Harnessing Non-Uniform Pressure Distributions: The Next Generation of Soft Robotic Actuators

The primary goal of this work is to demonstrate how to teach a set of bladders a specific behavior - embodying code into matter. Specifically, we discuss complex motion in soft, fluid-driven actuators composed of elastomer bladders arranged around a neutral plane and connected by slender tubes is demonstrated. Rather than relying on complex feedback control or multiple inputs, the motion is generated with a single pressure input, leveraging viscous flows within the actuator to produce nonuniform pressure between bladders. Using an accurate predictive model coupling with a large deformation Cosserat rod model and low-Reynolds-number flow, all dominating dynamic interactions, including extension and curvature, are captured with two governing equations. Given insights from this model, five design elements are described and demonstrated in practice. By choosing the relative timescales between the solid, fluid, and input pressure cycles, the tip of the actuator can obtain almost any desired trajectory and can be placed anywhere temporarily within its 2D workspace. Finally, a six-legged untethered walking robot showcases the benefits of viscous-driven soft actuators. This work lays the foundation for a new class of morphologically intelligent, soft robotic appendages capable of complex deformations and multifunctionality without explicit drivers; whereby generating nonuniform pressure distributions, their infinite degrees of freedom can be exploited.