DESIGN PROPOSAL
STEPPING STOOL
Meiluo Li
Audrey Markovich
Andy Meyer
25 February 2009
Team F
ME 340 Project #2 2/25/09
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Executive Summary
The focus of this project is to implement the design process in attempt to reach a unanimous
decision regarding a solution to the given problem. This is exactly what has been completed for
the problem at hand. The process consisted of creating multiple concepts and analyzing each one
based on their simplicity, cost, ease to use and ability to be stored easily. The problem statement
called for the design and development of a device that could assist individuals back to their
wheelchairs after a non-fatal fall had occurred. This task was attempted and successfully, a
single best solution remained at the completion of the design process. The solution is similar to a
common stepping stool meaning that the design is not very original. In essence, it is easier,
cheaper and less time consuming to implement an existing design than to create a new one. This
is why the solution is based off a previously developed stepping stool. The stool will be
collapsible and storable within the wheelchair itself, thus allowing for quick access when needed.
The solution was designed around this important detail. By keeping the design as simple as
possible, overall cost could be minimized. Additionally, the desire for this device to be stored
within a standard wheelchair could be honored; this feature ensures that the user has the
necessary equipment to get back into the wheelchair with relative ease. Although other solutions
were considered, the stepping stool design remains as the single best solution to the given
problem. Details and the breakdown of the completed process are described within the following
paragraphs.
Table of Contents
Executive Summary
1. Introduction
1.1 Background
1.2 Task Description
2. Problem Definition
3. Customer Needs Assessment
3.1 Gathering Customer Input
3.2 Weighting of Customer Needs
4. Engineering Specifications
4.1 Establishing Target Specifications
4.2 Relating Specifications to Customer Needs
5. Concept Generation
5.1 External Search
5.2 Design Concepts
6. Concept Selection
7. Final Design
8. Conclusions and Recommendations
9. References
Appendices
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1. Introduction
1.1 Background
For years, problems existed for those who are permanently wheel chair bound. Without working
legs, it is extremely challenging to engage in activities of daily life. In these situations,
individuals rely heavily upon wheelchairs and may experience some fears of falling. Paraplegic
individuals have made this a concern, especially since it limits their independence. This problem
deserves some attention; our design team’s task is to explore possible solutions. A final, logical,
solution to the problem is desired and if achieved, the product will be marketed towards
paraplegic individuals.
1.2 Task Description
The overall task of this project is to follow the steps of the design process in order to determine a
single best solution to the problem at hand. The objective is to brainstorm and work as a team
while collecting and combining thoughts and ideas in a casual setting. This allows for open
discussion of details that will contribute to the development of the finalized product. The design
team will then undergo a process of elimination based on the given criteria and constraints. A
single solution should result from this process and at this point, the concept prototyping would
begin. This specific project does not require a physical prototype to be created; however, the
design team needs to prepare and present their solution as if the complete design process has
been carried out.
2. Problem Definition
According to the patient safety authority, “Wheelchairs falling and tipping cause more deaths in
persons over 65 years of age. Falls are more likely to occur when using a wheelchair if footrests,
wheel locks or other parts do not work well or are loose.” This document was used as
justification of the problem statement. It is important to attempt to reduce fatalities due to falling
from a wheelchair and this is what needs to be addressed.
Solving the overall problem was one task; however, it was decided to attempt to meet an
additional need that has been recognized. Based on the selection criteria chart, it was determined
that the ability to store the device within the wheel chair itself was crucial. In the event of an
incident, it is necessary to have the step device within an arm’s reach. Therefore, our team
needed to design a wheel chair assistance device that could be stored underneath a standard
model wheel chair. While keeping all this in mind, the task of designing a logical solution to the
problem was then given attention. The device needed to be easy to use, durable, and able to hold
an average weight of 250 lbs. This all needed to be done without the use of motors or any
electronics, costing less than $100, and weighing less than 30 lbs. These constraints restricted the
concept development process; however, a final result was eventually achieved with hope that it
would benefit the paraplegic population.
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3. Customer Needs Assessment
3.1 Gathering Customer Input
Customer input was gathered through extensive internet searches as well personal input from a
wheelchair bound individual. The father of Professor Laura Pauley was the main source of
information, answering questions such as:
1) How high can you lift yourself off of the ground using your own arm strength?
2) How important would it be to have the device located within the wheelchair?
This is how we developed many of the details found in our final design. From these questions, it
was determined that a paraplegic person could lift himself/herself roughly 4 inches off the
ground. The second question helped to expose the overall importance of the device being easily
accessible. The best way to achieve this is to store it in the wheelchair itself.
3.2 Weighting of Customer Needs
In order to determine the specific needs that require the most attention, it is crucial to weight the
individual customer needs. Due to many design constraints, it is unlikely that all customer needs
will be met. Therefore, using this process shown in the table below, various customer needs
receive a ranking of their importance.
Weighted customer needs
Need
Weighting
Ease of use
Ease of manufacturing
Portability
Storing within chair
Durability
Figure 1
30%
5%
20%
20%
25%
4. Engineering Specifications
4.1 Establishing Target Specifications and Metrics
Our team chose to use the weighted matrix method. The customer needs selection criteria is as
follows: easy to use, looks good, stable, reliable, portable with wheels, self propelled, can store it
in the wheelchair, inexpensive, lightweight, and durable. The metric needs selection criteria
includes: total mass, unit manufacturing cost, no electronics, stress, material, ability to move
freely, and ability to be compact. This shows how the customer needs relate to the engineering
requirements.
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7
Ability to be compact
6
Ability to Move Freely
5
4
Stress
Material
3
2
Unit Manufacturing Cost
No Electronics
1
Total Mass
Customer Needs
easy to use
looks good
stable
reliable
portable with wheels
self propelled
store in wheelchair
inexpensive
lightweight
durable
No.
No.
1
2
3
4
5
6
7
8
9
10
Metric
4.2 Relationship of Engineering Specifications to Customer Needs
X
X
X
X
X
X
X
X
X
X
X
Figure 2
5. Concept Generation
5.1 External Search
In the conduction of several patent searches and research endeavors, it was discovered that
personal lifting devices similar to our design contained motors and electronics. Most of these are
specifically manufactured for use in nursing homes or hospitals. These lifting devices are
typically fixed to the ceiling and therefore not portable.
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Benchmarking of Patent Products
Selection
Ease of Use
Ease of
Manufacturing
Portable
Store in Chair
Durability
Design 3:
Patient
Design 1:
Design 2:
Lifting and
Weight
Personal Lift
Patient Life Transferring
(%)
Device
Mechanism System
30
2
3
2
5
20
20
25
Total (out of 5)
1
0
0
4
2
0
0
4
2
0
0
4
1.65
2
1.7
Figure 3
5.2 Design Concepts
Compressed Air Design
The compressed air design is
a platform with wheels that has a
seat for the individual to sit on.
There are two metal bars that would
balance the seat. In between these
bars are air bags that would fill with
compressed air. The seat would
slowly lift off the ground to the
height of the chair.
Figure 4
Car Jack Design
The car jack design is
basically a car jack but modified
to lift an individual from the
floor into his or her wheelchair.
There is a seat that has an
attached hand crank. This will
allow the individual to rotate the
crank until the desired height is
reach.
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Figure 5
Stair Step Design
The stair
step design is a
very simple design.
It consists of a set
of stairs that the
individual will be
able to lift
themselves up onto.
Each stair will be
used as a different
platform allowing an individual to lift themselves up one level at a time.
Figure 6
Concept Classification Tree
Figure 7
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6. Concept Selection
Decision Matrix:
Concepts
Weight
Air Pressure
Jack
Stair-Step
Ease of Use
30%
2
4
5
Ease of
Manufacture
5%
1
2
4
Portable
20%
3
3
4
Storability in
Wheel Chair
20%
4
4
5
Durability
25%
4
5
5
Total Points
100%
3.05
3.95
4.75
3
2
1
Final Standings
Figure 8
The characteristic of this device is organized into above seven factors. Ease of Use weighs the
most since the design focus is on the adaptation of using the device. Durability is the second
most weighted factor that assures the device can withstand long-term use. Ease of Manufacture
is the least important due to the assumption that manufacturing will be easy if the device is a
simple structured, being able to be stored within the wheel chair. The result is very statistically
significant since the winner has a point value of 4.75 out of a possible 5.
7. Final Design
Dimensioned Drawings
1) Frame (See Appendix)
2) Board 1 (See Appendix)
3) Board 2 (See Appendix)
Material Description
The boards are made of Acrylic Plastic and the frame is made of A513 Steel. Material properties
and stock prices are listed below. The materials are chosen based on cheap and strong
characteristics.
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Plastic
Acrylic
Shear
Tensile
Compressive
Tensile
Strength, Elongation
Strength
Strength, ksi
ksi
at break
(Yield), ksi
10
17
Material
ASTM A513 (low-carbon) Steel
Sut, ksi
87
Rockwell
Stock Size, in
Price
Color
M93
12 x 12 x 0.5
$14.28
Clear
Sy, ksi Elongation Rockwell Brinell
72
10%
B89
Stock Size
1" OD x 0.12" WALL x 0.76" ID
Price
$5.25
Description
1 ft long
Figure 9
Manufacturing Cost
According to the dimension, overall material price is approximately $50; the manufacturing cost
including welding, milling and surface finishing will not exceed $20. Since the overall cost is
about $70 and if the retail price is set to $90, the design confidently meets the $100 limit.
The device is designed for easy use. The simple, stair-step structure will not confuse the users; it
is easy to adapt into the device. The simple structure is also designed for collapsibility and
portability, so that the device can be easily stored in the wheelchair. Since the device consists of
three plastic boards and metal tubes, it is very light weight. The device requires minimal
maintenance; therefore, the user will not have to constantly spend money on necessary upkeep.
Its’ long term durability provides the user with a reliable, long lasting tool for assistance when
needed. The previously described advantages of the device combined with a relatively low retail
price will ensure success in the market. Overall, the design is very feasible, both economically
and technically.
Board 2
Bolts
Frame
Board 1
Figure 10
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8. Conclusions and Recommendations
The stair step design is a simple device designed to aid paraplegic individuals who have fallen to
the floor. These individuals will no longer need any assistance since this device is self-propelled.
By using the stair step design, the individual will use each step to guide him or herself back into
their wheelchair seat one step at a time. There are grip bars on each side of the device for the
individual to lift him/herself back up to the seat level. As an added feature, the device will slide
out from under the wheelchair when needed. This is extremely beneficial since the individual
will not be able to move very far from his or her position on the floor. After use, the stair step
can be folded and returned to its' original position quickly and easily. There is a possibility for a
design patent to prevent other companies from repeating our design. Our team will deliver on
this promise. We have performed much research and have finalized our ideas while developing
this final design. We also have many references cited in our research. The stair step design is
guaranteed to work and guaranteed to meet the needs of our target demographic. There is no
room for error. The paraplegic individual will appreciate this design because of its' easy to use
features and overall usefulness. There is high economic potential for the stair step design and it
is expected to do well in the market. This design will be easy to manufacture and will definitely
satisfy the customers' needs. This means that the design process has been successful, resulting in
a plausible and logical solution to the initial problem. Hopefully with this new product on the
market, the initial problem will become non-existent. If this would occur, our design team could
comfortably see that we have accomplished our overall goal.
9. References:
Capaldi, Guido; Sinreich, Mark G. “Patient lift mechanism” US Patent 5,809,591. September 22,
1998
Chepurny, Mark; Molnar, Gordon J.; Wilson, Michael F. “Personal lift device” US Patent
7,240,621. July 10, 2007
Doering, Mike. "How to Reduce Your Risk of Falling." Patient Safety Authority. 17 Mar. 2008.
Patient Safety Authority. 24 Feb. 2009
<http://www.psa.state.pa.us/psa/lib/psa/tips_for_consumers/falls_consumer_article_1108.pdf/>.
Onlinemetals.com. 1998. 24 Feb. 2009 <http://www.onlinemetals.com/>.
Roy, Duane L. “Patient Lifting and Transfer System.” US Patent 5,694,654. December 9, 1997.
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Appendices:
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