Pneumatic Bellows Muscles Contracting by Positive Pressure

We propose a pneumatic bellows muscle, a rigid, foldable origami bellows mechanism composed of plates and hinges that contracts through air pressure. While various pneumatic artificial muscles have been developed for contraction motion, their power output has been limited by dead space, the use of soft materials, and geometric constraints. Specifically, traditional designs tend to either expand spherically under pressure or require thick cylindrical shapes before pressurization, both of which reduce efficiency and compactness. In this study, we build on two previously proposed rigid origami structures—the Rigid Origami Tube and the Zipper Tube—to achieve high power and compact actuation by utilizing pressurized inner chambers. Geometrical analysis of their kinematics predicted contraction ratios of 23.9% and 29.3% for the Rigid Origami Tube and Zipper Tube, respectively. The experimental result of the first prototype showed a maximum contraction ratio of 8.6%, attributed to plate deformation, hinge resistance, and fabrication limitations, which restricted smooth folding and reduced contraction performance. These findings highlight the need for further improvements in structural rigidity and hinge design to minimize deformation and enhance contraction efficiency under pressure. Future work will focus on optimizing material selection, improving manufacturing methods, and developing design strategies that align geometric parameters with performance requirements. By addressing these challenges, the bellows muscle has the potential to become a tough, compact, and high-performance solution for fluid-driven actuation in soft robotics.