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Nanometer Positional Control using Magnetic Suspension for Vacuum-to-Air Mass Metrology



Nicholas A. Vlajic, Melissa L. Davis, Corey A. Stambaugh


This paper explains the control scheme that is to be used in the Magnetic Suspension Mass Comparator, an instrument designed to directly compare mass artifacts in air to those in vacuum, at the United States National Institute of Standards and Technology. More specifically, the control system is used to apply a magnetic force between two chambers to magnetically suspend mass artifacts, which allows for a direct comparison (i.e., a calibration) between the mass held in air and a mass held in vacuum. Previous control efforts, which have been demonstrated on a proof-of-concept of this system, used PID-based control with measurements of the magnetic field as the control signal. Here, we implement state-feedback control using a laser interferometric displacement measurement with a noise floor of approximately 5 nm (root-mean-square). One of the main challenges in this system is that, in order to achieve the necessary accuracy, the suspension system is mounted onto the end of an unconstrained pendulum of approximately 1 m length and gravity is the only restoring force in the lateral direction. The results presented here demonstrate an improvement from previously reported results wherein the control strategy utilized magnetic field measurements and a PID- based control scheme.
Journal of Dynamic Systems Measurement and Control-Transactions of the ASME


State-feedback, vacuum-to-air mass metrology, magnetic suspension
Created July 2, 2018, Updated November 10, 2018