The low-power, compact valve can be used wherever valves are required in harsh environments.
The extreme conditions on Venus (460 °C and 92 atm) prevent the use of any of the existing science instruments outside of the lander. To transfer a sample into the lander, a pneumatic mechanism was conceived that could bring sample powder into the lander. The mechanism is critically dependent on the availability of valves that can operate at the conditions on Venus. The ability to perform the sample transfer will enable the use of instruments that require direct access to the sample, but cannot sustain Venus’ ambient environment.
Piezoelectric stack actuators offer effective actuation capability for operation at extreme temperatures that can be as cold as –180 °C, as on Titan and Europa, and as hot as on Venus where the temperature can be as high as 460 °C and pressure as high as 92 atm. However, even though they generate large forces, the produced displacement is small, in the micron range. To produce a compact, lightweight valve, a mechanism was developed that leverages the generated large force to create large displacement that can open and close a valve. The valve can be used for operation in pneumatic or hydraulic systems.
The valve consists of a sealed enclosure with a number of openings/ports. The port openings are controlled by a fixed seat and a moving seal disk. The disk is mounted on a cantilevered flexure beam controlled by a set of piezoelectric actuators. In passive state, the beam preloads the disk against the seat and prevents the flow through the opening/ port. When the actuators are activated, the disk is moved away from the seat and the flow through the port opening is permitted.
Two piezoelectric actuators are mounted off-axis of the cantilevered beam to create a small arm with respect to the cantilevered arm pivoting point. This way, a small displacement on the piezoelectric stacks will generate a large displacement at the free end of the cantilevered beam. The seal disk is mounted at the free end of the cantilevered beam using a set of flexures that allows for adjusting the disk misalignment with the seat resulting from large variations during actuation or extensive temperature change. The two ports of the valve are the passages that allow the flow to pass through the valve, and the seal disk controls this flow.
The materials and the flexure stiffness for each implementation should be chosen depending on each application. For example, for a Venus application, the valve’s chamber and seat are made of ceramic materials, while the lever-arm is made of high-temperature metal. The ceramic seat is the interior surface of the valve body that will contact the disk on the lever arm to form a leak-tight seal. When the disk is moved away from the seat of the entry/exit port of the valve, it opens the valve. When it is returned by the flexure on the lever, the disk comes into contact with the seat and the valve is shut. The seat always remains stationary relative to the body of the valve. The piezoelectric stack actuators are selected from piezoelectric materials with a Curie temperature high above the working temperature.
This work was done by Mircea Badescu and Yoseph Bar-Cohen of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
Mail Stop 321-123
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Refer to NPO-49276.
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