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Analysis of contact pressure of the face using finite eleent analysis on 3D scan datablase

Handong Global University
Handong Global University

Abstract: 3D body scanning has been used broadly including digital human modeling, simulation, ergonomic product design, and so forth. This research used template-registered faces of 336 Koreans in order to use them to design an oxy-gen mask that provides good fit to Korean faces. The finite element analysis method is applied onto the template-registered faces to predict the contact pres-sure of a mask design onto different faces. The average and variation of the esti-mated contact pressure values among all the Korean faces were analyzed for eval-uation of the appropriateness of a mask design for Koreans. The proposed meth-od can be usefully applied to find an optimal shape of wearable products for a specific target population.

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1 Wonsup Lee1, Jin-Gyun Kim2, Johan M. F. Molenbroek3, Richard H. M. Goossens3, Hayoung Jung4, and Heecheon You4 1 School of Global Entrepreneurship and ICT, Handong Global University, South Korea 2 Department of Mechanical Engineering, Kyung Hee University, South Korea 3 Faculty of Industrial Design Engineering, Delft University of Technology, Netherlands 4 Department of Industrial and Management Engineering, Pohang University of Science and Technology (POSTECH), South Korea
2 Contents Introduction Background Objectives of the Study Template Model Registration Contact Pressure Estimation by Finite Element Analysis Discussion Q & A
3 Limitation of Previous Study Our previous study (Lee et al., 2018) proposed a virtual fit simulation method to find the optimal shape of an oxygen mask (OM) design for fighter plots A mask design drawn by CAD was virtually fit to each of 3D face images and the distance between the mask and face was calculated Limitation: The material properties of the face and mask need to be considered for more realistic virtual fit analysis and more optimized OM design 3D Face Scanning Editing & Measurement Mask DesignVirtual Fit Simulation Lee et al. (2018). Ergonomic evaluation of pilot oxygen mask designs. Applied Ergonomics, 67, pp. 133-141.
4 Contact Pressure Estimation A simple FE method is needed using a sufficient number of faces (say, over 100) for contact pressure analysis A finite element analysis (FEA) approach using FEA software such as ANSYS, LS-DYNA (Dai et al., 2011; Lei et al., 2012) was applied for realistic analysis of contact pressure of a mask over a face Only one or a few face scans were applied to analyze the contact pressure of a mask over the face A complex procedure and a significant amount of time (several hours) are needed to manipulate 3D face and mask images using FEA software
5 1. Applying a sufficient number of 3D face scans to designing an optimal shape of mask 2. Application of finite element analysis (FEA) method to considering material properties of the face and mask 3. Simplification of the face and mask images and FE model for easy use of sufficient 3D face scans in FE analysis Objectives of the Study A study on realistic virtual fit analysis with considering material properties of the face and mask
6 3D Face Scan Data Faces of Korean Air Force pilots and KAF Academy cadets (Lee et al., 2013) n = 336 (male: 278, female: 58) small narrow medium narrow medium wide large wide
7 Template Face Model Characteristics of the template face model Average size Symmetry Unevenly distributed mesh (more meshes around mask-fit area) Number of vertex = 1,340 Number of faces = 2,624 24 landmarks on vertex points
8 registration Template Model Template Registration Illustration of registration of the template face model to each 3D face Template-registered image
9 Application of FEA: Concept of FEA Each triangular mesh consisting the face image has 9 degrees of freedoms (DOFs) = 3 vertex 3 DOFs per vertex 3 DOFs mean possibilities of translation in x, y, and z directions In total of 9 DOFs is describing the change of each mesh The change of mesh is described as a 99 stiffness matrix (called as K ) vertex 1 vertex 2 vertex 3 x, y, z translation of node 1 x, y, z translation of node 2 x, y, z translation of node 3 triangular mesh k11 k12 k13 k14 k15 k16 k17 k18 k19 k21 k22 k23 k24 k25 k26 k27 k28 k29 k31 k32 k33 k34 k35 k36 k37 k38 k39 k41 k42 k43 k44 k45 k46 k47 k48 k49 k51 k52 k53 k54 k55 k56 k57 k58 k59 k61 k62 k63 k64 k65 k66 k67 k68 k69 k71 k72 k73 k74 k75 k76 k77 k78 k79 K81 k82 k83 k84 k85 k86 k87 k88 k89 k91 k92 k93 k94 k95 k96 k97 k98 k99 Km = ux1 uy1 uz1 ux2 uy2 uz2 ux3 uy3 uz3 ux1 uy1 uz1 ux2 uy2 uz2 ux3 uy3 uz3 where, m is the mesh number (1 ~ 2624) k is component of the stiffness matrix E is Youngs modulus, 僚 is Poisson ratio = (, 僚) defining the material property of the face
10 Application of FEA: Estimation of Force (f) Estimated force at each vertex consisting of the face is calculated as Contact pressure is assumed as a measure that is proportionally equivalent to the force 1 2 3 = 11 21 31 12 22 32 1 2 3 f uK= triangular mesh f3 f1 f2 where, K is an assembled stiffness matrix of all Km (K is different by faces) u is displacement vector of the vertex vertex 3 vertex 1 vertex 2 u1 u2 u3 estimated pressure at each vertex of the face (illustrated)
11 Virtual Fitting with Different Designs of Mask The face-contacting part of the mask is drawn as a single curvature Then, the curvature was virtually fit to 3D faces The facial areas pushed by the curvature were simply calculated by f=Ku using Matlab Design A Design B Different mask designs (illustrated) Template-registered faces
12 Virtual Fitting & FE Analysis (Video) Front view Side view
13 Results: Average Contact Pressure Average of the estimated contact pressure were analyzed by the vertex point, then visualized by color Design B shows smaller and more equally-distributed contact pressure then the design A Mask design A Mask design B
14 Results: Variation of Contact Pressure Standard deviation of the estimated contact pressure were analyzed by the vertex point, then visualized by color Design B shows less varied contact pressure then the design A Mask design A Mask design B
15 Discussion & Further Study (1/2) This study developed a FEA-based virtual fit method for design and evaluation of the pilot OM The template model registration was applied to 3D face scan database All the 3D faces have same mesh topology Average and variation of the estimated contact pressure could be analyzed per each vertex point Further study: Design of the optimized shape of the mask based on the information of average and variation of the contact pressure
16 Discussion & Further Study (2/2) A simplified FE model was applied to estimate realistic interaction between the faces and mask design Material property of the face and mask was considered Contact pressure of the mask over the face was estimated As a preceding research, this study limitedly applied the material properties Need more realistic material properties for more accurate estimation of the contact pressure Need to apply different material properties by facial area (e.g., around nasal bone, around cheek, around chin) The proposed method could be applied for optimal design of wearable products
more questions to W.Lee@handong.edu (Wonsup Lee)

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Analysis of contact pressure of the face using finite eleent analysis on 3D scan datablase

  • 1. 1 Wonsup Lee1, Jin-Gyun Kim2, Johan M. F. Molenbroek3, Richard H. M. Goossens3, Hayoung Jung4, and Heecheon You4 1 School of Global Entrepreneurship and ICT, Handong Global University, South Korea 2 Department of Mechanical Engineering, Kyung Hee University, South Korea 3 Faculty of Industrial Design Engineering, Delft University of Technology, Netherlands 4 Department of Industrial and Management Engineering, Pohang University of Science and Technology (POSTECH), South Korea
  • 2. 2 Contents Introduction Background Objectives of the Study Template Model Registration Contact Pressure Estimation by Finite Element Analysis Discussion Q & A
  • 3. 3 Limitation of Previous Study Our previous study (Lee et al., 2018) proposed a virtual fit simulation method to find the optimal shape of an oxygen mask (OM) design for fighter plots A mask design drawn by CAD was virtually fit to each of 3D face images and the distance between the mask and face was calculated Limitation: The material properties of the face and mask need to be considered for more realistic virtual fit analysis and more optimized OM design 3D Face Scanning Editing & Measurement Mask DesignVirtual Fit Simulation Lee et al. (2018). Ergonomic evaluation of pilot oxygen mask designs. Applied Ergonomics, 67, pp. 133-141.
  • 4. 4 Contact Pressure Estimation A simple FE method is needed using a sufficient number of faces (say, over 100) for contact pressure analysis A finite element analysis (FEA) approach using FEA software such as ANSYS, LS-DYNA (Dai et al., 2011; Lei et al., 2012) was applied for realistic analysis of contact pressure of a mask over a face Only one or a few face scans were applied to analyze the contact pressure of a mask over the face A complex procedure and a significant amount of time (several hours) are needed to manipulate 3D face and mask images using FEA software
  • 5. 5 1. Applying a sufficient number of 3D face scans to designing an optimal shape of mask 2. Application of finite element analysis (FEA) method to considering material properties of the face and mask 3. Simplification of the face and mask images and FE model for easy use of sufficient 3D face scans in FE analysis Objectives of the Study A study on realistic virtual fit analysis with considering material properties of the face and mask
  • 6. 6 3D Face Scan Data Faces of Korean Air Force pilots and KAF Academy cadets (Lee et al., 2013) n = 336 (male: 278, female: 58) small narrow medium narrow medium wide large wide
  • 7. 7 Template Face Model Characteristics of the template face model Average size Symmetry Unevenly distributed mesh (more meshes around mask-fit area) Number of vertex = 1,340 Number of faces = 2,624 24 landmarks on vertex points
  • 8. 8 registration Template Model Template Registration Illustration of registration of the template face model to each 3D face Template-registered image
  • 9. 9 Application of FEA: Concept of FEA Each triangular mesh consisting the face image has 9 degrees of freedoms (DOFs) = 3 vertex 3 DOFs per vertex 3 DOFs mean possibilities of translation in x, y, and z directions In total of 9 DOFs is describing the change of each mesh The change of mesh is described as a 99 stiffness matrix (called as K ) vertex 1 vertex 2 vertex 3 x, y, z translation of node 1 x, y, z translation of node 2 x, y, z translation of node 3 triangular mesh k11 k12 k13 k14 k15 k16 k17 k18 k19 k21 k22 k23 k24 k25 k26 k27 k28 k29 k31 k32 k33 k34 k35 k36 k37 k38 k39 k41 k42 k43 k44 k45 k46 k47 k48 k49 k51 k52 k53 k54 k55 k56 k57 k58 k59 k61 k62 k63 k64 k65 k66 k67 k68 k69 k71 k72 k73 k74 k75 k76 k77 k78 k79 K81 k82 k83 k84 k85 k86 k87 k88 k89 k91 k92 k93 k94 k95 k96 k97 k98 k99 Km = ux1 uy1 uz1 ux2 uy2 uz2 ux3 uy3 uz3 ux1 uy1 uz1 ux2 uy2 uz2 ux3 uy3 uz3 where, m is the mesh number (1 ~ 2624) k is component of the stiffness matrix E is Youngs modulus, 僚 is Poisson ratio = (, 僚) defining the material property of the face
  • 10. 10 Application of FEA: Estimation of Force (f) Estimated force at each vertex consisting of the face is calculated as Contact pressure is assumed as a measure that is proportionally equivalent to the force 1 2 3 = 11 21 31 12 22 32 1 2 3 f uK= triangular mesh f3 f1 f2 where, K is an assembled stiffness matrix of all Km (K is different by faces) u is displacement vector of the vertex vertex 3 vertex 1 vertex 2 u1 u2 u3 estimated pressure at each vertex of the face (illustrated)
  • 11. 11 Virtual Fitting with Different Designs of Mask The face-contacting part of the mask is drawn as a single curvature Then, the curvature was virtually fit to 3D faces The facial areas pushed by the curvature were simply calculated by f=Ku using Matlab Design A Design B Different mask designs (illustrated) Template-registered faces
  • 12. 12 Virtual Fitting & FE Analysis (Video) Front view Side view
  • 13. 13 Results: Average Contact Pressure Average of the estimated contact pressure were analyzed by the vertex point, then visualized by color Design B shows smaller and more equally-distributed contact pressure then the design A Mask design A Mask design B
  • 14. 14 Results: Variation of Contact Pressure Standard deviation of the estimated contact pressure were analyzed by the vertex point, then visualized by color Design B shows less varied contact pressure then the design A Mask design A Mask design B
  • 15. 15 Discussion & Further Study (1/2) This study developed a FEA-based virtual fit method for design and evaluation of the pilot OM The template model registration was applied to 3D face scan database All the 3D faces have same mesh topology Average and variation of the estimated contact pressure could be analyzed per each vertex point Further study: Design of the optimized shape of the mask based on the information of average and variation of the contact pressure
  • 16. 16 Discussion & Further Study (2/2) A simplified FE model was applied to estimate realistic interaction between the faces and mask design Material property of the face and mask was considered Contact pressure of the mask over the face was estimated As a preceding research, this study limitedly applied the material properties Need more realistic material properties for more accurate estimation of the contact pressure Need to apply different material properties by facial area (e.g., around nasal bone, around cheek, around chin) The proposed method could be applied for optimal design of wearable products
  • 17. more questions to W.Lee@handong.edu (Wonsup Lee)