Volume 6 (2017) Pages 110-121
The present study proposes control target for the motion of an active self-feeding spoon by analyzing skilled spoon motions reflecting the grasping actions of healthy people eating specific foods. We measured spoon motions in terms of time (t), rotational (θ) and azimuthal angles (φ) while five healthy participants ate soup, malt balls, firm tofu, pudding, and yogurt. We developed a wireless angle measurement spoon with which to evaluate changes in the inclination angles (IAs) of the spoon and the correlation between θ and φ during scooping and transporting spoon motions. A negative θ value indicates that the surface of the spoon bowl has rotated toward the participant. A negative φ value indicates that the tip of the spoon bowl has rotated downward. After observing eating actions and measuring IAs (θ, φ, t), we examined the correlation between θ and φ using the coefficient of determination R2 with a second-order curve regression (2OCR) model. R2 of the scooping action exceeded 0.55 while that of the transporting action was less than 0.25. We found the effects of food type on the grasping action as follows. For soup, the scooping and transporting times were longer than those for the other foods. The spoon was rotated negatively to avoid spilling soup and malt balls at the end of scooping and at the start of transporting. Firm tofu and pudding required cutting and scooping actions. The grasping action of food at the end of transporting affected the IAs (θ, φ). The correlation R of the relationship between the 2OCR model for pudding (R2 = 0.79, highest among food types) and the 2OCR models for other foods exceeded 0.94. We suggest the control target of the active self-feeding spoon as follows: set IAs (θ, φ, t) at the start and end of scooping and transporting actions to avoid spillage induced by the inertial force of foods and to facilitate putting food into the mouth. IAs (θ, φ, t) during the scooping and transporting actions were applied to the 2OCR models for pudding (highest R2) and liquid food.