THE VELOCIPROBE: PUSHING THE LIMITS WITH FAST AND ROBUST CONTROL

摘要

The Advanced Photon Source Upgrade (APS-U) at Argonne National Laboratory (ANL) will be capable of producing X-rays 100 times brighter than the present APS. X-ray microscopy with the high-flux X-rays of the APS-U requires fast and robust scanning capability of the X-ray zone plate optics. The control algorithm presented in this article enables the microscope to push the resolution and bandwidth limits by solving an optimization problem that incorporates the closed-loop objectives of large tracking bandwidth, good positioning resolution, robust stability to unmodeled dynamics, good disturbance rejection and adequate noise attenuation. Shorter scanning time and increased X-ray imaging resolution can be achieved with the proposed control algorithm. Up to 190% and 180% improvement in positioning resolution was achieved with H_∞ controllers for both scanning modes; in first mode the measured zone-plate stage displacement and in the second mode the measured relative displacement between the zone-plate and sample stage being the controller feedback, respectively, compared to the open loop.