This document describes a project to measure ankle supination torque. Force sensing resistors were attached to an insole and a voltage divider circuit was used to convert pressure readings to electrical signals. The signals were acquired using a data acquisition system and analyzed in LabVIEW. Testing on 4 subjects found increased ankle supination torque when walking in a controlled supinated manner compared to normal walking. The system provides a way to monitor ankle supination torque and help with athlete training.

1. MEASUREMENT OF ANKLE
SUPINATION TORQUE
Submitted By: Guide:
ASHOK KUMAR GUPTA CHAITANYA SRINIVAS
(07BMD012) L.V.
MANISH KUMAR ASSISTANT PROFESSOR
(07BMD025) BIO-MEDICAL DIVISION
ROOPAM DEY Room No: 107, CBMR.
(07BMD047)
Place Of Work: VELLORE INSTITUTE OF TECHNOLOGY, VELLORE.

2. INTRODUCTION 1
The objective of this project was to calculate the Ankle Supination
Torque by converting the pressure applied by the foot into electrical
signal.
Ankle supination points the muscle
weight of the body outside the foot
and hence high arch of supination
can cause Achilles tendonitis,
Peroneal tendonitis, Ankle sprains.
Though there are clear symptoms of
higher degree of ankle supination
but there is hardly any sign Fig 1 – Supination Posture of a foot
for minor damage in an ankle leading to supination. Hence this
project aims to be very simple and sensitive, the results can be used
as a feedback system for training athletes.

3. PREPARATION 2
The overview of this project was taken from the work done by the
Chinese scientists Daniel Tik-Pui Fong et al[2].
The sensors used by us are Force Sensing Resistors (FSR),
manufactured by Interlink Electronics. The work done by Indian
scientist Dr. N.K. Rana of RGIT[1] helped us to work with the
sensors.
A thorough study of FSR[4]was done that helped us to narrow down
to a voltage-divider circuit using LM 324.
The manual of National Instruments on Lab VIEW Analysis
Concepts[8] gave us the basic idea of signal processing and analysis
in Lab VIEW.
Introduction to Data AcQuisition[9] is the tutorial of National
Instruments that gives the overview of the DAQ and its functions.

4. METHODOLOGY 3
Fig 2 – FSRs attached to the In-Sole Fig 3 – Voltage dividing circuit
for a single FSR
Fig 5 – The Visual Basic GUI Main Frame Fig 4 – PIC Microcontroller Circuit

5. 3-PS SYSTEM 4
Sensor Locations :
S-60 : Second/Third Distal Phalange
S-72 : Third Metatarsalphalangeal Joint Fig 9 - FSR
S-98 : Fourth/Fifth Metatarsalphalangeal Joint
SupT (Nm)= -2.068+0.00190827*e^0.01252 (1023-S60)
+0.002763846 *e^0.01252 (1023-S72)
+ +0.003248253*e^
0.01252(1023-S98)….1
Fig 7 – Linear increase in the ADC output
Fig 6 – Sole Divisions with increase in output voltage. Fig 8 – Sensor Points

6. FORCE SENSOR RESISTOR (FSR) 5
Sensor Characteristics :
1. Resistance inversely proportional to applied pressure.
2. Can withstand 1000N of force. Resistance stabilizes above this point.
3. Gives a resistance of 0.25KΩ at 100N and 1.25KΩ at 10N.
4. Size used 0.5” diameter model 402.
5. Lifetime of the sensor is >10 million actuations.
6. Temperature Range is -30°C to 170°C.
Fig 10 – The Internal Structure of a FSR Fig 11 – Output Characteristics of FSR

7. VOLTAGE DIVIDER CIRCUIT 6
a b
Fig 12 – (a)The theoretical design and (b) the practical output of Voltage Divider Circuit
Vout = Vin * [1 / (1 + Rfsr / Rm ) ]
To convert the pressure of the foot into voltage a voltage divider
circuit was implemented. The above given formula was used.
5V was used as the Vin.

8. 7
a b
Fig 13 – (a) Outputs using different Rm values (b) Perfect linearity observed by using 8.2KΩ
with Rfsr being 0.25KΩ.
Rm is the resistor applied in series with the Rfsr to divide the input
voltage. In this project 8.2KΩ was used as Rm.
The output of the circuit was given to LM324, a linear quad-op amp
that accepts PnP inputs, that reduces the noise of the converted signal.

9. 8
PRACTICAL OUTPUT OF VOLTAGE DIVIDER
CIRCUIT
Fig 14 – Output of the Voltage Divider Circuit Fig 15 – Graphical Output

10. DATA ACQUISITION KIT 9
Fig 16 – The interfacing of the Voltage Divider Circuit with the Data AcQuisition (DAQ).
Main function of this block is to sample, analog to digital conversion
and digital analog conversion.
The signal was sampled at 500 Hz and 1000 samples were taken that
gave us one sample in 2 milliseconds.

11. WORK DONE IN Lab VIEW 10
Fig 15 – The Block Diagram designed in Lab VIEW to calculate and store the values of
Ankle Supination Torque

12. 11
Fig 16 – The VI designed in Lab VIEW to display the calculated values of Individual Sensors
and Ankle Supination Torque

13. FINAL RESULTS 12
Fig 17– Averaged Ankle Supination Torque sensed from 4 different subjects during
normal walking and controlled supination walking

14. 13
a b
c
Fig 18 – Output of each sensors during supination walking and normal walking (a) S 60, (b) S72
and (c) S 98.

15. CONCLUSION 14
This work was successful in calculating the ankle supination torque
in real time, while the subject walks
An increase in the ankle supination torque was observed when the
subject walked in the controlled supinated way. The average specific
increase being 158.6585 N-m
These values can be further used to find out the exact threshold of
ankle supination torque that an ankle can withstand. This will help
in safe training of the athletes.
In future a wireless devices can be made to calculate the supination
torque which will be a boon to the sports world.

16. PROBLEMS FACED 15
Availability of FSR with desired dimensions in low cost
Status- Solved (Purchased the sensors from Chennai)
To get the best sensitivity of the voltage divider circuit to get a linear
output.
Status- Solved (Tried and tested the circuit with several resistors
and incorporated 8.2K)
Implementation of hardware for calculating ankle supination torque
by serial communication using microcontroller
Status- Partially solved in simulation.

17. REFERENCES 16
[1] Application of Force Sensing Resistor (FSR) in Design of Pressure Scanning System for
Plantar Pressure Measurement
By: Dr. N. K. Rana, Department of Instrumentation Engineering, Rajiv Gandhi Institute of
Technology
[2] A three-pressure-sensor (3PS) system for monitoring ankle supination torque during sport
motions
By: Daniel Tik-Pui Fong, Yue-Yan Chan, Youlian Hong, Patrick Shu-Hang Yung, Kwai-Yau
Fung, Kai-Ming Chan
[3] LM 324 Datasheet
By- Phillips Electronics
[4] FSR an Overview of the technology
By- Tech Storm Inc
[5] MAX 232 Datasheet
By- Texas Instruments
[6] PIC 16F873 Datasheet
By- Microchip
[7] 3-Terminal 1A Positive Voltage Regulator
By- FAIRCHILD SEMICONDUCTORS
[8] Lab VIEW Analysis and Concepts
By- National Instruments
[9] Introduction to Data Acquisition
By- National Instruments

18. THANK YOU