Lifting Assist for a Powered Wheelchair

Designers: Paul A. Lisi and Andrew D. Steinberg
Client Coordinators: Nancy Curtis
Supervising Professor: Dr. Larry N. Bohs

Our client is a seventeen-year-old girl with cerebral palsy.  She cannot get into her motorized wheelchair comfortably without the assistance of others.  The goal of this project was to build a device to allow her to ascend into her wheelchair as independently as possible.  We constructed a lift that attaches to her wheelchair and uses the seat-height actuator as a lifting mechanism. The device lifts her about 8” off the ground to make sitting in the wheelchair easier; it also serves as a footrest at all times during use of the wheelchair.

How this project helped
Evaluation of the Lifting Assist on the client’s wheelchair indicated that it functions as intended, and can lift the client into a position where she requires only minor assistance to sit.  Before the device can be delivered to the client, further work is required to ensure safety in all wheelchair modes, and to provide a more comfortable resting foot position.  The client’s physical therapist said, “The finished product will enable only one person to assist instead of two because they will not have to lift her.  Also, more people will be able to assist – for instance, her sister who is smaller than her mother and other friends who don’t have special training.  It will also give [her] more independence in the future [when she is] away at college and in a more independent living situation in a dorm or apartment.  It will also assure that those helping her will not have to risk back injuries.”

The Lifting Assist (Figure 1) uses seat-height actuator of the powered wheelchair as the lifting force. The operational sequence is as follows: First, the client stands on a platform with the seat in the lowered position.  Second, the seat actuator is extended, causing the wheelchair seat and platform to rise by about 8”.  Third, the platform is locked into place vertically.  Fourth, the seat actuator is retracted, lowering the seat to its minimum height.  At this point, the client is approximately 8” closer to the seat vertically than she was on the ground.  Finally, the client sits down with minimal assistance.

The final design, based on this concept, comprises a mounting component, a linear stabilization component, a platform, and a locking system.  The mounting component consists of a rectangular plate, connected by two ¾” square insertion rods to the footrest attachment sleeves below the wheelchair seat.  Two shaft clamps and a vertical lock bar attach to the front of the rectangular plate.

The linear stabilization component includes two 25-mm diameter shafts, the tops of which are secured to the shaft clamps.  Two pillow-block linear bushings slide freely on the shafts, and attach to the rear of the platform, allowing it to move vertically.  Locking collars mount on the shafts below the bushings, causing the platform to rise as the seat actuator extends.

The platform base has a trapezoidal shape, 12” on the end nearer the wheelchair, 14” on the other end, and 11.5” deep; these dimensions give the client maximum space given the constraints of the wheelchair.  The base is covered with a piece of non-slip rubber.  The rear of the platform is 12” horizontally by 6” vertically.  The platform sides taper from 6” at the rear to 1” at the front, providing rigidity and maximum foot visibility for the client.

The locking system includes two spring pins attached through the platform’s rear wall.  The first spring pin locks into a vertical stationary bar on the wheelchair, originally intended for stationary platform mounting. A custom square rod attaches to the vertical stationary bar, extending its height. As the seat rises to maximum height, this spring pin locks into a hole in the vertical stationary bar extension, thus fixing the vertical height of the platform.  When the chair is lowered to its minimum height, the second pin locks into the vertical bar attached to the rectangular plate of the mounting component.  If the client tilts her chair, this latter spring pin holds the platform in the proper position while the first spring pin slides out from its hole in the stationary bar extension.  To get out of the chair, an assistant pulls on the rings of the lock pins, which allows the platform to slide back down to floor level.

The cost of parts for the Lifting Assist was approximately $1000.

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