Device To Measure The
Elasticity Of A Shoe Sole
Brant Kochsiek
Steve Pauls
Tim Rand
Brian Schwartz
BSAC
Team Leader
Communicator
BWIG
Client:
David Beebe, Ph. D
Biomedical Engineering
Advisor:
Justin Williams, 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. We have proposed the
use of Flexi-Force piezoelectric force sensors
combined with an integrated circuit to indirectly
measure shoe sole elasticity. Once calibrated,
each circuit will have a diode that lights when the
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://www.boston.com/marathon/
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
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.
Flexi-Force offers custom
made sensors that contain
multiple sensing regions,
which could be designed to
measure all areas of
maximum pressures.
http://www.uni-essen.de/~qpd800/index.html
FlexiForce® Sensors
http://www.tekscan.com/flexiforce/flexiforce.html
Comparison of forces
from top to bottom
http://www.btinternet.com/~bury_rd/cheatah.jpg
Force Sensor Circuit
Comparator/LED
Differential Amplifier
Drive Circuit
Voltage regulator
Advantages of 2 Sensor
Design
Compatibility with different types of shoe
soles
Differential force ratios are similar for
runners of different weights
Differential force ratios eliminate the need
for exact sensor readouts.
Our Semester Strategy
Search the internet for improved products
Re-evaluate design from last semester
– Sensors used
– Assumptions made
– Circuit design
– Testing plans
Findings
Loads on sensors will not
be as high as originally
expected
– Voltage regulator stage
unnecessary
Sensors
– Sensors first considered
could not withstand heat in
sole molding process
– High temperature version
FlexiForce® & Tekscan Inc.
Better bulk price for sensors
Re-examined force requirements
Incorrect sensor model supplied
http://www.tekscan.com/flexiforce/flexiforce.html
Sensor Tests
Product specifications
Recreate results
Incorrect sensors
http://www.tekscan.com/flexiforce/flexiforce.html
Programmable IC
SoC (System on Chip)
Analog components
integrated on chip
Programmable
parameters
Programmable
configuration
http://www.anadigm.com/_doc/DS030600-U002.pdf
Circuit Designs
Analog
Digital
+
Easy to assemble
Simple, efficient
Available components Flexible, accurate
Familiar principles
Pre-manufactured
-
Delicate construction Advanced principles
Difficult bulk assembly Too nice
Price
Price
Future Testing
Acquire numerous old shoes and remove the
shoe soles
Measure the elasticity of the shoe soles
Insert Flexi Force sensors into shoe soles
Apply a static load to simulate standing forces
and measure the voltage output
Construct a graph showing the relationship
between elasticity and voltage output
Future Testing of the Concept
Behind Our Design
Voltage Output (Ratio of Top Sensor/
Bottom Sensor)
Voltage Ouput Vs. Elasticity of Shoe Soles
Elasticity
With increasing shoe sole wear, the elasticity will decrease and
so will the voltage output (ratio of top sensor / bottom sensor)
Determining the Threshold Value
Voltage Ouput Vs. Elasticity of Shoe Soles
Voltage Output (Ratio of Top Sensor/
Bottom Sensor)
Acquire running shoes
with 300 miles of wear
Apply a static force to
simulate standing
The voltage output will be
the threshold value
Calibrate circuit response
to this threshold value by
adjusting the comparator
Threshold
Value
Elasticity
Future Testing
Simulate 300 miles of
wear on a new pair of
running shoes using the
MTS Servohydraulic
Machine
Every 20 miles we will
apply a static force to
simulate standing and
record voltage output
http://www.mts.com/menusystem.asp?DataSource=0&NodeID=1483
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.
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 Justin Williams
John W. Dreger
Ivar Meyvantsson
Professor Mitch Tyler
Paul Victorey