Static and dynamic properties of McKibben pneumatic actuator for self-stability of legged-robot motion

Abstract

A McKibben-type pneumatic actuator is widely used for utilization of its self-stabilization characteristics with a simple actuator model and a simple control method. However, how its characteristics act on the stability of robot motion have not been sufficiently discussed. The purpose of the paper is to analyze how various characteristics of McKibben pneumatic actuator (MPA) influence the stability of movements generated by MPA. In this paper, at first, we introduced two static models of the MPA which were proposed in the previous research and verified the models through validation experiments. The models of MPA form as simply as possible for a stability analysis. Next, we showed that the tension of MPA monotonically decreased according to the contraction velocity through validation experiments. Finally, the model was applied to a same simple robot model with the previous study and the stability of motions generated by the actuators was analyzed based on control theory. From the stability analysis, it was verified that the stability of the constant posture was achieved by the relatively simple static MPA model, the verified tension–velocity dependency of actuator, and the interaction with the properties of the actuator and the mechanical structure of the robot. This result suggests that the properties of MPA, particularly the verified velocity-dependent property, can contribute to the self-stability of a robot generated by the actuators, and it is important to consider the interaction between the mechanical structure and the actuator.