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JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.1(1-12)Aerospace Science and Technology()Contents lists available at SciVerse ScienceDirectAerospace Science and Technology/locate/aescteAid tool for the design of process and aircraft assembly linesBernard Anselmettia,b, Benot FricerocaLURPA, ENS Cachan, 61, avenue du Prsident Wilson, 94235 Cachan, FrancebIUT Cachan, Universit Paris-Sud, 9, avenue de la division Leclerc, 94230 Cachan, FrancecEADS IW, 12 rue Pasteur, 92152 Suresnes, Francea r t i c l ei n f oa b s t r a c tArticle history:Received 3 December 2010Received in revised form 19 September2011Accepted 21 September 2011Available online xxxxKeywords:Assembly graphAssembly planningViewerCADPLMThe joint design of a new complex industrial process and of a new production system implies that severalteams with various skills collaborate. This article describes a computer aided design tool based on thecombination of a graph to describe the process with three viewers to visualize the process, the layoutof the workshop and the production facilities. Different processes and configurations of the site can betested to realize simultaneously several products. This paper presents the process planning model basedon a graph and the viewers with a multi-scale approach.2011 Elsevier Masson SAS. All rights reserved.1. Problematic1.1. Industrial needThis study was realized within the framework of the clusterSystemtic PARIS REGION, project “Digital Production 2”. The aimis to create a computer aided tool for the design of a new processand a new workshop. The experiment theme deals with aircraft as-sembly, but the field of use must cover all the mechanical systems,including machining or forging for example.Today, available tools for CAD simulate and represent solutionsthat are perfectly defined, sometimes in a very realistic way. Onthe other hand, it is very difficult to make such a project evolve,for example to compare different processes or to test different con-figurations for production lines. For instance, it is hard to managedisplacements of workstations when all the parts are positionedin the CAD reference frames each one separately from the others.Every length variation of a part imposes a very precise parameteri-zation though the product is not well defined yet and that differenttechnical solutions have to be considered.The needs are clearly multi-scales with a progressive design ofthe project and the intervention of numerous internal or externalactors. It is necessary to study several product variations and to beable to simulate several processes and several workshop configu-rations.*Corresponding author at: LURPA, ENS Cachan, 61, avenue du Prsident Wilson,94235 Cachan, France.E-mail address: bernard.anselmettilurpa.ens-cachan.fr (B. Anselmetti).The automated search for an optimal solution is not realisticyet for a complex industrial project because it would impose todescribe all the constraints of the technical solutions. The designteam must describe and imagine the solutions considered.1.2. Industrial use caseIn order to design a new aircraft and define its main character-istics, some high level studies are performed with the customers.Then, engineers start to work on the design and imagine severaldesign alternatives: motors under the wings or under the horizontal tail plane, the wings in the middle of the center fuselage (like most ofthe Airbus aircrafts) or on the top of the barrel (A400M solu-tion), the work sharing will impose the use of sections/barrels tobuild the structure (as is solution) or it is also possible to splitthe aircraft in one long lower shell and one long upper shell.And so on.For each alternative, designers go deeper and deeper in theproduct definition in order to get relevant information on the fea-sibility and the performance of the solution.Further the more, each choice will impact the product, themanufacturing process and the layout design. It means that de-signers have a lot of studies to perform. Unfortunately, there areno tools to assist users during this innovative design phase and toensure the traceability of all these ideas and choices. Then it can1270-9638/$ see front matter2011 Elsevier Masson SAS. All rights reserved.doi:10.1016/j.ast.2011.09.009JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.2(1-12)2B. Anselmetti, B. Fricero / Aerospace Science and Technology()happen for a new program that studies are redone with the sameconclusion.This paper will propose a solution to avoid this rework, to en-able designers to evaluate more alternatives and finally to traceall the information and studies performed in a single tool and amethod.The use case presented in this article is a simplified productbased on real produced aircrafts.1.3. State of artThe simulation of a production process is still not somethingusual for aspects that do not especially deal with production man-agement. Software like WITNESS (LANNER GROUP) permits to de-fine the charge of stations and the implantation of resources froma symbolic representation of production machines and products.Usually, the process plan is described with a paper document orthanks to classical office software. This method is not well adaptedto analyze a process for a complex product, especially since variouspartners share this process with confidentiality problems whichimpose to screen some pieces of information.For the layout of the workshop, the basic solution consists inmaking a 2D model or even 3D model with the help of modu-lar systems like “LEGO”, for instance. The digital model allowsvisualizing process and products using DELMIA-like softwares,by Dassault Systmes, but it is difficult to make modificationsand comparisons. So it is necessary to complete CAD model withdescriptions of process and production facilities. Rogederer 12proposes a design of workshops and processes in CAD system.Sternheim 13 take into account transport devices in Spirit soft-ware, with graphical and textual description. Milbert 10 workson planning aids and assembly-oriented design.In the 1980 s, Bourjault 1, proposed different assembly se-quences using graphs. Perrard 11 continues the task to search thedifferent assembly solutions and to compare them with the help ofindicators and evaluation functions. The consideration of assemblyconstraints is usually processed with matrix 3,16,14. The processcan also be described using an automated sequencer (Grafcet or aPetri network) 18. Homem de Mello uses the AND/OR graph toselect of the best assembly plan 5.Godot 2 proposes a model dedicated to mechanical modelingof assemblies combining surfaces geometry. Gu 4 represents me-chanical assembly sequences by OBDD symbolic. Jabbour 8 andMascle 9 describe the assembly by functional features. The STEPstandard proposes a hierarchical structure of an assembling 17.1.4. Proposed approachThe problem is to allow engineers and technicians to describequickly a new process and a new production site to realize vari-ous products. Modifications have to be very quick. It is necessaryto be able to develop and compare several solutions before mak-ing a decision. Every kind of contributor must be able to studythe solution, with a multi-scale view and an information screeningconsidering users.When the process and the factory layout are well defined, itmust be possible to simulate a production with a task schedulingso all the resources are correctly resized.Finally it is necessary that all the data can be transferred toother specialized software.So the proposed process is based on two major ideas: The process of a product is described by a multi-level graphrepresenting parts flow according to time. This graph is com-pleted each day, step by step, following the evolution of theproject thanks to the contribution of work teams.Fig. 1. Assembling of two parts. The process and the manufacturing plant must be visible ina CAD environment using four dedicated viewers: a “pro-cess viewer”, a “layout viewer”, a “production viewer” and a“scheduling viewer” working on the same model.The entire project is finally described with graphs. Viewers onlygive a dynamic and realistic image of the graphs.The work presented in this document shows the specificationsof the software which should satisfy the different requisites, butthe corresponding computer model is not created yet.1.5. Description of the assembling of two partsFig. 1 represents the assembly of the central fuselage with theforward fuselage. Each component is described by a CAD model.This model can be very schematic at the beginning of the project,but it could be updated each time a more mature release is avail-able.Several reference frames are determined on each section. Themain reference frame is marked R0 followed by one or two lettersreferring to the part (i.e. R0_c for the central fuselage).Several auxiliary reference frames marked R1, R2.are createdon the real surfaces of junction with other parts. The designermust also describe an accosting trajectory (ta) which is definedby several reference frames, speeds and accelerations.In Fig. 1, the assembly of parts is described thanks to the fol-lowing instruction:Assemble R1_f on R1_c,ta=1Thanks to the previous steps, the central fuselage (c) is alreadyplaced on an assembly workstation. The ending point of the ac-costing trajectory (ta) number 1 is positioned on the referenceframe R1_c. The forward fuselage (f) is placed so that referenceframes R1_f is at the start of the accosting trajectory. The forwardfuselage follows the accosting trajectory until its reference frameR1_f reaches the reference frame R1_c.The accosting trajectory only describes the final approach at themoment of the assembly. The aim is to validate the displacementof parts or to spot crashes between the components.When the CAD model of a fuselage changes, it is only neces-sary to reposition the reference frames on the new model. This jobcan be automated by a geometric recognition of the positioningsurfaces in the CAD model.When the model is fully described, the “process viewer” cansimulate in real time the assembly, moving the CAD model of theforward fuselage following the trajectory of accosting.JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.3(1-12)B. Anselmetti, B. Fricero / Aerospace Science and Technology()3Fig. 2. Basic process graph.Fig. 3. Step of the graph.1.6. Process descriptionsA whole assembly process or manufacturing process is thendescribed by a graph (Fig. 2) inspired of the Sequential FunctionChart defined in the standard IEC 60848 (GRAFCET) 7. The ver-tical direction is time. The graph describes the creation of oneproduct from elementary parts or sub-assemblies coming fromprocesses represented by other graphs.The steps describe the activities (assembly, machining, inspec-tion, etc.). The transition under a step represents the product ob-tained after this step. An initial step 0 defines the nomenclature ofthe components to assemble. Input steps enable to introduce com-ponents in the assembly. The output point identifies the productstemmed from the process.The formalism will be itemized in Section 2.2. Design of production process2.1. General description of a stepThe step (Fig. 3) is identified by a number in the graph and anoperation name. Current assembly and isolated parts are settingup on the top of the step. The obtained assembly outputs on thebottom to the step. Thus the transition represents this new inter-mediary product.The major and minor furniture necessary for the step enter onthe left. Litter and defective mechanisms output on the right. Ifnecessary, these components can be managed inside the graph orprocessed by sub-graphs.Each activity is described by five main tags: Description: free and short text which describes the step.JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.4(1-12)4B. Anselmetti, B. Fricero / Aerospace Science and Technology()Fig. 4. Graphic language. Activities: list of instructions which describes precisely thestep and drives the simulation. Detailed definition: free text and/or images and/or hypertextlinks to cast out to other documents. CAD models: this tag enables to store all the references of allthe CAD models of the step, giving for example the contractualtolerancing to respect.According to the type of activity of the step, various tags are avail-able to describe for instance accosting trajectories or the machin-ing time of the step.The values contained in a tag are indexed according to the pro-cessed object. For example, machining time will not be the samefor the short variant and the long variant of the same part.The initial step 0 is composed of three main tags: The nomenclature: the list of components to assemble for eachvariant of products to manufacture. Tests: this tag counts several variables to make choices duringsimulations (machine-tool out of order, part out of tolerance,etc.). Default values: this tag contains every default value, for in-stance moving speed between stations and accosting speed.Normally, the intermediary assembly at the end of a step isobtained from the inputs of the step and the activities of the step.2.2. Designation of the partsEach component (part or mechanism) is designed by a shortalias of 1 to 3 letters (Ex: b for body).Identical parts are identified by an instance number. Ex:b.1,b.2.A part which is symmetrical with another is identified with thesymbol “”. Ex: b is the symmetric part of b, which avoids to de-scribe the symmetric part.A variant of parts is identified with a “/”. Ex: b/1 and b/2.If the shape of a part changes during its manufacturing process,the alias depicts the phase number. Ex: b_00 and b_10.For example, the designation of the second instance of the sym-metric bag in variant 1 is bag/1.2.A nomenclature is associated to each graph to define elemen-tary parts to assemble and to give a name to the component ob-tained at the output step.A process can be applied to different products. Thus the aliasused in a graph is assigned to each part during the initializationusing the nomenclature.2.3. Graphic formalismIn graph (a) of Fig. 4, the double line indicates that the threesteps 21, 31 and 41 are launched in parallel and run simulta-neously and independently to the others. The convergence on adouble line indicates that both steps 23 and 44 have to be finishedbefore starting step 50. There is a transition before the double lineto describe the intermediary product after each branch consideredindividually; then a transition after the double line to describe theshape when all the branches are finished.This graph also includes synchronization milestones identifiedwith numbered triangles. The process stops on the milestone aslong as its condition on the right side of the triangle is not reachedor over passed. A milestone without condition is immediately overpassed. In this example, the process stops on the milestone 22and waits for the milestone 43 to be reached. Inversely, the thirdbranch stops on the milestone 43 and waits for the milestone 22 tobe reached. With this typing, steps 23 and 44 will be synchronizedand launched at the same time.At step 41, the symbol “2s” (simultaneous) indicates that twoidentical parts d are assembled simultaneously on the part t. Inthe same way, the symbol 2r (repetition) indicates that both partswill be assembled one after the other. Fig. 2 shows the non-simultaneousassembly of the 2 engines at step 60.JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.5(1-12)B. Anselmetti, B. Fricero / Aerospace Science and Technology()5In graph (b) of Fig. 4, the single horizontal line indicates thatthe branches can be executed in any order, but only one branchat a time, for instance, because the operation to perform is in thesame working area. So it is necessary to wait for a branch to befinished to be able to start another branch. During real produc-tion, the branch selection will be done naturally according to theavailability of resources. For the viewer, selection is made by testswhich use the contents of the “test” tag of the initial step of thegraph.Step 50 separates part w from the others.Graph (c) of Fig. 4 introduces the notion of process plan vari-ants. This graph includes two equivalent processes but realized indifferent orders. The double-lined diamond allows choosing be-tween several process plans. The attempt choice is defined in ini-tial step.This step 70 also entails a right exit in case of default. The partproceeds to step 75 to be repaired, then goes back to step 70. Thedefault can be simulated by a value indicated in “test” tag.After step 70, a test selects one or another step, for example,according to the part variant.2.4. Activities of a stepThe activity tag describes the operations to realize during thestep, with the help of an instruction list. The structure of an in-struction is:Transfer R0_b on R1_d,ti=4,to=3,c=c1,s=1000,F=1,2,4This instruction moves the reference frame R0 of part b on ref-erence R1_d. The input trajectory (ti) is the trajectory #4. Part bis coming from a place defined by a previous step of the graphor in the initial step. The output trajectory from previous stationwas defined in the step which positioned this part on this station.The move is made along the corridor c1. The moving speed (s) is1000 mm per minute. If one of the filters (F) 1, 2 or 4 is active, theinstruction is not detailed and the result is given directly. The out-put trajectory to=3 will be used to leave this workstation. Thisorder is given by a following step.Fourteen keywords have been defined to write the needed in-structions:Fix: To place an object in a specific point (machine-tool, robot,storage material, etc.).Transfer: To move an object to a given point.Assemble: To move an object to assemble it with another. (Justafter this instruction, both objects are linked. Every move of onedrives the other.)Separate: To separate an object from the assembly it belongs to.Change: To replace an object by another (in order to change theshape of a part after machining, for example).Wait: To make a pause for a given time (to simulate a move lessactivity).Extract: To extract a part from its station with its output trajectory.Move: To move an object according to one another, following acomplex trajectory (painting for instance).Remove: To suppress an object.Invisible: To make an object invisible.Visible: To make an object visible.Datum: To create a reference frame beside one or several others.Call: To call software dedicated to a particular application.Exit: End of procedure or return to main procedure.Fig. 5. Activities of one step.Fig. 6. Manufacturing of a part.2.5. Description of the steps of an activityGenerally, the activity of a step corresponds to a single instruc-tion, but it is possible to define an ordered series of instructions tolighten the graph, without making sub-graphs (see Fig. 5).The symbol enables to make comments. Instructions precededby a % are realized at the initialization of the process plan. Se-quences separated by the symbol $ run in parallel but withoutsynchronization possibility. Tests must be limited to local tasks.Filters allow hiding certain operations considering the user.2.6. Transformation stepDuring a step of machining or forging, the part shape changes.The original object is just replaced by a new one. As the position-ing surfaces of each object can be different, the reference framesare different. The transformations of Fig. 6 are obtained with fourdifferent CAD models, which impose three reference frame D1, D2,D3. This process is described by the following instructions:Transfer R0_b_00 on D1 setting up of the raw part.Change b_00 in R0_b_10 on D2, t=55 s manufacturing ofthe pocket in 55 s.Change b_10 in R0_b_20 on D3, t=25 s manufacturing ofthe left face in 25 s.Change b_20 in R0_b on D3, t=10 s Drilling of the hole in10 s.Instruction “Datum” gives the coordinates of the origin and thedirection of the first two vectors of the new reference system inthe reference frame:Datum D2 on D1(15,25,0;1,0,0;0,1,0)Datum D3 on D1(13,25,0;1,0,0;0,1,0)To visualize these transformations, the viewer only replaces a CADmodel by another. The instruction “Move” can possibly representthe movement of a tool to simulate the machining process. On theother hand, a software dedicated to the process simulation can beJID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.6(1-12)6B. Anselmetti, B. Fricero / Aerospace Science and Technology()Fig. 7. Macro-step and sub-graph.executed in a specific window using the “call” instruction (machin-ing simulation, material flow, etc.).In manufacturing, a phase corresponds to a set of operationsrealized on one machine-tool with one setting-up. The CAD modelcorresponds to the phase-drawing, which is the state of the work-piece after the corresponding phase. If needed, this manufacturingstep can be considered as a macro step and decomposed into op-eration steps. In this case, operation drawings describe the shapeof the part after each operation b_11,b_12, etc. The setting up andthe datum is fixed.2.7. Process viewerWhen the graph is built, it is possible to visualize the processwithin the viewer. In the case of Fig. 2, components are assem-bled around the central fuselage which is the part carrying theinitial step. When the project started, the viewer does not knowthe positions of the assembly workstations. The central fuselage isrepresented on the center of the screen.If needed, sub-assemblies are assembled simultaneously, but indifferent points of the screen arbitrarily placed next to main sys-tem or defined in initial step.The assembly is simulated so that the sub-assembly is readyright at the moment of its assembly on the main structure.The process can be tested with part variants, for example witha long central fuselage or with a new product. In this case, allthe parts are perfectly positioned, thanks to reference frames onjunction surfaces.The viewer can be launched from each transition to representthe following steps of the process. In this case, the process is ac-tivated in its current intermediary shape defined in the transition.The other branches are activated in their states at the same time.3. Multi-scale functioning3.1. Macro-stepsA step can be detailed by a sub-graph. This multilevel structurethen includes a main graph with a macro-step which calls a sub-graph.In Fig. 7, step 30 is a transformation step. The input of the sub-graph is the intermediary shape after step 20. The shape of theproduct after the sub-graph must correspond to the transition afterphase 30 of the main graph.A sub-graph can possibly be called by different macro-steps toproduce different parts. So the call establishes the connection be-tween the names of the parts and the references used by the maingraph and the sub-graph.In the graph editor, a macro-step which is linked with a sub-graph is represented with a double line. A double click must beable to open a window with the sub-graph.The macro-step includes a symbolwhich switches into?simply by selection and inversely. During the viewer execution, ifthe symbol is, the sub-graph is activated, and its result is trans-mitted to the following step of the main graph. If the symbol is?,the sub-graph is not called and the instruction transformed showsdirectly the result of the transformation, which avoids to go intodetail.3.2. Progressive enrichmentAt the beginning of the project, a first team of designers de-fines the main graph (Fig. 7) essentially with “Change” functionsgiving the CAD models which characterize the product after eachstep and assigning an execution time. Thus this graph is a deliveryrequirement for the continuation of the project.In a second time, another team studies the realization processof transformation for instance step 30, proposing the sub-graph.The CAD model of the transition 30 has to be compared withthe result of the assembly of the component obtained in the sub-graph.When all the steps of the main graph are explained with thehelp of sub-graphs, the process can be executed with a new prod-uct. Then the intermediary shape must be registered for this newproduct in the transition after the macro-step to permit later totake the viewer again at this step or to avoid developing themacro-step. Durations calculated by the sub-graph allow updatingeffective durations of step 30. Change function is finally suppliedby the sub-graph.JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.7(1-12)B. Anselmetti, B. Fricero / Aerospace Science and Technology()7Fig. 8. Alternatives of process.3.3. Attempts and process plan alternativesDuring a process design, several solutions are considered. Withthis approach, all the solutions are integrated in the same graphwith tests which allow activating some steps.Example (c) of Fig. 4 presents two different sequences selectedby a test. In Fig. 8, macro-steps 20 and 40 are identical and call thesame sub-process. Both alternatives a and b are managed activatingthe tests with a table.After step 30, the intermediary shape depends on the processplan alternative chosen.When the process is chosen, useless parts of the graph can besuppressed, but it is interesting to keep them in a hidden formnoting the reasons why the solution was rejected.This structure also permits to keep process plan alternativesputting in place choice standards, well according to the availabilityof production machine.3.4. Modularity of the processIn consequence, a complete project is constituted with multipleindependent graphs built by different teams.A graph can count macro-steps to call sub-graphs on severallevels (descending process).Two independent graphs can be placed end to end in a sin-gle graph (concatenation process) or considered as sub-graphs of amain graph (ascending process).In consequence, a complete project is constituted with multipleindependent graphs, which allows a simultaneous work of numer-ous work teams studying various solutions.A graph can cover different products or product variants de-scribing the corresponding nomenclatures.The “process viewer” can simulate the process on any part ofone of the graphs avoiding if needed to get in certain sub-graphsto lighten the simulation.4. Production site design4.1. Definition of the siteThis section defines the position of workstations in order todescribe the movement of components inside the production site(Fig. 9). A table is used to indicate on which workstation each stepof the graph is executed (Table 1).Fig. 9. Two configurations of production site.JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.8(1-12)8B. Anselmetti, B. Fricero / Aerospace Science and Technology()Table 1Location of production resources.The production site is the studied entity that can correspondto a factory or a building (Fig. 9). This site is described with ahierarchical structure 15.The site is divided into workshops. Each workshop is dividedinto stations. Each station can counts several workstations. So theworkstation is the elementary unit of work where an activity takesplace. The layout of a site is then described on three levels. It isimportant that the vocabulary used can be adapted to a dedicatedsite and to a company culture.Thus the “layout viewer” will be able to represent the moves ofcomponents in the different stations during the production.The number of workstations can be quite low, because there isonly need to position the main part of the component during itstransfer to another station. Then all the other movements are doneaccording to the references frame Ri defined on the other parts. Sothe only workstations to define belong to the assembly line and tothe different storage areas.The different units (workshops, stations and workstations) havea name. Ex: Sw for a wings assembly station. Duplicate units areidentified by an instance number. Ex: Ss.1 and Ss.2 for two identi-cal storage stations.Corridors are defined at the level of the site and if needed atworkshops level.By default, a station counts a workstation on its reference framewith the same name (Sx=Wx). Several other workstations can beadded (Wm, Wc, etc.). Generally, a workstation counts only oneJID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.9(1-12)B. Anselmetti, B. Fricero / Aerospace Science and Technology()9workpoint, but it is possible to define several workpoints for du-plicated components. Ex: Wf.1, Wf.2 and Wf.3 (Fig. 9).This approach enables to design the layout of a station regard-less to the others, to test different locations of machines and toduplicate stations without having to redefine them. The site canbe reconfigured moving the workshops, the stations or the work-stations inside the stations.4.2. Location of the workstationsThe position of the workstations is defined by a multilevelstructure which must allow to move quickly a station or a work-shop for instance and to consider different configurations of theproduction site. Table 1 illustrates the approach with a simpleEXCEL spreadsheet. The principle consists in defining the positionof workshops in the site (range 1), then the position of the sta-tions inside each workshop (range 2 to 5), and finally the positionof each workstation inside the station (range 6 to 16). The stations10 to 16 are not detailed in this table.A station is represented on several lines if a workshop that canbe placed at several positions according to the configuration stud-ied. For instance, both configurations A and B uses configurationsa and b of the workshops that point then on configurations 1 and2 of stations.This way, the position of each workstation in the site can becalculated spreading the coordinates for each configuration. It isquite easy to create a new configuration when the project is pend-ing by adding a new column in this table.4.3. Setting up of steps in workstationsLots of components movements are made directly according todefined reference frame on components that are already placed,which does not make any problem:Transfer R0_b_10.2 on R1_c,.On the other side, when a part is directly positioned on the site,the movement is described according to reference frame D thatdepends on site configuration chosen. By default, the position ofthis reference frame D is given in the initial step.Fig. 10 shows the movement of the wing on a preparation sta-tion before it is assembled on the fuselage with this instruction:Transfer R0_w on D1,.In configuration A, D1 is the datum R4_c defined according to thedatum R3_c of the fuselage.In configuration B, D1 is on the workstation Wwl (left wing) ofthe station Sl dedicated to this preparation.For this example shown in Fig. 10, Table 2 indicates the nameof the datum used for this assembly step, according to the config-uration chosen.The names of datum D1,D2.are specific for each step. Thereis generally few or no reference in each step. If needed, referenceframe can be built with Datum instruction considering other refer-ence frames.4.4. Layout viewerWith both Tables 1 and 2 and the graph, the “layout viewer”represents the assembly with the movement of every part throughproduction site.Fig. 10. Example of process adaptation to two configurations of site.By default, each part moves in a straight line from the end pointof the output trajectory from a workstation, until the start point ofthe input trajectory of the next workstation. If a part move doesnot exist in the scene, it appears automatically at the beginning ofthe input trajectory.To increase realism, it is necessary to add steps in the graph tomake the parts visible at the input point of the site, and to movethem to the different checkpoints or along corridors in productionsite.This process allows testing the production of a product variantwith a given configuration of the site and a process plan. For in-stance it is easy to double a workstation and to experiment thedifferent moves.This model can be exchanged with tools dedicated to flow sim-ulation, for example to determine the number of each stations orthe capacity of storage systems.5. Production facilities5.1. Positioning of the machineThe aim of this section is to describe all the equipments, toolsand people needed for each operation inside the graph.At the beginning of the project, the graph describes the productrealization process, regardless to the environment. Then the graphis completed with steps describing the production and transportmaterials and the storage systems including building structuresand finally operators (Fig. 11). These complementary steps are rep-resented in the graph by a rectangle with rounded corners andwithout transition because there is no transformation of the prod-uct during these logistical steps.5.2. Positioning of the part-holderThe “layout viewer” moves all the components of the productin the production site. The strategy consists in setting up transportresources, jigs and tools with regard to the parts and the mecha-nism being manufactured.Table 2Allocation of workstations.StepsDatumConfiguration AConfiguration BWorkshopStationWorkstation/DatumWorkshopStationWorkstation/Datum35D1WaSwR4_cWaSlWwlJID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.10(1-12)10B. Anselmetti, B. Fricero / Aerospace Science and Technology()Fig. 11. Transfer of handling and production resources.Fig. 12. Displacement of the part-holder.For instance, in Fig. 12, the part-holder is assembled below thepart. As the 2 components are assembled, the movement of thepart also moves the part-holder until they are separated. Fig. 12illustrates following instructions: Transfer R0_a on D1 displacement of part a on D1. Assemble R1_hm on R0_a displacement of the part-holderunder the part. Transfer R0_a on D2 displacement of both part a and thepart-holder on D2. Separate a part a is isolated from the part-holder. Transfer R0_a on D3 displacement of part a on D3. Transfer R1_hm on D4 displacement of part-holder on D4.It is also possible to define a machine-tool that performs anoperation on a part at a given step. The position of the machineis calculated according to this step, but if the instruction is %Fix.the machine will be positioned right at the initialization of thescene at the calculated point using the position of the part atthis step. It is evenly possible to position equipments (compres-sor, stocker, etc.) or building structures on specific stations of theproduction site, if needed by creating a “building” station and a“building” sub-graph.This way, any modifications of the production site layout or ofthe definition of a part for example will be spread on productionfacilities. This requires defining production facilities by CAD mod-els with a few parameters. Fig. 13 shows a footbridge which mustbe positioned under the fuselage. The height of poles and the num-ber of steps have to be set and calculated according to the heightof the fuselage in order that the footbridge bottom touches theground.5.3. Operators workOperators work is described by different realistic positions:steady man, kneeling man, etc. and by a reference frame on hishands or on the tools he is holding (Fig. 14). Thus the operatoris represented schematically moving his reference frame on theworkstation, given that his feet must stay on the ground, whichallows calculating the orientation of his arms.5.4. Production viewerThe graph is now completed by the description of all produc-tion facilities. The “layout viewer” simulates the movements of thecomponents of the product to manufacture, without any represen-tation of production facilities.“Production viewer” now adds every production resource need-ed. Some components have a fix position since the beginning ofthe simulation. Others are moving from a storage place to a spe-cific point considering the product. The movements and actions ofthe operators can also be illustrated.It is possible to locate and display simultaneously all the facili-ties needed for all the products to test conflicts and collisions.This very complete animation allows then the users to have abetter understanding of the facilities used to put the parts in po-sition as well as the tools needed for a good development of eachstep of the process.JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.11(1-12)B. Anselmetti, B. Fricero / Aerospace Science and Technology()11Fig. 13. Equipment with parameters.Fig. 14. Human task.Fig. 15. Simulation of a graph with DELMIA (Dassault Systmes).This animation has to remain perfectly coherent if the positionof a station or a workstation is modified.6. Conclusion and prospectsThe proposed graph enables to describe a production processincluding manufacturing or assembly operations. The variants ofproducts can be processed with the help of nomenclatures. Thus aprocess can be applied to a new product. Different process planscan be tested on different configurations of a production site.During the project, independent teams can build graphs. Thenthe graphs are detailed by sub-graphs or gathered by concatena-tion or inside a higher level graph.The “process viewer” displays the production process in a fixedpoint in space, to show the production of a single product and tovalidate the process.JID:AESCTEAID:2704 /FLAm5Gv1.5; v 1.58; Prn:5/10/2011; 15:10 P.12(1-12)12B. Anselmetti, B. Fricero / Aerospace Science and Technology()The “layout viewer” represents the same process but enrichedwith the movements of the different components in the productionsite.The “production viewer” sets up all the fixed machines and an-imates the transport systems, tools and operators.It should be possible to use a fourth viewer named “flow view-er” to simulate the flow of products and resources in the site inorder to dimension them. For that it is necessary to generate ascheduling of tasks and to define an initial step. This last topiccould not be dealt yet within this project.The management of the processes and the research of solutionsremain entirel