Power-free shape retention of soft pneumatic actuators via snap-through multistability

Shape retention in soft pneumatic robots without continuous power input reduces energy cost and prevents unexpected collapse through puncture or burst. Existing pneumatic actuation methods cannot achieve state locking for deformation combining both extension and bending, a common operational mode of soft robots. In this work, a design paradigm is introduced to develop a soft pneumatic actuator that can retain its shape with no energy cost during both extension and bending. The key mechanism involves integrating a pneumatic transmitter and a multistable guider, whose interaction is instrumental to attain flexural and extensional lockability, a functionality unachievable by employing either of the two alone. This work sheds light onto the existence of four distinct regimes of deformation. The actuator constituents first interact during inflation to deform into locked extension and bending configurations, and then cooperate under vacuum to return to the initial state for fully reversible functionality. The strategy is applied to design a soft robotic arm capable of locking at programmable curvature states at zero-power, and a gripper that safely grasps and holds fragile objects of various shapes and sizes with puncture resistance.