P11011: MOTION-TRACKING SYSTEMFINAL DESIGN REVIEWBrittany BochetteLindsey ClarkMike OstertagMaya RamaswamyAndrei 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

+/- 80 degrees of tilt and +/- 100 degrees of rotation

Accuracy 5-10 degrees error

Reproducibility 5-10 degrees

Speed of Attachment and Removal 2 minutes, 5 seconds

CONCEPT OVERVIEW

FTDI 3.3V Breakout Board

Razor 9DOF IMU

USB

Brass screws

Attachment Snaps

Foam stabilizer

Protective enclosure

SYSTEM ARCHITECTURE

Base Unit

SYSTEM ARCHITECTURE

Knee Flexion

Head-Tilt

Options

Quit

USB

ATTACHMENT METHODS

Head attachment and enclosure

Leg attachments with enclosures

ENCLOSURES

Internals:

Brass screws and nuts were used, along with rubber washers for interference free operation

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

XX

YY

ZZ

AAgg

DETERMINING HEAD ORIENTATION

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

Anterocollis Retrocollis Laterocollis Torticollis

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

Eq. 4

XX

YY

ZZ

AAgg

DETERMINING HEAD ORIENTATION Torticollis (yaw) was determined using the

three-axis magnetometer and the following procedure:1. The magnetometer readings were corrected for

tilt based upon the pitch and roll found previously.

2. A current magnetic heading was found with the following equation:

3. The difference between the initial and current magnetic heading is the amount that the head has rotated.

Eq. 5

Eq. 6

TESTING 30˚ rotation in the

pitch, roll, and yaw directions

Changes in degree during four knee flexion cycles

RESULTSSpecification Expected Actual

Measurement Tilt: +/- 80˚Rotation: +/- 100˚

Tilt: +/- 90˚Rotation: +/- 180˚

Accuracy 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

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

On schedule with exception of rescheduled D3 meetings

Expected ActualDr. Mowder $300 $315Dr. Barbano unlimited $315

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