Study on the humanoid robot wrist actuated by Pneumatic Muscle Actuators

Pneumatic Muscle Actuator (PMA) is a novel pneumatic flexible actuator with high power-weight ratio, compliance nature and easy operation, and is widely used as the actuators of robots. In this paper the authors developed a mechanism of humanoid robot wrist which is compact and lightweight. The humanoid robot wrist has a platform attached to a spherical axletree actuated by four parallel PMAs, which has two degree of freedom (DOF) and is fixed on the terminal of a robot arm to serve as a human wrist. In this paper the geometric analysis of the mechanism model of the humanoid robot wrist is done and its work space and track programming are also explained. Due to the compressibility of the air, PMA has the properties of obvious nonlinearity and time lag, which cause much difficulty to control. The position control of single PMA is studied with PID and fuzzy PID control algorithms, and experiments show that the control fuzzy PID algorithm is obviously effective and the precision of position control reaches a high degree. Furthermore, the position control of the humanoid robot wrist is also carried out to testify the correctness of the analysis of the mechanism. With control of the four PMA, the platform of the wrist can be successfully driven to any position of its workspace. The track programming is also deeply investigated in the paper and a circle track is done to demonstrate the track programming.