pack-aging an artefact surrounded with tissue paper and thenwrapping in successive layers of bubble wrap The arte-fact is placed inside a container and then tissue or someother cushioning material is used to fill in the excess area

bull Cushioning braces This technique involves using acushioning bracket to hold the artefact in place

Figure 1 Examples of packaging techniques (left) cav-ity packaging and (right) sparse layered packagingccopyFenimore Art Museum and Darla Jackson sculpture blog

These techniques demonstrate how the shape of the arte-fact plays a critical role in the production of the packing so-lution Carving or designing a package around a shape is stilla laborious process mostly done manually

The advent of 3D technologies for the routinely documen-tation of artefacts in collections (see [KREPlowast12]) representsan opportunity to use this data for packaging purposes Re-ciprocally the opportunity to enhance packaging techniquesmay motivate the adoption of 3D technologies for document-ing as information on the shape of the artefact can sup-port different kinds of applications The digital 3D shape ofthe artefact enables a completely automatic design and pro-duction pipeline of the 3D-fitted container for the artefactThe next section will introduce different types of structureswhich might be suitable for the internal structure of the pack-aging solution to be 3D printed

3 Low density structures and 3D printing

Low density structures are frequently found in nature andare widely studied in engineering architecture as well as inproduct design where they are used as efficient structuresthat serve a variety of purposes ranging from bridges androofs to internal structures of car seats or toys

One benefit of low density structures is that they re-duce the amount of building material Hence reducing costsandor final weight of the whole structure while guarantee-ing some mechanical properties that are desired for the prod-uct Today low density structures also inspire projects thatare environmentally sustainable since by minimizing mate-rial usage there is a reduction of waste The potential to pro-duce more durable and reusable packaging solutions is alsoan advantage

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 2 Two low density structures can be observed inthe Figure (left) an example of a truss used in a bridgestructure and (right) an example of a honeycombed struc-ture found in Durvillaea antarctica alga ( ccopyAndre-PhilippeDrapeau Picard)

An example of these type of structures are trusses whichare illustrated in figure 2-left These are well known in archi-tecture and engineering [Gor03] In the language of struc-tural engineering a lattice truss or space frame is a con-nected network of struts pin-joined or rigidly bonded attheir connections The purpose of such frames is to createstiff strong load-bearing structures while minimizing ma-terial usage The mechanical properties of trusses have beenwidely studied and plenty of references are available as wellas software that deals with the calculations [CF12]

Other examples of low density structures can also befound in nature where efficient structures with a reducedamount of material can be frequently observed For exam-ple figure 2-right illustrates a transversal cut of the leaf of aalga specimen showing the air-filled honeycomb structuresthat provides its buoyancy

Moreover internal structures referred to as cellular mate-rials can be found within bones as well as in honeycombsand are famous for their exceptional mechanical propertiesand for their light weight [Chr00] provides a detailed surveyon this type of structure Cellular materials are also knownas lattice-structured materials or cellular solids They arecharacterized by their relative density and are a hot topicof research nowadays due to the wide range of applicationsrecently found in industry

In product design honeycomb inspired structures broughtinnovation to aircraft design motor vehicle technology aswell as to light-weight construction They have also formedthe basis for the development of honeycomb structured pan-els [Bit97 Wad06]

The application of low density structures as a solution fordesigning internal structures have gained prominence withthe advent of 3D printing or rapid prototyping 3D printingis a manufacturing approach that can theoretically build anythree-dimensional shapes and topologies by different mech-anism The most popular is known as additive manufactur-

ing which produces a 3D shape by adding materials layerby layer [GRS09]

The range of base materials that are used in 3D printing iswide The study of 3D printed objectrsquos mechanical proper-ties with varying materials is still a topic of research Thusthe structural analysis of 3D designs can suffer from the lackof information In this work we are not going to explore thepossibilities in varying the base materials or studying in de-tail their structural analysis

The recent improvements on the strength and durabilityof the base materials that are used in additive manufacturinghas expanded the range of its applications Therefore ad-ditive manufacturing is bringing a great change to differenttypes of industries including the packaging industry

In this paper we propose a solution for printing a 3Dfitted container for packaging heritage artefacts We arguethat the internal structure of the fitted frame should be de-signed using low density structures to benefit from its ad-vantages Several projects in product design that take ad-vantage of such internal structures along with 3D printingtechniques are being proposed [A 12] There is also com-mercial software available for instance the Selective SpaceStructures (3S) Software from Netfabb [Net12] which is ahigh-end design tool that allows the development of com-plex unit cell structures for additive manufacturing purposesSeveral mesh generation tools are available as well The fol-lowing section will introduce the proposed structure beforediscussing its implementation

4 Proposed low density structure for packagingheritage artefacts

Inspired by the evidences exposed in section 3 we proposeto model the internal structure of our 3D-fitted packagingsolution as a low density structure In order to design thecontainerrsquos internal structures we looked for ways to fill thespace with such sparse structures that could be efficient fromthe structural point of view

In the Computer Graphics literature the structures we arelooking for are the widely studied 3D meshes In special the3D meshes adopted for the finite elements methods (FEM)are directly related to the solution that we are looking forWhen considering to adopt FEM 3D meshing algorithms wehave to have in mind that they intend to serve the purpose ofFEM calculations and are built to produce virtual meshesThus mechanical properties of the mesh itself are not rele-vant to that field of application In our case after generatingthe 3D mesh wire-frame model we will need to process itin order to turn it into a 3D mesh surface aiming to achievea 3D printable truss That is essentially the 3D mesh wire-frame model with thickness attributed to its edges

There are lots of commercial and open-source meshingsoftware available in the literature A review on those meth-

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

ods and software is beyond the scope of the present pa-per A survey on 3D meshing software by Owen [Owe98]from 1998 is a review of the fundamental algorithms thenavailable for 3D mesh generation Owenrsquos survey classi-fies the 3D mesh generators into two broad classes that arestructured and unstructured 3D meshes The classification ismade based on the criteria of interior nodes elementrsquos ad-jacency Structured meshes have equal number of adjacentelements while unstructured meshes relax the node valencerequirement allowing any number of elements to meet at asingle node More recently FEM simulations in medicinemolecular biology and engineering has increased the needfor quality 3D meshes in Zhang [ZBS05] the authors pro-pose an algorithm and make an extensive comparison toother tetrahedral extraction methods from imaging data

We adopt the branch of structured 3D meshes for they aremore stable from the mechanical point of view In [Wad06]Wadley argues on the strength of such kind of structurewithin the context of industrial applications One interestingsubset of structured 3D meshes are the space-filling polyhe-drons [Cox73 Cri73]

A space-filling polyhedron is a type of polyhedron whichcan be used to generate a tessellation of space The cubeis the only platonic solid possessing this property and itstessellation is widely adopted in Computer Graphics theclassics Octree data structure and the Marching Cubes algo-rithm explore this basic tessellation of space However othercombinations of polyhedrons can also fill the space A spe-cific configuration of octahedron and tetrahedron do fill thespace Figure 3 illustrates the octahedron frame (left) anda diagram that shows an exploded view of the octahedronand tetrahedron filling-space configuration (right) Other op-tions of space filling structures are available in the litera-ture [FH99 CJT11] Additionally topological interlockingof platonic solids [DEKBP03 EDP11] are argued to havevery good mechanical properties

Figure 3 Basic unit of the octet-frame

The octahedron tetrahedron filling-space configuration isknown in architecture domain as Octet Truss and its me-chanical properties have been studied by Deshpande et alin [DFA01] The authors submit a prototype of the octettruss made of aluminium to a sequence of tests as well astheir theoretical values are predicted by means of finite el-ements calculations The authors conclude that the stiffness

and strength of the octet truss material compare favourablywith the corresponding properties of metallic foams and thatits high strength-to-weight ratio relative ease of manufac-ture and potential for multi-functional applications makesthe octet truss material an attractive alternative to metallicfoams We thus conclude that the octet truss is a good start-ing point for the internal structure of our container

From the computer graphics point of view 3D meshed ofspace filling frames can be constructed by placing copies ofthe basic figures in proper places until a desired amount ofspace is completely filled Although the resultant 3D meshis not the most efficient to solve the intersection of the octet-frame with another mesh We observe that the edges of theoctet frame are aligned within the same direction and can betaught as a segment of a straight line This leads us to the ab-straction of the aligned edges as rays that starts at one faceof the frame bounding box to its interior Such abstractionpermits to use the same concept of ray tracing when calcu-lating the intersection of the 3D frame with the object meshThis will be the abstraction that will guide the implementa-tion described in the next section

5 Implementation using generative modelling

Generating an octet truss which fits tightly to the shape ofan artefact presents different challenges The truss needs tobe easily adaptable to fit any 3D model which needs to bepackaged despite its shape and size In addition two opera-tions need to be taken into account The first is defining theempty space in the centre where the artefact is going to fitSecondly the truss needs to be cut in half or in more piecesif there are undercuts or recessed surfaces in the artefact inorder to allow the artefact to be placed and released from thestructure

Figure 4 Example mesh for experimenting with 3D fittedframe

Before building the octet truss it is necessary to have in-formation on the 3D shape of the artefact For this a 3Dmodel with low level of detail can be used as accuracy isnot a critical issue This is specially the case if the artefactstill requires of some cloth or other wrapping case to pro-tect the artefact surface This might be particularly useful for

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

artefacts which are not completely rigid or are very fragileHence cost effective techniques such as photogrammetry( [VG06] and [Aut12]) are possible for many artefacts Fordemonstration purposes we used a delicate artefact (shownin Figure-4) which shape data had been acquired using a 3Dscanner The 3D mesh was post-processed and simplified us-ing the Meshlab tool [Mes12] by using a Poisson surface re-construction

In order to address the challenges described before weconsidered using a combination of a mesh generation orgrid generation tool with a modelling package for definingthe empty space For this different public and commercialmesh generation packages are available Schneiders presentsa comprehensive list of examples of these systems [Sch12]Nevertheless these are focused on producing mainly wire-frames or grid structures In addition the use of modellingpackages introduce many complexities to the constructionof the truss and require of manual intervention each timea new solution is created Instead we required of an inte-grated modelling solution which could produce a mesh us-ing a tetahedral-octahedral as the basic unit but most im-portantly that produced a printable solution and not only awireframe

We found a suitable solution by using the generative mod-elling language (GML) [Hav05] This tool allowed us todefine the sequence of processing steps to define the octetframe and convert this into an octet tryss while allowing theparameterising of its construction As such a GML scriptwas developed which can be easily adapted and configuredfor different types of objects using a set of parameters Theseparameters include the number of units which will determinethe width height and depth of the octet truss as well as forthe cross section the radius of the prism and the number ofedges (eg 3 makes a triangular prism while 20 approxi-mates a cylinder)

The simplest approach for implementing the octet-frameis by building a basic tetahedral-octahedral unit in wireframeand repeating this in a loop in order to create a box with aspecified width length and depth This approach was initallytested but it proved problematic once the artefact had to befitted inside This is because a further implementation of aboolean operation algorithm needs to be implemented forgenerating the empty space where the artefact is going to beplaced Hence the problem with this approach is two-fold

bull It is complex to decide whether the edge of a specific basicunit is within the artefact

bull It is complex to decide which segment of the edge is out-side the artefact if there is an intersection

Instead a better approach is to consider the whole framecomposed of various lines or rays rather than the indivudalbasic units Then the 3D shape of the artefact can be usedalong with the ray-casting technique in order to determinewhere the rays intersect with the 3D mesh

Figure 5 Initial wireframe produced by using rays

Thus firstly the frame is constructed in GML by usingrays that travel from each face on the frame Each face con-tains a list of vertices that define a tetrahedron These raysneed to travel in the directions of the edges connected tothat vertex These rays will always be outside the artefactand attached to the edge of the bounding polyhedron Thisapproach also optimizes the frame structure as it minimizesthe number of lines and therefore minimizes the number ofintersection tests that need to be done Once this frame is cre-ated this must be translated and scaled to enclose the artefactthat is being intersected against it The resulting frame in thisstep is shown in figure 5

The next step is to convert the rays into a set of lines thatare truncated to fit within the bounding polyhedron Theselines are then checked for intersection with the artefact Ifthere is an intersection the line is split in two leaving agap where the artefact will fit tightly within the octet frameHence the line is replaced by a line from its start point to thefirst point of intersection and a line from its end point to thelast point of intersection (see figure 6-top) Additionally theimplementation erodes the lines that intersect the artefact sothat there will be enough space to place the physical artefactinside the frame once this is printed (see figure 6-bottom)

Finally the octet frame is cut in half so that this can beopened and closed to place and release the artefact insideFor this the lines are intersected against a plane that goesthrough the middle of the frame to produce two sets of linesThe final step is to convert all lines into prisms along thelength of the line and create the 3D model which representsthe octet truss for the two surface models (base and summit)These are the 3D models which will be printed as the finalsolution

The final octet truss is shown in figure 7 along with theprotective case and the object fitted inside As illustrated inthe figure this approach allows for fitting a shell case to pro-tect further the artefact if this was required This shell casecan easily be developed in a modelling package by scalingthe artefact cutting it in half and shelling each side Hencethe object has a double casing to further protect the heritageartefact during transportation

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 6 Wireframe intersected with the 3D shape

Figure 7 Final octet truss ready for printing

In order to verify the suitability of the approach and thescript we tested the script with a mixture of 3D shapes offragile artefacts These have been acquired with a variety of3D acquisition technologies Nevertheless the steps to pro-duce the octet truss are the same producing promising resultsso far These results are illustrated in figure 8 The octet trussis feasible for different types of objects although we did nottested undercuts

Figure 8 Examples of different 3D shapes tested to producean octet truss for packaging

6 3D Printing the structure

As a proof of concept we are in the process of finding theadequate density and thickness dimensions for printing thestructure We are experimenting with a Zcorp 510 machineusing a plaster based powder (ZP150) to generate the struc-ture layer by layer This machine has several advantages toother 3D printing technologies For instance internal sup-ports can be generated that are separate to the structure itselfand so can be easily removed upon excavation of the struc-ture or that the porous powder can be infiltrated with epoxyresin to significantly increase the material strength

In order to compare the octet-frame proposed in section4 to other 3D printed structures an hexahedron (six quadri-lateral faces) unit cell based structure has been designed andwill be printed as well The intention is to investigate theeffects of element type on the overall performance of thestructure

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

In order to print both frames an initial attempt was con-ducted by using an initial design of the structures in particu-lar considering their density and thickness The initial objec-tive was to minimise as much as possible the usage of ma-terial For this we selected a 25 cm length for the struct ofthe basic unit and a truss wall thickness of 10 mm This hasresulted in failure with the selected thickness as the struc-ture broke down during the excavation due to its fragilityThe failed attempt is illustrated in Figure 9 In following tri-als we are varying the thickness up to 30 mm wall thicknessas we estimate this is a critical measurement for providingstrength to the overall structure Hence carefully estimatingits ideal value is an important part of the research and is cur-rently work in progress By using the parametric implemen-tation for the mesh generation the density and the thicknessvariation is straightforward

Further prototypes will be generated using other tech-niques to allow for a direct comparison and evaluationThese include using a VFlash 3D printing machine whichprints directly in acrylic (a softer material which is not asstrong as the epoxy resin infused powder material) and us-ing a laser cutter to produce a lattice of cardboard slices togenerate a 3D structure with an accurate contour bed for theobject to lie in

The testing experiments planned involve testing the loadcapacity of the structures supporting a small fragile objectThis will include both a compression load test case and adrop load test case The compression load case involvesloading the structure with 1kg masses and increasing theload by 1 kg per increment to investigate the maximum loadcapacity of the structure before the fragile object breaks Thedrop test will be conducted in a similar fashion dropping thestructure in a controlled drop test from an initial height of 10cm increasing this by 10 cm thereafter

The materials used in a further experiment may provide astrong and sturdy support for the object and this can be donesetting consistently the mesh density Ideally the material inimmediate contact with the object will be softer and moreforgiving to the surface of the object and this can be achievedby either using a multiple density 3D printing machine (egObjet Connex 500) or by manipulating the structural den-sity surrounding the object such that thinner walled less stiffstructures can be used to surround the object Similarly theoverall density of the structure needs to be considered to op-timise the weight of the structure whilst providing sufficientstrength and stiffness to withstand load cases that are typi-cal for stacking and transit Although we could not explorethe wide range of possibilities regarding the production ofa prototype we are convinced that the proposed structure isfeasible and a rigorous exploration of the range of possibili-ties and technology limitations is left as future work

Figure 9 3D printing failure at the first attempt

7 Conclusions

The movement of heritage artefacts is a process most her-itage organisations need to undertake Packaging artefactscorrectly is critical as artefacts are at their most vulnerablewhen transited Hence this paper has introduced an innova-tive approach for packaging the artefacts based on 3D tech-nology The proposed solution makes use of a Tetrahedral -Octahedral Frame This is produced using a generative mod-elling approach so that it can parametrically produce struc-tures that will fit any artefact The resulting structure pro-vides a number of advantages

bull A bespoke packaging solution that is tailored to specificartefact

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

bull An easier and more automatic process than traditionalmethods

bull Requires the 3D documentation of the artefact which inturn can be used for different purposes (eg conservationcondition assessment)

Although such packaging solution might incur a higher costof production when compared to traditional methods we es-timate that this is balanced by the fact that less time needs tobe spent producing the packaging

Further work beside the ongoing printing and testingwork involves developing structural analysis of the fittedpackage frame and considering the artefact weight to dy-namically adapt the structure The final goal is to minimizematerial needs while guaranteeing that the package frameprotects the artefact in transportation and potentially stor-age conditions

The proposed octet truss achieved so far can be improvedin different ways One is to consider the production of a pro-tective case for the object to be place in between the objectand the octet truss To do so a possible approach would beto 3D print the protective case by means of off-setting theobject mesh as proposed by Liu in [LW11] and then fit theprotective case to the octet truss Other trusses could be alsoconsidered as alternatives

8 Acknowledgements

We would like to acknowledge CAPES (the Coordenaccedilatildeo deAperfeiccediloamento de Pessoal de Niacutevel Superior) Brazil forsupporting this research We also thank the 3D-COFORMintegration project which has received funding from theEuropean Communityrsquos Seventh Framework Programme(FP72007 2013) under grant agreement No 231809 formaking available technology and 3D models for this re-search

References[A 12] A KAWAMOTO ET AL Prototyping lightweight car seat

structures using topology optimization and additive manufactur-ing Additive Manufacturing Conference Proceedings (2012) 3

[Aut12] AUTODESK LABS 123d catch 2012 httphttpwww123dappcomcatch 5

[Bau93] BAUER E Packing museum objects for shipment Con-serve 0 Gram 17 1 (July 1993) 1ndash4 1

[Bit97] BITZER T Honeycomb Technology Materials DesignManufacturing Applications and Testing Chapman amp Hall1997 3

[CF12] CONNOR J FARAJI S Fundamentals of Structural En-gineering Springer 2012 3

[Chr00] CHRISTENSEN R Mechanics of cellular and other low-density materials International Journal of Solids and Structures37 1acircAS2 (2000) 93 ndash 104 3

[CJT11] CONWAY J H JIAO Y TORQUATO S New familyof tilings of three-dimensional euclidean space by tetrahedra andoctahedra Proc Natl Acad Sci U S A 108 27 (2011) 11009ndash124

[Cox73] COXETER H Regular Polytopes Dover books on ad-vanced mathematics Dover Publications 1973 4

[Cri73] CRITCHLOW K Order in Space A Design Source BookThames and Hudson 1973 4

[DEKBP03] DYSKIN A ESTRIN Y KANEL-BELOV APASTERNAK E Topological interlocking of platonic solids away to new materials and structures Philosophical MagazineLetters vol 83 issue 3 (2003) 4

[DFA01] DESHPANDE V FLECK N ASHBY M Effectiveproperties of the octet-truss lattice material Journal of the Me-chanics and Physics of Solids 49 8 (2001) 1747 ndash 1769 4

[EDP11] ESTRIN J DYSKIN A PASTERNAK E Topologicalinterlocking as a material design concept Materials Science andEngineering C Biomimetic and Supramolecular Systems vol 31issue 6 (2011) 4

[FH99] FRIEDRICHS O D HUSON D H Tiling space by pla-tonic solids i Discrete amp Computational Geometry 21 2 (1999)299ndash315 4

[Gor03] GORDON J Structures Or Why Things Donrsquot FallDown Da Capo Press 2003 3

[GRS09] GIBSON I ROSEN D STUCKER B Additive Man-ufacturing Technologies Rapid Prototyping to Direct DigitalManufacturing Springer 2009 3

[Hav05] HAVEMANN S Generative Mesh Modeling PhD thesisInstitute of Computer Graphics Braunschweig Technical Univer-sity 2005 5

[KREPlowast12] KAMINSKI J RODRIGUEZ ECHAVARRIA KPALMA G SCOPIGNO R STEVENSON J MARC P ARNOLDD Insourcing outsourcing and crowdsourcing 3d collection for-mation perspectives for cultural heritage sites In VAST The 13thInternational Symposium on Virtual Reality Archaeology and In-telligent Cultural Heritage (Brighton UK 2012) 2

[LW11] LIU S WANG C C L Fast intersection-free offsetsurface generation from freeform models with triangular meshesIEEE T Automation Science and Engineering 8 2 (2011) 347ndash360 8

[Mes12] MESHLAB httpmeshlabsourceforgenet 2012httphttpmeshlabsourceforgenet 5

[Net12] NETFABB httpwwwnetfabbcomstructurephp 2012httphttpwwwnetfabbcomstructurephp 3

[Owe98] OWEN S J A survey of unstructured mesh generationtechnology In IMR (1998) pp 239ndash267 4

[Sch12] SCHNEIDERS R Mesh generatorshttpwwwrobertschneidersdemeshgenerationsoftwarehtml2012 5

[US99] US NATIONAL PARK SERVICE Chapter 6 Handlingpacking and shipping NPS Museum Handbook Part I MuseumCollections (1999) 2

[VG06] VERGAUWEN M GOOL L V Web-based 3d recon-struction service Mach Vision Appl 17 6 (2006) 411ndash426 5

[Wad06] WADLEY H Multifunctional periodic cellular metalsPhilos Transact A Math Phys Eng Sci 364 1838 (2006) 31ndash683 4

[ZBS05] ZHANG Y BAJAJ C SOHN B-S 3d finite elementmeshing from imaging data Computer Methods in Applied Me-chanics and Engineering 194 48 49 (2005) 5083 ndash 5106 4

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

heritage artefacts Section 3 will describe and review theconcept of low density structures and 3D printing In section4 and 5 we propose our 3D low density structure and de-scribe its implementation which takes advantage of genera-tive modelling technologies Finally in section 6 we presentour prototype followed by some conclusions and furtherwork

2 Packaging heritage artefacts

Several solutions for packing heritage artefacts have beenproposed within museum communities Proper packing tech-niques are critical to ensure artefacts are stored and trans-ported safely In contrast an artefact packed incorrectly canbe permanently damaged Another complexity is that eachartefact requires a unique packaging solution Hence tradi-tional methods for designing and producing packing mightinvolve several hours or even days depending on the spe-cific case In addition different considerations need to bemade for selecting the most suitable method for packaging afragile and valuable heritage artefact This includes the ma-terial weight stiffness and the shape of the artefact

Packing materials are diverse and can have different ef-fects on the artefacts For instance fragile artefacts madeof material such as glass charcoal or corroded metals arevulnerable to damage from abrasion polished metals var-nished woods oriental lacquer and other smooth-surfacedartefacts are vulnerable to get imprints from plastic bubblesand foams

Different shapes weight and stiffness pose specific chal-lenges to the packaging solution While the main goal is toprotect the artefact from potential damage during storageor transportation another important objective of this pro-posal is to minimize the material usage the size and the finalweight of the solution This will have a direct impact on thecost

There are a variety of techniques that are traditionallyused These rely mostly on using cushioning materials in or-der to absorb shock vibration and buffer the humidity Theyinclude materials such as foam products that can be used ina variety of cushioning techniques As described in [US99]these techniques include

bull Cavity packaging This simple technique involves plac-ing the artefact into a cut made in polyethylene foam withthe shape of the artefact This method is clean and easy touse for repacking (see Figure 1-a)

bull Sparse layered packaging This technique is similarto cavity packaging but the cushioning material is dis-tributed sparsely around the artefact (see Figure 1-b)

bull Double boxing This technique involves packing an arte-fact using two sequential boxes in order to cushion theartefact For this the artefact is cushioned inside one boxThen another box at least 5 cm larger on all sides is usedwith further cushioning in between

bull Padding negative spaces This technique involves pack-aging an artefact surrounded with tissue paper and thenwrapping in successive layers of bubble wrap The arte-fact is placed inside a container and then tissue or someother cushioning material is used to fill in the excess area

bull Cushioning braces This technique involves using acushioning bracket to hold the artefact in place

Figure 1 Examples of packaging techniques (left) cav-ity packaging and (right) sparse layered packagingccopyFenimore Art Museum and Darla Jackson sculpture blog

These techniques demonstrate how the shape of the arte-fact plays a critical role in the production of the packing so-lution Carving or designing a package around a shape is stilla laborious process mostly done manually

The advent of 3D technologies for the routinely documen-tation of artefacts in collections (see [KREPlowast12]) representsan opportunity to use this data for packaging purposes Re-ciprocally the opportunity to enhance packaging techniquesmay motivate the adoption of 3D technologies for document-ing as information on the shape of the artefact can sup-port different kinds of applications The digital 3D shape ofthe artefact enables a completely automatic design and pro-duction pipeline of the 3D-fitted container for the artefactThe next section will introduce different types of structureswhich might be suitable for the internal structure of the pack-aging solution to be 3D printed

3 Low density structures and 3D printing

Low density structures are frequently found in nature andare widely studied in engineering architecture as well as inproduct design where they are used as efficient structuresthat serve a variety of purposes ranging from bridges androofs to internal structures of car seats or toys

One benefit of low density structures is that they re-duce the amount of building material Hence reducing costsandor final weight of the whole structure while guarantee-ing some mechanical properties that are desired for the prod-uct Today low density structures also inspire projects thatare environmentally sustainable since by minimizing mate-rial usage there is a reduction of waste The potential to pro-duce more durable and reusable packaging solutions is alsoan advantage

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 2 Two low density structures can be observed inthe Figure (left) an example of a truss used in a bridgestructure and (right) an example of a honeycombed struc-ture found in Durvillaea antarctica alga ( ccopyAndre-PhilippeDrapeau Picard)

An example of these type of structures are trusses whichare illustrated in figure 2-left These are well known in archi-tecture and engineering [Gor03] In the language of struc-tural engineering a lattice truss or space frame is a con-nected network of struts pin-joined or rigidly bonded attheir connections The purpose of such frames is to createstiff strong load-bearing structures while minimizing ma-terial usage The mechanical properties of trusses have beenwidely studied and plenty of references are available as wellas software that deals with the calculations [CF12]

Other examples of low density structures can also befound in nature where efficient structures with a reducedamount of material can be frequently observed For exam-ple figure 2-right illustrates a transversal cut of the leaf of aalga specimen showing the air-filled honeycomb structuresthat provides its buoyancy

Moreover internal structures referred to as cellular mate-rials can be found within bones as well as in honeycombsand are famous for their exceptional mechanical propertiesand for their light weight [Chr00] provides a detailed surveyon this type of structure Cellular materials are also knownas lattice-structured materials or cellular solids They arecharacterized by their relative density and are a hot topicof research nowadays due to the wide range of applicationsrecently found in industry

In product design honeycomb inspired structures broughtinnovation to aircraft design motor vehicle technology aswell as to light-weight construction They have also formedthe basis for the development of honeycomb structured pan-els [Bit97 Wad06]

The application of low density structures as a solution fordesigning internal structures have gained prominence withthe advent of 3D printing or rapid prototyping 3D printingis a manufacturing approach that can theoretically build anythree-dimensional shapes and topologies by different mech-anism The most popular is known as additive manufactur-

ing which produces a 3D shape by adding materials layerby layer [GRS09]

The range of base materials that are used in 3D printing iswide The study of 3D printed objectrsquos mechanical proper-ties with varying materials is still a topic of research Thusthe structural analysis of 3D designs can suffer from the lackof information In this work we are not going to explore thepossibilities in varying the base materials or studying in de-tail their structural analysis

The recent improvements on the strength and durabilityof the base materials that are used in additive manufacturinghas expanded the range of its applications Therefore ad-ditive manufacturing is bringing a great change to differenttypes of industries including the packaging industry

In this paper we propose a solution for printing a 3Dfitted container for packaging heritage artefacts We arguethat the internal structure of the fitted frame should be de-signed using low density structures to benefit from its ad-vantages Several projects in product design that take ad-vantage of such internal structures along with 3D printingtechniques are being proposed [A 12] There is also com-mercial software available for instance the Selective SpaceStructures (3S) Software from Netfabb [Net12] which is ahigh-end design tool that allows the development of com-plex unit cell structures for additive manufacturing purposesSeveral mesh generation tools are available as well The fol-lowing section will introduce the proposed structure beforediscussing its implementation

4 Proposed low density structure for packagingheritage artefacts

Inspired by the evidences exposed in section 3 we proposeto model the internal structure of our 3D-fitted packagingsolution as a low density structure In order to design thecontainerrsquos internal structures we looked for ways to fill thespace with such sparse structures that could be efficient fromthe structural point of view

In the Computer Graphics literature the structures we arelooking for are the widely studied 3D meshes In special the3D meshes adopted for the finite elements methods (FEM)are directly related to the solution that we are looking forWhen considering to adopt FEM 3D meshing algorithms wehave to have in mind that they intend to serve the purpose ofFEM calculations and are built to produce virtual meshesThus mechanical properties of the mesh itself are not rele-vant to that field of application In our case after generatingthe 3D mesh wire-frame model we will need to process itin order to turn it into a 3D mesh surface aiming to achievea 3D printable truss That is essentially the 3D mesh wire-frame model with thickness attributed to its edges

There are lots of commercial and open-source meshingsoftware available in the literature A review on those meth-

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

ods and software is beyond the scope of the present pa-per A survey on 3D meshing software by Owen [Owe98]from 1998 is a review of the fundamental algorithms thenavailable for 3D mesh generation Owenrsquos survey classi-fies the 3D mesh generators into two broad classes that arestructured and unstructured 3D meshes The classification ismade based on the criteria of interior nodes elementrsquos ad-jacency Structured meshes have equal number of adjacentelements while unstructured meshes relax the node valencerequirement allowing any number of elements to meet at asingle node More recently FEM simulations in medicinemolecular biology and engineering has increased the needfor quality 3D meshes in Zhang [ZBS05] the authors pro-pose an algorithm and make an extensive comparison toother tetrahedral extraction methods from imaging data

We adopt the branch of structured 3D meshes for they aremore stable from the mechanical point of view In [Wad06]Wadley argues on the strength of such kind of structurewithin the context of industrial applications One interestingsubset of structured 3D meshes are the space-filling polyhe-drons [Cox73 Cri73]

A space-filling polyhedron is a type of polyhedron whichcan be used to generate a tessellation of space The cubeis the only platonic solid possessing this property and itstessellation is widely adopted in Computer Graphics theclassics Octree data structure and the Marching Cubes algo-rithm explore this basic tessellation of space However othercombinations of polyhedrons can also fill the space A spe-cific configuration of octahedron and tetrahedron do fill thespace Figure 3 illustrates the octahedron frame (left) anda diagram that shows an exploded view of the octahedronand tetrahedron filling-space configuration (right) Other op-tions of space filling structures are available in the litera-ture [FH99 CJT11] Additionally topological interlockingof platonic solids [DEKBP03 EDP11] are argued to havevery good mechanical properties

Figure 3 Basic unit of the octet-frame

The octahedron tetrahedron filling-space configuration isknown in architecture domain as Octet Truss and its me-chanical properties have been studied by Deshpande et alin [DFA01] The authors submit a prototype of the octettruss made of aluminium to a sequence of tests as well astheir theoretical values are predicted by means of finite el-ements calculations The authors conclude that the stiffness

and strength of the octet truss material compare favourablywith the corresponding properties of metallic foams and thatits high strength-to-weight ratio relative ease of manufac-ture and potential for multi-functional applications makesthe octet truss material an attractive alternative to metallicfoams We thus conclude that the octet truss is a good start-ing point for the internal structure of our container

From the computer graphics point of view 3D meshed ofspace filling frames can be constructed by placing copies ofthe basic figures in proper places until a desired amount ofspace is completely filled Although the resultant 3D meshis not the most efficient to solve the intersection of the octet-frame with another mesh We observe that the edges of theoctet frame are aligned within the same direction and can betaught as a segment of a straight line This leads us to the ab-straction of the aligned edges as rays that starts at one faceof the frame bounding box to its interior Such abstractionpermits to use the same concept of ray tracing when calcu-lating the intersection of the 3D frame with the object meshThis will be the abstraction that will guide the implementa-tion described in the next section

5 Implementation using generative modelling

Generating an octet truss which fits tightly to the shape ofan artefact presents different challenges The truss needs tobe easily adaptable to fit any 3D model which needs to bepackaged despite its shape and size In addition two opera-tions need to be taken into account The first is defining theempty space in the centre where the artefact is going to fitSecondly the truss needs to be cut in half or in more piecesif there are undercuts or recessed surfaces in the artefact inorder to allow the artefact to be placed and released from thestructure

Figure 4 Example mesh for experimenting with 3D fittedframe

Before building the octet truss it is necessary to have in-formation on the 3D shape of the artefact For this a 3Dmodel with low level of detail can be used as accuracy isnot a critical issue This is specially the case if the artefactstill requires of some cloth or other wrapping case to pro-tect the artefact surface This might be particularly useful for

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

artefacts which are not completely rigid or are very fragileHence cost effective techniques such as photogrammetry( [VG06] and [Aut12]) are possible for many artefacts Fordemonstration purposes we used a delicate artefact (shownin Figure-4) which shape data had been acquired using a 3Dscanner The 3D mesh was post-processed and simplified us-ing the Meshlab tool [Mes12] by using a Poisson surface re-construction

In order to address the challenges described before weconsidered using a combination of a mesh generation orgrid generation tool with a modelling package for definingthe empty space For this different public and commercialmesh generation packages are available Schneiders presentsa comprehensive list of examples of these systems [Sch12]Nevertheless these are focused on producing mainly wire-frames or grid structures In addition the use of modellingpackages introduce many complexities to the constructionof the truss and require of manual intervention each timea new solution is created Instead we required of an inte-grated modelling solution which could produce a mesh us-ing a tetahedral-octahedral as the basic unit but most im-portantly that produced a printable solution and not only awireframe

We found a suitable solution by using the generative mod-elling language (GML) [Hav05] This tool allowed us todefine the sequence of processing steps to define the octetframe and convert this into an octet tryss while allowing theparameterising of its construction As such a GML scriptwas developed which can be easily adapted and configuredfor different types of objects using a set of parameters Theseparameters include the number of units which will determinethe width height and depth of the octet truss as well as forthe cross section the radius of the prism and the number ofedges (eg 3 makes a triangular prism while 20 approxi-mates a cylinder)

The simplest approach for implementing the octet-frameis by building a basic tetahedral-octahedral unit in wireframeand repeating this in a loop in order to create a box with aspecified width length and depth This approach was initallytested but it proved problematic once the artefact had to befitted inside This is because a further implementation of aboolean operation algorithm needs to be implemented forgenerating the empty space where the artefact is going to beplaced Hence the problem with this approach is two-fold

bull It is complex to decide whether the edge of a specific basicunit is within the artefact

bull It is complex to decide which segment of the edge is out-side the artefact if there is an intersection

Instead a better approach is to consider the whole framecomposed of various lines or rays rather than the indivudalbasic units Then the 3D shape of the artefact can be usedalong with the ray-casting technique in order to determinewhere the rays intersect with the 3D mesh

Figure 5 Initial wireframe produced by using rays

Thus firstly the frame is constructed in GML by usingrays that travel from each face on the frame Each face con-tains a list of vertices that define a tetrahedron These raysneed to travel in the directions of the edges connected tothat vertex These rays will always be outside the artefactand attached to the edge of the bounding polyhedron Thisapproach also optimizes the frame structure as it minimizesthe number of lines and therefore minimizes the number ofintersection tests that need to be done Once this frame is cre-ated this must be translated and scaled to enclose the artefactthat is being intersected against it The resulting frame in thisstep is shown in figure 5

The next step is to convert the rays into a set of lines thatare truncated to fit within the bounding polyhedron Theselines are then checked for intersection with the artefact Ifthere is an intersection the line is split in two leaving agap where the artefact will fit tightly within the octet frameHence the line is replaced by a line from its start point to thefirst point of intersection and a line from its end point to thelast point of intersection (see figure 6-top) Additionally theimplementation erodes the lines that intersect the artefact sothat there will be enough space to place the physical artefactinside the frame once this is printed (see figure 6-bottom)

Finally the octet frame is cut in half so that this can beopened and closed to place and release the artefact insideFor this the lines are intersected against a plane that goesthrough the middle of the frame to produce two sets of linesThe final step is to convert all lines into prisms along thelength of the line and create the 3D model which representsthe octet truss for the two surface models (base and summit)These are the 3D models which will be printed as the finalsolution

The final octet truss is shown in figure 7 along with theprotective case and the object fitted inside As illustrated inthe figure this approach allows for fitting a shell case to pro-tect further the artefact if this was required This shell casecan easily be developed in a modelling package by scalingthe artefact cutting it in half and shelling each side Hencethe object has a double casing to further protect the heritageartefact during transportation

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 6 Wireframe intersected with the 3D shape

Figure 7 Final octet truss ready for printing

In order to verify the suitability of the approach and thescript we tested the script with a mixture of 3D shapes offragile artefacts These have been acquired with a variety of3D acquisition technologies Nevertheless the steps to pro-duce the octet truss are the same producing promising resultsso far These results are illustrated in figure 8 The octet trussis feasible for different types of objects although we did nottested undercuts

Figure 8 Examples of different 3D shapes tested to producean octet truss for packaging

6 3D Printing the structure

As a proof of concept we are in the process of finding theadequate density and thickness dimensions for printing thestructure We are experimenting with a Zcorp 510 machineusing a plaster based powder (ZP150) to generate the struc-ture layer by layer This machine has several advantages toother 3D printing technologies For instance internal sup-ports can be generated that are separate to the structure itselfand so can be easily removed upon excavation of the struc-ture or that the porous powder can be infiltrated with epoxyresin to significantly increase the material strength

In order to compare the octet-frame proposed in section4 to other 3D printed structures an hexahedron (six quadri-lateral faces) unit cell based structure has been designed andwill be printed as well The intention is to investigate theeffects of element type on the overall performance of thestructure

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

In order to print both frames an initial attempt was con-ducted by using an initial design of the structures in particu-lar considering their density and thickness The initial objec-tive was to minimise as much as possible the usage of ma-terial For this we selected a 25 cm length for the struct ofthe basic unit and a truss wall thickness of 10 mm This hasresulted in failure with the selected thickness as the struc-ture broke down during the excavation due to its fragilityThe failed attempt is illustrated in Figure 9 In following tri-als we are varying the thickness up to 30 mm wall thicknessas we estimate this is a critical measurement for providingstrength to the overall structure Hence carefully estimatingits ideal value is an important part of the research and is cur-rently work in progress By using the parametric implemen-tation for the mesh generation the density and the thicknessvariation is straightforward

Further prototypes will be generated using other tech-niques to allow for a direct comparison and evaluationThese include using a VFlash 3D printing machine whichprints directly in acrylic (a softer material which is not asstrong as the epoxy resin infused powder material) and us-ing a laser cutter to produce a lattice of cardboard slices togenerate a 3D structure with an accurate contour bed for theobject to lie in

The testing experiments planned involve testing the loadcapacity of the structures supporting a small fragile objectThis will include both a compression load test case and adrop load test case The compression load case involvesloading the structure with 1kg masses and increasing theload by 1 kg per increment to investigate the maximum loadcapacity of the structure before the fragile object breaks Thedrop test will be conducted in a similar fashion dropping thestructure in a controlled drop test from an initial height of 10cm increasing this by 10 cm thereafter

The materials used in a further experiment may provide astrong and sturdy support for the object and this can be donesetting consistently the mesh density Ideally the material inimmediate contact with the object will be softer and moreforgiving to the surface of the object and this can be achievedby either using a multiple density 3D printing machine (egObjet Connex 500) or by manipulating the structural den-sity surrounding the object such that thinner walled less stiffstructures can be used to surround the object Similarly theoverall density of the structure needs to be considered to op-timise the weight of the structure whilst providing sufficientstrength and stiffness to withstand load cases that are typi-cal for stacking and transit Although we could not explorethe wide range of possibilities regarding the production ofa prototype we are convinced that the proposed structure isfeasible and a rigorous exploration of the range of possibili-ties and technology limitations is left as future work

Figure 9 3D printing failure at the first attempt

7 Conclusions

The movement of heritage artefacts is a process most her-itage organisations need to undertake Packaging artefactscorrectly is critical as artefacts are at their most vulnerablewhen transited Hence this paper has introduced an innova-tive approach for packaging the artefacts based on 3D tech-nology The proposed solution makes use of a Tetrahedral -Octahedral Frame This is produced using a generative mod-elling approach so that it can parametrically produce struc-tures that will fit any artefact The resulting structure pro-vides a number of advantages

bull A bespoke packaging solution that is tailored to specificartefact

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

bull An easier and more automatic process than traditionalmethods

bull Requires the 3D documentation of the artefact which inturn can be used for different purposes (eg conservationcondition assessment)

Although such packaging solution might incur a higher costof production when compared to traditional methods we es-timate that this is balanced by the fact that less time needs tobe spent producing the packaging

Further work beside the ongoing printing and testingwork involves developing structural analysis of the fittedpackage frame and considering the artefact weight to dy-namically adapt the structure The final goal is to minimizematerial needs while guaranteeing that the package frameprotects the artefact in transportation and potentially stor-age conditions

The proposed octet truss achieved so far can be improvedin different ways One is to consider the production of a pro-tective case for the object to be place in between the objectand the octet truss To do so a possible approach would beto 3D print the protective case by means of off-setting theobject mesh as proposed by Liu in [LW11] and then fit theprotective case to the octet truss Other trusses could be alsoconsidered as alternatives

8 Acknowledgements

We would like to acknowledge CAPES (the Coordenaccedilatildeo deAperfeiccediloamento de Pessoal de Niacutevel Superior) Brazil forsupporting this research We also thank the 3D-COFORMintegration project which has received funding from theEuropean Communityrsquos Seventh Framework Programme(FP72007 2013) under grant agreement No 231809 formaking available technology and 3D models for this re-search

References[A 12] A KAWAMOTO ET AL Prototyping lightweight car seat

structures using topology optimization and additive manufactur-ing Additive Manufacturing Conference Proceedings (2012) 3

[Aut12] AUTODESK LABS 123d catch 2012 httphttpwww123dappcomcatch 5

[Bau93] BAUER E Packing museum objects for shipment Con-serve 0 Gram 17 1 (July 1993) 1ndash4 1

[Bit97] BITZER T Honeycomb Technology Materials DesignManufacturing Applications and Testing Chapman amp Hall1997 3

[CF12] CONNOR J FARAJI S Fundamentals of Structural En-gineering Springer 2012 3

[Chr00] CHRISTENSEN R Mechanics of cellular and other low-density materials International Journal of Solids and Structures37 1acircAS2 (2000) 93 ndash 104 3

[CJT11] CONWAY J H JIAO Y TORQUATO S New familyof tilings of three-dimensional euclidean space by tetrahedra andoctahedra Proc Natl Acad Sci U S A 108 27 (2011) 11009ndash124

[Cox73] COXETER H Regular Polytopes Dover books on ad-vanced mathematics Dover Publications 1973 4

[Cri73] CRITCHLOW K Order in Space A Design Source BookThames and Hudson 1973 4

[DEKBP03] DYSKIN A ESTRIN Y KANEL-BELOV APASTERNAK E Topological interlocking of platonic solids away to new materials and structures Philosophical MagazineLetters vol 83 issue 3 (2003) 4

[DFA01] DESHPANDE V FLECK N ASHBY M Effectiveproperties of the octet-truss lattice material Journal of the Me-chanics and Physics of Solids 49 8 (2001) 1747 ndash 1769 4

[EDP11] ESTRIN J DYSKIN A PASTERNAK E Topologicalinterlocking as a material design concept Materials Science andEngineering C Biomimetic and Supramolecular Systems vol 31issue 6 (2011) 4

[FH99] FRIEDRICHS O D HUSON D H Tiling space by pla-tonic solids i Discrete amp Computational Geometry 21 2 (1999)299ndash315 4

[Gor03] GORDON J Structures Or Why Things Donrsquot FallDown Da Capo Press 2003 3

[GRS09] GIBSON I ROSEN D STUCKER B Additive Man-ufacturing Technologies Rapid Prototyping to Direct DigitalManufacturing Springer 2009 3

[Hav05] HAVEMANN S Generative Mesh Modeling PhD thesisInstitute of Computer Graphics Braunschweig Technical Univer-sity 2005 5

[KREPlowast12] KAMINSKI J RODRIGUEZ ECHAVARRIA KPALMA G SCOPIGNO R STEVENSON J MARC P ARNOLDD Insourcing outsourcing and crowdsourcing 3d collection for-mation perspectives for cultural heritage sites In VAST The 13thInternational Symposium on Virtual Reality Archaeology and In-telligent Cultural Heritage (Brighton UK 2012) 2

[LW11] LIU S WANG C C L Fast intersection-free offsetsurface generation from freeform models with triangular meshesIEEE T Automation Science and Engineering 8 2 (2011) 347ndash360 8

[Mes12] MESHLAB httpmeshlabsourceforgenet 2012httphttpmeshlabsourceforgenet 5

[Net12] NETFABB httpwwwnetfabbcomstructurephp 2012httphttpwwwnetfabbcomstructurephp 3

[Owe98] OWEN S J A survey of unstructured mesh generationtechnology In IMR (1998) pp 239ndash267 4

[Sch12] SCHNEIDERS R Mesh generatorshttpwwwrobertschneidersdemeshgenerationsoftwarehtml2012 5

[US99] US NATIONAL PARK SERVICE Chapter 6 Handlingpacking and shipping NPS Museum Handbook Part I MuseumCollections (1999) 2

[VG06] VERGAUWEN M GOOL L V Web-based 3d recon-struction service Mach Vision Appl 17 6 (2006) 411ndash426 5

[Wad06] WADLEY H Multifunctional periodic cellular metalsPhilos Transact A Math Phys Eng Sci 364 1838 (2006) 31ndash683 4

[ZBS05] ZHANG Y BAJAJ C SOHN B-S 3d finite elementmeshing from imaging data Computer Methods in Applied Me-chanics and Engineering 194 48 49 (2005) 5083 ndash 5106 4

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 2 Two low density structures can be observed inthe Figure (left) an example of a truss used in a bridgestructure and (right) an example of a honeycombed struc-ture found in Durvillaea antarctica alga ( ccopyAndre-PhilippeDrapeau Picard)

An example of these type of structures are trusses whichare illustrated in figure 2-left These are well known in archi-tecture and engineering [Gor03] In the language of struc-tural engineering a lattice truss or space frame is a con-nected network of struts pin-joined or rigidly bonded attheir connections The purpose of such frames is to createstiff strong load-bearing structures while minimizing ma-terial usage The mechanical properties of trusses have beenwidely studied and plenty of references are available as wellas software that deals with the calculations [CF12]

Other examples of low density structures can also befound in nature where efficient structures with a reducedamount of material can be frequently observed For exam-ple figure 2-right illustrates a transversal cut of the leaf of aalga specimen showing the air-filled honeycomb structuresthat provides its buoyancy

Moreover internal structures referred to as cellular mate-rials can be found within bones as well as in honeycombsand are famous for their exceptional mechanical propertiesand for their light weight [Chr00] provides a detailed surveyon this type of structure Cellular materials are also knownas lattice-structured materials or cellular solids They arecharacterized by their relative density and are a hot topicof research nowadays due to the wide range of applicationsrecently found in industry

In product design honeycomb inspired structures broughtinnovation to aircraft design motor vehicle technology aswell as to light-weight construction They have also formedthe basis for the development of honeycomb structured pan-els [Bit97 Wad06]

The application of low density structures as a solution fordesigning internal structures have gained prominence withthe advent of 3D printing or rapid prototyping 3D printingis a manufacturing approach that can theoretically build anythree-dimensional shapes and topologies by different mech-anism The most popular is known as additive manufactur-

ing which produces a 3D shape by adding materials layerby layer [GRS09]

The range of base materials that are used in 3D printing iswide The study of 3D printed objectrsquos mechanical proper-ties with varying materials is still a topic of research Thusthe structural analysis of 3D designs can suffer from the lackof information In this work we are not going to explore thepossibilities in varying the base materials or studying in de-tail their structural analysis

The recent improvements on the strength and durabilityof the base materials that are used in additive manufacturinghas expanded the range of its applications Therefore ad-ditive manufacturing is bringing a great change to differenttypes of industries including the packaging industry

In this paper we propose a solution for printing a 3Dfitted container for packaging heritage artefacts We arguethat the internal structure of the fitted frame should be de-signed using low density structures to benefit from its ad-vantages Several projects in product design that take ad-vantage of such internal structures along with 3D printingtechniques are being proposed [A 12] There is also com-mercial software available for instance the Selective SpaceStructures (3S) Software from Netfabb [Net12] which is ahigh-end design tool that allows the development of com-plex unit cell structures for additive manufacturing purposesSeveral mesh generation tools are available as well The fol-lowing section will introduce the proposed structure beforediscussing its implementation

4 Proposed low density structure for packagingheritage artefacts

Inspired by the evidences exposed in section 3 we proposeto model the internal structure of our 3D-fitted packagingsolution as a low density structure In order to design thecontainerrsquos internal structures we looked for ways to fill thespace with such sparse structures that could be efficient fromthe structural point of view

In the Computer Graphics literature the structures we arelooking for are the widely studied 3D meshes In special the3D meshes adopted for the finite elements methods (FEM)are directly related to the solution that we are looking forWhen considering to adopt FEM 3D meshing algorithms wehave to have in mind that they intend to serve the purpose ofFEM calculations and are built to produce virtual meshesThus mechanical properties of the mesh itself are not rele-vant to that field of application In our case after generatingthe 3D mesh wire-frame model we will need to process itin order to turn it into a 3D mesh surface aiming to achievea 3D printable truss That is essentially the 3D mesh wire-frame model with thickness attributed to its edges

There are lots of commercial and open-source meshingsoftware available in the literature A review on those meth-

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

ods and software is beyond the scope of the present pa-per A survey on 3D meshing software by Owen [Owe98]from 1998 is a review of the fundamental algorithms thenavailable for 3D mesh generation Owenrsquos survey classi-fies the 3D mesh generators into two broad classes that arestructured and unstructured 3D meshes The classification ismade based on the criteria of interior nodes elementrsquos ad-jacency Structured meshes have equal number of adjacentelements while unstructured meshes relax the node valencerequirement allowing any number of elements to meet at asingle node More recently FEM simulations in medicinemolecular biology and engineering has increased the needfor quality 3D meshes in Zhang [ZBS05] the authors pro-pose an algorithm and make an extensive comparison toother tetrahedral extraction methods from imaging data

We adopt the branch of structured 3D meshes for they aremore stable from the mechanical point of view In [Wad06]Wadley argues on the strength of such kind of structurewithin the context of industrial applications One interestingsubset of structured 3D meshes are the space-filling polyhe-drons [Cox73 Cri73]

A space-filling polyhedron is a type of polyhedron whichcan be used to generate a tessellation of space The cubeis the only platonic solid possessing this property and itstessellation is widely adopted in Computer Graphics theclassics Octree data structure and the Marching Cubes algo-rithm explore this basic tessellation of space However othercombinations of polyhedrons can also fill the space A spe-cific configuration of octahedron and tetrahedron do fill thespace Figure 3 illustrates the octahedron frame (left) anda diagram that shows an exploded view of the octahedronand tetrahedron filling-space configuration (right) Other op-tions of space filling structures are available in the litera-ture [FH99 CJT11] Additionally topological interlockingof platonic solids [DEKBP03 EDP11] are argued to havevery good mechanical properties

Figure 3 Basic unit of the octet-frame

The octahedron tetrahedron filling-space configuration isknown in architecture domain as Octet Truss and its me-chanical properties have been studied by Deshpande et alin [DFA01] The authors submit a prototype of the octettruss made of aluminium to a sequence of tests as well astheir theoretical values are predicted by means of finite el-ements calculations The authors conclude that the stiffness

and strength of the octet truss material compare favourablywith the corresponding properties of metallic foams and thatits high strength-to-weight ratio relative ease of manufac-ture and potential for multi-functional applications makesthe octet truss material an attractive alternative to metallicfoams We thus conclude that the octet truss is a good start-ing point for the internal structure of our container

From the computer graphics point of view 3D meshed ofspace filling frames can be constructed by placing copies ofthe basic figures in proper places until a desired amount ofspace is completely filled Although the resultant 3D meshis not the most efficient to solve the intersection of the octet-frame with another mesh We observe that the edges of theoctet frame are aligned within the same direction and can betaught as a segment of a straight line This leads us to the ab-straction of the aligned edges as rays that starts at one faceof the frame bounding box to its interior Such abstractionpermits to use the same concept of ray tracing when calcu-lating the intersection of the 3D frame with the object meshThis will be the abstraction that will guide the implementa-tion described in the next section

5 Implementation using generative modelling

Generating an octet truss which fits tightly to the shape ofan artefact presents different challenges The truss needs tobe easily adaptable to fit any 3D model which needs to bepackaged despite its shape and size In addition two opera-tions need to be taken into account The first is defining theempty space in the centre where the artefact is going to fitSecondly the truss needs to be cut in half or in more piecesif there are undercuts or recessed surfaces in the artefact inorder to allow the artefact to be placed and released from thestructure

Figure 4 Example mesh for experimenting with 3D fittedframe

Before building the octet truss it is necessary to have in-formation on the 3D shape of the artefact For this a 3Dmodel with low level of detail can be used as accuracy isnot a critical issue This is specially the case if the artefactstill requires of some cloth or other wrapping case to pro-tect the artefact surface This might be particularly useful for

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

artefacts which are not completely rigid or are very fragileHence cost effective techniques such as photogrammetry( [VG06] and [Aut12]) are possible for many artefacts Fordemonstration purposes we used a delicate artefact (shownin Figure-4) which shape data had been acquired using a 3Dscanner The 3D mesh was post-processed and simplified us-ing the Meshlab tool [Mes12] by using a Poisson surface re-construction

In order to address the challenges described before weconsidered using a combination of a mesh generation orgrid generation tool with a modelling package for definingthe empty space For this different public and commercialmesh generation packages are available Schneiders presentsa comprehensive list of examples of these systems [Sch12]Nevertheless these are focused on producing mainly wire-frames or grid structures In addition the use of modellingpackages introduce many complexities to the constructionof the truss and require of manual intervention each timea new solution is created Instead we required of an inte-grated modelling solution which could produce a mesh us-ing a tetahedral-octahedral as the basic unit but most im-portantly that produced a printable solution and not only awireframe

We found a suitable solution by using the generative mod-elling language (GML) [Hav05] This tool allowed us todefine the sequence of processing steps to define the octetframe and convert this into an octet tryss while allowing theparameterising of its construction As such a GML scriptwas developed which can be easily adapted and configuredfor different types of objects using a set of parameters Theseparameters include the number of units which will determinethe width height and depth of the octet truss as well as forthe cross section the radius of the prism and the number ofedges (eg 3 makes a triangular prism while 20 approxi-mates a cylinder)

The simplest approach for implementing the octet-frameis by building a basic tetahedral-octahedral unit in wireframeand repeating this in a loop in order to create a box with aspecified width length and depth This approach was initallytested but it proved problematic once the artefact had to befitted inside This is because a further implementation of aboolean operation algorithm needs to be implemented forgenerating the empty space where the artefact is going to beplaced Hence the problem with this approach is two-fold

bull It is complex to decide whether the edge of a specific basicunit is within the artefact

bull It is complex to decide which segment of the edge is out-side the artefact if there is an intersection

Instead a better approach is to consider the whole framecomposed of various lines or rays rather than the indivudalbasic units Then the 3D shape of the artefact can be usedalong with the ray-casting technique in order to determinewhere the rays intersect with the 3D mesh

Figure 5 Initial wireframe produced by using rays

Thus firstly the frame is constructed in GML by usingrays that travel from each face on the frame Each face con-tains a list of vertices that define a tetrahedron These raysneed to travel in the directions of the edges connected tothat vertex These rays will always be outside the artefactand attached to the edge of the bounding polyhedron Thisapproach also optimizes the frame structure as it minimizesthe number of lines and therefore minimizes the number ofintersection tests that need to be done Once this frame is cre-ated this must be translated and scaled to enclose the artefactthat is being intersected against it The resulting frame in thisstep is shown in figure 5

The next step is to convert the rays into a set of lines thatare truncated to fit within the bounding polyhedron Theselines are then checked for intersection with the artefact Ifthere is an intersection the line is split in two leaving agap where the artefact will fit tightly within the octet frameHence the line is replaced by a line from its start point to thefirst point of intersection and a line from its end point to thelast point of intersection (see figure 6-top) Additionally theimplementation erodes the lines that intersect the artefact sothat there will be enough space to place the physical artefactinside the frame once this is printed (see figure 6-bottom)

Finally the octet frame is cut in half so that this can beopened and closed to place and release the artefact insideFor this the lines are intersected against a plane that goesthrough the middle of the frame to produce two sets of linesThe final step is to convert all lines into prisms along thelength of the line and create the 3D model which representsthe octet truss for the two surface models (base and summit)These are the 3D models which will be printed as the finalsolution

The final octet truss is shown in figure 7 along with theprotective case and the object fitted inside As illustrated inthe figure this approach allows for fitting a shell case to pro-tect further the artefact if this was required This shell casecan easily be developed in a modelling package by scalingthe artefact cutting it in half and shelling each side Hencethe object has a double casing to further protect the heritageartefact during transportation

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 6 Wireframe intersected with the 3D shape

Figure 7 Final octet truss ready for printing

In order to verify the suitability of the approach and thescript we tested the script with a mixture of 3D shapes offragile artefacts These have been acquired with a variety of3D acquisition technologies Nevertheless the steps to pro-duce the octet truss are the same producing promising resultsso far These results are illustrated in figure 8 The octet trussis feasible for different types of objects although we did nottested undercuts

Figure 8 Examples of different 3D shapes tested to producean octet truss for packaging

6 3D Printing the structure

As a proof of concept we are in the process of finding theadequate density and thickness dimensions for printing thestructure We are experimenting with a Zcorp 510 machineusing a plaster based powder (ZP150) to generate the struc-ture layer by layer This machine has several advantages toother 3D printing technologies For instance internal sup-ports can be generated that are separate to the structure itselfand so can be easily removed upon excavation of the struc-ture or that the porous powder can be infiltrated with epoxyresin to significantly increase the material strength

In order to compare the octet-frame proposed in section4 to other 3D printed structures an hexahedron (six quadri-lateral faces) unit cell based structure has been designed andwill be printed as well The intention is to investigate theeffects of element type on the overall performance of thestructure

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

In order to print both frames an initial attempt was con-ducted by using an initial design of the structures in particu-lar considering their density and thickness The initial objec-tive was to minimise as much as possible the usage of ma-terial For this we selected a 25 cm length for the struct ofthe basic unit and a truss wall thickness of 10 mm This hasresulted in failure with the selected thickness as the struc-ture broke down during the excavation due to its fragilityThe failed attempt is illustrated in Figure 9 In following tri-als we are varying the thickness up to 30 mm wall thicknessas we estimate this is a critical measurement for providingstrength to the overall structure Hence carefully estimatingits ideal value is an important part of the research and is cur-rently work in progress By using the parametric implemen-tation for the mesh generation the density and the thicknessvariation is straightforward

Further prototypes will be generated using other tech-niques to allow for a direct comparison and evaluationThese include using a VFlash 3D printing machine whichprints directly in acrylic (a softer material which is not asstrong as the epoxy resin infused powder material) and us-ing a laser cutter to produce a lattice of cardboard slices togenerate a 3D structure with an accurate contour bed for theobject to lie in

The testing experiments planned involve testing the loadcapacity of the structures supporting a small fragile objectThis will include both a compression load test case and adrop load test case The compression load case involvesloading the structure with 1kg masses and increasing theload by 1 kg per increment to investigate the maximum loadcapacity of the structure before the fragile object breaks Thedrop test will be conducted in a similar fashion dropping thestructure in a controlled drop test from an initial height of 10cm increasing this by 10 cm thereafter

The materials used in a further experiment may provide astrong and sturdy support for the object and this can be donesetting consistently the mesh density Ideally the material inimmediate contact with the object will be softer and moreforgiving to the surface of the object and this can be achievedby either using a multiple density 3D printing machine (egObjet Connex 500) or by manipulating the structural den-sity surrounding the object such that thinner walled less stiffstructures can be used to surround the object Similarly theoverall density of the structure needs to be considered to op-timise the weight of the structure whilst providing sufficientstrength and stiffness to withstand load cases that are typi-cal for stacking and transit Although we could not explorethe wide range of possibilities regarding the production ofa prototype we are convinced that the proposed structure isfeasible and a rigorous exploration of the range of possibili-ties and technology limitations is left as future work

Figure 9 3D printing failure at the first attempt

7 Conclusions

The movement of heritage artefacts is a process most her-itage organisations need to undertake Packaging artefactscorrectly is critical as artefacts are at their most vulnerablewhen transited Hence this paper has introduced an innova-tive approach for packaging the artefacts based on 3D tech-nology The proposed solution makes use of a Tetrahedral -Octahedral Frame This is produced using a generative mod-elling approach so that it can parametrically produce struc-tures that will fit any artefact The resulting structure pro-vides a number of advantages

bull A bespoke packaging solution that is tailored to specificartefact

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

bull An easier and more automatic process than traditionalmethods

bull Requires the 3D documentation of the artefact which inturn can be used for different purposes (eg conservationcondition assessment)

Although such packaging solution might incur a higher costof production when compared to traditional methods we es-timate that this is balanced by the fact that less time needs tobe spent producing the packaging

Further work beside the ongoing printing and testingwork involves developing structural analysis of the fittedpackage frame and considering the artefact weight to dy-namically adapt the structure The final goal is to minimizematerial needs while guaranteeing that the package frameprotects the artefact in transportation and potentially stor-age conditions

The proposed octet truss achieved so far can be improvedin different ways One is to consider the production of a pro-tective case for the object to be place in between the objectand the octet truss To do so a possible approach would beto 3D print the protective case by means of off-setting theobject mesh as proposed by Liu in [LW11] and then fit theprotective case to the octet truss Other trusses could be alsoconsidered as alternatives

8 Acknowledgements

We would like to acknowledge CAPES (the Coordenaccedilatildeo deAperfeiccediloamento de Pessoal de Niacutevel Superior) Brazil forsupporting this research We also thank the 3D-COFORMintegration project which has received funding from theEuropean Communityrsquos Seventh Framework Programme(FP72007 2013) under grant agreement No 231809 formaking available technology and 3D models for this re-search

References[A 12] A KAWAMOTO ET AL Prototyping lightweight car seat

structures using topology optimization and additive manufactur-ing Additive Manufacturing Conference Proceedings (2012) 3

[Aut12] AUTODESK LABS 123d catch 2012 httphttpwww123dappcomcatch 5

[Bau93] BAUER E Packing museum objects for shipment Con-serve 0 Gram 17 1 (July 1993) 1ndash4 1

[Bit97] BITZER T Honeycomb Technology Materials DesignManufacturing Applications and Testing Chapman amp Hall1997 3

[CF12] CONNOR J FARAJI S Fundamentals of Structural En-gineering Springer 2012 3

[Chr00] CHRISTENSEN R Mechanics of cellular and other low-density materials International Journal of Solids and Structures37 1acircAS2 (2000) 93 ndash 104 3

[CJT11] CONWAY J H JIAO Y TORQUATO S New familyof tilings of three-dimensional euclidean space by tetrahedra andoctahedra Proc Natl Acad Sci U S A 108 27 (2011) 11009ndash124

[Cox73] COXETER H Regular Polytopes Dover books on ad-vanced mathematics Dover Publications 1973 4

[Cri73] CRITCHLOW K Order in Space A Design Source BookThames and Hudson 1973 4

[DEKBP03] DYSKIN A ESTRIN Y KANEL-BELOV APASTERNAK E Topological interlocking of platonic solids away to new materials and structures Philosophical MagazineLetters vol 83 issue 3 (2003) 4

[DFA01] DESHPANDE V FLECK N ASHBY M Effectiveproperties of the octet-truss lattice material Journal of the Me-chanics and Physics of Solids 49 8 (2001) 1747 ndash 1769 4

[EDP11] ESTRIN J DYSKIN A PASTERNAK E Topologicalinterlocking as a material design concept Materials Science andEngineering C Biomimetic and Supramolecular Systems vol 31issue 6 (2011) 4

[FH99] FRIEDRICHS O D HUSON D H Tiling space by pla-tonic solids i Discrete amp Computational Geometry 21 2 (1999)299ndash315 4

[Gor03] GORDON J Structures Or Why Things Donrsquot FallDown Da Capo Press 2003 3

[GRS09] GIBSON I ROSEN D STUCKER B Additive Man-ufacturing Technologies Rapid Prototyping to Direct DigitalManufacturing Springer 2009 3

[Hav05] HAVEMANN S Generative Mesh Modeling PhD thesisInstitute of Computer Graphics Braunschweig Technical Univer-sity 2005 5

[KREPlowast12] KAMINSKI J RODRIGUEZ ECHAVARRIA KPALMA G SCOPIGNO R STEVENSON J MARC P ARNOLDD Insourcing outsourcing and crowdsourcing 3d collection for-mation perspectives for cultural heritage sites In VAST The 13thInternational Symposium on Virtual Reality Archaeology and In-telligent Cultural Heritage (Brighton UK 2012) 2

[LW11] LIU S WANG C C L Fast intersection-free offsetsurface generation from freeform models with triangular meshesIEEE T Automation Science and Engineering 8 2 (2011) 347ndash360 8

[Mes12] MESHLAB httpmeshlabsourceforgenet 2012httphttpmeshlabsourceforgenet 5

[Net12] NETFABB httpwwwnetfabbcomstructurephp 2012httphttpwwwnetfabbcomstructurephp 3

[Owe98] OWEN S J A survey of unstructured mesh generationtechnology In IMR (1998) pp 239ndash267 4

[Sch12] SCHNEIDERS R Mesh generatorshttpwwwrobertschneidersdemeshgenerationsoftwarehtml2012 5

[US99] US NATIONAL PARK SERVICE Chapter 6 Handlingpacking and shipping NPS Museum Handbook Part I MuseumCollections (1999) 2

[VG06] VERGAUWEN M GOOL L V Web-based 3d recon-struction service Mach Vision Appl 17 6 (2006) 411ndash426 5

[Wad06] WADLEY H Multifunctional periodic cellular metalsPhilos Transact A Math Phys Eng Sci 364 1838 (2006) 31ndash683 4

[ZBS05] ZHANG Y BAJAJ C SOHN B-S 3d finite elementmeshing from imaging data Computer Methods in Applied Me-chanics and Engineering 194 48 49 (2005) 5083 ndash 5106 4

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

ods and software is beyond the scope of the present pa-per A survey on 3D meshing software by Owen [Owe98]from 1998 is a review of the fundamental algorithms thenavailable for 3D mesh generation Owenrsquos survey classi-fies the 3D mesh generators into two broad classes that arestructured and unstructured 3D meshes The classification ismade based on the criteria of interior nodes elementrsquos ad-jacency Structured meshes have equal number of adjacentelements while unstructured meshes relax the node valencerequirement allowing any number of elements to meet at asingle node More recently FEM simulations in medicinemolecular biology and engineering has increased the needfor quality 3D meshes in Zhang [ZBS05] the authors pro-pose an algorithm and make an extensive comparison toother tetrahedral extraction methods from imaging data

We adopt the branch of structured 3D meshes for they aremore stable from the mechanical point of view In [Wad06]Wadley argues on the strength of such kind of structurewithin the context of industrial applications One interestingsubset of structured 3D meshes are the space-filling polyhe-drons [Cox73 Cri73]

A space-filling polyhedron is a type of polyhedron whichcan be used to generate a tessellation of space The cubeis the only platonic solid possessing this property and itstessellation is widely adopted in Computer Graphics theclassics Octree data structure and the Marching Cubes algo-rithm explore this basic tessellation of space However othercombinations of polyhedrons can also fill the space A spe-cific configuration of octahedron and tetrahedron do fill thespace Figure 3 illustrates the octahedron frame (left) anda diagram that shows an exploded view of the octahedronand tetrahedron filling-space configuration (right) Other op-tions of space filling structures are available in the litera-ture [FH99 CJT11] Additionally topological interlockingof platonic solids [DEKBP03 EDP11] are argued to havevery good mechanical properties

Figure 3 Basic unit of the octet-frame

The octahedron tetrahedron filling-space configuration isknown in architecture domain as Octet Truss and its me-chanical properties have been studied by Deshpande et alin [DFA01] The authors submit a prototype of the octettruss made of aluminium to a sequence of tests as well astheir theoretical values are predicted by means of finite el-ements calculations The authors conclude that the stiffness

and strength of the octet truss material compare favourablywith the corresponding properties of metallic foams and thatits high strength-to-weight ratio relative ease of manufac-ture and potential for multi-functional applications makesthe octet truss material an attractive alternative to metallicfoams We thus conclude that the octet truss is a good start-ing point for the internal structure of our container

From the computer graphics point of view 3D meshed ofspace filling frames can be constructed by placing copies ofthe basic figures in proper places until a desired amount ofspace is completely filled Although the resultant 3D meshis not the most efficient to solve the intersection of the octet-frame with another mesh We observe that the edges of theoctet frame are aligned within the same direction and can betaught as a segment of a straight line This leads us to the ab-straction of the aligned edges as rays that starts at one faceof the frame bounding box to its interior Such abstractionpermits to use the same concept of ray tracing when calcu-lating the intersection of the 3D frame with the object meshThis will be the abstraction that will guide the implementa-tion described in the next section

5 Implementation using generative modelling

Generating an octet truss which fits tightly to the shape ofan artefact presents different challenges The truss needs tobe easily adaptable to fit any 3D model which needs to bepackaged despite its shape and size In addition two opera-tions need to be taken into account The first is defining theempty space in the centre where the artefact is going to fitSecondly the truss needs to be cut in half or in more piecesif there are undercuts or recessed surfaces in the artefact inorder to allow the artefact to be placed and released from thestructure

Figure 4 Example mesh for experimenting with 3D fittedframe

Before building the octet truss it is necessary to have in-formation on the 3D shape of the artefact For this a 3Dmodel with low level of detail can be used as accuracy isnot a critical issue This is specially the case if the artefactstill requires of some cloth or other wrapping case to pro-tect the artefact surface This might be particularly useful for

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

artefacts which are not completely rigid or are very fragileHence cost effective techniques such as photogrammetry( [VG06] and [Aut12]) are possible for many artefacts Fordemonstration purposes we used a delicate artefact (shownin Figure-4) which shape data had been acquired using a 3Dscanner The 3D mesh was post-processed and simplified us-ing the Meshlab tool [Mes12] by using a Poisson surface re-construction

In order to address the challenges described before weconsidered using a combination of a mesh generation orgrid generation tool with a modelling package for definingthe empty space For this different public and commercialmesh generation packages are available Schneiders presentsa comprehensive list of examples of these systems [Sch12]Nevertheless these are focused on producing mainly wire-frames or grid structures In addition the use of modellingpackages introduce many complexities to the constructionof the truss and require of manual intervention each timea new solution is created Instead we required of an inte-grated modelling solution which could produce a mesh us-ing a tetahedral-octahedral as the basic unit but most im-portantly that produced a printable solution and not only awireframe

We found a suitable solution by using the generative mod-elling language (GML) [Hav05] This tool allowed us todefine the sequence of processing steps to define the octetframe and convert this into an octet tryss while allowing theparameterising of its construction As such a GML scriptwas developed which can be easily adapted and configuredfor different types of objects using a set of parameters Theseparameters include the number of units which will determinethe width height and depth of the octet truss as well as forthe cross section the radius of the prism and the number ofedges (eg 3 makes a triangular prism while 20 approxi-mates a cylinder)

The simplest approach for implementing the octet-frameis by building a basic tetahedral-octahedral unit in wireframeand repeating this in a loop in order to create a box with aspecified width length and depth This approach was initallytested but it proved problematic once the artefact had to befitted inside This is because a further implementation of aboolean operation algorithm needs to be implemented forgenerating the empty space where the artefact is going to beplaced Hence the problem with this approach is two-fold

bull It is complex to decide whether the edge of a specific basicunit is within the artefact

bull It is complex to decide which segment of the edge is out-side the artefact if there is an intersection

Instead a better approach is to consider the whole framecomposed of various lines or rays rather than the indivudalbasic units Then the 3D shape of the artefact can be usedalong with the ray-casting technique in order to determinewhere the rays intersect with the 3D mesh

Figure 5 Initial wireframe produced by using rays

Thus firstly the frame is constructed in GML by usingrays that travel from each face on the frame Each face con-tains a list of vertices that define a tetrahedron These raysneed to travel in the directions of the edges connected tothat vertex These rays will always be outside the artefactand attached to the edge of the bounding polyhedron Thisapproach also optimizes the frame structure as it minimizesthe number of lines and therefore minimizes the number ofintersection tests that need to be done Once this frame is cre-ated this must be translated and scaled to enclose the artefactthat is being intersected against it The resulting frame in thisstep is shown in figure 5

The next step is to convert the rays into a set of lines thatare truncated to fit within the bounding polyhedron Theselines are then checked for intersection with the artefact Ifthere is an intersection the line is split in two leaving agap where the artefact will fit tightly within the octet frameHence the line is replaced by a line from its start point to thefirst point of intersection and a line from its end point to thelast point of intersection (see figure 6-top) Additionally theimplementation erodes the lines that intersect the artefact sothat there will be enough space to place the physical artefactinside the frame once this is printed (see figure 6-bottom)

Finally the octet frame is cut in half so that this can beopened and closed to place and release the artefact insideFor this the lines are intersected against a plane that goesthrough the middle of the frame to produce two sets of linesThe final step is to convert all lines into prisms along thelength of the line and create the 3D model which representsthe octet truss for the two surface models (base and summit)These are the 3D models which will be printed as the finalsolution

The final octet truss is shown in figure 7 along with theprotective case and the object fitted inside As illustrated inthe figure this approach allows for fitting a shell case to pro-tect further the artefact if this was required This shell casecan easily be developed in a modelling package by scalingthe artefact cutting it in half and shelling each side Hencethe object has a double casing to further protect the heritageartefact during transportation

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 6 Wireframe intersected with the 3D shape

Figure 7 Final octet truss ready for printing

In order to verify the suitability of the approach and thescript we tested the script with a mixture of 3D shapes offragile artefacts These have been acquired with a variety of3D acquisition technologies Nevertheless the steps to pro-duce the octet truss are the same producing promising resultsso far These results are illustrated in figure 8 The octet trussis feasible for different types of objects although we did nottested undercuts

Figure 8 Examples of different 3D shapes tested to producean octet truss for packaging

6 3D Printing the structure

As a proof of concept we are in the process of finding theadequate density and thickness dimensions for printing thestructure We are experimenting with a Zcorp 510 machineusing a plaster based powder (ZP150) to generate the struc-ture layer by layer This machine has several advantages toother 3D printing technologies For instance internal sup-ports can be generated that are separate to the structure itselfand so can be easily removed upon excavation of the struc-ture or that the porous powder can be infiltrated with epoxyresin to significantly increase the material strength

In order to compare the octet-frame proposed in section4 to other 3D printed structures an hexahedron (six quadri-lateral faces) unit cell based structure has been designed andwill be printed as well The intention is to investigate theeffects of element type on the overall performance of thestructure

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

In order to print both frames an initial attempt was con-ducted by using an initial design of the structures in particu-lar considering their density and thickness The initial objec-tive was to minimise as much as possible the usage of ma-terial For this we selected a 25 cm length for the struct ofthe basic unit and a truss wall thickness of 10 mm This hasresulted in failure with the selected thickness as the struc-ture broke down during the excavation due to its fragilityThe failed attempt is illustrated in Figure 9 In following tri-als we are varying the thickness up to 30 mm wall thicknessas we estimate this is a critical measurement for providingstrength to the overall structure Hence carefully estimatingits ideal value is an important part of the research and is cur-rently work in progress By using the parametric implemen-tation for the mesh generation the density and the thicknessvariation is straightforward

Further prototypes will be generated using other tech-niques to allow for a direct comparison and evaluationThese include using a VFlash 3D printing machine whichprints directly in acrylic (a softer material which is not asstrong as the epoxy resin infused powder material) and us-ing a laser cutter to produce a lattice of cardboard slices togenerate a 3D structure with an accurate contour bed for theobject to lie in

The testing experiments planned involve testing the loadcapacity of the structures supporting a small fragile objectThis will include both a compression load test case and adrop load test case The compression load case involvesloading the structure with 1kg masses and increasing theload by 1 kg per increment to investigate the maximum loadcapacity of the structure before the fragile object breaks Thedrop test will be conducted in a similar fashion dropping thestructure in a controlled drop test from an initial height of 10cm increasing this by 10 cm thereafter

The materials used in a further experiment may provide astrong and sturdy support for the object and this can be donesetting consistently the mesh density Ideally the material inimmediate contact with the object will be softer and moreforgiving to the surface of the object and this can be achievedby either using a multiple density 3D printing machine (egObjet Connex 500) or by manipulating the structural den-sity surrounding the object such that thinner walled less stiffstructures can be used to surround the object Similarly theoverall density of the structure needs to be considered to op-timise the weight of the structure whilst providing sufficientstrength and stiffness to withstand load cases that are typi-cal for stacking and transit Although we could not explorethe wide range of possibilities regarding the production ofa prototype we are convinced that the proposed structure isfeasible and a rigorous exploration of the range of possibili-ties and technology limitations is left as future work

Figure 9 3D printing failure at the first attempt

7 Conclusions

The movement of heritage artefacts is a process most her-itage organisations need to undertake Packaging artefactscorrectly is critical as artefacts are at their most vulnerablewhen transited Hence this paper has introduced an innova-tive approach for packaging the artefacts based on 3D tech-nology The proposed solution makes use of a Tetrahedral -Octahedral Frame This is produced using a generative mod-elling approach so that it can parametrically produce struc-tures that will fit any artefact The resulting structure pro-vides a number of advantages

bull A bespoke packaging solution that is tailored to specificartefact

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

bull An easier and more automatic process than traditionalmethods

bull Requires the 3D documentation of the artefact which inturn can be used for different purposes (eg conservationcondition assessment)

Although such packaging solution might incur a higher costof production when compared to traditional methods we es-timate that this is balanced by the fact that less time needs tobe spent producing the packaging

Further work beside the ongoing printing and testingwork involves developing structural analysis of the fittedpackage frame and considering the artefact weight to dy-namically adapt the structure The final goal is to minimizematerial needs while guaranteeing that the package frameprotects the artefact in transportation and potentially stor-age conditions

The proposed octet truss achieved so far can be improvedin different ways One is to consider the production of a pro-tective case for the object to be place in between the objectand the octet truss To do so a possible approach would beto 3D print the protective case by means of off-setting theobject mesh as proposed by Liu in [LW11] and then fit theprotective case to the octet truss Other trusses could be alsoconsidered as alternatives

8 Acknowledgements

We would like to acknowledge CAPES (the Coordenaccedilatildeo deAperfeiccediloamento de Pessoal de Niacutevel Superior) Brazil forsupporting this research We also thank the 3D-COFORMintegration project which has received funding from theEuropean Communityrsquos Seventh Framework Programme(FP72007 2013) under grant agreement No 231809 formaking available technology and 3D models for this re-search

References[A 12] A KAWAMOTO ET AL Prototyping lightweight car seat

structures using topology optimization and additive manufactur-ing Additive Manufacturing Conference Proceedings (2012) 3

[Aut12] AUTODESK LABS 123d catch 2012 httphttpwww123dappcomcatch 5

[Bau93] BAUER E Packing museum objects for shipment Con-serve 0 Gram 17 1 (July 1993) 1ndash4 1

[Bit97] BITZER T Honeycomb Technology Materials DesignManufacturing Applications and Testing Chapman amp Hall1997 3

[CF12] CONNOR J FARAJI S Fundamentals of Structural En-gineering Springer 2012 3

[Chr00] CHRISTENSEN R Mechanics of cellular and other low-density materials International Journal of Solids and Structures37 1acircAS2 (2000) 93 ndash 104 3

[CJT11] CONWAY J H JIAO Y TORQUATO S New familyof tilings of three-dimensional euclidean space by tetrahedra andoctahedra Proc Natl Acad Sci U S A 108 27 (2011) 11009ndash124

[Cox73] COXETER H Regular Polytopes Dover books on ad-vanced mathematics Dover Publications 1973 4

[Cri73] CRITCHLOW K Order in Space A Design Source BookThames and Hudson 1973 4

[DEKBP03] DYSKIN A ESTRIN Y KANEL-BELOV APASTERNAK E Topological interlocking of platonic solids away to new materials and structures Philosophical MagazineLetters vol 83 issue 3 (2003) 4

[DFA01] DESHPANDE V FLECK N ASHBY M Effectiveproperties of the octet-truss lattice material Journal of the Me-chanics and Physics of Solids 49 8 (2001) 1747 ndash 1769 4

[EDP11] ESTRIN J DYSKIN A PASTERNAK E Topologicalinterlocking as a material design concept Materials Science andEngineering C Biomimetic and Supramolecular Systems vol 31issue 6 (2011) 4

[FH99] FRIEDRICHS O D HUSON D H Tiling space by pla-tonic solids i Discrete amp Computational Geometry 21 2 (1999)299ndash315 4

[Gor03] GORDON J Structures Or Why Things Donrsquot FallDown Da Capo Press 2003 3

[GRS09] GIBSON I ROSEN D STUCKER B Additive Man-ufacturing Technologies Rapid Prototyping to Direct DigitalManufacturing Springer 2009 3

[Hav05] HAVEMANN S Generative Mesh Modeling PhD thesisInstitute of Computer Graphics Braunschweig Technical Univer-sity 2005 5

[KREPlowast12] KAMINSKI J RODRIGUEZ ECHAVARRIA KPALMA G SCOPIGNO R STEVENSON J MARC P ARNOLDD Insourcing outsourcing and crowdsourcing 3d collection for-mation perspectives for cultural heritage sites In VAST The 13thInternational Symposium on Virtual Reality Archaeology and In-telligent Cultural Heritage (Brighton UK 2012) 2

[LW11] LIU S WANG C C L Fast intersection-free offsetsurface generation from freeform models with triangular meshesIEEE T Automation Science and Engineering 8 2 (2011) 347ndash360 8

[Mes12] MESHLAB httpmeshlabsourceforgenet 2012httphttpmeshlabsourceforgenet 5

[Net12] NETFABB httpwwwnetfabbcomstructurephp 2012httphttpwwwnetfabbcomstructurephp 3

[Owe98] OWEN S J A survey of unstructured mesh generationtechnology In IMR (1998) pp 239ndash267 4

[Sch12] SCHNEIDERS R Mesh generatorshttpwwwrobertschneidersdemeshgenerationsoftwarehtml2012 5

[US99] US NATIONAL PARK SERVICE Chapter 6 Handlingpacking and shipping NPS Museum Handbook Part I MuseumCollections (1999) 2

[VG06] VERGAUWEN M GOOL L V Web-based 3d recon-struction service Mach Vision Appl 17 6 (2006) 411ndash426 5

[Wad06] WADLEY H Multifunctional periodic cellular metalsPhilos Transact A Math Phys Eng Sci 364 1838 (2006) 31ndash683 4

[ZBS05] ZHANG Y BAJAJ C SOHN B-S 3d finite elementmeshing from imaging data Computer Methods in Applied Me-chanics and Engineering 194 48 49 (2005) 5083 ndash 5106 4

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

artefacts which are not completely rigid or are very fragileHence cost effective techniques such as photogrammetry( [VG06] and [Aut12]) are possible for many artefacts Fordemonstration purposes we used a delicate artefact (shownin Figure-4) which shape data had been acquired using a 3Dscanner The 3D mesh was post-processed and simplified us-ing the Meshlab tool [Mes12] by using a Poisson surface re-construction

In order to address the challenges described before weconsidered using a combination of a mesh generation orgrid generation tool with a modelling package for definingthe empty space For this different public and commercialmesh generation packages are available Schneiders presentsa comprehensive list of examples of these systems [Sch12]Nevertheless these are focused on producing mainly wire-frames or grid structures In addition the use of modellingpackages introduce many complexities to the constructionof the truss and require of manual intervention each timea new solution is created Instead we required of an inte-grated modelling solution which could produce a mesh us-ing a tetahedral-octahedral as the basic unit but most im-portantly that produced a printable solution and not only awireframe

We found a suitable solution by using the generative mod-elling language (GML) [Hav05] This tool allowed us todefine the sequence of processing steps to define the octetframe and convert this into an octet tryss while allowing theparameterising of its construction As such a GML scriptwas developed which can be easily adapted and configuredfor different types of objects using a set of parameters Theseparameters include the number of units which will determinethe width height and depth of the octet truss as well as forthe cross section the radius of the prism and the number ofedges (eg 3 makes a triangular prism while 20 approxi-mates a cylinder)

The simplest approach for implementing the octet-frameis by building a basic tetahedral-octahedral unit in wireframeand repeating this in a loop in order to create a box with aspecified width length and depth This approach was initallytested but it proved problematic once the artefact had to befitted inside This is because a further implementation of aboolean operation algorithm needs to be implemented forgenerating the empty space where the artefact is going to beplaced Hence the problem with this approach is two-fold

bull It is complex to decide whether the edge of a specific basicunit is within the artefact

bull It is complex to decide which segment of the edge is out-side the artefact if there is an intersection

Instead a better approach is to consider the whole framecomposed of various lines or rays rather than the indivudalbasic units Then the 3D shape of the artefact can be usedalong with the ray-casting technique in order to determinewhere the rays intersect with the 3D mesh

Figure 5 Initial wireframe produced by using rays

Thus firstly the frame is constructed in GML by usingrays that travel from each face on the frame Each face con-tains a list of vertices that define a tetrahedron These raysneed to travel in the directions of the edges connected tothat vertex These rays will always be outside the artefactand attached to the edge of the bounding polyhedron Thisapproach also optimizes the frame structure as it minimizesthe number of lines and therefore minimizes the number ofintersection tests that need to be done Once this frame is cre-ated this must be translated and scaled to enclose the artefactthat is being intersected against it The resulting frame in thisstep is shown in figure 5

The next step is to convert the rays into a set of lines thatare truncated to fit within the bounding polyhedron Theselines are then checked for intersection with the artefact Ifthere is an intersection the line is split in two leaving agap where the artefact will fit tightly within the octet frameHence the line is replaced by a line from its start point to thefirst point of intersection and a line from its end point to thelast point of intersection (see figure 6-top) Additionally theimplementation erodes the lines that intersect the artefact sothat there will be enough space to place the physical artefactinside the frame once this is printed (see figure 6-bottom)

Finally the octet frame is cut in half so that this can beopened and closed to place and release the artefact insideFor this the lines are intersected against a plane that goesthrough the middle of the frame to produce two sets of linesThe final step is to convert all lines into prisms along thelength of the line and create the 3D model which representsthe octet truss for the two surface models (base and summit)These are the 3D models which will be printed as the finalsolution

The final octet truss is shown in figure 7 along with theprotective case and the object fitted inside As illustrated inthe figure this approach allows for fitting a shell case to pro-tect further the artefact if this was required This shell casecan easily be developed in a modelling package by scalingthe artefact cutting it in half and shelling each side Hencethe object has a double casing to further protect the heritageartefact during transportation

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 6 Wireframe intersected with the 3D shape

Figure 7 Final octet truss ready for printing

In order to verify the suitability of the approach and thescript we tested the script with a mixture of 3D shapes offragile artefacts These have been acquired with a variety of3D acquisition technologies Nevertheless the steps to pro-duce the octet truss are the same producing promising resultsso far These results are illustrated in figure 8 The octet trussis feasible for different types of objects although we did nottested undercuts

Figure 8 Examples of different 3D shapes tested to producean octet truss for packaging

6 3D Printing the structure

As a proof of concept we are in the process of finding theadequate density and thickness dimensions for printing thestructure We are experimenting with a Zcorp 510 machineusing a plaster based powder (ZP150) to generate the struc-ture layer by layer This machine has several advantages toother 3D printing technologies For instance internal sup-ports can be generated that are separate to the structure itselfand so can be easily removed upon excavation of the struc-ture or that the porous powder can be infiltrated with epoxyresin to significantly increase the material strength

In order to compare the octet-frame proposed in section4 to other 3D printed structures an hexahedron (six quadri-lateral faces) unit cell based structure has been designed andwill be printed as well The intention is to investigate theeffects of element type on the overall performance of thestructure

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

In order to print both frames an initial attempt was con-ducted by using an initial design of the structures in particu-lar considering their density and thickness The initial objec-tive was to minimise as much as possible the usage of ma-terial For this we selected a 25 cm length for the struct ofthe basic unit and a truss wall thickness of 10 mm This hasresulted in failure with the selected thickness as the struc-ture broke down during the excavation due to its fragilityThe failed attempt is illustrated in Figure 9 In following tri-als we are varying the thickness up to 30 mm wall thicknessas we estimate this is a critical measurement for providingstrength to the overall structure Hence carefully estimatingits ideal value is an important part of the research and is cur-rently work in progress By using the parametric implemen-tation for the mesh generation the density and the thicknessvariation is straightforward

Further prototypes will be generated using other tech-niques to allow for a direct comparison and evaluationThese include using a VFlash 3D printing machine whichprints directly in acrylic (a softer material which is not asstrong as the epoxy resin infused powder material) and us-ing a laser cutter to produce a lattice of cardboard slices togenerate a 3D structure with an accurate contour bed for theobject to lie in

The testing experiments planned involve testing the loadcapacity of the structures supporting a small fragile objectThis will include both a compression load test case and adrop load test case The compression load case involvesloading the structure with 1kg masses and increasing theload by 1 kg per increment to investigate the maximum loadcapacity of the structure before the fragile object breaks Thedrop test will be conducted in a similar fashion dropping thestructure in a controlled drop test from an initial height of 10cm increasing this by 10 cm thereafter

The materials used in a further experiment may provide astrong and sturdy support for the object and this can be donesetting consistently the mesh density Ideally the material inimmediate contact with the object will be softer and moreforgiving to the surface of the object and this can be achievedby either using a multiple density 3D printing machine (egObjet Connex 500) or by manipulating the structural den-sity surrounding the object such that thinner walled less stiffstructures can be used to surround the object Similarly theoverall density of the structure needs to be considered to op-timise the weight of the structure whilst providing sufficientstrength and stiffness to withstand load cases that are typi-cal for stacking and transit Although we could not explorethe wide range of possibilities regarding the production ofa prototype we are convinced that the proposed structure isfeasible and a rigorous exploration of the range of possibili-ties and technology limitations is left as future work

Figure 9 3D printing failure at the first attempt

7 Conclusions

The movement of heritage artefacts is a process most her-itage organisations need to undertake Packaging artefactscorrectly is critical as artefacts are at their most vulnerablewhen transited Hence this paper has introduced an innova-tive approach for packaging the artefacts based on 3D tech-nology The proposed solution makes use of a Tetrahedral -Octahedral Frame This is produced using a generative mod-elling approach so that it can parametrically produce struc-tures that will fit any artefact The resulting structure pro-vides a number of advantages

bull A bespoke packaging solution that is tailored to specificartefact

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

bull An easier and more automatic process than traditionalmethods

bull Requires the 3D documentation of the artefact which inturn can be used for different purposes (eg conservationcondition assessment)

Although such packaging solution might incur a higher costof production when compared to traditional methods we es-timate that this is balanced by the fact that less time needs tobe spent producing the packaging

Further work beside the ongoing printing and testingwork involves developing structural analysis of the fittedpackage frame and considering the artefact weight to dy-namically adapt the structure The final goal is to minimizematerial needs while guaranteeing that the package frameprotects the artefact in transportation and potentially stor-age conditions

The proposed octet truss achieved so far can be improvedin different ways One is to consider the production of a pro-tective case for the object to be place in between the objectand the octet truss To do so a possible approach would beto 3D print the protective case by means of off-setting theobject mesh as proposed by Liu in [LW11] and then fit theprotective case to the octet truss Other trusses could be alsoconsidered as alternatives

8 Acknowledgements

We would like to acknowledge CAPES (the Coordenaccedilatildeo deAperfeiccediloamento de Pessoal de Niacutevel Superior) Brazil forsupporting this research We also thank the 3D-COFORMintegration project which has received funding from theEuropean Communityrsquos Seventh Framework Programme(FP72007 2013) under grant agreement No 231809 formaking available technology and 3D models for this re-search

References[A 12] A KAWAMOTO ET AL Prototyping lightweight car seat

structures using topology optimization and additive manufactur-ing Additive Manufacturing Conference Proceedings (2012) 3

[Aut12] AUTODESK LABS 123d catch 2012 httphttpwww123dappcomcatch 5

[Bau93] BAUER E Packing museum objects for shipment Con-serve 0 Gram 17 1 (July 1993) 1ndash4 1

[Bit97] BITZER T Honeycomb Technology Materials DesignManufacturing Applications and Testing Chapman amp Hall1997 3

[CF12] CONNOR J FARAJI S Fundamentals of Structural En-gineering Springer 2012 3

[Chr00] CHRISTENSEN R Mechanics of cellular and other low-density materials International Journal of Solids and Structures37 1acircAS2 (2000) 93 ndash 104 3

[CJT11] CONWAY J H JIAO Y TORQUATO S New familyof tilings of three-dimensional euclidean space by tetrahedra andoctahedra Proc Natl Acad Sci U S A 108 27 (2011) 11009ndash124

[Cox73] COXETER H Regular Polytopes Dover books on ad-vanced mathematics Dover Publications 1973 4

[Cri73] CRITCHLOW K Order in Space A Design Source BookThames and Hudson 1973 4

[DEKBP03] DYSKIN A ESTRIN Y KANEL-BELOV APASTERNAK E Topological interlocking of platonic solids away to new materials and structures Philosophical MagazineLetters vol 83 issue 3 (2003) 4

[DFA01] DESHPANDE V FLECK N ASHBY M Effectiveproperties of the octet-truss lattice material Journal of the Me-chanics and Physics of Solids 49 8 (2001) 1747 ndash 1769 4

[EDP11] ESTRIN J DYSKIN A PASTERNAK E Topologicalinterlocking as a material design concept Materials Science andEngineering C Biomimetic and Supramolecular Systems vol 31issue 6 (2011) 4

[FH99] FRIEDRICHS O D HUSON D H Tiling space by pla-tonic solids i Discrete amp Computational Geometry 21 2 (1999)299ndash315 4

[Gor03] GORDON J Structures Or Why Things Donrsquot FallDown Da Capo Press 2003 3

[GRS09] GIBSON I ROSEN D STUCKER B Additive Man-ufacturing Technologies Rapid Prototyping to Direct DigitalManufacturing Springer 2009 3

[Hav05] HAVEMANN S Generative Mesh Modeling PhD thesisInstitute of Computer Graphics Braunschweig Technical Univer-sity 2005 5

[KREPlowast12] KAMINSKI J RODRIGUEZ ECHAVARRIA KPALMA G SCOPIGNO R STEVENSON J MARC P ARNOLDD Insourcing outsourcing and crowdsourcing 3d collection for-mation perspectives for cultural heritage sites In VAST The 13thInternational Symposium on Virtual Reality Archaeology and In-telligent Cultural Heritage (Brighton UK 2012) 2

[LW11] LIU S WANG C C L Fast intersection-free offsetsurface generation from freeform models with triangular meshesIEEE T Automation Science and Engineering 8 2 (2011) 347ndash360 8

[Mes12] MESHLAB httpmeshlabsourceforgenet 2012httphttpmeshlabsourceforgenet 5

[Net12] NETFABB httpwwwnetfabbcomstructurephp 2012httphttpwwwnetfabbcomstructurephp 3

[Owe98] OWEN S J A survey of unstructured mesh generationtechnology In IMR (1998) pp 239ndash267 4

[Sch12] SCHNEIDERS R Mesh generatorshttpwwwrobertschneidersdemeshgenerationsoftwarehtml2012 5

[US99] US NATIONAL PARK SERVICE Chapter 6 Handlingpacking and shipping NPS Museum Handbook Part I MuseumCollections (1999) 2

[VG06] VERGAUWEN M GOOL L V Web-based 3d recon-struction service Mach Vision Appl 17 6 (2006) 411ndash426 5

[Wad06] WADLEY H Multifunctional periodic cellular metalsPhilos Transact A Math Phys Eng Sci 364 1838 (2006) 31ndash683 4

[ZBS05] ZHANG Y BAJAJ C SOHN B-S 3d finite elementmeshing from imaging data Computer Methods in Applied Me-chanics and Engineering 194 48 49 (2005) 5083 ndash 5106 4

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

Figure 6 Wireframe intersected with the 3D shape

Figure 7 Final octet truss ready for printing

In order to verify the suitability of the approach and thescript we tested the script with a mixture of 3D shapes offragile artefacts These have been acquired with a variety of3D acquisition technologies Nevertheless the steps to pro-duce the octet truss are the same producing promising resultsso far These results are illustrated in figure 8 The octet trussis feasible for different types of objects although we did nottested undercuts

Figure 8 Examples of different 3D shapes tested to producean octet truss for packaging

6 3D Printing the structure

As a proof of concept we are in the process of finding theadequate density and thickness dimensions for printing thestructure We are experimenting with a Zcorp 510 machineusing a plaster based powder (ZP150) to generate the struc-ture layer by layer This machine has several advantages toother 3D printing technologies For instance internal sup-ports can be generated that are separate to the structure itselfand so can be easily removed upon excavation of the struc-ture or that the porous powder can be infiltrated with epoxyresin to significantly increase the material strength

In order to compare the octet-frame proposed in section4 to other 3D printed structures an hexahedron (six quadri-lateral faces) unit cell based structure has been designed andwill be printed as well The intention is to investigate theeffects of element type on the overall performance of thestructure

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

In order to print both frames an initial attempt was con-ducted by using an initial design of the structures in particu-lar considering their density and thickness The initial objec-tive was to minimise as much as possible the usage of ma-terial For this we selected a 25 cm length for the struct ofthe basic unit and a truss wall thickness of 10 mm This hasresulted in failure with the selected thickness as the struc-ture broke down during the excavation due to its fragilityThe failed attempt is illustrated in Figure 9 In following tri-als we are varying the thickness up to 30 mm wall thicknessas we estimate this is a critical measurement for providingstrength to the overall structure Hence carefully estimatingits ideal value is an important part of the research and is cur-rently work in progress By using the parametric implemen-tation for the mesh generation the density and the thicknessvariation is straightforward

Further prototypes will be generated using other tech-niques to allow for a direct comparison and evaluationThese include using a VFlash 3D printing machine whichprints directly in acrylic (a softer material which is not asstrong as the epoxy resin infused powder material) and us-ing a laser cutter to produce a lattice of cardboard slices togenerate a 3D structure with an accurate contour bed for theobject to lie in

The testing experiments planned involve testing the loadcapacity of the structures supporting a small fragile objectThis will include both a compression load test case and adrop load test case The compression load case involvesloading the structure with 1kg masses and increasing theload by 1 kg per increment to investigate the maximum loadcapacity of the structure before the fragile object breaks Thedrop test will be conducted in a similar fashion dropping thestructure in a controlled drop test from an initial height of 10cm increasing this by 10 cm thereafter

The materials used in a further experiment may provide astrong and sturdy support for the object and this can be donesetting consistently the mesh density Ideally the material inimmediate contact with the object will be softer and moreforgiving to the surface of the object and this can be achievedby either using a multiple density 3D printing machine (egObjet Connex 500) or by manipulating the structural den-sity surrounding the object such that thinner walled less stiffstructures can be used to surround the object Similarly theoverall density of the structure needs to be considered to op-timise the weight of the structure whilst providing sufficientstrength and stiffness to withstand load cases that are typi-cal for stacking and transit Although we could not explorethe wide range of possibilities regarding the production ofa prototype we are convinced that the proposed structure isfeasible and a rigorous exploration of the range of possibili-ties and technology limitations is left as future work

Figure 9 3D printing failure at the first attempt

7 Conclusions

The movement of heritage artefacts is a process most her-itage organisations need to undertake Packaging artefactscorrectly is critical as artefacts are at their most vulnerablewhen transited Hence this paper has introduced an innova-tive approach for packaging the artefacts based on 3D tech-nology The proposed solution makes use of a Tetrahedral -Octahedral Frame This is produced using a generative mod-elling approach so that it can parametrically produce struc-tures that will fit any artefact The resulting structure pro-vides a number of advantages

bull A bespoke packaging solution that is tailored to specificartefact

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

bull An easier and more automatic process than traditionalmethods

bull Requires the 3D documentation of the artefact which inturn can be used for different purposes (eg conservationcondition assessment)

Although such packaging solution might incur a higher costof production when compared to traditional methods we es-timate that this is balanced by the fact that less time needs tobe spent producing the packaging

Further work beside the ongoing printing and testingwork involves developing structural analysis of the fittedpackage frame and considering the artefact weight to dy-namically adapt the structure The final goal is to minimizematerial needs while guaranteeing that the package frameprotects the artefact in transportation and potentially stor-age conditions

The proposed octet truss achieved so far can be improvedin different ways One is to consider the production of a pro-tective case for the object to be place in between the objectand the octet truss To do so a possible approach would beto 3D print the protective case by means of off-setting theobject mesh as proposed by Liu in [LW11] and then fit theprotective case to the octet truss Other trusses could be alsoconsidered as alternatives

8 Acknowledgements

We would like to acknowledge CAPES (the Coordenaccedilatildeo deAperfeiccediloamento de Pessoal de Niacutevel Superior) Brazil forsupporting this research We also thank the 3D-COFORMintegration project which has received funding from theEuropean Communityrsquos Seventh Framework Programme(FP72007 2013) under grant agreement No 231809 formaking available technology and 3D models for this re-search

References[A 12] A KAWAMOTO ET AL Prototyping lightweight car seat

structures using topology optimization and additive manufactur-ing Additive Manufacturing Conference Proceedings (2012) 3

[Aut12] AUTODESK LABS 123d catch 2012 httphttpwww123dappcomcatch 5

[Bau93] BAUER E Packing museum objects for shipment Con-serve 0 Gram 17 1 (July 1993) 1ndash4 1

[Bit97] BITZER T Honeycomb Technology Materials DesignManufacturing Applications and Testing Chapman amp Hall1997 3

[CF12] CONNOR J FARAJI S Fundamentals of Structural En-gineering Springer 2012 3

[Chr00] CHRISTENSEN R Mechanics of cellular and other low-density materials International Journal of Solids and Structures37 1acircAS2 (2000) 93 ndash 104 3

[CJT11] CONWAY J H JIAO Y TORQUATO S New familyof tilings of three-dimensional euclidean space by tetrahedra andoctahedra Proc Natl Acad Sci U S A 108 27 (2011) 11009ndash124

[Cox73] COXETER H Regular Polytopes Dover books on ad-vanced mathematics Dover Publications 1973 4

[Cri73] CRITCHLOW K Order in Space A Design Source BookThames and Hudson 1973 4

[DEKBP03] DYSKIN A ESTRIN Y KANEL-BELOV APASTERNAK E Topological interlocking of platonic solids away to new materials and structures Philosophical MagazineLetters vol 83 issue 3 (2003) 4

[DFA01] DESHPANDE V FLECK N ASHBY M Effectiveproperties of the octet-truss lattice material Journal of the Me-chanics and Physics of Solids 49 8 (2001) 1747 ndash 1769 4

[EDP11] ESTRIN J DYSKIN A PASTERNAK E Topologicalinterlocking as a material design concept Materials Science andEngineering C Biomimetic and Supramolecular Systems vol 31issue 6 (2011) 4

[FH99] FRIEDRICHS O D HUSON D H Tiling space by pla-tonic solids i Discrete amp Computational Geometry 21 2 (1999)299ndash315 4

[Gor03] GORDON J Structures Or Why Things Donrsquot FallDown Da Capo Press 2003 3

[GRS09] GIBSON I ROSEN D STUCKER B Additive Man-ufacturing Technologies Rapid Prototyping to Direct DigitalManufacturing Springer 2009 3

[Hav05] HAVEMANN S Generative Mesh Modeling PhD thesisInstitute of Computer Graphics Braunschweig Technical Univer-sity 2005 5

[KREPlowast12] KAMINSKI J RODRIGUEZ ECHAVARRIA KPALMA G SCOPIGNO R STEVENSON J MARC P ARNOLDD Insourcing outsourcing and crowdsourcing 3d collection for-mation perspectives for cultural heritage sites In VAST The 13thInternational Symposium on Virtual Reality Archaeology and In-telligent Cultural Heritage (Brighton UK 2012) 2

[LW11] LIU S WANG C C L Fast intersection-free offsetsurface generation from freeform models with triangular meshesIEEE T Automation Science and Engineering 8 2 (2011) 347ndash360 8

[Mes12] MESHLAB httpmeshlabsourceforgenet 2012httphttpmeshlabsourceforgenet 5

[Net12] NETFABB httpwwwnetfabbcomstructurephp 2012httphttpwwwnetfabbcomstructurephp 3

[Owe98] OWEN S J A survey of unstructured mesh generationtechnology In IMR (1998) pp 239ndash267 4

[Sch12] SCHNEIDERS R Mesh generatorshttpwwwrobertschneidersdemeshgenerationsoftwarehtml2012 5

[US99] US NATIONAL PARK SERVICE Chapter 6 Handlingpacking and shipping NPS Museum Handbook Part I MuseumCollections (1999) 2

[VG06] VERGAUWEN M GOOL L V Web-based 3d recon-struction service Mach Vision Appl 17 6 (2006) 411ndash426 5

[Wad06] WADLEY H Multifunctional periodic cellular metalsPhilos Transact A Math Phys Eng Sci 364 1838 (2006) 31ndash683 4

[ZBS05] ZHANG Y BAJAJ C SOHN B-S 3d finite elementmeshing from imaging data Computer Methods in Applied Me-chanics and Engineering 194 48 49 (2005) 5083 ndash 5106 4

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

In order to print both frames an initial attempt was con-ducted by using an initial design of the structures in particu-lar considering their density and thickness The initial objec-tive was to minimise as much as possible the usage of ma-terial For this we selected a 25 cm length for the struct ofthe basic unit and a truss wall thickness of 10 mm This hasresulted in failure with the selected thickness as the struc-ture broke down during the excavation due to its fragilityThe failed attempt is illustrated in Figure 9 In following tri-als we are varying the thickness up to 30 mm wall thicknessas we estimate this is a critical measurement for providingstrength to the overall structure Hence carefully estimatingits ideal value is an important part of the research and is cur-rently work in progress By using the parametric implemen-tation for the mesh generation the density and the thicknessvariation is straightforward

Further prototypes will be generated using other tech-niques to allow for a direct comparison and evaluationThese include using a VFlash 3D printing machine whichprints directly in acrylic (a softer material which is not asstrong as the epoxy resin infused powder material) and us-ing a laser cutter to produce a lattice of cardboard slices togenerate a 3D structure with an accurate contour bed for theobject to lie in

The testing experiments planned involve testing the loadcapacity of the structures supporting a small fragile objectThis will include both a compression load test case and adrop load test case The compression load case involvesloading the structure with 1kg masses and increasing theload by 1 kg per increment to investigate the maximum loadcapacity of the structure before the fragile object breaks Thedrop test will be conducted in a similar fashion dropping thestructure in a controlled drop test from an initial height of 10cm increasing this by 10 cm thereafter

The materials used in a further experiment may provide astrong and sturdy support for the object and this can be donesetting consistently the mesh density Ideally the material inimmediate contact with the object will be softer and moreforgiving to the surface of the object and this can be achievedby either using a multiple density 3D printing machine (egObjet Connex 500) or by manipulating the structural den-sity surrounding the object such that thinner walled less stiffstructures can be used to surround the object Similarly theoverall density of the structure needs to be considered to op-timise the weight of the structure whilst providing sufficientstrength and stiffness to withstand load cases that are typi-cal for stacking and transit Although we could not explorethe wide range of possibilities regarding the production ofa prototype we are convinced that the proposed structure isfeasible and a rigorous exploration of the range of possibili-ties and technology limitations is left as future work

Figure 9 3D printing failure at the first attempt

7 Conclusions

The movement of heritage artefacts is a process most her-itage organisations need to undertake Packaging artefactscorrectly is critical as artefacts are at their most vulnerablewhen transited Hence this paper has introduced an innova-tive approach for packaging the artefacts based on 3D tech-nology The proposed solution makes use of a Tetrahedral -Octahedral Frame This is produced using a generative mod-elling approach so that it can parametrically produce struc-tures that will fit any artefact The resulting structure pro-vides a number of advantages

bull A bespoke packaging solution that is tailored to specificartefact

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

bull An easier and more automatic process than traditionalmethods

bull Requires the 3D documentation of the artefact which inturn can be used for different purposes (eg conservationcondition assessment)

Although such packaging solution might incur a higher costof production when compared to traditional methods we es-timate that this is balanced by the fact that less time needs tobe spent producing the packaging

Further work beside the ongoing printing and testingwork involves developing structural analysis of the fittedpackage frame and considering the artefact weight to dy-namically adapt the structure The final goal is to minimizematerial needs while guaranteeing that the package frameprotects the artefact in transportation and potentially stor-age conditions

The proposed octet truss achieved so far can be improvedin different ways One is to consider the production of a pro-tective case for the object to be place in between the objectand the octet truss To do so a possible approach would beto 3D print the protective case by means of off-setting theobject mesh as proposed by Liu in [LW11] and then fit theprotective case to the octet truss Other trusses could be alsoconsidered as alternatives

8 Acknowledgements

We would like to acknowledge CAPES (the Coordenaccedilatildeo deAperfeiccediloamento de Pessoal de Niacutevel Superior) Brazil forsupporting this research We also thank the 3D-COFORMintegration project which has received funding from theEuropean Communityrsquos Seventh Framework Programme(FP72007 2013) under grant agreement No 231809 formaking available technology and 3D models for this re-search

References[A 12] A KAWAMOTO ET AL Prototyping lightweight car seat

structures using topology optimization and additive manufactur-ing Additive Manufacturing Conference Proceedings (2012) 3

[Aut12] AUTODESK LABS 123d catch 2012 httphttpwww123dappcomcatch 5

[Bau93] BAUER E Packing museum objects for shipment Con-serve 0 Gram 17 1 (July 1993) 1ndash4 1

[Bit97] BITZER T Honeycomb Technology Materials DesignManufacturing Applications and Testing Chapman amp Hall1997 3

[CF12] CONNOR J FARAJI S Fundamentals of Structural En-gineering Springer 2012 3

[Chr00] CHRISTENSEN R Mechanics of cellular and other low-density materials International Journal of Solids and Structures37 1acircAS2 (2000) 93 ndash 104 3

[CJT11] CONWAY J H JIAO Y TORQUATO S New familyof tilings of three-dimensional euclidean space by tetrahedra andoctahedra Proc Natl Acad Sci U S A 108 27 (2011) 11009ndash124

[Cox73] COXETER H Regular Polytopes Dover books on ad-vanced mathematics Dover Publications 1973 4

[Cri73] CRITCHLOW K Order in Space A Design Source BookThames and Hudson 1973 4

[DEKBP03] DYSKIN A ESTRIN Y KANEL-BELOV APASTERNAK E Topological interlocking of platonic solids away to new materials and structures Philosophical MagazineLetters vol 83 issue 3 (2003) 4

[DFA01] DESHPANDE V FLECK N ASHBY M Effectiveproperties of the octet-truss lattice material Journal of the Me-chanics and Physics of Solids 49 8 (2001) 1747 ndash 1769 4

[EDP11] ESTRIN J DYSKIN A PASTERNAK E Topologicalinterlocking as a material design concept Materials Science andEngineering C Biomimetic and Supramolecular Systems vol 31issue 6 (2011) 4

[FH99] FRIEDRICHS O D HUSON D H Tiling space by pla-tonic solids i Discrete amp Computational Geometry 21 2 (1999)299ndash315 4

[Gor03] GORDON J Structures Or Why Things Donrsquot FallDown Da Capo Press 2003 3

[GRS09] GIBSON I ROSEN D STUCKER B Additive Man-ufacturing Technologies Rapid Prototyping to Direct DigitalManufacturing Springer 2009 3

[Hav05] HAVEMANN S Generative Mesh Modeling PhD thesisInstitute of Computer Graphics Braunschweig Technical Univer-sity 2005 5

[KREPlowast12] KAMINSKI J RODRIGUEZ ECHAVARRIA KPALMA G SCOPIGNO R STEVENSON J MARC P ARNOLDD Insourcing outsourcing and crowdsourcing 3d collection for-mation perspectives for cultural heritage sites In VAST The 13thInternational Symposium on Virtual Reality Archaeology and In-telligent Cultural Heritage (Brighton UK 2012) 2

[LW11] LIU S WANG C C L Fast intersection-free offsetsurface generation from freeform models with triangular meshesIEEE T Automation Science and Engineering 8 2 (2011) 347ndash360 8

[Mes12] MESHLAB httpmeshlabsourceforgenet 2012httphttpmeshlabsourceforgenet 5

[Net12] NETFABB httpwwwnetfabbcomstructurephp 2012httphttpwwwnetfabbcomstructurephp 3

[Owe98] OWEN S J A survey of unstructured mesh generationtechnology In IMR (1998) pp 239ndash267 4

[Sch12] SCHNEIDERS R Mesh generatorshttpwwwrobertschneidersdemeshgenerationsoftwarehtml2012 5

[US99] US NATIONAL PARK SERVICE Chapter 6 Handlingpacking and shipping NPS Museum Handbook Part I MuseumCollections (1999) 2

[VG06] VERGAUWEN M GOOL L V Web-based 3d recon-struction service Mach Vision Appl 17 6 (2006) 411ndash426 5

[Wad06] WADLEY H Multifunctional periodic cellular metalsPhilos Transact A Math Phys Eng Sci 364 1838 (2006) 31ndash683 4

[ZBS05] ZHANG Y BAJAJ C SOHN B-S 3d finite elementmeshing from imaging data Computer Methods in Applied Me-chanics and Engineering 194 48 49 (2005) 5083 ndash 5106 4

ccopy The Eurographics Association 2012

Asla Saacute amp K Rodriguez Echavarria Parametric 3D-fitted frames

bull An easier and more automatic process than traditionalmethods

bull Requires the 3D documentation of the artefact which inturn can be used for different purposes (eg conservationcondition assessment)

Although such packaging solution might incur a higher costof production when compared to traditional methods we es-timate that this is balanced by the fact that less time needs tobe spent producing the packaging

Further work beside the ongoing printing and testingwork involves developing structural analysis of the fittedpackage frame and considering the artefact weight to dy-namically adapt the structure The final goal is to minimizematerial needs while guaranteeing that the package frameprotects the artefact in transportation and potentially stor-age conditions

The proposed octet truss achieved so far can be improvedin different ways One is to consider the production of a pro-tective case for the object to be place in between the objectand the octet truss To do so a possible approach would beto 3D print the protective case by means of off-setting theobject mesh as proposed by Liu in [LW11] and then fit theprotective case to the octet truss Other trusses could be alsoconsidered as alternatives

8 Acknowledgements

We would like to acknowledge CAPES (the Coordenaccedilatildeo deAperfeiccediloamento de Pessoal de Niacutevel Superior) Brazil forsupporting this research We also thank the 3D-COFORMintegration project which has received funding from theEuropean Communityrsquos Seventh Framework Programme(FP72007 2013) under grant agreement No 231809 formaking available technology and 3D models for this re-search

References[A 12] A KAWAMOTO ET AL Prototyping lightweight car seat

structures using topology optimization and additive manufactur-ing Additive Manufacturing Conference Proceedings (2012) 3

[Aut12] AUTODESK LABS 123d catch 2012 httphttpwww123dappcomcatch 5

[Bau93] BAUER E Packing museum objects for shipment Con-serve 0 Gram 17 1 (July 1993) 1ndash4 1

[Bit97] BITZER T Honeycomb Technology Materials DesignManufacturing Applications and Testing Chapman amp Hall1997 3

[CF12] CONNOR J FARAJI S Fundamentals of Structural En-gineering Springer 2012 3

[Chr00] CHRISTENSEN R Mechanics of cellular and other low-density materials International Journal of Solids and Structures37 1acircAS2 (2000) 93 ndash 104 3

[CJT11] CONWAY J H JIAO Y TORQUATO S New familyof tilings of three-dimensional euclidean space by tetrahedra andoctahedra Proc Natl Acad Sci U S A 108 27 (2011) 11009ndash124

[Cox73] COXETER H Regular Polytopes Dover books on ad-vanced mathematics Dover Publications 1973 4

[Cri73] CRITCHLOW K Order in Space A Design Source BookThames and Hudson 1973 4

[DEKBP03] DYSKIN A ESTRIN Y KANEL-BELOV APASTERNAK E Topological interlocking of platonic solids away to new materials and structures Philosophical MagazineLetters vol 83 issue 3 (2003) 4

[DFA01] DESHPANDE V FLECK N ASHBY M Effectiveproperties of the octet-truss lattice material Journal of the Me-chanics and Physics of Solids 49 8 (2001) 1747 ndash 1769 4

[EDP11] ESTRIN J DYSKIN A PASTERNAK E Topologicalinterlocking as a material design concept Materials Science andEngineering C Biomimetic and Supramolecular Systems vol 31issue 6 (2011) 4

[FH99] FRIEDRICHS O D HUSON D H Tiling space by pla-tonic solids i Discrete amp Computational Geometry 21 2 (1999)299ndash315 4

[Gor03] GORDON J Structures Or Why Things Donrsquot FallDown Da Capo Press 2003 3

[GRS09] GIBSON I ROSEN D STUCKER B Additive Man-ufacturing Technologies Rapid Prototyping to Direct DigitalManufacturing Springer 2009 3

[Hav05] HAVEMANN S Generative Mesh Modeling PhD thesisInstitute of Computer Graphics Braunschweig Technical Univer-sity 2005 5

[KREPlowast12] KAMINSKI J RODRIGUEZ ECHAVARRIA KPALMA G SCOPIGNO R STEVENSON J MARC P ARNOLDD Insourcing outsourcing and crowdsourcing 3d collection for-mation perspectives for cultural heritage sites In VAST The 13thInternational Symposium on Virtual Reality Archaeology and In-telligent Cultural Heritage (Brighton UK 2012) 2

[LW11] LIU S WANG C C L Fast intersection-free offsetsurface generation from freeform models with triangular meshesIEEE T Automation Science and Engineering 8 2 (2011) 347ndash360 8

[Mes12] MESHLAB httpmeshlabsourceforgenet 2012httphttpmeshlabsourceforgenet 5

[Net12] NETFABB httpwwwnetfabbcomstructurephp 2012httphttpwwwnetfabbcomstructurephp 3

[Owe98] OWEN S J A survey of unstructured mesh generationtechnology In IMR (1998) pp 239ndash267 4

[Sch12] SCHNEIDERS R Mesh generatorshttpwwwrobertschneidersdemeshgenerationsoftwarehtml2012 5

[US99] US NATIONAL PARK SERVICE Chapter 6 Handlingpacking and shipping NPS Museum Handbook Part I MuseumCollections (1999) 2

[VG06] VERGAUWEN M GOOL L V Web-based 3d recon-struction service Mach Vision Appl 17 6 (2006) 411ndash426 5

[Wad06] WADLEY H Multifunctional periodic cellular metalsPhilos Transact A Math Phys Eng Sci 364 1838 (2006) 31ndash683 4

[ZBS05] ZHANG Y BAJAJ C SOHN B-S 3d finite elementmeshing from imaging data Computer Methods in Applied Me-chanics and Engineering 194 48 49 (2005) 5083 ndash 5106 4

ccopy The Eurographics Association 2012