Digital logic for soft devices

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. Although soft devices (grippers, actuators, and elementary robots) are rapidly becoming an integral part of the broad field of robotics, autonomy for completely soft devices has only begun to be developed. Adaptation of conventional systems of control to soft devices requires hard valves and electronic controls. This paper describes completely soft pneumatic digital logic gates having a physical scale appropriate for use with current (macroscopic) soft actuators. Each digital logic gate utilizes a single bistable valve—the pneumatic equivalent of a Schmitt trigger—which relies on the snap-through instability of a hemispherical membrane to kink internal tubes and operates with binary high/low input and output pressures. Soft, pneumatic NOT, AND, and OR digital logic gates—which generate known pneumatic outputs as a function of one, or multiple, pneumatic inputs—allow fabrication of digital logic circuits for a set–reset latch, two-bit shift register, leading-edge detector, digital-to-analog converter (DAC), and toggle switch. The DAC and toggle switch, in turn, can control and power a soft actuator (demonstrated using a pneu-net gripper). These macroscale soft digital logic gates are scalable to high volumes of airflow, do not consume power at steady state, and can be reconfigured to achieve multiple functionalities from a single design (including configurations that receive inputs from the environment and from human users). This work represents a step toward a strategy to develop autonomous control—one not involving an electronic interface or hard components—for soft devices.