Stepping Stones Systems Document Final

2016

Stepping stones: Systems Documentation

RACHEL AIGEN, TAYLOR BEST, NATHAN CLARK, EMILY KOEHLER, OLIVIA LICATA

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Contents

1.0 Phase 1: Operations ................................................................................................................................. 4

1.1 System Overview ................................................................................................................................ 4

1.2 Contributors ........................................................................................................................................ 4

1.3 Mission Objectives .............................................................................................................................. 4

1.3.1 Mission Overview ........................................................................................................................ 4

1.3.2 Mission Requirements.................................................................................................................. 4

1.3.3 Mission Operations: Phases of Use ............................................................................................. 5

1.3.4 Prioritized Functional Requirements............................................................................................ 6

1.3.5 Prioritized Performance Requirements ....................................................................................... 7

1.3.6 Environmental Conditions ........................................................................................................... 8

1.4 System Overview ................................................................................................................................ 8

1.4.1 Sensors ......................................................................................................................................... 8

1.4.2 Structure ....................................................................................................................................... 9

1.4.3 Power ........................................................................................................................................... 9

1.4.4 Control/Data Handling ................................................................................................................. 9

1.4.5 Interface program ....................................................................................................................... 10

1.5 Functional Flow ............................................................................................................................... 11

1.5.1 Block diagram ............................................................................................................................ 11

1.5.2 Examples of Use ........................................................................................................................ 11

1.5.3 Future Implications and Possibilities ......................................................................................... 12

1.5.4 Nominal Operation, Major/Minor Failures ................................................................................ 12

2.0 Phase 2: Mechanical ............................................................................................................................. 13

2.1 Mechanical Overview ....................................................................................................................... 13

2.2 Mechanical Components ................................................................................................................... 16

2.2.1 Pressure Sensor .......................................................................................................................... 16

2.2.2 Microcontroller .......................................................................................................................... 18

2.2.3 Wireless Transmitter .................................................................................................................. 19

2.2.4 Battery ........................................................................................................................................ 20

2.2.5 Fan.............................................................................................................................................. 22

2.3 Materials ........................................................................................................................................... 23

2.3.1 Top and Side Coating ................................................................................................................. 23

2.3.2 Bottom Material ......................................................................................................................... 24

2.3.3 Cushion Material ........................................................................................................................ 25

2.3.4 Power Box .................................................................................................................................. 25

2.4 Accuracies ......................................................................................................................................... 26

2.5 Protection Mechanism ...................................................................................................................... 26

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3.0 Phase 3: Software .................................................................................................................................. 27

3.1 Scope ................................................................................................................................................. 27

3.2 Front End Description ....................................................................................................................... 28

3.2.1 Setup .......................................................................................................................................... 29

3.2.2 Calibration .................................................................................................................................. 30

3.2.3 Run ............................................................................................................................................. 30

3.2.4 Data Output ................................................................................................................................ 32

3.3 Software Architecture ....................................................................................................................... 33

3.4 Software Requirements ..................................................................................................................... 34

3.4.1 Application Architecture ............................................................................................................ 34

3.4.2 Communication .......................................................................................................................... 34

3.4.3 Data Storage Model ................................................................................................................... 35

3.4.4 User Interface ............................................................................................................................. 35

3.5 Mini Spec .......................................................................................................................................... 36

3.6 Impact on Systems ............................................................................................................................ 36

4.0 Phase 4: Electrical ................................................................................................................................. 38

4.1 Electrical Overview .......................................................................................................................... 38

4.2 Notable Electrical Systems ............................................................................................................... 38

4.2.1 Components ............................................................................................................................... 39

4.3 Electrical Architecture ...................................................................................................................... 43

4.4 Circuit Schematic .............................................................................................................................. 44

4.5 Power Consumption .......................................................................................................................... 45

5.0 Phase 5: Controls .................................................................................................................................. 46

5.1 Control Specifications ....................................................................................................................... 46

5.1.1 Define Control Problem: ............................................................................................................ 46

5.1.2 Limitation ................................................................................................................................... 46

5.1.3 Requirements ............................................................................................................................. 46

5.1.4 Damping Ratio-N/A ................................................................................................................... 46

5.1.5 Steady-state error (ex: accuracy of 3 degrees) ........................................................................... 46

5.1.6 Bandwidth-N/A .......................................................................................................................... 47

5.1.7 Rise time .................................................................................................................................... 47

5.1.8 Overshoot -N/A .......................................................................................................................... 47

5.2 Control Hierarchy ............................................................................................................................. 47

5.3 System Model ................................................................................................................................... 47

5.3.1 Calculate Drift Speed of 12 Gauge Braided Copper .................................................................. 47

5.3.2 Heat Transfer Equation .............................................................................................................. 48

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6.0 Physical Therapy Overview .................................................................................................................. 50

7.0 References ............................................................................................................................................. 51

8.0 Appendix ............................................................................................................................................... 54

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1.0 Phase 1: Operations

1.1 System Overview Over 800,000 people experience a new or recurrent stroke annually. As a result, stroke is the

leading cause of disability among adults in the United States. Gait rehabilitation for post stroke patients is

critical in regaining mobility and full use of their lower extremities. One of the key aspects of relearning

walking mechanics is efficient weight transfer.

Currently, physical therapists observe issues in gait and weight distribution first hand, and then

correct the patient with either verbal cues or physical interventioni. A system of sensors would allow for

measurement of weight distribution in real time; this could directly feed to a user interface that provides

feedback on how the patient needs to correct themselves. The patient’s center of mass could be

determined whether they are standing upright or advancing forward and compared to norm.ii

1.2 Contributors Rachel Aigen- Controls

Taylor Best- Software

Nathan Clark- Electrical

Emily Koehler- Mechanical

Olivia Licata- Operational Concepts and Requirements

1.3 Mission Objectives

1.3.1 Mission Overview

The primary objective of this system is to give patients who have suffered from stroke,

and are weakened on one side of the body, a feedback mechanism in which to visually display

their body weight placement in both standing and walking positions. The system will consist of

an array of sensors to determine body weight distribution, which will be relayed to a user

interface. Feedback on a visual display will aid therapists and increase patients’ conscious

perception of proper weight placement. This system will be universally applicable to patients of

different weights and stroke severity.

1.3.2 Mission Requirements

Needs and Requirements High Level Implication

1. Do no harm to the patient The system design should have minimal risk

of injury to the patient as the main objective is

to aid the patient through rehabilitation.

2. Improve walking capability through proper

weight distribution

The device will require sensors that relay to

software comparing the user’s weight

distribution to ‘correct’ walking pattern.

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3. Improve patient’s conscious perception of

their weight distribution

Allowing the patient to see that they are off

balance and self-correct in real time. Requires

feedback from device sensors.

4. Can be used by all patients with little effort

by therapists

The device should be universal for patients, so

that only one is necessary per facility.

1.3.3 Mission Operations: Phases of Useiii iv

Phase Systemv Software User Interface

Installation - Secure -Needs to be installed

on computer

- Needs to be

installed on top of

software

Power on - Power switch needs

to be easily accessible

-Software started - Started and

synchronized with

software

System Calibration - Zeroed out with no

applied weight

-Sets baseline of zero

for system

-Relays progress of

calibration

User Calibration -System requires an

initial calibration to set

as baseline.

-Assigns proper

weight distribution

comparison as

baseline

-Visually displays

that system is

calibrated

System takes in

stationary data

-Senses where weight

is distributed

-Relays to software

-Uses comparison

from proper baseline

to establish

displacement

- Visually relays

weight distribution

and displacement

from norm

System takes in data

from dynamic

movement

-Senses where weight

is distributed

-Relays to software

-Compares input to set

parameters and

establishes

displacement

-Visually relays

sequential weight

distribution

Shutdown Procedure -Switched off

-Save patient’s data

session

-Switched off

Cleaning/Storage -Sanitized

-Stored

-Batteries recharged

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1.3.4 Prioritized Functional Requirements

System Rationale

1. Has an easily accessible safety switch or

method turn off power.

Our number one requirement is to not harm

the patient/user and the safety switch will

ensure that the user will not be electrocuted or

burnt in case of an electrical failure.

2. The array of sensors does not impede

movement or hinder walking in any way.

Our number one requirement is to not harm

the patient/user. We must facilitate walking,

not slipping. Components will be designed to

minimize this risk.

3. Senses distribution of weight with sensors. The purpose of the device is to accurately

gauge whether the user is distributing their

weight appropriately. The system will require

pressure sensors that will allow for detection

of how much weight a patient is placing on

each foot.

4. Relays accuracy to user visually and/or

audibly (user feedback).

Visual interface will allow patients feedback

on their rehabilitation progress. Perspective

on how they are placing their weight and

consciously making the corrections to an even

distribution will allow the patients to become

more accustomed to walking properly.

5. Adjustable between patients of varying

weight and recovery-level.

One device/system should meet the needs of

varying patients (not a specific system per

patient).

6. Powered with a rechargeable battery. To allow versatility in use, the system should

not be restricted to proximity to outlet. Our

mission is to facilitate walking on a flat

surface and stairs. Portability is optimal.

Software Rationale

1. Can connect to sensor array. To allow relay of pressure input.

2. Determines relative spatial orientation of

sensors and user.

To determine where the pressure is being

applied in relation to the rest of the user’s

foot. Allows for versatility in sensor array

placement.

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3. Has access to baseline parameters of proper

weight distribution and gait.

Improve walking capability by having a

comparison.

4. Has ability to compare patient’s weight

distribution with baseline.

To determine displacement from proper

weight distribution to allow for corrections

and assess severity.

5. Relay displacement from parameters to

interface in real-time.

To optimize feedback to patient and therapist.

1.3.5 Prioritized Performance Requirementsvi vii

Sensor Array System Rationale

1. Sensing accuracy as defined by resolution

of sensors, to determine where on the sensor

array the weight is being placed and how

much weight is being placed there within 5%

error.

The purpose of the device is to gauge whether

the user is distributing their weight

appropriately and therefore the accuracy of

weight sensing is pertinent to the objective.

2. Repeatable calibration for the same user. This would measure the overall accuracy of

the calibration step and indicate another level

of accuracy for the system as a whole.

3. Range of weight supported fits our

population of users.

In order to make this a universal system, the

sensor array will be required to support the

weight range of users of the system without

malfunction.

4. Range of operable incline (angle) is at

minimum 30 degrees

In order to increase the versatility, the system

should be operable on any surface that will be

used in therapy. 30 degrees would exceed

most wheelchair ramp ranges and therefore

will be useful in improving walking capability

of the patients.

Softwareviii Rationale

1. Software accuracy in communication in

mat is defined by the precision in which the

software can determine where the user is

placing their weight and how much weight is

being place within 5% error.

The accuracy of the software is pertinent in

order to improve patient walking capability as

the therapist can only reposition the patient if

the information they are receiving is correct.

2. Communication from mat to software is

<1s so allows real time feedback to user.

The speed at which the software can

determine where the weight is placed and the

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weight displacement is essential to allow for

proper feedback to the user.

3. Adjustable for different sizes and recovery-

level of patients.

The same system should be applicable for

various patients in one hospital setting and

therefore the software should determine and

compare to norm for any weight range and

recovery level.

User Interface Rationale

1. User Interface accuracy is defined by the

accurate display of results of the user’s weight

displacement from the norm (within 5%

error).

Accuracy is utmost importance as it will allow

for the proper correction in weight

distribution, allowing the patients to relearn

walking properly, improving their walking

capability.

2. The ease of interpretation of results will be

determine by trial with target population to

determine if they can understand and self-

correct based off the visual display.

To allow clear perception of problem areas in

order to improve walking ability through

conscious corrections.

1.3.6 Environmental Conditionsix

The system will be utilized in a hospital/rehabilitation environment and therefore it has to

be durable to last through repeated sessions. The hospital floors may be laminate, which is a low

friction surface. Risk of the user slipping on the floor must be minimized so that the patient does

not lose their balance.

The hospital/rehabilitation unit must have a secure Wi-Fi connection for relaying input

from the mat to the software.

1.4 System Overviewx Given the requirements established for this system, the logical format for the array of

sensors would be a standard foam mat. This mat could be used in the hospital setting then stored

when not in use. To allow for modification of the walking path, several mats could be used in

conjunction. xi

1.4.1 Sensors

The system will consist of a sensor array in order to convert applied pressure from the

user’s weight to a voltage. Potential options for the type of sensor include Force Sensing

Resistors (FSRs) or capacitive piezoelectric sensors. A force-sensing resistor is a piezoresistivity

conductive polymer, which changes resistance in a predictable manner following application of

force to its surface. Applying a force to the surface of the sensing film causes particles to touch

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the conducting electrodes, changing the resistance of the film. A capacitive touch sensor relies on

the applied force either changing the distance between the plates or the effective surface area of

the capacitor. In such a sensor the two conductive plates of the sensor are separated by a

dielectric medium, which is also used as the elastomer to give the sensor its force-to-capacitance

characteristics [1]. When a compressive stress is applied to the sides of a piezoelectric crystal, it

produces a voltage.

The primary goal of this system is to determine and correct the weight distribution of

stroke patients when they are performing simple tasks such as relearning to walk or using stairs.

Since it is not uncommon amongst stroke victims to be unable to tell how much weight they are

applying to a specific body part, piezoelectric sensors would be an ideal way in determining and

pinpointing these problem areas in the patients. If the patient is applying more pressure on one

leg than the other, more mechanical stress will be applied to certain sensors than others and that

will create a voltage difference between the two legs. Whichever sensors contain a higher

voltage, it will show how unevenly the patient’s weight is being distributed between two legs and

then these problem areas can be targeted in physical therapy.

1.4.2 Structure

The sensor array will be contained in a cushioned mat; this will serve as a walking path

for the patient. This will allow for easy cleaning, setup and storage since any user can walk

across it. Customization will be implemented through an initial calibration phase.

If an issue arises and a mat is no longer usable, it will be easier to replace it as an

independent piece, instead of removing it from mats that rely on one another. For this reason,

there will be multiple independent and identical mat sections. The mats can be designed in set

dimensions; from there the therapist can choose to lay out as many or as few mats as they’d like.

This can be specific to the task or the space restrictions of the room. The mats can be designed to

fit the standard dimensions of stair steps as well. This would allow therapists to help patients

prepare to return home where they might use stairs often. Most stair dimensions run a width of

8.5-9 inches.

1.4.3 Power

Each mat will contain a rechargeable battery pack that will distribute power to the other

components. It is essential that this power source is portable so that the mats do not need to rely

on a wall outlet in order to operate, as that would limit their range of use. The power source will

need to be of a relatively high voltage and amp hours in order to provide enough power to the

large number of sensors that each of the mats will contain for multiple therapy sessions. It will be

housed inside of a small, hard plastic covering on the edge of the mat.

1.4.4 Control/Data Handlingxii

All of the information collected when the patient is stepping on the mat will be

transmitted to a program for professionals to assess the status of the patient’s weight distribution

on the mats in real time. A microcontroller would be helpful in handling this data, and could be

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housed in the compartment with the battery. Each mat would require their own microcontroller

to transmit their individual information from their array of sensors.

1.4.5 Interface program

Ideally, this program will be able to take images and show live progression of the

movement, so that therapists can understand where the patient is lacking and where they can

successfully place loads in relation to walking or standing still. This will require use of a wireless

transmitter that will operate using Wi-Fi, which will be able to stream the data to a computer

program so that the real time data can be displayed while the system is in use. The program will

have to contain a visual graph and data display that will highlight the differences in weight

distribution in order to be able to better determine and assess the problem areas of the patient.

This is an essential portion of our system due to the fact that the physical therapists can attempt

to aid the patient in properly adjusting their body and posture to compensate for the uneven

weight distribution.

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1.5 Functional Flowxiii xiv

1.5.1 Block diagram

Figure 1. Functional diagram of system use.

1.5.2 Examples of Use

This product is developed for use alongside physical therapists in hospitals. The product

will be used to assist stroke patients while relearning walking mechanics like weight transfer,

forward motion, and stair-climbing. For patients that are in the early stages of recovery, this

system could be used in conjunction with parallel bars.

A typical session using this system would start with a therapist setting the mats on the

floor or stairs. The therapist then turns on the system and runs a calibration. The calibration

checks that each mat reads zero for pressure outputs. Failure to read zero would result in some

kind of system reset and then a retest.

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Once the mats are on and calibrated and the program is running properly, the patient is

called to the therapy room and stands on the mat. The system runs a calibration when the patient

is standing statically. The program checks that the measured weight is within an acceptable

percentage of the inputted weight of patient. Once the system has passed calibration the patient

can begin the day's exercise. This can be simple standing to ensure weight is evenly distributed

between feet. Other tests may be walking forward and measuring left/right foot weight transfer

as well as weight transfer from the heel strike to toe off during walking. The product can also be

used as the patient walks up stairs.

After the patient finishes their therapy session and leaves the clinic, the therapist can save

the day’s data under a patient's file. The mats can be left out for another session or can be picked

up and stored easily.

1.5.3 Future Implications and Possibilities

This product also has potential in other fields besides stroke rehabilitation. Proper weight

transfer is important to many industries.

- Athletes can use the mats to practice agility by laying them side-by-side. Enhanced

weight transfer would allow for faster takeoff times and increased performance.

- Footwear designers. Creating shoes that don’t inhibit natural walking is critical. For

example, shoes designed to compensate for over pronation could be tested to see if

weight transfer is properly distributed between the medial and lateral edges of the foot.

- The prosthetic industry could also utilize this technology. Visual analysis is traditionally

used by most prosthetists to adjust lower limb prosthetics. By using the mat, weight

distribution could be known despite misleading factors like odd gait motion or bulky

shoes. The prosthetic could then be adjusted so the patient's gait includes proper weight

transfer throughout a step

1.5.4 Nominal Operation, Major/Minor Failuresxv

Table 1. Nominal Operation/Failure table

Types of Failure Potential Outcome Solution

Sensor Breaks Holes in feedback, poor data Replace sensor/mat

Power doesn't reach battery System does not turn on Replace cords and/or battery

Incorrect mapping of mats in

software w.r.t. layoutxvi

Bad data, incorrect transition

between steps

Trouble shoot if mat is to blame,

restart software

System won't calibrate to zero Bad data Reset system

Display is not getting proper weight Bad data Recalibrate

Mats move across floor during

dynamic motion Patient falls

Make bottoms grip to floor better

with cleaning (brush off dust)

Tripping up stairs due to added

material/bulk Patient falls Ensure mat is secured down

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2.0 Phase 2: Mechanical

2.1 Mechanical Overview This system is composed of independent mats containing pressure sensors that will be used to analyze

pressure distribution and gait during post-stroke rehabilitation. The pressure distribution and the gait

accuracy will be determined through a software interface and be visually displayed for feedback to patient

and therapist. An image of the functionality is seen below.xvii

Figure 2. Functional illustration of Stepping Stones. Mats can be arranged into any length/orientation on floor depending on need. Mats can also be ordered to stair size. Patients apply pressure to mats, which in turn, sends data to a visual output (not shown above).

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xviii Figure 3 Dimensions of electrical housing units. Placement of electrical components found in section 4.4.

In order to do this our system needs to contain:

Independent non-slip mats made from:

o Bottom layer of natural rubber designed to created friction with floor to prevent

slipping

o A middle cushion layer consisting of polystyrene foam

o A layer of UNEO sensors

o Top layer of ethylene vinyl acetate (EVA) to provide water resistance and transfer

pressure accurately to sensor.

Each mat containsxix:

UNEO Pressure sensor arrays, custom made to fit a 2’x 2.5’ mat, for walkway mat, and

7.5”x 30” mat, for stairs, that outputs a location and value for each sensor in real time

Arduino UNO Microcontroller

Arduino Wi-Fi shield

Physio Lifepak 2.4Ah battery. Battery will be used to power circuits and wireless

transmitter

The total weight of the system (each mat) is: xx

Stair=1.79lb

Walkway =2.87lb

This is determined through:

Component Weight: 1.65lb

Battery- 1.58lb

Wi-Fi shield- .02lb

Uno .06lb

Sensors=N/A

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Figure 4. Cad Drawing of mat system. Layout and composition of stairway mat (dimensions are in inches). Power supply box is not to scale in this image.

Densities of materials:

Polystyrene= 1.9g/cm^3

Natural rubber = 1.1 g/cm^3

EVA = .95 g/cm^3

Using d=M/V and finding the volume of both the stair and the normal sized mat, we can

solve for the mass of each material in both mat sizes.

STAIR: =1.78lb

NORMAL=2.43lb

Each value was rounded up slightly (~.01lb) to allow for error.

The setup of each individual mat is shown below.xxi The placement of the circuitry within each

mat can be seen in section 4 figure X.xxii

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2.2 Mechanical Components

2.2.1 Pressure Sensor

Table 2 Pressure Sensor Requirements and Criteria.

Requirements Criteria

Pressure sensors can withstand

the load of a human Pressure sensors should be able to withstand loads > 100lb per

sensor (due to distribution of force over matrix)

Pressure sensors can accurately

detect weight distribution and gait Pressure sensors will need to encompass minimum 3 sensors/step.

Lower average foot size in America is 9 inches so sensors must be

a maximum of 3 inches apart [2].xxiii

Pressure sensors will fit inside

system Pressure sensors dimensions are less than .2in thickness.

Pressure sensors can be combined

in an array Pressure sensors have circuitry that will allow them to connect to

voltage analyzer and can tell the location of the pressure sensor.

Data from 150 sensors must be arranged in an array consisting of

10 rows with 15 columns. Each data point then has a value and

location. If no pressure is being applied, location (x,y) will have a

zero value.xxiv

Pressure sensors are inexpensive

bought in bulk Ordering a custom mat keeps material costs low and ensures no

sensors are wasted.

Figure 5. Realization of walkway mat system.

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Table 3. Pressure Sensor trade offs

Options Properties Decision and

Justification

Force sensors

Honeywell Sensing and

Productivity Solutions T&M

060-2443-08 [3]

Price

$1.62 /unit

UNEO pressure sensors

These sensors are highly

customizable; we can

request the sensors in a

desired size, shape and

thickness. They meet the

requirement of a 300 lb

load, because they can be

manufactured to sense a

finger touch up to 1 ton of

load. These sensors, unlike

the Tekscan pressure

films, are independent of a

corresponding interface

system and sensing cuffs,

and are easily connected to

a microcontroller.xxv The

microcontroller can be

connected to a LAN

transmitter and sent to the

software interface.

In comparison to single

pressure sensors, ordering

them as sheets will allow

us to have a premade

matrix of sensors that will

better detect load force

and save time, as opposed

to creating our own sensor

array. Similarly, most thin

pressure sensors do not

have the capacity to

handle the 100-pound

load, which is a necessity

when placing an adult on

our mats, especially while

walking up stairs.

Dimensions .8 in diameter

0.13 in thickness

Load 50lbs

Force Sensing Resistor

FlexiForce A301 Sensor [4]

Price $11.2/ unit (may be

cheaper in bulk)

Dimensions 1 in diameter

.08 in thickness

Load 0-100lb when

connected to Op

Amp (loss in

resolution)

1 inch Shunt FSR [5]

Price $6/unit

Dimension 1 in diameter

.017 in thickness

Load 1-100 lbs

Pressure Map

UNEO Pressure Analysis Sensor

[6]

Price Contact Company

Dimensions Customizable

0.01 in thickness

Load .01-300 psi

Speed 100 us response time

Pressure Mapping Sensor 5320

[7]

Price Contact company

Dimensions Area: 20.5x 22.86 in

Tab length 15.39 in

.004 in thickness

Load 285 psi

Problems Requires use of their

data analysis and

software tools

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2.2.2 Microcontrollerxxvi

Table 4. Microcontroller Requirements and Criteria


Able to process all data received by sensors

(RAM) 3000 (20x150) bytes of data at every sampling during

the run.

Samples at appropriate time for system 10 Hz; 1/10 = .1 sec because human perception is

0.15 sec

Converts JSON message after sampling to

Wi-Fi shield ~7,500 bytes/0.1 sec=75,000 bytes/sec; 3,000 of those

bytes are from the sensor, 3500 for the JSON

coding/inscribing of data

7-12V unit The battery will be able to power the microcontroller

but will still be sufficient enough to power other

components of the system (Wi-Fi and sensors).

Fits inside power box that sits outside of mat. The power box is 9.5(L) x 4.5(W) x 2(H) in

Table 5. Microcontroller Tradeoffs

Options Properties Decision and Justification

Arduino Mega 2560

Microcontroller

Dimension 4.00in x 2.10in, 54 pins

Arduino Uno

Arduino microcontrollers have

the most assisted open source

code, large library industry

standard. The Uno has the

necessary pins to support the

data train. It also is compatible

with Arduino Wi-Fi shields and

is inexpensive. [8]

Price $45.95

Input Voltage 7-12V

Clock Speed 16 MHz

Dimensions $49.95/unit

Arduino Uno

Dimensions 2.7in x 2.1in, 14 pins

Price

$24.95/unit

Input Voltage 7-12V

Clock Speed 16 MHz

Arduino Micro-8 bit

Dimension 1.89in x 0.51in, 20 pins

Price $24.99/unit

Input Voltage 7-12V

Clock Speed 16 MHz

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2.2.3 Wireless Transmitter Table 6. Wireless Transmitter Requirements and Criteria


Have a speed that would allow for dynamic data

transfer to give real time feedback Be able to respond to speed of gait;

< 1 sec; human perception is 0.15 s xxvii

Needs to transport data within a room The Wi-Fi range is minimum 10m.

Communicates to separate computer with

interface system program at a high enough

sampling frequencyxxviii

The sampling frequency in order to be imperceptible

to humans is 10 Hz. The Wi-Fi transmitter has to be

capable of more than this rate.

Table 7. Wireless Transmitter tradeoffs


1Km 2.4G USB serial Port

Wireless [9]

Price $39.99

Arduino Wi-Fi Shield 101.

SSID and password

protection ensures patient

confidentiality. It also can

be encrypted with WEP and

WPA2. It piggybacks off of

the Arduino boards power

supply (3.3V). The 101

shield has an extensive

library and draws 60% of

the memory. This is okay

because that still leaves

102,400 bytes of space for

processing. The input pin in

the microcontroller where

the Wi-Fi Shield will be

attached draws a max

current of 50 mA [10]. xxix

Weight 0.15kG

Power DC 5V

Distance 3280.84’

Rate/Freq 38400bps /

2405MHz (16

channels)

Core 2530 2.4GHz Wireless Data

Transmission Communication

Module [11]

Price $14.45

Weight 0.18 oz

Power 2.0-3.6V

Distance 1148’4”

Rate/Freq 38400bps/ 2.4GHZ

(16channels)

Input Pins

433MHz Wireless Data

Transmission [12]

Price $25.39

Weight .22lb

Power 3.7-6V (either USB

or DF 13)

Other Open source SIK

firmware

Rate/Freq 12 MHz

Arduino Wi-Fi Shieldxxx Price $49.95/unit

Weight .04lb

Operating

Voltage

5V

Dimensions

2.11in x 2.49in x

.93in

Rate/Freq 16 MHz

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2.2.4 Battery Table 8. Battery requirements and criteria.


Battery must be rechargeablexxxi Each mat should have its own power supply,

removable battery is separate from system to ensure

system longevity.

Battery must be able to power Wi-Fi

transmitter and provide current for pressure

sensors during use

Wi-Fi transmission requires 6V max. Extra voltage is

needed to go through sensor circuit. Battery needs to

be at least 9V.

Retain power for multiple therapy sessionsxxxii 4 hours minimum at full use

Battery is not exceedingly heavy so that mats

can be moved and adjusted by personnel.xxxiii

Battery should not exceed 6 lb.

Table 9. Battery Tradeoffs


Rechargeable 9V

Lithium Polymer

Battery [13]

Dimension 1.05in x .70in x 1.83in

Physio Lifepak 2.4 ah

rechargeable battery

The Physio Lifepak 2.4 ah is

the most viable option since

it will provide the most

current, allowing for a longer

operation time for the overall

system. It also fits into the

required voltage range for

the selected microcontroller.

This option weighs less and

fits better into the side

compartment of the mats.

Similarly, it is under the

weight maximum thus being

the ideal choice for the

battery.

Price $13.95/unit

Life Span 10Yr, must use “Hitech

Lithium Ion Charger”

EBL 9V [14]

Dimensions 1.89in x .98in x .63in

Price $15.99 for 2 pack w/

charger

Life Span Recharged up to 1200 times

in unit

Amp Hours 280mAh

SLA battery

[15]xxxiv

Type Lithium Iron Phosphate

Capacity High

Amp Hours 22

Rechargeable Yes, via wall mount

charger

Lifetime Up to 2000

charge/discharge cycles

Price $295 each

Weight 6.06lbs

Dimensions 7.13 x 2.99 x 6.54 inches

21

12 V Physio

Lifepak 1.2Ah

[16]

Type Nickel Cadmium

Capacity High

Amp Hours 1.2


charger

Charge time 4 hours

Price $78.44

(charging

station)

$401.39

Total $479.83

Weight 2.0lbs

Dimensions 10 x 4.5 x 1.5 inches

12 V Physio

Lifepak 2.4Ah

[17] [18]

Type Nickel Cadmium

Capacity High

Amp Hours 2.4


charger

Charge time 3 hours

Price $113.55

(charging

station)

$401.39

Total $514.94

Weight 2.0lbs

Dimensions 5.52in(L) x 3.68in (W) x

1.55in(H)

22

2.2.5 Fanxxxv

Table 10. Fan requirements and criteria


Must blow air Circulate air for entire battery box to guide excess

heat towards the vent.

Be small enough to fit on outside of mat in

‘battery box’

9.3 x 4.3 x 2 in dimensions of box

Table 11. Fan tradeoffs


Rosewill RFA-

120-K - 120mm

Computer Case

Cooling Fan with

LP4 Adapter -

Sleeve Bearing,

Silent [19]

Price $4.99/unit

None (Vents)

The Rosewill fan and Deepcool

Wind Blade are essentially the

same and both what we are

looking for; small enough and both

require 12V to power. This poses

an issue because our battery

operates at 12V and already has

multiple other components to

power. Therefore, we decided on

going with vents in our battery

box, which we will hope will

create a gradient between the

internal box heat being a higher

temperature than the room

temperature, forcing the hotter air

out of the box.

Length 4.72in

Speed 2000 RPM

DEEPCOOL WIND

BLADE 120 Hydro

Bearing Semi-

transparent Black

Fan with Blue LED

[20]

Price $5.99/unit

Speed 1300 RPM

Length 4.72in

xxxvi

23

2.3 Materials

The mats will consist of a top coating material over the sensors, a foam layer for cushion, and a

textured bottom that will allow for minimal slippage. There will also be an adjacent compartment

housing the battery, microcontroller, and Wi-Fi transmitter, which must meet certain safety

requirements.

2.3.1 Top and Side Coating

The top and side coating must be water resistant, allow for transfer of pressure to sensors and not

introduce a slipping hazard. Materials considered for the upper layer included neoprene, silicone

elastomer, and ethylene-vinyl-acetate (EVA) [21].

Table 12. Top Coating material comparison table

Top Coating E (GPa) Density ρ

(g/cm3) E/ρ Fracture

Toughness KIC (MPa√m)

Yield

Stress MPa

Wear

Resistance

Neoprene 0.0007 -

0.002 1.23 - 1.25 0.00057 -

0.0016 0.1 - 0.3 3.4 - 24 good

Silicone

Elastomers 0.005 -

0.02 1.3 - 1.8 0.0038 -

0.0111 0.03 - 0.5 2.4 - 5.5 good

EVA 0.01 -

0.04 0.945 - 0.955 0.0106 -

0.0419 0.5 - 0.7 12 - 18 good

Choice: EVA

All three materials demonstrate very good resistance to water. Neoprene is often used in seals

found in wetsuits, O-rings, and footwear. Silicone elastomers are used in electronic insulation

and some medical implants. EVA can be found in packaging materials, films, and running shoes.

All three possess good wear resistance, which is necessary for the layer protecting our sensors.

This layer will also take the initial impact and force from users walking on it and potentially

dragging their feet. EVA is less dense than neoprene or a silicone elastomer and the specific

modulus indicates that EVA is stiffer than the alternatives, therefore the pressure will not be

distributed across the sensors, increasing resolution. The fracture toughness and yield stress

indicate that EVA will remain intact and protect the rest of the system.

24

2.3.2 Bottom Material

The bottom layer will likely be applied to a laminate floor, where it must remain flat and stable

so that the mat does not disengage from the floor. The materials considered for this segment

were Isoprene rubber, EVA, Natural rubber, and polyurethane thermoplastics. Table 13. Bottom coating material comparison table

Bottom

Material E (GPa) Density ρ


Toughness KIC

(MPa√m)

Yield

Stress (MPa)

Wear

Resistance

Isoprene Rubber 0.0014-

0.004 0.93 - 0.94 0.0015 -

0.0043 0.07 - 0.1 20 - 25 good

EVA 0.01 -

0.04 0.945 -

0.955 0.0106 -

0.0419 0.5 - 0.7 12 - 18 good

Natural Rubber 0.0015 -

0.0025 0.92 - 0.93 0.0016 -

0.0027 0.15 - 0.25 20 - 30 good

Neoprene (CR) 0.0007 -

0.002 1.23 - 1.25 0.00057 -

.0016 0.1 - 0.3 3.4 - 24 good

Polyurethane

Thermoplastics 1.31 -

2.07 1.12 - 1.24 1.17 -

1.67 1.84 - 4.97 40 - 53.8 average

Choice: Natural Rubber

Isoprene rubber is often used in tires, inner tubing, and shoes. It has a good wear resistance, a

higher yield stress, but too low fracture toughness. EVA, or Ethylene-vinyl-acetate, is used for

cushioning in running shoes as well as packaging and insulation products. EVA has a better

fracture toughness than rubber, which means that after a crack forms, it has a higher resistance to

subsequent branching fractures but its yield stress is too low, remove it from contention. Natural

rubber has a medium to high yield stress and facture toughness. Rubber also has a simpler

manufacturing and customizable process; it is easily glued to other materials making it the most

viable option

25

2.3.3 Cushion Material

The foam layer must be able to resist permanent deformation under loads of up to 300 pounds

applied repeatedly over time. The materials considered were polystyrene and rigid polymer

foam (HD).

Table 14. Cushion material comparison table

Cushion Material E (GPa) Density ρ


Toughness

(MPa√m)

Yield Stress

MPa Melting

Temp (F)

High Density Rigid

Polymer Foam 0.2 - 0.48 0.17 - 0.47 1.02 - 1.176 0.024 - 0.091 0.8 - 12 152.6 - 339.8

Polystyrene 2.28 -

3.34 1.04 - 1.05 2.19 - 3.18 0.7 - 1.1 28.7 - 56.2

165.2 - 230

Choice: Polystyrene

Both polystyrene and rigid polymer foam are used in cushioning and packaging applications.

Both met safety standards concerning melting temperature. Compared to high-density rigid

polymer foam, polystyrene has a higher yield stress and fracture toughness.

2.3.4 Power Box

The outer-casing for the unit must prevent any harm from coming to the user due to an electrical

failure. These failures could include overheating. For this reason, we considered the relative

flammability and melting temperature for ABS plastic and polycarbonate. Table 15. Power box material comparison table

Power Box Glass Transition

Temp (F)

Flammability

ABS Plastic [22] 221 Rating: 1

Material must be preheated before ignition

Polycarbonate [23] 311

Rating: B1

Will not burn for more the 30 seconds if 0.125”

or thicker

Choice: ABS plastic

The power box housing the battery and Wi-Fi router will be made of ABS plastic. This plastic

needs to provide safety features for electrical failure like high melting point and low

flammability. While polycarbonate does well in both those categories, ABS plastic is more

affordable and easier to manipulate.

26

2.4 Accuracies The basic design of Stepping Stones allows for a large tolerance of bending. The stretchy

and thin characteristics of the sensor mat from UNEO would allow for sensors to be bend

upwards of 90 degrees before invoking damage. The added support of the hard foam and rubber

layers however would ideally prevent the mats from bending any more than the recommended

amount. Consumers will be advised to place mats on flat surfaces for best results.

According to UNEO’s website, an individual sensor is capable of measuring a scale

between a human touch and a ton. Fear of damage to sensors by accidentally dropping

something on them (i.e. a treadmill, medical device, tables or chair) is not substantial. The

sensors should not be damaged from anything found within a typical therapy environment.

Permanent deformation of the mat (including the foam and rubber elements) is of

concern. The yield stress of mat materials exceeds 25 MPa, which would be enough if only

humans were walking on top of the mat. Say for instance the mats are on the floor and a

shelving unit is knocked over allowing for the corner to hit the mat. A small surface area

conveying that large of a weight might exceed the yield of polystyrene and EVA foam. This

design does not have a way to resist that. In the event that a large, heavy object is dropped or

thrown on the mats and it exceeds a force of 3600 psi, the mats will become permanently

deformed. This should not affect the accuracy of sensors outside of the immediate area

however. If the dent is on the edge of the mat and patients do not typically utilize that portion of

the surface, the mats may still be usable.

Electrical failures can cause damage to the system. Batteries may short causing excessive

heat. Power boxes are placed on the side of mats and are not part of the usable surface. This

keeps patients away from any possible injury. The boxes themselves are made from ABS plastic

which has a flammability rating of 1. This means the box will get hot but will not self-combust

due to heat given out by 12V battery system.

2.5 Protection Mechanism

To assure that the system is safe for use and implementation in a clinical setting, several

design parameters will be applied to ensure no harm comes to users. All circuitry will be

enclosed. Otherwise, internal wires that we will use to configure the pressure sensors will not be

open to the environment or the patient’s feet. In addition, an external power switch on the master

mat will cut off power to the entire system.

The underside of the mat, specifically, will be a natural rubber layer to allow for maximal

traction of the mats with the surface floor. Patients will not have to worry about slipping or the

mats moving from under them. Tripping will also be avoided when our system utilizes a battery

instead of wall power outlet. In addition, part of the design will allow customers to purchase

mats that are sized for stairs, and are smaller than an actual stair’s dimensions. This is so that

patients do not trip with excess mat overhang when being tested to walk up stairs.

27

3.0 Phase 3: Software

3.1 Scope In order to benefit the user and the therapist, our system will provide visual feedback on how

well the subject is doing and store quantitative data to establish improvement. The Stepping

Stone mats’ will produce a voltage when pressure is applied. This data, along with the

coordinates and the time, will be transferred through a microcontroller to a Wi-Fi transmitter.

The data will be sent through a router to a secure server-side application that can be deployed

inside the hospital’s local network for access by a secure SSL-encrypted web page (for use on

laptop and mobile devices). The voltages created by inducing pressure in the sensors in the

walkway mats will be converted by the software by establishing a corresponding pressure value,

indicating the weight distribution from the user. The software will also analyze the user’s center

of mass, stride length, and gait. These parameters will be measured and compared to normal

ranges determined by their demographic. There will be real time feedback for the user and the

observing therapist using a visual, color coded, display where they can observe their COM and

pressure application. The quantitative data will be temporarily stored in the system’s time and

relational databases where they are further analyzed. At the end of each session the software will

produce a numerical assessment of the patient’s progress, determined by comparing to norm. The

therapists can then save the data on the hospital’s secure network and can use it to determine the

patient’s improvement during the rehabilitation process.

28

3.2 Front End Description

The Stepping Stones systems operation will appear to the user in the manner seen below:

Figure 6. Overview of user interface

29

3.2.1 Setup

Upon turning on the interface system, the user will

see the welcome screen as the application loads.

The next screen the user is prompted with is a mat

setup screen (figure 8). Mats are labeled on the

physical system and are interchangeable (i.e. the

mats can be put in any order). On this screen the

user will input what specific mats will be used,

stair or walk, and the order of each by selecting

each mat in the order that it is spatially located. At

this screen we also get a battery level to notify the

user mat operable level.

After this, the user is prompted to the next screen (figure

9), to input patient demographics. Here, the physicians are

to input the patient’s information so that the software can

compare the patient’s data to normal walking data to

determine deviation from norm. Gender, age height,

weight, shoe size, and a brief trauma description will be

added to the appropriate areas in the data prompt. In

addition, there will be a comments box for any additional

information to be added unique to that patient that

physicians feel necessary. They will also have the option

to retrieve data that was previous saved to the hospital’s

database, if the patient is not new to the system, so the

therapist can save time with the input and can see

previously performed tests.

Figure 7. Welcome screen

Figure 8: Input mat selection and order screen. User selects

from either stair mats or walkway mats, and selects each to

check battery level and manipulate their order in the system.

Figure 9: Input patient demographics screen.

Any extra information that the physician feels

necessary will go in the comments box under

patient picture.

30

3.2.2 Calibration

The third prompt will welcome you to either run or calibrate. It is recommended highly that

calibration is always done before putting the system into run mode.

Calibration is defined here as zero pressure

on the mat detected, even if there is slight

pressure present from external forces or

system error, we can calibrate so that it is

“equal” to zero prior to a patient stepping on.

Calibration will begin with no patient on the

mat the process will ensure that sensors in

the mats will activate when pressure is

applied without too long of a lag. While

calibration is occurring, the user will not be

able to use the software in any other way.

The screen will consist of a calibration in

process image, and no prompts to move

anywhere until completed (figure 11).

Once calibration has ended, our screen will notify us,

and return us to the original opening prompt (Figure

10). Now, users are urged to run the program.

Note: If at any time during run modes the system does

not seem to be accurate, there will always be an option

to re-calibrate and toggle back to this screen.

3.2.3 Run

Run brings the user to the domain where testing can occur. Run mode can be stagnant for use all

day after calibration and user demographics have been implemented. You must be in Run mode

to then test and record data.

If any time during the run operation a mat’s battery

goes below operable level a warning notice appears

on the system and the user has the option to switch it

out for another mat as seen in figure 12.

Figure 10: Calibration or run prompt.

Figure 11: Calibration screen. User cannot leave

this prompt until system is finished with calibration.

Figure 12. Warning notification for mat low mat battery.

Unlike calibration, user can dismiss the alert.

31

The system will present a list of a total of 3 test choices during Run mode.

3.2.3.1 Test 1: Left/Right Weight distribution

This test will be static, measuring the center of mass. It will allow the user to see what side, left or

right, the patient is more dependent on. This will allow

them to get available assistance when the user

progresses to the walking test. For example, if a patient

is left side dependent, then during walking the

physician knows to set up the mats with a possible rail

available to the left side or with physical therapists to

aid on that side. This will be displayed as red for the

side with more dependence, and green for the side with

less dependence. If the weight distribution is within 40-

60% and fairly even, the image of the pseudo patient

will become blue. They are able to see center of mass

via a moving dot on an axis surrounded by their feet, as

shown above. There will be an option to cover some of

the screen in order to allow the patient to only be able

to see the center of mass screen, and the therapists can

see the weight distribution screen.

3.2.3.2 Test 2: Walkway

Mats should be set up in a runway-style. Patient will

walk down and pressure sensing of their feet will

show up on the interface in real time. Users will be

able to take frames per mat of the pressure

distribution. A rainbow gradient scale will denote the

force per square inch of the patient walking on the

mats. However, seen by therapists will be a gradient

based on “high” and “low” pressure. A generalized

foot imprint will come up on the screen based on the

patient’s foot size, and then the matrix of pressure

sensors will fill in that outline compared to where

force/weight is being placed. During this experimental

run, the patient will have the option to not see

themselves walking, so as not to get dependent on the

system to aid their walking, or see it to benefit them

in earlier stages of therapy.

Figure 13: Test 1, center of mass and weight

distribution. User can rotate pseudo image of patient to

analyze different angles. If more weight is distributed on

one side, that side is red. When the patient is within a

normal weight balance range, the image will turn blue.

User can minimize this screen and maximize the center

of mass screen at the top left.

Figure 14: Tests 2 and 3. A live feed of the

mat receiving the pressure imprints from

the patient will run with the test. At any

time, the user can take frames of each mat

to zoom and analyze where pressure

application is high/low.

32

3.2.3.3 Test 3

Mats are set up on stairs, and prompt screen is similar to that of the walking test. Pressure and weight

distribution is still measured in the same way. The only difference is that the stair mats will be used,

which would mean the user would have to go back to the first prompt and do set-up and calibration. For

stairs, cadence/mechanics are not as important. Also due to hanging onto a railing, weight distribution is

going to be different. Stair mode should focus on weight transfer and stability of each individual

foot. Weight transfer will be demonstrated similarly to walking mode. Footprints demonstrate weight

distribution in real time. The stability test looks at an individual foot during climbing and performs a

COM equation on it. The COM should be centered medially/laterally and slightly towards toes. This

could be demonstrated in a dot just like in walking. It is aimed more towards therapist assistance.

3.2.4 Data Output After the ‘Run’ and tests are performed, therapists will be able to determine how the patient is doing from

a “derivation from norm” data system that implements the patient’s demographics and compares them

with a healthy patient of similar demographic.

After comparison, the system will grade the patient’s

performance for the session and output a

standardized number. Here, results from each test

selected in the Run mode are consolidated and

compared to determine a final output of patient

performance on a 1-10 scale; 10 being within ranges

of the norm for their demographic, and 1 being

entirely hemiparetic.

After the therapists view the data there will be a

prompt to save all data to the patient’s file that is

located outside of the Stepping Stones’ system in the

hospital’s servers (in order to maintain HIPAA

compliance). Then, the user will be prompted to

either test again or calibrate.

Figure 15: Once each test has run, the system will take the

user to the results screen. Here they can click on each test

and individually analyze the results, or see the total

combined results from all tests done in a run phase.

Different sets of results are easily viewed with the blue

arrows. The final performance score is based on an average

of all tests done in Run, and compared with normalizations of

the patient’s demographic population that is healthy. Center

of mass and progress charts will be shown.

33

3.3 Software Architecture

Data is acquired from sensors as a voltage array. It, along with time stamp are sent via Wi-Fi to the

computational system. Once there, the data is filtered and converted into weight values. Data is then

portrayed in real time by using the already established grid and assigning colors to it. Tests use

established values to compare current results and output a grade that can be recorded for quantitative

Figure 16. Software architecture flow chart with pseudo code.

34

improvement values. All data is saved temporarily by the system to take retrospective measurements. A

more comprehensive software architecture diagram can be found in Appendix A.

3.4 Software Requirements

3.4.1 Application Architecturexxxvii

The system is comprised of a secure server-side application that can be deployed inside the

hospital’s local network for access by a secure SSL-encrypted web page that can be integrated

into local identity providers which will act as a means of authentication. The application will be

HIPAA-compliant in that it will never require any identifying information about the patients

being processed and that all data it stores will be secured in an enterprise database deployed

under the application on the hospital’s local network [24]. The application architecture then

resembles:

3.4.2 Communication

The application will have to be designed to listen for inbound HTTP/1.1 requests and respond

with the information after validating access and authorization to the data or action

requested. Though HTTP/2.0 is available as another option, it was determined that it is an

unnecessary complication in terms of maintenance, debugging, and support for the payoff of

performance, given the number of estimated mat clients and administrative computers planned

per deployment [25].

Over this protocol, the application will need to communicate in a well-formed message that can

be transmitted through the wireless data transmission module, across the hospital’s Wi-Fi and

onto the computer running the Stepping Stones’ software. The data that a message packet

leaving each mat needs to convey is:

Mat Identification number

Location of activated pressure sensors

Voltage produced by each pressure sensor

Timestamp of when pressure sensor was activated

Battery status of each mat

An example of the base message that this system will send was created in JSON and will be

transferred using HTML 1.0. JSON will be used due to the fact that it is easy for humans to read

Figure 17. Application Architecture. Wi-Fi transmitters in mats transfers messages to router. The data can be stored behind the facilities fire wall. Results are presented on a computer screen.

35

and write, along with the fact that it is complete with libraries for use in most popular languages

[26]. These messages will be transmitted between the server and various clients (both mats and

the administrative computer) throughout the process of this application’s use. An example of

what a JSON message from a mat to the server might look like this:

{

"mat_id": "ab5lk39djj208dl23893",

“Battery power”: .51

"sensors": [

{

"coordinates": [

X,

Y

],

"voltage": V

},

],

"timestamp": "10-20-2017 T12:00:00.122265"

}

This is a simplified version of the actual message as the array of pressure sensors will have

coordinates X and Y with X ≤15 and Y≤ 10 (for the first mat in the system). Each packet will

transmit 150 coordinates and associated voltages (with sensors not reading pressure transmitting

0V). The transmission rate is expected to be 10Hz, or 10 frames a secondxxxviii. This will be a

fast enough speed as human recognition requires approximately .15s to process information and

it would be updating the information every .1 seconds. The packet of data will be approximately

7500 bytes (determined through converting the sample message, +149 coordinates and voltages,

into bits through notepad propertiesxxxix) and therefore the Wi-Fi transmitter needs to transmit

750000 bps, which is smaller than what our Wi-Fi limit, 256KB.

3.4.3 Data Storage Model

Two database systems will be used to store the data temporarily during the duration of the

therapy session. Since our gait analysis is dependent on timing, it requires the “footprint” data to

be stored in a time sensitive manner; therefore, a time-series based database should be utilized

[27]. In conjunction with this, we will use a relational database management system (RDBMS)

because we need to relate information across tests and runs from a single patient. RDBMS is

optimized for this type of storage and will allow us to query the data across all trials and can

allow us to produce an output value for patient’s performance at the end of the tests [28]. After

the session users have the option to save the data to the patient’s file but that will not occur

within our databases, rather it will occur in the hospital’s, allowing us to maintain a HIPAA

compliant environment.

3.4.4 User Interface

The system will be sold with mats and a key to download the software onto the hospital’s server.

The application’s user interface will be a website that can only be accessed over the secured local

network of the hospital by using a secured SSL-protected HTTP/1.1 connection to the

36

administrative computer’s web browser. This design will allow versatility in how the software is

accessed as it can support mobile browsing and the use of tablets in these rehabilitation

sessions.

3.5 Mini Spec

X COM Accepts weights in array

Creates int variable Sum = x1(weight1) + x2(weight2)...

Create int variable weight = weight1+ weight2 + weight3

Create int variable COM = Sum/weight

Iterates through x and y coordinates: updating Sum and weight

Returns COM

Y COM Accepts weights in array

Creates int variable Sum = y(weight) + y2(weight2)...

Create int variable weight = weight+ weight2 + weight 3

Create int variable COM = Sum/weight

Iterates through x and y coordinates: updating Sum and weight

Returns COM

Stride Length Measurement Accepts array of time stamped left and right footsteps

Creates int variable Difference = abs(y_footstep0 - y_footstep1)

Stores Difference values in a StrideLength_Array

The StrideLength_Array is stored and sent to the GUI. From there isNormal references

acceptable values to establish whether the patient is exhibiting a healthy stride length (See

Appendix A).

3.6 Impact on Systems

Thermal - Power required by the system without impacting the integrity of the mats

The power source must be able to supply this power to each mat in a parallel circuit, while also

powering the microcontroller and Wi-Fi transmitter attached to the master mat. The Wi-Fi

transmitter operates with a voltage of 3V independent of the mats, and the microcontroller will

operate at 9-12V. The sensors will just require a current traveling through the mats to produce a

voltage output to be interpreted by the microcontroller. The power source must be able to

adequately distribute power amongst the entire system without the risk of overheating or being

cumbersome to the design of the device for both practicality and storage purposes. The primary

composition of the mats will be comprised of a polyurethane foam, which has a melting point

resting between 150 and 250 degrees Celsius, depending on the application. Therefore, the

composition will minimize the risk of burning or melting, which would compromise the integrity

of the system and safety of the patient.

37

Electrical - how software functionality changes

The electrical circuitry setup of the system will revolve primarily around the layout between the

components powering the mats and the circuitry designed to transfer data between the sensors

and user interface. The software of the system is coded in a way that will give a digital readout of

the mats surface so that when any individual sensor has a pressure applied to it, the sensor sends

a signal through the circuitry, through a microcontroller programmed in terms of location,

voltage, and time of application, for it to then be transmitted to the wireless interface. This

modified signal is then transmitted to the program where it is then converted into a specific

colored pixel on the digital readout, which translates to an applied pressure at that specific

sensor. Similarly, the messages being sent to the server include battery life and therefore the

circuitry needs to be designed for a battery life readout and a means by which to communicate

this to the microcontroller/Wi-Fi transmitter.

Mechanical - are all physical parameters met/accomplishable

All of the physical parameters of the mechanical aspects of the design have remained constant,

with the only major change being a interface that will require a small monitor for the PT and

patient to be able to clearly see the data readout, which could be a laptop, tablet or phone

connected to the hospital network. A microcontroller will need to be utilized in between the data

transfer from the sensors and Wi-Fi transmitter with the purpose of both data acquisition and

controlling current draw to sensors. Aside from this, the dimensions of the sensor mats will be

150 sensors per mat, each spaced 2.1 inches apart from one another. The circuitry involved in the

power supply and data acquisition will still be laid intertwined amongst one another throughout

the entire system in order to maximize the use of space.

Controls - tolerance and accuracies

The largest margin for error that would affect the test results would be contributed to the distance

between the sensors in each of the different mats. The more sensors available, the smaller the

distance between the sensors, reducing that margin of error, however with more sensors comes

more circuitry and power which also increases the cost. The dimensions we are using in each mat

however are adequate enough due to the number of sensors we are using and the distance they

are separated (150 sensors, 2.1 in apart) so that we can best maximize surface area of each

individual mat.

Operations - How objectives may have changed

The only aspects to have changed are the real time patient visual readout in order to keep them

focused and concentrated on the physical aspect of the test using sensory rather than using a

visual to adjust their body weight. The overall design objective has not changed, rather the

internal components and how they interact with one another both physically and in terms of data

acquisition is what has primarily changed in our system design.

38

4.0 Phase 4: Electrical

4.1 Electrical Overview The Stepping Stones system will be measuring changes in voltage based on pressure to

indicate weight distribution during the rehabilitation process. To achieve this, the necessary

electrical components for the Stepping Stones system are:

● Battery- 12 V LifePak NiCd Battery 2.4 Ah

● Microcontroller- Arduino Uno

● Wi-Fi Transmitter- Arduino Wi-Fi Shield 101

● Sensors- UNEO Pressure Analysis Sensor

The battery will be used to power the microcontroller, which will be powering the sensors

and the Wi-Fi transmitter. The sensors will be sending data back to the microcontroller using a

data bus and the microcontroller will be packing the data to be transmitted out of the Wi-Fi

shield. The system will last approximately 13 hours, which will be longer than necessary for a

day of therapy sessions. The battery will be able to be removed and recharged outside the mat

system in order to be able to swap the batteries out if they are low powered and at failure. This

will extend the lifespan of the mat system.

4.2 Notable Electrical Systems Requirements for System:

The electrical power for this system will have to allow for multiple therapy sessions

daily, and provide for the multiple components needed seen in our design flow chart (fig 4). The

environment in which we are testing must be equipped with standard 120V American electrical

sockets, available to charge the mat batteries.

The ability for the batteries to be charged outside of the device will require less wiring

within the circuit, overall simplifying our design and cutting down on costs. In addition, we

suggest that the user purchase additional spare batteries for the system being that we have

allocated one battery per mat, in the instance that different mat’s batteries need to be replaced

after a multitude of uses, and replaced with fully charged batteries. This will ensure that we will

always have additional batteries to power the mat in case they run low on power. Tradeoffs for

the system requirements exist, but the removable battery system deems best in terms of

practicality and ease. Users will have to keep track of the multiple components to our system,

including the mats themselves, the batteries, and the charging station for the batteries, however

we strongly feel that this design is better in preserving the life of the mat-system. If damage

occurs to a mat with a permanent battery implanted in its design, then replacement of the entire

mat will be necessary. However, with our removable batteries, we are ultimately saving cost and

materials if damage occurs to the mat but not the battery, and vice versa.xl

39

4.2.1 Components

Sensors:

To estimate how much power would be required for our 150

pressure sensor customized mat we can use similar components

for the specs such as 1-inch force sensing resistors (FSR)

(shown in figure 17). Wired up in parallel the voltage going

through each sensors will be equivalent and depend on the

voltage output supplied by the microcontroller. The max draw

of each sensor is .5mA which means that 150 sensors would

require 75mA [29].

Microcontroller:

The microcontroller the system will be using is the Arduino

Uno microcontroller. This microcontroller was chosen as it

can handle the data collected by the sensors. The sensors

transfer approximately 20 bytes of information (x location, y

location, voltage output and timestamp), so the microcontroller

will have to handle receiving 3000 (20 x 150) bytes of data at

every sampling. We decided to sample at 10 Hz [note 10 Hz

comes from 1/0.1sec, Human perception is 0.15 sec] meaning

the microcontroller must handle 3000 bytes every 0.1 seconds

and then convert it to a JSON message to be passed into the

Wi-Fi shield. The JSON message has about 7500 bytes of data

in every data packet. The added 3500 bytes are due to the way JSON codes and inscribes data.

At a sampling rate of 10 Hz the microcontroller needs to be able to process 7,500 bytes/0.1sec

=75,000 bytes/sec. This controller has 256KB of RAM which exceeds our required RAM of

75,000 bytes. It requires a 7-12 volt operating power. It has a clock speed of 16MHz which

means it is more than capable of handling our sampling frequency of 10 Hz [30]. The average

current draw on this type of microcontroller operating at a 10 Hz frequency is 4.5mA [31].

Wi-Fi Transmitter:

Arduino Wi-Fi Shield 101. SSID and password

protection ensures patient confidentiality. It also can be

encrypted with WEP and WPA2. It piggybacks off of

the Arduino boards power supply (3.3V). The 101

shield has an extensive library and draws 60% of the

memory. This is okay because that still leaves 102,400

bytes of space for processing. The input pin in the

microcontroller where the Wi-Fi Shield will be attached

draws a max current of 50 mA [10].

Figure 18. Example of FSR sensor

Figure 19 Arduino Uno Microcontroller

Figure 20 Arduino Wi-Fi Shield 101

40

Battery:

The battery required will be between 7-12 volts in order

to power the microcontroller, which will supply power

to the Wi-Fi shield and the sensors. The battery needs to

be rechargeable outside of the unit (a change from our

previous sections). Further requirements will be that it

should retain power for the length of multiple therapy

sessions before requiring it to be recharged (minimum 4

hours at full use). Finally, the last requirement is that

the battery does not significantly weigh down the

system as these systems are expected to be portable.

We will be using the removable battery packs that also

require the separate charging unit. This is because if any

damage occurs to the mat or batteries during use or storage, it will not compromise the rest of the

system like a permanently implanted battery. They are separate entities from the rest of the

system and can be replaced and used as needed without removal of mat placement during testing.

We chose the Physio Lifepak 2.4Ah battery as it fits these requirements (as seen in section 2.2.4)

Cabling:

Table 16. Cabling requirements and criteria

Requirementsxli Criteria

Able to withstand load being applied by

patients Wires have ability to be malleable against constant

pressure but maintain its position.

Wiring for power distribution among all

sensors Wires need to connect from the power source to each

sensor without adding bulk to the system.

Table 17. Wires tradeoffs


Solid Copper Wire [32]

Corrosion Less surface area, less

corrodibility

Braided Wire

The best option would be to

use a braided wire, due to

the fact that is durable, has

good conductivity, and is

strong yet malleable all at

the same time. The biggest

negative has to do with its

price, however since we will

not be using a thick wire, the

cost will be relatively close

to its competitors. The other

Durability Rigid and strong, not

malleable under

pressure

Price $0.25/ foot (Sized

AWG 10)

Diameterxlii .04in

Stranded Wire

Corrosion Higher surface area,

multiple small wires

wound together

Durability Good conductor,

shorting out more likely

Figure 21. Physio LifePak 2.4 Ah battery

41

Price $0.29/foot (sized AWG

10)

wiring options contain too

many traits that could lead to

many long term internal

component problems.

Diameter .04in

Braided Wire Corrosion High surface area,

mesh covering makes

corrosion less likely

Durability High surface area,

mesh insulator allows

for a strong, malleable

wire

Price Variable price

depending on thickness

and # of wires in braid

Diameter .08in

Table 18. Wire Insulation tradeoffs [33]

Options Properties Decision and

Justification

THWN-2

Application Branch circuits in

commercial and

industrial appliances

TEW Insulation

It is most useful in smaller

internal applications,

whereas the other

insulations had primary

uses in much larger wiring

apparatuses that are

exposed to more extreme

conditions.

*Note, thickness of

insulation so miniscule it

should not play a big role

in decision, softness

negligible as well for this

decisionxliii

Resistance Heat, moisture,

gasoline, oil Composition Thermoplastic nylon

sheath

XHHW-2

Application Conduit and branch

circuit wiring

Resistance High heat, moisture,

sunlight

Composition Cross linked

polyethylene

TEW

Application Machine tool wiring,

internal appliance

wiring

Resistance High heat, moisture, oil

resistant

Composition Polyvinyl chloride

42

Fuse:

The kill switch that we will use is required to shut off the power leaving the battery and entering

the circuitry by shorting the system.

Table 19. Fuse tradeoff

Type Properties Choice

Temperature fuse:

Klixon - 7A M202

- 75 degrees Celsius (167

F) cutoff - Optimal for smaller

circuitry and devices - 0.70" x 0.41" x 0.16."

1.75" leads

Klixon 7A M202

Ideal for temperature and current

protection for smaller internal

applications, such as electric motors

and battery packs.

Given more time we would have

probably utilized an ammeter fuse but

we do not have the time to change our

circuit diagrams.

Ammeter Fuse

-Shut off based on too

high of a current

43

4.3 Electrical Architecture

xliv Figure 22. Electrical System flow chart. The battery will power the microcontroller which in turn uses a current draw to power

the Wi-Fi and pressure sensors.

Our system flowchart and setup is truly quite simple in terms of components and how

they interact. One 12V battery, our main source of power for the mat system, can be removed

and externally charged as needed. We will allocate one battery per mat. This allows the system to

operate as a separate unit aside from the batteries, and replacement power sources can be

acquired without having to replace the entire mat, or vice versa. These batteries will be charged

in a charging station that can be plugged into a regular wall socket (US standard 120V.)

A kill switch is installed to ensure safety to the system. It will be enacted (if needed to

be) during use, so as to cut off all power going into the system and its components. A fuse is

added in conjunction with the power line going to sensor grid so that if the temperature and

voltage of the system ever gets too high, it will trigger the kill switch and shut the system down

44

before any damage is done to the patient or system itself. Each mat will have its own kill switch

that activated based solely on that mat’s performance. The kill switch uses the fuse to ‘monitor’

temperature. Once temperature increases past the safe zone, the characteristics of the current

through the fuse change and cause it to blow. Due to the wiring schematic, the system will short

and no current will flow, successfully ceasing operation in that mat. Due to the wiring schematic,

the system will short and no current will flow, successfully ceasing operation in that mat.xlv

4.4 Circuit Schematic From our battery, we are powering the microcontroller, which powers the 150 pressure

sensors and the Wi-Fi transmitter via a current draw. The Wi-Fi component will then transmit the

pressure sensor data to the computer running the software. The data will be interpreted by the

interface program to produce visual displays for the patient.

Figure 23. Circuit schematic including power source, microcontroller, sensors and kill switch.

In order to collect all the data from 150 sensors through 1 pin at the microcontroller a

data bus of sorts will be utilized. Data from each sensor will be taken at independent times and

compiled under the same time stamp for each sampling. This means that every 0.1sec, all 150

sensors will be measured i.e.

at t=0 sensor 1,1 will be measured

At t=0.0006s sensor 1,2 will be measured

At t=0.0012s sensor 1,3 will be measured

Once all the sensors have reported data they will be processed into the same JSON package and

shipped out as the same time stamp. (Note: processing at 0.0006sec is still slower than the

16MHz speed of the microcontroller.)

45

4.5 Power Consumption Each mat will have its own 12V rechargeable battery, an Arduino microcontroller, and a

Wi-Fi shield. The optimal supplied voltage range for the Arduino board is between 7-12 Volts.

The battery will provide an external power source that will be supplied through the Vin pin of

the Arduino. The 5V pin will output a regulated 5V voltage to the sensor array. The 3.3V pin

will supply voltage to the Wi-Fi shield. Each sensor has a maximum current draw of 0.5mA. For

a mat with 150 sensors, this equals 75 mA of maximum current draw. The microcontroller will

draw 4.5 mA of current due to the low sampling rate. The shield will draw an additional 50mA

(maximum).

Table 19. Total power draw of Stepping Stones system/mat.

Source Voltage (V) Current (mA)

Sensor (150) from

microcontroller

75

Microcontroller 12V 4.5

Wi-Fi Shield from

microcontroller

50

Totals 12 129.5

As demonstrated in the component section, the Physio Lifepak 2.4A can support this power

requirement. 2.4A/.1295A (from total draw) gives over 18 hours of power. This exceeds the

required length for therapy sessions.

46

5.0 Phase 5: Controls

5.1 Control Specifications

5.1.1 Define Control Problem:

As introduced in Phase 4, Stepping Stones incorporates a safety shut off to prevent injury

due to overheating. One source of this occurs within the battery. Small particles of metal may

come into contact with other parts of the cell causing a short. Layers of films can build up on

electrodes and cause shorts. Batteries can also short due to random events; such as, temperature

changes, physical damage, vibrations and other stress inducing events. When shorts occur in the

battery, excessive heat is dissipated into the surrounding material. If a patient or therapist were

to come into contact with the black box that houses the battery they could experience a burn.

The heat may also fry the microcontroller, Wi-Fi shield and connections.

Shorts may also occur within the mat wiring if mats are folded or sharp items are dropped

on them. This may cause physical damage to the mats and upset the wire configuration.

In order to counteract this, a fuse is implemented in the circuit to monitor the temperature within

the system. According to a report by Safety Action, brief contact with a metallic surface that is

over 140 degrees Fahrenheit is too hot to touch. Brief contact with a non-metallic surface is

acceptable until it reaches a temperature of 185 F. Should it experience a temperature over 120 F,

the system will power down, since this is the lower acceptable threshold [34]

5.1.2 Limitation

Due to the randomness of short circuits, it is possible that damage done to the battery cannot be

undone. Damage incurred by microscopic metal particles creating a short within the battery are

non-compatible. In this scenario the system would continue to melt. It is important to note that

according to BCI Failure Mode Study in 2010, only 19% of battery failures were due to shorts

[35]

5.1.3 Requirements

Due to the way our control system works we have no constant value to maintain. Since our

feedback monitors but does not do anything until overheating occurs we have no oscillation.

Therefore. there is no damping ratio, bandwidth, or rise time. Our response is a single event,

throwing of a switch.

5.1.4 Damping Ratio Not available.

5.1.5 Steady-state error

The main source of input of this control problem comes from the temperature fuse. The 75 have

an accuracy of +/- 0.1 degree C. This accuracy holds true between 0 degrees C – 100 degrees C

(well within our working range) [36].

47

5.1.6 Bandwidth-N/A

5.1.7 Rise time

While the system does not include an oscillator it does have a time dependent aspect. The

cooling of the system occurs in a predictable way. The dynamic heat loss is explained farther is

section 5.3.2

5.1.8 Overshoot -N/A

5.2 Control Hierarchy

Due to the multiple sources of battery failure, multiple temperature monitors are used. Each

monitor is wired in parallel to their intended area. The monitors also form a one-way

communication network with the battery. This communication sends the message to turn off the

battery by cutting the circuit so a complete circuit cannot be achieved.

Both monitors are at the same level. Since they only tell the battery to stop, they cannot possibly

override each other. If they sent the message at the same time, or close to, it would not matter

because the first message would reach the battery and dislodge the circuit.

Figure 22. Temperature Monitoring Schematic. Separate systems monitor circuitry and battery

for overheating. Both monitors are capable of shutting batteries off.

5.3 System Model

5.3.1 Calculate Drift Speed of 12 Gauge Braided Copper

𝐸𝑙𝑒𝑐𝑟𝑜𝑛 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 ∶ 𝑛 = 𝐴𝑣𝑜𝑔𝑎𝑑𝑟𝑜𝑠 ∗𝐷𝑒𝑛𝑠𝑖𝑡𝑦

𝐴𝑡𝑜𝑚𝑖𝑐𝑀𝑎𝑠𝑠

= 6.02 ∗ 1023 ∗8.92𝑥103

63.2𝑥10−3 = 8.46𝑥1028𝑚−3

Fermi Energy for Copper = 7eV

𝐹𝑒𝑟𝑚𝑖 𝑆𝑝𝑒𝑒𝑑 = 𝑣𝐹 = 𝐶√(2𝐸𝑓

𝑚𝑐2) = 3𝑥108√(2 ∗

7

511000𝑒𝑉) =

1.57𝑥106𝑚

𝑠

Conductivity of Copper = 5.9x10^7/Ohm*m

48

𝐹𝑟𝑒𝑒 𝑝𝑎𝑡ℎ: 𝑑 =𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑡𝑦 ∗ 𝑚𝑎𝑠𝑠 ∗ 𝑓𝑒𝑟𝑚𝑖 𝑠𝑝𝑒𝑒𝑑

𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑑𝑒𝑛𝑠𝑖𝑡𝑦 ∗ 𝑐ℎ𝑎𝑟𝑔𝑒2

=5.9𝑥107 ∗ 9.11𝑥10−11 ∗ 1.57𝑥106

8.46𝑥1028 ∗ (1.6𝑥1019)2 = 3.9𝑥10−8 𝑚

Apply to Braided wire of 2.05232mm diameter and 0.1-meter length:

𝑅 =𝐿

𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑣𝑖𝑦 ∗ 𝐴=

0.1

(5.9𝑥107) 𝑃𝐼 ∗ 1.026162 = 5.12 ∗ 10−10 𝑂ℎ𝑚

𝑊ℎ𝑒𝑛 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 = 12𝑉 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 =2.34𝑥1010𝐴

𝑚2

𝐷𝑟𝑖𝑓𝑡 𝑆𝑝𝑒𝑒𝑑 = 𝑉𝑑 =𝑗

𝑛𝑒 =

(2.34𝑥1010𝐴

𝑚2 )

(( 8.46𝑥1028𝑚−3)(1.6𝑥1019))

=1.73𝑥10−38𝑚

𝑠

This equation indicates that a warning signal once felt at the battery traveling towards the

monitor (0.1m) and then sent back to the battery (this time to turn it off) would take only 5.19E-

37sec, not including the controller speed.

5.3.2 Heat Transfer Equation

BTU plastic has a thermal conductivity level of [37] 1.1 𝐵𝑇𝑈 ∗ 𝑖𝑛 ∗ ℉

ℎ𝑟 ∗ 𝑓𝑡2

Applying the initial conditions:

𝑖𝑛 = 2

𝑓𝑡2 = 9.35𝑖𝑛 ∗ 4.3𝑖𝑛 = .2792𝑓𝑡2

℉ = −47.2℉ This gives you

−371.9198 𝐵𝑇𝑈

ℎ𝑟

This is the amount of work (heat dissipated) the ABS plastic can do in an hour.

The amount of BTU associated with cooling an 80.41 cubic inch air sample from 120 degrees F

to 72.8 degrees F is found by [38]: . 24𝐵𝑇𝑈

1𝑙𝑑℉

∗. 0871𝑙𝑏

𝑓𝑡3∗ 1.483 ∗ 10−5 𝑓𝑡3 ∗ −47.2℉ = −1.463 ∗ 10−5𝐵𝑇𝑈

To find the time needed to cool the battery once powered down:

−371.9198 𝐵𝑇𝑈

ℎ𝑟∗

1

−1.463 ∗ 10−5𝐵𝑇𝑈= [

24521722.49

ℎ𝑟]

−1

= 3.933 ∗ 10−8ℎ𝑟 ∗3600𝑠𝑒𝑐

ℎ𝑟

= 1.42 ∗ 10−6𝑠𝑒𝑐

49

These calculations show that if the fuse’s temperature reaches a degree that is higher than 75

degrees Celsius the fuse would quickly short the circuit. The time it will take to send the

shutdown requirement to the battery would be 5.197 x 10-37 seconds. Once the battery is shut

down the heat can dissipate out of the power box through the vents. The speed of dissipation

1.42 ∗ 10−6𝑠𝑒𝑐 proves that a vent would be sufficient to dissipate the heat once the fuse shorts

the circuit. These calculation proves that our temperature controls would be sufficient to protect

our system and the user from temperature related harm.

50

6.0 Physical Therapy Overview

Below is the user manual that will be given to the physical therapists when using the Stepping

Stones product.

Installation:

1. Install Stepping Stones software on local hospital computer.

2. Connect the Stepping Stones system to hospital’s secure sever in order to save patient’s

data to this location

3. Using charging station, charge NiCd battery from each mat. These should have an

average of 18 hours of power but should be charged at the end of the day in order to

ensure sufficient power during the rehabilitation sessions.

4. Return the batteries to the housing unit and the system is ready for use.

Operational Use:

1. Before the therapy session begins, inspect the mats and make sure there is no damage.

Lay the mats out in any means you desire (with the most accurate results stemming from

either a walkway with no room between mats or using the stair mats on the stairs). Turn

on the Stepping Stones software and insert the mats’ spatial arrangement

a. The Stepping Stones mats are each assigned an individual number

b. Type in the corresponding number for the first mat that the user will walk on

c. Continue in the order that the user will walk

2. Once the patient arrives, go to the patient demographics screen. If it is a new patient

insert required fields (height, weight, gender, trauma type). If it is a returning patient, use

saved data and pull up patient’s profile from hospital’s server system.

3. Calibrate the mats to make sure that it is zeroed before the patient begins their therapy

session, by pressing the Calibrate button on the home screen.

4. Run the software and click on Test 1 (Center of Balance) in order to obtain feedback on

the patient’s weight displacement, as seen in Figure 13. Use the center of pressure visual

feedback to correct the patient or allow them to autocorrect.

5. Click Test 2 if using on walkway and Test 3 if used on stairs. This will produce an image

of the pressure on the foot so you can help correct the patient based on irregularities.

6. At the end of the session you will have the option to save the data on the hospital’s

server. No data will be saved in the system, following HIPAA compliance.

7. A results page will come up that will grade the patient’s mobility based on the norm of

the patient’s demographic.

8. Once the session is over you have the option to shut off the system, power down the

mats, or start a new session. Storage:

1. The mats are covered in EVA which will allow them to be cleaned and sanitized without

worry about eroding the sensors so clean the top of the mats at the end of each therapy

day. A damp cloth should be sufficient for most dust accumulation. Be sure to wipe the

bottom faces to allow a better grip to the floor.

2. Mats can be stacked and stored anywhere that is convenient.

51

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52

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54

8.0 Appendix

8.1 Appendix A

Data is sent to the GUI and GUI handler. Both of these classes feed into the start method. This

method creates the real time display and leads to the tests. The tests each output a specific value

(ie. COM, stride length, time in stride …). Each test has an associated isNormal method that

checks the outputted value against expected values for the patient’s demographics. The display

is made from assigning colors to the values in the weight array. The left/right distribution

display is created by first identifying right and left foot locations. This is done by finding

“edges” and “corners” in the array. Doing so allows for two separate legs to be identified and

then a total mass is counted. Left and right values are reported back to display. Stride length

and time in stride is similar and can be checked with an associated isNormal. These are further

developed in the figure below.

isNormal value to check Expected Value

Center of Mass COM should be 1.95 inches forward from heel and 1.30 inches laterally

from instep for a self-selected pace.

Stride Length distance Based on experimentally proven values we established a healthy stride to

be within 10% of 0.4 times the user’s height [47] [48]

Stride Length time Looking at only one leg, the ratio of time spent weight bearing vs time

spent in swing should be 3:2. An acceptable value is plus/minus 10%

[49]

55

56

8.2 Appendix of Changes

Phase 1 changes i Scope now includes current approach, prior to proposed design ii Scope was modified to allow for proper analysis before arriving to a solution (specifics were

removed) iii The mats are now referred to as a system or sensor array to not introduce bias iv User interface requirements were removed from the Functional Requirements Section, since

the needs were implicit and already stated v The Sensor array is referred to as a ‘system’ until the System Overview section vi Safety switch stopping accuracy and stability of mats were removed, since they are not

functional requirements vii Sensing accuracy as a requirement was refined to include resolution of sensors viii Wireless communication from mat to software was removed since it is not a ‘performance’

requirement ix At this point the system is still considered an array of sensors, so specifics in regards to

materials was eliminated from this section to be covered later x System Overview no longer contains specifics (since they are no longer applicable), instead a

higher level approach is used to separate the system into functional components. Corresponding

Circuitry and Environmental Requirements were removed since they are covered in their

appropriate sections. xi System Overview now addresses the recommended format for the sensor array xii Control/Data Handling was added to the System Overview, including a microcontroller with a

Wi-Fi shield xiii The mats no longer require a master-slave relationship, all mats are identical and can run

independently xiv Flow diagram for software was eliminated since it is referenced in its appropriate section later xv Since there is no longer a master-slave relationship between mats, several possible failures

were eliminated xvi Incorrect mapping was added as a potential failure

Phase 2 changes xvii Image changed to exclude USB ports and external Wi-Fi antenna on mat. In addition, mats no

longer plug into the wall for charging and dimensions have changed to accommodate the size of

the battery and microcontroller. xviii Added picture of electrical housing including units xix Added microcontroller, changed Wi-Fi transmitter, changed battery used. xx Added weight of the mat calculated through components and materials used xxi AutoCAD drawing; battery box size adjusted to current size. xxii Added reference to circuit placement xxiii Changed minimum distance of sensors to increase the resolution and accuracy of readings. xxiv Changed number of sensors in each mat

xxvi Added Microcontroller section xxvii Reasoning for why <1 ms is desired gait speed xxviii Added requirement

57

xxix Chose Arduino WiFi shield instead of 433MHz Wireless Data Transmission xxx Added Arduino Wi-Fi as tradeoff option xxxi Requirement changed xxxii Requirement added xxxiii Requirement added xxxiv Additional rechargeable battery chart added (from Phase 4) xxxv Fan spec added xxxvi Note: all USB components in system have been removed due to change of charging mats

with rechargeable batteries

Phase 3 changes xxxvii Caption expanded on figure 14 xxxviii Transmission rate lowered from 100 Hz to 10 Hz in order to increase time for the data train xxxix Described how determined bit transmitted per message

Phase 4 changes xl Grammar changed xli Deleted in unit rechargeable requirement to increasing charging efficacy and decrease bulk in

system. xlii Diameters added to all wiring choices xliiiInsulation note xliv Changed where kill switch fuse was located in architectural diagram xlv Thermistor changed to fuse

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