mask in design

8/8/2019 Mask in Design

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Note om Maskindesign

1. udgave

Jens Vinge Nygaard

Institut for MaskinteknikAalborg Universitet

Januar 2005


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Indholdsfortegnelse

FORORD................................................................. .................................................................. ........................................ 3

HISTORISK INTRODUKTION.......................................................... .................................................................. ......... 4

DE FRSTE DESIGNERE ...................................................................................................................................................4 UDGANGSPUNKTET FOR SYSTEMATISK DESIGN...............................................................................................................5 ROMERSK MASKINDESIGN ..............................................................................................................................................6 ARABISK MASKINDESIGN ................................................................................................................................................6 MIDDELALDERLIG MASKINDESIGN .................................................................................................................................7 RENSANSEN OG DEN INDUSTRIELLE REVOLUTION ........................................................................................................7 DESIGN AF MASKINER I DEN MODERNE VERDEN..............................................................................................................8 SYMBOLSK REPRESENTATION GRUPPE TEKNOLOGI ......................................................................................................9 UDVIKLINGEN AF DESIGNMETODIKKER ..........................................................................................................................9

METODIKKER TIL MASKINDESIGN .......................................................... ........................................................... 12

THEARTANDSCIENCEOFMACHINEDESIGN..................................................................................................12 Classification .......................................................... .................................................................... ............................ 13The Traditional Machine Design Procedure................................................................................................... ........ 15The Concurrent Engineering Machine Design Procedure................................................................... ................... 18

Axiomatic Foundation and Fundamental Rules of Machine Design................................................................... .... 20CONCEPTUALMACHINEDESIGN ............................................................ ............................................................ 22

Clarifying the Design Task................................................. ................................................................... .................. 22 Design Specifications-Quality Function Deployment .............................................................. ............................... 27The Machine Functional Concept ............................................................... ............................................................ 32

Design Alternatives: Task Decomposition ................................................................... ........................................... 35Development of Alternative System Design Concepts................................. ............................................................ 41Preliminary Evaluation of System Design Alternatives ........................................................................... ............... 41

EMBODIMENTDESIGN...........................................................................................................................................53 Design Synthesis ................................................................ .................................................................. ................... 53 Design Analysis and Evaluation ........................................................................ ..................................................... 56

MACHINEDETAILDESIGN .............................................................. ............................................................... ....... 56Codes and Standards.................................................. ................................................................. ............................ 56

PHILOSOPHICALANDLEGALASPECTSOFMACHINEDESIGN ........................................................... .......... 57 Aesthetics in Machine Design .................................................................... ............................................................. 57 Machine Design Ethics .................................................................. ................................................................ ......... 58The Legal Constraints: Product Liability ....................................................................... ........................................ 60Societal Constraints: Green Design, Recyclability ................................................................... .............................. 63

DESIGNPROCESSEN OG SAMTIDIG KONSTRUKTION (CONCURRENT ENGINEERING) ........................................................ 66DESIGN M.H.P. FREMSTILLING, SAMLING, ADSKILLELSE OG SERVICE ............................................................................66 VALG AF MATERIALER..................................................................................................................................................66 VALG AF FREMSTILLINGSPROCESSER............................................................................................................................66 CIM..............................................................................................................................................................................67 KVALITETSSIKRING ......................................................................................................................................................67 GLOBAL KONKURRENCE OG FREMSTILLINGSPRISEN .....................................................................................................67 LEAN PRODUCTION OG AGILE MANUFACTURING....................................................................................................67 MILJBEVIDST DESIGN OG FREMSTILLING ....................................................................................................................67 PRODUKT ANSVARLIGHED ............................................................................................................................................67 KONKLUSION................................................................................................................................................................67

PERSPEKTIVERING............................................................................................ ........................................................ 68

KONKLUSION.................................................................... .............................................................. ............................. 69

KILDER .................................................................. ................................................................. ....................................... 70


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ForordDenne note er skrevet som et supplement til kurset i Fagets formidling og metoder, der afholdesfor studerende p industrisektorens 2. semester.

Noten skal belyse de metoder som maskiningenirerne bruger indenfor mekanisk konstruktion til atsikre ydedygtige, effektive, konomiske og rettidige lsninger for produkt- og procesudvikling.Dette kan variere fra design af sm komponenter til meget store anlg, maskineri ellerbefordringsmidler.

Mlet for kurset er bl.a. at give indblik i produkt- og procesudvikling med den mekaniskekonstruktion som omdrejningspunkt.


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Historisk introduktionHvad definerer ingenirvidenskaben? Nogle af de vigtigste egenskaber ved ingenirens arbejde er:

Strrelse. Ingenirer behandler systemer af en vis strrelse, s det ervanskeligt for en fagmand at lave et tilsvarende system ved simpel gentagen.

Kompleksitet. Ingenirer behandler systemer af en vis kompleksitet, s deter vanskeligt for en fagmand at lave et tilsvarende system ved blot at sttesammen af mindre dele.

Innovation. Hvis der krves innovation for at designe et nyt system, s erder behov for en ingenir. Han vil kombinere viden fra forskellige dele ogsystemer, og sammen med viden fra ingenirdisciplinerne vil han syntetisereet grundlggende nyt system.

Forandring. Et eksisterende system har behov for en ingenir til at redesigne

det, hvis nogle af design parameterne ndre sig, f.eks. hvor let det er atskaffe sig et givent materiale. Rationel brug af ressourcer. En ingenir skal opn sine resultater ved et

minimumsforbrug af ressourcer.

Encyclopedia Britannica definere en maskine som et objekt med et unikt forml der supplere ellererstatter menneskelig indsats for at lse en fysisk opgave. Dette er en meget bred definition og derfindes mere en 12 forskellige definitioner p hvad en maskine er. Da det her er maskindesign der eri fokus, s der kan skabes maskiner der virker sikre, stabile og gode, er flgende definitionerfornuftige:

Et apparat bestende af forbundne enheder, eller Anordning der modificere kraft eller bevgelse.

Design af et objekt er formuleringen af en plan for dets struktur, funktioner og optrden underhensyntagen til procedure for en effektiv produktion, distribution, slag, servicering og afskaffelse.Design refererer til en rkke forskellige objekter, s som bygninger, inventar, tj, maskiner,industrielle produkter, organisationer, systemer og procedure. Maskindesign er rettet modmaskinbegrebet som defineret ovenfor.

De frs t e des ign ere

De frste tekniske fremskridt (6000 4000 f.kr.) er opnet igennem en lang evolution eller vedopfindelser og ikke ved en bevidst sgen efter en lsning p et givent problem. Ofte har detpolitiske og sociale system ikke tilladt liberal tnkning, som er centralt for udviklingen afvidenskabelige tanker. Teknologi har udviklet sig gennem trial and error i stedet for ved rationeltankegang.Den videnskabelige metode startede med den Ionske skole for natur filosoffer, hvis leder var Thales(640 546 f.kr.). Han er bedst kendt for hans opdagelse af de elektriske egenskaber af rav ogindfrte begrebet elektricitet, da han studerede den statiske elektricitets opstende, nr uld gnidesimod rav. Thales vigtigste bidrag er konceptet med det logiske bevis for et abstrakt forslag. Dennesgen efter rsager frte til udviklingen af den generaliserede videnskab som en adskildt metode tilde empirisk baserede regler. Denne udvikling af de videnskabelige metoder 600 500 f.kr. frste til


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en kraftig udvikling af ingenirvidenskaben i 400 100 f.kr, og nede sit hjdepunkt i det romerskerige i r 100 200.

Udgangspunk t e t f o r sys tem at i sk des ign

De frste designere var bronze hndvrkere i den grske og romerske civilisationer. De kendteikke til markedsfring, men kendte brugerne af deres produkter og havde lbende tilbagemeldingerom produkternes accept og ydelse. Under fremstillingen var der ogs kontakt til brugeren. Detvigtigste er at det var en enkelt person som forestod koncept, design og fremstilling. Frst langtsenere betd masseproduktionen at proces blev brudt ned i mindre dele og frste til en adskillelse afdesign og fremstilling.De underliggende ideer bag designfasen blev undersgt allerede tidligt i historien. Den frstedesignteori var del af en stetisk som inkluderede funktionerne og de etiske egenskaber. Funktionog stetik kunne ikke adskilles, da dette samfund havde ikke rd til ressource spild p renestetiske egenskaber.Den frste anvendelse af ordet maskine optrder i Homer og Herodotud til at beskrive politiskmanipulation. Den moderne mening af ordet blev frste gang brugt af Aeschylus til at beskrive enenhed p et teater til at flytte ting p scenen. Der er adskillige referencer til disse maskiner anvendt igrske spil. De var store mekanismer bestende af bomme, hjul og reb, med en vgt op til 1000 kg.Designerne af disse maskiner blev kaldt for mechanopoioi (maskindesignere). De designede ogbyggede maskiner ikke ud fra evolution eller opfindelse, men p order og med specifikationer frakunsterne. Kravene til maskinerne var vsentlige, da der blev flyttet heste, hestevogne og ryttereover scenen og med voldelige bevgelser. Det har krvet en vis styrke og balance afkonstruktionen.Aristoteles har skrevet den frste tekst om maskiner og deres problemer. P det tidspunkt varmekanismer de eneste kendte maskiner og han diskuterer flere kinematiske aspekter af disse:

Den vektorielle karakter af hastighed, superposition af hastighed ogparallellogrammer for addition af hastighed.

Koncepterne om absolut og relativ hastighed langs led i en maskine. Cirkulr bevgelse. Hastigheden af ethvert punkt p periferien er rettet

langs tangenten til den omskrivende cirkelbevgelse og proportional medradius og vinkelhastigheden.

Bevgelsen af to modsat roterende hjul med kontakt uden friktion. En 4-leds mekanisme og den relative hastighed af de modsatte led.

En rkke efterflgende vrker fra f.kr. behandler matematikken, geometrien og mekanikken af

uvalgte maskiner. Frst med Heros afhandling Problemer med maskiner i r 100 omhandlendepneumatiske maskiner, optiske instrumenter, vgte og artileri blev der taget hul p designmetodikker. Hans adskildte studiet af specifikke maskiner og generelle koncepter for maskiner frastandardiserede elementer, som i forskellige sammenhnge udgr en maskine. Han introduceredefem simple mekaniske elementer for at lse det generelle problem at flytte en masse med en givenkraft: hjul, aksel, vgtstang, spil, kile og skrue. Hans prsentation var den frste systematiskeudvikling af design lsninger til et givent mekanisk problem. Han tydeliggjorde ogs forskellenmellem hndvrk og ingenirkunst:

The mechanical engineer of Heros school told us that the study ofmachines consists of a theoretical and a practical part. The theoretical partincludes the natural sciences while the practical part consists of the


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engineering disciplines. They postulate that a necessary condition for anable designer of mechanical devices is a solid background in both naturalsciences and practical skills.

Med moderne terminologi understreger dette ogs hvad der krves af en maskiningenir idag. MedHeros skole er behovet for specialisering anderkendt. Det er ikke muligt for nogen at havekompetencer indenfor alle relaterede felter. Desuden klassificeres maskiningenirens arbejde somvrende relateret til flgende: hndtering af masse, militrt udstyr, hydraulik og storsledeopfindelser!Heros arbejde indeholder beskrivelser af en rkke maskiner, som med nutidige jne, ligner legetj.Faktisk er det et designstudie i alternative lsninger til enslignende, grundlggende designproblemer. Hero var meget eksplicit omkring hans intentioner om at skabe originalt design. En msrge for at undg forgngerens design, sledes at enheden vil fremst som noget nyt.Arkimedes (287-212 f.kr.) mestrede alle discipliner indenfor matematik og ingenirvidenskab. Hanvar bde en stor ingenir og opfinder, men hans bger konsentrede sig om anvendt matematik og

mekanik og matematiske beviser. Der er en klar forskel mellem hans arbejde og det senere arbejdeaf Hero. Deres metodikker afveg. Arkimedes var matematisk stringent, Hero anvendte numeriskemetoder.Philo (250 f.kr.) skrev en afhandling om artilleri hvori han beskrev analytiske metoder for design afen ballista (sten kaster). Philo er speciel fordi han som den frste udviklede en design-ligningimperisk baseret og med visse antagelser. For en ballista fandt han at d = (11/10)3100m, hvor d erdiameteren af den snoede line som udgjorde den lagrede potentielle energi i enheden dactyls. m ermassen af stenen med enheden drachmas. Sammen med denne formel introducerede Philo ideen omsimultude. Han postulere at strre maskiner kan bygges med deres dimensioner estimeret ud framindre maskiner ved at bruge sammenhngen: d1/d2 =

3m1/m2. Disse ligninger er de frste derdirekte relatere et objekt til en design parameter. I ligningen er den 3. rod fundet empirisk,konstanten 100 udledt for give sammenhng mellem enhederne og konstanten 11/10 er ensikkerhedsmargin, som tager hjde for fejlen i beregningen af den 3. rod. Sledes introduceredePhilo ogs begrebet om sikkerhedsfaktorer. Cotterell og Kamminga efterviste Philos formel i 1990!Denne metode med et systematisk design blev udbygget af Philo, da han introducerede ideen omflsomhed i et design overfor en designparameter. Hans arbejde var baseret p matematisk analyse,specielt overvejelser om energi bevarelse (F1s1 = F2s2) sknt han ikke var klar over at energien erudtrykt ved produktet af kraft og vej. Med Alexandrias fald endte den grske era indenfor design afmaskiner og emnet blev negliveret indtil romerne tog det op igen.

Rom ersk m ask ind esign

Romerne var ikke store filosoffer men dygtige ingenirer. De opdagede ikke grsk matematik frr 200. Romerne bidrog med dannelsen af professioner og administration. Sledes adskildte debygningsingeniren fra maskiningeniren og var de frste der fokuserede p miljpvirkninger.Deres bidrag er hovedsagelig af empirisk karakter og datidens designere erkendte at standardiseringer vejen frem, nr fremstillingsomkostningerne skal bringes ned og et design skal kunne anvendes iandre sammenhnge.

Arab i sk m ask ind esign

Araberne (700 1200) bevarede det grske arbejde og udvidede det ogs med deres egne bidraghovedsageligt med designet af mekanismer og automater. Ogs systematisk design blev studeret


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med lsninger til problemer med ure baseret p strmning af vand, vandledninger, vaskning afhnder og vandsjler.

Midde la lde r l ig m ask ind esign

I den frste halvdel af den 2. millenium skete der en massiv emigration af grkere til vesteuropa.Dette medfrte at Aristoteles arbejde blev bragt videre og der kom en stigende interesse formekanik og kinematik. Jean Buridan og Albert Rckmersdorf blev begge rektorer p universitetet iParis ca. 1350 og publicerede oversttelser af Aristoteles arbejde.Nicole Oresme (1330 1382) oversatte ogs Aristoteles arbejde og skrev hans egen afhandling ommekanik, hvor han introducerede det Cartesiske koordinatsystem. Han studerede den konstantaccelerede bevgelse og udledte ligningen s = g t2. Desuden indfrte han ideerne om etkontinuum og lagde p mde grundlaget for den moderne kontinuum mekanik. Men i disse tiderblev der ikke fokuseret p design metodikker fr Leonardo da Vinci kom til. da Vinci selvfremlagde ikke desiderede design metodikker, men hans skitser giver udtryk for hvordan hansystematisk udviklede design koncepter til specielle problemer. I hans bger, som frst blevpubliceret 1600 tallet, bliver hans designs fremstillet vha. tegninger, som er vsentlig lettere atforst for hndvrkere end tekst og matematiske ligninger.Behovet for at kunne fastlgge klokken i klostre medfrte udviklingen af pendul uret. Det er enbemrkelses konstruktion som fik stor indflydelse p efterflgende lsninger som startede medGalileos Galilei (1564 1642) arbejde. Det mekaniske urvrk er nok den frste rigtige maskine.Dets oprindelse kan dateres tilbage til Dante (1235 1321).

Rensansen og den i nd us t r i e ll e r evo lu t i on Den tidlige moderne ra ses i lyset af Galileo og Newton og inkludere den frste mekanisering ogden industrielle revolution. Anvendelsen af fossilt brndsel i maskiner medfrte der fre til relativt

mere energy per vgt maskine frste store problemer med sig. Den samtidige udvikling af calculusand kontinuum mekanik medfrte en hurtig udvikling af mekanikken omkring 1850erne. P dettetidspunkt var fysik og mekanik vsentlig mere udvikling end typisk antages. I den anden halvdel af1800 tallet var maskindesign begyndt at have indflydelse p andre end samfundets verste lag. Efterden industrielle revolution kom producenterne i reel konkurrence og produkter til folket begyndte atindholde stetiske vrdier som tidligere var forbeholdt velhavere.Udviklingen af maskiner i det 17. og 18. rhundrede blev stimuleret af udviklingen afdampmaskinen, prcis som udviklingen af ure havde gjort det i det 15. og 16. rhundrede. Mangefremskridt kan fres tilbage til en opfinder, som havde succes med systematisk rsonnement. Watt(1736 1819) beskrev den metode han brugte til at designe en forbindelse, som med densbevgelse skulle beskrive en ret linie. Han var den frste til at overveje koblede punkter og

systematisk syntese af forbindelsesled ud fra kinematiske overvejelser. Euler (1707 1783)grundlagde den kinematiske analyse ved at behandle plan bevgelse som en superposition aftranslation af et punkt og rotationen omkring det. Han brugte en klar adskillelse mellemkinematikken og dynamikken of en mekanisme, hvor det frste kun har med bevgelsen at greuden at tage hjde for de krfter som forrsager den.Tidligere havde Valturius (1472), Agricola (1550) Ramelli (1580) og Branca (1629) altid behandletmaskinerne som et hele eller kun enkelte adskildte dele. Leupold (1724) m have vret den frste,som overvejede mekanismer, som vrende et system bestende af forskellige elementer der erfunktionelt koblet og klassificeret ved den bevgelse de laver. Hans beskriver mekanismer derkonvertere en type bevgelse til en anden.


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Design a f m ask ine r i den m oderne ve rden cole Polytechnique, startet i Paris i 1794, var den frste skole der studerede kinematikken imaskiner. En af skolens ansatte, Hacette, prsenterede en systematisk klassification af mekanismerud fra dere evner. I 1808 foreslog han 6 grundlggende maskinelementer: Modtagere tog imodbevgelse fra primr bevgere. Kommunikatorer viderefrere af bevgelse. Modifikatorer omstter typen af bevgelse. Understtninger. Regulatorer indfre en udvekslings. Operatorer udfrer maskinens funktion. Dette arbejde blev viderefrt af Borgnis i 1818 med en indfrelsen afen klassifikation baseret p mekanismens funktion.I 1830 offentliggjorde Ampre et essay hvori han definerede maskinen som et instrument medhvilket retningen og hastigheden af en bevgelse kan ndres. Han ekskluderede krfterne fra denkinematiske analyse og gav dette studiet navnet kinematik fra det grske ord kinema der betyderbevgelse. Kinematikken er studiet af alt hvad der kan siges om bevgelser, uafhngigt af hvilketkrfter der skaber dem. Coriolis definerede i 1831 det sledes problemet for kinematikken sledes:

To find the motion of any machine in which certain parts are moved in agiven way.

I Cambridge, England, udviklede Willis kinematikken og klassificerede mekanismer ud fra hvordande ndrede retning og udvekslingsforhold og han udledte matematiske funktioner for hvermekanisme ved at anvende trigonometri og andre matematiske metoder. Redtenbacher, professorved Karlsruhe Tekniske Universitet, tog Willis ideer op og prsenterede dem for Reuleaux, somsammensatte et mekanisk alfabet for hans egne mekaniske enheder for at klassificerede dem. Ideenvar at klassificere mekaniske systemer p samme mde som det var sket indenfor biologien. Detblev til et komplet vrk fra 1875 om kinematik med titlen Theoretische Kinematik, som blevoversat til engelsk Kinematics of Machinery af Kennedy. Reuleaux brugte ogs tid p

mekanikken i den menneskelige krop.Rankines bog fra (1869) indfrte begrebet om en ramme. Han ans maskinen som opbygget af enramme hvor til bevgende dele refererede. Selv om introducerede elementr kombination afelementer, s var hans arbejde mindre generelt end Reuleaux. I efterflgende lrebger varhovedsageligt Reuleaux metodikker som blev prsenteret.Slutningen af det 19. rhundrede indebar afslutningen af en formativ periode. Efter en tid hvormange principper var blevet vist og analytiske metoder var blevet etableret. Vejen til syntese varblevet lagt og efterflgende bredte ideerne sig hurtigt til resten af verden. Da den industriellerevolution rullede i England blev mekaniseringen af produktionen indfrt, men dette frte ikke tilanderledes design metodikker. Revolutionen frte til en adskillelse af form og funktion fordi der varmodstridende interesser blandt forbrugerne, som var den nye middelklasse, og akademikere

diskuterede stetikken i industriel produktion. Industrien selv sgte nyskabelse ved at f inspirationfra gamle kulturer. Disse konflikter skadede den naturlige udvikling af formen og stod i kontrast tiludviklingen af produkters funktion. Fra Coles Journal of Design i 1850:

Design has a twofold relation, having in the first place a strict referenceto utility in the thing designed; and secondary, to beutifying or ornamentingthat utility. The word design, however, with the many has become identifiedrather with its secondary than with its whole signification with ornament, asapart from and often as opposed to, utility. This was the reason for many ofthose great errors in taste which are observed in the works of manydesigners


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Sym bo l sk r ep r esen t a t i on g r uppe t ekno l og i Gruppe teknologi er udviklet for godt 200 r siden. Efter automatisation i produktionen ogstandardiseringen af maskinelementer indfrte den svenske ingenir Christopher Pohlem (1661 1751) det mekaniske alfabet, en samling af forskellige komponenter markeret med et bogstav fraalfabetet. Enhver mekanisme kan syntetiseres ud fra elementerne i alfabetet.Igennem det 17. og 18. rhundrede havde den symbolske reprsentation af mekanismer vret brugtaf urmagere. I 1826 foreslog Babbage den frste komplette symbolske beskrivelse af funktion oggeometri af en forbindelse. Willis forsgte i 1841 at forbedre Babbage kinematiske notation tilmekanisk design generelt, men det blev Reuleaux som prsenterede en gennemfrt beskrivelse ogsymbolsk reprsentation mekanismer. Han definerede maskinen som en kombination af fastelegemener (solid bodies), arrangeret s de kan optage og viderefre de mekaniske krfter for atudfre et arbejde som et resultat af en forudbestemt rkkeflge af bevgelser. Hans ml var ikke atstudere en specifik maskine, men at fastlgge betingelserne som er ens for alle maskiner. Han ansdet for vigtigt at analysere hvordan opfindere havde opnet deres lsninger. P den mde var

Reuleaux den frste fuldt ud hengivet til den kinematisk syntese og efterflgende symbolskrepresentation af viden.

Udv i k l i ngen af des ignm etod i kk e r I Frankrig p cole Polytechnique blev en systematisk indgangsvinkel til designanalyse forsgt ligeefter de Napolionske krige. Behovet for at kontrollere dampmaskinen medfrte en rkkeundersgelser af kinematik og design af forbindelser. Syntesen af forbindelser kan ses som enformel design metode. Fordi, det er begrnset til udelukkende forbindelser kan dette ikke anses somen generel mekanisk design teori.I Tyskland skabte den von Humboldte model for universiteterne et tt samarbejde mellem deakademiske miljer og industrien i modstning cole Polytechnique, der udelukkende var en

militr skole finansieret af den franske stat. For Tyskland betd det en srlig udvikling indenforden praktiske ingenirvidenskab. Redtenbacher introducerede generelle mekaniske designprincipper:

Tilstrkkelig styrke. Tilstrkkelig modstand imod slid. Tilstrkkelig lav friktion. Optimalt brug af materialer. Let fremstilling. Let vedligeholdelse.

Simpelt

Redtenbachers principper er modstridende og overlappende til at kunne anvendes som axiomer i endesignteori. Et more abstrakt st af designprincipper blev udviklet af Reuleaux i 1854, somadskildte formen og funktionen af maskinen i to regler:

1. Funktion: Designet skal give en ensartet tilfredsstillelse af designkravene. F.eks. nr en lastskal fordeles, s skal alle dele jvnt bidrage til understtningen.

2. Form: Formen af designets krop skal beside strst mulig symmetri.

Det frste princip kan opfattes som en optimeringskrav. Ens lastet dele medfrer maksimalt brug af

materialet. Det samme som Redtenbachers 4. punkt. Det betyder, at nr designet brister, s brister


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det overalt. Det andet princip kan opfattes som et princip om minimum information. Det er tildelsafhngigt af det aktuelle design, og ikke totalt uafhngigt af det frste princip, fordi symmetri ofteresulterer i lavere fremstillingsomkostninger. Reuleaux principper frte til overvejelser om hvordanform og funktion kan indfres med balance imellem to to for je.

Bde Heinrich (1892) og Riedler (1913) inds at valget af materiale og fremstillingsmetoden og etdesign hvor tilstrkkelig styrke er opnet er lige vigtigt for succes af et design og at disse ting harindflydelse p hinanden. Roetscher (1927) overvejede de vsentligste karakteristika for et design:Det skal have specifikt forml, effektive veje hvor i krfter overfres (lastoverfrelse) og effektivfremstilling og samling. Lastoverfrelse skal flge den kortest mulige vej og hvis muligt somaksiale krfter i stedet for bjningsmomenter. Lange lastoverfrelsesveje spilder materiale, gerprisen og medfrer oftest en mere kompleks form geometri. Laudien (1931) foreslog hvorledeslastoverfrelsen br ske i maskindele:

For en sitv forbindelse, saml dele i samme retning som lasten.

Hvis fleksibilitet er krvet, s saml dele langs indirekte lastveje. Lav ikke undvendige foranstaltninger. Overspecificer ikke. Opfyld ikke mere end de opstillede krav. Spar gennem simplificeringer og konomisk konstruktion.

De moderne ideer om systematisk maskindesign blev prsenteret af Erkens (1928), da hanintroducerede en trinvis tilgang til designet. Ideen er baseret p en iterativ udvikling af systematisketests, evalueringer og med balance mellem krav der konflikter. En mere prcis gennemgang afdenne metode blev skrevet af Wgerbauer (1943) der introducerede ideen om opgave

dekomponering, dvs. adskillelsen af designprocessen i underliggende opgaver, som var endtenopeationelle eller implementerende. Hans tilgang starter med intuitivt at sge et design. Denneinitielle lsning blevet s modificeret mht. dets struktur, materialer og fremstillingsmetoder for atopn en kontinuert evaluering og forbedring af designet.Ad flere omgange prsenterede Kesselring en metode til succesive approksimationer og evalueringaf design variationer i forhold til et st tekniske og konomiske krav, som skal opfyldes sammenmed de underliggende ingenirvidenskabelige principper:

Minimum produktionsomkostninger Minimum rumlige krav. Minimum vgt.

Minimum tab. Optimal hndtering.

I 1956 introducerede Hansen fire skridt i designprocessen, som efterflgende blev forbedret afMueller (1970) og Yoshikawa (1983), s der blev dannet et fundament for designteori:

Analysis, kritik og specifikation af opgaven, som frer til et grundlggendelsningskoncept, som opfylder de overordnede funktionskrav, som er udledt fradesignopgaven.

En systematisk sgning efter lsningselementer og deres kombination til et brugbart

koncept.


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Analysis af problemerne med flere brugbare koncepter, hvor der tages hensyn til mlene fordesignet og eventuelt forbedringer.

Evaluering af disse forbedringer indfrt p koncepterne for at bestemme det bedste konceptfor opgaven.

Rodenacker videreudviklede metoden til systematisk design af et brugbart design koncept i 1970 og1991. Han brugte igen en trinvis tilgang for at opbygge en plan over sammenhngene mellemmaskinens logisk, fysisk og udformning. Han tilfrte en systematisk identifikation af fejlmulighederi designet ved kvalitativt, kvantitativt og konomisk at evaluere ethvert tidligt design skridt. Hanbaserede sin design metodik p logiske funktionsstrukturer forbundet via binr logik og opnede engennemgribende opgave dekomponering.Mlet med Roth (1994) arbejde er at inddele designprocesen ind i sm skridt, som kan beskrivesved en algoritme. P den mde skal det blive muligt at disse skridt fuldt ud og kontinuertli vha. encomputer. Det skal lede til en entydig produktmodel. Roth inddelte designprocessen i tre faser medtre tilhrende modeller:

1. fase: Problemformulering og modeller til representation af problemer, en kravspecifikationsom identificerer de vsentlige designopgaver og designkrav.

2. fase: Funktionalitet og tilhrende modeller, som inkludere logiske funktions strukturer;funktionsstrukturer som viser sammenhnge med strmmen af materiale, energi oginformation; fysiske funktions strukturer som viser fysisk, kemisk og andre effekter. Fysiskelsningsfunktioner.

3. fase: Indkorporering. Modeller der representere udformningen med geometrisk funktionellestrukturer baseret p allerede designede moduler og funktionelle elementer.

Endelig blev der i 1996 opstillet en model for designprocessen af Pahl og Beitz. Den er baseret pflgende faser:

Afklaring af opgaven: Saml information om kravene som skal indkorporeres i lsninger ogoplysninger om eventuelle bindinger.

Koncept design: Etabler funktionsstrukturer, sg efter brugbare lsningsprincipper ogkombiner dem til variationer af koncepter.

Udformningen af designet: Start fra konceptet, fastlg udformningen og formen og udvikl etteknisk produkt eller system i overensstemmelse med tekniske og konomiske overvejelser.

Detail design: Indfr arrangementet, formen, dimensionerne og overflade egenskaberne afalle individuelle dele. Specificer materialer og check igen den tekniske og konomiske

anvendelighed. Fremstil alle tegninger og anden produktions dokumentation.

I 1989 fremlagde Koller en algoritme til at beskrive designprocessen, s den kan implementeres i encomputer til automatisering af designfasen. Han udviklede 12 funktioner og deres inverse, som hankaldte for de grundlggende operationer, som beskriver strmningen af energi, stof og informationi maskinen. I funktionssyntesen, kobles de grundlggende operationer i en funktionsstruktur. I enkvalitativ syntese anvendes de fysiske effekter, overfring af effekt, principielle lsninger ogvariationer over disse til den endelig udformning. I en kvantitativ syntese, dimensioneresudformningen og der fremstilles produktionsdokumentation.


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Metodikker til maskindesignDe efterflgende afsnit er udvalgte uddrag fra Machine Design af Andrew D. Dimarogonas.

Dodge Intrepid. One of the first machines to be designed and manufactured with the concurrentengineering procedure.

Designing a machine is a long road. Its beginning is a vague initial description of the machine

design problem to be solved. Its end, is a concrete and unambiguous description of the machine,usually in the form of detailed design drawings of the whole machine and every single part of it,including a parts list describing the materials and the manufacturing processes by which every partwill be made. This description enables a manufacturing facility to make the machine exactly as thedesigner intended it.This chapter shows how we can develop a multitude of possible solutions and identify the mostpromising solution concept, described in generic form, usually in the form of a schematic thatdescribes the machine's operation and a set of detailed design specifications.

THE ART AN D SCI ENCE OF MACHI NE DESI GN

To an ever-increasing extent, our immediate visual environment is dominated by machinery andindustrial products. In the home and workplace, in schools, factories, offices, shops, even recreationareas, in public streets and transport systems, machines constitute the visible cultural landscape ofeveryday life, comprising in their totality a complex pattern of function and meaning in which ourperception of the world, our attitudes and sense of relationship to it, are closely interrelated.Because machines are themselves products of other machines, with a precision the human handcannot match, their space and design rarely yield to the layman any indication of the participationand personality of the designer and manufacturer. They are all, however, a manifestation of aprocess of a human design, of conception, judgment, and specification. The precise nature of thedesign process is infinitely varied and therefore difficult to summarize in a simple design formula,or book of formulas, or a precise definition.

It can be the work of a person. It can be the effort of a team. It may emanate from creative intuition, from executive decisions based upon

market research, or from a calculated judgment. It may be constrained by resource availability or organizational, political,

social and aesthetic considerations, aiming of course at acceptance by theend user, the customer.

Whatever the particular situation, machine design, as defined in the previous chapter, is a process ofcreation, invention, and definition, involving an eventual synthesis of contributory and often


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conflicting factors into a three-dimensional form capable of multiple reproduction, at marketableprice, with acceptable quality of products and with specified reliability (Orlov 1976).Machine design is an applied science relying heavily on engineering science because no machinecan defy Newton's Law or the strength limits of the materials the machine is made of.

Machine design is also an art (Dimarogonas 1997). A strength of materials problem usually has onesolution. A machine design problem usually has an infinite number of solutions. In roughmathematical terms, the number of unknown parameters is usually orders of magnitude greater thanavailable data or performance specifications, that is, equations. This uncertainty can be eliminatedto a small extent by optimization methods and to the full extent by good technical judgment by thedesigner. What is "good" and what is "bad" technical judgment? Though experience hasaccumulated rules, the final judge is the end user and the quantitative measure of acceptance ismarket success.With the dissemination of information the world is experiencing in our times, competing designershave at their disposal about the same amount of information. Proprietary information is usuallymuch less in reality than advertised. Why is one product (and the manufacturer) successful and the

other not? In most cases the main reason is the decisions made at design stage, not of course thosebased on engineering science but those based on engineering (and business) judgment.As stated above, this cannot be corrected with concrete rules. There are, however, guidelines thatcan help the designer with the decisions he has to make for a successful design. A product designed"by the book" is not guaranteed success. It is almost certain, however, not to be a total failure.

Classification

A machine is a device for doing useful work, such as manufacturing and transporting goods.Depending on the nature of its useful function, a machine may be simple or complex, fragile orstrong. Before the industrial age, machines were simple and low-powered, most of them very crude

devices designed to relieve people of backbreaking burdens such as lifting heavy loads, as in miningoperations and milling grain. Humans and animals, sails, windmills, and waterwheels providedpower for these early machines. The power produced by these sources were clearly adequate for theeasy tasks of the time. Thus, the lack of sources of highly concentrated mechanical power providedlittle incentive for anyone to make machines that were faster or more powerful. We have seen in theHistorical Introduction that crude steam and heat engines were invented by Hero of Alexandriaabout two millennia ago, but the needs and means of production at that time could not make use ofthese inventions. Thus, technical progress was slow, with few exceptions, in the fields of mechanicsand metallurgy. The development of the steam engine and the harnessing of the chemical energy incoal, just prior to the Industrial Revolution, provided the incentive needed for humans to build morecomplex and powerful machines.

Invention of the modem steam engine by James Watt in 1769 gave people the mechanical powerrequired for large-scale industry and mass transportation. Use of the steam engine for minepumping and railroads led to other and much improved power sources, such as the current internalcombustion engines, the turbine, the jet engine, and the rocket. In 200 years (1769-1969), humanityadvanced technically from a primitive steam engine to a powerful rocket engine that would carrypeople to the moon. The invention of the steam engine was one of the most important events inhistory.The explosive nature of the Industrial Revolution underscores the fundamental fact that industrialproduction is much more dependent on available sources of power than on supplies of raw materialsand production tools.The most dramatic development in the history of the machine came, no doubt, with the introduction

and rapid development of automatic operations, machines directed by machines instead of by


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humans. Termed automation, this interrelationship among machines initially depended on linkagesand cams, then on punch cards, and finally on magnetic tape and electronic equipment to direct andcontrol mechanical processes without the constant attendance of operators. At the heart ofautomation is the computer, a cybernetic machine for processing, storing, and retrieving

information.Another way of looking at the machine is that it enables work to be done with greater ease or speedthan would be obtainable without its use. The term is most commonly applied to mechanisms usedin the industrial arts for shaping and joining materials. Machines are frequently named from theiruse (e.g., screw cutter) or from the product made (e.g., bolt maker). Compound machines areformed when two or more simple machines are combined. Tools are the simplest implements of theindustrial art. Machines, on the other hand, are more complicated in structure.When machines act with great power, they generally take the name of engines (e.g., internalcombustion, steam, or aircraft).A machine is therefore essentially a structure consisting of a frame with various fixed and movingparts. The parts are rigid or resistant and are relatively constrained so that they can transmit power,

modify force or motion, and do useful work. In short, a machine is a device that transmits andchanges the application of energy.Machinery is a derived term used to represent (1) the internal working parts of a complex assembly,usually of large size, and (2) a grouping, such as the machinery of a plant or mill. Machines can beclassified broadly as basic or simple and complex or compound. A simple machine is a device withat least one mechanically actuated member (lever or screw) (Figure 1.1). A complex machine ismerely a combination of simple machines, as exemplified by a typewriter (Hinhede et al. 1983).Complex machines may be classified as stationary, portable, or mobile. As the name implies,mobile machines, such as self-propelled combines or street sweepers, move themselves in doinguseful work. This group includes all means of transportation, farm machinery, and constructionequipment. Stationary machines include most factory production machinery. Portable machines areprimarily items such as power tools, chain saws, and vacuum cleaners; that is, the user can carrythem.Complex machines are also classified as prime movers, secondary movers, and power-driven. Anymachine that utilizes a natural source of energy to produce power for other machines is a primemover. An automobile engine is a prime mover that converts the chemical energy of the fuel intomechanical energy. This in turn is used to propel and direct the entire vehicle along some selectedpath. An electric motor, by contrast, is a secondary mover because it receives energy directly orindirectly from a generator driven by a prime mover, usually a steam turbine. A power-drivenmachine or power absorption unit utilizes energy to do useful work. Typical power-driven machinesare pumps, machine tools, and air compressors.

Machines are thus dual in their makeup: they all have a power source separate from the parts doinguseful work. The power supplied to a machine is called input power, while the power delivered by amachine is called output power. Thus, the output power of one machine becomes the input power ofthe driven machine. It is common to have a single place for power input and another for outputpower. Some machines, however (e.g., trucks and tractors), have two output shafts, one to propelthe vehicle and another to drive accessories.


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Figure 1.1.

Five simple machines have been known since the time of Hero of Alexandria): lever; windlass,pulley and axle, wedge, screw (Figure 1.1). Simple machines provide a mechanical advantage (MA)by increasing force at the expense of speed; herein lies their primary importance. Sometimes,however, they are used in reverse to augment speed at the expense of force (MA < 1). The highspeeds of vehicles, for example, are obtained by using the wheel and axle with MA < 1.

The Traditional Machine Design Procedure

Machine design is a systematic process. Even if a new machine was conceived by invention,systematic machine design is needed to transform the invented concept into a working system thatusers will appreciate.The machine design process is subject to a large number of variations. In every text on the subject

of engineering design, a different division of the design process in distinct stages is proposed. Theyall make sense, although they seem very different from one another. This reflects the complexnature of the design process and the fact that every design problem requires a special treatment.This process cannot be exactly specified by an equation or an algorithm. A systematic approach isuseful only to the extent that the designer is presented with a strategy that he can use as a basis forplanning the required design strategy for the problem at hand.This strategy, proposed by Sandor (1964), is described in the flowchart of Figure 1.2. The flowchartis arranged in a V-shaped structure.

1. The two upper branches of the Y represent, on one hand, the evolution of the design task,and on the other hand, the development of the available, applicable engineering background.

2. The junction of the Y stands for the merging of these branches: generation of designconcepts.

3. The leg of the Y is the guideline toward the completion of the design, based on the selectedconcept.

The flowchart implies, but is not encumbered by, the feedbacks and iterations that are essential andinevitable in the creative process.


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Figure 1.2. Sequential design procedure. (Reprinted from G. N. Sandor, "The Seven Stages of

Engineering Design," Mechanical Engineering, 86(4) (1964):21, by permission of the AmericanSociety of Mechanical Engineers.)


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Stage IA: Confrontation. The "confrontation" is not a mere problem statement; it is the actualencounter of the engineer with a need to take action. It usually lacks sufficient information andoften demands more background and experience than the engineer possesses at the time.Furthermore, the "real need" may not be obvious from this first encounter with an "undesirable

situation."

Stage IB: Sources of infonnation. The sources of information available to the engineer encompassall human knowledge. Perhaps the best source is other people with expertise in the same or relatedfields.

Stage 2A: Fonnulation of problem. Because confrontation is often so indefinite, the designers mustclarify the problem that is to be solved: they must recognize and ferret out the "real need" and thendefine it in concrete, quantitative terms suitable for engineering action.

Stage 2B: Preparation of infonnation and assumptions. From the vast variety of sources of

information the designer must select the applicable areas, including theoretical and empiricalknowledge, and, where information is lacking, fill the gap with sound engineering assumptions.

Stage 3: Generation and selection of design concepts. Here the background developed by theforegoing preparation is brought to bear on the problem as it was just formulated, and allconceivable design concepts are prepared in schematic skeletal form, drawing on related fields asmuch as possible.

It should be remembered that creativity is largely a matter of diligence. If the designer lists all theideas that can be generated or assimilated, workable design alternatives are bound to develop, andthe most promising can be selected in the light of requirements and constraints.

Stage 4: Synthesis. The selected design concept is a skeleton. We must give its substance: fill in theblanks with concrete parameters with the use of systematic design methods guided by intuition.Compatibility with interfacing systems is essential. In many areas, advanced analytical, graphical,and combined, computer-aided methods have become available. However, intuition, guided byexperience, is the traditional approach.

Stage 5: Analyzable model. Even the simplest physical system or component is usually too complexfor direct analysis. It must be represented by a model amenable to analytic or empirical evaluation.In abstracting such a model, the engineer must strive to represent as many of the significant

characteristics of the real system as possible and necessary, commensurate with the available time,methods, and means of analysis or experimental techniques. Typical models: simplified physicalversion, free-body diagrams, and kinematic skeletal diagrams.

Stage 6: Experiment, analysis, optimization. Here the objective is to determine and improve theexpected performance of the proposed design.

1. Design-oriented experiment, on either a physical model or its analog, must take the place ofanalysis where the latter is not feasible.

2. Analysis or test of the representative model aims to establish the adequacy and responses ofthe physical system under the entire range of operating conditions.


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3. In optimizing a system or a component (getting the most out of it-see Chapter 7), theengineer must decide three questions in advance: (a) With respect to what criterion orweighted combination of criteria should he or she optimize? (b) What system parameterscan be manipulated? (c) What are the limits on these parameters; that is, what constraints is

the system subject to?

Although systematic optimization techniques have been and are being worked out (see Chapter 7),this stage is largely dependent on the engineer's intuition and judgment. The amount of optimizingeffort should be commensurate with the importance of the function or the system component and/ orquantity involved."Experiment," "analysis," and "optimization" form one integral "close-loop" stage in the designprocess. Their results may give rise to feedbacks and iterations involving any or all of the previousstages, including a possible switch to another design concept.

Stage 7: Presentation. No design can be considered complete until it has been presented to (and

accepted by) two groups of people:

1. Those who will utilize it2. Those who will make it

The engineer's presentation must therefore be understandable to the prospective user and contain allthe details necessary to allow manufacture and construction by the builder.

The Concurrent Engineering Machine Design Procedure

In recent years it has been observed that the sequential approach to the design procedure, as

outlined in the previous section, has some implementation advantages from an organizationstandpoint, such as:

Simple organization, well-defined responsibilities of each of the sections ofthe organization.

Easy and simple communication: at the end of each step, information issimply "thrown over the wall to the next section."

This method, however, has several shortcomings:

Because the duration of the product cycle development is the sum of the

durations of the different design steps, the product cycle from confrontationto production is very long.

During the process there is a need for several iterations due to the late inputfrom the sections down the serial structure and the development cost andtime increase.

The input of the manufacturer and the user arrives too late or is notconsidered at all so that the final product is of inferior quality.

The solution of the problem is the formation of multifunctional design teams that include personnelof all sections-activities of the design/manufacturing/ production/ distribution/finance/marketingcycle so that the development of the design is concurrent in all fronts (Figure 1.3).


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Concurrent engineering is the ideal of planning and implementing all machine development steps,from early product conceptualization to delivery and service, as early as possible. Team membersare responsible for each step, working together throughout.In the traditional machine development process, each step is conceived of as a unit with clear inputs

and outputs. Steps further downstream, such as manufaduring process development, are notsupposed to start until the results of previous steps, such as component design, are well defined.This production-line view of the development process assumes that time is wasted in downstreamsteps if upstream steps have not yet been completed, with plans solidified.Although it is true that downstream work must take upstream decisions into account, the majorproblem not dealt with in the traditional model is that upstream steps may arrive at results that areunrealistic, impractical, or not optimal for downstream implementation. For example, the engineermay unwittingly choose a design that is unnecessarily difficult to manufacture or is expensive torepair in the field. Automobiles have been made that required removal of the engine for changingthe spare plugs.Manufacturing and field support interaction with the designers could influence those decisions and

thereby lower the company's downstream costs.The best approach to making upstream and downstream decisions is an interactive one, in whichrepresentatives from all functions collaborate, sharing their decision-making processes throughout.In such a dynamic, give-and-take scenario, realistic decisions can be made that achieve the best,most workable results for all functions.

Figure 1.3. Sequential and concurrent engineering processes: (a) sequential; (b) concurrent.

The concurrent engineering model aims at starting all development process steps as early aspossible, even simultaneously (Figure 1.3). Its success comes from each step influencing the otheras the development process moves forward. With sufficient communication between peopleresponsible for each step, practical and optimal results are more likely for all steps.The method by which communication can occur frequently enough and at a detailed enough level toachieve these desirable results is to treat the people responsible for each development step as asingle "multifunctional" team, located together, and all with the same objective-the success of their

jointly developed product. More and more U.S. companies are adopting this style of product devel-opment, often referred to as "project," rather than "functional," organization. The objectives of such"project" organization are (Clausing 1994):

Earlier start of each development step, leading to earlier completion of allsteps.

Optimization of decisions at every step through dialogue and collaborationby representatives from all disciplines, leading to optimal product designand low production and delivery costs.

Overall lower development cost.


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Axiomatic Foundation and Fundamental Rules of Machine Design

Since very early times, designers have been confronted with the question of the feasibility of a

design theory, that is, the existence of a set of concrete principles upon which design can bedeveloped as a science using mathematics and reason.In the Historical Introduction we saw that F. Redtenbacher introduced design synthesis(Konstruktion), a systematic methodology for finding design solutions to machine design problems,and a set of general mechanical design principles:

Sufficient strength Sufficient resistance to wear Sufficiently low friction Optimum use of materials Easy manufacturing Easy maintenance Simplicity

Redtenbacher's principles are too contradictory and overlapping to some extent to become a formalsystem of design axioms. A more abstract set of design principles was introduced by his studentReuleaux (1854), professor at Zurich and Berlin, who separately addressed the function and theform considerations in the following two ground rules (Grundsiitze) of machine design (Reuleaux1876):

1. (Function rule): The design must provide a uniform satisfaction of the design requirements.

2. (Fonn rule): The form of the design embodiment must have the highest possible symmetry.

The first principle can be regarded as an optimization principle. It means that all the(nonreplaceable) parts of the machine should fail at the maximum value of the machine loading. Inother words, if a part fails, every part should fail. There is no point in letting half of the machine failwhile the rest remains intact. The part that did not fail was overdesigned and thus more expensivethan needed.The second principle is essentially a minimum information principle and aims at minimizing theresources needed for the manufacturing of the machine.In recent years, the need for a rigorous foundation of the design and manufacturing sciencesprompted Suh (1988) to introduce a modified form of Reuleaux's design principles as design

axioms, which stirred a very productive discussion on the subject:

Axiom I (function rule): The design should independently satisfy the design requirements.Axiom II (jonn rule): The design should have minimum information content.

While axiom II is essentially the same as Reuleaux's ground rule 2, axiom II sounds similar toReuleaux's ground rule 1 but is not quite the same. The mathematical form of axiom I is that theevery functional requirement of the design is related with only one design parameter and one designequation.The next problem is whether we should speak about rules or axioms. Aristotle (384-322), in hisPosterior Analytics, defined an axiom as "truth par excellence."


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Example 1.1 With the limited knowledge of what goes into the design of a Boeing 747 aircraft.discuss the application for that design of (a) the Reuleaux design rule, (b) the Sub design axioms,(c) the revised design rules.Solution The Reuleaux design rules: Rule I appears to be satisfied because there are no reports of

failures of one particular system of the aircraft while the others are yet intact. This is partly due tothe fact that the FAA demands certain parts to be changed at regular intervals. Rule 2 is nearlysatisfied, with one notable exception: the fuselage is not exactly a solid of revolution. Symmetry istradedoff for other operational requirements.The Suh axioms: Axiom 1 is not satisfied because, for example, the number of passengers specifiedis not related with one only design parameter (Le., length) but with many others (dimensions,engine thrust. etc.). Axiom 2 is nearly satisfied in the sense of satisfaction of Reuleaux rule 2,discussed above.The modified design rules: Both rules appear to be satisfied; better, from what is commonly known,there is no indication of violation of these rules.

CONCEPTUAL M ACHI NE DESI GN

Clarifying the Design Task

A designer has to start from some basic information when confronted with a designtask. Sources of the information and the assignment might be:

An assignment by a planning organization or customer; such an assignmentgenerally specifies the required parameters of the machine and the field andconditions of its use

A technical suggestion initiated by a designing organization or a group of

designers A research work or an experimental model based on the research An invention proposition or an invention prototype An existing machine prototype, which has to be reproduced with

modifications and alterations

As stated in the previous section, design starts with the confrontation with a particular problem, ataskassociated with a number of (usually loosely) defined specifications or requirements. A phaseof further data collection must then be initiated (Pahl and Beitz 1996). One starts with some initialquestions:

What is the problem really about? What implicit wishes and expectations are involved? Do the specified constraints actually exist? What paths are open for development?

Any idea for a solution should be subject to some initial scrutinizing questions:

What objectives is the intended solution expected to satisfy? What properties must it have? What properties must it nothave?


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Design requirements are distinguished as demands and wishes:

Demands are requirements that must be met under all circumstances,requirements without which the solution is not acceptable: e.g., for the

design of a car, gasoline consumption better than 20 miles to a gallon,satisfaction of federal standards of safety. Wishes are requirements that should be satisfied if possible, sometimes

further classified as of major, medium, or minor importance: e.g., for thedesign of a certain automobile, major importance wishes are gasolineconsumption better than 25 miles to a gallon and a certain maximum noiselevel and minor importance wishes might be gasoline consumption betterthan 35 miles to a gallon or indication of low tire pressure.

The list of demands and wishes should be distinguished as quantitative and qualitative:

Quantitative: All data involving numbers and magnitudes, such as,maximum weight, power output, throughput rate, volume flow rate.

Qualitative: All requirements that cannot be quantified, such as, waterproof, corrosion proof, aesthetically pleasing.

In the search for solutions, abstraction is used. This means ignoring what is particular or incidentaland emphasizing what is general and essential for the design of a particular machine leadingdirectly to the most important aspects of the design task.


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Requirement Numerical Value D(emand), W(ish)Basic Design Parameters:

Motor mains 3PH, -60 Hz, 120/220 V DWater flow 30 m3/hr DPump head 50 m DFluid city water D

Operation:

Noise and vibration (Low, residential building) WFully automatic operation DMotor overheat alarm WNo water in suction alarm D

Maintenance:

Lubrication permanent, no attendance 1 time/year W

Filter change in operation WTABLE 1.1. Requirement List for a Motor-Driven Water Pump

Consider, for example, the design of a water pump system. The task is described by means of anabstract sketch (Figure 1.4) where only the critical parameters are shown and not the noncriticalones, such as color. In addition are a requirements list and the formulation of the goal to beachieved-for example, the water pressure and flow and the characteristics of the power sourceavailable. The designer should also ask about other requirements, such as:

Improving quality, e.g., efficiency, durability, reliability Reducing weight or space Lowering costs Shortening delivery time Improving manufacturing methods

The next step is to analyze the requirements list in respect of the required function and essentialconstraints of the problem. The functional relationships contained in the requirements list should beformulated explicitly and arranged in order of their importance.This analysis, coupled with a step-by-step abstraction, will reveal the general aspects and essentialfeatures of the task, as follows:

Eliminate personal preferences. Omit requirements that have no direct bearing on the function and the

essential constraints. Transform quantitative into qualitative data and reduce them to essential

statements. Generalize the results of the previous step. Formulate the problem in solution-neutral terms.

Depending on either the nature of the task or the size of the requirements list, or both, certain stepsmay be omitted. For example, let us examine the task of improving the method of filling, storing


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and loading bags of animal feed (Krick 1969, Pahl and Beitz 1996). An analysis gave the situationshown in Figure 1.5.Some of the possible formulations would be:

Filling, weighing, closing, and stacking bags of feed Transferring feed from the mixing silo to stacked bags in the warehouse

Figure 1.4. Abstract sketch of a water pump system.

Figure 1.5. Method for filling, storing, and loading bags of feed. (Reprinted from E. V. Krick, AnIntroduction to Engineering and Engineering Design, 1969, by permission of John Wiley & Sons.)

Transfening feed from the mixing silo to bags on the delivery truck Transfening feed from the mixing silo to the delivery truck Transferring feed from the mixing silo to a delivery system Transfening feed from the mixing silo to the consumer's storage bins

Transfening feed from ingredient containers to the consumer's storage bins


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Transfening feed ingredients from their source to the consumer

Krick (1969) incorporated some of these formulations in a diagram shown in Figure 1.6. Theproblem formulation was systematically made as broad as possible in successive steps. Some

examples of abstraction and broad problem formulation are (Pahl and Beitz 1996):

Do not design a garage door, but look for means of securing a garage insuch a way that the car is protected from thieves and the weather.

Do not design a keyed shaft, but look for the best way of connecting gearwheel and shaft.

Do not design a packing machine, but look for the best way of dispatching aproduct safely or, if the constraints are genuine, of packing a productcompactly and automatically.

Figure 1.6. Alternative methods for filling, storing, and loading bags of feed. (Reprinted from E. V.Krick,An Introduction to Engineering and Engineering Design, 1969, by permission of John Wiley& Sons.)

Do not design a clamping device, but look for a means of keeping theworkpiece firmly fixed.

The final formulation can be derived in a way that does not prejudice the solution, that is, is

solution-neutral, and at the same time turns it into afunction, rather than a device:


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"Seal shaft without contact" instead of "Design a labyrinth seal." "Measure quantity of fluid continuously" instead of "Gauge height of liquid

with a float."

"Measure out feed" instead of "Weigh feed in sacks."

Design Specifications-Quality Function Deployment

The requirements listis the initial starting point for the design of a machine. However, the designgroup needs to reformulate these requirements in much more concrete terms that will berecognizable by all members of the team and will be more quantitative than qualitative so that theresults of evaluating different designs will be more concrete.A successful machine design effort many times indicates good planning, which starts with a cleardefinition of the design objectives and particular specifications. We distinguish here the specific

design objectives and design specifications from the clarification of the task of the previous section.Definition of the design objectives and specifications will provide guidance during the course ofdesign, but it will also eventually be used to judge the result of the design effort.The design objectives have the form of clearly stated specifications for the machine to be designed.Specifications for the machine are imposed from the task and also for safety reasons, availability ofcertain raw material, cooperation with other machines in production, and so on. Specifications forthe product of the machine are always imposed.Usually the starting objective is cost of the machine itself and of production. Many other objectivesmay be stated for the machine or its products without an immediate cost interpretation, such asappearance, surface texture, noise, and environmental impact.The machine should not be overspecified, that is, the design objectives should always be the

minima of the acceptable limits. Overspecified machines have an unnecessarily high cost. A friendof mine, a layman, told me once that he would file a lawsuit against Omega because his wristwatchwas accurate only to 1/ 10 of a second while at the time of purchase they told him that it wasaccurate to 11100 of a second. Obviously in this case the watch was overspecified.Overspecification also reduces creativity because it imposes restrictions and removes freedom fromthe designer's imagination and inventiveness.A systematic way in developing the design objectives with the broadest possible input has been themain achievement of quality function deployment (QFD). QFD was first developed in Japan toensure that the customer's requirements are met throughout the design process and also in the designof production systems. It was originated at Mitsubishi's Kobe shipyard site in 1972, based on worksof Yoji Akao, a professor of industrial engineering in Tokyo. Toyota started using QFD in the mid-

1970s and achieved impressive results. In the launch of their new van (January 1977 to October1979), they achieved a 20% reduction in startup costs, and by 1982, startup costs had fallen 38%and by 1984, 61 %. Development time fell by one third, and quality improved markedly. The firstU.s. implementations began in 1986. Ford, GM, and Xerox started training in 1986, and by 1988many companies were using QFD in design.The QFD process involves constructing one or more requirements development matrices (RDM)(sometimes called quality tables). The first of these matrices is called by many authors the house ofquality (HOQ). It displays the requirements list(the voice of the customeror the whats) along theleft (A) and the development team's technical response to meeting those wants, the design technicalspecifications, along the top (C). The requirements list is related to the technical specifications byway of a correlation matrix (D) that might consist of several sections or submatrices joined together

in various ways, each containing information related to the others (Clausing 1994) (Figure 1.7).


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Each of the labeled sections, A through F, is a structured, systematic expression of a product orprocess development team's understanding of an aspect of the overall planning process for a newproduct, service, or process. The lettering sequence suggests one logical sequence for filling in thematrix.

Figure 1.7. House of quality. (Reprinted from D. Clausing, Total Quality Development, 1994, bypermission of ASME Press.)

QFD authorities differ somewhat in the terminology. In general:

Section A contains a structured list of customer/user wants and needs. Thestructure is usually determined by qualitative market research. Usually thisis the set of initial specifications that are the result of the clarification of thetask.

SectionB contains three main types of information:

1. Quantitative market data indicating the relative importance of the wants and needs to thecustomer/user and the customer/user's satisfaction levels with the organization's and itscompetition's current offerings.2. Strategic goal-setting for the new machine.3. Computations for rank ordering the customer/user wants and needs.

Section C contains, in the designer's technical language, a high-leveldescription of the machine they plan to develop. Normally this technicaldescription is generated (deployed) from the customer's wants and needs inSectionA.

SectionD contains the development team's judgments of the strength of therelationship between each element of their technical response and eachcustomer's wants and needs.

Section E, technical correlations, is half of a square matrix, split along its

diagonal and rotated 45. Because it resembles the roof of a house, the term


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house of quality has been applied to the entire matrix and has become thestandard designation for the matrix structure. We shall use here the termsystem requirements development matrix (System RDM). SectionEcontainsthe development team's assessments of the implementation

interrelationships between elements of the technical response.

Section Fcontains three types of information:

1. The computed rank ordering of the technical responses, based on the rank ordering ofcustomer wants and needs from SectionB and the relationships in Section D.

2. Comparative information on the competition's technical performance.3. Technical performance targets.

Beyond the RDM, QFD optionally involves constructing additional matrices for the machinesubsystems and components, which further guide the detailed decisions that must be made

throughout the machine development process (Table 1.1). Figure 1.8 illustrates one possibleconfiguration of a collection of interrelated matrices. It also illustrates a standard QFD technique forcarrying information from one matrix into another. In Figure 1.8 we start with the system RDM. Weplace the requirements list (whats) on the left of the matrix. Whats is a term often used to denotebenefits or objectives we want to achieve. The design technical specifications (hows) are correlatedwith the whats at this stage, but they become whats in the next stage, usually the RDM for asubsystem at a lower hierarchical level in the task decomposition scheme. This process continuesuntil designers reach the component level, as shown in Figure 1.8.Other multiple-matrix QFD schemes are considerably more elaborate than the three-matrix schemedescribed in Figure 1.8. Some QFD matrix schemes involve as many as 30 matrices that use thevoice of the customer(VOC) priorities to plan multiple levels of design detail, quality improvementplans, process planning, manufacturing equipment planning, and various value engineering plans.QFD is a central tool in support of concurrent engineering. It brings the multifunctional teamtogether in the first place to develop the top-level system requirements development matrix. At eachstep in the process, it helps keep the team focused on customer/user satisfaction, the primaryingredient of product success.

Figure 1.8. Successive requirements development matrices.


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Matrix What HowRequirements Requirements list Technical Perfonnance

Development matrix Measures, TechnicalSpecifications

Subsystem design matrix Technical perfonnance measuresPiece-partcharacteristics

Piece part design matrix Piece-part characteristics Process parametersProcess design matrix Process parameters Production operations

TABLE 1.2. Typical Model for QFD

Example 1.2 Build a system RDM for the design of a hand-held power tool for making holes forconcrete, with the following requirements list:

1. Holes for the usual steel anchors for concrete b. Fast drilling2. One-man handling3. Reliable4. Safe5. Low noise6. Reasonable cost

Compare it with model Tof the same company and model X of the main competitor.

Solution The requirements list given will be listed in roomA of the HOQ. We assign importance (0-

10) and units. No unit appears in this list. The technical perfonnance measures (technicalspecifications) for room C of the HOQ, technical hows, are:

Capacity for 6-25 mm diameter holes Drilling speed 0.2 mm/sec minimum Maximum weight 200 N MTBF 6,000 hours Should comply with applicable UU and other standards. The noise level at 3 m distance should not be more than 70 DB above

background noise. Manufacturing cost should be less than $150. Should not exceed the IS04 allowable vibration levels at the hands of the

user.

We assign numerical values, units, direction of improvement (higher-lower) and importance (1-10).


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Now we fill room D with the relationships of the users and the engineering metrics. Then 'a"especify the correlation of the engineering metrics in roomE(roof).Finally we do the benchmarking. In room B we compare the new design specifications with model

Tof the same company and model X of the best competitor. In room B the benchmarking is made


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on the basis of the user's perception of quality, in room Fon the basis of an engineering assessmentof quality. Now we multiply importance factors with ratings in both rooms B and Ffor the threedesigns T, X,N.In roomB we see that the quality sum for the new machineNis 155, slightly less than machine Tof

the same company and better than machine X of the competitor.In room Fwe see that the quality sum for the new machineNis 259, much greater thanmachine Tof the same company and better than machine X of the competitor.

The new design has specifications better than those of the older machine of the company and muchbetter than those of the competing machine. Should this not be the case, one can see very easilywhat specification improvements will result in a better competitive standing of the new machine,observing also the organizational difficulty row (top of room F), because some improvements canbe made more easily than others in a certain organization.

The Machine Functional Concept

The design requirements do not necessarily determine the function, that is, the relationship betweenthe inputs and outputs of a machine. A machine functional conceptneeds to be developed first.The designer should always generalize the task as much as possible because:

There might be another way to accomplish the task. The specifications might be widened to include other possible uses of the

machine, without leading to a substantial cost increase, thus widening themarket for the product.

Designers can use several methods to generate functional concepts:

Conventional Methods

1. Literature and design records survey. In the open literature and in the designer'sorganization a substantial body of information may be available on how people in the pasthave solved the design problem. With computerized searches available today one canaccumulate a substantial number of existing solutions. Links for searching journal articles,conference proceedings, libraries, and so on are available through most libraries andorganizations.

2. Patent survey. Right after the victorious conclusion of the War of Independence, the U.S.Congress established the procedure for patenting and invention. In fact, one of the first

inventors to receive a patent was George Washington. This was already the practice in someEuropean countries at that time and today is a global practice for awarding patents for theprotection of intellectual property. According to the Global Association for Tarifs and Trade(GATT) agreement, a patent protects the owner from infringementS for 20 years after thedate of submission of the application. Unfortunately, each country issues its own patents, soa thorough patent search is a very complex operation. The U.S. depository of patents,however, includes nearly 6,000,000 patents (year 1998), and most major inventions havebeen patented in the United States due to its huge internal market. Depositories of patentsexist in most major U.S. cities. Searching used to be quite difficult and was the job ofprofessionals. Today, however, with the available computerized searches, a patent search isnot so difficult and any designer can perform it from the design office through the Internet.Free patent search sites can be found at the U.S. Patent and Trademark Office web site


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(http:/ / 'Ir'WW.uspto.gov /patft/index.html) and an ffiM server(http://patent.womplex.ibm.com/ibm.html). Un:mwnately, they cover only a little more thanthe past 20 years. For the years before 1976, one currently ~ to do the search the hard way,in a patent directory.

3. Asking experts and experienced people in the trade. One has to be careful, however, usingthis resource because the more expertise one has in a certain field, the less creative one isbecause past experience causes a bias toward using the solutions that are well known.

Intuitive Methods

We will not discuss here why people are creative. It suffices to say that people can generate ideaswith a conscious and subconscious mental operation that we commonly call intuition. These ideascan be completely new or can be initiated by reflection on other ideas of solutions for the problemat hand. Several such methods, such as brainstorming, method635, the gallery method, theDelphimethod, and synectics, are described in more detail in books on design methodology, such as Pahland Beitz (1996). In general, the problem is given to a small number of participants, 5-8, possibly

with the participation of a team leader or moderator, and they start generating ideas on how to solvethe problem at hand and enhancing these ideas by sharing them with other members of the group.This is done in one or more successive sessions until a number of alternatives are generated. Ingeneral, as they generate the ideas they do not judge them immediately because one nonfeasibleidea might help the generation down the line of better, feasible ideas. In some methods(brainstorming, method 635), the participants need to have very diverse backgrounds; in others(Delphi), the participants need to be experts in the field of the problem at hand.One method that a designer can use without involving an organization to pursue intuitive methods isthe bottom-up development of the functional concept. To this end we start from the end goal, forexample, of a power tool: drill holes in concrete. By stating "power tool" in the problem statementwe have already decided that me solution will involve a drill with some kind of a motor. Even if theproblem statement has a solution bias (which many times seems logical-the Black & Decker Co. ishighly unlikely to pursue a solution radically different from an elecmc motor coupled to a drillthrough a shaft or gear train), we need to generalize the problem so that we will be able to identifyother solution principles that might surface later if and when the competition or the company startsdoing research on iliem for a possible future product. Sometimes this helps a company to identifymat a certain technology is becoming obsolete and search for alternatives.

The Systematic Method

We start by listing possible physical effects that can be used to achieve the task: for example,drilling holes in concrete, or removing material from a mass of concrete in a focused way, that is,

forming a hole of uniform diameter, for only such holes can be used to locate anchors in theroncrete. Searches in the literature, the patent depository, and the market and in terviews withexperts in the field have identified the following three possible physical effects that can be used todrill holes in concrete:

1. Cutting away the concrete2. Burning the concrete3. Chemically altering the concrete to a gas- or water-soluble substance

The physical principles that can accomplish these physical effects are now specific enough to bequantified by application of the laws of physics and mathematical methods. For the case at hand, the

physical principles could be as in the second column in Table 1.3. Further, each physical principle


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can be implemented with a physical device, as shown in the third column of Table 1.3. The result isthat there are at least eight physical devices that can, in principle, perform the function of makingholes in concrete. At this point, a decision should be made on which physical device should beselected.

To this end, we construct a decision matrix (Table 1.4). In the first column, rows 2 on, we place therequirements list. In the next column we place the "Importance Factor" from room C of the systemRDM, the engineering requirements. We then assign a "degree of satisfaction" for each requirementby each physical device in the range 1-10 (could be any range). Then for every physical device wecalculate the total score by summing the products of the elements of the respective column times theimportance factor and placing the sum at the bottom cell. The bottom row (weighted total) nowgives the merit of every one of the solution functional concepts, in this case the helicoidal impactdrill. Now, however, we have explored all possible solution principles and in fact can identifysolution 7 as a possible, though somewhat distant, alternative.

Physical Effect Physical Principle Physical Device

a. Cutting away the Shearing the concrete by Hollow cylindricalconcrete: rotational shear cutting tool

Helicoidal impact drillShearing the concrete in the Cylindrical punchdirection of the holeImpacting with a sharp solid Speeding bulletto generate high, Jackhammernonunifonn compressivestresses, thus shear

b. Burning the concrete: By high-temperature flame Oxyflame burner

By high-speed friction and "Diamond" -head rotatingwear rodc. Chemically altering the By flow of an acid Sitrring acid flow throughconcrete to a gas or an orificewater soluble substance:

TABLE 1.3. Systematic Development of a Machine Functional Concept for a Concrete Drill


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Figure 1.9. Task decomposition (VDI standard 2221, 1993, by pennission of the Society of Gennan

Engineers (VDI).

In our bottom-up procedure, we now need to identify other components of the power tool that willcomplete the functional concept. Because we use as a basis an impact drill, a search in our sourcesof information (our experience, literature, patents, experts, etc.) will reveal that we need amechanism to generate the rotary motion of the drill, the periodic impact, the static force that must

be applied to the drill, and a power source that will power all of the above.

Design Alternatives: Task Decomposition

In the previous section, we outlined the method for finding one (possibly more) machine functionalconcept. The selected concept can be embodied in a variety of ways, called design alternatives ordesign variants. For example, in the power tool design, the functional concept is a high-speed motorconnected through a speed reducer to a drill holder. Now, there are many different types of motors,speed reducers, and tool holders. Moreover, there might be solutions combining the above basicelements-for example, a variable speed motor that might not need a speed reducer. The search fordesign alternatives is more systematic and capable for machine implementation than the highlyintuitive search for a basic functional concept.Depending on the complexity of the problem, the resulting functional concept will in turn be moreor less complex. By complexity we mean the relative lack of transparency of the relationshipsbetween inputs and outputs, the relative intricacy of the necessary physical processes, and therelatively large number

mask in design

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