Active damping and disturbance rejection control of a six-axis magnetic levitation stage.

This paper presents the design and application of a novel active damping and disturbance rejection controller for a magnetic levitation stage. Feedback linearization, based on the rigid-body dynamics of the levitated stage, and force distribution, based on a time-varying force distribution matrix that takes six-axis motion of a floater into account, are adopted to establish a decoupled and linearized dynamics between the six inputs and the six-axis motion. By integrating an augmented state estimator that provides full state and disturbance estimation, a linear controller that provides active damping for each axis is designed, providing the whole controller with active damping and disturbance rejection capability. In addition, the parameters of the designed controller can be easily selected based on the desired damping and natural frequency, while the parameters of the augmented estimator can be determined according to the desired estimator bandwidth and first system resonance, which make the parameter tuning have a clear physical meaning. Finally, the designed controller was implemented in a field programmable gate array-based control system. Experimental results of the proposed controller and comparison with the previously designed controller are provided to illustrate the feasibility and effectiveness of the designed control algorithm.

Automated MicroSPECT/MicroCT Image Analysis of the Mouse Thyroid Gland.

BACKGROUND: The ability of thyroid follicular cells to take up iodine enables the use of radioactive iodine (RAI) for imaging and targeted killing of RAI-avid thyroid cancer following thyroidectomy. To facilitate identifying novel strategies to improve 131I therapeutic efficacy for patients with RAI refractory disease, it is desired to optimize image acquisition and analysis for preclinical mouse models of thyroid cancer. METHODS: A customized mouse cradle was designed and used for microSPECT/CT image acquisition at 1 hour (t1) and 24 hours (t24) post injection of 123I, which mainly reflect RAI influx/efflux equilibrium and RAI retention in the thyroid, respectively. FVB/N mice with normal thyroid glands and TgBRAFV600E mice with thyroid tumors were imaged. In-house CTViewer software was developed to streamline image analysis with new capabilities, along with display of 3D voxel-based 123I gamma photon intensity in MATLAB. RESULTS: The customized mouse cradle facilitates consistent tissue configuration among image acquisitions such that rigid body registration can be applied to align serial images of the same mouse via the in-house CTViewer software. CTViewer is designed specifically to streamline SPECT/CT image analysis with functions tailored to quantify thyroid radioiodine uptake. Automatic segmentation of thyroid volumes of interest (VOI) from adjacent salivary glands in t1 images is enabled by superimposing the thyroid VOI from the t24 image onto the corresponding aligned t1 image. The extent of heterogeneity in 123I accumulation within thyroid VOIs can be visualized by 3D display of voxel-based 123I gamma photon intensity. CONCLUSIONS: MicroSPECT/CT image acquisition and analysis for thyroidal RAI uptake is greatly improved by the cradle and the CTViewer software, respectively. Furthermore, the approach of superimposing thyroid VOIs from t24 images to select thyroid VOIs on corresponding aligned t1 images can be applied to studies in which the target tissue has differential radiotracer retention from surrounding tissues.