Advanced human body modelling to support designing products for physical interaction

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(1)Advanced human body modelling to support designing products for physical interaction.

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(3) Advanced human body modelling to support designing products for physical interaction. Proefschrift. ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus prof. dr. ir. J.T. Fokkema, in het openbaar te verdedigen ten overstaan van een commissie, door het College voor Promoties aangewezen, op maandag 13 december 2004 te 10.30 uur door. Cornelis Christiaan Marie MOES natuurkundig ingenieur. iii.

(4) Dit proefschrift is goedgekeurd door de promotoren: Prof. dr. I. Horv´ ath Prof. W.S. Green Samenstelling promotie commissie: Rector magnificus Prof. dr. I. Horv´ ath Prof W.S. Green Prof. dr. J. Duhovnik Prof. dr. ir. F.J.A.M. van Houten Prof. dr. ir. I.S. Sariyildiz Prof. dr. P. Vink Prof. ir. K.H.J. Robers Prof. dr. ir. J.C. Brezet. voorzitter Technische Universiteit Technische Universiteit Univerza v Ljubljani University of Twente Technische Universiteit Technische Universiteit Technische Universiteit Technische Universiteit. Delft, promotor Delft, promotor Delft Delft Delft Delft, (reservelid). Niels CCM Moes Advanced human body modelling to support designing products for physical interaction, Ph.D. Thesis, Delft University of Technology. ISBN 90-9018829-0 Keywords. advanced human body modelling, ergonomics, physical interaction, computer aided design, conceptual design, shape conceptualization, vague modelling, finite elements modelling, human tissues, knowledge engineering.. Typesetting: plain TEX, eplain, apalike. c by Niels CCM Moes. All rights reserved. No part of materials protected by Copyright this copyright notice may be reproduced or utilized in any form or by any means electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the author.. iv.

(5) Voor Els, mijn lieve vrouw. v.

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(7) Acknowledgements This research has been carried out with the support of the Faculty of Industrial Design Engineering. The research started when I was still a member of the ergonomics department. The main part of the research has been done in the CADE section, where I entered in the year 2000. I want to express my gratitude to the faculty, and particularly to my current department for the opportunity to accomplish this thesis, and for the means that were needed. I realize that my colleagues have had consideration with me, and that they have taken other tasks from me. Special gratitude I want to give to my professor, Imre Horv´ ath. Imre taught me real scientific thinking, to persevere, to be patient, and to cooperate. He showed so much warmth, patience and involvement, his critics were always sharp and clear, and proved to be a great help to deepen in and to progress with the project. Many other people have helped me. I would like to mention them all, but I can just mention a few of them. In the first stage of my research Hans Houtkamp was of a great help for me in the study of pressure distribution, as well as in the project for the calibration of the pressure distribution measuring device. His significant contribution was related to the development of the calibration device. Adrie Kooijman also gave me support when computer help was needed. Henk Lok constructed the mirror box and the pressure distribution measuring device; he was of great help in the preparation of the ergonomic measurements. Peter Pesch greatly supported the computations related to the calibration needed for the pressure measurements. Zolt´ an Rus´ ak did many of the computations related to VDIM. Willem Smit introduced the great TEX system to me. Erik Ulijn was my guru for TEX and Linux. Many students contributed in the routine measurements as part of their education, and by participating as patient subjects during the measurements of pressure distribution, body shape and pelvic angle. Michelle Williams, from the university of Bath (UK), was of a great help during the measurements of the rotation of the pelvis. Cynthia Smeets and Annemarieke Moes contributed by doing a good part of the data analysis of the mirror box results, and Thelma Oskam and Sarah Los assisted in the shape measurements. I want to express my special gratitude to the members of the Promotion Committee. They invested their precious time to reading and commenting the concept thesis. My good friends helped me during the difficult years of the project of the thesis. Wim van den Boogaard, my great friend and music companion, was always willing to give an ear for my struggles, and helped me time after time to open my eyes for seeing things clearly. Hans and Yolanda Lebbe always knew how to give comfort after the hectic weeks with a glass of their excellent wines and a good, relaxing talk. Carlo van Nierop taught me associative thinking, and was of a great help to survive several turbulent years. Last but certainly not least I want to say “thank you so much” to my family. My wife Els has been missing her husband for a long time. She showed an unbelievable patience during the years of research and thesis writing, and was always the wise wife of a chaotic husband. She always knew how to let me feel the earth below my often airborne feet. Together with our children, Annemarieke, Michiel, Janneke and Jeroen, she kept on encouraging me to go on, and was careful to take only limited attempt on my energy. To her I owe most of my thesis work. I am also grateful to my children for their patience, criticism, optimism, realism, love and humour. They were a significant support and helped me to persevere. vii.

(8) Glossary AHBM CACD CSG dof FBD FE FEA FEM HBM HCD ifp lfp MCS pdf SCI SI SIAS SIPS TOL VDIM WCS. Advanced Human Body Model Computer Aided Conceptual Design Constructive Solid Geometry degrees of freedom Free Body Diagram Finite Elements Finite Elements Analysis Finite Elements Model conventional human body model Human Centred Design interstitial fluid pressure lymph fluid pressure measuring coordinate system probability distribution function spinal cord injury sacro-iliac Spina Iliaca Anterior Superior Spina Iliaca Posterior Superior tolerance Vague Discrete Interval Modelling working coordinate system. caudal contact area cranial dermis. in the direction of the feet the surface that is shared by the user and the product in the direction of the head the deeper layer of the skin, containing blood vessels, nerves, etc. ulcers caused by prolonged pressure or rubbing on vulnerable areas of the body. in the direction of the back the set of outward layers of the skin from the germinative layer to the stratum corneum. cell that generates fibres. unsufficient oxygen a type of extracellular fluid. in left-right direction a colorless, watery fluid originating from interstitial fluid. the death of one part or area of tissue, especially of bone or an organ, in a living organism. the difference between the osmotic pressures of the blood and the interstitial fluid. the pressure that can build in a space that is enclosed by a membrane that is permeable to a solvent such as water but not to solutes.. decubitus dorsal epidermis fibroblast hypoxia interstitial fluid lateral lymph necrosis oncotic pressure osmotic pressure. viii.

(9) Photoplethysmography infrared light is emitted into the skin. More or less light is absorbed, depending on the blood volume in the skin. The backscattered or transmitted light corresponds with the variation of the blood volume. sagittal in forward direction.. Legend of symbols ecto endo meso A b. C cdf d Eaverage Ei Etotal E F. fbf Fsf f. Fsf FG FS G h H H I J K K m. M n n e N. e n NA NC. ectomorphic index endomorphic index mesomorphic index magnitude of area vector of body characteristics coefficient of the Mooney constitutive equations regression coefficient for factor f and distribution trajectory. d skin thickness average strain energy of the elements adaptive error criterion for element i sum of the strain energy of the elements Lagrangian strain tensor deformation gradient tensor coefficient of the b-th body characteristic for the f -th factor f -th underlying body factor for the s-th subject force f -th underlying factor for the s-th subject body weight sitting force gradient of pressure distribution stature Hermann pressure variable hyper surface strain invariant Jacobian of matrix bulk modulus stiffness matrix midpoint of ischial tuberosities body mass direction cosine of vector normal vector eigen vector eigen value number of adaptive elements number of contact nodes ix.

(10) NF NP NS NT p P P. Rxy r r S. S t u. v V w W W. x X x. yf. number of underlying statistical factors number of postures number of subjects number of distribution trajectories hydraulic pressure particle first Piola-Kirchhoff stress tensor operator for rotation around the x and the y axes coefficient of correlation reference vector second Piola-Kirchhoff stress tensor shape traction pressure displacement vector velocity volume weight factor strain energy virtual work point (unslanted italic) material vector space vector front depth. greek symbols. αa αp α βx p γ Γ. Γ Ξ. ε ε. ζ ζb η λ µ µ ρ. σ τ Φv x. antenna angle angle of the rotation of the pelvis derivative of x with respect to the pelvis tilt lateral angle between ischial tuberosities reference frame gradient for search point cloud metric occurrence vector of strain components location index estimation location index viscosity stretch ratio coefficient of friction coefficient of friction radius of a curvature Cauchy stress tensor Kirchhoff stress tensor volume flow.

(11) Contents.

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(40) List of Figures Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig.. 1-1 1-2 1-3 1-4 1-5 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 3-1 3-2 3-3 3-4 3-5 3-7 3-6 3-8 3-9 3-10 3-11 3-12 3-13 3-14 3-15 3-16 3-17 3-18 3-19 3-20 3-21 3-22 3-23 3-24 3-25 3-26 3-27 3-28 3-29 3-30 3-31 3-32 3-33 3-34 3-35 3-36. Reach of Human Centred Product Design . . . . . . . . . . . . . . . . . . . 2 Subdisciplines Human entred design . . . . . . . . . . . . . . . . . . . . . . . 5 Efforts for knowledge incorporation . . . . . . . . . . . . . . . . . . . . . . . 7 Design for physical interaction . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Knowledge in advanced human body model . . . . . . . . . . . . . . . . 14 Reasoning model literature study . . . . . . . . . . . . . . . . . . . . . . . . 19 Sources of uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 shape measurement methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 hydraulic pressure in transportation tissues . . . . . . . . . . . . . . . . 32 Tubular structure lymph system . . . . . . . . . . . . . . . . . . . . . . . . 33 Cross section spinal nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Front view female pelvis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Aspects of tissue load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Principle conceptual solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 general process diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Basic submodels AHBM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Formation morphological model . . . . . . . . . . . . . . . . . . . . . . . . . 55 knowledge structure basic models . . . . . . . . . . . . . . . . . . . . . . . . 56 Assembly levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Flow diagram shape instantiation . . . . . . . . . . . . . . . . . . . . . . . 58 Lumbar curvature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Pelvis rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Circular disc model ischial tuberosities . . . . . . . . . . . . . . . . . . . . 61 Hamstrings and quadriceps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Distribution interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Generating minimal and maximal closure . . . . . . . . . . . . . . . . . . 63 Generation of distribution trajectories . . . . . . . . . . . . . . . . . . . . 64 Uncertainty of generated interval . . . . . . . . . . . . . . . . . . . . . . . . 65 Rotation for vertical alignment . . . . . . . . . . . . . . . . . . . . . . . . . 66 Translation for common origin . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Projecting measured points on distribution trajectory . . . . . . . . . 68 Computation of location index . . . . . . . . . . . . . . . . . . . . . . . . . . 68 morphological types of muscle . . . . . . . . . . . . . . . . . . . . . . . . . . 71 FE process for internal loadings . . . . . . . . . . . . . . . . . . . . . . . . . 73 Scheme for behavioural modelling . . . . . . . . . . . . . . . . . . . . . . . 73 simplification of geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Three levels of simplification . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Strong deformations may reduce the resolution . . . . . . . . . . . . . . 78 Meshed micro structure for muscle . . . . . . . . . . . . . . . . . . . . . . . 78 Micro structure for skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Cross section of a vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Modelling micro-pore transport . . . . . . . . . . . . . . . . . . . . . . . . . 79 Kelvin – Maxwell models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Contact tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Vessel forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Assessment of the physiological effects and criteria . . . . . . . . . . . 86 Particle position vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Extracting changes from FEA data . . . . . . . . . . . . . . . . . . . . . . 86 xvii.

(41) Fig. 3-37 Fig. 3-38 Fig. 3-39 Fig. 3-40 Fig. 3-41 Fig. 3-42 Fig. 3-43 Fig. 3-44 Fig. 3-45 Fig. 3-46 Fig. 3-47 Fig. 3-48 Fig. 3-49 Fig. 3-50 Fig. 3-51 Fig. 4-1 Fig. 4-2 Fig. 4-3 Fig. 4-4 Fig. 4-5 Fig. 4-6 Fig. 4-7 Fig. 4-8 Fig. 4-9 Fig. 4-10 Fig. 4-11 Fig. 4-12 Fig. 5-1 Fig. 5-2 Fig. 5-3 Fig. 5-4 Fig. 5-5 Fig. 5-6 Fig. 5-7 Fig. 5-8 Fig. 5-11 Fig. 5-9 Fig. 5-10 Fig. 5-12 Fig. 5-13 Fig. 5-14 Fig. 5-15 Fig. 5-16 Fig. 5-17 Fig. 5-18 Fig. 5-19 Fig. 5-20 Fig. 5-21 Fig. 5-22 Fig. 5-23 Fig. 5-24 xviii. Displacements in sitting region . . . . . . . . . . . . . . . . . . . . . . . . . 89 Semantic scheme blood flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Blood circulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Interstitial and lymphatic pressure . . . . . . . . . . . . . . . . . . . . . . . 94 Five compartment model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Tissue viability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Tissue viability of skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Physiological effects for muscles . . . . . . . . . . . . . . . . . . . . . . . . . 98 Physiological effects for nerves . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Procedures shape generation artefact . . . . . . . . . . . . . . . . . . . . . 99 Transformation nodes to vague model . . . . . . . . . . . . . . . . . . . . 99 Trajectories of contact nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Vague domain of subjects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Regions of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Shape instantiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Feasibility testing and tool development . . . . . . . . . . . . . . . . . . . 108 omputation of vague geometric model . . . . . . . . . . . . . . . . . . . . 110 Example measured shape data . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Projecting a data point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Positioning knee midpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Connecting two bones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Closing distal end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Holes in mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Gap parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Wedge elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Initial contact body and support . . . . . . . . . . . . . . . . . . . . . . . . 131 Load cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Measuring skin fold thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Measuring width and girth . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Measuring bony landmarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Mirror box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Noise reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Alignment trochanter and epicondyle . . . . . . . . . . . . . . . . . . . . . 147 MicroScribe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Visual grid on skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Maximum and minimum of measured data . . . . . . . . . . . . . . . . . 149 Not aligned geometric data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Aligned geometric data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Closures and distribution trajectories . . . . . . . . . . . . . . . . . . . . . 151 Length and angle metric occurrence . . . . . . . . . . . . . . . . . . . . . . 151 length and caudal distance metric occurrence . . . . . . . . . . . . . . . 151 Generated minimal and maximal closures . . . . . . . . . . . . . . . . . . 152 Location index: best and worst . . . . . . . . . . . . . . . . . . . . . . . . . 153 Average location index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 Location index: frequency distribution . . . . . . . . . . . . . . . . . . . . 155 Relative distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 Scanning anatomical images . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 Scanning anatomical images: ischial tuberosity . . . . . . . . . . . . . . 156 Bones: scanned contours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Bones: surface elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Bones: assembled surface elements . . . . . . . . . . . . . . . . . . . . . . . 160.

(42) Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig.. 5-25 5-26 5-27 5-28 5-29 5-30 5-31 5-32 5-33 5-34 5-35 5-36 5-37 5-38 5-39 5-40 5-41 5-42 5-43 5-44 5-45 5-46 5-47 5-48 5-49. Connection pelvis femur . . . . . . . . . . . . . . . . . . . . . . Assembly bone-skin . . . . . . . . . . . . . . . . . . . . . . . . . . Auxilliary elements . . . . . . . . . . . . . . . . . . . . . . . . . . Hexmeshing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hexmeshed model . . . . . . . . . . . . . . . . . . . . . . . . . . . Surface finite elements mesh . . . . . . . . . . . . . . . . . . . Solid finite elements mesh . . . . . . . . . . . . . . . . . . . . . Continuity conditions for non-uniform load . . . . . . . . . Measuring pressure distribution and pelvis angle . . . . . Maximum pressure and tissue thickness . . . . . . . . . . . Search for best elasticity . . . . . . . . . . . . . . . . . . . . . . Relationship constitutive coefficient and Cauchy stress Applied surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum interface pressure and curvedness . . . . . . . . Deformed body shape . . . . . . . . . . . . . . . . . . . . . . . . Displacement of nodes . . . . . . . . . . . . . . . . . . . . . . . . Total shear stress . . . . . . . . . . . . . . . . . . . . . . . . . . . Iterative shape design . . . . . . . . . . . . . . . . . . . . . . . . Extracted point cloud for decreased curvedness . . . . . . Extracted point cloud for modal curvedness . . . . . . . . Extracted point cloud for increased curvedness . . . . . . Rendered view extracted point clouds . . . . . . . . . . . . Rendered basic chair . . . . . . . . . . . . . . . . . . . . . . . . . Customized seats . . . . . . . . . . . . . . . . . . . . . . . . . . . Customized seats: rendered . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . 160 . 160 . 160 . 163 . 164 . 165 . 165 . 167 . 170 . 173 . 174 . 175 . 176 . 176 . 176 . 179 . 179 . 182 . 183 . 183 . 183 . 183 . 184 . 184 . 185. xix.

(43) List of Tables Table Table Table Table Table Table Table Table Table Table Table. 2-1 2-2 2-3 3-1 3-2 5-1 5-2 5-3 5-4 5-5 5-6. Physical contact between the internal tissues . . . . . . . . . . . Aspects for physiologically acceptable pressure distribution . Overview FE models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Properties human body models . . . . . . . . . . . . . . . . . . . . . Aspects constitutive models . . . . . . . . . . . . . . . . . . . . . . . Body characteristics: statistics . . . . . . . . . . . . . . . . . . . . . Body characteristics: factor loadings . . . . . . . . . . . . . . . . . Properties finite elements model . . . . . . . . . . . . . . . . . . . . Sitting force and maximum pressure . . . . . . . . . . . . . . . . . Regression results force and maximum pressure . . . . . . . . . Mooney-Rivlin coefficients . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. . 28 . 42 . 43 . 76 . 81 . 146 . 146 . 166 . 171 . 171 . 172. . . . . . . . . . . . .. . . . . . . . . . . . .. . 111 . 114 . 115 . 118 . 119 . 122 . 126 . 128 . 128 . 130 . 131 . 135. List of algorithms Algorithm Algorithm Algorithm Algorithm Algorithm Algorithm Algorithm Algorithm Algorithm Algorithm Algorithm Algorithm. xx. 1 2 3 4 5 6 7 8 9 10 11 12. Alignment of point clouds . . . . . . . . . . . . . . . . . . Conversion point cloud to distribution trajectories Building a vague shape model . . . . . . . . . . . . . . . Computation of shape instances . . . . . . . . . . . . . Assembling bone in skin . . . . . . . . . . . . . . . . . . . Algorithm to create a solid mesh . . . . . . . . . . . . . Assignment of sets . . . . . . . . . . . . . . . . . . . . . . . Assignment of boundary conditions . . . . . . . . . . . Implementation of constitutive modelling . . . . . . . Assignment of adaptive elements . . . . . . . . . . . . . Application of force . . . . . . . . . . . . . . . . . . . . . . Product modelling . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. ... . . . . . . . . . . . ..

(44) Summary We are using many designed artefacts in our daily life. These artefacts are typically in physical interaction with the human body, and cause stresses and deformations inside the tissues. When these stresses exceed a given level, the proper physiological functioning of the tissues is limited, and ergonomics discomfort or even medical complications can appear. It is important to consider these effects in designing artefacts. However, consideration of these effects is not straightforward, because we need more knowledge about the mechanisms of human-product physical interaction, about the behaviour of the tissues in the contact region, and about the opportunities to influence the interaction in a positive way. There are no means available to directly study the internal effects that appear inside the body of the user when a particular artefact is used. Therefore we have to use a mechanical-physiological model of the human body to generate the information needed for an ergonomically proper designing of artefacts. Apart from the simulation of the internal loads, this model is supposed to be able to model the physiological functioning. In the past several efforts have been made to develop combined anthropometric and mechanical models, that can approximate the behaviour of the human body. However, these models are not able to represent complex biomechanical properties, anthropometric variability, tissue relocation, complex mechanical properties, and physiological functioning of the involved tissues. The goal of this thesis is to explore knowledge, and to develop and verify conceptual solutions for complex behavioural modelling of various human bodies and parts of it. The research hypothesis was that this goal can be achieved by the development of a knowledge intensive, multi-representational model of the human body, which has been called ‘advanced human body model’. This advanced model (i) considers the anthropometric variability of the whole body and its constituents, (ii) is able to compute the effects of the external loads on the internal structures and tissues of the body, (iii) provides information about the deformed shape of the body when it interacts with the used artefact, and (iv) integrates these aspects into one consistent system of knowledge and processing algorithms. In addition to collecting and structuring the knowledge needed for an advanced human body model, algorithms and procedures have been developed. The knowledge structures and the algorithms have been tested and validated in a pilot application. Commercial software tools were used together with newly developed programs to operationalise the advanced human body model. The software tools are able to support the consideration of anthropometric variability, to represent a cluster of shapes of the human body, to generate instances, to represent the mechanical and biophysical properties, to analyse the restructuring and loading of the internal tissues, to determine the physical deformation of the body being in contact with the artefact, and to facilitate using this information in an ergonomically proper designing of the artefact. In our application the artefacts were various sitting supports. The results obtained with the pilot implementation show that (i) useful shape models can be developed based on a small set of descriptive parameters, (ii) the simulation of the material properties based on the generalised Mooney-Rivlin constitutive equations provides no adequate results, and asks for further research, (iii) the current finite element based simulation packages can not sufficiently cope with the complexities of human body modelling, and (iv) advanced human body models open up new opportunities in optimising the shape of products according to ergonomics criteria.. xxi.

(45) Samenvatting In het dagelijks leven gebruiken wij vele ontworpen gebruiksgoederen. Kenmerkend voor het gebruik van dergelijke producten is een fysieke interactie met het menselijk lichaam. Dit veroorzaakt spanningen en vervormingen in de zachte weefsels van het lichaam. Wanneer deze spanningen een bepaald niveau overschrijden, kunnen deze weefsels hun normale fysiologische functies niet meer vervullen. Dit heeft een vermindering van ergonomisch comfort tot gevolg, en er kunnen zelfs medische complicaties optreden. Alhoewel het belangrijk is dergelijke effecten te betrekken bij het ontwerpen van producten, is dit gemakkelijker gezegd dan gedaan. De belangrijkste reden hiervoor is en gebrek aan voldoende kennis van de mechanismen die een rol spelen in de fysieke interactie tussen mens en product, van het gedrag van de menselijke weefsels in de regio waar het contact plaats vindt, en van de mogelijkheden om deze interactie op een gunstige manier te kunnen be¨ınvloeden. Er is geen reële mogelijkheid om tijdens de mens-product interactie de interne gevolgen te bestuderen in het inwendige van het lichaam van de gebruiker. Dit vraagt om een mechanisch-fysiologisch model van het menselijk lichaam teneinde die informatie te genereren, welke nodig is voor het ergonomisch ontwerpen van producten. Een dergelijk model moet niet alleen de belasting binnen het lichaam simuleren, maar ook het fysiologisch functioneren. In het verleden zijn verschillende pogingen gedaan om gecombineerde antropometrischemechanische modellen te ontwikkelen, die het gedrag van het menselijk lichaam in meer of mindere mate kunnen benaderen. Deze modellen waren echter niet in staat de complexe biomechanische eigenschappen, de antropometrische variaties, het verschuiven van weefsels, de complexe mechanische eigenschappen, en het fysiologisch functioneren van de betrokken weefsels te representeren. De doelstelling van dit proefschrift ligt zowel in het navorsen van benodigde kennis, als in het ontwikkelen en verifiëren van conceptuele oplossingen ten teneinde het modelleren van het complexe gedrag van delen van het menselijk lichaam en van het lichaam als geheel mogelijk te maken. In de onderzoeks-hypothese werd geformuleerd dat dit doel kan worden bereikt door het ontwikkelen van een model, dat kennisintensief is, en het lichaam vanuit verschillende benaderingen kan representeren. Zo’n model werd hebben wij een ‘geavanceerd model van het menselijk lichaam’ (advanced human body model) genoemd. Dit geavanceerde model moet het mogelijk maken (i) de antropometrische variabiliteit van het lichaam en de samenstellende delen te beschrijven, (ii) de gevolgen van externe belastingen op de structuren en weefsels binnen het lichaam te berekenen, (iii) de gegevens met betrekking tot het vervormde lichaam tijdens de interactie met een product te produceren, en (iv) deze aspecten te integreren in één enkel consistent systeem van ingebouwde kennis en procesalgoritmen. In dit onderzoek is niet alleen de kennis verzameld en gestructureerd teneinde een geavanceerd model te kunnen maken; ook de benodigde algoritmen en procedures werden ontwikkeld. Deze kennis-structuren en algoritmen werden getest en gevalideerd met een proeftoepassing. Om het geavanceerde model te operationaliseren werd commercieel verkrijgbare programmatuur gebruikt, gecombineerd met programmatuur die in het kader van dit onderzoek werd ontwikkeld. De synergie van deze programmatuur maakt het mogelijk de diverse aspecten van deoprationalisatie te ondersteunen: de antropometrische variabiliteit, de representatie van clusters van lichaamsvormen, het generen van specifieke lichaamsvormen, van de representatie van de mechanische en biofysische weefseleigenschappen, het analyseren van het herstructureren en het belasten van de weefsels, het vaststellen van de fysieke vervorming van xxii.

(46) het lichaam terwijl het in contact is met het product, en de toepassing van deze informatie in het ontwerpen van een ergonomisch correct product. Onze proeftoepassing betrof verschillende zittingen. De resultaten, die met deze proeftoepassing werden verkregen, laten zien dat (i) bruikbare vorm-modellen kunnen worden ontwikkeld op basis van een klein groep beschrijvende parameters, (ii) het simuleren van de materiaaleigenschappen op basis van de vaak gebruikte gegeneralizeerde Mooney-Rivlin vergelijkingen voor het gedrag van materialen geen adequate resultaten opleveren, en aanleiding geven voor vervolgonderzoek, (iii) de huidige generatie simulatie-programmatuur, die is gebaseerd op de eindige elementen technologie, onvoldoende in staat is de complexiteiten van de menselijk lichaam te simuleren, en (iv) geavanceerde modellen van het menselijk lichaam nieuwe mogelijkheden bieden om de vorm van producten te verbeteren, rekening houdend met ergonomische criteria.. xxiii.

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(48) Chapter 1 Introduction. 1.1 Background of promotion research To achieve certain goals a person usually has to interact with the environment. In the interaction with the environment, artefacts are typically used. As it is generally known, an artefact is any non-natural, i.e., human made, physical ‘thing’ that is also called product. The nature of the used artefact depends on the goals to be achieved. The type of interaction can be physical (defined by the transmission of force), semiphysical (processing or exchange of information), or non-physical (perception of the environment and physiological reactions). The interaction is called physical if there is a transmission of force through a contact area. A typical example is when a chair or a hand tool is used. The goal of use as well as the functionality of the artefacts may be completely different. Some of the products are for extending the human physical capacities (orthoses or exoskeletons, e.g. hand tools), others for increased well-being (e.g. supports, protective means), and often a combination of these two (a tool with protective part). The interaction is called semi-physical if generation and exchange of information is the dominant activity. In this case there is no contact by touch and, consequently, there is no physical contact area. This is the case when someone reads a scale for temperature. If no artefact is used at all, as it is for instance, in the case of the perception of temperature, light and sound, or more general, the whole environment, then the interaction is called non-physical. Many physiological effects can be perceived this way. We use artefacts of different functionality and usability. For instance, when chop-sticks are used, it is handy, fully functional, but might not provide the best interaction for an inexperienced user. Furthermore, when we use a multi-functional artefact, typically very sophisticated interaction is needed, that should be designed in a purposeful way. The design of such interaction requires sufficient knowledge of the human capabilities and characteristics. The increasing level of complexity of artefacts as well as the increasing expectations towards usability, require more and more knowledge about the rules of designing products for interaction and usability. The knowledge should extend to the human perception and cognition of the artefact, the environment and the use situation. Having recognised all these necessities, the related research has to make intensive efforts to discover and apply such knowledge. This endeavour is high in the field of Ergonomics or Human Factors Research. Ergonomics has been decomposed according to the types of interaction to the subdisciplines of physical, informational, and sensory ergonomics. A current trend is to combine the scientific and practical methods of the sub-disciplines of ergonomics and computer-aided design and engineering, which has given rise to the rapidly growing sub-disciplines of Human Centered Product Design (HCPD). The intention of the promotion research, reported on in this thesis, was to contribute to the methodological.

(49) 2. Introduction — Ch. 1. further development of HCPD in a specific field of attention. As its title implies, this thesis summarises the process of research, the achieved results, and the drawn conclusions related to advanced modelling of the human body for HCPD. The objectives of the research were to understand the knowledge that is needed to generate a quasi-organic, multi-functional human body model, that is capable to support the representation of not only the anthropometric (geometric) aspects, but also to support the simulation of the behaviour of the human body in interaction. The ultimate goal is to use this sophisticated model in HCPD with a special attention to designing body supports. In the following section we first explain the issues related to HCPD, then discuss the requirements for an advanced human body model together with the technical questions related to its implementation.. 1.1.1 On the development and the methodology of Human Centred Product Design HCPD is an integral methodology of designing products for people. Although Human Centred Design covers designing for people in general, including products, environments, services, and systems, we confine ourselves to designing physical products. According to (Nemeth, 2004), from which reference several concepts will be used in this section, HCPD considers both the human and the technical subsystems in a broader context. Historically, ergonomics provided the knowledge for human oriented development of artefacts and workplaces (Sanders and McCormick, 1993, ch. 1). In the context of HCPD, the body of knowledge, the modelling techniques, and the methods of design support, new requirements emerged for ergonomics. Actually, HCPD is multi-disciplinary (Green, 2002). It amalgamates not only the traditional methods and means of ergonomics, but also modern design science, research methods, knowledge of aesthetics, materials science, the relevant technologies of applied information technology, manufacturing, etc. The flow diagram in figure 1 shows the stages of a typical HCPD-process1 . The first stage is to define the global design problem, based on an analysis of a practical problematic situation. Inherent to the problem definition is the global formulation of the solution elements as the basic functionalities, or the goal the product has to fulfil. The basic functionalities are analysed for design-relevant aspects such as physical interaction, exchange of information and the aesthetical appeal; this is conform the objectives as defined by. The stage ends with the formulation of a set of functional and human-oriented requirements or criteria (in this place we will not discuss the ‘other’, not human-oriented requirements). In the second stage, ergonomics knowledge is collected about the relevant human characteristics and capacities, the aspects of person-product interaction, the ergonomical concerns of safety, efficiency, effectivity, comfort and aesthetics, together with the human conditioning factors, such as motivation, fixation, etc. This ergonomics knowledge is needed for the conversion and extension of the global human-centred requirements to more concrete terms. In the third stage, conceptual solutions are concieved by interrelating and combining the filtered pieces of knowledge, including opposing views and synergic views. A conceptual solution, or a principle of a solution, contains the synthesised knowledge and is still considered on a non-material level. Practically, a conceptual solution can be created by the investigation of the possibilities of an actual implementation, and 1. This diagram does not show the regular contacts between the designer and the stakeholders..

(50) Sec. 1.1 — Background of promotion research. orientation on the problem. rough product design problem. informational. aesthetic. provisional overview of usage aspects and rough formulation of requirements. rough formulation of human centred requirements. human characteristics - anthropologic - anthropometric - physiological - psychological - behaviour. human capacities - social - emotion - cognition - association - force exertion. application filter - motivation - social context. application filter - motivation - social context. conceptual solution and implementation. gathering human centred knowledge. basic functionalities of artefact. physical. other requirements. design concepts. 3. person-product interaction - anticipation of usage. safety efficiency effectivity comfort aesthetics. knowledge synthesis for a conceptual solution. implementation of knowledge other detailed requirements. detailed human centred requirements. human conditioning - motivation - social context - laziness - emotion - fixation - attractiveness - experience - use strategies - (not) intended usage - association. design of physical product. physical prototype of product. no sufficient performance of basic functionalities?. interaction. usage. physical effects. cognitive responses. yes. emotional responses. manufacturing. quality of performance. Figure 1-1.. Overview of the scope of Human Centred Product Design.

(51) 4. Introduction — Ch. 1. the elaboration of the human centred product requirements, which express the designer’s vision on the product and how the product is intended to be used. Using these requirements, a designer develops design concepts of the physical product, which results in the end in a physical prototype of the product. In the fourth stage, the physical, emotional and cognitive effects of the product usage are evaluated by user trials and the assessment of responses of product usage, the quality of the performance, based on the ergonomical concepts of safety, efficiency, etc. Such trials must take into consideration the human conditions and the total environment of the system. If the trials show that the performance2 agrees with the formulated basic functionalities, that were derived from the global design problem, then the artefact can be manufactured. Otherwise the design process must be iterated. This HCPD scheme has been developed in a slightly comparable way by (Nemeth, 2004). He discusses in depth the human factors aspects, especially on the first two stages and the last stage of the scheme of figure 1.. 1.1.2 Aspects of Human Centred Design in the current research For the purpose of our discussion on advanced human body modelling to support designing product for physical interaction, we need a part of the reach of the field of HCPD, that has been described in subsection 1.1.1. In the remainder of this work we consider HCPD in the specific context of designing products for physical interaction. Therefore we will discuss the integration of specific sub-disciplines and aspects. The sources of the knowledge for HCPD are ergonomics, industrial design engineering, computer science and research methodologies. It became known that there are several subfields of ergonomics where the currently available knowledge is not in all cases sufficient for optimum design of artefacts for physical or semi-physical interaction with humans. The research in physical interaction has explored that in order to develop the artefacts according to the satisfaction of the users, comprehensive modelling of the human body is needed (Dirken, 1997). However, the overwhelming majority of current human body models manifests in morphological and mechanical representations (Jones and Rioux, 1997). The disciplines of ergonomics and Industrial Design Engineering overlap in certain respects. The knowledge about artefacts and design processes is delivered by industrial design engineering (Roozenburg and Eekels, 1995). With other words, industrial design engineering gives the methodological and technological framework of HCPD by pursuing a synergism of knowledge of marketing and innovation, form and colour design, aesthetics, ergonomics, materials and technologies, and information and knowledge (Mital and Karwowski, 1991)(Wilson and Corlett, 1995)(Dirken, 1997). Industrial design has recently been extended with the concepts and technologies of Global Product Realization in collaborative virtual design environments (Horv´ ath et al., 2003). Due to the complexity of the design tasks and to the distributed nature of product development, computer-based design support systems are indispensable in the practice of industrial design engineering. Computer science and applied information technology offer methods and tools based on which the challenging problems of HCPD can be treated and solved in a efficient way (McMahon and Browne, 1998). Certain design tasks can not be performed efficiently by humans (Sanders and McCormick, 1993). As far as HCPD is concerned, the modelling, simulation, data management, and knowledge representation means of applied information technology play a, especially 2. The performance has been defined as the sum of all elements’ activities and interactions in the context of the total environment..

(52) Sec. 1.1 — Background of promotion research. 5. significant rˆ ole. As the first results indicate, a completely new approach can be developed to organic modelling of human bodies (Rus´ ak, 2003) by combining the above mentioned elements. One remarkable new concept is resource integrated modelling of humans, products, and environments (van der Vegte and Horv´ ath, 2003). Research in ergonomics and design explores new knowledge about the relationship of humans and artefacts and about the realization of artefacts with the view to the users. The methods of research vary in a wide range, involving literature study, observational studies, experimental investigations, comparative analysis, model based interpretations, statistical processing, system implementation, participatory sessions, to mention just the most important ones. HCPD is currently considered as a combination of activities of explorative research and activities of product development. If sufficient knowledge is not available related to a design problem, various combinations of research methods are needed such as the empirical explorative research including a literary survey (Wijvekate, 1971)(Meerling, 1989). Within HCPD various methodics3 have been developed, for instance, design for interaction with physical artefacts, design for transmission of information, and design for controlling the environment. The applicable methodics always depends on the design problem at hand. Various aspects of the methodological development can be seen in figure 2, which illustrates how the different disciplines aggregate the knowledge needed for design for physical artefact interaction as well as for the other fields of interest of HCPD, and how this knowledge is utilised in applications. This thesis concentrates on the knowledge aggregation and the model development issues related to design for physical artefact interaction with the aim of achieving optimum interaction between the human body and the body supporting artefact from a physical ergonomics point of view. ergonomics. industrial design engin.. computer science. research methodologies. physical ergon. inform./cognitive ergonomics sensory ergon. .... product definition product realization service design .... programming languages process control geometric modelling finite elements modelling .... fundamental research applied research operational research literature review .... physical artefact interaction. supports tools protective means loads. information transmission. environmental control. .... informational interfaces. climate controllers. .... .... Figure 1-2. Associations among the sub-disciplines, aspects of HCPD and the fields of applications. The keywords that are relevant for this promotion research are shown in bold. 3. A methodics is a purposefully arranged set of methods (Eekels, 1982); according to (Wikipedia, 2004): a methodic is a way of solving a problem..

(53) 6. Introduction — Ch. 1. A great deal of the physical ergonomics knowledge is available for HCPD in the form of guidelines, statistical tables, mathematical relationships (Rodgers, 1983), and ergonomic design methods (Wilson and Corlett, 1995). In addition, descriptive information carried by invariant data and properties is also at the disposal of designers. However, designers often lack information, especially related to the application of the latest computer technologies, and about the specific ergonomics methods and the use of highly specialised knowledge. Whenever knowledge is needed within the context of an ergonomics design problem, concerning the human body, individual body properties, or internal physiological processes, the direct access to the knowledge is not in all cases possible. This highly specialised knowledge is typically indispensable when designers need to model the physiological processes within the human body, for instance to describe the behaviour of the body under extreme external loads. The risk of disfunctioning was recognised within the context of long term sitting or lying a few decades ago. This is typical for wheelchair users and bed ridden people (Kosiak et al., 1958)(Kosiak, 1961)(Kett and Levine, 1987). Such physical interaction induces high interface loads and internal stresses, as well as large deformations. Sitting is indeed a typical representative of a kind of physical interaction involving severe mechanical loadings and showing far reaching medical consequences (Brienza et al., 2002). When the problem of designing optimum shapes for sitting supports is considered in HCPD, designers need knowledge about the physiological and mechanical processes inside the body. Although a lot is known about the physiology of the human tissues and the mechanical behaviour, which is usually expressed in terms of stresses and strains in the tissues, no theory has until now been developed, which could quantitatively describe these processes. Therefore this knowledge must be obtained differently. In ergonomics, physiology and medical research, information about the human body can be obtained ‘in vitro’, ‘in vivo’, or by simulation. Measuring the biomechanical properties, the physiological processes, and the stress and strain conditions of the tissues in vitro can not be considered in our case. The reason is that the in vitro body properties significantly differ from the in vivo properties of the tissues (Stidham et al., 1997). For instance the Young’s modulus is significantly different when measured in vivo or in vitro. As a consequence, the results of the in vitro measurements can not be considered as a proper representative of the living tissues. Moreover, it is our goal to measure and obtain data from living interaction between a person and the sitting support used. The mechanical loading of the concerned tissues has consequences for the physiological functioning. This requires in vivo gauging of the stresses and the deformations inside the tissues, and the monitoring the conduct of the physiological processes. Since such processes do not happen on the surface of the body only, but also in the deeper structures, the measurements would require penetration through the skin. Obviously, using such kind of intrusive means is out of the scope of a nonmedical research. Also in this research we did not count on it. At the same time, the need has emerged for a fully featured simulation of the integral behaviour of complex organic systems. Due to the nature of real life experimentation and investigation, it seems to be necessary to develop substituting computer based solutions. This is the reason why we have considered the exploration of the theoretical fundamentals in this thesis together with the development of an advanced human body model. These are important constituents of the realization of HCPD in our specific field of application. Through a knowledge intensive human body model the behaviour in physical interaction can be simulated as it happens with true organic bodies..

(54) Sec. 1.1 — Background of promotion research. 7. 1.1.3 Levels of modelling a human body We have seen that HCPD relies on a wide area of disciplines, and covers in principle any aspect of the functioning of the human body and mind. An ideal model would simulate all properties and their relationships. Building such a holistic model, which is able to represent all above aspects, requires (i) sufficient data that describes the functioning quantitatively, (ii) interpretative skills of the model builders, (iii) specialised modelling skills and computational tools, (iv) the skills to handle the inherent complexity, (v) the validation of such model for validity and robustness, and (vi) the knowledge, the skills and the power to use the model in an application. Although such a model would make a perfect simulation possible, there are two reasons to refrain from such a knowledge and work explosion. First, the modelling effort would exceed the typically available reach of human capabilities. Second it will definitely never be needed for design purposes. effort. ideal. optimal advanced simple 0%. 100% knowledge. Figure 1-3. Graphical presentation of the relationship between the incorporated amount of knowledge and the required efforts for data gathering, modelling, etc. The major issues for computational model generation and processing are complexity, fidelity, robustness and validation. Complexity originates from the need (i) to aggregate a large body of knowledge for multiple applications, (ii) to structure the knowledge consistence for a computational and interactive use, and (iii) to validate the model for all aspects and problems of application. Having this in mind, we had to consider a possible reduction of the knowledge, incorporated in the model. On the basis of the extent of reduction, we can talk about models of various levels. For instance, we could build a model that were able to simulate all relevant aspects of a particular person-product interaction, and to deliver all knowledge, necessary for designers and engineers. This model could be called an optimal model. However, practically speaking, for most applications this is remaining a dream. The next level of modelling could offer the knowledge that (i) is available or can be obtained without unreasonable efforts, (ii) can be interpreted with respect to the application, (iii) can be effectively used in a sufficiently precise modelling of the human body, and (iv) can offer a solution for handling reasonable complexities. This level of complexity of models makes sense and the validation of these models is also sensible. Such a model has been called an advanced model. Besides these we can also consider a less perfect model, that must be suited to test the feasibility of just one or more aspects of the.