P11011: Modular Motion Tracking Knee Flexion Unit V1
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Concept Decision Matrices

NOTE: Following the Detailed Design Review, the team re-scoped the needs for the modular motion tracking system. As a result, the potentiometer was no longer used and instead, the Razor 9DOF sensor was used for both systems.

Knee Flexion

The following decision matrices were used to help select the concept that best fit our needs and specifications for a device that measures knee flexion.


Knee Sensor Decision Matrix
Based on the matrix, we selected the Honeywell 785-380C3100K Potentiometer.


*NOTE: Calculating Expected Potentiometer Lifetime

From the paper Expected Values for Steps per Day in Special Populations, the mean steps per day for a poststroke patient is approximately 4000 steps/day. Since the knee flexion device will only measure the motion of one knee, the number of rotations the device will experience will be 2000 steps/day. For a minimum cycle count of 100k cycles prior to failure, the device will last for at least 50 days of daily use. For a minimum cycle count of 1 million cycles, the device will last for at least 500 days or approx 1 year and 3 months of use on a daily basis.

If the device is being used in the clinic, it will be used by approximately 15 patients per week for 20 weeks out of the year. Dr. Mowder approximated that each patient will take 100 steps per session (50 steps per leg). At 50 steps/session, 15 patients per week, a 100k minimum cycle device will function for 133.3 weeks or 6.67 clinic years. A 1 million cycle device will last for 1333.3 weeks or approximately 66.7 clinic years. A 25k cycle device will last for 33.33 weeks, or approximately 1.67 clinic years.

Knee Attachment Decision Matrix


Head Tilt

The following decision matrix was used to help select the concept that best fit our needs and specifications for a device that measures head tilt and motion.


Head Tilt Sensor Decision Matrix
Based on the matrix, we selected the Razor IMU.


Head Tilt Attachment Decision Matrix
Based on the matrix, we selected the headlamp strap.


Connection Interface

The following decision matrix was used to help select the concept that best fit the specifications for a device that would regulate the connection interface between the sensors and the base unit.


Connection Interface Decision Matrix
Based on the matrix, we selected the Arduino Board.


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