MIME Senior Design Clinic, Spring 2007

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MIME Senior Design Clinic, Spring 2007
MIME Senior Design Clinic, Spring 2007
Midterm Report
Adaptation of van with a wheelchair lifting system
2007-01-08
Group Members:
William Fotoples – Group Leader
Chad Wainscott – Technical Liaison and Web Page Specialist
Ryan Keeler – Purchasing Agent
Faculty Advisors:
Dr. Hefzy
Dr. Pourazady
Client Advisor:
Ms. Jill Caruso
Project Sponsors:
Ability Center of Greater Toledo
National Science Foundation
Table of Contents
Table of Contents
2
List of Figures
3
List of Tables
4
Nomenclature
5
Executive Summary
6
Introduction
6
Project Objectives
8
Project Team
8
Design and Analysis
9
Design #1: Platform Lift
10
Design #2: Side-Bar Lift
11
Design #3: Under-Seat Lift
12
Design #4: Winch Assisted Lift
13
House of Quality Analysis and Design Selection
14
Preliminary Testing
15
Material Selection
16
Design Calculations
17
Current Design Status and Future Activities
19
Project Deliverables
19
Summary
20
Budget
20
Timeline
21
References
23
Appendices
24
2
List of Figures
Figure 1: Client’s Rigid, Non-Foldable Wheelchair
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Figure 2: Platform Lift Design Concept
10
Figure 3: Side-Bar Lift Design Concept
11
Figure 4: Under-Seat Lift Design Concept
13
Figure 5: Winch Assisted Lift Design Concept
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Figure 6: Wooden Replica of Van Interior
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Figure 7: Van in Entry Position
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Figure 8: Winch Attachment Bolt Layout
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Figure 9: FBD of Winch Support Beam Section
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Figure 10: Timeline and Project Work Schedule
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3
List of Tables
Table 1: House of Quality Analysis
15
Table 2: Approved Project Budget
20
4
Nomenclature
House of Quality - An analysis device that uses numerical values to define the
relationship between customer desires and product capabilities in terms of importance
and requirements.
MIME - Mechanical, Industrial, and Manufacturing Engineering
Moment - quantity that represents the magnitude of force applied to a rotational system
at a distance from the axis of rotation
Spina Bifida (SB) - A birth defect caused by an incomplete closure of the fetus’s spine
that results in improper development of the spinal cord.
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Executive Summary
The objective of this project is to design, analyze, build and test a device that will
assist an individual in lifting a non-foldable wheelchair into a minivan. The proposed
solution to this problem is to design a system that includes an electrical winch placed in
the van that can be attached to the wheelchair and used to pull the wheelchair along
guided tracks into position in the van. This lifting system is compact and can be easily
transplanted into another vehicle should that prove necessary.
Many steps have already been taken in preparation for final assembly of the
device. Several hours of testing using a wooden replica to reflect the van’s interior space
constraints has been used in order to determine the best possible placement of the
wheelchair in the van and the angle at which the chair should enter. Calculations have
been performed both by hand and computer in order to assess the amount of stress and
strain at various points in the design. These calculations include, but are not limited to,
bolt analysis, eccentric buckling and displacement analysis, and torque and horsepower
requirements. Materials have been selected based on the progressing final design and the
results of the aforementioned calculations. A winch has been purchased which meets the
required specifications and has been used to give more accurate calculations of the forces
present throughout the design. Final drawings of all components are being drafted for the
MIME machine shop in preparation for material arrival.
Introduction
Due to Spina Bifida (SB), a birth defect caused by an incomplete closure of the
fetus’s spine that results in improper development of the spinal cord [1], Ms. Jill Caruso
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is paralyzed from the waist down. She currently uses a foldable wheelchair for mobility
and transportation reasons, but is switching to a rigid, non-foldable wheelchair for added
durability and comfort. Jill is able to get into the drivers seat from her wheelchair when it
is placed along side of the van and is able to maneuver the chair into whatever position
necessary for loading it into the van. The purpose of the project is to develop a lifting
system that will allow Jill to load the wheelchair and place it in the back of the van
through the drivers’ side rear sliding door.
Several constraints were identified and
include a limited amount of room in the
minivan and the fact that Jill wishes to
have little to no damage done to the van
during the implementation of the design.
She also would like to be able to use the
device in future vehicle purchases, so it
must be easily transported.
Figure 1: Client's Rigid, Non-Foldable Wheelchair
Literature review indicated that most commonly available units consist of full
platform lifts, used to lift not only the chair but the person as well, something the client
specifically asked not to have. Other existing wheelchair lifting systems either involved
foldable wheelchairs or required that both passenger seats be removed from the minivan
in order for a generic mechanical lift be used to put the non-foldable wheelchair into the
vehicle. Both of these solutions proved inadequate since not only is the wheelchair rigid
(can not be folded), but also only one of the passenger seats can be removed since the
other is needed for a child safety seat. There are no readily available products or designs
that can be modified to meet these restrictions and the individual’s needs and preferences.
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Project Objectives
The objective of the project is to create a lifting system to assist an individual in
loading a rigid, non-foldable wheelchair quickly and safely through the sliding driver’s
side passenger door of a minivan. When the project is completed, the individual will be
able to load the wheelchair into the van with considerably less effort than is currently
required, and the lifting system will be able to be moved into a future vehicle purchase if
necessary. The design will allow the individual to use different wheelchairs without
having to worry about how the wheelchair will be loaded in and out of the van.
Project Team
Each member of the group has been assigned a role to assist in accomplishing the
team goals. The group leader for this project is William Fotoples. His responsibilities as
the group leader consist of setting up and coordinating group meetings. He is the primary
contact for the client and client advisor. He is also responsible for presenting the mini
preliminary design presentation and submitting the senior design weekly project report.
Chad Wainscott has been designated the role of technical liaison and web designer.
Chad, as the technical liaison, is responsible for submitting drawings to the machine shop
supervisor, John Jaegly. He will also maintain contact with Mr. Jaegly to assure the
feasibility of desired projects. As web designer, Chad’s roles and responsibilities consist
of maintaining the group’s web page by assuring that all pertinent and relative
information is uploaded to the page. Ryan Keeler is the purchasing agent. As the
purchasing agent Ryan will be in contact with Ms. Carrie Schonter. When it comes time
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to purchase material and equipment he will provide her with the necessary purchase
requisitions. Ryan is also responsible for assuring that the project stays within the
allotted budget.
Design and Analysis
The project requires a device in order to assist the client in putting a non-foldable
wheelchair into a minivan. Due to client preferences and restrictions, it cannot be a
traditional platform lift (one which lifts both the passenger and the wheelchair) and the
rear passenger bucket seat must remain in the van due to a child safety seat. The client
also wants limited damage to her current vehicle and the flexibility to be able to place the
device into a different van in the future. The client is able to get into the drivers seat
from the wheelchair placed alongside of the van, and is also able and willing to assist in
making the process go as smoothly and easily as possible by setting up the chair in a
required position. Due to the fact that once in the driver’s seat, the client is no longer
able to reach the door handle to close the rear sliding door, this door will need to be
modified to allow her to shut it safely and easily from the driver’s seat. It is also
important to note that the door opening is roughly 28 inches wide and the floor space
available is roughly 38 inches deep. The footprint of the wheelchair is approximately 26
X 34 inches. This constraint requires that the wheelchair is rotated approximately 90
degrees from its initial position (parallel to the vehicle) in order to fit through the door
opening.
Several meetings with the client identified the major issues that she was having
with loading the wheelchair into the van, the most important of these being the force
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required to pull the wheelchair from ground level into the van. The client is able to lift
the front wheels of the chair into the van, however, pulling the back wheels of the chair
into the vehicle is very strenuous on her back and arms due to not only the weight of the
chair but the awkward angle at which she must pull the chair in through the van door.
After meetings with the client and looking more closely at the interior layout of the van,
several ideas were created which led to four possible designs to be considered. All
designs involved varying degrees of preparation required by the client in terms of chair
placement and position in order for the device to work properly. These designs are a
Platform Lift Design, a Side-Bar Lift Design, an Under-Seat Lift Design, and a Winch
Assisted Lift Design.
Design #1: Platform Lift
Figure 2: Platform Lift Design Concept
Unlike many standard platform lifts available on the market, the lift presented in
Figure 2 is not intended to lift both the person and the wheelchair at the same time, rather
the person is able to get into the vehicle under their own power and the lift is used only to
load the empty wheelchair into the vehicle. In this design, the platform would have guide
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tracks to allow for consistent repeatable placement of the chair onto the platform. The
device could then be motorized or manually powered and would lift the chair off of the
ground and into the vehicle, while rotating 90 degrees so that the chair may fit through
the side passenger door. This design is the safest overall for the individual since it
requires a minimum amount of setup and effort if the system’s motor is electrical. The
system would also be fairly easy to use with a remote pad to control the lift function from
the driver’s seat. The main concern with this design is the amount of space that it would
require in the vehicle. The ramp platform would have to be large enough for the entire
wheelchair and robust enough to support its weight. Also, given the limited depth of the
space, there may not be sufficient space for the motor along with the ramp platform
without making modifications to the vehicle, something that the client does not wish to
have done. Also, the design is overall quite cumbersome and not easily transported to
another vehicle if necessary.
Design #2: Side-Bar Lift
The
side-bar
lift
design would require less
space than a traditional lift
design, yet still be able to
rotate the wheelchair the
A
necessary 90 degrees so it
could fit through the door.
B
The
design
features
a Figure 3: Side-Bar Lift Design Concept
scissor lift that would be mounted directly behind the driver’s seat. On top of the lift
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there would be a sliding bar that would be hinged near one end. When the lift is in the
stowed position (in the van) the sliding bar would be fully retracted as shown in Figure
3A. In order to remove the wheelchair from the van, the sliding bar would be extended
beyond the hinge (Figure 3B) so that the hinge can rotate as the scissor lift is lowered. It
would place the chair on the ground in the position parallel to the van. The process is
simply reversed when loading the chair.
The design is much less intrusive than a
traditional platform lift design and could still easily be operated by a remote control pad
in the driver’s seat. The lift would also be more easily transported into another vehicle
due to its more compact nature of design.
However, the idea requires that the lift be attached to either the arm of the
wheelchair or the spokes of the wheel. After further analysis, the group is concerned
about the ability of the wheelchair to withstand the large forces due to moments in
multiple directions. Also, as stated before, the design requires that the lift be mounted
directly behind the driver’s seat. The first concern is that there may not be enough room
to place the lift there securely. Second, placing the lift close to the seat will limit the
range of motion of the driver’s seat and this is something the client is not willing to
sacrifice. There is also a safety issue in regard to the scissor lift portion of the design,
which could cause pinching or jamming issues.
Design #3: Under-Seat lift
The under-seat lift design is intended to address the issue of limited space on the
sides of the chair by making the device narrow enough to have all of its working parts fit
between the wheels of the wheelchair. Rather than picking up the chair from beneath the
wheels, the under-seat lift design would pickup the wheelchair from beneath the seat.
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Again, this would allow for a much
narrower lift and it would not
interfere with the limited space on
the sides.
The design is less
intrusive than both the Platform Lift
and Side-Bar Lift designs, and also
Figure 4: Under-Seat Lift Design Concept
easier to remove from the current van and place in another vehicle. It is also the simplest
design mechanically since the chair is rotated into position by the individual rather than
the lift itself, allowing for a much simpler entry path into the van. The largest concern
with the design is the potential for inconsistent results. Because the lift is located
underneath the seat of the chair, placing the chair in the proper position on the lift would
prove extremely difficult since an inch out of position to either the left or the right would
cause the chair to hit the van when being loaded into the vehicle. It would also require
the client to reach very far away from the vehicle in order to load the chair into position,
which could prove to be a safety hazard. The more compact design can also lead to
stability issues when lifting the chair, which can cause the chair to wobble or even fall off
the lift during the loading process.
Design #4: Winch Assisted Lift
The Winch Assisted Lift design consists of a plywood platform with guide tracks
and a winch that will be used to pull the wheelchair into the van. The wheelchair will be
attached to the winch by a bar located underneath the seat of the chair. The chair will
than be pulled into the van by the winch, guided along a retractable ramp which will
reduce the stress on both the winch and the wheelchair. The chair is removed by
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reversing the direction of the winch, allowing enough slack rope to push the wheelchair
slightly out of the van so that the winch may be used to slowly lower the wheelchair to
the ground.
It was established using direct measurements that the wheelchair will need to
travel through the opening at a slight angle in order to have sufficient clearance to enter
the vehicle without interference. The
client stated and demonstrated that she
has no trouble loading the front wheels
of the chair into the van, but she is
unable to get the back wheels in. The
tracks
will
allow
for
consistent,
accurate results, and making the
Figure 5: Winch Assisted Lift Design Concept
system on a plywood base means that
it will be easy to remove and install in another vehicle.
It will also be relatively
lightweight and will require minimal attachment to the frame of the vehicle. While the
design is the least intrusive and easiest to put into a new vehicle, it also requires the most
work by the individual in terms of setup and unloading of the chair.
House of Quality Analysis and Design Selection
During meetings with the client, it was established that the most important aspects
of the design to the client were that the device was simple to use, that it was unobtrusive
and would not decrease the value of the van, and that the lifting system could be easily
transported into a new vehicle if one were purchased in the near future. Safety and
reliability were also important and were considered during the house of quality analysis.
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Each design was analyzed based on these weighted factors to determine which design
best met the overall needs of the client and the restrictions present. Based on this
analysis in the house of quality (Table 1), the Winch Assisted Lift design was deemed the
best design to use for the project. Despite the fact that this method will require a
significant portion of the work to be done by the client from the front seat of the vehicle,
the client has assured the team that this is the direction in which she would like to
proceed.
Table 1: House of Quality Analysis
Preliminary Testing
In order to determine the capabilities of the Winch Assisted Lift, we needed to
conduct multiple tests and setup within the interior of the van. Since accessing the van
whenever necessary proved impossible, the best alternative was to take all important
interior and exterior van measurements and create a replica of the area which we would
Figure 6: Wooden Replica of Van Interior
Figure 7: Chair in Entry Position
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be working with. Testing using the replica of van interior brought to light many smaller
issues and problems which could not easily be seen without the mockup testing. The
winch placement was moved from originally being flat on the floor of the van to being
elevated to create a 20 degree angle relative to the bar on the chair that the winch hook is
attached to. The increase of height not only made it easier for the chair to be loaded into
the van by the winch, but it also set the winch height even with the chair bar, thus causing
the chair to be pulled on a horizontal when in the van rather than being dragged down at
an angle. The testing also showed that a small ramp was needed in order to put the point
of contact below the midpoint of the wheel.
This will ensure that the motion is
transferred upwards rather than wedging the wheel under the van, and will also
significantly lessen some of the forces being exerted onto the chair. These two aspects
along with the angle of entry for the van were the main solutions created during testing
on the van interior mockup.
Material Selection
Due to the constricting nature and limitations imposed by the limited interior
space in the van, material selection was based mainly on what would plausibly fit within
the allowable space. From that point, calculations were conducted to make sure the
selected material was safe and would hold up to the forces and stresses present in the
system. As the system was tested and preliminary calculations done, the material was
changed several times and revised to fit the necessary requirements.
While the
composition of the material changed, the price for the materials were relatively similar,
so concerns of budget constraints were not present. Currently, the design incorporates
0.060” sheet metal for the ramp, supported by 3/16” thick, 1.5” length angle iron to be
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used both as the track for the chair and support for the ramp. The tracks inside of the van
are the same as those on the ramp, and the winch platform is now a 15” long piece of
1/8x3x1” rectangular steel tubing welded to a 1/8” steel platform. The base of the device
is still planned to be carpeted plywood for aesthetic purposes.
Design Calculations
In order to verify that the components of the assembly will not experience failure,
stress analysis of each component was performed. All of the stresses determined from
the analysis are significantly lower than the yield stresses of the materials. By comparing
the actual stresses to the yield stresses a factor of safety can be determined.
The calculations that were determined to be the most important were bolt analysis
of the backing plate of the winch, weld analysis, deflection of the support arm, and also
the power necessary from
the
winch
determined.
was
also
The bolt
analysis of the backing
plate gave us a 37.067lbf
in two of the bolts and a
90.952lbf in the third
bolt. These forces were
used to calculate the shear
Figure 8: Winch Attachment Bolt Layout
stress in each bolt to
determine if it would fail. From these calculations the lowest factor of safety for the
provided bolts in shear stress was 29.81. Plate bearing failure was also taken into
17
consideration. The backing plate will be bolted to a 1/8 inch thick steel tube so this
thickness was used in calculating the stresses that will be experienced by the plate. From
the stress analysis calculations the lowest factor of safety for plate bearing failure is
8.993. Please see Appendix (A) for detailed calculations. Further bolt analysis is still
being conducted and should be completed by March 26th.
Deflection of the support beam due to both bending and eccentric vertical loading
was also analyzed.
The calculations determined that the beam will experience a
deflection of 0.021inches.
Please see Appendix (C) for
detailed calculations.
The support beam will be welded to a 0.25” plate at the
base where a 0.25” weld is to be used. By calculating the
moment that will be experienced at the weld location the total
shear stress can be determined. Through the weld analysis
procedure the factor of safety was determined to be 11.85.
Detailed calculations for the weld analysis can be seen in
Appendix (B).
To ensure that the winch was capable of supplying the
necessary power to lift the chair into the van an analysis was
performed. The required horse power was compared to the
rated horse power of the winch. The purchased winch has a
horse power that is 39 times higher than the required power.
Therefore this winch has been determined to be of a sufficient
size. For detailed calculations on winch analysis please see Figure 9: FBD of Winch
Support Beam Section
18
Appendix (D). Calculations and FEA analysis of the ramp portion of the design are still
pending and should be completed by March 26th.
Current Design Status and Future Activities
The overall design of the lifting system has been finalized with the only possible
changes being material for support purposes at the base of the winch platform and at the
ramp; although current calculations show that the chosen material is acceptable and will
meet the necessary safety criteria. Final material selection should occur on or before
March 26th so that all material may be ordered and the parts machined so that final
assembly can begin.
Near future activities involve material procurement after all calculations have
been finalized, after which all CAD drawings will be drafted and turned in to the
University of Toledo machine shop. Final assembly and testing should occur during the
week of April 7th in order to leave enough time to work out any issues that may be
present.
Project Deliverables
The deliverables upon completion of the project will be a lifting system that will
assist an individual in loading a rigid, non-foldable wheelchair into the driver’s side
passenger door of a minivan. The device will include an electric winch to lift the
wheelchair into the van and a small ramp and track system to guide the chair into the
required position. Engineering calculations and analysis will be performed in order to
ensure that the design will withstand the forces and stress inflicted upon it and also that
the design will be safe for the client to use.
19
Summary
The necessary research and preliminary design stages of the project have been
completed. Based on this, a design was chosen from which the current design is based
on. Analysis of the design using a wooden replica of the interior layout of the van
allowed for further design specification in order to address problems that were
encountered during the testing. The updated design was than given specific dimensions
in order to conduct analysis calculations to ensure that the design would meet both the
client’s needs, engineering specifications and safety requirements, and also so appropriate
materials may be ordered.
A winch used to lift the wheelchair into the van was
purchased in order to ensure more accurate calculations and to finalize certain aspects of
the design of the system. After the design analysis and drawings have been completed,
the material will be ordered so that the machine shop can construct the parts so that final
testing of the lifting system can be performed to ensure that it is working properly and
meets the client’s specifications and needs.
Budget
Table 2: Approved Project Budget
20
Our original preliminary budget had been revised to reflect recent changes in
design and material selection. The largest portion of the budget was reserved for the
electric winch at $200.00, however, an acceptable alternative was found for a much lower
price. The winch, along with material used to build the wooden replica of the van interior
for preliminary testing, have been the only purchases thus far during the project.
Miscellaneous materials such as screw, bolts, hinges, and plywood will be
purchased from Home Depot, while the metal material will be purchased from All Metals
Inc., which allows for quick availability and low price. All machining and welding costs
are donated through the University of Toledo machine shop. The projected cost of the
project is estimated to be considerably lower than the approved budget of $538.00 as
shown in Table 2.
Timeline
Figure 10: Timeline and Project Work Schedule
21
The timeline of the project is shown in Figure 10. Calculations and analysis of
the design should be completed by March 26th, and the materials order shortly thereafter.
After materials are procured, drawings will be given to the shop so that the parts may be
machined and the lifting system assembled starting in the beginning of April so that final
testing may occur.
22
References
[1] Spina Bifida Association website. Copyright 2006. “About Spina Bifida Overview”
January 30, 2006. http://www.sbaa.org
23
Appendix A
24
25
Appendix B
26
Appendix C
27
28
Appendix D
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