Digital logic for soft devices

TLDR

Soft devices are rapidly entering robotics, yet fully autonomous soft systems are only just beginning to be developed and typically rely on hard valves and electronics. This paper presents completely soft pneumatic digital logic gates designed for use with current macroscopic soft actuators. Each gate employs a single bistable valve— a pneumatic Schmitt trigger based on the snap‑through instability of a hemispherical membrane—to switch internal tubes and provide binary high/low pressure inputs and outputs. The authors demonstrate NOT, AND, and OR gates that build circuits such as a latch, shift register, detector, DAC, and toggle switch, which can control a soft actuator, scale to high airflow volumes, consume no power at steady state, and be reconfigured for multiple functions, advancing autonomous soft device control without electronics.

Abstract

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.