Vanderbilt University

Department of Biomedical Engineering

Senior Design Project

Instrumented Wheel For Wheelchair Propulsion Assessment

Date Reported: April 22, 2008

Group #2

Jacob Connelly

Andrew Cramer

John Labiak

Advisor: W Mark Richter, PhD.

Abstract

The development of upper extremity (UE) pain and/or injury is a prevalent health

concern amongst manual wheelchair users. The UEs serve as the principle means for

mobility for this population, therefore, any impeding factors, such as pain or injury, will

lead to a decreased quality of life. The development of UE pain and injury may be a

result of improper propulsion biomechanics or poor wheelchair seating configurations. In

order to quantitatively assess a manual wheelchair user’s propulsion technique for

training or seating purposes, there is a need for an affordable instrumented assessment

tool. The goal of the project was to develop an instrumented wheelchair wheel utilizing

strain gauges that have the capability of quantitatively measuring resultant force during

propulsion. Strain gauges were placed on the top and bottom of each of the pushrim tabs

that couple the wheel to the pushrim. The strain gauges were then wired into a

Wheatstone bridge circuit which was then connected to an instrumentation amplifier

circuit. The output voltages were then sent via a data acquisition unit with Bluetooth

capabilities to a local computer to be recorded, processed, and analyzed in LabView. A

standard curve was created relating resultant force to output voltage. The prototype wheel

developed demonstrates the ability to assess wheelchair propulsion by measuring strain

created by resultant force. Small changes in voltage created by flexion in the pushrim can

be sufficiently amplified in order to gain the appropriate sensitivity to clearly track the

resultant force applied during propulsion.

Introduction

The development of upper extremity (UE) pain and/or injury is a prevalent health

concern amongst manual propulsion wheelchair users. Sie et al. found that 64 percent of

individuals within a study of 239 paraplegic patients experienced UE pain [1]. Similarly,

Dalyan et al. and Gellman et al. reported the prevalence of UE pain within manual

wheelchair user populations to be 59 and 68 percent, respectively [2-3]. The UEs serve as

the principle means for mobility, therefore, any impeding factors, such as pain or injury,

can lead to a decreased quality of life. The development of UE pain and injury may be a

result of improper propulsion biomechanics or unsuitable seating conditions. In order to

quantitatively study, classify, or train a manual wheelchair user's (MWU) propulsion

techniques, there is a necessity for an instrumented assessment tool.

Current commercially available assessment tools, such as the SmartWheel

developed by Three Rivers [6], are exceedingly expensive and measure several

biomechanical forces and parameters, many of which are unnecessary for clinical

applications. An instrumented wheel designed to asses solely resultant propulsion force

and push cadence would severely decrease cost by providing only the necessary clinical

data.

A successfully designed instrumented wheel would provide a much needed tool in

seating and mobility clinics. This assessment tool would provide important information

on the propulsion habits of wheelchair users. Improper propulsion could be quickly and

accurately characterized, then corrected through clinical training programs that promote

ideal propulsion techniques set forth by the Consortium of Spinal Cord Medicine [4].

Furthermore, modified pushrim systems could be prescribed and fitted for special case

MWUs with non-correctable propulsion conditions. Pain and injury in MWUs could also

be avoided by improving customized seating conditions. Typically seating is determined

solely by the user's biometrics; however, it is important to also consider the user's

propulsive style and needs. Richter et al. showed that propulsion characteristics are

directly altered by changing wheelchair seating configurations [5]. By analyzing

resultant force characteristics it is possible to optimize the user's position in relation to

the pushrim to improve propulsive technique and lessen the likelihood of developing UE

pain and injury. Essentially, the instrumented wheel will serve as a means to

quantitatively compare various wheelchairs and seating configurations to optimize the

degree of comfort and propulsive capabilities of MWUs. With comparative propulsion

data, the instrumented wheel will also serve as justification for the selection of particular

wheelchair equipment for insurance reimbursement purposes.

Methodology

Design of the Instrumented Wheel

In order to

quantifiably assess

manual wheelchair

propulsion, a standard 24''

wheelchair wheel [a] and

pushrim were

instrumented with strain

gauges. The pushrim is

coupled to the wheel by Figure 1. The thinness of the tab design allows for some degree of pushrim flexibility.

three connection tabs. The

pushrim tabs, which were

designed in SolidWorks [b], are

shown in Figure 1. The pushrim

with the tabs connected is shown

in Figure 2. Standard pushrims

have six tabs that connect the

wheel to the pushrim, providing

a highly rigid and robust system

with an extremely high safety factor. By reducing the number of pushrim tabs to three,

the overall rigidity of the pushrim-wheel system is decreased allowing for a small degree

of flexibility. Uniaxial strain gauges were attached to the top and bottom of each pushrim

tab [c]. Application of force to the pushrim results in a change in the electrical resistance

of the strain gauges. In addition, the increased flexibility of the pushrim from reduction to

only three pushrim tabs allows for an adequate change in the resistance of the strain

gauges that can be

accurately measured.

The strain gauges

were wired into a

Wheatstone bridge circuit,

Figure 3. When force is

applied to the pushrim, the

resistance of the strain

Figure 2. The pushrim design consists of three tabs connecting the pushrim to the wheel.

Figure 3. A Wheatstone bridge is used to determine the change in resistance of the strain gauges.

gauges change corresponding to being in tension or compression. These changes in

resistance are reflected in changes in the two voltage outputs from the Wheatstone bridge.

However, the changes in the differential output voltage from the Wheatstone bridge were

small, approximately 10mV, and required amplification. An instrumentation amplifier,

seen in Figure 4, was implemented with a gain of 400. Calculations are shown below.

Each of the three tabs utilize one Wheatstone bridge and one instrumentation amplifier

which generate an output voltage due to the force applied to that tab. A printed circuit

board (PCB) containing the Wheatstone bridges and instrumentation amplifiers for each

of the three tabs was designed [d,e]. The wheel was then wired with 0.015'' diameter wire

allowing the strain gauges to be connected to the PCB. The wire was run through the

interior of the wheel, protecting it from environmental exposure and damage. The power

supply for the wheel is four AAA batteries providing 6V, however a 5V-5V dc-dc

converter was used in the PCB to provide a constant voltage through the circuit. The

three output voltages from the three instrumentation amplifiers were then sent to an 8-pin

data acquisition unit (DAQ) [f].

The PCB, DAQ, and power

supply were mounted on a black

plastic board. The plastic board

was securely mounted to the

spokes of the wheel.

The data was sent from

the DAQ to LabView [g] via a

USB compatible Bluetooth

Figure 4. An instrumentation amplifier is used to amplify the output voltage of the Wheatstone bridge.

transceiver [h]. Within LabView the data was recorded, processed through low-pass

filters, and analyzed. A standard curve relating voltage to applied resultant force was

created by applying known forces (5-25lb) to the pushrim with a spring scale and

recording the changes in the output voltages.

Determination of Resultant Force

In order to determine the overall applied resultant force, each tab was analyzed

individually. When a force is applied to the pushrim, each tab will be strained leading to

one strain gauge being in compression (C) while the other is in tension (T). The resulting

strain will cause the resistance of each strain gauge to change; tension causes resistance

to increase and compression causes resistance to decrease. As the resistance of the strain

gauges change, there is a corresponding change in the output voltage of the Wheatstone

bridge ( ). This change in output voltage is governed by the following equation:

(1)

where (which is the same as the nominal value of the strain gauges) and

. The output voltage from the Wheatstone bridge in then amplified using the

instrumentation amplifier shown in Figure 4 according to the following equation:

(2)

where is the voltage output of the instrumentation amplifier. The gain associated

with the instrumentation amplifier is equal to:

(3)

where , (desired output voltage) and

(approximated change in voltage from the Wheatstone bridge), thus:

(4)

The value of the resistor is equal to:

(5)

A standard curve relating output voltage and resultant force was created by

applying the known forces of 5, 10, 15, 20, and 25 pounds to the pushrim using a spring

scale. The forces were applied in close proximity to each of the three tabs. Each time a

force was applied to the pushrim, the magnitude of the change in output voltage for each

of the three tabs would change in relation to the location of the applied force. From the

three output voltages corresponding to each tab a single voltage corresponding to the

resultant force was determined using the following equation:

(6)

For each applied force (5-25 lbs)

we determined . We then

used these values to create a

Voltage vs. Force Standard

Curve.

Results

Figure 5. The instrumented wheel is used to assess the propulsion techniques of manual wheelchair users.

Figure 5 shows an

image of the final design of the

instrumented wheel. The wheel

was constructed in order to

maximize the voltage output

for a given applied force. The

final design utilized only three

tabs of a thin aluminum design.

This was intended to maximize

the displacement of the

pushrim upon the application

of a force, increase strain on

the pushrim attachments, and

in turn increase the change in

gauge resistance and voltage

output accordingly. Strain

gauges were mounted to the

top and bottom of each tab using adhesive, and wiring was run from the strain gauges

through the wheel well (Figure 6) to the Wheatstone bridge. The electronic circuit

constructed included a half-bridge circuit and an instrumentation amplifier for each of the

three tabs respectively. The instrumentation amplifier performed according to the

anticipated specifications and calculations made in the Methods section. The recorded

output voltages, seen in Table 1 below, are approximately 350.0 times higher than the

Figure 6. Wiring was run from the strain gauges, through the wheel well, to the Wheatstone bridge.

Figure 7. The Wheatstone bridge, instrumentation amplifier, and DAQ w/ Bluetooth wireless transceiver were mounted to the spokes of the wheel.

voltage output from the corresponding strain gauges. When compared to the calculated

gain of 400, the amplifier yielded an insignificant level of error and achieved the desired

result of amplification. The Wheatstone bridge, instrumentation amplifier, DAQ with

wireless Bluetooth transceiver, and power supply were mounted to the wheel spokes, as

seen in Figure 7.

Trial 1 Trial 2 Average

Tab

Force (lb)

5 0.1 0.3 0.05 0.45 0.05 0.4 0.2 0.65 0.550

10 0.4 0.2 0.25 0.85 0.15 0.75 0.2 1.1 0.975

15 0.6 0.2 0.3 1.1 0.2 0.8 0.35 1.35 1.23

20 0.85 0.35 0.3 1.5 0.3 0.9 0.4 1.6 1.55

25 1.1 0.3 0.3 1.7 0.4 1.25 0.4 2.05 1.88

Table 1. Output voltage data was recorded over a range of applied force values and was used to construct the standard curve.

Table 1 shows the voltage data from trial 1 and 2 and their average. Trial 3

produced inaccurate data

and as a result the data

was omitted. Using the

average values for each

applied force we created

a Voltage vs. Force

standard curve, which is

y = 0.0645x + 0.2675R2 = 0.9946

00.20.40.60.8

11.21.41.61.8

2

0 5 10 15 20 25 30

Force (lb)

Volta

ge (V

)

Figure 8. The standard curve shows the relationship between voltage output and applied force.

shown in Figure 8. The graph shows a strong linear relationship between voltage and

force, with a correlation coefficient of 0.9946. For any output voltage the applied force

can be determined using the equation for the best-fit line:

(4)

Though our prototype has fulfilled the project goals by producing a measurable

change in voltage in response to an applied resultant force and a strong linear correlation

based on recorded experimental data, there still remain a few challenges in producing a

marketable product. The first of these challenges is the sensitivity within the electronic

instrumentation of the wheel. Due to the initially small voltage outputs from the strain

gauges and the necessity of high gain amplification, the components within the circuit

have caused imprecision within our results. Despite acquiring highly relatable voltage

differentials, the raw voltage data is significantly different. That is, the baseline voltage

for each of the three tabs – 0.0, 1.4, and 2.0 V for tab 3, 2, and 1, respectively – varies

depending on the actual resistivity amongst each nominal resistor in the bridge and gain

resistor in the amplifiers. During experimentation we found that the 1.0% tolerance of the

350 Ohm resistors used in the half-bridge significantly affected the baseline voltage

output for the respective tab.

As a secondary challenge, the voltage differential decreases as the applied force

moves farther away from the tab's point of attachment. This causes a lower and

unrepresentative change in voltage compared to the applied force, rendering the standard

curve ineffective. However, this problem can be easily fixed by incorporating an angle

sensor to supply multiplicative calibration factors in order to augment the decreased

voltage differential depending on the point of application (coinciding with wheel angle).

Another option is to include software coding that supplies similar calibration factors

based on force application (coinciding with percent differences in voltage differential). A

simple suggestion for such function is shown in Appendix I.

Economic Analysis

Market Analysis

The instrumented wheel will be primarily target seating and training clinics,

rehabilitation centers, and research labs across the U.S. These centers will benefit from

use of the instrumented wheel since it gives them a means of assessing the propulsion

techniques of manual wheelchairs users which can then be used to properly seat and train

users as to the most biomechanically efficient propulsion technique. As shown in Table 2,

there are approximately 130-200 centers across the United States that could benefit from

use of the instrumented wheel. The SmartWheel, which is priced at around $25,000, is

currently in use in over 60 rehab centers across the U.S. [6]. Given that the price of the

instrumented wheel will be considerably less, we feel we can expect the instrumented

wheel to be put into use by approximately 100-150 centers in the U.S.

Center NumberSeating & Training Clinics 50-100

Spinal Cord Injury Hospitals and Rehabilitation Centers

30-50

Research Labs ~50Total ~130-200

Table 2. There are approximately 130-200 centers in the U.S. that could benefit from use of the instrumented wheel.

Development Cost Analysis

Table 3 shows the estimated cost of development of the instrumented wheel,

including parts and labor. The product will be sold as a pair of wheels; one will be

instrumented, and the other will be weighted as to have the same inertial effects. As

shown in Table 3, the estimated cost for parts is $1032 and the estimated cost for labor is

$180, for a total estimated cost of $1212.

Cost Quantity TotalParts

Transducer Quality Strain Gauges

$7 6 $42

Printed Circuit Board $20 3 $60DAQ $250 1 $250

Bluetooth $60 1 $60Wheelchair Wheels $250 2 $500

Push Rim $50 2 $100Electrical Supplies(i.e. wire; solder)

$20 n/a $20

Labor $15/hour 12 hours $180Total $1212

Table 3. The estimated cost of labor and parts for the instrumented wheel is $1212.

Overhead Analysis

The marketing plan for the instrumented wheel consists of contacting targeted

seating and training clinics, rehabilitation centers, and research labs by telephone first to

see if they have a need/desire for a device that offers wheelchair propulsion assessment.

If a potential customer is found, a representative will travel to the potential customer in

order to demonstrate use of the instrumented wheel and address any concerns there may

be. Therefore, it is expected that a primary overhead will be the cost of travel. Additional

overhead will include insurance, legal fees, taxes, rent, and utilities. Given these

considerations, we estimate an overhead cost of approximately $1000/month.

Benefit Analysis

It is difficult to perform a quantitative benefit analysis on the instrumented wheel,

because many of the benefits of the instrumented wheel cannot be expressed strictly in

dollar terms. However, qualitatively the instrumented wheel will provide the seating and

training clinics, rehabilitation centers, and research labs that will use it an important tool

for achieving their ultimate goal: the improvement in the quality of life of their

customers. Specifically, by offering feedback on the propulsion techniques of manual

wheelchair users, the instrumented wheel will help to determine the proper way to seat

manual wheelchair users and the most biomechanically efficient method for propelling

the wheelchair on a patient specific basis, both of which will prevent overuse injuries and

go a long way in improving the quality of life of manual wheelchair users.

Life Cycle/Cost of Maintenance

We do not expect there to be any additional costs of maintenance over the cost

necessary to maintain an ordinary wheelchair wheel, aside from costs associated with

powering the instrumentation of the wheel, which requires four AAA batteries. The parts

used in the construction of the wheel are such that the wheel should be resistant to any

forms of mechanical failure. Exposed wire was run through the wheel well and exposed

wire was insulated to prevent any damage that might lead to the malfunction of the

circuitry. The only concern with the current prototype is that the power supply, DAQ, and

circuit board are exposed to the environment on the side of the wheel nearest the user,

making it susceptible to damage; however, any model going to market would utilize a

hub to completely enclose these elements.

Pricing

Given the above costs, the expected benefits, and the expected life of the

instrumented wheel, it is feasible that it can be brought to the market for a price of

$5,000.

Safety Analysis

There are minimal human safety concerns associated with the use of the

instrumented wheelchair wheel for propulsion assessment. Although not proposing a

serious threat or danger, there are concerns regarding: (1) exposure of wiring within

range of human contact, (2) incorrect calibration of the instrument, and (3) subjects'

rights protection during instrument validation studies.

While the vast majority of the wiring connecting the strain gauges, PCB, and

DAQ are confined and isolated within the construction of the wheel, there are still small

sections of wire exposed near the pushrim tabs and strain gauges. While the wire is

insulated with a solid rubber coating there are still small sections that were stripped in

order to make solder connections with the strain gauges. In order to avoid short circuiting

and human contact with live wires, efforts were taken to completely insulate these

connection wires using Plasti-dip. While the voltage in these connection wires is

extremely low (5V), it is still necessary for the integrity of the instrument and for human

safety to take every effort to minimize the risk of human contact to these wires.

Currently, it is unknown how the instrument will perform over an extended period

of time. It is highly likely that the instrument will need to undergo calibration in order to

ensure accurate measurements each time it is used. Inaccurate measurements have the

potential to lead to improper decisions to be made in relation to resultant force regarding

wheelchair seating configurations or propulsion technique recommendations.

Before the instrumented wheelchair wheel is provided on the market, it will

undergo a validation study to ensure that it functions correctly and accurately. This study

will consist of comparison measures between the instrumented wheel and a previously

validated propulsiometer through the investigation of the accuracy of resultant force

measurement in various environments, including pushing on a motor driven treadmill and

pushing on public sidewalks and/or ramps. The goal will be to statistically prove that the

strain gauge based instrumented wheel provides accurate measurements of the resultant

forces in comparison to the propulsiometer. Before subjects will be able to participate,

there must be IRB approval to protect their rights during the study.

The instrumented wheelchair wheel is not classified as a medical device and

consequently does not require FDA regulation or approval. However, in the best interests

of MAX mobility and other contributing business entities, every effort will be taken to

ensure the maximum safety of the device and the consumer during use. Although there is

a minimal amount of risk surrounding the continuing development, validation, and

market dissemination of the instrumented wheel, it is believed that the benefits of

providing an affordable tool to quantitatively assess a manual wheelchair user’s

propulsion technique for training or seating purposes far exceeds any potential risk.

Conclusion

The prototype wheel developed here demonstrates the ability to assess wheel

chair propulsion by measuring strain created by resultant force. Small changes in voltage

created by flexion in the pushrim can be sufficiently amplified in order to gain the

appropriate sensitivity to clearly track the resultant force applied to the system. Though

there are a few modifications that need to be made in order to introduce this technology

to the market – incorporation of circuit elements with finite tolerances and the ability to

locate force application – this prototype serves as a solid basis for future designs utilizing

strain gauges to instrument wheelchair wheels for propulsion assessment.

Recommendations

Design considerations for the improvement of the current prototype include the

use of more precise circuit components (<1% tolerance), as the imprecision of circuit

components can cause imbalances in the bridge circuit which lead to deviations in the

output voltage of respective tabs, thereby skewing our results. In addition, improvements

can be made by measuring the tolerances of individual components to ensure they are all

equal. Furthermore, to more accurately gauge resultant force over the entire pushrim,

software or hardware additions, such as an angle sensor, are necessary in order to

determine the location of the applied force. The use of additional pushrim tabs would

enable better tracking of the applied propulsion forces, and is another option for future

modification. As we have found, however, there is a trade off between the use of

additional tabs and maintaining an appropriate level of pushrim rigidity. Therefore, the

use of additional tabs may necessitate the use of more sensitive circuit elements.

References

1. Sie IH, Waters RL, Adkins RH, Gellman H. Upper extremity pain in the

postrehabilitation spinal cord injured patient. Arch Phys Med Rehabil.

1992;73:44–48.

2. Dalyan M, Cardenas DD, Gerard B. Upper extremity pain after spinal cord injury.

Spinal Cord. 1999;37:191–95.

3. Gellman H, Sie IH, Waters RL. Late complications of the weight-bearing upper

extremity in the paraplegic patient. Clin Orthop. 1988;233:132–35.

4. Preservation of upper limb function following spinal cord injury: a clinical practice

guideline for health-care professionals. J Spinal Cord Med. 2005;28(5):434-70.

5. Richter WM. The effect of seat position on manual wheelchair propulsion

biomechanics: a quasi-static model-based approach. Medical Engineering &

Physics. 2001;23:707-12.

6. "The SmartWheel". Three Rivers Holdings, LLC.

<http://www.3rivers.com/swhome.php>.

Suppliers

a. Spinergy Wheel. Spinergy 6231 Yarrow Drive, Suite C, Carlsbad, CA 92011 USA.

b. SolidWorks. SolidWorks Corporation, 300 Baker Avenue, Concord, MA 01742

c. Transducer Quality Strain Gauges. SGT-1/350-TY13. OMEGA Engineering, INC. One Omega Drive Stamford, Connecticut 06907.

d. Printed Circuit Board. Express PCB. http://www.expresspcb.com/index.htm

e. Circuit Components (resistors, dc-dc convertors, connectors, operational amplifiers). Mouser Electronics. 1000 North Main Street | Mansfield, TX 76063.

f. BlueSentry AD data acquisition. RN-800S-CB. Roving Networks. 809 University Avenue, Los Gatos, CA 95032 USA. g. LabView. National Instruments. 11500 N Mopac Expwy, Austin, TX 78759-3504

h. Bluetooth USB Adapter. RN-USB-T. Roving Networks. 809 University Avenue, Los Gatos, CA 95032 USA.

Appendix

I. Resultant Force Calculation for Propulsion Assessment Using Vector Exclusion to Derive Calibration Factors

Because the voltage differential decreases as the application of force moves

farther away from the tab's point of attachment, it is necessary to augment these changes

in order to use the standard curve seen in the Results section. The purpose of this

program is to calculate the appropriate calibration factors based on the percent difference

in voltage differential. Because there is a defined relationship between the magnitude of

the voltage response and the distance of applied force from the tabs on the wheel, it is

possible to locate the position of force application based on these differences. In order to

accomplish this, each voltage differential is ranked highest to lowest. The highest

response indicates the tab most near the point of application. The second highest rank

indicates the tab second closest to the point of application. The program excludes voltage

data from the third tab and then calculates the fraction of the highest ranked tab over the

second highest. This fraction is then compared to a calibration table seen in the matrix

data, which holds experimental data relating the fractional voltage response of every

point of the wheel corresponding to the distance from each tab. The calculated fraction

then calls a specific calibration factor from data. The voltage output from the highest

ranked tab is multiplied by the calibration factor in order to gain the value of the voltage

output that would have been recorded given the force were applied directly above that

tab. When this voltage output is determined, the standard curve created in the Results

section can be used to relate the modified voltage output to a resultant force value.

Matlab Code

function [ResultantForce] = ResultantForce

%%% Resultant Force Calculation for Propulsion Assessment Using Vector %%%%%% Exclusion to derive Calibration Factors. %%%%

load(data.dat) %voltage output dataload(calibration.dat) %theta and scaling factor derived from performed %calibration on the wheel

%%FROM LOADED DATA FILES RECORDED IN LABVIEW%% N=length(data.dat); %length of input vector from DAQV1=data(1:end,1); %output voltage vector from tab 1V2=data(1:end,2); %output voltage vector from tab 2V3=data(1:end,3); %output voltage vector from tab 3theta=calibration(1:end,1); %degree angle value matched to a percent diff.percentdiff=calibration(1:end,2); %percent difference between dominant tab %and secondary tab to give wheel loactionfactor=calibration(1:end,3); %scaling factor to return resultant force from %fractional output at the dominant tab.

%%FROM THE CALCULATED CALIBRATION CURVES IN EXCEL%% slope1=value; %slope of the Excel calibration curve for tab 1 slope2=value; %slope of the Excel calibration curve for tab 2 slope3=value; %slope of the Excel calibration curve for tab 3intercept1=value; %y intercept of the Excel calibration curve for tab 1intercept2=value; %y intercept of the Excel calibration curve for tab 2intercept3=value; %y intercept of the Excel calibration curve for tab 3

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

V1min=V1(1); %baseline value from tab 1V2min=V2(2); %baseline value from tab 2V2min=V2(2); %baseline value from tab 2

V1diff=(max(V1)- V1min); %Voltage change caused by force to tab 1V2diff=(max(V2)- V2min); %Voltage change caused by force to tab 2V3diff=(max(V3)- V3min); %Voltage change caused by force to tab 3if V1diff >= V2diff && V2diff >= V3diff perdiff1=V1diff/V2diff; [m,n]=find(percentdiff==perdiff1); theta1=theta(m,n); factor1=factor(m,n); scalevolt1=factor1*max(V1); ResultantForce=slope1*scalevolt+intercept1;endelseif V1diff >= V3diff && V3diff >= V2diff perdiff1=V1diff/V3diff; [m,n]=find(percentdiff==perdiff1); theta1=theta(m,n); factor1=factor(m,n); scalevolt1=factor1*max(V1); ResultantForce=slope1*scalevolt+intercept1;endelseif V2diff >= V1diff && V1diff >= V3diff perdiff2=V2diff/V1diff; [m,n]=find(percentdiff==perdiff2); theta2=theta(m,n); factor2=factor(m,n); scalevolt2=factor2*max(V2); ResultantForce=slope2*scalevolt+intercept2;endelseif V2diff >= V3diff && V3diff >= V1diff perdiff2=V2diff/V3diff; [m,n]=find(percentdiff==perdiff2); theta2=theta(m,n); factor2=factor(m,n); scalevolt2=factor2*max(V2); ResultantForce=slope2*scalevolt+intercept2;endelseif V3diff >= V1diff && V1diff >= V2diff perdiff3=V3diff/V1diff; [m,n]=find(percentdiff==perdiff3);

theta3=theta(m,n); factor3=factor(m,n); scalevolt3=factor3*max(V3); ResultantForce=slope3*scalevolt+intercept3;endelseif V3diff >= V2diff && V2diff >= V1diff perdiff3=V3diff/V2diff; [m,n]=find(percentdiff==perdiff3); theta3=theta(m,n); factor3=factor(m,n); scalevolt3=factor3*max(V3); ResultantForce=slope3*scalevolt+intercept3;end

II. Innovation Workbench

Ideation Process

Project Initiation

Project name:Instrumented Wheel for Wheelchair Propulsion AssessmentProject timeline:Expected Completion Date: Senior Design Day-April 2008Project team:Jacob ConnellyAndrew CramerJohn Labiak

Innovation Situation Questionnaire

Brief description of the situation Improper wheelchair propulsion techniques lead to upper extremity injury.

Detailed description of the situation Wheelchair propulsion necessitates force production. The force production required for wheelchair propulsion acts not only on the wheelchair wheel itself, but on the bones in the upper extremities of the user. When the user is using improper techniques to propel the wheelchair the stress on the upper extremities will be higher. After years of wheelchair propulsion via improper techniques, wheelchair users will develop upper extremity injuries. By recording the forces involved in wheelchair propulsion it is possible to determine the most biomechanically efficient technique for wheelchair propulsion. By teaching users proper propulsion techniques the number of upper extremity injuries from wheelchair usage can be reduced.

Supersystem - System - Subsystems

System nameInstrumented wheelchair wheel

System structureThe system consists of the wheelchair wheel, strain guages to measure output voltage and a circuit to process the output voltage and convert it to a strain that can then be used to determine resultant force.

Supersystems and environmentWheelchair user.

Systems with similar problemsPeople who use crutches or any other device to assist in walking can develop upper extremity injuries due to improper use.

Input - Process - Output

Functioning of the systemThe system will function by using strain gauges to measure the strain that results from wheelchair propulsion. That strain can then be used to determine the resultant forces.

System inputsThe input that is responsible for the problem is improper wheelchair propulsion techniques.

System outputsBy determining the resultant forces involved in wheelchair propulsion we can determine the most biomechanically efficient method for wheelchair propulsion and then use that information to train users as to the proper technique.

Cause - Problem - Effect

Problem to be resolvedWheelchair users experience upper extremity injury

Mechanism causing the problemImproper propulsion technique

Undesirable consequences if the problem is not resolvedChronic overuse injury; loss of upper extremity function Other problems to be solvedTeach wheelchair users proper propulsion technique

Past - Present - Future

History of the problemThe problem began with the advent of the wheelchair. Advancements have been made to design wheelchairs that are more biomechanically efficient; however, users still experience upper extremity injury due to improper propulsion techniques. Pre-process timeIf users are properly trained on propulsion techniques they will reduce the likelihood of upper extremity injury.

Post-process timeThe only way to prevent the upper extremity injury that can result is via disuse.

Resources, constraints and limitations

Available resourcesWe are able to use the facilities of Max Mobility LLC.

Allowable changes to the systemOnly minimal changes are allowed.

Constraints and limitationsWe are constrained economically. We only have a limited amount of funds, which necessitates that our design be economically efficient.

Criteria for selecting solution conceptsWe would like to create an instrumented wheelchair wheel for approximately several thousand dollars. Similar technology is going for approximately $25k. We would like to use this low cost instrument to measure the force that results from wheelchair propulsion. We will accomplish this by using strain gauges.

Problem Formulation and Brainstorming

Instrumented Wheel for Wheelchair propulsion assesment

12/5/2007 11:22:10 PM.

Find a way to eliminate, reduce, or prevent Upper extremity injuries in order to avoid Loss of upper extremity function under the conditions of Improper propulsion techniques.

Design wheelchair that requires proper technique in order to function (i.e the wheels will only turn when they are "properly" pushed).

12/5/2007 11:20:18 PM.

Find an alternative way to obtain Determine the proper propulsion technique that offers the following: provides or enhances Teach wheelchair users proper techniques does not require Info about forces involved in wheelchair propulsion.

Use the information that is available from previous studies to determine the most biomechanically efficient method for wheelchair propulsion and use that information to train users.

12/5/2007 11:18:18 PM.

Find an alternative way to obtain Info about forces involved in wheelchair propulsion that offers the following: provides or enhances Determine the proper propulsion technique does not require Design instrumented wheel.

Record wheelchair wheel velocity and acceleration under propulsion using an accelerometer and use the data to determine resultant forces.

12/5/2007 11:15:35 PM.

Find an alternative way to obtain Design instrumented wheel that provides or enhances Info about forces involved in wheelchair propulsion.

Use strain gauges to record strain and use that information to determine the forces involved in wheelchair propulsion.

12/5/2007 11:01:02 PM.

Find a way to eliminate, reduce, or prevent Improper propulsion techniques in order to avoid Upper extremity injuries.

Train users as to proper propulsion techniques.

Improperpropulsiontechniques

Upper extremityinjuries

Loss of upperextremity function

Designinstrumented

wheel

Info about forcesinvolved inwheelchairpropulsion

Determine theproper propulsion

technique

Teach wheelchairusers propertechniques