A linear actuator system with 1-angstromclosed-loop control resolution and 50-milimeter travel rangeDeming Shu, Yufeng Han, Thomas S. Toellner, and Esen E. AlpAdvanced Photon SourceArgonne National Laboratory9700 S. Cass Av. Argonne, IL 60439, U.S.A.ABSTRACTWe have designed and tested a novel linear actuator system with 1-angstrom closed-loop control resolution and 50-mm travelrange.There are two major ultraprecision motion control techniques that have been applied to this actuator:· A novel laser Doppler encoder system with multiple-reflection optics.· A specially designed high-stiffness weak-link mechanism with stacked thin metal sheets having sub-angstromdriving sensitivity with excellent stability.In this paper, we present the system design and test results of this linear actuator. Applications of this new actuator systemare also discussed.Keywords: linear encoder, angular encoder, laser encoder, high resolution, actuator1. INTRODUCTIONThe Advanced Photon Source (APS) at the Argonne National Laboratory is a national user facility for synchrotron radiationresearch. The high-brilliance x-ray beams of this third-generation synchrotron radiation source provide powerful tools forforefront basic and applied research in the fields of materials science; biological science; physics; chemistry; environmental,geophysical, and planetary science; and innovative x-ray instrumentation. Instrument developers at the APS are facing manytechnical challenges. One of the challenges is to develop a state-of-the-art linear actuator system for x-ray instruments withultrahigh resolution, stability, and a large dynamic range.Since 1997, a prototype laser Doppler linear encoder (LDLE) with multiple reflections has been developed at the APS [1,2].With a customized commercial laser Doppler displacement meter (LDDM) [3], this novel linear encoder achieved sub-angstrom sensitivity in a 300-mm measuring range. The laser Doppler displacement meter is based on the principles of radar,the Doppler effect, and optical heterodyning [4]. We have chosen a LDDM as our basic system, not only because of its highresolution (2 nm typical) and high measuring speed (2 m/s) but also because of its unique performance independent ofpolarization, which provides the convenience to create a novel multiple-reflection-based optical design to attain sub-angstromlinear resolution extension.Fig. 1a. Schematic of the laser Doppler displacement measurement system.Fig. 1b. Schematic of the laser Doppler displacement measurement system with multiple-reflection optics.
