This paper proposes an exoskeleton that supports activities of an upper extremity including a wrist joint so that a patient with muscle weakness could work on a table or a desk with his/her hand in a daily activity. The exoskeleton compensates gravity of the upper limb using two counterweights in order to reduce loads of a shoulder joint and an elbow joint. The exoskeleton also supports a wrist joint against its own gravity by interlocking with elbow joint angle so that a user could carry an object on his/her palm by keeping it horizontal. An orientation of a grasping object is partially constrained by a hand frame of the exoskeleton for object stable improvement. Through some experiments, the gravity compensations of upper limb's joints are confirmed based on bioelectric potentials of muscles when subjects drink water from an aluminum can.
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