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LIFT ASSIST DEVICE

Mohamed Samir Hefzy1,2, Shelley Killen3, Bradley Diedrich2, Ken Singer2 and Matt Forewerck2 1Dept. of Orthopaedic Surgery, King Faisal Special Hospital & Research Center, Riyadh, Saudi Arabia 2Biomechanics Labs., Dept. of Mech., Ind. & Mfg. Eng., The Univ. of Toledo, Toledo, Ohio, 43606 3Department of Physical Medicine, Medical College of Ohio, Toledo, Ohio, 43699

ABSTRACT

This paper describes the design and development of a device to assist a patient out of a wheelchair who is physically unable to come to standing under his own power. The design of this lift assist device incorporates a seat with a hydraulic jack mounted underneath it. The substitute seat can be easily fixed to a standard wheelchair via a hinge. The jack provides the input needed to tilt the seat to in order to assist the patient to raise from a seated position on his own. A footpedal is used by the wheelchair occupant to pump the jack. Details are provided so that the lift assist device can be duplicated.

BACKGROUND

Patients who are able to ambulate short distances are often not able to come to standing from a seated position under their own power when using a wheelchair. Because of their weak quadriceps muscles, they can't come to a standing position without physical assistance. With the use of a lift assist device, they can be raised from a seated position in the wheelchair to a position from which they can come to full standing and ambulate with a walker without the physical assistance of another person.

STATEMENT OF THE PROBLEM

A patient requires a lift assist device to help him to come to standing under his own power when using a wheelchair. This device should satisfy the following three basic requirements:

1. it should assist the wheelchair user to come to standing using his own power from a seated position without compromising safety so that the user can be as independent as possible;

2. it should be compact, easy to store and portable so that it can be easily installed into the wheelchair.

3. it should be affordable to those who do not have adequate coverage to supply them with expensive equipment;

RATIONALE

The lift assist device was designed and constructed because a similar and affordable device was not commercially available to the patient.

DESIGN & DEVELOPMENT

The proposed design incorporates a mechanical seat in which an input will assist the patient to come to standing out of a wheelchair. Due to the size and style deviation of various wheelchairs, this project was limited to develop a device that retrofits only RIDE-LITE 9000 series wheelchairs manufactured by INVACARE Corporation. Several design concepts were proposed in order to provide the input force including using a hydraulic jack, a spring and damper mechanism, and an airbag. The design that utilizes a hydraulic jack was found to be the most effective in satisfying the design requirements.

The design concept that was thus used incorporates a hydraulic jack to provide the force required to tilt the seat from horizontal to a 45 degrees angle. The jack is mounted under a substitute seat that is fixed to the wheelchair via a hinge. The wheelchair occupant uses a foot pedal to pump the jack. A cushion is placed on top of the seat for comfort. The prototype retrofitted to a wheelchair is shown in Figure 1.

The prototype of this lift assist unit includes five main parts:

1) seat, seat frame and seat subframe, 2) jack, 3) jack to seat and jack to chair connections, 4) jack input foot pedal, 5) lateral stabilizers.

Before retrofitting the unit to the wheelchair, the original cloth seat was removed to make room for the lift assist unit.

Figure 1. Lift assist unit retrofitted to a wheelchair

The seat, seat frame and seat subframe component is shown in Figure 2. The seat is made of plywood. The seat subframe is designed to fit into the standard seat mounting brackets of the wheelchair. Due to the resulting forces of the upward jack and the downward patient weight, very little force is needed to fix the subframe to the chair. Therefore, the subframe is attached to the wheelchair frame using industrial plastic ties. The subframe is fixed to the seat frame via a 1 foot long hinge. The seat frame is constructed of 1 in. wide by 0.25 in. thick steel bar stock.

Figure 2. Seat, seat frame and seat subframe component

The jack to seat and jack to chair connections are shown in Figure 3. The jack is a 4 ton hydraulic bottle jack. The jack to seat connection consists of an axle (bearing rod) welded to the top of the jack screw extension with two shielded ball bearings attached at each end of the axle. The bearings have an outside diameter of 1.625 in., an inside diameter of 0.75 in., and a width of 0.5 in. As the jack raises, the bearings ride in grooves that are part of the seat frame. Two 1.5 in. by 0.25 in. pieces of steel angle stock are used to provide a base for the jack. The angle stocks are fixed to the chair via U-bolts.

Figure 3. Jack to seat and jack to chair connections

The jack input consists of a foot pedal and a steel extension tube. The input device allows the user to raise the seat by flexing and extending the hip. The foot pedal includes a cloth strap that allows the user to pump the jack with their foot. The input device is attached to the jack by sliding the steel extension tube into the standard jack sleeve. It takes approximately 20 vertical repetitions to raise the seat to the desired 45 degree angle.

In order to prevent side to side movement during operation after installing the lift assist unit, lateral stabilizers were added to the wheelchair. These stabilizers replace the lateral stabilizing unit attached to the original cloth seat which is removed before installing the lift assist unit. These stabilizers are constructed using 0.125 in. braided steel cable and standard conduit fasteners. Total expenses for materials and supplies were $300.

EVALUATION

As designed the system is limited to retrofit only RIDE-LITE 9000 series wheelchairs. Experience to this date indicates that the goal of this project has been accomplished. When the device was tested, it was found that a patient is able to be raised from a seated position to a position at which he/she can continue to come to standing with minimal effort as shown in Figure 4.

DISCUSSION

An assistive device that improves the quality of life of a patient using wheelchairs has been developed and tested. This patient is unable to come to standing from a seated position under his own power, but once up he is able to ambulate short distances. The evaluation has been conducted using the criterion for the assessment of Assistive Technology (AT) (1). These criterion require AT services to be functional, simple, easy to use, acceptable in appearance, affordable, and to provide independence.

Figure 4. Lift assist unit being evaluated

REFERENCES:

1. DeRuyter, F., "Evaluating Outcomes in Assistive Technology: Do We Understand the Commitment?", Assistive Technology, Vol. 7, No. 1, pp. 3-8, 1995.

ACKNOWLEDGEMENT

This work was supported in part by grant BCS-9308700 from Aiding the Disabled Program of the Bioengineering Division of the National Science Foundation.

Mohamed Samir Hefzy, Ph.D., P.E. Department of Orthopaedic Surgery King Faisal Specialist Hospital and Research Center P.O. Box 3354, Dept. MBC 77, Riyadh 11211 Kingdom of Saudi Arabia Tel: 9-011-966-1-442-7591 Fax: 9-011-966-1-442-7597

Presently, Dr. Hefzy is on sabbatical from:

Biomechanics Laboratories Dept. of Mech., Ind. and Mfg. Engineering The University of Toledo Toledo, Ohio, 43606 Tel: 419-530-8234 fax: 419-530-8206 E-mail: mhefzy@uoft02.utoledo.edu