Soft kink valves

Completely soft, autonomous fluidic robots require valves made of soft materials. Such a soft valve has been demonstrated recently to enable complex movements of soft robots using a single source of air of constant pressure. This paper studies the mechanics of the valve using a combination of experiments and calculations. The valve is made of an elastomeric tube, subject to axial compression. At critical compression, the tube snaps into a kink and blocks the flow of the air in the tube. At another critical compression, the tube snaps open the kink and lets the air flow in the tube. The instability functions as a digital, on-and-off valve, and this function is unaffected by inaccurate deformation of the ends of the tube. A kinked tube blocks fluid flow in the tube up to a certain pressure. Because the elastomer readily undergoes large and reversible deformation, the kink valve can close and open repeatedly without damage. We map out the functional characteristics of the kink valve—the kink-close compression, the kink-open compression, and the breakthrough pressure—in the design space of material and geometry. It is hoped that this study will stimulate further work to harness diverse elastic instabilities for functions needed in soft robots.