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ABSTRACT infonnation along with using the preserved reasoningCapturing the basic reasoning of why and how a design (functional properties) in the search for solutions. The

is developed is important in fully preserving and basis for this paper was the development of a genericdocumenting the design of industrial products. To maintain architecture for a function driven mechanical designcaptured design information and reuse the information solution library capable of being implemented in any formduring solution retrieval requires different types of (i.e., object-oriented, relational, etc.) on a computer system.information transferral and preservation than those The solution library was initially targeted for the plastictraditionally used in CAD systems. This paper develops the injection molding domain, but applications from otherbasic database structure for preserving and transferring the design areas (e.g., sheet metal, casting, etc.) can also bedesign information along with using the reasoning implemented. The solution library uses a specific(functional properties) in the search for solutions. The architecture to maintain and transfer information related tobasis for this paper was the development of an architecture the interface between features. This architecture allows thefor a function driven mechanical design solution library that designer to retrieve saved solutions through its functionalcan be applied to multiple design areas. The solution properties, transfer the retrieved solution's information tolibrary uses a specific architecture to maintain and transfer the developing design, and to capture the design reasoningthe infonnation between features. The architecture allows or intent of the design during development. The solutionthe designer to retrieve saved solutions to a CAD system library consequently, 1) preserves the information ofthrough the desired functional paran1eters, transfer the interfacing features within the product's database, 2)retrieved solution's information, and to capture the maintains a database of features with their fundamentalreasoning or intent of the design during development. properties and corresponding functions used by experienced

design engineers, and 3) transfers the information within theINTRODUCTION solution's database to the design under development.

Capturing the basic reasoning of why and how a design The fIrst section of this paper presents the background

is developed is important in fully preserving and infonnation of the study. The second section describes the

documenting the design of industrial products. To maintain architecture or structure that is critical to search for

the captured design information and reuse the information solutions. This structure, called a "function-object," is used

in solution retrieval requires different types of information as the search mechanism for the library and serves to

transfer and preservation than those traditionally used in maintain functional information of the solution that relates-

CAD systems. This paper develops the basic database to or interacts-with other objects. The third section presents

structure for preserving and transferring the design an example of feature selection from the functions driving

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the product's development (Form follows Function). The where the designer models the object with primary featurespaper concludes with the extension of the architecture for that are converted into secondary features with additionalcomponents and assemblies followed by specific information. In his model, primary features are formedrecommendations for integration with future CAD systems. from concepts the designer desires to express and

manipulate, while secondary features contain informationBA.CKGROUND about applications (e.g., manufacturing features are

To implement a generic architecture or structure, for a secondary features to manufacturing methods and toolfunction driven mechanical design solution library (Wood, shapes). ~signing-with-features "is a synonym for all1995), the designer's desired functionality is used to obtain design work involving predefmed details, commonly detailssolutions, from the most primitive design structure - the of shape, form features" (Sigurjonsson, 1992). Althoughfeature, to the most complicated design structure - the features are used for many aspects of a design, the retrievalassembly. Each potential solution is accessed through the and application using the basic reasoning behind their usagefunctionality associated with it. The solution library, has not been extensively investigated. For this study,prototyped at the feature level using the object-based features are considered the primary building blocks of arelational PC database "Paradox", uses the function structure, i.e. the specific geometrical forms that satisfy theinformation derived from the analysis of thousands of functional needs pertaining to a component.features on plastic injection molded parts developed in a Features have many functions associated with themprevious study, (Wood, 1996). By using a feature's (Wood, 1996); consequently, only the functions that arefunctionality for the search criteria during the design of used predominantly by the engineers to satisfy designmechanical components, the design engineer has access to problems are used in the search for solutions. It is througha wide variety of design solutions related "functionally" to the functionality of the individual features that a basicthe problem. capability of capturing some of a design's functional intent

The ability to present a wide selection of design is possible. Using the function information of each featuresolutions allows the designer to make use of technologies is necessary for implementing design reasoning into thethat he/she may be unfamiliar with. It is literally next generation CAD systems.impossible for a design engineer to be an expert in all How the term "function" is used in this study alsodomain fields such as plastics, casting, machining, sheet- needs clarification due to the many different interpretationsmetal, etc., along with the usage of a variety of components of the word. A "function" is defmed here as the behaviorwhich are found within the multitude of catalogs that exist or action that the feature must satisfy in order for thein the design world. Consequently, a solution library can product to achieve its overall purpose. In general, abring that knowledge and information to the designer when function in its simplest form can be expressed as a verbneeded. A knowledge of the features, components and (e.g., 'position','support', 'align', etc.) (Hundal, 1991). Theseassemblies is contained within the solution library, so the functions are used by the designer to describe what thedesigner need not be an expert in the domain field to use feature should do and are associated with the featuresthe solutions. according to their use.

For this study, features, also known as "form" features, The use of functions for the search for solutions is notwere the primary focus to test the architecture of the new, prominent design theory researchers (pahl & Beitzsolution library. Each of the features satisfies a function 1984, Andreasen 1991 ,Anderson 1991, Dighe 1992,(e.g., such as a hole to position an interfacing object). The Horvath 1990, Iyengar 1992, Bardasz 1990) have suggestedterm "feature" is an expression used in describing the solution library contexts revolving around complete designcharacteristics of an object, which according to McGinnis solutions. Other researchers (Cunningham 1988, Joshi(1990) comprises "any particular or specific characteristic 1990, Kimpel 1991) have investigated designing-with-of a design object that contains or relates information about features by using feature-based solution libraries, similar tothat object," or according to Aasland (1993), "primarily the one developed here. These investigations are relevant'chunks of geometry' distinguished by their ability to because they are the first step towards designing withperform a function with one or more other features." These features, but they either have not made a complete use ofviews, along with those recently presented by Shah (1991) the functional attributes or have not modelled the entirein a comprehensive review of many current ideas on feature solution in a functional way.technology and terminology, all share the concept that Library systems based on complete product solutionsfeatures are central to design object modeling. Dixon are useful in their specific application but fail in several(1988) proposed the method of designing-with-features, contexts. First, these library systems do not maintain the

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development history of those solutions; consequently, the system, introduced constraints due to the relationships toreasoning and detailed functional development of the adjacent objects, or the actual functional problem underdesign's solution are unavailable. Secondly, the solutions investigation. An example of an issue in a design contextaccessed from a complete product library neither present could be to mOW1t a roller bearing. The function "tosolutions which are incomplete, nor present solutions from mount" and the subsequent subfunctions (e.g., such as toa completely different design domain, or from a different supporl in axial and radial directions) are then used in thelevel of development (such as a feature to replace a search for solutions.component or a component to replace an assembly). Thisends up reducing or limiting the development of newdesign variations and innovations. Additionally, the ARCHITECTURE NK>DEL

selection of a solution by the satisfaction of a function and To design a computer data structure or architecturethe preserving of functional information from that selection model that maintains the search information, several mainis not a standard design practice. issues need to be considered. These include: (a) the

Feature based solution libraries also have the defmition of those elements that are used to store anddeficiencies associated with library systems previously retrieve the information from the search, (b) the selectionmentioned, but also possess the drawback of requiring the of features, components and assemblies that satisfy theengineer to have an idea of the solution and its capabilities required function, and (c) the mechanism(s) that elaboratebefore actually using the library. This limits the design to on both the found solution and the main search contexts forsolutions that are known to the designer. Consequently, the storage or retrieval. This section discusses these issues innovice engineer will, in general, design with a limited the development of a search data structure or searchnumber of features, and the expert with many. Other mechanism which I term a "function-object."feature based design systems, such as ProEngineer The fIrst issue is to develop the defmition of the(Parametric Technology, 1994), are prime examples of this elements that are used to store and retrieve the informationdeficiency; they require the feature and its data to be known from the search. Many authors (pahl & Beitz 1984,beforehand. Additionally, these systems do not possess the Tikerpuu 1988, Ullman 1992, Hubka 1984) have put forthreasoning behind the selection of a solution. To overcome useful and necessary database elements for feature andthese deficiencies, a "function driven" solution library has component storage. Some of these ideas have beenbeen developed. combined into a comprehensive data structure specifically

The implemented solution library serves as a computer developed for the solution library. Specifically, thedesign assistant to aid engineers in the development of a database contains information about ~ the solution isdesign by using the functionality of the desired solution as best suited for and.wb.Y (the reasoning behind the solutionthe primary index to search for design solutions. This concept).approach to search for solutions is accomplished by To develop the ~ and .wb.Y attributes (i.e., theincorporating and using a solution's known functionality functions and uses) within the "function-object," the(obtained from previous studies) into the library. relationships and attributes between features, componentsConsequently, only solutions that satisfy the function and assemblies must be determined. This wasrequired to be fulfilled by the designer are retrieved. The accomplished, for the initial solution librarynumber and variety of retrieved solutions are related to the implementation, at the feature level in the plastic injectionfunction or functions being searched for, thereby producing molding domain (Wood, 1996) by an in depth analysis ofsolutions that help the designer in developing a concept or known features in that domain. With the knowledgeduring a redesign. derived from the study, the necessary database structure for

The solution library is accessed during the decision the function-object was obtained. The informationprocess where issues are decided upon through arguments representing the relationships between features comprisedthat support a solution. In the design cycle, solutions are of the attributes between interfacing features (i.e., theaccessed from the library when alternatives are requested. functionality and what occurred at the interface). TheThe function which is at issue (i. e., to be satisfied), which attributes were identified and incorporated in the searchwas developed during the early stages of the design's mechanism for the solution library. Some of the attributesanalysis, is passed to the solution library along with relating contained are transferring of energy, materials and/orsearch criteria. This criteria may consist of any of the information between objects, a function/verb and noun usedfollowing: reasoning or usage of the feature, type of to represent the base relationship in addition to location,application, boundary conditions, initial constraints on the and other relating information.

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The function-object is a database representation in depth search of a library of solutions. The function-containing infonnation from the engineering specifications, object does 1NJt possess every relationship that existsfunctional decomposition infonnation and other relating between objects. The intention is to develop a criteriadata between features, components and assemblies. The template that can be used in a search algorithm while alsofunction-object maintains the information about the presenting information in greater detail about the objectsrelationships between the interfacing physical/implicit under investigation. The following listing shows theobjects and interfaces with other function-objects. The function-object's data slots that contains the infonnation forfunction-object maintains four of the five items Ullman searching for solutions, maintains the interface or(1993) states in his OREO design representation model. In connection between objects within the developed design,his model, one object's relationship to another is considered and preserves the basic reasoning behind the design. Theto contain: which objects are related, type of connection, infonnation slots as mentioned before were obtained fromtype of transmission, and relation action. The fifth item, the analysis of features found upon designed components,relative positioning, is not maintained in the function-object and verified by comparing the infonnation with the databut within the part's database itself. required for a component's database discussed by various

The function-object also contains infonnation about the authors (pahl & Beitz 1984, Tikerpuu 1988, Ullman 1992,relationships between the objects and the functions Hubka 1984).involved. One of these, the degree of resolution or thecomplexity of the system or object has great importance. FUNC110N - OBJECTThe degree of resolution is the degree that a function has FUNcDOO-:been broken down or resolved. Where the function can not (A function is any action verb that represents the functionbe resolved further is the lowest degree a design can be to be satisfied. Examples of a function include verbs like:represented. The degree of resolution maintains the level to position, tosupport, and to hold.)of abstraction within the developing function structure. AUX FUNcDOO- [l..n]:Additionally, the degree of resolution aids in keeping track (An array of action verbs representing functions ofof each function level as each is satisfied with a solution. secondary, tertiary, ... n-th importance)Other infonnation contained within the function-object, NOON:which contain information about the relationships between (A noun representing the physical effect that is manipulatedobjects, is the transmission or conversion of energy, by the function. Examples of a noun include: force,infonnation, and/or material data (pahl & Beitz 1984, friction, load, torque.)HundaI1991) that is acted on by the "verb" between the PERFUWING-OBJECf:objects. (A performing-object is an object that performs the

The type of physical connection that is possible or function. Examples of performing-objects are: a boss todirectly specified between the two interfacing objects is also position a computer board, a screw to hold 2 parts together,included within the function-object. This infonnation a motor to transmit a force.)provides connection infonnation between components with INmAL STAlE of PERFmMER:a specific type and degree of freedom (DOF). According (The initial state of the performer is a sentence thatto Agogino (1988) this is necessary, "since the basic effect describes the initial state of performing-object. Thison a body of being connected to another is to reduce its comprises of a list of the attribute names that represent thefreedom of motion, a classification of virtual bodies by known information at the initial state of the design (e.g.,degrees of freedom and type of motion is appropriate." horsepower, load, etc.).)Specifying the type of OOF presents a constraint which F1NAL STAlE of PERFmMER:narrows the number of solution possibilities. The physical (The final state of the performer is a sentence that describesconnection infonnation is maintained in the function-object the fmal state of performing-object. It is the new state onceas the type-of-interface. This category includes the degrees the function has fmished its task and comprises of a list ofof freedom, type of connection (e.g., [flexible, fIXed, the attributes that represents the infonnation derived fromtemporary, permanent], [surface, line, point],[rigid, planar the fmal design state.)pin, slider, gear contact, prism, helix, cylinder sphere, plane RECElVING-OBJECf:sliding]) and a part-of pointer to another object. (A receiving object is the object that receives the effects of

The function-object in its entirety contains the the function. Or in other words, the receiving-object is theinfonnation to describe the basic functionality between two object that has been acted upon by the performing-object.)objects. This data structure contains the data needed for an

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1YPE OF FUNcn~: (Location/object material is transmitted from)(Functional, manufacturing, mating, assembly. These FNmGY HDW mO\f:categories divided specify the basic domain the function is (Location/object energy is 1ransmitted from)concerned with, i.e., functional - used in the product's SIGNAIJIN~n~ HDW mO\f:application, manufacturing - used to aid in the (Location/object information is 1ransmitted from)manufacturing process, mating - used during the connection ENERGY ~with other components, assembly - used in DFA (Design (Type of energy)for assembly). SIGNAI.JIN~n~ ~PRECEDING FUNcn~: (Type of information)(The function that directly proceeds it in the function SIGNAI.JIN~n~:breakdown of the design that was developed earlier in the (The information)design process. The preceding function may be the parent ASSUMPn~S:or a brother/sister function. The preceding function is (Any known assumptions with respect to any or each of theobtained when the current function (issue) under above material, energy, or signal/information)investigation is fIrst passed to the function-objects.)Degree of Resolution for ~ preceding fmrtion: Qjlendional InfOmKllion(The depth or complexity level of the function in the Operation information is the data that specifies or describesfunction breakdown. This depth, which may be represented the interface between objects (e.g., features, components orin a tree structure format, shows the design's level of assemblies) and is comprised of the following information:abstraction. )

SUCCEEDING FUNcn~: 1YPE OF INTERFACE:(The function that directly succeeds it in the breakdown - degrees of freedom (0 to 6),This may be a parent or a brother/sister function) type of connection:

Degree of Resolution of~ succeeding fmrtion:(as above) (The type of connection represents the information at thePARAUEL FUNcn~(s): interface junction: [flexible, fIXed, tempormy, permanent],(An object's co-existing functions. These are functions [surface, line, point),[rigid, planar pin, slider, gear contact,which the object also possesses or additionally acts at the prism, helix, cylinder, sphere, plane sliding])interface. ) .-ut-of:DEGREE ofRESoum~: (the component or assembly the object is part ot).(The depth of the current function/primary function under Inrelfocing features, co~ne~, ~e~ies:investigation) (objects that interface with the feature)PARENT FUNcn~(s): cmS1RAINTS:(parent functions from the function breakdown) (Any constraints which are known to act on the system.)CIHID FUNcn~S: (l'ERAn~AL RE[An~:(Child functions from the function breakdown) (The relationship between objects in the transformed design

object. )T~fer tI' the inteifoce mlking the flO1Ction jlossihle: (l'ERAn~AL FUNcn~:The 1ransfer at the interface of two objects is commonly (Function that represents the 1ransformed design object -agreed to be the 1ransformation between an input and an may differ from the above function)output with respect to material, energy and information(signals) (pahl & Beitz 1984, Roth 1987, Hundal 1991). It must be noted that other elements can be added toThis transfer at the interface is represented in the function- this function-object template as long as the aboveobject by the following: parameters are also included. The basic set above is

necessary for the solution library to access the functionalMl\.1mIAL HDW ill information for a search.(Location/object material is 1ransmitted to)ENm.GY HDW ill AN EXAMPLE ltiing fmrtions aI:M:I ~ fmrtion-object for(Location/object energy is 1ransmitted to) semching for solutionsSIGNAI.JINFmMA:n~ HDW ill The following example describes the use of functions(Location/object information is transmitted to) to search for the necessary features required in theMl\.1mIAL HDW FR(M: development of a design, and the mechanism(s) that

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elaborate on the found solution and the search conditions FIgure 1 FWlCtion ~jectfor storage or retrieval. Note: The function-object

r infonnation has been abbreviated for viewing the pertinentinfonnation. FUNCll0N. S rt

This example describes the developme?t of a ~aring AUX FUNCll~ml]: Mountass~bly for .co~only used roller bearings usmg ~e AUX FUNCll0N [2]: LimitreqUired functionalIty to fmd the features. The assembly m NOUN. Loadits fmal.consists o~ the. ~g h?using, mount/shaft and PERFORMING-OBJECT: Blank-stock partthe bearmg. For S1IllpliCIty we WIll assume that the roller (h. )~g mount/shaft has previ.ously bee? developed and ~ow ~~ STA1E of PERFORMER: Free radialdesIre to develop the bearing housmg. The functions tired . fy th d . ed b . th movemenrequ. to satls e esI,gn are us to 0 tam . e FINAL STA1E of PERFORMER: Zero radialsolutions. Of the feature solutions presented by the solution t +/ toll .b th d ' 1 1 th that . fy th movemen - erances1 rary e esIgne~ se ects ~n y , ose satls. e RECEIVING-OBJECT: Roller Bearing

functions ~d meet his/her SpecI~catIO~. Upo~ completion PRECEDING FUNCll0N: Unknown (for thisof the desIgn example, an object dIagram IS presented 1showing the br~?own of the desi~ asse~bly. . ~~t~ING FUNC110N: Su rt (axial. Before begmnmg the roller-~g.housm.g desIgn, the forces) ppo

?asic knowledge of the ~oller-bearing IS .obtamed such ~ ENERGY FLOW TO: Blank-stock (housing)'; ~er an.d o.uter ~ce dIameters and. ~I,cknesses.. ThIS ENERGY FLOW FROM Roller bearing

~'!;;; infonnat~on IS o~tamed to develop the .mItial c.o~~ts on ENERGY FORM Mechanical~;;..:; the housmg desIgn. To start the desIgn an mitial blank- ASSUMPllO ~T S' U ' D 11 Bearin tram, ts,~,

k s: . ed th 11 bearin h ' '1'1, smg ~o er g cons\~:~ stoc -lonn IS us to represent e ro er g ousmg.': The initial parameters for the housing is selected by the'::, designer to satisfy the boundary conditions of the outer and, inner races of the roller-bearing and mount. Using this

information the functions that are required to be satisfied byfeatures on the roller-bearing housing design are functionality and relationships between the objects isdetermined: preserved. By linking the function-object to the design-* Position, mount and limit the roller bearing in the radial object maintains the integrity of the design from the search.direction. The search function-object shows the infonnation that is* Limit, position and support the roller bearing in the axial required at the interface before the functions are used todirection (right). fmd a solution form; this infonnation is then passed to the* Limit, attach, position and assist in the axial direction object to maintain the infonnation at the interface.(left). The search for a component to position and limit the To begin the search, the fIrst combination of functionsroller bearing in the opposite radial direction. (position, mount and limit, Figure 2) are used to obtain* Assist and guide the roller bearing onto the assembly.

To initiate a so~ution .search f~r the fIrst function FIgure 2. FIlSt fWlCtion combimtionparameters the function-object that IS used to start thesearch receives the function infonnation and any knownconstraint parameters, So the function object would appearas in figure I, (Note: only pertinent data in the function- F u ncti onNl'r b Ip ositio nobject for the example will be shown,)

Using this function-object and similar ones containingthe functions and infonnation of the second, third, and Auxiliol:f Function 1: Imount Ifourth function parameters (above) solutions are searched . . .""). . .for and presented to the designer to. The designer then AUXlllor)'Funct,on ~. Ilimitl Iselects a "best" solution from the list presented and the Auxilior:f Function 3. I Ifunction-object above is passed to the bearing-housing .

database attached to the solution that satisfies the Auxilior.,. Function 4: I Ifunction/so Consequently, the infonnation about the basic

6

solutions (Figures 3, 4, 5,6). From the solutions presented Figure 6. Wall solution

Figure 3. Snap solution

. by the designer to fulfill the initial roller-bearing housingFigure 4. GIOOve solution functions.

Q~,t\!!~N~T~::oov. Name: Roller bearing housing hole (Figure 7)IXsign functions: Position roller bearing and support

Feature Shape .tangentIal forces and related movements.

/~~~ : .,'l Assembly functions: Stop motion during the assembly~~:J::// operation of the roller-bearing.

Figure 7. Blank stock wid1 hole

Figure 5. ~le solution

Feature Shape

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The function object within the housing database associatedwith the feature "hole" would be as follows:

i the designer determines which solution would be most, applicable to the design. Unfortunately, saving the

designer's rational behind the decision is only possiblethrough notes attached to the feature. This wasaccomplished by including a note pad for the designer's use.For the function combination case the hole can be selected

7

I

F1U1CtiOn-())ject functions are limit, position and support axial forces (right)FUNCTION: Support and their related movements. A new function-object isAUX FUNCTION [I]: Mount created for this solution search containing the informationAUX FUNC110N [2]: Limit of restraining and mounting roller-bearings in the housing,NOUN: Load and the limit-movement, position and support-axial forcesPERFORMING-OBJECT: Blank-stock part (housing) functions are used to as the search keys. The solutionsINIllAL STATE of PERFORMER: Free radial movement found within the database to limit or restrain the movementFINAL STATE of PERFORMER: zero radial movement in one axial direction consist of a boss, depression, groove,

+/- tolerances gusset, hole, protrusion, snap, and wall. Solutions forRECEIVING-OBJECT: Roller Bearing limiting and positioning are boss, depression, groove, hole,PRECEDING FUNC110N: Unknown (for this example) protrusion, snap, wall and solutions for limiting and

~gree of Resolution:" "" supporting are boss, gusset, peg, protrusion, undercut, wall.

SUCCEEDING FUNC110N: Support (axial forces) Solutions that possess all three are the boss, peg, protrusion,~gree of Resolution: Unknown (for this example) wall. From these, the designer evaluates each solution

PARALLEL FUNC110N: Null according to the current design. For this case, four of theDEGREE of RESOLUllON: 1/1 solutions fulfill the functional requirements, each withPARENT FUNCTION: Null different means of solving the problem. From the foundCHILD FUNCTIONS: Null solutions the wall is selected.

T~fer m the intelfoce nNIkill!! the_function possible: Name: Roller bearing housing wallMATERIAL FLOW TO: Null ~sign functions: Support of axial forces andENERGY FLOW TO: Blank-stock (housing) related movements.SIGNAL FLOW TO: Null Assembly functions: Stop motion during the assemblyMATERIAL FLOW FROM Null operation of the roller-bearing.ENERGY FLOW FROM Roller bearingSIGNAL FLOW FROM: Null Once the wall solution is combined with the previousENERGY FORM Mechanical solution (Figure 8), the functions, limit, attach, position andSIGNAL FORM Null assist are used to fmd a solution for the axial directionSIGNAL: Null (left). A search to restrain the bearing in the opposite axialASSUMPllONS: Using Roller Bearing constraints direction would come up with various solutions as

~mtional Infonmtion mgure 8. Wall combined1YPE OF INTERFACE:

degrees of freedom: 0type of connection: temporary, surface, rigidpart-of: unknown (for current example)Interfacing features, components, assemblies: Null

CONS1RAINTS: Cylindrical hole in blank-stock (housing)due to Roller Bearing constraints wan

OPERA 11 ONAL RELA 11 ON: unknownOPERA110NAL FUNC110N: unknown

The selected feature is then saved with its relatingfunction-object and checks are made to determineinterfacing components and known connection types. The"part-of' is initially classified as unknown so the designeris requested a name: roller bearing housing. Next checks presented before. Of these solutions, only the snap (seeare made to decide what assembly the roller bearing Figure 2) would satisfy the functional requirements. Thehousing is part of, ie., roller-bearing assembly. other solutions, such as wall and boss, are not removable.

With the first feature selected the next function Therefore mounting the roller bearing would be impossible.combination are used to obtain feature solutions; these For the prototype solution library, component solutions

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have not been entered into the solution library. Once FIgure 10. OJamfer solutioncomponent solutions are entered in the library, a search fora component to restrain, attach, position and assist the roller Feature Name:.J~hamf;; lbearing would produce a solution such as a retaining ringand corresponding groove. To accomplish this with Feature Shape

features the designer must evaluate the solution accordingly.Consequently, the retaining ring is represented as a snap,since it locks in similar to a snap.

Searching for a solution solving the functions limit,attach, position and assist produces the solutions:depression, groove, and rib. The groove is selected toattach the retaining ring (Figure 9).

FIgure 9. Groove solution

Feature Shape: FIgure 11. Roller Bearing J:i)ming mdl OOaring aIKlroller OOaring mJlmt

~:;~~~~~~~~ H 0 u sin g

Groove

Chamfer

Wall

Hole

Bearing

(

Name: Roller bearing housing retaining ring groove~ign Functions: To seat a retaining ring to support

axial forces and related movements. Mount/ShaftAssembly Functions: Realization of a detachable

connection with the roller bearing (with the helpof a retaining ring) housing is combined with the roller bearing mount and the

roller bearing into an assembly the complete objectTo fmish the design of the roller-bearing housing, the structure would be as in Figure 12.

functions assist and guide are searched for to obtain afeature to aid in the assembly of the roller-bearing on the Name: Roller 00ari~ homi~housing. From the search solutions of chamfers, tapers and ~ign Functions: Position, supportcomer radii are found. The chamfer solution is selected to ~scription: Bearing-seat housing: roller-bearingcomplete the design (Figure 10). mount/housing.

Input:Load upon housing from roller bearing.Name: Roller bearing housing chand"er Output:Stresses on housingAssembly Functions: Aid in mounting the roller Participants: Children: hole feature, wall feature, groove

bearing during the assembly process. feature, chamfer featureType of interface: degrees of freedom: 0

Manufacturing Functions: Realization of a defmite type of connection: temporary, surface, rigidform of the edge. part-of: unknown (for current example)

Connection requirement features, components,All of the above features combine together to form the assemblies: Retaining ring, Roller-bearingroller bearing housing (Figure 11). When the roller bearing

9,

,,'

Figure 12. O>ject stnrture function! function-combination (e.g., friction,transverse stress, heat transfer).

r Domlin: The manufacturing domain (e.g., plastic injectionfi~:Support,... -molded, sheet-metal, cast, composites, ceramics).

A: Feature a~: A description of the design (e.g., bearing, gear

electric motor)Description: A descriptive list of terms used to describe

the situations under which the object best serves itsPart purpose (e.g., helical gear: high load, high number of

revolutions per minute, parallel shafts etc.).Bearing - Seat AssessDEnt: Limiting constraints (e.g., minimum weight,~y minimum cost, maximum speed, maximum efficiency,

etc.).Shape: The rough shape of the component or assembly

(e.g., cylindrical, rectangular).T~ cl~ification: Topology & shape form.

The retrieval of components and assemblies has beeninvestigated by many researchers (Pabl & Beitz 1984, 1988;Hubka 1984, 1988, 1992; Bardasz 1990, 1992; Andreasen1991; Sigurj6nsson 1992). Of these, the research of

This example demonstrates the search and retrieval of Bardasz and Zied (1992) using an Analogical Problemsolutions using the function requirements that make up a Solving (APS) scheme, based on case-based reasoningdesign. The example also demonstrates how features are using semantic network, is one of the most promising.obtained from the functions derived from a function Using this scheme, but only by focusing primarily on thebreakdown. With this technique features are combined into functionality of the product as the primaIy index for thecomponents which are in turn combined into assemblies. search, and by using the other criteria as delimitating

The information residing in the function-object is used factors, allows for the reasonable selection of solutionsby the solution library to search for solutions and for within the entire population of solutions. To accomplishrepresenting the basic information about the interface this, the primaIy index is fIXed and delimitating factors andbetween objects. The function information and the indices are developed to be used during the design process.function-objects discussed in this paper were used forobtaining feature solutions, but adapting this concept to Cadusia1components and assemblies is also possible. The search for Capturing the basic reasoning of why and how a designsolutions of complicated structures requires delimitating is developed is important in fully preserving andfactors to be used in order to reduce the potential search documenting the design of industrial products. Therefore,area. The number of component and assembly solutions is the maintenance of captured design information and it's re-extremely high and requires the search area to be reduced use during solution retrieval requires different types ofto a manageable level. Solutions that are not directly information transferral and preservation than thoseapplicable to the design problem inhibit the designers traditionally used in CAD/Design systems. This paperability to make sound design selections. To incorporate develops the basic database structure for preserving anddelimiting factors the same function-object is used as the transferring design infomlation along with using theprimary search mechanism, but additional delimitating reasoning (functional properties) in the search for solutions.elements are implemented. The following delimitating The designer retrieves saved solutions throughcomponent and assembly concepts were obtained from the functional properties, transfers the retrieved solution'sresearch ofBardasz and Zied (1992). These concepts were information, and captures the design rationale or intent ofmodified and incorporated into the function-object to reduce the design during development. To accomplish thesethe search space for component and assembly searches. actions several main issues are considered: (a) the definition

of the elements that are used to store and retrieve theType: (e.g., undefmed, feature, component, assembly) information from the search, (b) the selection of the~noDEna: The physical phenomena used to satisfy the features, components and assemblies that satisfy the

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function, and (c) the mechanism(s) that elaborate on both Engineering Design, Volwne I, Zurich, V. Hubka, editor,the found solution and the main search contexts for storage HEURISTA, pp. 17-24.

r or retrieval. Andreasen, M M, 1991, "~sign Methooology,"The database structure, termed a "function-object," Jownal of Engineering Design, Vol. 2, No.4, pp. 321-334.

maintains the functional, constraint, and information Bardasz, T., and. Zeid, I., June 1992, "Cognitive Mooelparameters that occur at the interface between two objects. of Memory for Mechanical-~sign problems," Computer-This function-object is used in the search for solutions by Aided Design, Butterworth-Heinemann Ltd, Volwne 24,using the contained function information for the solution Nwnber 6, pp.327-342.search keys. The function-object is additionally combined Bardasz, T., and Zeid, I., August 1990, "Proposingwith the object's (feature, component, or assembly) database Analogical Problem Solving to Mechanical ~sign,"to maintain the connection information with other Proceedings ASME Intemctional Computers in Engineeringcomponents. It is through the function-object that the Conference, New York, pp. 181-186.design's purpose or "reasoning" is preserved. Cunningham, J. J., and Dixon, J. R, August 1988,

The information presented in this paper targets some of "~signing with Features: The Origin of Features,"the aspects that need to be developed and applied to future Proceedings A SME Intemctiond Computers in EngineeringCAD/Design systems. First, a new generation CAD system Conference, New York, pp. 237-243.should include feature based design that is based on Dighe, R, and Jakiela, M J., September 1992,functional reasoning. This system should focus on features "Computer-Automated Functional ~sign of Injectionand the functions they fulfill. This would allow designers Molded proouct Housings," Design Theory a1dto develop a proouct through the fulfillment of its functions Methodology - DTM '92, ASME, N.Y., pp. 45-55.

(function generates form). Second,asystemusingfeatures Dixon, J.R, et al., August 1988, "A Proposedand functions could capture some design rationale, but only Taxonomy of Mechanical ~sign Problems," Proceedingswith features and functionality embedded in the system. ASME Intemctiond Computers in Engineering Conference,Third, once the features and functionality are contained New York, pp. 41-55.within the system, the product under development could be Horvath, I., August 1990, "Selection and combinationunderstood more completely by evaluating the multifunction of Part Segments by Function," Proceedings of the 1990aspects of certain features. Fourth, the features and Intemaional Conference on Engineering Design (ICED),corresponding functionality could help designers from one Volwne 1, JUDEKO, Dubrovnik, pp. 91-98.discipline understand features specified by designers from Hubka, V., 1992, "~sign for Quality and ~signanother, and thus avoid design conflicts. Fifth, since the Methooo10gy," Jownal of Engineering Design, Vol. 3, No.interaction between components in a proouct is at the 1, pp. 5-15.interface between features, it is necessary to understand the Hubka V., and Eder, W. E., 1988, Theory of Technicalinterface or the functionality that is represented at the Systems, Springer-Verlag, Berlin, Heidelberg, N.Y.,interface. Only by introoucing functionality into CAD London, Paris.algorithms can feature-based design be effectively used. Hubka, V., 1984, Principle of Engineering Design,

Butterworth Scientific, London, Boston.Hundal, MS., 1991, "A Methooical Procedure for

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