Transcript The Problem - Washington University in St. Louis

In Shoe Pressure Measurement and Analysis in relation to Foot Strike
Saba Naghipour
Department of Electrical and Systems Engineering
Procedure Highlights
Abstract
The In Shoe Pressure System project is a research effort to reduce
running injuries and prevent FootStrike. Despite the money that has been
dispensed into reducing running injuries by designing better shoes, the
ideal way to reduce running injuries may be to simply work on foot
posture finding a way to see the impact of the force and pressure in
different parts of the foot while running. In Shoe Pressure System
seems to be the very reasonable solution to prevent FootStrike.
Experiment Setup
Sensor selection criteria
• Pressure range for running(2.5-76psi)
• Sufficient accuracy(5%)
• Corrosion and dust resistance
• High sensitivity
• Extremely thin & easy to adjust in shoes
Sensor position selection
Overview
There are 15 areas on the sole foot that support body weight but we select the
heel and metatarsal areas to see if a person, favors HeelStrike or Forefoot
Strike.
Circuit Design
•
Goal:
To display the maximum pressure in different parts of foot while
running and to inform the person if they run on their heels.
Approach:
1. Design a circuits to collect data output from sensors
2. Convert the data to pressure
3. Use the data to calculate peak pressure, mean pressure, center of
pressure in both recorded and real time.
Design & develop an electronic interface circuit for the resistive
sensors
• Extract voltage signals from the sensors
• Filter out the noise using a low pass filter at 15Hz.
As the frequency increases above 15Hz the gain decreases. 15Hz is the
frequency of the steps, and anything above that is noise that need to be
filtered. The attach shows that my experimental result matches my
theoretical result.
Results
Application:
• Footwear research for design
• Compare, screen, and isolate food function
• Identify pressure range for medical purposes and personal running
regulation.
Background
The final design of the circuits ended up as an inverting low-pass amplifier
with variable input resistance. Each of the FlexiForce pressure sensors in the
insole are connected to a 2.2nf capacitor, a 5M𝞨 resistor , LM324N 𝑂𝑝 𝐴𝑚𝑝
and grounded though the connector. The -0.5 voltage is input to each of the
sensors.
Biomechanics of Running
Heelstrike runners experience more running injuries such as hip injuries, IT
band syndrome and hip bursitis. The Heelstrike runners land on their heel
first so that the impact force of the heel on the ground causes significant
transient force to their body via the skeletal system. Even though the heel is
the hardest bone of the body, it does not absorb the impact force but it
combines the gravitational forces and compresses them toward the skeleton.
Daniel Lieberman, a researcher at Harvard University said: “Heelstrike can
cause a direct force of up to three times more than a runner’s body weight
on the feet, ankles, knees and hips between 1000-1500 times per time.”
Since MidFoot Strike is considered a preferred type of FootStrike and we
consider the HeellStrike as the worst case, Mid and Heel are the most
important parts of foot that we consider in this research.
Effects of running barefoot or with shoes in relation to
foot strikes
Forefoot
Future Work
Data processing
• Convert embedded analog to digital (A/D) using the Elvis board
• Convert voltage to pressure using calibration
using multiple known masses to came up with voltage for given pressure
then the system convert it to linear equation for easier analysis.
• Convert the data to an array of numbers, record and sample data.
II. Midfoot strike (24%)
III. Toestrike(1%)
2.Add additional sensors to reduce the error and be more accurate
When the pressure increase the resistance of the sensors decrease and
the voltage increase. The Voltage and pressure are proportional by a
constant of k=0.040885.
𝑅𝑓
𝑅𝑓
𝑅𝑓𝑃
Vout= -Vin(
𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑅
)= -Vin(
𝑘/𝑝)
)=-Vin
𝑘
Acknowledge
I would like to thank Professor Morley for all of his help. I am so grateful to Professor
Richter, who made this project possible . Many thanks to the Electrical Engineering
Department at Washington University for their support .
Three basic types of FootStrikes:
Heelstrike(75%)
1.Develop a portable technology suitable for outdoor activities.
Data analysis
Barefoot runners are mostly front foot strikers when running. The heel
cushions and arch supports within athletic shoes have made our feet weaker
and adapted many people to favor HeelStrike. That is the reason that
changing back to barefoot may cause injury to weakened feet.
I.
Heel
Challenges Using Different Methods
 Using accelerometer
Advantage: most smart phones have the application and no need to do
any additional programing on the phone.
Disadvantage: the output is the peak force and there is no way of
seeing the comparison pressure range in different parts of the foot.
 Using versatile Tekscan sensor
Advantage: It gives us a perfect picture of foot pressure
Disadvantage: High resolution requiring advance equipment and skill
References
http://barefootrunning.fas.harvard.edu/4BiomechanicsofFootStrike.html
http://www.livestrong.com/article/553745-the-impact-of-running-sneakers-on-thefoot/#ixzz1rPBjHyRI
http://www.tekscan.com/medical/system-fscan1.html
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=05378500