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Project Number: P15005
STAND-UP MOTORIZED PLATFORM
Gabe Luce
Mechanical Engineering
Olivia Robertson
Electrical Engineering
Alexandra Silberglied
Mechanical Engineering
George Bishop
Mechanical Engineering
Michael Fleszar
Industrial Engineering
Lawrence Fredsell
Electrical Engineering
Abstract
Spending day after day confined to a sitting position can be very detrimental to the health and well-being of
persons suffering from disabilities affecting their lower extremities. The scope of this project was to develop and
build a fully-functional standing wheelchair. With this chair our customer, a young woman afflicted with movement
and structural impairments, will be able to stand and move about safely. The device has dual functionality: it operates
both as an ordinary power wheelchair, and can be lifted into and driven in a standing position. For movement, the
customer is able to operate the chair using a regular joystick control. A switch located in the back of the wheelchair
operates the transition between sitting and standing mode. While in standing mode, the customer is supported at her
torso and legs by a chest bar and shin pad respectively.
Introduction
The vast majority of individuals suffering from disabilities which affect their balance and muscle coordination
have no choice but to spend the majority of their lives seated in wheelchairs. The negative effects of spending a life
confined to a chair are numerous. A few of the afflictions commonly suffered by individuals in this position are muscle
and coordination deterioration, bed sores, digestive problems, and emotional problems, such as depression. The
overall quality of life of these individuals could be vastly improved by using modern technology to develop a way to
assist in standing.
Being the first of its kind, the scope of this project is to design a safe, reliable, and inexpensive device which
would allow an individual with physical disabilities to stand up while moving about. Although this wheelchair was
designed for the use of one individual customer, it was designed to be as adjustable as possible for any future growth.
In order to do this the team was provided with a two thousand dollar budget from RIT and gifted a fourteen year old
retired wheelchair from the customer. Some parts from the old chair were able to be re-purposed and incorporated
into the new designs of the wheelchair, the most important of which included the base of the old chair, motor, and
control system.
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Figure 1: Donated Wheelchair
Design Process
The first step in the design process was to meet with the customer and make a clear and concise list of all of the
requirements for our project. These requirements were known as the customer requirements. Once this list was
developed, each requirement was then evaluated based upon importance. The most important requirements would we
given a value of “9” and a “3” or “1” would be given to the moderately and least importance's respectively. These
customer requirements were then used to develop the engineering requirements. Our final list is shown in the Figure
below. Customer requirements were translated into measurable engineering requirements which could be easily tested
and evaluated .Each requirement will be address as follows:
Adjustable Joystick placement/ Shorter Armrest: The same hardware that was previously used for the Joystick
is still being used, which will allow the joystick to swivel. However, the placement of the joystick will be much
closer to Megan (< 17 inches) and there will be a shorter armrest that will allow her to reach it more comfortably.
The team will be working with Matt McGarvey, Megan’s everyday wheelchair specialist to adjust the sensitivity of
the joystick as well as the wheelchair speed.
Must fit In Van/ attach with S clips: The design currently uses the old base of the electric wheelchair in
combination with two mechanical actuators that are connected to the base and back of the chair. The overall
footprint of the chair has not changed and will still be able to fit within the Downey’s van doorway (52’’x 29.5’’).
Since the base of the chair has not changed, the S-clip attachments have also stayed and will continue to be the main
securing mechanism to the van. The addition of the actuator support system on the rear of the chair can also be used
as a solid structure to secure the chair into the van.
Stabilization, able to reach in all directions, trunk support, able to reach worktable.
To keep the user safe, new features based off of current standing wheelchairs were implemented. These include a
custom made chest bar and shin block. They were made using waterproof vinyl and high density craft foam that
will take the wear and tear of everyday life. The shin block is attached to the footplate, which is for her feet to rest
on. The footplate is attached to the chair via a hitch port located on the bottom of the given wheelchair base. The
shin pad’s height and angle are adjustable to maximize support for the user. In order to increase stability of the
chair and to alleviate tipping, casters were added beneath the foot platform. Calculations show the center of gravity
of the chair in the standing position will not tip on hills with up to a 24 degree slope, however because Invacare
specifies that their power chairs should not exceed 12 degrees, the user will be advised to use the chair under 12
degrees. While the chair preforms well on inclines the additional casters provide a solid point of contact beneath the
user’s feet.
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Long lasting / indoor and outdoor use
Due to the team’s utilization of the previous base and power system, the chair will have similar battery life and
durability that it had previously. Elements of the original base were weather resistant and the additions were coated
to prevent degradation from weather. .
Adjustable with Growth
Each end of the chest bar is attached to the arm bars and is vertically adjustable. The chest bar can also be moved
towards and away from the users body by adjusting the telescoping tubing of the along a track located on the arm
bars. The placement of the bar allows upper body support, and the ability to better access a work or dinner table at a
comfortable position closer than a normal power chair.
Sit and Stand Functionality
The sitting to standing function is performed using two electric linear actuator that are powered using the same
batteries that power the chair’s movement. In line with the customer requirements, the person sitting in the chair
cannot access the linear actuator controls that raise and lower the chair. . The assisting person will be able to decide
how high or low to position the user. Limit switches cause the actuators to turn off once the chair reaches a certain
predetermined sitting or standing position to avoid any injuries.
Figure 2: Sit and Stand Functionality
Neutral Mode
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The chair has a neutral mode that cuts power from wheel motors and allows for manual pushing and steering of the
chair. This function is achieved by switching two control levels at the rear of the chair, directly behind the wheel,
from the drive to the neutral position.
Category
Requirement
Value
Units
Requirement
Achieved?
General
Speed
0-5
Miles per hour
Yes
Total Weight chair can handle
<200
Pounds
Yes
Size
52 x 29
Inches
Yes
Weather proofed
Y/N
Battery Life
>24
Hours
Yes
Controller distance from body
<30
Inches
Yes
Neutral Mode
Y/N
Adjustable arm rest
20-30
Inches
Yes
Supports user’s weight by trunk
>200
pounds
Yes
Θ1 (while Standing)
120130
degrees
Yes
Θ2 (while Standing)
90-95
Degrees
Yes
Θ1 (while Sitting)
0-5
Degrees
Yes
Θ2 (while Sitting)
<30
Degrees
Yes
Balance on incline while standing
<30
Degrees
Yes
Electrical
Mechanical
Yes
Yes
Table 1- Engineering Requirements
Benchmarking
The next step in our design process was to research and benchmark other standing wheelchair concepts. We
quickly discovered that numerous products with similar applications to our own already existed, however many of
these devices were priced far out of the reach of the average consumer.
Figure 3: Invacare Dragon Vertic
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With only a two thousand dollar budget, cost was a limiting constraint. To save money, many of our critical
design considerations revolved around utilizing our donated wheelchair to the best of its capacity.
After benchmarking other designs we, broke our project down into more manageable subsystems to be designed
independently. These subsystems included the Frame, Lifting Mechanism, Torso Supports, Leg Supports, and the
Electrical Control System.
Frame/ Drive train
The first major design decisions of our standing wheelchair was the design of the frame and drivetrain. After
some light dis-assembly of the donated wheelchair we assessed it for structural and electrical capability. We
discovered that with the exception of the batteries, most of the components were in good shape and reusable for our
project. This ended up saving us an enormous amount of money and time on the project as we were able to skip the
design of components such as the frame, motors and drive train control system.
Figure 4: Salvaged Frame & Drive train
A new pair of 12V lead acid batteries was purchased to replace the original.
Lifting Mechanism
Arguably the most complex and technically challenging subsystem of the standing wheelchair to design was the
lifting mechanism. The purpose of the lifting mechanism was to move the occupant from a sitting to a supported
standing position, comfortably and at a safe speed. Numerous designs for this mechanism were considered including
four-bar linkages and scissor mechanisms. Also, several type of systems were considered including hydraulics,
pneumatics, and electrical systems. In the end an electrical linear actuator was selected to propel the device based on
cost, safety, and complexity. Electric linear actuators are currently widely used within the industry which helped aid
in the team’s decision.
Figure 5: An Example of a Linear Actuator
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At the beginning of the project the team was provided with their customer’s previous electric wheelchair and
because of the good condition of the components, the drive-train was able to be reused. The team was required to
design a lifting mechanism that would be compatible with the existing frame geometry. This constraint combined
with limited funds were the biggest factors contributing to the final lifting design. The lifting mechanism used to raise
the seat of the chair involved welding a 3.5 inch lever arm to the front center of the seat. This would convert linear
motion to an angular change in the seat’s position. A linear actuator was connected from this lever arm to a support
structure built on the frame of the rear of chair. The originally geometry of the chair was too small, so the team was
required to design an additional frame on the rear of the chair. An actuator mount designed by the team was then
welded to this support system to connect the motor end of the larger, bottom actuator. In order to design this system,
a free body diagram of the seat of the chair was first constructed as shown below in Figure 6. By summing the
moments about the point of rotation at the front of the seat, the force required to lift the seat was calculated. Knowing
this force, an actuator which was capable of providing the desired force while also meeting the geometric constrains
of the frame was chosen.
While the seat frame is raised, the back of the chair needs to remain perpendicular to the ground. In order to
achieve this the team purchased another, smaller actuator. The second “top” actuator connected to a lever arm
designed by the team that connects to the back center of the seat frame of the chair. This lever arm unlike the one for
the bottom actuator is in a Z shape, which not only extends out horizontally from the seat but also vertically. This
was done so the actuator would be at an angle giving it mechanical advantage while keeping the back of the chair
upright. The top of the actuator was connected to a pin that was inserted between two cross braces welded between
the left and right seat back bars. The pin that the actuator is connected to was chosen for its shear strength and to
minimize deflection of the braces. As the bottom actuator retracted and the seat of the chair rose, the top actuator
would also be retracting, forcing the back of the chair to remain perpendicular to the ground. There was also a proof
of concept model made to demonstrate how the two actuators would move the seat and back.
Figure 6: Force Calculations
Torso Supports
In order to safely lift a user to a standing position, their body needs to be supported throughout the lifting process
and while they’re in a standing position. Numerous concepts were considered including harnesses that went through
the legs (like a baby bouncer), around the legs (like a rock climbing harness) and separate chest and arm support bars.
One of the most important requirements stated that we must fully support the chair’s passenger but also allow for full
range of motion with her arms. Our final decision for a torso support was separate chest and arm support bars due to
ease of use, cost, and an industry expert recommendation. The existing arm rests were modified and extensions were
added to position the chest bar. The extensions are built out of perforated square steel tubing which is not only cost
effective but allows for easy adjustments to be made in the forward-backward direction. The chest bar is also
vertically adjustable for the user’s comfort
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Leg Supports
In addition to her torso, leg supports are also a critical component in our system. Our customer not only suffers
from cerebral palsy and scoliosis but also has a malformed hip socket which causes pain in her hips and legs. Putting
her into a partial standing position helps to relieve the pressure on her hip. To maintain the standing position we
designed a foot plate to stand on and a shin block that would keep her safe while supporting her legs and keeping
stress off her knees.
Electrical System
Two parallel systems are used to control the function of the chair. One system controls the existing Invacare
electric wheel chair base while the other controls the lifting mechanism to position the chair from sitting to standing.
Both systems are powered using two 12 volt, 55 Amp-Hour Duracell AGM electric batteries in series. The drive
system uses the entire 24V potentials produced by the batteries while the lift circuit only used 12V .The entire system
schematic is shown below in figure 6.
Figure 7. Electrical System Schematic
Due to proprietary constraints the electric wheelchair base was left as is. There were no modifications made
to the system since it was still fully functional. The electric wheelchair has two modes; drive and push. To change the
mode of the chair, two switches, located near the back casters on the base of the chair, must be flipped. Once the chair
is in drive mode, the user has the ability to be in fast mode or slow mode. The user is then able to change which mode
they are in by flipping a switch located on the Invacare joystick. The user can then control their movement and speed
using the same joystick.
The other electrical subsystem in the chair is the lift circuit that controls the movement of the seat position.
This circuit is in parallel with the electric wheelchair base circuit. This circuit controls the two linear actuators
mentioned previously that extend and retract when powered to change the angle of the seat. In order to control the
actuators, a momentary switch is implemented that will change the actuator’s direction until released or a limit switch
is hit. To ensure correct function of this circuit, power diodes were placed within the circuit. These diodes direct the
current to the desired actuators based on the direction the actuators are being engaged.
Limit switches are also implemented in the circuit that will stop the actuators once they reach the desired
position. A total of three limit switches were installed. These limit switches not only determine the final position of
the chair, but also protect the actuators from potentially damaging the chair. One limit switch is to determine when
the actuator controlling the seat bottom reached standing. Another to determine when the upper actuator is positioned
for standing and finally one for when the top actuator had arrived at the sitting position.
Project P15005
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CNC Operator (MRF machine)
ProEngineer, SolidWorks, AutoCAD
MatLab
Patran/Nastran (FEA)
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Root cause analysis
Microsoft programs
Excellent communication
Team leadership skills
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Testing
and
Evaluation
In order to ensure that the chair was able to perform at the desired standards, a variety of tests were designed. A
series of tip tests, load tests and longevity trials were undergone. To ensure that the chair would be able to safely lift
and support the customer with a reasonable factor of safely a load test was performed. For this test, the chair was
raised and lowered while subjected to a variety of weights. There were no appreciable differences in the time to raise
or lower the user and no components showed stress under the additional weights.
To ensure the chair would not tip or become unstable while in a standing position while ascending or descending
on any sort of terrain, a tip test was performed. In order to perform the test, a passenger was raised into standing mode
and the chair was driven up and down a variety of grades, several times, and at several speeds. It was found that the
steepest grade that the chair can safely handle is twelve degrees.
Conclusions
Overall, this project achieved its goal of creating a safe and versatile device to allow our customer, a woman
with several severe disabilities to move about while in a standing position. There is certainly room for improvement
with the team’s design. Potential future iterations of this project could make improvements to the design and increase
functionality such as adding a micro-controller. By adding this component, a smoother transition between lifting and
lowering could be achieved.
The scope of this project was somewhat limited by the very specific needs and requirements of our customer.
Although the prototype developed for this project had very specific specifications pertaining to our customer, a more
generic version has potential for much greater commercial applications. An affordable, standing wheelchair could
potentially provide a much needed service to thousands of people with disabilities.
Project P15005