Cerebral Palsy is a number of conditions characterized by a diminished amount of muscle control. An individual suffering from Cerebral Palsy will often have very stiff and awkward movements. The spastic movements will greatly interfere with the person’s ability to manipulate controls and devices. Functioning in an ordinary environment often will require a greater degree of fine motor control than is available to a palsied person. Often palsied individuals are limited to using a wheelchair as a means of transportation.

The disability is especially pronounced in children, who naturally have a lesser degree of muscle control than adults have. The controls of a wheelchair can be difficult for a child to manipulate with a certain degree of accuracy. The movement of the wheelchair may be erratic and less efficient as a means of transportation than is possible. The operator of the chair may sometimes jerk the chair in an undesirable direction or make movements too suddenly.

The scope of this project is to design a compensating device for an existing controller. This device will reduce the erratic motion of the wheelchair due to spastic motions of the operator. Different degrees of compensation should also be within the scope of the device.

Compensation for the controlling of the wheelchair is provided by programmable controls within the wheelchair’s motors. Maximum speed, acceleration and time delay constants are programmable variables. However, for a child with cerebral palsy, additional damping is often necessary.

Using a mechanical damping device was decided upon. A mechanical damping device will be simple to implement and cost effective. A force-based system using a mechanical damper will also provide feedback to the operator as a form of rehabilitation.

A compensating device for a controlling element on a wheelchair will provide a greater degree of independence for the user by increasing his control over his motion. The device will be easy to adapt to existing controllers and compensate a variety of ranges of motion. By designing a versatile component to compensate the controller of a wheelchair, the operator will experience greater control over the movement of a wheelchair.

The piece has been designed such that the lower half has a larger diameter than the upper half. It is believed the smaller top half will become more flexible with less material to allow the joystick the freedom of movement it had before. The wider lower half allows for the piece to be mounted properly on the top of the joystick. In order to do this, four through holes were placed in the section of the piece; a through hole located at each quadrant.

On the inside of the rubber damper there exist variation of the inner diameter. On the inside of the piece, on the lower half, an insert was placed. This was done to accommodate a rise on the joystick unit that would make placement of the damper on top of the joystick somewhat difficult if not taken into account. Higher up in the lower section of the rubber piece the diameter is changed again. It was decided that in order to obtain the maximum resisting force just slightly larger than the shaft where possible. Since at this point a spring surrounded the shaft of the joystick, the diameter here was made wider to keep the rubber material from having any interaction with the spring. It was feared the spring may get caught up in the rubber and get damaged or bent out of shape. This same diameter was continued up and into the upper half of the piece. Eventually, near the top of the damper, the diameter was again reduced to being just larger than the joystick shaft diameter.

A metal "o"-ring or washer type piece was designed to go along with the rubber damper. It was determined that stresses across the top of the lower half would cause tearing after short use.

The washer was designed to fit over the top of the stress evenly across the surface. A similar square piece was made to fit under the top of the joystick to allow for use of a nut. Specifications of these pieces are located in the following section.

Production: Due to the softness of the rubber, molding is the method used to manufacture the part. The mold is pictured below.

• Primary function. Act as a motion compensation device (rehabilitative device) that will reduce the uncontrolled extensor motion by providing a resisting force to dampen that applied by the user.
• Material. Rubber and or any composite compounds. (Initially started out with Chloro-Butyl and Neoprene) The exact durameter for use is unknown due to the variations in the strength factor of the people being dealt with. Although, materials with a Young's Modulus of .92, 1.5 or 2.20 MPa are being looked at. These numbers correspond to a hardness value of 30, 40, and 50 respectively. Difficult to tear and
• Measurements:

Bottom Half 2.5 in

Upper Half 1.5 in

Diameter/Height (Inner)

Rise 1 3/16 / 1.375 in

Shaft Opening 7/16 in

Shaft closing .25 in

Holes for Screws (4 in number)

Diameter 1/8

• Material A-36 Steel
• Measurements:
• Height 3.0 in
• Diameter. 5.0 in

The graph "Electrical Characteristics" represents the electrical output, in volts, versus the amount the joystick is displaced. 100% represents fully forward while –100% represents fully in reverse. The top line is the absolute output. The point corresponding to a displacement of zero is the bias point. The bias point is 5 volts and is specified by the manufacturer. The swing is approximately ± 1.4 volts. The bottom line in the graph represents the absolute difference in the voltage from the bias point. The absolute difference is a non-linear relationship. If the joystick is displaced 50% in either direction, the output is approximately 75% of its maximum difference. If the joystick is displaced 75% in either direction, the output is approximately 95% of its maximum difference. The significance of this is that if the damping device restricts the motion of the joystick to only 75% in both directions, the output will still be 95%.