Tilting Desk for Power Wheelchair

Designers: Amy L. Caribardi and Lauren E. Schaffer
Client Coordinators:
Supervising Professor: Dr. Larry N. Bohs

The client is a man with quadriplegia who uses a power wheelchair. Most commercially available wheelchair desks attach to the armrests, often interfering with the control joystick on power wheelchairs. The goals of this project were to construct a desk that easily attaches to the client’s wheelchair, and that provides access to the wheelchair’s joystick and a tilt feature that he can control himself. The project consists of a wooden desktop, supported by a steel frame. The frame inserts into clamps mounted to the footrests of the power wheelchair, avoiding the control switch. A ratchet mechanism allows the client to tilt the desk without assistance. summary of impact The client could not find a commercial desk that was suitable for his needs, and therefore had difficulty finding surfaces on which he could read, write, and eat. The wheelchair desk fastens to his power wheelchair without interfering with the joystick control. Its non-slip surface allows him to read, write, and eat without the task of finding a non-slip table or transporting certain dishes and bowls. The client can tilt the desk without the help, thereby extending his independence.

The desktop is constructed of 3/4″ maple for durability and to accommodate the client’s aesthetic preference. It is comprised of three boards joined together, 26″ wide, the width of the wheelchair’s armrests. The corners are rounded, and the surface sanded and finished with polyurethane to make it waterproof. The center area is routed to accommodate a 12″x12″ sheet of hard rubber, which provides a non-slip surface for writing and eating. A wooden ledge, attached below the rubber insert, holds reading material in place when the desk is tilted. Facilitating independent desk tilting for the client was an important structural consideration. Three pieces of 3/4″ square metal tubing are welded together with a solid steel rod to form a rectangle. Two vertical supports of 3/4″ square tubing are welded to this frame. The solid rod rotates within holes in wooden tie braces, attached to the bottom of the desktop. One end of the solid rod attaches to the drive point of a 1/2″ socket wrench. The arm of the wrench is bolted to the bottom of the desktop. An extension bar is attached to the ratchet mechanism of the wrench, and extends 6″ above the desktop surface. When the extension bar is pushed forward, the desk can be lifted to a desired tilt angle; it will stay at the highest  angle achieved until the extension bar is pulled backward, which allows the desk to return to horizontal.

The extension bar attaches to the ratchet mechanism using a screw and a milled
groove, which keeps the bar and ratchet mechanism in contact under considerable force. The desk is attached to the power wheelchair using two custom support brackets, which clamp to the foot rests of the chair. Screw-and-hinge clamps attach each bracket to two sites along the curved rods of each of the footrests. These clamps attach to a metal plate with an adjustable mounting, so that the exact fit of the brackets can be adjusted on the chair. The clamps are lined with foam rubber to prevent slipping. Also attached to each metal plate is a piece of square steel tubing, slightly larger than the vertical support poles of the desktop frame. The support poles are tapered slightly to make attachment and removal of the desk easier.

Two safety features of the desk help prevent damage to fingers that might be underneath the surface when it is lowered into the resting horizontal position. First, a strip of foam weather-stripping is attached to the underside of the desktop to cushion the area between the desktop and the metal frame. Second, an anti-slam lid support, as used for toy boxes, was attached between the desktop and frame. The device consists of a sliding track with a rubber disk that glides with adjustable friction. This lid support is adjusted using a single screw to create the desired damping effect.

Materials for the desk cost approximately $210; machining costs were approximately $300.

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