1. Elastic Measurements in an Operating Shoe Sole
BME 301
Steven Pauls, Timothy Rand
Brian Schwartz, Brant Kochsiek
Advisor: Professor Naomi Chesler
Client: Professor David Beebe
March 5, 2004

2. University of Wisconsin – Madison
Biomedical Engineering Design Courses
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3. Problem Statement Device should fit into the sole of a shoe
Inform runner when shoe is worn
Decrease incidence of injury due to shoe
wear
Measure the elasticity of the shoe sole
Direct measurement
Other methods

4. Problem Motivation Running shoes last 300-500 miles
Worn shoes not always “worn”
Incidence of injury increases with worn shoes
Diagnostic tool in relation to running style

5. Client Requirements Lightweight Ergonomic with sole
Operable for life of the running shoe
Should not hinder performance
Have clear indicator

6. Elastic Effect Elastic recoil cushions impact
Age/Wear decreases elastic effect
Similar stresses create more strain on material

7. Shoe Materials Ethylene and Vinyl Acetate (EVA) Polyurethane (PU)
Upper
Footbridge
Midsole
Outsole

8. Pronation Styles
Wet sand imprints indicating foot shape and pronation style
Most common strides (note: underpronation is also termed supination)

9. Shoe Wear Patterns Forefoot Striking Neutral Overpronation Supination

10. Principles Design Matrix
Electrical
Mechanical
Chemical
Complexity 3 1
Feasibility 2
Cost
Performance
Total 11 8 7

11. Strain Gauge Directly affected by elasticity (ε = σ ∕ E) Inexpensive
Small
Requires calibration
Incorrect alignment

12. Conductive Polymer Force Sensor
Resistive elements
Medium to high pressure range
Compact
Indirect Measurement
Requires calibration

13. Force Differential
Impact creates force (F), smaller dispersal force (f)
F α f as a function of shoe sole force absorbance
Force absorbance during impact is a function of elasticity
Set ratio F:f will trigger sensor, indicate elastic wear

14. Retroreflectors Advantages Disadvantages Small, lightweight, & cheap
Only taking one measurement (distance) instead of two
Virtually no wear on device
Disadvantages
Need for clear polymer in some portions of the shoe sole
Distance measurement may not correlate to shoe sole elasticity

15. Future Work Polymer which degrades faster than EVA or polyurethane
Integrate retro-reflector, strain gauge, & a conductive polymer force sensor into polymer mold
Perform tests to determine which device is able to detect wear (elasticity) the best
Determine correlation between shoe wear and output of each device
Select ultimate wear value
Integrate chosen device into a shoe sole for field testing
Possible patent application

16. Prototype Design Matrix
Retro-Reflectors
Strain Gauge
Conductive Polymer
Performance
Cost
Reliability
Size/Weight
Totals

17. Acknowledgments Professor Naomi Chesler Professor David Beebe
Professor John Webster
UW Biomedical-Engineering Dept.