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.Computers in Industry 39 1999 113125A modular modeling approach by integrating feature recognitionand feature-based designYuan-Jye Tseng)Department of Industrial Engineering, Yuan Ze Uniersity, 135 Yuan-Tung Road, Chung-Li, Taoyuan Hsien 320, TaiwanReceived 19 July 1997; accepted 23 October 1998AbstractA modular modeling approach is developed by combining feature recognition and feature-based design for the purpose ofintegrating design and process planning. A part is divided into several isolated sections based on its functional and geometricconsiderations. Each section is represented with a functional module. In design, from the functional point of view, afunctional module performs a unique functional role in the part. From the machining point of view, a functional module is acompound feature containing a set of basic machining features. During design, the designer selects a functional module froma module library for each of the sections to complete the design of an entire part. In each module, the basic machiningfeatures are recognized using a modular feature recognition method. The basic machining features of the part are recognized.and the final boundary is evaluated for use in automated process planning. This approach is performed in four stages: 1. . .module creation stage, 2 modular feature recognition stage, 3 design with modules stage, and 4 process planningpreparation stage. This approach has been implemented for the design and modeling of electrical motor shafts. Examples arepresented and discussed. q 1999 Elsevier Science B.V. All rights reserved.Keywords: CADrCAM; CAPP; Feature recognition; Feature-based design1. IntroductionMachining features can be used to link CAD. computer-aided design and CAPP cess planning for machining parts. Since theCAD data are typically in a low level format, e.g.,.boundary representation Brep , the CAD data needto be transformed into high-level features suitable forCAPP applications.In the feature recognition approach, features arerecognized from a part description after the design iscompleted. The feature information is not explicitly)Fax: q886-3-463-8907; e-mail: .twprovided by the CAD data, and hence, needs to berecognized and extracted. Therefore, methods andalgorithms capable of recognizing features from CADmodels are crucial. Rotational parts are typicallyrepresented in the form of 2-D models and rotationalfeatures are recognized from 2-D profiles or edgepatterns of the part. Methods for recognizing rota-tional features can be found using syntactic patternwx wxrecognition 13 , expert systemrlogic approach 4 ,wxand graph-based approach 5 . Recently, prismatic3-D features have been commonly represented usingsolid models. Recognition of 3-D prismatic featureshas involved geometric reasoning associated withsearching and matching 3-D face adjacency relation-0166-3615r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.PII: S0166-3615 98 00142-0()Y.-J. TsengrComputers in Industry 39 1999 113125114ships or volumetric patterns. Feature recognition ap-proaches for 3-D prismatic features have been sum-wxmarized by Joshi and Chang 6 and Tseng and Joshiwx7 . Recent approaches are presented by Sakurai andwx wx w xDave 8 , Trabelsi and Meeran 9 , Wu and Liu 10 ,wx wxDong and Vinayan 11 , Qamhiyah et al. 12 , andwxAllada and Anand 13 .The feature recognition approach has the advan-tage of allowing different CAD systems as inputdata. The approach itself imposes no restrictions onthe designer in creating the geometry of the parts.However, the recognition procedure starts from thebeginning and none of the designers concepts areutilized to assist in the recognition. Also, the func-tional information of the design is not represented inthe feature data and thus needs to be interpreted afterthe recognition procedure begins. In addition, insome cases, there may exist unrecognized results.A portion of a part geometry may be unrecognizeddue to the constraints and limitations of the specificmethod. Several unrecognized results can occur indifferent situations.1 The designed part may be incomplete or incor-rect due to a designers mistake. For example, adesigner may design a slot but specify two walls thatare not parallel to one another. Thus, if the featurerecognition method searches for a pattern involvingtwo parallel walls, the slot will not be recognized.2 There may exist features that are not prede-fined. The designer may design a new shape in a partand thus, the new geometry will be unrecognized bythe feature recognition method. .Fig. 1. a The overall flow of the four stages of the approach. b The overall flow of the modular modelling approach by integrating designwith modules and modular feature recognition.()Y.-J. TsengrComputers in Industry 39 1999 113125 115.Fig. 1 continued .3 The feature recognition algorithms may beincomplete. For example, the reasoning and search-ing procedure in the feature recognition method doesnot cover all of the possible situations. In somecases, unrecognized results may occur due to alteredboundaries caused by feature interactions. The spe-cial geometry may be undefined and thus unrecog-nized. A recovery procedure is required if an unre-cognized result occurs.On the other hand, in the traditional feature-baseddesign approach, features are incorporated directly inthe process of creating a new part. Predefined fea-tures are retrieved from a library and manipulated todesign a part. The feature-based part description canbe directly used in CAPP activities. Reviews anddiscussions on the feature-based design approach canwx wxbe found in Chang 14 , Shah and Roger 15 andwxShah 16 . In a typical feature-based design, theshapes that can be used in design are limited toindividual basic machining features. The designermay be forced to consider the geometry from themachining point of view without using functionalconsiderations. Also, all of the shapes are createdusing basic machining features even though the()Y.-J. TsengrComputers in Industry 39 1999 113125116shapes may be frequently used groups or compli-cated modules.Recently, the integration of feature-based designand feature recognition was discussed by Laakko andwx wxMantyla 17 and De Martino et al. 18 . The mainsubject discussed in the above approach is to recog-nize and update features after a feature-based designprocedure. The purpose is to separate the interactingfeatures and maintain a valid set of features in afeature-based design model. The approach presentedwxby Han and Requicha 19 recognizes features utiliz-ing information available in the solid model and thedesign features. The primary idea is to use the designfeatures or human interventions as hints to the fea-ture recognition procedure.This paper presents a new approach. The first ideais to strengthen the technical support provided todesigners. This approach is developed based on theobservation that designers are more familiar withfunctional modules from the functional design pointof view. Thus, it is more convenient for a designer touse functional modules in design than individualmachining features. From the functional point ofview, a functional module performs a unique role ina part. From the machining point of view, a func-tional module can be considered as a compoundfeature that contains a group of basic machiningfeatures. In this way, a compound feature that fre-quently appears in designs can be defined as amodule to facilitate the design procedure.The second idea is to simplify the load on featurerecognition procedures. It has been observed that fora fixed product type, such as motor shafts, onlylimited types of functional modules exist. In eachfunctional module, only limited types of machiningfeatures exist. Therefore, feature recognition meth-ods can be simplified by applying only the necessaryfeature recognition and searching on each singlemodule. In typical feature recognition methods, usu-ally an attempt is made to develop a method that isas complicated and as complete as possible for rec-ognizing as many special cases as possible. The ideain this new approach is to eliminate the necessity toperform very complex feature recognition andsearching of the whole part. Based on the character-istics of each module, only the necessary featurerecognition procedures are performed on each mod-ule. As a result, the design is enhanced using theidea of design by modules, and the feature recogni-tion is simplified by only recognizing the machiningfeatures in each module.In this approach, two phases are executed in fourstages. In the first phase, existing parts are analyzed.The module creation stage and modular featurerecognition stage are performed. In the applicationphase, new parts can be created. The design withmodules stage and CAPP preparation stage are per-formed. The flow chart of the four stages is shown inFig. 1a. The overall flow of the approach is shown inFig. 1b.In the following presentation, the four stages arediscussed. An implementation of this approach on amotor shaft design and process planning environ-ment is also discussed. Finally, the conclusions arepresented in Section 7.2. Module creation stageFirst, a type of part is analyzed and decomposedinto several isolated functional sections. Each sectionFig. 2. The five functional sections are divided for a motor shaft illustrated using example part A.()Y.-J. TsengrComputers in Industry 39 1999 113125 117performs a distinct function and plays a unique rolein the whole part. In each functional section, thegeometric shapes may vary. Different geometricshapes may perform the same function but may varyin their individual detailed geometric shapes. Thesedifferent geometric shapes are called functional mod-ules for the functional section. In this stage, variousfunctional modules are created for each functionalsection.From another point of view, a functional modulemay be considered as a compound feature containinga set of basic machining features. Each functionalsection is analyzed to determine its geometric andmachining characteristics.For example, the shaft of an electrical motor maybe divided into five functional sections. The five.functional sections can be named LE load-side end. .section, LB load-side bearing section, C centerFig. 3. A portion of the module set for each of the five sections.()Y.-J. TsengrComputers in Industry 39 1999 113125118. section, FB fan-side bearing section, and FE fan-.side end section. The detailed functions of eachsection in a motor shaft are lengthy and are notdiscussed here. To ensure a useful division, this taskrequires intensive discussions with designers andmanufacturers. After the division, each section per-forms a unique role in the shaft but may be designeddifferently with detailed geometries under specificconsiderations. A different geometric shape consti-tutes a possible functional module for the functionalsection. Using a motor shaft as an illustration, thefive functional sections are shown in Fig. 2. Aportion of the module sets for the five sections isshown in Fig. 3. The procedure for summarizing thisstage is presented as follows.1 Divide a part into several functional sectionsbased on the functional design concept. In a part,there are n sections divided and denoted as S , S ,12S , . . . , S . For example, a motor shaft can be di-3 nvided into five sections and denoted as LE, LB, C,FB, and FE sections.2 Design functional modules for each functionalsection. In each section, the section may be designedwith different geometric shapes based upon differentdetailed considerations. Each different design is amodule for the section. Therefore, for each S sec-ition, various M modules are created.ijSection S : Modules M , M , . . . ;1112Section S : Modules M , M , . . . ;22Section S : Modules M , M , . . . ;33132.;Section S : Modules M , M , . . . , M .nn1 n2 nmAs illustrated in Fig. 3, in a motor shaft, differentmodules can be created for each section.For LE section, the modules LE , LE , LE , . . . ,123and LE are created;mFor LB section, the modules LB , LB , LB , . . . ,123and LB are created;nFor C section, the modules C , C , C , . . . , and123C are created.p.It can be observed that this method is moresuitable for a fixed product type. In practical cases, ifthe product type is fixed, the number of differentmodules for each section can be controlled within alimited number. Based on observations at a localelectrical motor manufacturing company, althoughthe sizes of motors vary from 5 to 150 hp, thenumber of different modules in a section of a shaft iswithin 20. The primary reason is that if the mainfunction of a section is determined, then the mainshape is usually fixed. Thus, the variation in shapesof the modules may be only in the details. Thelargest number often occurs in the LE section, sincethe load side is usually customer-oriented. After allof the modules for all the sections are created, all ofthe modules are input into the next stage for featurerecognition.3. Modular feature recognition stageIn this stage, a feature recognition method isapplied to the boundary representation data for eachof the modules created in the previous stage. From amachining point of view, each module is a com-pound feature and corresponds to a set of basicmachining features. Each section has its distinctcharacteristics. Only limited types of basic machin-ing features exist in the modules of a section. There-fore, the feature recognition method can be simpli-fied by applying only necessary feature recognitionand searching on a specific section. A method usingedge adjacency graphs to recognize and classify 2-Dmachining features is presented as follows.1 The 2-D boundary representation data of amodule are retrieved from the CAD system. The 2-D.geometric data represented in x, z coordinates areinput into the recognition method. Since the part isrotational and the edges of the part are symmetrical,only the upper half is input for processing.2 The edges of the module are traversed fromright to left in the order of descending x coordinate.values . The edges of the module are classified intolinear edges and circular arc edges. The adjacencyrelationships between adjacent edges are identified.The adjacency relationship between two connectededges can be classified as concave adjacency orconvex adjacency. If the angle between two edgesmeasured from the exterior of the part is -1808,then the two edges have concave adjacency. Other-wise, the two have convex adjacency.3 The edges of the module are represented asnodes and the connecting vertex of two edges isrepresented as an arc in a graph.4 The feature patterns are represented as edgeadjacency graphs called feature graphs. Each feature()Y.-J. TsengrComputers in Industry 39 1999 113125 119pattern has a unique feature graph. The feature pat-terns for this application include outside diameter. . . .H , end face E , taper T , chamfer M , step with. .round corner R , step with angular corner P , groove. .U , and v-groove V . The feature patterns and thefeature graphs are shown in Fig. 4.A horizontal edge is an edge parallel to the cen-ter-line of the part. A vertical edge is an edgeperpendicular to the center-line of the part. A slantedge is an edge neither parallel to nor perpendicularto the center-line of the part. The angle of a slantedge is measured between the center-line and the.slant edge. An outside diameter H is a horizontal. .edge. An end face E is a vertical edge. A taper Tis a slant edge connected with at least one concave.adjacent edge. A chamfer M is a slant edge con-nected with two convex adjacent edges. A step with.round corner R is a circular arc edge connected.with a horizontal edge. A groove U is composed ofthree edges. The first edge and the third edge arevertical edges. The second edge is a horizon edge.An adjacent pair of edges presents a concave adja-.cency. A v-groove V is composed of two con-nected slant edges with a concave adjacency rela-Fig. 4. Feature patterns and the feature graphs.()Y.-J. TsengrComputers in Industry 39 1999 113125120.tionship. A step with angular corner P is composedof two concave adjacent edges and one of the edgesis a vertical edge.5 The entire module is searched for predefinedfeature patterns. If a portion of the edge graph of themodule matches a predefined feature graph, then thefeature pattern is recognized and classified. A searchis performed with three passes. In the first pass, thesearch and match is performed using three edges at atime. In the second pass, it is performed using twoedges at a time. And in the third pass, it is performedusing one edge at a time. The results can be repre-sented in the following form. From the predefined.feature set f , . . . ,f , the features of each module1 nare recognized.Section S : Module M “recognized features f ,111 1f , f ,.;23Module M “recognized features f , f , . . . ;12 a bFig. 5. The recognized machining features in each module.()Y.-J. TsengrComputers in Industry 39 1999 113125 121Section S : Module M “ recognized features221f,f,.;cdModule M “recognized features f , f , . . . ;22 r sSection S : Module M “recognized features f ,331 tf , f ,.;uv.;Section S . . . .nFor example, Fig. 5 shows the features recognizedin each of the modules. Based on the characteristicsof each module, only necessary recognition is per-formed on the modules of each section. For example,.in the application case, tapers T exist only in the. .center C section, and v-grooves V exist only in.the load-side bearing LB section. The round cor-. .ners R and v-grooves V will never occur in the.center C section. The types of features that exist ineach section are described as follows. This informa-tion enables a modular feature recognition approachthat uses a limited recognition scheme without usinga complex total search of the whole part. In actualapplication as shown in Fig. 5,

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