Aging is becoming a serious problem in Japan. Physical load during a caring operation may not be tolerable for the elderly and very often it produces secondary lesions in care assistants. Practical power-assist devices are highly desired in the field of caring or welfare. A Pneumatic Artificial Rubber Muscle (PARM) is noticed as an actuator of an assist device because it is flexible and has a high mass-power rate. In this study, we have developed an assist device for caring that uses PARM to reduce a physical load. A two-link arm was designed to assist caring motions. The position controller using a disturbance observer was applied to a two-link arm to correspond to the difference of weight of members in need of caring. The disturbance observer is effective in terms of not only compensation for disturbance, but also nominalization of a controlled object. Robustness of the employed disturbance observer is realized by internal stabilization. A two-link arm was controlled by the position controller, however, improvement such as enlarging the rigidity in a perpendicular direction is necessary for it.
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