Handicapped persons who spilled food unconsciously were studied with the aim to investigate the spilling conditions related to the spoon angles (rotational and azimuthal angles) and the inclination angle of the liquid food surface estimated from the acceleration of the spoon when used by a handicapped person to eat food. Image captures of eating behaviors were recorded from three directions using three cameras, with markers attached to the wrist of the subject and to the spoon. Both the position and the acceleration of the spoon measured by three-dimensional (3D) image processing were investigated to determine the spilling conditions. Spilling of liquid food was observed at a rotational angle of -18 deg and an azimuthal angle of +16 deg at the start of the spoon motion. Thus, we predicted that spilling of liquid food during spoon movement was affected not only by the spoon angle but also by the spoon acceleration speed. Evaluation of spilling conditions using a two-dimensional spoon model (L60×W36×D7 mm, liquid food filled to 40% of the spoon depth) showed that spill could be avoided at rotational angles in the range of ±17 deg and at azimuthal angles in the range of +8 to -13 deg. When the liquid food inclination angle was estimated from measured spoon acceleration speed, we found that during actual eating the liquid food was inclined at angles within the spilling condition. Theses results suggest that the spilling of liquid food during spoon movement is related not only to the spoon angle, but also to the inclination angle of the liquid surface induced by spoon acceleration.

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