Development of Spherical Joint Robot Using Pneumatic Artificial Muscles

This paper describes a robot with a structure that imitates that of humans. For a robot that functions in humans' daily life, it is important to consider imitating humans in the characteristics of structure and human safety. The robot with a wrist joint that comprises a spherical joint is developed considering structural features of a human's wrist joint. Furthermore, this robot is actuated by a pneumatic artificial muscle, which has high power to weight ratio and an effective passive compliance characteristic. Basic characteristics of the artificial muscle are presented. Inverse kinematics of the wrist joint composed of the spherical joint are also presented considering characteristics of a metal wire and the artificial muscle. Posture control of the wrist joint using a PID feedback system which includes a pressure control system as a minor loop control is demonstrated. Sufficient accuracy and the possibility of achievement of a robot that can work in human daily life are obtained experimentally.