銑床等臂杠桿機械加工工藝規(guī)程及鉆2-φ8孔夾具設(shè)計【鉆2-φ8孔】 【版本2】,鉆2-φ8孔,版本2,銑床等臂杠桿機械加工工藝規(guī)程及鉆2-φ8孔夾具設(shè)計【鉆2-φ8孔】,【版本2】,銑床,杠桿,機械,加工,工藝,規(guī)程,夾具,設(shè)計,版本 A functional approach for the formalization of the fixture design processR. Huntera, J. Riosb,*, J.M. Pereza, A. VizanaaDepartment of Mechanical and Manufacturing Engineering, Escuela Tecnica Superior de Ingenieros Industriales, Universidad Politecnica de Madrid,Jose Gutierrez Abascal, 2, 28006 Madrid, SpainbCurrently in Enterprise Integration (Bldg 53), Cranfield University, Cranfield, MK43 0AL, UKReceived 14 January 2005; accepted 14 April 2005Available online 26 August 2005AbstractThe design of machining fixtures is a highly complex process that relies on designer experience and his/her implicit knowledge to achievea good design. In order to facilitate its automation by the development of a knowledge-based application, the explicit definition of the fixturedesign process and the knowledge involved is a prior and a fundamental task to undertake. Additionally, a fundamental and well-knownengineering principle shouldbe considered: the functional requirements and their associated constraints should be the first input toany designprocess. Considering these two main ideas, this paper presents the development undertaken to facilitate the automation of the fixture designprocess based on a functional approach.In this context, the MOKA methodology has been used to elicit fixtures knowledge. IDEF0 and UML have been used to represent thefixture design process. A methodology based on the function concept and aiming to formalize such design process is proposed. Fixturefunctional requirements have beendefined and formalized. Functional fixtures elements havebeen used tocreate a functionaldesign solution,the link of these elements with the functional requirements and with typical commercial fixture components has been defined via tables andrules mapping. And finally, a prototype knowledge-based application has been developed in order to make an initial validation of theproposed methodology.q 2005 Elsevier Ltd. All rights reserved.Keywords: Fixture design process; Fixture knowledge modelling, Fixture functional requirements1. IntroductionThe main objective of any design theory is to provide asuitable framework and methodology for the definition ofa sequence of activities that conform the design process of aproduct or system 1. In general, all of them identifyrequirements as the starting point in the design process. Infact, the engineering discipline dealing with product designcan be defined as the one that considers scientific andengineering knowledge to create product definitions anddesign solutions based on ideas and concepts derived fromrequirements and constraints 24.For this research, a relevant issue when consideringrequirements, taking this as a general concept, is to makeexplicit the meaning of two main terms: FunctionalRequirement (FR) and Constraint (C). A functionalrequirement, as it stated by different authors, representswhat the product has to or must do independently of anypossible solution, 2,4. A FR is a kind of requirement, andconsidering some basic principles widely recognized in thefield of Requirements Engineering, we could add it is aunique and unambiguous statement in natural language of asingle functionality, written in a way that it can be ranked,traced, measured, verified, and validated. A constraintcan be defined as a restriction that in general affects somekind of requirement, and it limits the range of possiblesolutions while satisfying the requirements. So, a constraintshould be always linked to a requirement, and its purpose isto narrow the design outcome to acceptable solutions.Considering the Theory of Axiomatic Design 4,functional requirements should be defined in the functionaldomain, which brings on the scene the issue of how to defineand represent the functionality of a product. The way used torepresent it will affect the reasoning process of the designer,and in that sense, the mapping between the functionalInternational Journal of Machine Tools & Manufacture 46 (2006) - see front matter q 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.ijmachtools.2005.04.018*Corresponding author. Tel.: C44 1234 754936; fax.: C44 1234750852.E-mail address: j.rioscranfield.ac.uk (J. Rios).and the physical domains, being the later the one where thedesign solutions are developed. Several authors haveinvestigated the concept of functionality and functionalrepresentation 2,58. Their design approach provides aview based on the Function-Behaviour-Structure frame-work, where function is defined using structure andbehaviour 6. The objective is to fill the gap that allowsa designer to progress from FRs to physical designsolutions. The approach is that product functions areachieved by means of its structure, which seems to lead toan iterative causal approach, where solutions are soughtuntil the selected structure causes the intended functionality.The approach adopted in the research presented in this paperis based on the definition of Fixture Functional Components(FFC), which can satisfy the fixture functionality, and on themapping between such FFC and fixture commercialelements.An advanced approach to the definition of requirementsand functions comes from the creation of ontologies. Theontological approach pursues the definition of the meaningof terms making use of some kind of logic, and the definitionof axioms to enable automatic deduction and reasoning 9.The ontological approach has got a higher relevance sincethe representation of knowledge is considered the key factorin whatever engineering process, and it has been recognizedas a way to facilitate the integration of engineeringapplications 10, to describe functional design knowledge7, and to define requirements 11. Considering a puristapproach, if an ontology does not include axioms to enablereasoning then it could be considered more like aninformation model, and in this sense, this is the approachdeveloped in the work presented in this paper.When considering the methodologies developed for thedesign of fixtures, it can be stated that in general they arerational and propose a series of steps to follow. For example,the methodologies proposed by Scallan and Henriksen 12,13, make use of this approach to describe in general termsthe information needed in each stage of the fixture designprocess. Basically, the importance of modelling in detailsuch information, which mainly is related to fixturerequirements, fixture functionality, fixture components,manufacturing resources, manufacturing processes, anddesign rules; resides on the possibility to automate thedesign process through the development of a knowledge-based application or system. It is relevant to mention thatseveral authors have already aimed to develop knowledge-based applications for fixture design, none of them based ona functional approach, some of the most recently publishedworks can be found in the Refs. 1419.Inthefollowingsections,thispaperpresentsamethodology to formalize the design process of machin-ingfixturesbasedontheengineeringconceptsoffunctional requirements and fixture functions 20. Theformalization of the functional requirements is achievedthrough the application of a structured way of specifica-tion via natural language. Additionally, IDEF0, MOKAmethodology, and UML diagrams are used to capture,represent and formalize knowledge, being the ultimategoal to facilitate the automation of the fixture designprocess.The IDEF0 method is used to create an activity model ofthe fixture design process, allowing the identification of theinformation used in each one of the different tasks itcomprises. UML has been used to complement the IDEF0model by representing the interaction between the activitiesof the process. The MOKA methodology together withUML, are used to capture and represent knowledge involvedin the fixture design process. Finally, to validate theproposed methodology, partial results obtained from thedevelopment of a prototype knowledge-based applicationare presented.2. Analysis of machining fixtures requirementsIn Section 1, two terms have been defined: functionalrequirement and constraint. Requirements have alwaysexisted, the way in which they are expressed, and howthey are integrated in the product design process, are aspectsthat are addressed from different disciplines, for example:product design engineering and requirements engineeringamong others. In general, Requirements Engineering refersto the discipline dealing with the capture, formalization,representation, analysis, management and verification ofrequirements fulfilment. However, all these aspects need tobe integrated in the product design process, and require-ments should lead to the definition of the possible productdesign solutions, which in general demands an integratedview of the requirements issue. It is important to keep inmind that the development of such discipline is stronglyrelated to Software Engineering and Systems Engineering,and in fact much of the research related to requirementscome from authors from these engineering areas 2123.When considering the analysis of requirements, prob-ably, the first aspect to think about is how the requirementsare represented or declared. As it has been previouslymentioned, the way of expressing requirements definitivelyaffects their interpretation and the creation of a designsolution. In this sense, it is widely accepted, that the use ofnatural language is the most common way of expressingrequirements and in consequence, their writing becomes animportant issue. The anatomy proposed by Alexander et al.24 to write requirements in a semi-structured way is usedas basis to declare the functional requirements andconstraints of fixtures 20.In machining, work holding is a key aspect, and fixturesare the elements responsible to satisfy this general goal. Intheir design process, the starting point is the definition of themachining fixtures functional requirements and constraints.Usually, a fixture solution is made of one or several physicalelements, as a whole the designed fixture solution mustsatisfy all the FRs and the associated Cs. Centring, locating,R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697684orientating, clamping, and supporting, can be considered thefunctional requirements of fixtures, what a fixture must doindependently of any particular solution. In terms ofconstraints, what limits the range of possible solutions,there are many factors to be considered, mainly dealingwith: shape and dimensions of the part to be machined,tolerances, sequence of operations, machining strategies,cutting forces, number of set-ups, set-up times, volume ofmaterial to be removed, batch size, production rate, machinemorphology, machine capacity, cost, etc. At the end, thesolution can be characterized by its: simplicity, rigidity,accuracy, reliability, and economy.2.1. Functional requirementsFrom the literature review 2527, and from theinterview with designers of machining fixtures 28, it canbe concluded that basic functional requirements that anyfixture solution must satisfy are related to: centring,locating, orientating, clamping, and supporting.However, the way that designers deal with these FRs isfar from being independent of the solution they areconsidering, and in general the FRs are not explicit butimplicit in the design process. Chakrabarti et al. 29 pointout some of the problems that appear in relation torequirements during the design process, for examplerequirements during conceptual and embodiment designsresult mainly from analysis of proposed designs, which infact it is in contradiction with the basic principle, presentedby different authors, of functional definition prior to anydesign solution identification. Adopting the ideas ofToyotas Set-based Concurrent Engineering 30 andAxiomatic Design Theory 4, it seems logical to statethat the FRs should be clearly identified and defined prior toselecting any possible design solution and as the designprogresses the different constraints linked to the FRs shouldbe refined to narrow the set of possible solutions.Chakrabarti et al. 29 also conclude that in order forrequirements to be adequately fulfilled by the final design,they must be identified, understood, remembered and used.Thisconclusion is not new, and in this sense, it demonstrateshow actual and relevant this issue is. It also reinforces acouple of ideas widely recognized in engineering design,one is the need to capture, formalize and documentknowledge, and the second is to make use of it in thedevelopment of Knowledge-Based Engineering (KBE)applications that could help the designers to carry outtheir job and make use in an automatic way of as muchscientific knowledge as possible 31. In this particular caseapplied to the design of machining fixtures.When addressing the development of a KBE application,there are two different sorts of FRs that need to be identifiedand documented. One kind is the functional requirements ofthe application itself; in this case a KBE application forthe design of machining fixtures; and the second one is thefunctional requirements of the components subject of theapplication; in this case machining fixtures. An example ofthe former ones for an application developed in collabor-ation with an industrial partner is presented by Rios et al.28. For this kind of FRs specification, UML seems to beFig. 1. MOKA Entity form for fixture FRs.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697685a good methodology: activity, component, and use casediagrams help to specify and give a view of the system.However, when getting into the logical view where classand interaction diagrams have to be defined, it is needed tohave a complete understanding of the object of theapplication: machining fixtures. With this objective, andconsidering that the design of machining fixtures based onfunctional requirements would be the aim of a KBEapplication, the capture and documentation of the machin-ing fixtures FRs is part of the subject of the work developed20, and it is commented next.In this context, the approach adopted was to use part ofthe tools provided by the MOKA methodology 31, thenamed: Illustrations, Constraints, Activities, Rules andEntities forms, to elicit knowledge about machiningfixtures as a first step in the formalization of the FRs andCs. Based on these forms, it is possible to represent themain components linked with the fixture design process:non-functional requirements, functional requirements,constraints, design rules, fixture functional elements,fixture commercial components, etc. 20. Figs. 1 and 2present an example of application to the definition offixture FRs and Cs.After this first phase, the requirements capture iscompleted with the formalization of the functionalrequirements syntax. At this point, it is important toremember that the declaration of a FR is a sentence writtenin a way that allows the FR to be measured, verified, andvalidated. The structure proposed is based on Alexandersanatomy 24, and it has similarities with the functionrepresentation presented by Takeda et al. 6, where it isstated that a function is a combination of a function body(verb), an objective entity (on which the function occurs onor to), and functional modifiers (adverb). The structureproposed in this research is made up of four maincomponents: action, object, resource, and qualifiers(Fig. 3). And unlike with the Takeda approach, all themodal adverbs (i.e.: firmly, precisely, in general allInside the working area of the table:X = 200 mmY = 400 mmZ = 400 mmTolerance for all the dimensions: 1 mmObjectResourcePart A in vertical ma chining center DM T50 ActionQualifierSupport Fig. 3. Functional requirement structure.MOKA ICARE: ENTITYNameReferenceEntity TypeFunctionBehaviourContext, Information,ValidityDescriptionManagementAuthorDateVersionStatusConstraints Functional Requirements for the FixtureConstraints Functional Requirements (CFR)StructureDefine constrains to Functional Requirements for the fixtureNot ApplicableDefine constraints that support the functional requirementsThe constraints will be structured thinking on the functional requirements structureWith this target it has been defined a group of constraints associated with eachfunctional requirement of the fixture, such as:OrientationSupportLocateClampMachiningResourcesRenato Hunter03-07-041.0In progressFig. 2. MOKA Entity form for fixture Cs.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697686the adverbs ending with the suffix y) are not considered as amodifier, since they do not have a quantitative value, and inconsequence they cannot be measured neither validated.The Action component is expressed by an active verb thatrefers to the function of the fixture. As named previously,these functions are: centre, position, orientate, clamp, andsupport. A noun expresses the Object component, and refersto the physical object on which the action is performed. Inthe first level of fixture FRs definition, Object will be thepart to be machined. A noun expresses the Resourcecomponent, and it refers to where the action will beperformed. In the first level of fixture FRs definition,part_requirementscost_requirementsprocess_requirementsorientation_requirements-identificacion : char-nombre : char-descripcion : char-accion : char-que : char-recurso : char-calificador : chardocumentation_requirementFixture_requirementslocate_requirementssupport_requirementsclamp_requirements-Requirements1-Documentation1.*accesibility_requirements-Process1.*-Part1formal_representation_requirements-identificador : char-nombre : char-descripcion : char-accion : char-que : char-recurso : char-calificador : charfunctional_requirements-identificador : char-nombre : char-descripcion : char-accion : char-que : char-recurso : char-cualificador : charno_functional_requirements-identificador : char-nombre : char-descripcion : char-accion : char-que : char-recurso : char-calificador : charstructure_requirementscentre_requirementsmachine_tool_requirementsmachining_feature_requirements-Part1-feature1.*-Process1-Feature1.*-Identificator: char-name: char-description: char-action: char-object: char-resource: char-qualifier: char-Identificator: char-name: char-description: char-action: char-object: char-resource: char-qualifier: char-Identificator: char-name: char-description: char-action: char-object: char-resource: char-qualifier: char-Identificator: char-name: char-description: char-action: char-object: char-resource: char-qualifier: charFig. 4. UML model of the fixture functional requirements.Table 1Instances of fixture FRsActionObjectQualifiersQualifier typeOrientatePartIn the machine tool (M0)(Resource)Respect to the coordinated system of thepart (M1)(How)On the orientation part activity (M2)(When/Where)Modifier (M0)Respect to system axis of machine toolModifier (M0)In a vertical milling machineModifier (M1)Respect to the tool pathConstraintsMachine tool type (Vertical or horizontalmill)Work area: lengths in X, Y, ZSupportPartIn machine tool (M0)(Resource)On static equilibrium (M1)(How)On the support part activity (M2)(When/Where)Modifier (M0)In a vertical milling machineModifier (M1)When the sum of forces is equal to zeroModifier (M2.1)Vertical degree of freedom of the partModifier (M2.2)When the orient activity propose a resultConstraintsWork area: lengths in X, Y, Z Shape andsize of the base plateR. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697687Resource will be the machine tool on which the machiningis performed. A quantitative adjective group or noun groupexpresses a Qualifier for the action. The Qualifierscomponents refer to limits of the FRs, and allowrepresenting the constraints (Cs) associated with them.Each quantitative qualifier must have at least a nominalnumerical value, a unit of measure, and a tolerance. Each FRmust have at least one quantitative qualifier. Considering theprevious concept of constraints refinem