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It is first clarified through simulational analysis that co-activation between agonist an muscle and its antagonist both having nonlinear elasticity is indispensable for the stiffness adjustment on an articulator movement. An antagonistic muscle-like actuator (AMA) is then proposed as an approach of imitating a skeleto-muscular articulation system. The AMA has two nonlinear springs which drive one joint antagonistically and provides the joint with the feasibility of stiffness adjustment. The development of the forearm prosthesis which has 6 d.o.f. is developed as an application of the AMA. Two d.o.f. for the wrist and 4 d.o.f. for the two fingers are driven by only one DC motor and one stepping motor for exchanging the driving mode. The whole mechanism is designed as almost the same volume as an adult's forearm. A shape fit mechanism for the finger is proposed, by which the three joints of one finger automatically adjust their angle according to the shape of the object to be grasped.
Koganezawa et al. (Wed,) studied this question.