Abstract
A human arm is mechanically redundant because its elbow can rotate without moving a grasped object. However, human upper extremities usually have regular postures when they perform various motions and works in daily life. Revealing rules behind this phenomenon is important for human-like motions of artificial arms and for design of convenient man-machine systems.
The authors measured and analyzed 9 types of upper extremity motions of 5 subjects. Relationship between the wrist position and one shoulder angle is elucidated into an equation. The angle calculated by this equation agree with the shoulder angle for an arbitrary wrist position. Using this kinematic relationship, the shoulder angles are estimated and human-like postures of upper extremities are determined. This equation kinematically expresses a rule which prescribes the postures of human upper extremities.
