A wheelchair user is able to walk only for short periods of time. Because of her condition, this individual can not lift her wheelchair into her vehicle. The purpose of this project was to design and fabricate a lifting system that will allow the user to raise and lower her wheelchair in and out of the rear hatch area of her PT Cruiser without assistance from another person and without restricting use of the backseats. The lifting system that was developed was securely mounted in the rear of the PT Cruiser and includes a main fixed post and a rotating cantilever arm attached to the post. A pulley was attached at the end of the arm for lifting and lowering the chair. Bearings were used in the main post allowing the arm to rotate freely which makes it easy for the user to maneuver the chair in and out of the PT Cruiser. The system includes a 12 Volt DC gear-motor unit that is used to lift the wheelchair and is powered by the car battery. The system is operated using a controller that is mounted on the motor. Figure 1 depicts the wheelchair being lifted into the car.
Congenital Myasthenia Gravis, Wheelchair, PT Cruiser, Lifting System
An individual (the “Client”) with Congenital Myasthenia Gravis (1), an uncommon hereditary disorder of the neuromuscular junction, has limited walking capabilities, thus requiring the use of a manual wheelchair in order to move freely on a daily basis. The disorder is characterized by periods of increased muscle fatigue. The Client wishes to be more independent in general travel; however this is hindered due to lack of strength for loading and unloading the wheelchair. Without being able to lift the wheelchair into the designated vehicle, the Client requires outside help which might not always be available and safe. Currently, there are several types of products in the market that are used to assist in the lifting of a wheelchair into different areas of vehicles. However, not all fit the exact requirements of the Client’s vehicle. More important, the Client desires to use only the rear cargo area of the car to house the lifting mechanism and the wheelchair. Current lifting mechanisms for internal vehicle storage restrict the use of the backseats (2). The Client wants to avoid this in order to reserve the seating area for full vehicle occupancy. The purpose of this project was thus to develop a system that is able to lift and lower a wheelchair into and out of the designated vehicle, a Chrysler PT Cruiser. Such a lifting system would need to operate safely, quickly, and be able to store the wheelchair securely in the rear of the vehicle without restricting the use of the back seats and with limited manual labor on the part of the user.
The basic design requirements for the lift were first determined. The lift must first and for most provide a total vertical lifting distance of 26” in order to clear the rear bumper of the PT Cruiser. It was then decided that the lifting power would be provided by using a power in/power out electric motor controlled by a free hanging two-button controller. The hand held control for the motor would allow the Client to be positioned away from the system during the lifting and the lowering of the wheelchair as well as rest on the rear bumper during the process. Another design concern was the path the wheelchair would take into and out of the rear of the vehicle. It was determined that the best path would be provided by a single degree of freedom cantilever beam setup which would also provide ease of use during manual rotation into and out of the vehicle. The actual lift dimensions were determined by the need to locate the main fixed post as close to the rear bumper as possible, and these were finalized through the use of computer generated sketches and actual cardboard prototypes.
Safety of the lift was of utmost concern. A dual pin setup has been installed on the main support post of the lift providing the lift to be locked in the loading and storing positions. This setup provides that the lift will not rotate out unnecessarily during operation and storage. Other safety design features include a power in/power out motor and a rigid steel frame construction.
Two radial ball bearings and one thrust bearing were included in the main post. The radial ball bearings are being used to support the eccentric load due to the wheelchair, and the thrust bearing is intended to support the entire weight of the lift. The radial ball bearings are capable of handling a dynamic load of 2,405 lbs and are rated for a maximum speed of 9000 RPM. The thrust bearing at the bottom of the main shaft assembly is rated to withstand a dynamic load of 6,700 lbs at a maximum speed of 3800 RPM. The material chosen to construct the main parts of the lift was 1018 steel. The main shaft of the lifting system is comprised of two circular tubes. The outside tube has an outer diameter of 2.5” and a wall thickness of 0.25”. The inner tube has an outer diameter of 1” and a wall thickness of 0.120”. The arm of the lifting system is square tube steel with dimensions of 1.5” x 1.5” and a thickness of 0.120”. Steel plates, 0.25” thick, were used as the base for the lift. The motor was mounted on the arm and a pulley was placed at the end of the arm. With the use of the bearings in the main shaft, the cantilever arm could rotate freely making it easy for the Client to maneuver the wheelchair in and out of the rear of the vehicle. The motor was tested to lift a 45lb weight which enough to cover the 32 lb weight of the Clients’ manual wheelchair.
A lifting system was developed to allow a user to raise and lower her wheelchair in and out of the rear hatch area of her PT Cruiser without assistance from another person and without restricting use of the backseats. The total cost of the parts used in the system is about $450.00. Machining was done at no cost since it was done at the University. The Client has used the system and is happy with it. It will allow her to do everyday activities more independently. These activities include going to and from school, the grocery store, doctor’s appointments and various other activities. She will not need to depend on traveling with some one or asking a stranger for help in lifting her wheelchair into and out of her PT Cruiser.
This work was supported by grant BES-0625023 from the Research to Aid Persons with Disabilities Program from the BES Division of the NSF.
c/o Mohamed Samir Hefzy
Biomechanics and Assistive Technology Laboratory
Department of Mechanical, Industrial and Manufacturing Engineering
The University of Toledo
Toledo, Ohio 43606
Phone: (419) 530.6086
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