stepping stones systems document final
TRANSCRIPT
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
Requirements 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
Requirements 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
Options Properties Decision and Justification
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.
Requirements 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
Options Properties Decision and Justification
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
Rechargeable Yes, via wall mount
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
Rechargeable Yes, via wall mount
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
Requirements 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
Options Properties Decision and Justification
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
(g/cm3) E/ρ Fracture
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
(g/cm3) E/ρ Fracture
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
Options Properties Decision and Justification
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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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