Pneumatic artificial muscles (PAMs) are an extensively investigated type of soft actuator. However, the PAM motions have been limited somewhat to uniaxial contraction and extension, restraining the development of PAMs. Given the current strong interest in soft robotics, PAMs have been gaining renewed attention due to their excellent compliance and ease of fabrication. Herein, under the inspiration of the elephant trunk, a family of bending and helical extensile PAMs (HE-PAMs)/helical contractile PAMs (HC-PAMs) was proposed and analyzed. Through both experiment and analysis, a model of generalized bending behavior of PAMs was built and developed to investigate the properties of axial, bending, and helical PAMs in the same theoretical framework. The topological equivalence and bifurcation were found in the analysis and utilized to explain the behaviors of these different PAMs. Meanwhile, a coupled constant curvature and torsion kinematics model was proposed to depict the motion of PAMs more accurately and conveniently. Moreover, a soft tandem manipulator consisting of bending and helical PAMs was proposed to demonstrate their attractive potential.
Keywords: bending; bionic; helical; kinematics; pneumatic artificial muscle; soft robotics.