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Vibration Response Study to Understand Hand-Arm Injury Shrikant Pattnaik, Robin DeJager-Kennedy Jay Kim Department of Mechanical Engineering, University of Cincinnati, Cincinnati, OHIO 1

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Research focus: how vibration affects hand and arm injuries 2 Develop hypotheses that can explain the mechanism with scientific rationale – Musculoskeletal disorder – Vascular disorder Develop scientific approaches – Engineering models – Develop numerical analysis methods – Direct or indirect Experimental validation

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Presentation summary Vibration analysis models A hypothetical model proposed to explain a cause of vascular system disorder Plan to work on discrete system models 3

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Initial FEA Vibration Model 4 Goals: Obtain basic data for further analysis of Musculoskeletal and vascular systems Step 1 : Pre compression, non linear contact analysis Step 2 : Extraction of natural modes Step 3 : Steady state dynamic analysis Displacement Strain

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Issues Overly simplified boundary conditions and models – Un-modeled parts, initial configuration/posture, grip, significantly influences natural modes and dynamic responses significantly – Effects of grip force and length of handling are not difficult to be considered Overly simplified muscle forces – Active tendon forces are not included – Most finger musculo-tendon structure extends to elbow 5

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LifeMOD Building a Model Segments Joints Soft Tissues Passive Modeling Contact Hybrid III Parameters Active Modeling Motion Capture integration LifeMOD Inverse and Forward dynamics Post Processing and Export The LifeMOD Biomechanics Modeler is a plug-in module to the ADAMS physics engine. LifeMOD allows full functionality of ADAMS/View. Human models can be combined with any ADAMS model for full dynamic interaction.

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Multi-level Approach based in Adams/LifeMod 7

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The LifeMOD Suite CervicalSIM KneeSIM LifeMOD LumbarSIM HipSIM HandSIM – shrikant

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Development of Hand Model 9

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Tissue-wrapping 10 Forearm model with the flexor digitorum profundus set up to slide with respect to the third metacarpal bone. The flexor digitorum profundus muscle group before slide points are introduced (left) and after (right).

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Muscle Model (Nonlinearity) 11 Muscle Matrix for the active muscle groups A – they are tension only elements B – there is redundancy

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Active + Passive contribution 12

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Muscle Fatigue 13 Tetanic Frequency full motor unit recruitment maintained for a short period of time, 6 s 70% max the blood flow is completely occluded and fatigue hyperbolic relationship with an asymptote at roughly 15% of maximum strength

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Frequency Analysis In terms of passive muscle, this means that at very low or high frequencies the forcing function and muscle response are practically in phase elastically dominated by either the series elastic element (K SE ) for very high frequencies (i.e., the dashpot cannot respond sufficiently quickly, eliminating the parallel elastic element from the model) or by a combination of both elastic elements K SE /(K SE + K PE ) for very low frequencies (i.e., the dashpot responds, stretching the parallel elastic element with it). Around the critical break frequency the muscle is fully viscoelastic with the dashpot involved. 14

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FRF Analysis: Input point impedance 15

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Strategy of complete Frequency Analysis 16 o Grip the required hand tool o Find the equilibrium o Train the muscle and joints o Find natural Frequencies and modes o Identify critical elements from the natural modes Forced response for particular configuration Introduce fatigue model – endurance analysis connect with individual flexible part in Adams/Flex

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Integration of Rigid + Flexible body Originally ADAMS – rigid body with 3 translation and 3 rotational DOF. Adams/Flex, flexible body Deformation = linear combination of linear mode shapes from FEA or Experimental modal analysis Component Mode Synthesis – selected modes transferred using MNF (mode neutral files) from say Abaqus. Generalized stiffness is diagonalized, Mass matrix formulated using inertia invariants, Damping specified as fraction of critical damping. Subset of mode shapes goes to solver 17

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Test/Demo Case I Initial Equilibrium Analysis using the full hand-arm model; for the given contact force; – Find how muscles/tendons are loaded – Find how joint forces are loaded Detail analysis of the fingertip by a ABACUS model – Contact analysis – Vibration analysis – Review the time histories of the forces in the bone joint and tendon 18

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Test/Demo Case I – continue 1 st Phalange 2 nd Phalange 3 rd Phalange Hand 19 Muscle and Joints Shown is the example of 1 st phalange

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Test/Demo Case II LifeMod model of Hand-Arm Find Gripping force to hold two different type of tools Ensuing vibration analysis – Response characteristics; comparison to discrete models; possible experiments 20 Tools lifted Tools pushed

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Integration Hand Model 5%ile Pressure Data Motion Capture Hand Model 50%ile Hand Model 50%ile Hand Model 95%ile Hand Model 95%ile Risk+Pain+Discomfort Assessment Muscle/Tendon Forces Joint Forces Joint Forces Ergonomic Standards Test New Designs Guidelines for new packages Validation Consumer Research Database Pain Locations Chosen Hand configurations

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Data Collection Pressure Mat Vicon Motion Capture Cyber Glove Pressure Map

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Example Animation with plot

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Vascular system disorder: A view from wave propagation / fluid-structure dynamics Desire to understand why vibration is detrimental to vascular disorder Blood in an artery comprise a fluid-structure system Optimal wave propagation condition may be responsible 24

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Wave propagation in Artery wall 25 Moens-Korteweg wave speed Fluid flow in artery Continuity Fluid eq. Artery cross-section Artery wall, radius R Surrounding tissue p

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Wave propagation in artery wall 26 Wall-blood wave Section behaves like a cylindrical shell of n=0 mode (membrane mode) Critical condition: when the resonance frequency of the cylindrical membrane of length coincides with disturbance

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Artery wall as a cylindrical shell 27 Circular cylinder shell simply supported Assumed solution Equations of motion m=1 natural frequency when n=0 and m=1

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Rough estimation of resonance condition of a typical rat tail artery 28 Critical Frequencies, f* = 950Hz, 1850Hz f(n=0,m=1) The above is only a very preliminary estimation Data should be refined Is the surrounding tissue has a more added mass effect or Winkler foundation effect?

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Comparison of Various Lumped Parameter Hand-Arm Models 29 Lumped parameter hand-arm model A compact tool Vibration response of hand-held tool Vibration response of free-suspended tool Comparison of the prediction of the pair by the model and measurement to qualitatively evaluate hand-arm models

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Research Plan Select models to compare. Collect acceleration data for two or three tools. Use data to determine input force to apply to models. Simulate response of models. Compare simulated response to measured response of hand-held tool. 30

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Hand-Arm Models 31 Models vary in complexity from 1 DOF to many DOFs. Various values for constants are available for the different models.

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Data Collection Acceleration data collected for: – Free suspended – Held in hands Test procedure is with grinder running freely. 32

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Sample Acceleration Data 33 Data collected for DeWalt handheld DW818 grinder

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Open Discussions Refinement of the models Expansion or simplification of the models Possible validations – Direct / indirect validations – Qualitative / quantitative validations Application ideas Criticisms and suggestions 34

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