A Bistable Valve for Pneumatic Control

Compared to traditional hard valves, soft valves are better suited to maintain the compliant morphologies of pneumatic soft robotic systems and can eliminate the need for additional electronic controls. This paper describes a novel bistable soft valve that can be triggered by both pneumatic and mechanical inputs. The valve features a truncated cone membrane with bistable characteristics, with only two stable states corresponding to "open" and "closed". When vacuum pressure or an external mechanical force is applied, the membrane buckles down which causes side-mounted tubes to kink and cut off airflow. Multiple independent tubes can be attached to a single valve, allowing simultaneous control of several pneumatic systems. The external elastic membrane allows the valve to be directly triggered by mechanical compression, expanding beyond just pneumatic activation. Finite element analysis is used to characterize the membrane’s buckling instability and experimental results demonstrate that only 2.03N mechanical force or -2.32kPa vacuum pressure is needed to trigger valve closure. Thanks to its bistable characteristic, the valve by itself can be configured as a NOT gate. When combined, these valves can perform logic operations, leading to the design of soft logic gates triggered by both pneumatic and mechanical inputs.