Foldable flex joint actuator with ultralow operating air pressure

Pneumatic joint actuators are essential components in robotic systems, enabling soft robots to replicate natural movements observed in animals and humans, such as grasping, walking, and swimming, by generating rotation deformations through pneumatic actuation. However, conventional joint actuators typically require high operating pressures (≥5 kPa), which result in complex system architectures and high energy consumption. This study introduces a novel pneumatic joint actuator inspired by the folding membrane structures found in spider hydraulic joints. This foldable flex joint actuator integrates two elastic air chambers with a folding membrane structure, where the expansion of the folding membrane drives the elastic chambers’ deformation, enabling efficient rotational motion under ultralow operating pressures. Through finite element simulations and orthogonal optimization, the actuator achieves an ultra-wide operating pressure range of 0.5–20 kPa. It demonstrates rotational capability at an exceptionally low pressure of 0.5 kPa, delivers an output force of 9 N at 20 kPa and has effective service life of over 41,000 cycles. Furthermore, this actuator achieves a rotation angle density of 8.8°/kPa and a force density of 17.28 mN/(mm³·MPa), substantially outperforming traditional flexible joint actuators. Additionally, grasping experiments were conducted to validate the actuator's functionality, showcasing its performance and significant potential for practical applications in robotics.