Almost all pneumatic and hydraulic actuators useful for mesoscale functions rely on hard valves for control. This article describes a soft, elastomeric valve that contains a bistable membrane, which acts as a mechanical “switch” to control air flow. A structural instability—often called “snap-through”—enables rapid transition between two stable states of the membrane. The snap-upward pressure, ΔP₁ (kilopascals), of the membrane differs from the snap-downward pressure, ΔP₂ (kilopascals). The values ΔP₁ and ΔP₂ can be designed by changing the geometry and the material of the membrane. The valve does not require power to remain in either “open” or “closed” states (although switching does require energy), can be designed to be bistable, and can remain in either state without further applied pressure. When integrated in a feedback pneumatic circuit, the valve functions as a pneumatic oscillator (between the pressures ΔP₁ and ΔP₂), generating periodic motion using air from a single source of constant pressure. The valve, as a component of pneumatic circuits, enables (i) a gripper to grasp a ball autonomously and (ii) autonomous earthworm-like locomotion using an air source of constant pressure. These valves are fabricated using straightforward molding and offer a way of integrating simple control and logic functions directly into soft actuators and robots.

Significance: Soft devices offer many useful characteristics, including safe operation in close proximity to humans, the ability to adapt to their surroundings, ease of sterilization, simplicity, low cost, and light weight. Current soft devices, however, are still actuated by hard valves and electronic controls, and reliance on these components limits the use of soft devices in applications where hard structures or electronics are not compatible. This work demonstrates completely soft digital logic gates that can be integrated into soft devices and that allow computation and control within these devices, without hard valves or electronics. We demonstrate data storage, signal processing, digital-to-analog conversion, environmental sensing, and collaborative interaction between humans and soft devices.

An elastomeric device converts a constant input pressure into multiple oscillating, temporally offset output pressures.