High Vacuum Pressure Constant-Mass Soft Origami Actuation for Passive Constant-Force Operation

This letter introduces a novel origami-inspired vacuum pneumatic actuator that operates as a passive force-generating element, capable of producing a near-constant force without active control. The actuator is fabricated from a Yoshimura-patterned film structure incorporating rigid facets and internal reinforcements, enabling large contraction strokes and consistent force output under constant vacuum conditions. A central feature of the design is its pre-vacuumed, sealed operation, which maintains stable internal pressure throughout the entire stroke without needing external pressure regulation. The combination of stable passive pressure and stable isobaric force results in a constant and passive force generated by the actuator. A numerical model based on conservation of energy and Boyle's law is presented to predict actuator behavior under both isobaric and constant-mass conditions. Experimental validation confirms the model's accuracy and demonstrates the actuator's stable force output at high constant-mass pressures. The actuator is further implemented in a wearable support suit aimed at reducing lower back strain during squatting and stooping motions. This work demonstrates a new approach for passive actuation using soft robotics principles and highlights potential applications in assistive wearable devices.