ASSISTIVE TRUNK LOADING WHEELCHAIR LIFT

Michael Leitzinger and Jeffrey A. Drinkard Department of Mechanical Engineering The University of Alabama Tuscaloosa, Alabama USA

ABSTRACT

Loading a wheelchair into the trunk of a car can be a truly arduous task. More often than not, the wheelchair being loaded is heavy and extremely cumbersome. This makes the loading of a wheelchair into the trunk of a car very difficult for many people, especially for disabled people themselves. This has created a need for a device that will assist in loading and unloading a wheelchair into and out of the trunk of a car. A need that has been satisfied with an assistive trunk loading wheelchair lift. A trailer hitch mounted device that through the use of a motorized winch loads and unloads a wheelchair. The device was designed, built, and tested for under $175.

BACKGROUND

Persons with disabilities which confine them to wheelchair are often assisted by friends or relatives when traveling. If the person aiding the impaired individual does not have the use of a specially equipped vehicle, difficulties may arise in loading and unloading the wheelchair. The wheelchair itself can be heavy as well as cumbersome, especially when loading the chair into the trunk of a vehicle. Assistance may be required in the loading and unloading process. Wheelchair lifts are available to the public at costs ranging from $1,000 to $3,000 which, for the average consumer, is too expensive. Therefore an affordable alternative is needed.

PROBLEM STATEMENT

The decided task is to design, build, and test a mechanism that will assist a disabled person with limited mobility or an individual of limited strength in loading and unloading a wheelchair into and out of the trunk of an automobile. This device should not require a permanent modification to the trunk or the wheelchair. Changing of the structure of the wheelchair or car such that it can not be returned to its original condition without remanufacturing would be impractical and expensive. The device should also be compact, durable, and easily operated by individuals with limited strength and ability.

RATIONAL

In deciding on a design for the wheelchair lift, several constraints were considered. The first of these which was cost. The device would need to be inexpensive in order to make it cost effective for the average person. A $250 cost limit was chosen. Meeting the budget requirements in part called for a simple yet durable design which would be easy to manufacture. Another consideration was making the device universal. It had to be able to be used with any vehicle that had a trunk with enough room to store and transport a wheelchair. This in turn would keep costs down by reducing the amount of time needed to develop individual designs for specific vehicles. If the lift were to be a motor assisted mechanism, it would be limited to the power provided by a 12 volt automotive battery. The lift should also allow the user access to objects normally stored in the trunk, such as the spare tire and jack.

When considering the user of the lift, it was assumed that a person using the device would be able to lift 25 pounds with a minimal amount of difficulty. The user should not, however, be required to do any excessive lifting. They should also be able to load or unload the chair in a minimal amount of time so as not to expose them to foul weather for a long duration. As for the safety and convenience of the user, it was decided that the device meet the applicable codes and regulations set by the Americans with Disabilities Act and the Occupational Safety and Health Act (OSHA)

DEVELOPMENT

In making the lift universal to all vehicles, a trailer hitch mounted mechanism was decided upon onto attach the lift to the vehicle. A two part frame for the mechanism was designed so that it would insert into a class three "Draw-Tite" style hitch. The frame was designed as a two piece structure, constructed of 2 inch square steel tubing

Figure1. Assistive Wheelchair Lift

of 3/32 inch thickness. The device could be disassembled and put in the trunk with the wheelchair when not in use. Although a smaller size of tubing could be used safely, the larger tubing gave a visual sense of security. When a person sees a structure that is made of members which are small in proportion the size of the mechanism, the small members appear visually to be weak. Therefore a larger size member will appear stronger. The corners of the frame were given extra support with 3 inch gussets.

A stress analysis of the frame was conducted using the average measured weight of a standard wheelchair, 40 lb., in order to check for safety in the mechanism. Three critical points were determined. The most critical of which was on the 1 inch pin at the pivot point of the frame. The bending moment was calculated followed by the stress due to bending at that point. Finally the factor of safety was determined to be 3.4 using

where Sy is the yield strength, n is the factor of safety, and s is the stress due to bending. (Shingley and Mischke, 1989)

The lifting mechanism could have been a hand-cranked or motor driven winch. Because of the time required to lift the wheelchair with the hand winch, a motor driven winch was more feasible. In regard to weight considerations however a 1500lb capacity winch was too cumbersome to use. A winch had to be designed for lifting small loads in a short amount of time. To accomplish this a small electric motor was combined with a hand winch, Figure 2.

Figure 2. Specially Designed Winch

A specially designed shaft/coupling replaced the original shaft in the motor. This coupling enabled the winch to be directly driven. The motor was then bolted to the winch via a custom made sheath and the winch was bolted to the upper piece of the frame. A 1/4 inch coated cable was run from the winch through the frame to the end of the boom The end of which is attached to the wheelchair.

DESIGN

The lift is a two piece trailer hitch mounted device The bottom piece extends approximately 3 inches past the end of the hitch. Then the frame angles 90 degrees to the left and reaches 26 inches from the center of the car parallel to the ground. This was done so the user would not need to maneuver the wheelchair around the device while guiding it into and out of the trunk. From here the frame turns upward and rises 23 inches to a pivot point. A 1 inch diameter steel pin is used as the pivot. This is also the separation point for the top and bottom sections. Taking the device apart allows for easy storage when it is not in use, as well as, reducing the weight of each piece that must be put in the trunk.

The top piece is an L shaped boom that slides down on top of the pivot pin with the winch and motor attached opposite to the boom. The top piece extends upward another 23 inches where it then angles 90 degrees and continues out 26 inches. The motor direction is controlled by a directional switch on the boom.

To operate the lift, the user slides the bottom section into the trailer hitch and inserts the locking pin. The user then joins the top section to the bottom. Placing his/her left hand on the boom so that their thumb is over the control switch and depresses the switch in the down direction to let out the cable. Once the cable is out, attach the clip hook to the folded wheelchair. The hook is attached to a metal ring that is clamped to the frame of the chair at the approximate center of gravity. The user then presses the switch in the up position lifting the chair off the ground. When it is raised up, the chair will want to swing so that it is parallel to the ground. Placing the right hand on the locked wheel will control the motion. As the horizontal chair clears the edge of the trunk, using the left hand, the user swings the boom over the trunk and presses the down switch. While the chair lowers, the user guides it into the trunk with his/her right hand which is still on the locked wheel. After the wheelchair is in the trunk, the cable is detached and rewound. The lift is then disassembled and placed in the trunk with the wheelchair. Total time for the procedure is around 75 seconds. Removing the chair from the trunk follows the same steps in reverse.

RESULTS

The assistive wheelchair lift has been designed, built, tested, and demonstrated. The final design for the lift costs approximately $150. Well below the $250 limit. If the lift were to be manufactured the production cost would decrease. The mechanism was developed and constructed in about 25 hours. After numerous uses in testing and demonstration, it has had no difficulties with operation.

REFERENCES

Shigley, Joseph Edward and Charles R. Mischke, Mechanical Engineering Design, Fifth Edition, McGraw-Hill, Inc. 1989

ACKNOWLEDGMENTS

This project was completed in fulfillment of course requirements for ME 489, Senior Design I, at The University of Alabama. The students who worked on the project include: Greg Emerson, Martin Schmurr, Jeff Drinkard, and Michael Leitizinger, with special assistance from Tim Patterson. The students were assisted and directed by Dr. Joey Parker and The University of Alabama. Materials were supplied by The University of Alabama, Wal-Mart, and Rick's Hardware.

Michael Leitzinger Department of Mechanical Engineering Box 870276, The University of Alabama Tuscaloosa, AL 35487-0276