Multi-Disciplinary Engineering Design Conference
Kate Gleason College of Engineering
Rochester Institute of Technology
Rochester, New York 14623
Project Number: P08006
MOTION TRACKING SYSTEM CONFERENCE PAPER
Team Member Discipline
Affiliation
Dr. Brown
EE
Faculty Conultant
Eric Danielson
CE
Individual Contributor
Wade Daugherty
EE
Individual Contributor
Dr. DeBartolo
ME
Faculty Conultant
Brian Leigh
EE
Individual Contributor
Jennifer Mallory
ME
Individual Contributor
Dr. Marshall
ISE
Faculty Conultant
Josemaria Mora
EE
Project Leader
Dr. Phillips
EE
Faculty Conultant
George Slack
EE
Project Guide
ABSTRACT
The objective of this project is to develop a device that will
assist the Nazareth College Physical Therapy Clinic in their
assessment of patients with neurological damage. Currently, the
physical therapy clinic cannot measure joint angle excursions
while the patient is walking, only when they are static. Our
final product, the Motion Tracking System, allows the clinic to
easily obtain quantitative measurements of the specified joint
angles while the patient is walking in a safe, reliable manner.
INTRODUCTION
The Nazareth College Physical Therapy Clinic treats patients
who have suffered neurological damage, most commonly being
a stroke. As a result of the stroke, these patients experience
difficulty coordinating their muscles, causing an irregular gait
(walking motion). At the moment, the clinic has several devices
that measure such features as balance and weight distribution.
However, they do not have a method for measuring the
patient’s angles of the hip, knee, and ankle joints while in
motion. The clinic only has means of making a qualitative
assessment of the patient’s motion and progression, lending to
an incomplete evaluation of each patient. If the clinic did
want to obtain the measurements of the joint angles, they could
do so while the patient was static through the use of a
goniometer. The goniometer measures a patient’s range of
motion, usually requiring two physical therapists to obtain the
measurements. This method is both inefficient and inaccurate in
that it does not make exceptional use of the therapist’s time and
it does not provide an accurate assessment of the patient’s
dynamic progress.
The Motion Tracking System provides the therapists an
automated method of quantitatively assessing the progression
of the patient’s gait, specifically the joint angles. Furthermore,
the tracking device could be combined with exercise machines
and telemedicine to provide a complete solution for
rehabilitation. It is of the utmost importance that the system be
functional, accurate, safe, reliable, and easy to use for both the
patient and the therapist.
While systems similar to the Motion Tracking System do exist,
they are usually beyond the price range of small clinics like the
one at Nazareth College. Keeping this in mind, the project was
kept inexpensive and simple consisting of mainly position
sensors to acquire the data, yet still maintaining its durability.
DESIGN PROCESS
Needs and Specifications
First and foremost, it was asked by the Nazareth College
Physical Therapy Clinic that our final product be safe for both
the patient and the therapist using it. It is imperative that this
criterion be met and adhered to in the design for a successful
© 2005 Rochester Institute of Technology
Proceedings of the Multi-Disciplinary Engineering Design Conference
outcome. Along the safety guidelines, it is vital that the
developed system does not interfere with any additional
medical devices the patient may have in their possession.
Another request of the clinic was that the system itself is easy
to use, not only from the therapist’s side but from the patient’s
as well. It is desired that the only training a therapist will
require to use the system can be gained through a simple user’s
manual. In addition to being easy to use, the system should also
not take a great deal of time to operate. The clinic requested
that the maximum amount of time to operate the system to be
one patient’s session, which is the duration of an hour. Also,
seeing that the patient’s mobility is already limited, the method
of attaching the system to the patient cannot be restrictive in
any manner. More specifically, the system needs to be
lightweight and portable.
The final product, the Motion Tracking System, is expected to
obtain and store the joint angles of the patient in motion, then
display the results in a user friendly environment. The system is
anticipated to be fully functional, providing comparable data
that may be reused for future studies. It also should have the
potential to be used for applications outside of the initially
desired use.
Issues and Risks
Whenever one is dealing with a project involving other human
beings, especially within the medical field, there are always
numerous risks and issues to address. In the case of this project,
the majority of the potential issues and risks revolve around
obtaining, analyzing, displaying, and storing accurate, reliable
data.
The main issues foreseen with this project are obtaining the
movement information from the sensors on the patient and
coordinating that information with the data obtained from the
other sensors. Obtaining a correlation between the patient
motion and the information displayed is also a high ranked
issue.
Some of the other issues and risks anticipated during the
completion of this project are being able to transmit the
information wirelessly to a computer and analyzing and
displaying the data. Ensuring a robust method of attachment is
also an item of great concern. As with any engineering project,
there are always the concerns of producing a reliable end
product and meeting schedule constraints.
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environment. Therefore the translational motion and out of
plane displacement will need to be taken into consideration.
It was determined that to meet our needs and specifications,
there were only two sensors that could be chosen. Either an
accelerometer or a gyroscope could be used to determine the
joint angles of a walking patient. It was also known that a
microcontroller would be needed to retrieve the data obtained
by the sensors. Since a class is offered through the Electrical
Engineering Department at the Rochester Institute of
Technology on the MSP430, that microcontroller would most
likely be the one used.
The method of attaching the sensors to the patient was also
narrowed down based on the needs and specifications. The
sensors needed to be protected by a small, lightweight, yet
durable enclosure. The chosen microcontroller would also need
to be protected by a similar enclosure as well. As for physically
attaching the sensors to the patient, a number of ideas were
generated ranging from using ECG electrodes with snaps on the
enclosures to using double sided tape.
As for the software side of the project, in result of having a
large budget it was deemed that buying a laptop for the clinic
would be a good investment. The laptop would solely be used
for the developed user interface, ensuring that internet viruses
or other hazardous applications would not interfere with the
integrity of the product.
Finalized Concept
Sensors
Since both sensors were of fairly equal caliber, Analog
Devices’ generous donation of eight gyroscopes led us to the
final decision of choosing the gyroscope for our project instead
of the accelerometer. To ensure that the gyroscopes would
work sufficiently enough for our applications, a few rough
preliminary tests were performed. The test consisted of simply
holding the gyroscope in our hand with our elbow firmly on a
table top. Next, we simply swept up and then down 90° by
moving our elbow. The output, as shown in figures one and
two, were fairly accurate upon converting the sensor output
voltage to an angle. The MATLAB program used to convert
can be found in Appendix A.
Concept Generation
The direct measurement of an angle can be completed using
numerous different methods: goniometers, protractors, or
gyroscopes are just a few examples. An indirect measurement
can be done by obtaining three points and relating them to
calculate an angle. However in the case of this specific project,
additional difficulty in obtaining the measurement is present
because the patient will be walking in a three dimensional
Paper Number P08006
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Proceedings of the KGCOE Multi-Disciplinary Engineering Design Conference
measure the hip, knee, and joint angles during motion, the
gyroscope sensors need to be attached at the anatomical
locations shown in figure four. The anatomical reference points
for the measured joint angles are shown in table one.
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Voltage (mV)
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Figure 1: ±90° Sensor Output (Voltage vs. Time)
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Figure 4: Anatomical Locations of Sensor Attachment
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Angle
Pelvic
Knee
Ankle
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Figure 2:±90° Converted Voltage to Angle vs. Time
The output of the gyroscope sensor is an angular velocity, so in
order to analyze the gait motion using gyroscopes, a rotation
from a given point (i.e. knee or ankle) will need to be obtained
first. The angular velocity will then be integrated to obtain the
angular displacement. The main concerns with this sensor are
initializing the sensor so the measurements are absolute and
relating the measured angle to the angle of interest. The angle
relationship used to determine the joint angle is shown in figure
three.
G1
Center
Reference 1
Reference 2
Greater Trochanter
Fibular Head
Lateral Malleolus
Pelvis
Upper Thigh
Lateral Malleolus
Upper Thigh
Lateral Malleolus
Fibular Head
Table 1: Anatomical Reference Points for Measured Joint
Angles
Preliminary Testing
The preliminary gyroscope data suggests that measuring gait
angles with this sensor is possible. A more controlled
experiment using a test fixture was performed in order to
evaluate the techniques further. Figures five and six show one
of the arms on the fixture being moved 180° while the other
arm is kept stationary (at 0°). (Note: The timescale on the
oscilloscope is 0.5 sec/sq.)
G1
φ1
Knee
θ
φ2
G2
G2
Figure 3: Angle Relationship to Determine Desired Angle
In order to obtain accurate joint angle measurements, the
correct placement of the sensors is imperative. To indirectly
Copyright © 2005 by Rochester Institute of Technology
Figure 5: Oscilloscope Display
Proceedings of the Multi-Disciplinary Engineering Design Conference
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from same patient, and a graphical display of acquired data
shown in figure seven.
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Figure 6: Converted Voltage Output to Angle versus Time
Methods of Attachment
The method of attaching the gyroscope sensors to the patient
consists of a plastic enclosure, an ECG electrode, and medical
tape. Each gyroscope sensor will be enclosed in a plastic box
from Polycase Inc. with dimensions: 38.1mm (1.5”) x 31.75mm
(1.25”) x 20.32 mm (0.8”). The plastic enclosure will be
attached to the patient’s skin using an ECG electrode. In order
to attach the enclosure to the electrode, a small snap has been
hot glued to the outside of the enclosure. Also, the gyroscope
has been hot glued inside the enclosure to ensure that it does
not move during testing. Since the electrode attachment does
not eliminate possible rotation of the enclosure once attached to
the patient, medical tape will be used to prevent this from
happening.
In order to protect the MSP430 microcontroller from any
potential damage, it also will be enclosed within a plastic case
from Polycase with dimensions: 88.9mm (3.5”) x 114.3mm
(4.5”) x 31.75mm (1.25”). Once enclosed, the MSP430 will be
put into a nylon pouch purchased from McMaster Carr, which
is then worn on the patient’s support belt.
Figure 7: Graphical User Interface
Another aspect of the Motion Tracking System is that it is
completely wire free. No additional wires will be needed to
transfer data from the patient or to the computer. This highly
advantageous feature was accomplished using a Bluetooth
application.
Motion Tracking System Operation
The Motion Tracking System is very easy to use as long as a
few simple steps are followed:
1.
In addition to enclosing each individual subsystem, it is also
important to enclose the entire Motion Tracking System. To do
so, a plastic briefcase type enclosure with dimensions:
342.9mm (13.5”) x 254mm (10”) x 95.25mm (3.75”) was
purchased from McMaster Carr.
2.
Software
5.
The software application of the Motion Tracking System was
developed in Java. Its main purpose will be to take the raw data
from the gyroscope sensors, convert it into numeric angular
measurements, and then convert it into a readable format that
the therapist can understand, such as a graphical display. The
raw data obtained from the gyroscopes will be converted into
an angular measurement through the integration of Java Builder
for MATLAB. In addition to converting the data, the software
application will have many other features including: ability to
file results to specific patient accounts, allow therapists to add
custom notes for each result, compare results to previous data
3.
4.
The therapist zeroes the system while it is still in the
package.
The therapist attaches each sensor to the patient via
electrode and then zeroes the system again.
The therapist pushes the start button and the patient
begins walking.
The system begins transmitting results from the
gyroscopes to the laptop.
The therapist stops the system when an adequate
amount of data has been collected.
RESULTS/DISCUSSIONS
The attachment methods were adequate in attaching the
gyroscopes to the patient’s leg. The MSP430 currently collects
and sends data via the Bluetooth. However, the data taken from
the gyroscopes relays a pattern of motion and not the specific
joint angles as once anticipated. It was found that if more then
one cycle of motion was completed, the range of error was very
extreme. Yet, a pattern of motion could be acquired easily, as
Paper Number P08006
Proceedings of the KGCOE Multi-Disciplinary Engineering Design Conference
shown in figure eight, with the pattern of the gait cycle starting
with heel contact.
Foot Sensor
0.4
0.2
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The last angular data set obtained was from the ankle, shown in
figure ten, which had an angle range from 70° to 95°. This
results in an angular change of approximately 25°, which is
accurate in comparison to normative data.
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Calf Sensor
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Figure 8: Gait Pattern of Motion
In order to obtain angular data, one cycle of motion was
acquired using the gyroscopes and the angular data graphically
displayed. First the hip angular data was displayed as shown in
figure nine. The physical therapists were not concerned with
obtaining accurate angular measurements, just determining that
there was flexion in the hip.
Figure 11: Ankle Angular Displacement
After obtaining a normative data set, an imitated stroke patient
set of data was acquired by keeping the knee completely
straight. Figure twelve shows a side by side comparison of the
normal knee data on the left to an irregular set of knee data on
the right.
Figure 12: Comparison of Knee Data
Figure 9: Hip Angular Displacement
The next angular data set obtained was from the knee, shown in
figure ten, which had an angle range from 130° to 180°. This
results in an angular change of approximately 60°, which is
accurate in comparison to normative data.
Figure 10: Knee Angular Displacement
Throughout the project there were many successes and failures
along the way. Some of the successes of the project were: the
Bluetooth communication, MSP430 data collection, the
attachment methods, and the software GUI in figure seven.
Some of the failures encountered were: measurement accuracy
within ± 5% and the transfer rate on the laptop. In respect to the
measurement accuracy, it is believed that the problem can be
solved through the use of several filters. It is currently unknown
why the transfer rate on the laptop would not be the same as the
transfer rate on the desktop, but for this reason the laptop could
not be used in the acquisition of data.
CONCLUSIONS/RECOMMENDATIONS
In conclusion, the Motion Tracking System was completed on
time and under budget. The entire project was a learning
experience from the execution of the idea to the handling of the
different obstacles encountered along the way. The devise had
to be revised several times as a result of these obstacles and as
the project revolved. We also learned how to work with limited
resources, in respect to a monetary budget and the tools at our
disposal.
Copyright © 2005 by Rochester Institute of Technology
Proceedings of the Multi-Disciplinary Engineering Design Conference
Some improvements for the future are a pattern recognition
algorithm that recognizes the motion pattern already obtained
using MATLAB. This would be an added feature for the
therapists to track the improvement in gait motion. Also, a
faster sampling rate and making the system a two-legged
system would improve the overall quality of the system.
ACKNOWLEDGMENTS
First and foremost we would like to thank the National Science
Foundation for their funding, which without we would not have
had the opportunity to complete this project. We would also
like to take this opportunity to acknowledge the individuals
who have helped in the completion of this senior design project.
They include our sponsor, Nazareth Physical Therapy Clinic,
and staff with which we communicated with. We would also
like to thank our consulting faculty Dr. DeBartolo and Dr.
Phillips. Several other faculty members have impacted this
project and we would like to acknowledge them as well. They
include Professor George Slack, Dr. Marshall, Dr. Brown, and
Dave Hathaway. We feel that without the input of these
individuals our project would not have been as successful as it
was.
Paper Number P08006
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