Abstract
This paper describes consideration of the capable head movement of a child severely disabled with cerebral palsy who can't speak or control her extremities. This consideration aims to be able to operate a couple of switches for some augmentative and alternative devices. Now, she can only express her intention, "yes" or "no", only by her head movement to the right or the left, and only while she is supported by her mother. First, this head movement was measured by using an ISOTRAK system which can measure a three-dimensional position and the Euler angles. As a result, small movements to the left (identified as "left?") were found in addition to normal movements to the right and the left. In consideration of the helical axes and dynamic energy, it can be said that the normal movements were made possible by positive utilization of gravity, while the small movements (left?) occurred because she couldn't utilize the gravity when she tried to move her head to the left. Next, a seating system to facilitate head movement without her mother's support was developed. This decreased the physical burden on her mother. In addition to body support, this system also has the function of buffing the involuntary extension movement of her body. The backrest was separated into 3 segments which were respectively fitted to her head, chest and pelvis. Each segment was connected with an elastic pin joint so that, if she extended her body, the backrest would lean backward following her movement; if her extension became weaker, the backrest would return to a normal position at the effect of the joint's elasticity. In this way, her sitting posture remained stable. Then, her head movement on this seating system was measured by using the ISOTRAK system. As a result, when she kept her head nearly straight forward, she could push the right and left switch. And it became clear that she rotated her neck during these movements. These were different from the movements made with her mother's support. The rotation movement was considered an efficient action which was caused by reducing the effect of the friction between her head and the headrest. Moreover, it is found that a large movement to the left or the right disturbed her effort to return her head to a medium position. While her head returned from far right position with difficulty, the potential energy increased before this action. So, it is considered that gravity is very effective even with the seating system. Therefore, it is important to cautiously set up the seating position related to gravity, such as the tilting angle, headrest position and so on. As a result of this study, the possibility that this child can use augmentative and alternative devices by herself was suggested.
