A person having direct contact with a piece of furniture becomes part of an arrangement known as anthropotechnical system made up of an animate part (human body) and an inanimate part (technical facility – a piece of furniture). The aim of the research project was to present anthropotechnical aspects of furniture design for sitting and meal consumption. In particular, the author discussed the methodology of the assessment of ergonomics of a chair, a table and a chair + table set, where the assessment criteria were: anthropometric dimensions of the user, stiffness of seats and the value of contact strains on the seat surface.Osoba koja je u izravnom doticaju s namještajem postaje dio sustava poznatoga pod nazivom antropotehnički sustav. Njega čine pokretni dio (ljudsko tijelo) i nepokretni dio (tehnički objekt – određena vrsta namještaja). Cilj istraživanja bio je prikazati antropotehničko gledište projektiranja namještaja za sjedenje i objedovanje. U radu je posebna pozornost pridana metodologiji vrednovanja ergonomije stolice, sustava stola i stolice te grupe stolova, pri čemu su kriteriji vrednovanja bili antropometrijske dimenzije korisnika, krutost sjedala i vrijednost deformacije na površini sjedala

Jerzy Smardzewski

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Jerzy Smardzewski1Antropotechnicalaspects of furniture designAntropotehni~ka gledi{taoblikovanja namje{tajaOriginal scientific paper · Izvorni znanstveni radReceived – prispjelo: : 5. 1. 2009.Accepted – prihva}eno: 25. 2. 2009.UDK: 630*836.1; 674.23ABSTRACT • A person having direct contact with a piece of furniture becomes part of an arrangement known asanthropotechnical system made up of an animate part (human body) and an inanimate part (technical facility – apiece of furniture). The aim of the research project was to present anthropotechnical aspects of furniture design forsitting and meal consumption. In particular, the author discussed the methodology of the assessment of ergonomicsof a chair, a table and a chair + table set, where the assessment criteria were: anthropometric dimensions of theuser, stiffness of seats and the value of contact strains on the seat surface.Keywords: furniture, dimensions, ergonomy, anthropometry, mechanical propertiesSA@ETAK • Osoba koja je u izravnom doticaju s namje{tajem postaje dio sustava poznatoga pod nazivom antro-potehni~ki sustav. Njega ~ine pokretni dio (ljudsko tijelo) i nepokretni dio (tehni~ki objekt – odre|ena vrsta nam-je{taja). Cilj istra`ivanja bio je prikazati antropotehni~ko gledi{te projektiranja namje{taja za sjedenje i objedo-vanje. U radu je posebna pozornost pridana metodologiji vrednovanja ergonomije stolice, sustava stola i stolice tegrupe stolova, pri ~emu su kriteriji vrednovanja bili antropometrijske dimenzije korisnika, krutost sjedala i vrijed-nost deformacije na povr{ini sjedala.Klju~ne rije~i: namje{taj, dimenzioniranje, ergonomija, antropometrija, mehani~ka svojstva1 INTRODUCTION1. UVODUsing furniture a person becomes part of a struc-ture often referred to as an anthropotechnical system.The elements making up this system include: the ani-mate part, i.e. the human body and the inanimate part,i.e. a technical facility. An anthropotechnical system isalways developed as a result of a purposeful action of aman on a technical facility, in this particular case – apiece of furniture. The superior objective initiatingsuch systems is the aesthetic improvement of interiorsof human dwellings as well as upgrading their functio-nality, safety and users’ comfort. Using technical facili-ties, we usually try to harmonise them with the charac-ter of our work as well as with our own psycho-physicalpossibilities. This approach aims at humanising workby appropriate organisation of the system: human be-ing-machine – environment conditions in such a waythat the performed work is carried out at an as low aspossible biological cost and, at the same time, highlyeffectively (Smardzewski et al, 2008).The procedure of engineer-technical design pro-vides the structural basis for ergonomic designing. Themutual interrelationships of technical and ergonomicdesign originates from the principle characteristic foranthropocentric ergonomy and recognises the priorityof human traits and requirements in shaping technicalstructure. The technical structure is, obviously, furnitu-re and its most demanding representative is the group offurniture used directly, i.e. the furniture that comes intodirect contact with the human body during use (furnitu-re for sitting, lying and resting). A person remaining indirect contact with a piece of furniture becomes part ofDRVNA INDUSTRIJA 60 (1) 15-21 (2009) 15......................... Smardzewski: Antropotechnical aspects of furniture design1 The author is professor at the Department of Furniture Design, Faculty of Wood Technology, Poznan University of Life Sciences, Poznañ, Po-land.1 Autor je profesor u Zavodu za dizajn namje{taja Fakulteta drvne tehnologije Sveu~ili{ta u Poznanu, Poljska.a structure known as ’an anthropotechnical system’made up of an animate part (human body) and an inani-mate part (technical facility – a piece of furniture)(Winkler, 2005).Therefore, during the designing process, the prio-rities are as follows: increased safety of the product per-formance taking into consideration all interactions oc-curring between the object and the user concerning vi-sual, acoustic and tactile stimuli. That is why, whenstarting to design a new piece of furniture, it is neces-sary to evaluate criticlally its form, construction, exe-cution technology, functionality and ergonomy of simi-lar products because the human being – object system isthe focus of ergonomic design.The aim of this study was to present the aspects ofanthropotechnical designing of furniture for sitting andmeal consumption. In particular, the author discussedthe methodology of the ergonomic assessment of a cha-ir, a table and a chair + table set assuming the followingfurniture assessment criteria: anthropometric dimen-sions of the user, stiffness of seats and the value of con-tact strains on the seat surface.2 MATERIAL AND METHODS2. MATERIJAL I METODEThe investigations were carried out on a selectedchair and table (with a foldable tabletop) manufacturedby a Polish producer of household furniture, Figure 1.In order to perform an anthropotechnical evalua-tion of a chair, a table and a chair + table set in the CADenvironment, the author developed natural size virtualmodels of a chair, a table and a human phantom makingup elements of the human-seat and human-tablesystems, Figures 2 and 3.Then a catalog of anthropometric dimensions ap-propriate for a Polish user of the 50th centile was deve-loped for the human phantom in a sitting position (Juer-gens et al, 2005, Kroemer et al, 1994), Figure 4.Two models of the assessed furniture were elabo-rated on the basis of the listed anthropometric dimen-sions: a chair model employed to assess the correctnessof linear and angle dimensions as well as geometricproportions of the manufactured chair and a table mo-del used for the ergonomic evaluation of the tabletopsurface. The chair representation included two models:the first of them represented a user sitting on the chairwith legs bent in the knee joint at the straight angle, Fi-gure 5a, while the second model showed a user sittingon the chair with legs bent in the knee joint at the angleof 45 degrees, Figure 5b.16 DRVNA INDUSTRIJA 60 (1) 15-21 (2009)Smardzewski: Antropotechnical aspects of furniture design ..........................Figure 1 A table and chair selected for anthropotechnical ex-perimentsSlika 1. Stol i stolica kori{teni u antropotehni~kom eksperi-mentuFigure 2 Virtual human phantom in CAD environmentSlika 2. Virtualni CAD model ~ovjekaa) b)Figure 3 Virtual models of human-technical object systems: a) at a folded table, b) at an unfolded tableSlika 3. Virtualni CAD model sustava ~ovjek-tehni~ki objekt: a) osnovnih dimenzija, b) s izvla~nim plo~amaThe table model specified the minimum workingsurface per one user taking into account the elbow spa-ce between successive persons, Figure 6a, as well as thereach of the upper limbs allowing a free access to ob-jects found on the table surface, Figure 6b.Putting together the two models made it possibleto perform a complete anthropometric assessment ofthe table–chair system from the point of view of free-dom of movement of lower limbs, their collision withtable legs and considering other persons sitting at thetable as well as the required clearance between thethighs and tabletop, Figure 7.Another quality assessment criteria of the anal-ysed system was the rigidity of the chair seat expressedby the measure of the local rigidity coefficient LWS =P/L in which P = value of the external load, L – va-lue of the displacement corresponding to load P. Theexperiments were conducted on a Zwick 1445 testingmachine for three different seat designs: A – polyuret-hane foam on a hard plywood base, B - polyurethanefoam on elastic upholterer’s straps and C - polyuretha-ne foam on a spring panel base, Figure 8.The last assessment criterion of the table-chairsystem ergonomics was the stress level determined onthe basis of numerical analysis of the contact phenome-non between the human body and the seat manufactu-red in accordance with the design of type a, c. For thispurpose, the author developed two flat netlike modelsof polyurethane foam T4060 (of 40 kg/m3 density) andT2838 (of 28 kg/m3 density) according to these designs.Human buttocks were modelled as an analytical curveof 160 mm diameter. Similar studies have already beeninvestigated erlier and published in different journals(Gefen et al, 1999, 2005; Honma and Takahashi, 2001;Hu and Desai, 2005; Linder–Ganz and Gefen, 2004;DRVNA INDUSTRIJA 60 (1) 15-21 (2009) 17......................... Smardzewski: Antropotechnical aspects of furniture designFigure 4 Anthropomentric traits of a Polish user representing the population of the 50th centileSlika 4. 50-postotni reprezentant antropometrijskih zna~ajki Poljakaa) b)Figure 5 Chair model: a) for a user sitting on the chair with legs bent in the knee joint at the straight angle, b) for a user sitting onthe chair with legs bent in the knee joint at the angle of 45°Slika 5. Model stolice: a) pri sjedenju na njoj koljena savijenih pod pravim kutem, b) pri sjedenju na njoj koljena savijenih podkutem od 45°18 DRVNA INDUSTRIJA 60 (1) 15-21 (2009)Smardzewski: Antropotechnical aspects of furniture design ..........................Figure 6 Table model: a) minimum working surface, b) reach of upper limbsSlika 6. Model stola: a) minimalni radni prostor, b) dohvatni prostor rukuFigure 7 Assembling of table and chair modelsSlika 7. Grupa modela stola i stolicea) b) c)Figure 8 Method of seat stiffness examination: a) polyurethane foam on a hard plywood base, b) polyurethane foam on elasticupholterer’s straps, c) polyurethane foam on a spring panel baseSlika 8. Metoda ispitivanja krutosti sjedala: a) poliuretanska pjena postavljena na podlogu od furnirske plo~e, b) poliuretanskapjena postavljena na tekstilne trake, c) poliuretanska pjena postavljena na opru`nu jezgruLinder-Ganz et al, 2005; Okamoto et al, 1998; Qunli,2005; Smardzewski et al, 2007; Smardzewski andGrbac, 1998; Smardzewski et al, 2008).4 RESULTS4. REZULTATIOn the basis of juxtaposition of the chair and tablepatterns with the actual model of the examined table,Figure 9, it is quite evident that at the elbow width (S4),four adult persons representing the 50 centile popula-tion can sit comfortably at it. When the width of theworking surface is reduced to the hip width (S1), thefreedom of upper limbs reach is somewhat limited butthe advantage is in the fact that six adult men, Figure10, or eight women, Figure 11, can now sit at the tablewith lower limbs allowing sufficient mobility. Fromthis point of view, this design is fully ergonomic.Runs of displacements shown in Figure 12 indicatethat seat systems with B and C designs exhibited themost favourable stiffness because the relatively largestdisplacement increments corresponded to the consecuti-ve increments of small forces. On the other hand, LWSvalues presented in Figure 13 prove that these coeffi-cients were characterised by linear nature, i.e. one thatcan easily be subjected to simple analytic modelling.Assessing the value of acceptable stresses in thecontact between the human body and the elastic type Aand C seat, the author (Grbac and Dalbelo-Ba{i}, 1996;Grbac and Domljan, 2007; Grbac and Ljuljka, 1995;Grbac, 2006; Smardzewski et al, 2008; Winkler, 2005)assumed that the comfort threshold is defined as thestress level at which the user can sit comfortably on achair for a period of more than 4 hours, Figure 14. In ad-dition, a comfortable seat should ensure a uniform di-stribution of stresses spread over the entire surface ofsupport instead of stresses concentrated at points or ona small surface.It was established, on the basis of numerical calcu-lations, that polyurethane foams T4060 in the type A seatgenerated parabolic distribution of stresses of 36 kPa, Fi-gure 15a, whereas T2838 foams in the C type seat gene-rated uniform stress distribution of 4.6 kPa, Figure 15b.DRVNA INDUSTRIJA 60 (1) 15-21 (2009) 19......................... Smardzewski: Antropotechnical aspects of furniture designFigure 9 Virtual juxtaposition of the chair model and tablemodel (a man S4) with the assessed table modelFigure 10 Virtual juxtaposition of the chair model and tablemodel (a man S1) with the assessed table modelFigure 11 Virtual juxtaposition of the chair model and tablemodel (a woman S1) with the assessed table modelSlika 11. Virtualni postav modela stolica i stola (za `enu S1)Figure 12 Stiffness of seats with A, B and C designsSlika 12. Naprezanja sjedala A, B i C konstrukcijeTherefore, the latter foams are a better padding materialaffecting more distinctly the comfort of the user.5 CONCLUSION5. ZAKLJU^AKWhen designing furniture for sitting at tables, it isnecessary not only to take care of correct chair dimen-sions but also to select appropriate dimension relation-ships between these two pieces of furniture. In addition,it is also important to pay attention to the proper heightof the tabletop, height of the underframe (restricting legmovement), width of the tabletop ensuring freedom ofoperation on the working surface as well as the depth ofthe tabletop allowing comfortable reach in relaxed sit-ting position. By making virtual chair and table models20 DRVNA INDUSTRIJA 60 (1) 15-21 (2009)Smardzewski: Antropotechnical aspects of furniture design ..........................Figure 14 Impact of stresses on the period of seat exploitationSlika 14. Utjecaj naprezanja na trajanje sjedenjaFigure 13 Local stiffness coefficient (LWS) for seats with A, B and C designsSlika 13. Podru~je koeficijenta naprezanja (LWS) za sjedalo A, B i C konstrukcijea) b)Figure 15 Stress distribution in the seat with foam of type: a) T4060, b) T2838Slika 15. Raspodjela naprezanja sjedala s poliuretanskom pjenom tipa: a) T4060, b) T2838that allow the adjustment of their dimensions to indivi-dual types of human phantoms, it is possible – as earlyas the design phase - to validate the product developedand identify weaknesses of the adopted functional orconstruction solutions. By comparing the virtual modelof an actual dining-room table with a chair model forthe user, for example of 50 centile traits, it is possible toeliminate the basic ergonomic and functional mistakesof this system. This kind of design bears the hallmarksof anthropotechnical designing.REFERENCESLITERATURA1. Gefen, A.; Chen, J.; Elad, D. 1999: Stresses in the normaland diabetic human penis following implantation of an in-flatable prosttfesis. Med Biol Eng Comput 37:625–631,2. Gefen, A.; Gefen, N.; Linder–Ganz, E. 2005: In vivo mu-scle stiffening under bone compression promotes deeppressure sores. Journal of Biomechanical Engineering.127:512–524,3. Grbac, I.; Dalbelo-Ba{i}, B. 1996: Comparasion of ther-mo-physiological properties of different mattress structu-res. Proceedings of the 18th Internacional Conference onInformation Technology Interfaces, Pula, 113–118,4. Grbac, I.; Domljan, D. 2007: Namje{taj i zdrav `ivot. Si-gurnost 49(3):263–279.5. Grbac, I.; Ljuljka, B. 1995: Study of the man-bed interac-tion. Conference on the occasion of the 125th anniversaryof teaching in forestry in Croatia, Bilten ZIDI, 51–91.6. Grbac, I. 2006: Krevet i zdravlje. University of Zagreb,Faculty of Forestry, Zagreb.7. Honma, T.; Takahashi, M. 2001: Stress analysis on thesacral model for pressure ulcers. Jpn. J. Pressure Ulcers3:20-26.8. Hu, T.; Desai, J.P. 2005: Characterization of soft-tissuematerial properties, Large deformation analysis. Programfor robotics, Intelligent Sensing, and Mechatronics(PRISM) Laboratory 3141 Chestnut Street, MEM Depar-tment, Room 2-115, Drexel University, Philadelphia, PA19104, USA.9. Juergens, H.W.; Aune, I.W; Piepe, U. 2005: Internationa-ler anthropometrischer Datenatlas. 20–07–2005.10. Kroemer, K.; Kroemer, H.; Kroemer-Elbert, K. 1994:Ergonomics, How to design for ease and efficience. Pren-tice Hall, New York.11. Linder-Ganz, E,; Gefen, A. 2004: Mechanical compres-sion – induced pressure sores in rat hindlimb, Muscle stif-fness, histology and comptational models. Journal ofApplied Physiology, 96: 2034-2049,12. Linder-Ganz E.; Yarnitzky, G.; Portnoy, S.; Yizhar, Z.;Gefen, A. 2005: Real-time finite element monitoring ofinternal stresses in the buttlock during wheelchair sittingto prevent pressure sores, Verification and phantom re-sults. II International Conference on Omputational Bio-engineering. H. Rodrigues et al. (Eds.), Lisbon, Portugal,September 14-16,13. Okamoto, K.; Nakabayashi, K.; Mizuno, K.; Okudaira, N.1998: Effects of truss mattress upon sleep and bed clima-te. Applied Human Science 17(6):233-237,14. Qunli, S. 2005: Finite element modeling of human but-tlock – thigh tissue in a seated posture. Summer Bioengi-neering Conference, June 22–26, Vail Cascade Resort &Spa, Vail, Colorado,15. Smardzewski, J., Grbac, I.; Prekrat, S. 2007: Nonlinearelastic of hyperelastic furniture foams. 18-th Internatio-nal Scientific Symposium Ambienta, Zabreb, 77-84.16. Smardzewski, J.; Grbac I. 1998: Numerical analysis of er-gonomic function of upholstered furniture. Me|unarodnoZanstveno Savjetovanje Ambienta, Zagreb: 61–68,17. Smardzewski, J.; Kaba³a, A.; Matwiej, £; Wiaderek, K.;Idzikowska, W.; Papie¿, D. 2008: Antropotechniczneprojektowanie mebli do lezenia i siedzenia. UniwersytetPrzyrodniczy w Poznaniu, Raport koñcowy projektu ba-dawczego MNiSzW nr 2 PO6L 013 30, umowa nr0998/P01/2006/30,18. Winkler, T. 2005: Komputerowo wspomagane projekto-wanie systemów antropotechnicznych. WydawnictwaNaukowo-Techniczne. Warszawa.Corresponding address:prof. dr hab. JERZY SMARDZEWSKI, PhDPoznan University of Life SciencesFaculty of Wood TechnologyDepartment of Furniture Designul. Wojska Polskiego 38/4260-637 Poznañ, Poland.e-mail: jsmardzewskiºup.poznan.plDRVNA INDUSTRIJA 60 (1) 15-21 (2009) 21......................... Smardzewski: Antropotechnical aspects of furniture design

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