P11011: MOTION-TRACKING SYSTEM
FINAL DESIGN REVIEW
Brittany Bochette
Lindsey Clark
Mike Ostertag
Maya Ramaswamy
Andrei Stihi
PROJECT BACKGROUND
Motion-tracking system that measures knee
flexion and head-tilt
 Continuation of past senior design groups

P10010 Sensors
 P10011 Attachment Methods


Customers are Nazareth Physical Therapy Clinic
and Rochester General Hospital
KEY CUSTOMER NEEDS

Measurement


Accuracy


5-10 degrees error
Reproducibility


+/- 80 degrees of tilt and +/- 100 degrees of rotation
5-10 degrees
Speed of Attachment and Removal

2 minutes, 5 seconds
CONCEPT OVERVIEW
USB
FTDI 3.3V
Breakout
Board
Brass
screws
Attachment
Snaps
Razor 9DOF IMU
Protective
enclosure
Foam
stabilizer
SYSTEM ARCHITECTURE
SYSTEM ARCHITECTURE
Base Unit
USB
Knee Flexion
Head-Tilt
Options
Quit
ATTACHMENT METHODS
Head attachment and
enclosure
Leg attachments with
enclosures
ENCLOSURES

Brass screws
and nuts were
used, along with
rubber washers
for interference
free operation

Internals:
Foam padding was
used on the
backside to
stabilize it when
used with various
attachment
methods through
the use of snaps
DETERMINING KNEE FLEXION
Sensor is placed on the side of the leg
with gravity being felt in the X and Y
components of the accelerometer
 The orientation of the sensor relative
to gravity was calculated with
Equation 1.
 The amount of flexion is the
difference between the two angles as
seen in Equation 2.

Eq. 1
Eq. 2
Y
Z
X
Ag
DETERMINING HEAD ORIENTATION
Anterocollis
Retrocollis
Laterocollis
Torticollis
Head has complex motion due to three-axes of
rotation
 Breaking down motion to three individual axes
(seen above) simplifies the process of determining
orientation

DETERMINING HEAD ORIENTATION

Antero/retrocollis (pitch) and laterocollis (roll)
were determined using a three-axis
accelerometer


Angles were determined by comparing the
components of acceleration caused by gravity (Ag)
Eq. 3
Z
X

Eq. 4
Y
Ag
DETERMINING HEAD ORIENTATION

Torticollis (yaw) was determined using the threeaxis magnetometer and the following procedure:
1.
2.
The magnetometer readings were corrected for tilt
based upon the pitch and roll found previously.
A current magnetic heading was found with the
following equation:
Eq. 5
3.
The difference between the initial and current
magnetic heading is the amount that the head has
rotated.
Eq. 6
TESTING


30˚ rotation in the
pitch, roll, and yaw
directions
Changes in degree
during four knee
flexion cycles
RESULTS
Specification
Expected
Actual
Tilt: +/- 80˚
Rotation: +/- 100˚
Tilt: +/- 90˚
Rotation: +/- 180˚
5-10˚
Roll: within 5˚
Pitch: within 10˚
Yaw: within 8˚
Precision
5-10˚
Roll: 2˚
Pitch: 6˚
Yaw: 2˚
Speed of
attachment/removal
2 minutes/5 seconds
28 seconds/3 seconds
Measurement
Accuracy
CURRENT STATE OF DESIGN


Design is functional
Meets all engineering specifications except


Measurement of shift –discussed this with the customer and it
is an option for future designs
Budget requirements - $1000 allowed, $735.76 spent
After changing scope, we used the more expensive Razor IMU
for both systems
 This caused a slight budget overrun for the knee device


Expected
Actual
Dr. Mowder
$300
$315
Dr. Barbano
unlimited
$315
On schedule with exception of rescheduled D3 meetings
RISK ASSESSMENT



Contacting our customers and scheduling
meetings with them proved to be one of the most
relevant risks.
The device not meeting customer needs was also
something that was a possible risk up until week
nine.
Not being able to communicate with the base unit
was another risk we had to address
PROJECT EVALUATION




Project was originally scoped too large
The intent of the project became clearer after a
re-scoping at the end of MSD I
Base unit and sensor sub-systems should be one
group
With a similar project, a prototype should be the
first step rather than a fully functioning system
RECOMMENDATIONS



Being able to measure shift of the head would be
something desired by Dr. Barbano in the future.
Dr. Barbano also voiced a need to have something
on the device that helped him to level the device
on the patient so that human error was reduced
or even eliminated.
Dr. Mowder suggested using Dysom or some
other rubber-like material to prevent the strap on
the calf from slipping