The figure shows parts of a shutter mechanism designed to satisfy a number of requirements specific to its original intended application as a component of an atomic clock to be flown in outer space. The mechanism may also be suitable for use in laboratory and industrial vacuum systems on Earth for which there are similar requirements. The requirements include the following:
- To alternately close, then open, a 1.5- cm-diameter optical aperture twice per second, with a stroke time of no more than 15 ms, during a total operational lifetime of at least a year;
- To attenuate light by a factor of at least 1012 when in the closed position;
- To generate little or no magnetic field;
- To be capable of withstanding bakeout at a temperature of 200 °C to minimize outgassing during subsequent operation in an ultrahigh vacuum; and
- To fit within a diameter of 12 in. (305 mm) — a size limit dictated by the size of an associated magnetic shield.
The light-attenuation requirement is satisfied by use of overlapping shutter blades. The closure of the aperture involves, among other things, insertion of a single shutter blade between a pair of shutter blades. The requirement to minimize the magnetic field is satisfied by use of piezoelectric actuators. Because piezoelectric actuators cannot withstand bakeout, they must be mounted outside the vacuum chamber, and, hence, motion must be transmitted from the actuators to the shutter levers via a vacuum-chamber-wall diaphragm.
The mechanism inside the vacuum chamber must be fabricated in one piece to eliminate pockets from which trapped gas could later escape, ruining the ultrahigh vacuum. The smallness of the displacement produced by the piezoelectric actuators gives rise to a need for mechanical amplification of the stroke by a factor of about 700. The requirement for mechanical amplification is satisfied by use of two pairs of lever arms that are mirror images of each other. The requirement for one-piece construction dictates the use of flexures, instead of bearings, to accommodate the pivoting of the levers.
The piezoelectric actuators, which are also mirror images of each other, are mounted outside the vacuum system (underneath the frame shown in the figure), where they are connected to the lower ends of the lower levers. The upper ends of the lower levers are coupled to the upper ends of the upper levers through a cross-coupled flexing intertie, which is also connected to supports to fix the pivot locations and to hold the diaphragm against atmospheric pressure. The shutter blades are mounted on the lower ends of the upper levers.
This work was done by Robert Glaser and Robert Bamford of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Mechanics category.
NPO-40394
This Brief includes a Technical Support Package (TSP).
Piezo-Operated Shutter Mechanism Moves 1.5 cm
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Overview
The document outlines the technical details and development of a Piezo-Operated Shutter Mechanism, specifically designed for NASA's PARCS (Photonics Atomic Reference Clock System) project. This innovative device is engineered to block a 1.5 cm diameter opening and actuates in the 10 ms time range, utilizing piezoelectric technology to minimize magnetic fields, which is crucial for sensitive applications like atomic clocks.
The mechanism operates through a complex system of levers and diaphragms. It employs a double lever design that requires approximately 700 times motion magnification due to the small stroke of the piezo actuators. The device activates two pairs of piezos in a mirror-symmetric configuration, allowing for precise control and operation. The lower levers are connected to upper levers via a cross-coupled intertie, which is also supported by surrounding structures to maintain stability against atmospheric pressure. The shutter blades, responsible for blocking light, are positioned at the opposite end of the upper lever from the intertie.
The document also discusses the operational capabilities of the shutter mechanism, which can actuate twice per second for an entire year, making it suitable for long-term applications. The design's mirror symmetry helps prevent unwanted excitation of large motion modes during launch, ensuring reliability in space environments.
In terms of development status, the hardware was built and delivered around the start of the last fiscal year, with the first full operation occurring in October. Life testing is scheduled to begin in December. The technology is still in the prototype stage and requires further optimization for flight packaging.
The motivation behind this innovation stems from the need to attenuate laser light by 12 orders of magnitude to protect sensitive components in the PARCS clock. The document emphasizes that while this technology is a significant advancement, it has not yet been commercialized or utilized outside of NASA's Jet Propulsion Laboratory.
Overall, the Piezo-Operated Shutter Mechanism represents a critical advancement in aerospace technology, with potential applications in various fields requiring precise light control and minimal magnetic interference.
