A proposed "kinematic inchworm"-type linear actuator would move a mass as large as 2 kg along rails, with lengthwise position controllable in increments as small as 50 nm. The actuator could be operated in microgravity or in normal Earth gravitation and at any temperature from ambient down to cryogenic. The actuator could be used, for example, to position an optical assembly precisely on a long interferometer arm, as a translation stage for a scanning tunneling microscope, or as a translation stage for inspecting integrated-circuit chips.
The figure schematically illustrates the proposed actuator as it would be used to move a stage along two parallel outer rails. The stage would include two chassis connected lengthwise by a magnetostrictive device, which would comprise a Tb/Dy-alloy rod surrounded by a drive coil. The kinematic relationship between the outer rails and the stage would be established by free legs and alignment legs on the two chassis. A noncontact inner rail made of a magnetic material would lie between the two outer rails. Each chassis would contain an electromagnet coil above the magnetic rail; this coil could be energized to provide a clamping force and an associated frictional force that would prevent the chassis from sliding along the outer rails.
Referring to the figure, a cycle of operation to move the stage one increment of distance to the right would comprise the following steps:
- Coil 1 would be energized to clamp the left chassis in place.
- The drive coil would be energized, causing the magnetostrictive rod to lengthen slightly, thereby pushing the right chassis a short distance to the right. The power would have to be applied to the drive coil gradually enough not to generate sufficient inertial force to overcome the friction holding the left chassis in place.
- Coil 2 would be energized to clamp the right chassis in place.
- Coil 1 would be deenergized, leaving the left chassis free to slide along the rails.
- The drive coil would be deenergized, causing the magnetostrictive rod to shorten slightly, thereby pulling the left chassis to the right. At this point, both chassis would have moved one increment to the right.
The cycle could be repeated as many times as needed to move the stage a required distance to the right. By simply interchanging coils 1 and 2 in the sequence, one could obtain motion from right to left.
The size of the increment could be controlled by varying the current applied to the drive coil. Position feedback could be used for precise control of motion. For operation in a cryogenic system, it would be best if the drive and electromagnet coils were made of superconductive material to minimize waste heat. It would be especially desirable to use superconductive coils with persistent-current switches if electromagnetic clamping were to be used to hold the stage once it reached the desired final position.
This work was done by Robert Chave, Christian Lindensmith, Jennifer Dooley, Brent Fultz, and Marius Birsan of Caltech for NASA's Jet Propulsion Laboratory.For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Materials category.
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
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Refer to NPO-20272