Research on the Spherical Joint Robot Driven by the Pneumatic Muscle Actuator

This paper describes a robot with a spherical joint that imitates the shoulder joint of humans. The robot with a spherical joint is developed considering structural features of a human’s shoulder joint. The spherical joint has three degrees of freedom: abduction or adduction, flexion or extension and internal rotation or external rotation. Furthermore, this robot is actuated by a group of pneumatic artificial muscles (PMA), which have high power to weight ratio and an effective passive compliance characteristic. Basic characteristics of the artificial muscle are presented. Finally, because of the strong nonlinear and time lags of the PMA, model-free adaptive control which is an advanced control method and does not require building an off-line mathematical model. At last, sufficient accuracy of 0.5 degrees is obtained experimentally.