  Pneumatic systems are common in manufacturing, healthcare, transportation,
robotics, and many other fields. Failures in these systems can have very
serious consequences, particularly if they go undetected. In this work, we
present an air-powered error detector device that can detect and respond to
failures in pneumatically actuated systems. The device contains 21 monolithic
membrane valves that act like transistors in a pneumatic logic "circuit" that
uses vacuum to represent TRUE and atmospheric pressure as FALSE. Three
pneumatic exclusive-OR (XOR) gates are used to calculate the parity bit
corresponding to the values of several control bits. If the calculated value of
the parity bit differs from the expected value, then an error (like a leak or a
blocked air line) has been detected and the device outputs a pneumatic error
signal which can in turn be used to alert a user, shut down the system, or take
some other action. As a proof-of-concept, we used our pneumatic error detector
to monitor the operation of a medical device, an intermittent pneumatic
compression (IPC) device commonly used to prevent the formation of
life-threatening blood clots in the wearer's legs. Experiments confirm that
when the IPC device was damaged, the pneumatic error detector immediately
recognized the error (a leak) and alerted the wearer using sound. By providing
a simple and low-cost way to add fault detection to pneumatic actuation systems
without using sensors, our pneumatic error detector can promote safety and
reliability across the wide range of pneumatic systems.
