We have developed a prototype instrument with a novel interferometrically controlled differential scanning stage system. The system consists of 9 DC-motor-driven stages, 4 picomotor-driven stages, and 2 PZT-driven stages. A custom-built laser Doppler displacement meter system provides two-dimensional (2D) differential displacement measurement with subnanometer resolution between the zone-plate x-ray optics and the sample holder. The entire scanning system was designed with high stiffness, high repeatability, low drift, flexible scanning schemes, and possibility of fast feedback for differential motion. Designs of the scanning stage system, as well as preliminary mechanical test results, are presented in this paper.
An optimal instrument control strategy for a dual-stage actuator system is presented. Resolution extension by signal conditioning and digital averaging techniques was implemented during the instrument design. The motion controller was developed based on robust PID (proportional-integral-derivative) algorithm and coarse/fine relay mechanism. The closed-loop residual noise and optimal dynamic performance are demonstrated by experiments.
We have designed and tested a novel linear actuator system with 1-angstrom closed-loop control resolution and 50-mm travel range. 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-Angstrom driving sensitivity with excellent stability. In this paper, we present the system design and test results of this linear actuator. Applications of this new actuator system are also discussed. -Å