Team Members

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• Team Members
• Steve Pauls Team Leader
• Tim Rand Communicator
• Brian Schwartz BWIG
• Brant Kochsiek BSAC

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• Client
• David Beebe, Ph. D
• Biomedical Engineering
• Advisor
• Justin Williams, Ph. D
• Biomedical Engineering

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Abstract

• Many running injuries are caused by continued use
  of improper or worn running shoes. The increase
  in incidence of injury can be directly correlated
  to the degradation of the materials within in the
  shoe sole. Our team has designed a device which
  integrates two Flexi-Force conductive polymer
  sensors into shoe soles in order to measure the
  force dissipated by the shoe sole. A circuit has
  been designed to create a ratio of the two force
  measurements which we hypothesize will correlate
  to the elasticity of the shoe sole. Preliminary
  testing has shown that this differential output
  of the circuit is proportional to the elasticity
  of the shoe soles. Testing has also shown that
  the differential circuit output for each shoe
  sole was dependent on the magnitude of force
  applied. Testing was only done on a limited
  number of samples and future work will look to
  expand on and replicate the current data.

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Problem Motivation

• Running shoes last 300-500 miles
• Worn shoes do not always appear worn
• Incidence of injury increases with worn shoes

350 miles of running wear
Less than 50 miles of running wear
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Client Requirements

• Design a device that
• Measures shoe sole elasticity
• Fits ergonomically into the shoe sole
• Is lightweight and small so as to not hinder
  performance
• Is durable enough to last the life of a running
  shoe (300-500 miles)
• Has a clear indicator so the runner will know
  when the shoe is sufficiently worn

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Proposed Design Components

• Three stage circuit
• Single inverting amplification stages
• Differential amplifier
• Comparator

• Two Flexi-Force sensors with 0-100 pound range

http//www.tekscan.com/flexiforce/flexiforce.html
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Proposed Placement of Sensors

• Two Flexi-Force sensors molded centrally in heel
  of the shoe sole
• Sensors 1 and 2 are parallel in horizontal plane

1
2
2
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Shoe Sample Preparation

• Extracted shoe soles from 9 different pairs of
  shoes
• Two cuts were made in the heel of each shoe sole
  a vertical distance of 5/8 apart
• All cuts were done with a scalpel and made to be
  as smooth and as horizontal as possible

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Circuit Response Testing Procedure

• Sintech 10 GL 10,000 pound test machine

http//www.mts.com/menusystem.asp?DataSource0Nod
eID1483
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• One sensor was inserted into both slits and
  connected to the differential circuit
• A gradually increasing load from 0 to 50 lbs. was
  applied to each shoe sole
• A metal cylinder (1 inch diameter) was used to
  focus the force onto shoe sole
• Output from the differential circuit was recorded
  in real time on an oscilloscope

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Results

• 14 sample results were thrown out due to
  inconsistencies in materials
• Air Pockets
• Multiple Materials
• Data from remaining 4 samples was analyzed for
  each test
• Elasticity test
• Voltage response test

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Elasticity Testing Procedure

• Blocks were cut out of the shoe sole sensing
  regions using a table saw
• Simple compression test was used to generate
  stress vs. strain curve

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Elasticity Determination

• Refine data from Compression/Elasticity test to
  isolate linear region
• Elasticity is the slope of this linear region
  (1.024 psi in this sample)

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Elasticity Results
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Analysis of Circuit Test Results

• Voltage output vs. Force response was measured
  and plotted
• Voltage vs. Force graphs displayed for multiple
  shoe soles (thus elasticity values)
• Trend shows larger voltage output in shoes with
  higher elasticity for equal force application
• Voltage output increases within same shoe sample
  when applied force is increased
• Trends for limited sampling match expected
  results

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Testing Problems

• Majority of the shoes contained either air
  pockets or imperfections
• Caused unpredictable and irregular contact
  between the shoe sole and the sensors
• Data from these samples was thrown out
• Difficult to predict the exact placement and
  orientation of sensor when inserted in shoe sole

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Future Work

• Continue testing with a much larger sample size
  of strictly running shoes
• Explore other more effective means of placing
  sensors for testing
• Purchase new shoes, determine the initial
  elasticity, and test the progression of wear
  through dynamic testing
• Investigate marketability of our design
• Discuss potential patent possibilities with WARF

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Special Thanks

• Professor David Beebe
• Professor Justin Williams
• John W. Dreger
• Paul Victorey