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Feature recognition in axisymmetrical parts modeled by solids in an Internet-oriented CAD/CAM system

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Feature recognition in axisymmetrical parts modeled by solids in an Internet-oriented CAD/CAM system
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  Journal of Materials Processing Technology 179 (2006) 260–267 Feature recognition in axisymmetrical parts modeled by solids in anInternet-oriented CAD/CAM system Jo˜ao Carlos E. Ferreira ∗ , Darlan Vivian Universidade Federal de Santa Catarina, Departamento de Engenharia Mecˆ anica, GRIMA/GRUCON,Caixa Postal 476, CEP 88040-900, Florian´ opolis, SC, Brazil Abstract In the last years more and more people have been having access to the Internet, which has reduced or even eliminated the distances amongpeople and/or groups located physically distant among them. The Internet has also enabled the development of applications for the support to thedesign and manufacturing activities of industrial parts. In this work, a system will be presented for the recognition of features in cylindrical partscreated with the ACIS solid modeling kernel through the Internet. In the part design stage, the user inputs in the browser the elements that composethe part. These data are analyzed, and if there is no inconsistency, they are sent via Common Gateway Interface (CGI) to the software that is inthe server. To visualize the part, the file with the solid in the Standard ACIS Text (SAT) format is transformed into the Virtual Reality MarkupLanguage (VRML) format, and soon afterwards it is sent to browser of the remote user. The part may contain cylinders, cones and chamfers. Theuser can slice the part along the rotation axis, and he can also obtain the file in the SAT format from the server, in case he wants to handle the partin his own CAD software. After finishing the design of the part, the software recognizes the features in the part, which it is accomplished throughthe automatic analysis of half of the profile of the part in 2D. These features can be used in the process of generating the NC program for the CNCmachine.© 2006 Elsevier B.V. All rights reserved. Keywords:  Computer-aided design; Features; Internet; Solid modeling; Axisymmetrical parts 1. Introduction Nowadays the access to Internet technology has become acommon and necessary fact, which has been significantly facili-tatingthecommunicationbetweenpeopleand/orgroupslocatedphysicallydistantamongthem.TheInternethasalsoenabledthedevelopment of several applications, including the design andmanufacture of parts. With the growth in popularity of the web-based navigators, it can be noticed that the network-orientedenvironment for part design guided can be increasingly used inthe near future.Cybercut (http://www.cybercut.berkeley.edu), developed bySmith and Wright [1], is among these applications, through which a prismatic part can be designed and machined through aCAD/CAM system developed in Java via applets.Manytechniqueshavebeendevelopedforthedevelopmentof systems for modeling feature-based parts. Features are defined ∗ Corresponding author.  E-mail addresses:  jcarlos@emc.ufsc.br (J.C.E. Ferreira),darlan@inf.ufsc.br (D. Vivian). by Shah and M¨antyl¨a [2] as “generic forms or product charac- teristics with which an engineer can associate certain attributesand knowledge that will be useful in the reasoning about theproduct”. Thus, features represent a significant encapsulationof information about the parts that compose the geometry of theproduct,informationthatwillbeusefulforproductmanufacture.Thesemodelingtechniquesbasedonfeaturescanbedivided,according to Shah and M¨antyl¨a [2], in two main categories: design by features and feature recognition. This second cate-gory can be subdivided in other two: interactive recognition of features and automatic recognition of features. In this last cate-gory,ageometricmodeliscreatedandlateraprogramprocessesthe model to find the features automatically.According to ´Alvares and Ferreira [3], the automatic recog- nition of features has the advantage that the designer does notneed to have a deep manufacturing knowledge. Thus, he hasmore time to study the form of the desired part and its func-tional aspects.In this context, the objective of this work is the implementa-tionofasystemthatallowsthedesignandrecognitionoffeaturesof axisymmetrical parts through the Internet, independent of theplatform of the user’s browser. The features in the part can be 0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2006.03.074   J.C.E. Ferreira, D. Vivian / Journal of Materials Processing Technology 179 (2006) 260–267   261 used in the determination of the appropriate NC program forthe CNC machine that will machine the part. Therefore, the partcan be manufactured and sent later for the designer, and conse-quently he will have a functional prototype within a few daysfor a lower cost than the one corresponding to own production. 2. Feature recognition method The feature recognition method is based on a recursive algo-rithm that can be applied to parts that have countless differentdiameters,includingthosethatmayneedtwofixturings.Therawmaterial for the part is assumed as being a cylindrical bar, withdiameterequaltothelargestdiameterofthepart.Thecoordinatesystem that was adopted is  XZ   (  X   for the diameter and  Z   for thelength), because it is the same used by the machine CNC.The method begins by analyzing half of the profile of thepart in 2D, which should contain only line segments. Anotherrequirement of the method is that the profile corresponds to a  polyline .To obtain all of the vertices and edges (Fig. 1) that compose half of the 2D profile of the part, firstly the solid is sliced twicealongitsrotationaxis,andthefacethatrepresentsthe2Dprofile Fig. 1. Example of a part profile and the points along it.Fig. 2. Recognized faces, which will be swept.Fig. 3. Flowchart of the feature recognition method.  262  J.C.E. Ferreira, D. Vivian / Journal of Materials Processing Technology 179 (2006) 260–267  ofthepartisidentified.Then,theverticesandedgesareidentifiedand ordered. The points associated to the vertices are classifiedas points on the border (e.g. point 12 in Fig. 1) and on internal points (e.g. points 4–11 in Fig. 1).Then,theareasareidentifiedthatwillbeusedinthesweepingoperation for creating the ring-type solids, that are recursivelyadded to the srcinal part until it reaches the form of a solidcylindrical bar. These areas are represented by faces, such asfaces F 1 , F 2 , F 3  and F 4  in Fig. 2. The sweeping operation con- sists of creating a solid starting from a face. In this paper, suchoperationisaccomplishedbysweepingtheface360 ◦ aroundthe  Z   axis, creating a solid in the form of a ring.In Fig. 3, a diagram is presented to facilitate the understand- ingofhowthefeaturerecognitionalgorithmworks.Theprocessbegins when the user finished the part modeling (blue rect-angle) and ends when there are no more internal points (redrectangle). 3. Used technologies For the implementation of the feature recognition method,the ACIS kernel for solid modeling was used. Other used tech-nologies were: Java Server Pages (JSP), Java, Java Beans, C++,CommonGatewayInterface(CGI),VirtualRealityMarkupLan-guage (VRML) and Server Side Includes (SSI).The ACIS solid modeler (www.spatial.com), described byCorney and Lim [4] was used for construction of classes in theC++ language [5], that compose the CGI program present in the server,andtheyareresponsibleforthegenerationofthesolidandforfeaturerecognition.TheACISsolidmodelerisalsowritteninC++anditconsistsofaframeworkcomposedbyseveralclassesand methods that can be used to create a 3D application for thefinaluser.TostoreanACISsolid,theStandardACISText(SAT)format is used, which contains all of the necessary informationfor the visualization of the solid.The pages with the forms in which the user defines the char-acteristicsofthesolidweredevelopedusingJSP[6],technology used to serve dynamic content for the user, using logic and dataon the side of the server. The verification of the consistence of the data input by the user was developed using Java Beans, thatareclasseswrittenintheJava[7,8],thatfollowagroupofsimple conventions of design and naming.The CGI technology was used for sending the forms datato the server responsible for creating the solid. A CGI allows Fig. 4. Flowchart of the software structure.   J.C.E. Ferreira, D. Vivian / Journal of Materials Processing Technology 179 (2006) 260–267   263 interactivity between a client and a server through Hyper TextTransfer Protocol (HTTP). A CGI program is executed in realtime, and so it can present result as a dynamic information, suchas the generated solid.VRML (www.vrml.org) was necessary to allow the visual-ization 3D of the solid in any browser. VRML is a languageindependent of the platform that allows the creation of virtualenvironments that enable the visualization of objects from dif-ferent angles, and to interact with them.Finally, the SSI tool [9] enabled the inclusion of the solidin VRML in the answer page, in the SHTML format, sent bythe server to the user’s browser. SSI commands are quite usefultools in the dynamic creation of web pages, and they are usuallyused as interface for CGI programs. 4. System structure The structure of this system [10] is represented in Fig. 4, which is composed of several files, each one responsible for astage in the creation of the solid. Besides axisymmetrical parts,the user can model simple solids such as a box, a cylinder, acone, a prism and a wedge.Throughtheinitialpage( Select solid.jsp ),theuserselectsthesolid type that he wants to model. After that, the option contain-ingthesolidtypeissenttothe Principal.jsp page,whichdecideswhat form should be shown to the user among the specificationsof the solid.Then,afterinputtingtheparametersofthesolid,theyaresentto the page that checks the data (e.g. file  vCone.jsp  in Fig. 4). If  the chosen solid is an axisymmetrical part, these data are sent toanother page ( ParametersShaft.jsp ) for obtaining more details(e.g. presence of chamfers) and later all these data are sent totheir respective verification pages.When some data are incorrect, the flow of the system returnsto the verification pages, being necessary so that the user per-forms the correction. To facilitate the identification of the error,the verification page itself shows, through a message, the loca-tion of the incorrect data.After verifying that the data are correct, they are sent, basedon the type of solid, to the  Modeling. cgi  program, located inthe server, which is responsible for creating the axisymmetricalpart and feature recognition, as well as the creation of the othersimple solids.After feature recognition is completed, the modeled axisym-metrical part that is in the SAT format is converted to VRMLin the same way of another simple solid. Then, the server sendsa SHTML page to the user’s browser, which contains the filein the VRML format for visualization of the 3D solid that wasgenerated.The CGI program that is in the server was created throughthe implementation of several classes in the C++ language. IntheclassdiagraminFig.5,onlythemainattributesandmethods of each class are presented. All of the classes have several typesof data and methods of the Application Program Interface (API)of the ACIS library.The  Modeling  class is the main class, which verifies whichsolid will be created and reviews the data for the appropriateinstance of the class. In order to the CGI program to receiveand identify correctly the data of the part coming from the JSPpage, the  cgiparser   library implemented by RudeServer [11],was used in the  Modeling  class, which supplies the necessarymethods for such operation.The  SimpleSolid   class is responsible for the creation of allthe simple solids such as box and wedge. It has the attribute solid body , which represents the solid that it will be generatedthrough the  create simple body () method. Fig. 5. Class diagram of the software that is executed via CGI.  264  J.C.E. Ferreira, D. Vivian / Journal of Materials Processing Technology 179 (2006) 260–267  Fig. 6. Graphical description of the  another edge () method.Fig. 7. Input of an axisymmetrical part—1st page. The  Shaft   class is responsible for the creation of the axisym-metrical part. It has two main attributes, both of the type BODY: shaft body , which represents the shaft created through the  cre-ate shaft  () method, and  shaft body sweep , which represents thepart during and after the execution of the  execute afr  () method.The  apply blends () method is called when the user inserts somechamfer in the shaft and therefore it should be executed beforefeature recognition.The  Save  class supplies: (i) the  save ent  () method that gen-erates the file in the Standard ACIS Text format and (ii) the Fig. 8. Input of an axisymmetrical part—2nd page.
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