Entirely soft valve leveraging snap-through instability for passive flow control

Abstract

The softness and flexibility of soft robots would be greatly enhanced with more soft parts in their makeup. This paper presents an entirely soft valve that leverages the snap-through instability of an elastomeric dome for flow control. The geometric instability enables the dome to snap upward or downward, depending on the pneumatic pressure on the surface. The dome can be configured to be bistable, pseudo-biostable, or monostable in its response to the actuation pressure. As the valve changes states, the dome alternately closes and opens a top and bottom hemispherical microchannel sitting above and below the dome, exhibiting the function of a switch for flow via the channels. When used in a microfluidic droplet system, the valve acts as a pneumatic switch to control droplet formation. Droplets of various sizes are continually created by adjusting the opening time and control pressure of the valve. The soft valve can also be applied as a low-pass filter to control the actuation of a soft pneumatic actuator. When the supply pressure exceeds the critical snap-upward pressure of the valve, the air built up in the bottom chamber to induce the snapping is vented out, relieving system pressure and keeping it within safe limits. The proposed soft valve is a viable alternative to hard commercial valves that could be useful in developing totally soft robotics or soft automation systems.