Elastic MeasurementsElastic Measurementsin an Operating Shoe Sole in an Operating Shoe Sole

BME 301BME 301Steven Pauls, Timothy RandSteven Pauls, Timothy Rand

Brian Schwartz, Brant KochsiekBrian Schwartz, Brant Kochsiek

Advisor: Professor Naomi CheslerAdvisor: Professor Naomi CheslerClient: Professor David BeebeClient: Professor David Beebe

March 5, 2004March 5, 2004

University of Wisconsin – MadisonBiomedical Engineering Design Courses

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Problem StatementProblem Statement

Device should fit into the sole of a shoeDevice should fit into the sole of a shoe

Inform runner when shoe is wornInform runner when shoe is worn

Decrease incidence of injury due to shoe Decrease incidence of injury due to shoe

wear wear

Measure the elasticity of the shoe soleMeasure the elasticity of the shoe sole Direct measurementDirect measurement Other methodsOther methods

Problem MotivationProblem Motivation

Running shoes last Running shoes last 300-500 miles 300-500 miles

Worn shoes not always Worn shoes not always “worn”“worn”

Incidence of injury Incidence of injury increases with worn increases with worn shoesshoes

Diagnostic tool in Diagnostic tool in relation to running stylerelation to running style

Client RequirementsClient Requirements

Lightweight Lightweight

Ergonomic with soleErgonomic with sole

Operable for life of the running shoeOperable for life of the running shoe

Should not hinder performanceShould not hinder performance

Have clear indicatorHave clear indicator

Elastic EffectElastic Effect

Elastic recoil cushions Elastic recoil cushions impactimpact

Age/Wear decreases Age/Wear decreases elastic effectelastic effect

Similar stresses Similar stresses create more strain on create more strain on materialmaterial

Shoe MaterialsShoe Materials

Ethylene and Vinyl Acetate (EVA)Ethylene and Vinyl Acetate (EVA)

Polyurethane (PU)Polyurethane (PU)

Outsole

Midsole

Upper

Footbridge

http://www.dummies.com/WileyCDA/DummiesArticle/id-450,subcat-SPORTS.html

Pronation StylesPronation Styles

Most common strides (note: underpronation is also termed supination)

Wet sand imprints indicating foot shape and pronation style

http://www.dummies.com/WileyCDA/DummiesArticle/id-450,subcat-SPORTS.html

Shoe Wear PatternsShoe Wear Patterns

Forefoot StrikingForefoot Striking

NeutralNeutral

• Overpronation

• Supination

http://www.fleetfeethouston.com/tips/basics.asp

Principles Design MatrixPrinciples Design Matrix

ElectricalElectrical MechanicalMechanical ChemicalChemical

ComplexityComplexity 33 33 11

FeasibilityFeasibility 33 22 11

CostCost 22 22 22

PerformancePerformance 33 11 33

TotalTotal 1111 88 77

Strain GaugeStrain Gauge

Directly affected by Directly affected by elasticity (elasticity (εε = = σσ ∕∕ E E))

InexpensiveInexpensive

SmallSmall

http://www.dur.ac.uk/richard.scott/gauges.htmlRequires calibrationRequires calibration

Incorrect alignmentIncorrect alignment

Conductive PolymerConductive PolymerForce SensorForce Sensor

Resistive elementsResistive elements

Medium to high Medium to high pressure rangepressure range

CompactCompact

http://interlinkstore.com

Indirect MeasurementIndirect Measurement

Requires calibrationRequires calibration

Force DifferentialForce DifferentialImpact creates force (F), smaller dispersal force (f)Impact creates force (F), smaller dispersal force (f)

F F αα f as a function of shoe sole force absorbance f as a function of shoe sole force absorbance

Force absorbance during impact is a function of Force absorbance during impact is a function of elasticityelasticity

Set ratio F:f will trigger sensor, indicate elastic wearSet ratio F:f will trigger sensor, indicate elastic wear

RetroreflectorsRetroreflectorsAdvantagesAdvantages Small, lightweight, & cheapSmall, lightweight, & cheap Only taking one measurement (distance) Only taking one measurement (distance)

instead of twoinstead of two Virtually no wear on deviceVirtually no wear on device

DisadvantagesDisadvantages Need for clear polymer in some portions of the Need for clear polymer in some portions of the

shoe soleshoe sole Distance measurement may not correlate to Distance measurement may not correlate to

shoe sole elasticityshoe sole elasticity

Future WorkFuture Work

Polymer which degrades faster than EVA or polyurethanePolymer which degrades faster than EVA or polyurethaneIntegrate retro-reflector, strain gauge, & a conductive Integrate retro-reflector, strain gauge, & a conductive polymer force sensor into polymer moldpolymer force sensor into polymer moldPerform tests to determine which device is able to detect Perform tests to determine which device is able to detect wear (elasticity) the bestwear (elasticity) the bestDetermine correlation between shoe wear and output of Determine correlation between shoe wear and output of each deviceeach deviceSelect ultimate wear valueSelect ultimate wear valueIntegrate chosen device into a shoe sole for field testingIntegrate chosen device into a shoe sole for field testingPossible patent applicationPossible patent application

Prototype Design MatrixPrototype Design Matrix

Retro-ReflectorsRetro-Reflectors Strain GaugeStrain Gauge Conductive PolymerConductive Polymer

PerformancePerformance

CostCost

ReliabilityReliability

Size/WeightSize/Weight

TotalsTotals

AcknowledgmentsAcknowledgments

Professor Naomi CheslerProfessor Naomi Chesler

Professor David BeebeProfessor David Beebe

Professor John WebsterProfessor John Webster

UW Biomedical-Engineering Dept.UW Biomedical-Engineering Dept.