A Hysteresis-Guided Pressure-Threshold Encoder for Soft Robots

Fluidic circuits offer an effective route to electronics-free control in soft robots. However, limited tunability of hysteresis in existing fluidic valves constrains their ability to exploit the analog characteristics of pressure inputs. As a result, many fluidic circuits rely on digital control with multiple external inputs, increasing system complexity. Here, we develop a hysteresis-guided pressure-threshold encoder (PTE) composed of hysteresis-tunable valves (HTVs) to convert a programmed pressure input into multiple digital outputs. By customizing the hysteresis behavior of the HTVs, the PTE provides a well-defined resolution for detecting variations in the input pressure. The PTE allows two modes of input-pressure programming: automated sequencing with an electronic device and manual sequencing with a mechanical pressure regulator. Integration of the PTE as an input module within digital fluidic circuits verifies its scalability and compatibility. Experimental demonstrations on soft joints and soft robotic hands confirm that the PTE enables multiactuator control using minimal inputs. Overall, this work provides an effective encoding method to reduce the number of external pressure lines from n to 2, providing a new approach for compact, electronics-free, and scalable control systems in soft robotics.