Kinematic and quasi-static analysis model of a novel variable stiffness pneumatic artificial muscle

Abstract

A novel variable stiffness axial expansion pneumatic artificial muscle based on hexagonal origami is proposed. Based on the presented assumptions, a kinematic analysis model of the pneumatic artificial muscles is presented, and the changes in crease angles, air cavity volume and geometric configurations of the pneumatic artificial muscles during the actuation process are obtained. The equivalent elastic modulus of the hyperelastic material is obtained by fitting the stress-strain curve. The stress state of the crease is simplified as the pure bending model of a straight beam, and the rotational stiffness of the crease is formulated. Based on the energy method, a quasi-static characteristic analysis model of the pneumatic artificial muscles is developed. The pressure-displacement curve under the unloading state and the output force-displacement curve under the loading state are calculated. The variable stiffness characteristics of the pneumatic artificial muscles are evaluated. Compared with the experimental and numerical simulation results, the analysis models are verified. The work will provide analysis models for the mechanical design and force-displacement control of this type of pneumatic artificial muscles.