Mechanically programmable sequential actuation of fluid-driven soft actuators

Fluid-driven actuators show great promise for robotics operating alongside human beings, for handling delicate and irregularly shaped objects, and for medical implants such as artificial muscles and even potentially heart prostheses. While soft actuators can be produced from materials that exhibit mechanical compliance close to that of human tissue, control of these actuators typically requires rigid elements such as electronic sensors, valves, and wires that may cause stress concentrations limiting the lifetime of the system. To circumvent this issue, we aim to replace the electronics by other modes of control using only soft elements that are embedded in the fluid that drives the soft actuators. Specifically, we focus on elastic hysteretic valves that allow us to program complex actuation patterns. We analyze the dynamic behavior using the electronic-hydraulic analogy and show that these circuits can deliver complex flows (e.g. pulsatile) to individual actuators, while fluidic power to the system is provided by a continuous fixed flow. We furthermore show that we can change the behavior of the soft system by varying the initial conditions, such that we can produce a soft robot that can be mechanically programmed to move using multiple gaits, without the need for electronics.