A modular modeling approach by__ integrating feature recognition.pdf
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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,2modular feature recognition stage,3design with modules stage, and4process planningpreparation stage. This approach has been implemented for the design and modeling of electrical motor shafts. Examples arepresented and discussed. q1999 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 planningfor 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: ieyjt.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 patternwxw xrecognition 13 , expert systemrlogic approach 4 ,w xand graph-based approach5 . 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-w xmarized by Joshi and Chang 6 and Tseng and Joshiw x7 . Recent approaches are presented by Sakurai andw xw xwxDave 8 , Trabelsi and Meeran 9 , Wu and Liu 10 ,wxwxDong 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 113125115.Fig. 1 continued . .3The 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 canwxwxbe found in Chang 14 , Shah and Roger 15 andwxShah16 . 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 andwxwxMantyla 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 toperformverycomplexfeaturerecognitionandsearching 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 113125117performs 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, LBload-side bearingsection, CcenterFig. 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 endsection. 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-3nvided 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 Mmodules are created.i jSection S : Modules M , M,.;11112Section S : Modules M, M,.;22122Section S : Modules M, M,.;33132.;Section S : Modules M, M,., M.nn1n2nmAs illustrated in Fig. 3, in a motor shaft, differentmodules can be created for each section.For LE section, the modules LE , LE , LE ,.,123and LEare created;mFor LB section, the modules LB , LB , LB ,.,123and LB are created;nFor C section, the modules C , C , C ,., and123Care 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. .1The 2-D boundary representation data of amodule are retrieved from the CAD system. The 2-D.geometric data represented inx, 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 113125119pattern 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 cornerRis 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-grooveVis 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 module1nare recognized.Section S : Module Mrecognized features f ,1111f , f ,.;23Module Mrecognized features f , f ,.;12abFig. 5. The recognized machining features in each module.()Y.-J. TsengrComputers in Industry 39 1999 113125121Section S : Module M recognized features221f , f ,.;cdModule Mrecognized features f , f ,.;22rsSection S : Module Mrecognized features f ,331tf , 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, the limited types offeatures in each section are summarized as follows.Section LE: features H, E, M, U, R, P;Section LB: features H, U, R, V, P;Section C: features H, T, P;Section FB: features H, U, R, P;Section FE: features H, E, M, U, R, P. .6 If there exists a portion of the edge graph in amodule that is undefined, then that portion of thegraph is output for further analysis. Several actionsmay be taken to handle the unrecognized portion. .a The module can be modified by the designerby selecting one of the existing modules. This is theidea of using the same shapes and same operationswhenever possible. .bA new machining feature may need to becreated such that the new edge graph can be includedas a new machining feature. .cA new module may need to be created toinclude this new machining feature. .These actions in step 6 are taken inside a mod-ule, and thus, these actions are constrained inside themodule creation stage.In practice, the creation of a new module or a newmachining feature needs to be closely supervised.Because new modules and new features can makethe design and the machining processes more com-plicated, existing modules and features should beused first whenever possible. Although the aboveactions may need to be taken on a particular section,the other sections can be executed in the normalway. These actions will not complicate the design ofthe other sections and the entire part.4. Design with modules stageIn the previous stages, all of the modules werecreated and analyzed for each of the sections. In thisstage, these modules are ready for use to design newparts. The methodology is developed based on theobservation that designers are familiar with the func-tional modules from a functional design point ofview. Therefore, in a design process, the designercan use these modules to create a new part. Forexample, when designing a shaft, a designer designsone section at a time. The designer selects a modulefrom the group of available modules created in theprevious stages to design a section. After all of thesections are designed, a part is completed. The fol-lowing procedure is performed. The example parts Aand B, and the modules used to design the sectionsof these parts are shown in Fig. 6. .1Design the sections of the part section bysection. For a section, there is a set of modules thatcan be used to represent the geometry of the section.The designer may select a module from the availableset to represent this section. .2 Specify the necessary parameters of the mod-ule, including the relative position, the orientation,the reference point, and the geometric boundary data. .3 After all of the sections are designed using themodules, the whole part is completed. The modulesof these sections are linked to produce a completepart. All of the associated geometric data and infor-mation of the modules are recorded for the completepart representation. .4If a new module is required to design asection, return to the previous module creation stageto create the new module. However, creation of afresh new module should be controlled to a mini-mum level to reduce lead time. Since new moduleswill complicate the design, process planning, andshop-floor machining operations, the creation of newmodules should be controlled and managed at the()Y.-J. TsengrComputers in Industry 39 1999 113125122Fig. 6. The example parts A and B created using design with modules. The modules and the machining features of each module are shownfor the part.supervisory level. The primary idea is to use existingmodules whenever possible.While the design task is simplified, different andvarious parts can still be created using differentcombinations of modules. The number of possibledistinct parts can be analyzed using a multiplicationcalculation. If there are five sections, and each sec-tion contains 20 different modules, then the differentparts that can be created can reach a large number,e.g., 1,000,000. Both the functional considerationsand the variety of parts can be maintained. Theactual number of different parts needs to be verifiedby considering an overall design concept. For exam-ple, the largest change may occur in the LE sectionsince the load side is usually customer-oriented, butthere is almost no change in the C section since thefunction and the shape of the center portion is rela-tively fixed.5. CAPP preparation stageIn this stage, all of the information for the part arecombined for downstream CAPP applications. Thegeometric data of all of the features in a module arelinked to define the module. All the modules arechained to define the part and complete the represen-tation. The design is completed by linking the refer-ence points of the modules to produce the final shapeof the part. A boundary evaluation is performed togenerate the final boundary. The output data of thepart includes the module of each section, the features()Y.-J. TsengrComputers in Industry 39 1999 113125123of each module, and the features of the whole part.The information associated with each feature is thegeometric definition of those features. The definitionof each feature is presented in boundary representa-tion format, in which the edges and vertices are.defined using 2-Dx, z coordinates. An example ofthe output format of features for Part A is presentedin Fig. 7. The method is described with a procedureas follows:For is1 to n,1. Determine the module M for the Section S ;ii2. Collect the features in the module M ;i3. The features in the module are denoted asf ,i1.f , f , . ;i2i3Fig. 7. The output data defining the features of the example partA.4. Link the reference points of the features f , f ,i1i2.f , . ;i35. Perform a boundary evaluation to generate thefinal boundary of M and denoted as BM ;ii6. Link the reference points of BM with BM;iiy17. Perform a boundary evaluation to generate thefinal boundary of the part and denoted as BP;8. If all the modules are processed, then output BP;Next i.6. Implementation and examplesThe approach presented has been implemented foran electrical motor shaft manufacturing environment.The CAD tasks were performed using 2-D boundaryrepresentation data. The integration of the four stageswas completed on a personal computer. In the firststage, various modules are created for each of thesections. For a motor shaft in this application case,.five functional sections, LE load-side end section,.LBload-side bearingsection, Ccentersection,.FB fan-side bearing section, and FE fan-side endsection, are developed. The geometric data of eachof the modules are output to the modular featurerecognition stage. In the modular feature recognitionstage, all of the feature information are recognizedand output to the next stage. The feature informationis recorded and linked with the modules. In thedesign with modules stage, new parts can be de-signed. The designer specifies a module and thenecessary parameters for each section. After all ofthe sections are completed, the design of a wholepart is completed. The definitions of the machiningfeatures and the machining information can berecorded and retrieved. The machining features of apart are represented using boundary representation.Brep format expressed inx, zcoordinates. Anexample of the output of the result for Part A isshown in Fig. 7.Based on observations of the practical case in anelectrical motor manufacturing system, the divisionof the sections can be fixed for a specific producttype. The number of modules for each section can becontrolled within a limited number. The largest num-ber of modules is in section LE. The primary reasonis that the load side of a motor needs to be connectedwith various customer-oriented equipments or de-()Y.-J. TsengrComputers in Industry 39 1999 113125124vices. Therefore, it is usually more complicated. Inthe practical case, the number of modules of LEsection is within 20. From a designers point ofview, to select a module from 20 modules to designa section is a relatively simple task as compared tothe traditional design with geometric elements ordesign with basic machining features. The designtask here can be completed by designing five sec-tions. In addition, the machining information re-quired for CAPP can be retrieved immediately afterthe design is completed, with no unrecognizedresults. Therefore, this new approach provides arelatively quick and simple method for designing anew part and a direct link to CAPP.7. ConclusionsIn this paper, a new modular modeling approachcombining modular feature-based design and modu-lar feature recognition is presented. The purpose is tosolve the problems associated with the traditionalfeature-based design approach and the traditionalfeature recognition approach. The new method iscompleted in four stages: module creation, modularfeature recognition, design with modules, and pro-cess planning preparation. With the new approach,the design activity can be supported from a designerspoint of view and the feature recognition activity canbe supported from a process planners point of view.A functional section plays a unique role in a partfrom the functional design point of view. Duringdesign, a functional module is used to represent asection. A functional module is also a compoundfeature that consists of a set of basic machiningfeatures. The functional modules support the designactivity since the designer can design a part byselecting a module for each section to complete thepart. It is not necessary to use basic geometricelements or individual machining features to designa part. The functional modules also simplify thefeature recognition activity since the number of dif-ferent features in a module is relatively limited andlocalized. Therefore, only the required feature recog-nition is performed inside a module but not on thewhole part. After all of the sections are completed,the design of the entire part is complete. The machin-ing information required for CAPP can be generatedautomatically.This research also solves the problem of unrecog-nized features which may occur due to the con-straints of the traditional feature recognition ap-proaches. Also, the inconvenience of using individ-ual basic machining features in the traditional fea-ture-based design approach can be improved. Inaddition, the functional modules preserve the func-tional considerations in each design.This new method has been implemented for anelectrical motor shaft design and manufacturing en-vironment. Currently, only 2-D rotational parts areanalyzed and the design data are restricted to 2-Dboundary representation data. It is observed that thepresented approach is more suitable for a fixed typeof products. This approach may not be suitable for asystem that has many completely different new parts.In future research, this approach may be applied todifferent types of parts and can be enhanced formore complicated 3-D parts and 3-D features. Insummary, this new approach combines the advan-tages of the traditional feature-based design and tra-ditional feat
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