Team Members:
Brant Kochsiek
Steve Pauls
Tim Rand
Brian Schwartz
BSAC
Team Leader
Communicator
BWIG
Client:
David Beebe, Ph. D
Biomedical Engineering
Advisor:
Naomi Chesler, Ph. D
Biomedical Engineering
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 used in shoe sole
construction. The degree to which a shoe sole
degrades is directly related to the changing
elasticity of the material. Two different methods are
proposed to measure elasticity in a shoe sole.
Strain gauges and Flexi-Force piezoelectric force
sensor devices have been added to an integrated
circuit that will indirectly measure shoe sole
elasticity. Once calibrated, each circuit will have a
diode that lights when a shoe sole is worn past its
useful life.
Problem Motivation
Running shoes last
300-500 miles
Worn shoes do not
always appear worn
Incidence of injury
increases with worn
shoes
http://members.cox.net/gumpisms/hanks1.jpg
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
– Operable for the life of a running shoe (300500 miles)
– Has a clear indicator so the runner will know
when the shoe is sufficiently worn
Shoe Materials
Ethylene Vinyl Acetate (EVA)
Polyurethane (PU)
Upper
Footbridge
Midsole
Outsole
http://www.dummies.com/WileyCDA/DummiesArticle/id-450,subcat-SPORTS.html
Nominal Running Style
• Heel strike
• Inward pronation
(rolling action of
the foot)
• Ball of foot strike
• Forefoot push off
http://www.dummies.com/WileyCDA/DummiesArticle/id-450,subcat-SPORTS.html
Pressure Distribution while
Running
Maximum pressures in
the midsole occur
beneath the heel, the
middle to inner portion of
the forefoot, and the big
toe.
http://www.uni-essen.de/~qpd800/index.html
Force Sensor Circuit
Comparator/LED
Differential Amplifier
Drive Circuit
Voltage regulator
FlexiForce® Sensors
http://www.tekscan.com/flexiforce/flexiforce.html
Comparison of forces
from top to bottom
http://www.btinternet.com/~bury_rd/cheatah.jpg
Strain Gauge Circuit
Comparator/LED
Differential Amplifier
Strain Gauge
Strain Gauge
Constant Poisson’s
Ratio (v),
Stress-Strain (δ-ε) for
Elasticity (E)
http://www.btinternet.com/~bury_rd/cheatah.jpg
www.sensorland.com/ HowPage002.html
Variable Force Strain Gauge
Sensors
3
4
Cost
Measurement
accuracy
Durability
Circuit
integration
Size
5
3
3
2
3
3
3
3
Performance
?
?
Total
16
16
1 = Worst
5 = Best
Advantage
FlexiForce®
Force
comparison
-Paper thin
-Allows for fine
adjustments
-More precise
Strain Gauge -Cost
Measurement -Simple circuit
-Simple
construction
Disadvantage
-Complicated
construction
-Complex
comparative
circuit
-More expensive
-More of an
indirect
measurement
-More bulky
Preliminary Testing
Sensor response Test
6
5
Voltage (V)
4
Tested
3
Projected
2
1
0
0
200
400
600
Load (lbs)
800
1000
Current Standing
Preliminary tests showed flaws in our
circuit and sensor set up
Circuit is being reworked and future testing
will soon follow
Research into exact placement of sensors
in shoe sole is ongoing
Testing Procedure
Apply static loads to sensors imbedded in
silicone polymer
Loads applied in sets of 4000 which
correlates to about a 6 mile run
Following each set:
– Elasticity of material will be measured
– Output of circuit will be read from multimeter
– Output vs. elasticity will be plotted
MTS Servohydraulic Machine
We plan to use an older version of this
machine found in the Materials Testing
Lab in Engineering Hall
http://www.mts.com/menusystem.asp?DataSource=0&NodeID=1483
Future Work
Mold strain gauge into silicon mold
Test both prototypes to simulate 500 miles of
running wear
Determine the correlation between the output of
each device and elasticity
Determine shoe sole wear threshold value
Integrate chosen device and corresponding
circuit into a shoe sole for testing
Research and go through necessary human
subject testing procedures
Undergo human testing of the prototype shoe
Possible patent application
References
“1000 Hz High-Cycle Fatigue Testing Systems.” MTS Inc. Accessed 4/28/04 URL:
http://www.mts.com/menusystem.asp?DataSource=0&NodeID=1483
“Anatomy of a Running Shoe.” American Running Association.
Accessed: 04/26/04 URL:
http://www.americanrunning.org/displayindustryarticle.com.
“Biomechanics Laboratory.” Accessed: 04/24/04 URL: http://www.uni-essen.de/~qpd800/index.html.
“BTopenworld”. Accessed: 04/24/04 URL:
http://www.btinternet.com/~bury_rd/cheatah.jpg.
“FlexiForce Force Sensors.” Tekscan. Accessed: 04/25/04 URL:
http://www.tekscan.com/flexiforce/flexiforce.html.
“Forrest Gump Pictures.” Cox Members High Speed Internet. Accessed 02/26/04 URL:
http://members.cox.net/gumpisms/hanks1.jpg
Hennig, E. M., & Milani, T. L. 1995. In-shoe Pressure Distribution for
Running in Various Types of Footwear. Human Kinetics Publishers
Inc., New York.
Mills, N., & Verdejo, R. 2002. Performance of EVA Foam in Running
Shoes. Blackwell Inc., UK, Birmingham.
“Runner’s World.” Runners World. Accessed:04/27/04 URL: http://www.runnersworld.com/.
“Running Shoes.” ePodiatry. Accessed: 04/26/04 URL:
http://www.epodiatry.com/running-shoes.htm,
Special Thanks
Professor David Beebe
Professor Naomi Chesler
Amelia Cosgrove
John W. Dreger
Ivar Meyvantsson
Professor Tim Osswald
Professor Mitch Tyler
Paul Victorey
Professor John Webster