Miniature inchworm actuators that would have relatively simple designs have been proposed for applications in which there are requirements for displacements of the order of microns or tens of microns and for the ability to hold their positions when electric power is not applied. The proposed actuators would be members of the class of microelectromechanical systems (MEMS), but would be designed and fabricated following an approach that is somewhat unusual for MEMS.
Like other MEMS actuators, the proposed inchworm actuators could utilize thermoplastic, bimetallic, shape-memory-alloy, or piezoelectric actuation principles. The figure depicts a piezoelectric inchworm actuator according to the proposal. As in other inchworm actuators, linear motion of an extensible member would be achieved by lengthening and shortening the extensible member in synchronism with alternately clamping and releasing one and then the other end of the member. In this case, the moving member would be the middle one; the member would be piezoelectric and would be shortened by applying a voltage to it. The two outer members would also be piezoelectric; the release of the clamps on the upper or lower end would be achieved by applying a voltage to the electrodes on the upper or lower ends, respectively, of these members.
Usually, MEMS actuators cannot be fabricated directly on the side walls of silicon wafers, yet the geometry of this actuator necessitates such fabrication. The solution, according to the proposal, would be to use the microfabrication technique known by the German acronym LIGA - "lithographie, galvanoformung, abformung," which means lithography, electroforming, molding. LIGA involves x-ray lithography of a polymer film followed by selective removal of material to form a three-dimensional pattern from which a mold is made. Among the advantages of LIGA for this purpose are that it is applicable to a broad range of materials, can be used to implement a variety of designs, including those of structures >1 mm high, affords submicron precision, and is amenable to mass production at relatively low unit cost.
Fabrication of the proposed actuators would involve some technological risks - in particular, in the integration of electrode connection lines and placement of actuator elements. It will also be necessary to perform an intensive study of the feasibility of growing piezoelectric crystals onto LIGA molds.
This work was done by Eui-Hyeok Yang of Caltech for NASA's Jet Propulsion Laboratory.
NPO-30429
This Brief includes a Technical Support Package (TSP).
Miniature Inchworm Actuators Fabricated by Use of LIGA
(reference NPO30429) is currently available for download from the TSP library.
Don't have an account?
Overview
The document is a NASA Technical Support Package detailing the development of miniature inchworm actuators fabricated using LIGA (Lithographie, Galvanoformung, Abformung) technology. These actuators are part of a broader initiative to create ultra-lightweight space telescopes utilizing microelectromechanical systems (MEMS) technology. The primary focus is on achieving precise, stiff, and high-bandwidth actuators that can operate effectively in space environments.
The proposed inchworm actuators are designed to provide micrometer-level displacements and the ability to maintain their position without continuous power, which is crucial for applications in space where power conservation is essential. The design features a novel piezoelectric actuation mechanism, where alternating voltages are applied to the top and bottom of piezoelectric blocks, allowing for simultaneous expansion and contraction. This mechanism enables relative motion between the actuator's components, facilitating precise control over movement.
A significant advantage of these actuators is their simplified geometry compared to traditional inchworm actuators, which are typically assembled from multiple discrete parts. The new design integrates male and female piezoelectric structures that work together to achieve the desired motion, enhancing reliability and reducing manufacturing complexity.
The document emphasizes the need for further research into the feasibility of growing piezoelectric crystals onto LIGA molds and establishing effective electrode connections through silicon segments. This research is critical for optimizing the performance and manufacturability of the actuators.
The work is conducted under the auspices of the Jet Propulsion Laboratory (JPL) and is sponsored by NASA, highlighting the collaboration between government and research institutions in advancing space technology. The document also includes a disclaimer regarding the use of trade names and the lack of endorsement by the U.S. government.
In summary, this technical report outlines a promising approach to developing miniature actuators that could significantly enhance the capabilities of space telescopes and other applications requiring precise motion control. The integration of MEMS technology with innovative fabrication techniques positions these actuators as a key component in the future of aerospace engineering.
