Soft robots driven by soft pneumatic actuators (SPAs) are known for their low cost, high adaptability to unknown environments, and safe human-robot interaction. [1] As an emerging area, researchers have developed various SPAs with different materials, structure designs, actuation modes, pressure ranges, and fabrication procedures. [2] A basic design principle has been carried out in most of the SPAs: the actuation is achieved by mediating the interaction between pressurized air and soft elastomeric materials. The dexterity, mobility, and efficiency of a SPA ultimately depend on the control of pressure. Previously, this pressure control was achieved mainly by conventional pneumatic systems, including solenoid valves, proportional regulators, displacement pumps, syringe drivers, and electronic controllers. [3,4] These bulky and nonintegrable devices limit the performance of pneumatic-driven soft robots, carrying challenges for the robot to be miniaturized, untethered, and agile.These existing limitations motivate researchers to develop different lightweight and integrable control devices for regulating pressure in SPAs. One category is the pneumatically driven soft valves, which directly receive pneumatic signals and correspondingly regulate the pressure in the pneumatic actuators. [5] Various fabrication techniques have been used including silicone casting [5] and 3D printing. [6] These devices can be used as the pneumatic correspondent of various electronic components including transistors, diodes, [7] oscillators, logic gates, [8] digital-analog converters (DACs), [9] and digital memories. [10] Pneumatically driven soft valves bring simplicity to the system as the conversion of sensory information into electrical signals is no longer required. The soft structure also means these valves can be integrated into the robots themselves without sacrificing the overall compliance of the robots. However, these devices come with a relatively long response time (ranging from 0.5 to 1.5 s), which limits their application in control.Electrostatic effect [11] and dielectric effect [12] have also been investigated in valve designs for controlling SPAs, introducing faster response time, but require a high operation voltage. The requirement of voltage amplifiers limits their application in soft robots, especially when the robot is demanded to be untethered and miniaturized.The devices listed above work in a digital ON/OFF manner. However, recent applications of soft robots require not only binary ON/OFF control, but also proportional control on their pressure or flowrate. The ability to continuously alter the pressure or flowrate of soft robots in an analog manner provides advantages in various applications. In human-robot interaction [13] and adaptive grasping, [14] the proportional pressure control is essential for controlling the interactive force between the actuator and its environment. For soft pneumatic manipulators, [15] the proportional pressure control is the key for trajectory following. In soft-matter computing, [16]
