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.
KEYWORDS: Digital signal processing, Actuators, Analog electronics, Control systems, Ferroelectric materials, Signal processing, Feedback control, Digital filtering, Computer programming, Data acquisition
We have designed and tested a new digital signal processor (DSP)-based closed-loop feedback controller for a linear actuator system with sub-angstrom resolution and 15-mm travel range. The linear actuator system consists of a laser Doppler encoder with multiple-reflection optics , a high-stiffness weak-link mechanism with high driving sensitivity and stability , and a Texas Instruments TMS320C40 DSP-based controller for high-performance closed-loop feedback control. In this paper, we discuss the DSP-based controller design, as well as recent test results yielding step sizes below 50 picometers obtained with the atomic force microprobe setup.