Explicit Communication

TITLE OF PAPER, INCLUDING ALL CONTENT IN ANY FORM, FORMAT, OR MEDIA (hereinafter, "The Work"): Explicit Communication of Geometric Design Intent in CAD: Evaluating Annotated Models in the Context of Reusability COMPLETE LIST OF AUTHORS: Jorge Camba, Manuel Contero, Jeffrey Otey and Pedro Company

ASME PUBLICATION TITLE: Proc. ASME 2014 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference Volume 7: 2nd Biennial International Conference on Dynamics for Design; 26th International Conference on Design Theory and Methodology, pp. V007T07A014 ISBN: 978-0-7918-4640-7 DETC2014-34527

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The final publication is available at ASME via: http://dx.doi.org/10.1115/DETC2014-34527

Proceedings of the ASME 2014 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2014 August 17-20, 2014, Buffalo, New York, USA

DRAFT DETC2014-34527 EXPLICIT COMMUNICATION OF GEOMETRIC DESIGN INTENT IN CAD: EVALUATING ANNOTATED MODELS IN THE CONTEXT OF REUSABILITY Jorge Camba Eng. Design Graphics Texas A&M University College Station, TX, USA Email: [email protected]

Manuel Contero I3BH. Universitat Politècnica de València València, Spain, 46010 Email: [email protected]

ABSTRACT CAD model reusability is largely determined by a proper communication of design intent, which is usually expressed implicitly within the model. Recent studies have suggested the use of 3D annotations as a method to embed design information in the model’s geometry and make part of the design knowledge explicitly available. In this paper, we evaluate the effectiveness of this method and analyze its impact in model alteration tasks. Our goal is to determine whether annotated models provide significant benefits when performing activities that require a direct manipulation of the geometry. We present the results of a study that measured user performance in two scenarios. First, we tested whether annotations are helpful when inadequate modeling assumptions can be made by designers. Second, we evaluated annotations as tools to communicate design decisions to select the most appropriate solution to a challenge when multiple options are available. In both cases, results show statistically significant benefits of annotated models, suggesting the use of this technique as a valuable approach to improve design intent communication. INTRODUCTION CAD model reuse is a key issue to leverage current commercial history-based parametric CAD systems. The degree of flexibility and the ease of alteration of a CAD model strongly depend on the modeling methodology rather than the technology. In the context of the Model-Based Enterprise (MBE), an efficient use of 3D CAD models determines the benefits of a successful implementation. In theory, modern mechanical CAD systems allow designers to reuse CAD elements throughout different stages of the product lifecycle, both as templates for new product configurations and as a

Jeffrey Otey Eng. Design Graphics Texas A&M University College Station, TX, USA Email: [email protected]

Pedro Company Inst. of New Imaging Technologies. Univ. Jaume I. Castelló, Spain, 12071 Email: [email protected]

starting point for new product developments, thus accelerating the design process and increasing productivity. However, it has been shown that CAD model reusability largely depends on a proper definition and communication of the geometric design intent, which are usually expressed implicitly within the CAD model. In feature-based CAD packages, the modeling strategy and the parent-child relations established among the features of the model are conveyed implicitly via the design tree or history tree. Implicit definition of design intent typically requires a thorough examination of the model structure and a detailed understanding of the modeling strategy prior to performing any alteration to the geometry, which often translates to significant amounts of manipulation time and effort, even when the alterations are minor. This is especially true for models being reworked by designers that are not the original creators of the models [1]. The inability to understand and modify existing CAD models negatively affects reusability and hinders the collaborative design process. Recently, some authors have suggested the use of model annotations as mechanisms to incorporate design information into the model’s geometry and make part of the design knowledge explicitly available. In this paper, we present the results of two experiments that evaluate the effectiveness of 3D annotation techniques as a tool to express and communicate design information. Our goal is to determine whether annotated models have a significant impact over non-annotated models in activities that involve model alteration and reusability. We begin by reviewing previous work in three relevant areas: CAD reusability (and how it relates to model alteration), design intent communication, and annotations in engineering design. Next, we describe the experimental procedure and how annotations were used in the study. Finally, we present the statistical analysis and discuss our findings.

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RELATED WORK CAD Model Reusability Today’s highly globalized markets are forcing engineering design and manufacturing firms to constantly increase performance and reduce development times and costs by delivering products that meet ever increasing customers’ expectations with minimum delays. To guarantee competitiveness, this situation naturally demands the implementation of new methods and processes [2]. For example, traditional product development models are progressively being replaced by distributed and concurrent approaches, and the Model-Based Enterprise (MBE) concept is gradually gaining more ground. In the context of distributed methodologies, CAD models have become essential assets that can be shared among designers, manufacturers, suppliers, and other stakeholders throughout the different stages of the product lifecycle [3-5]. In addition to their classic advantages such as improvement of product quality [6] and technical communication [7, 8], and reduction of product development times [9], CAD models provide even greater benefits when combined with Product Data Management (PDM) systems [10], as they become facilitators of the concurrent development that is possible in distributed environments [11]. According to many authors [4, 12, 13], an important success factor in new engineering design and development methodologies is the ability to apply knowledge obtained in previous design processes to new designs, which directly translates to CAD model reusability. As noted by Iyer et al. [13], citing Ullman [12], the majority of design problems found in industry involve the application of previous knowledge and the redesign of existing products. Today, the high pressure put on enterprises for optimizing and accelerating product development processes is giving design reuse a crucial role in industrial environments. There is evidence of the necessity of effective knowledge management methods for establishing efficient design and reutilization processes. Bodein et al. [14] reported that reusability of existing models was a critical factor when determining CAD modeling strategies in the automotive industry. According to an industry study by the Aberdeen Group [4], significant time and cost savings were reported in cases of companies reusing design elements. Furthermore, all engineering organizations surveyed in the study report the reuse of existing designs at some level, but the top performers intentionally dedicate resources and deploy methods and technologies to capitalize on reusability. There are, however, important problems that need to be overcome to effectively implement design reuse. As described by the same study [4], the obstacles related to CAD model reuse are the same obstacles that largely impede design reuse. These challenges as well as the procedures that companies are currently following to mitigate them are shown in Table 1.

Table 1. Challenges and responses to CAD model reusability (adapted from [4])

CHALLENGE

PROCEDURE

1. Model modification requires expert CAD knowledge 2. Models are inflexible and fail after changes 3. Users cannot find models to reuse 4. Only original designer can change models successfully

Train users to increase CAD skills Design for wide range of modifications Centralize design data in library accessible structure Detail design information in model

We can clearly see the relationship between challenges 1 and 2, as they are both involved in the creation of better designed models. CAD users need to be skilled and trained in CAD methods, tools, and technology in order to develop models that are reusable and easy to maintain. Challenge 3 can be categorized as a data management problem that requires effective tools and information management mechanisms such as Product Lifecycle Management systems (PLM) to be in place. Finally, challenge 4 demands formal methods to integrate various types of design information (Geometric Dimensioning and Tolerancing, material specifications, manufacturing instructions, etc.) within the CAD model. The development of Digital Product definition standards such as ASME Y14.41 [15] and ISO 16792 [16] has formalized the way some product information is presented in a 3D model, which has encouraged many companies to migrate their development processes to the Model-Based Enterprise concept. However, to ensure an effective CAD reusability it is necessary that users that interact with a particular model understand the reasons and rationale behind the modeling decisions. They need to know how and why the model was created in a specific manner, i.e., they need to understand its design intent [17, 18]. Design Intent Communication It is difficult to find a generic definition of the term “design intent” in the technical literature. In fact, different definitions have been proposed [19-24]. An extensive survey was conducted by Iyer and Mills [17] that identified elements in a number of definitions that are common to all interpretations of design intent. The authors used this information to provide their own comprehensive definition in the domain of 2D CAD: “Design intent contained in legacy CAD is the insight into the design variables (design objectives, constraints, alternatives, evolution, guidelines, manufacturing instructions and standards) implicit in the structural, semantic and practical relationships between the geometric, material, dimensional and textual entities present in the CAD representation.” [17]. Despite a lack of consensus on the exact meaning, there is agreement on the importance of design intent and the advantages of an explicit representation. According to PenaMora et al. [25], some of these advantages include:  Changes in complex projects require certain design decisions to be modified during the development process.

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W When the justtifications defi fined during thhe initial stagees are llost, they needd to be recreatted, which hass a negative im mpact oon project coosts and deveelopment timees. The abilitty to sstore, process, and rettrieve this information can ssignificantly improve produuctivity.  W When design intent inform mation is reprresented expliicitly aand is easily aavailable for review, r the oveerall quality oof the pproduct increaases.  E Explicit repreesentation of design intentt leads to a more m iintelligent usee of resources and knowledgge.  E Efficient com mmunication oof design intent is essentiaal for iintegrating sollutions and traansferring desiign knowledgee. D Despite those advantages, it has not yet bbeen solved. Inn the samee survey menntioned earlierr [17], the auuthors classifyy the captuure, representaation, and rettrieval of desiign intent as open issuees and suggestt avenues for future f researchh. A Although signnificant advannces in the areea of Model-B Based Definnition have been accomplished (such ass the definitioon of standdards and the development of Product aand Manufactuuring Inforrmation (PMII) modules, iit is still diffficult to repreesent desiggn intent infoormation expllicitly within the model uusing thesee tools. P PMI modulees represent practical im mplementationss of curreent Digital Prroduct Definiition standardds such as AS SME Y14..41[15] and ISO 16792 [16] are usuually availablle in modeern CAD sysstems. PMI toools allow users to incorpoorate produuct definitiion informaation such as Geom metric Dimeensioning aand Toleranccing (GD&T T), 3D texxtual annootations, surfaace finish aand material specificationns to different aspects of the CAD moodel, as shownn in Figure 1.

Figure 1. ANN NOTATED EXAM MPLE FROM ISO O 16792:2006

T The ultimate goal of a prooduct’s Modell-Based Definnition (MBD), a datasett that comprises the modeel’s geometryy and annootations that sppecify life cyccle support daata, is to proviide a compplete represenntation and deffinition of a prroduct withouut the needd for additionnal documentss. Representinng and manaaging

deesign intent information, however, has prooven to be a ddifficult tassk. Recent stuudies have sugggested the usse of 3D annootations as a method to carry design intent informaation [26-29]. In this paaper, we evalluate the effe fectiveness off this approach and annalyze its impaact in model allteration taskss. An nnotations iin Computerr-Aided Design In the dom main of 3D CAD, C an annnotation (alsoo called moodel-based annnotation or 3D D annotation) is defined as a block off information that is linkedd to a specifi fic aspect of a CAD moodel to proviide additional details [30]. 3D annotatioons are noormally used as a pointers to ddirect the attenntion of the deesigners to a specific paart of the moodel. They aree usually inseerted as texxtual notes orr comments, buut they can allso adopt other forms suuch as images, audio, hyperllinks, etc. Annotationns can be classsified in a variiety of ways. D Ding et al.. [30] suggested six major categories c of aannotations baased on auudience, targetted media, renndering system m, usage and fuunction, reppresentation, and storagee location. In the conttext of enngineering dessign, the signiificance of annnotations wass stated byy Bracewell annd Wallace [331] and Boujuut and Dugdalle [32], whho emphasizeed the role oof annotationss as mechaniisms to caapture the ratiionale behind design decissions and to m mediate intteractions bettween designners. Nevertheeless, they addmitted theese roles to bee poorly addreessed by currennt industrial toools. Active reseearch has beenn done to deteermine the suiitability off 3D annotatioons to carry deesign informattion [28, 29, 332, 33]. Paatel et al. [344] suggested supplementing s g CAD modeels with information thaat is relevant to the producct lifecycle (ssuch as deesign rationaale, context, views, etc.). Li et all. [35] reccommended a unification oof the represenntation of annootations to make them inndependent froom specific pllatforms and syystems. A number of proototypes have also been devveloped [27, 299, 32]. There are, however, a nnumber of chaallenges to ussing 3D annnotations to carry desiggn knowledgge. Some off these chhallenges are related to thhe technologyy, such as defining d eff fficient internaal structures annd data types ffor the annotattions or deeveloping an interface or system to ennter and retrieeve the information [300]. Other chaallenges invollve user interraction, suuch as the reprresentation of tthe annotationn content (whaat needs to be included in the annotation and inn what form, so the o the visualizaation of information is ccommunicatedd effectively) or heeavily annotatted models (tthe problem oof visual cluttter and annnotation overload). For our reseearch, we connducted two exxperiments to aanalyze usser interactionn with CAD models thatt incorporate design information in the form of annotations. Our objectivve is to deetermine emppirically the validity of 3D annotations as meechanisms to enhance moodel definition. In the folllowing sections, we w will describe the experimeental proceduure and prresent our finddings. EX XPERIMENT TAL SETUP A AND PROCE EDURE The basis oof our study is the applicaation and usee of 3D annnotations in history-basedd parametric modeling proocesses. Ouur goal is to determine whhether annotated models proovide a

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signiificant benefiit over non-aannotated moodels in term ms of reusaability, speciffically when performing tasks t that reqquire desiggn alterations oor manipulatioon of the model’s geometry.. W We conductedd two separaate studies wiith a total off 104 volunnteers. All participants had previouus experiencee in enginneering desiggn graphics aand parametricc solid modeeling, particularly usingg the CAD package SoolidWorks®. The mputer laboraatory expeeriments werre conductedd in a com envirronment, whhere participaants were eequipped witth a workkstation and tthe modeling software. Thee first experim ment was aimed at model alteration activities, whhereas the second f on deesign tasks. Foor both experim ments, particippants one focused weree randomly divvided into tw wo groups. Onne group serveed as the ccontrol group (participants used non-annnotated modeels to compplete the taskks) and the otther served ass the experim mental groupp (participantss used modelss that were preeviously annotated with relevant design informatioon by a membber of the reseearch m). team

grroups receivedd the same CA AD model in teerms of geomeetry and moodeling strateegy. Howeverr, an annotatioon indicating not to assume symmettrical arms waas added to thhe model provvided to thee experimentaal group. Thee initial CAD D model used in this stuudy is shown in Figure 2. D Dimensions haave been omittted for claarity.

Stud dy 1: Geome etry Modifica ation O Our first studdy was intendded to obtainn new insightts on CAD D modeling sttrategies and understand u whhether annotaations can bbe added to a CAD model to communicaate specific deesign intennt information,, so it is easierr for designerss to select the most approopriate modelling proceduree when certaiin alterations need to bee performed. IIn particular, we describedd a scenario w where desiggners run the rrisk of makingg inadequate aassumptions aabout the modeling m process if designn informationn is not expliicitly definned. W We prepared an experimenntal activity innvolving a num mber of aalterations to an existing parametric C CAD model. The activvity was preseented as a seriies of questionns in a classicc test form mat, using an online testinng tool. Eachh alteration inn the sequence was prresented as a separate quuestion, requuiring participants to suubmit their m modified CAD D model for each questtion. In orderr to accuratelyy analyze the modeling proocess followed by particcipants for the entire sequennce, questions were displlayed one at a time and backtracking was intentionnally disabbled. Thereforre, participantss were forcedd to submit a C CAD modeel for every qquestion before moving to tthe next, and were not allowed a to chaange the answeer to a questioon that had alrready beenn submitted. P Participants w were randomlyy divided into two groups oof 52. The first one wass a control ggroup, whereaas the secondd one serveed as the exxperimental grroup. All parrticipants in both

The modell was introduuced as a design that hadd to be moodified to meet new desiign requiremeents, so it coould be reuused as part oof a different product or assembly. Neithher user grroup was menttioned the exiistence of the annotation, noor were theey given furthher instructionns as to how thhey were suppposed to usse the informattion. For illustrattion purposes,, the basic moddeling steps innvolved in the creation oof the initial model m are show wn in Figure 33. Each steep is the resullt of applying a single modeeling operation using thee CAD packaage (Solidworkks® in our caase). The sequuence of moodifications requested r to participants p is shown in Fiigure 4. Allterations weere presentedd one at a time. Theerefore, paarticipants weere not allow wed to see altteration i unttil they coompleted alteraation i-1. The first modification m task involvess the addition of a second arm to thhe part. The new n arm is ideentical to the eexisting onne in both shaape and size. There T are, at least, two distinctive moodeling approoaches that can be follow wed: using sym mmetry toools to mirror all the featurees in the existting arm, or ccreating thee second arm m from scraatch by definning a new sketch, exxtruding it, annd cutting a neew hole, i.e. rrepeating the pprocess ussed to create thhe original arm m (see Figure 55). Instinctivelly, the first appproach seems easier and fastter than thee second one,, as it requiress fewer steps and no featurees need to be modeled ffrom scratch. The result is aan efficient m model as lonng as all feattures in both arms remain symmetrical in new

Figure 2. INITIAL MODEL PROV VIDED TO PART TICIPANTS IN STUDY 1

Figure 3. MODELING M PRO OCESS OF ORIIGINAL PART FOR STUDY 1

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Figure 4. S SEQUENCE OF F ALTERATIONS S REQUESTED D IN STUDY 1

variaations of the ppart or other ccases where thhe model needds to be reeused. In otheer words, whhen selecting tthis approachh, the desiggner is impliccitly assumingg that both aarms are likelly to remaain symmetriccal in future m models, which is reasonabble if “Alteeration 1” is tthe only piecee of informatiion she posseesses. Perfoorming the fiirst alteration to the modeel by creatingg the seconnd arm from m scratch maay not seem like an efficient strateegy, as it dooes require a number off additional steps. s How wever, the geoometry of eacch arm can be b controlled and editeed separately w without affectting the otherr, should onlyy one arm nneeded to be m modified (whiich is preciselly what happenns in upcooming alteratioons).

By analyziing the entirre sequence, it seems cleear that miirroring the exxisting arm (“aapproach 1”) m might not be the t best appproach, sincee both the anggle and the lenngth of the neew arm wiill be modifiied in Alteraation 3. In fa fact, if symm metry is assumed, alterattion 3 will reqquire the supprression or deleetion of alll mirrored features and thhe creation off the new arm m from scratch (which is precisely “approach “ 2”). If we were using a moore sophisticaated model witth a greater nuumber of featuures that deepended on tthe new arm m, performingg alteration 3 after miirroring wouldd likely cause major rebuildd errors and reequire a siggnificant amouunt of time annd effort to fixx. Since nonee of this information is aavailable to participants in the control ggroup at thee time they hhave to make a decision abbout Alterationn 1, we hyypothesized thhat:  

If using the non-annootated modell, the majorrity of participantss will assume symmetry annd use mirror ttools to perform Altteration 1. If using thhe model thaat was previoously annotateed with relevant deesign informaation, the majjority of partiicipants will create the second aarm by modeliing the new ffeatures from scratcch.

We define the modeling approach as the indeppendent caategorical variiable X1, withh values as shhown in Tablee 2. We noote that, as prreviously disccussed, in som me cases durring the exxperiment, as soon as altteration 2 w was presented, some paarticipants reallized the need to control thee two arms sepparately annd decided to rre-model the arm a from scraatch. This behaavior is lissted as “Approoach 3” in Tabble 2. Table 2. VALUES V OF X1

Va Values of X1 Appproach 1 Appproach 2 Appproach 3

Descriptioon of the modelling approach Alteration 1 A Alteration 2 Alteratioon 3 Delete previouus Editt previous mirrror and mirror and re--model Mirroor arm creaate new hole arm. Change dimennsions Moddel new Editt circle in arm ffrom skettch and of previous skketch scrattch upddate feature and update feaature Delete previous Change dimennsions mirrror and reof previous skketch Mirroor arm moddel arm from and update feaature scraatch

Fig gure 5. TWO MO ODELING APPR ROACHES FOR R "ALTERATION 1"

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T The results off our study aree shown in Tabble 3 and Figuures 6 and 7. Due to the nature of oour data, we performed a ChiSquaare Test to exaamine the diffference in moodeling approaaches betw ween the contrrol (non-annootated model) and experim mental (annootated modell) groups. Baased on the resulting p-vvalue (p