Electric Elevation Assist and Spasticity Control Arm

Wikis > Electric Elevation Assist and Spasticity Control Arm

Electric Elevation Assist and Spasticity Control Arm

Designers: Steven Moore, Donald Burke, Tiffany Borden
Client Coordinator: Linda Pierson, PT, Hueytown Elementary School


The purpose of this senior design project was to augment a mechanical arm support for Kylin, an 11 year-old boy who has dystonic cerebral palsy with choreoathetoid movement.  A device was desired that would restrict Kylin’s spasticity, but allow him to raise and lower his arm so that he could perform such day-to-day tasks.  The design constraints were the following:  It would be necessary to attach and remove the device to Kylin’s wheelchair both easily and quickly.  In addition, the product had to restrain posterior abduction of the humerus at a force of ~40-120 lb (measured by the students using a fish scale).  To accomplish daily tasks that involved hand to mouth motion of his right arm, augmentation of the device had to allow for 0º-110º flexion of the elbow, 50º-60º internal rotation at the shoulder, 30º-45º flexion, abduction of the humerus, and provide a lifting force of ~25 lb.  In addition, the device had to restrain his dystonic spasms of 40-120 lb.  It also had to be controlled by Kylin, and any electrical and mechanical components had to be properly installed.  A budget of $1500 was specified and the team had roughly four months to complete the design.



The final design incorporated an AC linear actuator to provide desired range of motion, a foot control to control movement, and a control box to convert AC power to DC power (Figure 19).  These devices were donated by LINAK (Louisville, KY) and were chosen based on size, weight, availability, appearance, and desired performance.  The LINAK linear actuator was wired to the control box.  Snap-connectors and heat-shrink tubing was added to secure the line.  The original distal joint of the arm support was removed and an aluminum conduit was used to fix the arm support segments into a set position.  Locking the arm at this joint functions in spasm control and also provides a stable mounting position for the actuator.   Steel bushings were placed in the piston rod eyes to accommodate for diameter size differences between the eyes and the mounting brackets.  A hole was drilled as close to the proximal joint as possible to allow for full extension of the actuator piston.  A conduit hanger was then bolted at the hole location to allow for attachment of the stationary piston rod eye.  The forearm support was adjusted to allow for the proper pivot angle and a stainless steel bolt was inserted through a mounting flange to attach the movable piston rod eye.  Vinyl bushings were then used to prevent lateral movement and a stop-pinion was removed to prevent overshoot complications.    The system is shown in Figure 19.  The linear actuator, control box and foot switch were donated by Linak, resulting in a total cost = $96.12.

19 - electric elevation assist
Figure 19.  Elevation arm with spasticity control