An Adaptive Multi-Population Approach for Sphericity Error Evaluation in the Manufacture of Hemispherical Shell Resonators.

The performance of a hemispherical resonant gyroscope (HRG) is directly affected by the sphericity error of the thin-walled spherical shell of the hemispherical shell resonator (HSR). In the production process of the HSRs, high-speed, high-accuracy, and high-robustness requirements are necessary for evaluating sphericity errors. We designed a sphericity error evaluation method based on the minimum zone criterion with an adaptive number of subpopulations. The method utilizes the global optimal solution and the subpopulations' optimal solution to guide the search, initializes the subpopulations through clustering, and dynamically eliminates inferior subpopulations. Simulation experiments demonstrate that the algorithm exhibits excellent evaluation accuracy when processing simulation datasets with different sphericity errors, radii, and numbers of sampling points. The uncertainty of the results reached the order of 10-9 mm. When processing up to 6000 simulation datasets, the algorithm's solution deviation from the ideal sphericity error remained around -3 × 10-9 mm. And the sphericity error evaluation was completed within 1 s on average. Additionally, comparison experiments further confirmed the evaluation accuracy of the algorithm. In the HSR sample measurement experiments, our algorithm improved the sphericity error assessment accuracy of the HSR's inner and outer contour sampling datasets by 17% and 4%, compared with the results given by the coordinate measuring machine. The experiment results demonstrated that the algorithm meets the requirements of sphericity error assessment in the manufacturing process of the HSRs and has the potential to be widely used in the future.

Single-slice rebinning reconstruction method for segmented helical computed tomography.

Recently, to easily extend the helical field-of-view (FOV), the segmented helical computed tomography (SHCT) method was proposed, as well as the corresponding generalized backprojection filtration (G-BPF) type algorithm. Similar to the geometric relationship between helical and circular CT, SHCT just becomes full-scan multiple source-translation CT (F-mSTCT) when the pitch is zero and the number of scan cycles is one. The strategy of G-BPF follows the idea of the generalized Feldkamp approximate cone-beam algorithm for helical CT, i.e., using the F-mSTCT cone-beam BPF algorithm to approximately perform reconstruction for SHCT. The image quality is limited by the pitch size, which implies that satisfactory quality could only be obtained under the conditions of small pitches. To extend the analytical reconstruction for SHCT, an effective single-slice rebinning (SSRB) method for SHCT is investigated here. Transforming the SHCT cone-beam reconstruction into the virtual F-mSTCT fan-beam stack reconstruction task with low computational complexity, and then some techniques are developed to address the challenges involved. By using the basic BPF reconstruction with derivating along the detector (D-BPF), our experiments demonstrate that SSRB has fewer interlayer artifacts, higher z-resolution, more uniform in-plane resolution, and higher reconstruction efficiency compared to G-BPF. SSRB could promote the effective application of deep learning in SHCT reconstruction.

Analytical reconstructions of full-scan multiple source-translation computed tomography under large field of views.

This paper is to investigate the high-quality analytical reconstructions of multiple source-translation computed tomography (mSTCT) under an extended field of view (FOV). Under the larger FOVs, the previously proposed backprojection filtration (BPF) algorithms for mSTCT, including D-BPF and S-BPF (their differences are different derivate directions along the detector and source, respectively), make some errors and artifacts in the reconstructed images due to a backprojection weighting factor and the half-scan mode, which deviates from the intention of mSTCT imaging. In this paper, to achieve reconstruction with as little error as possible under the extremely extended FOV, we combine the full-scan mSTCT (F-mSTCT) geometry with the previous BPF algorithms to study the performance and derive a suitable redundancy-weighted function for F-mSTCT. The experimental results indicate FS-BPF can get high-quality, stable images under the extremely extended FOV of imaging a large object, though it requires more projections than FD-BPF. Finally, for different practical requirements in extending FOV imaging, we give suggestions on algorithm selection.

Discrete fringe phase unwrapping algorithm based on Kalman motion estimation for high-speed I/Q-interferometry.

A discrete fringe phase unwrapping algorithm (DFPUA) based on Kalman motion estimation is proposed to accurately demodulate the phases of I/Q-interferometers with deeply under-sampled quadrature signals, thus to break through the limitations of the Nyquist frequency for high-speed measurement. The basic concept of DFPUA is to estimate the current displacement according to the former motion state, then confirm the actual phase integer number by comparing the estimated phase decimal with the actual phase decimal; in this way, peak acceleration/jerk instead of peak velocity becomes the factor that determines the sampling rate. Two types of DFPUA including velocity estimation and velocity-acceleration estimation are illustrated in detail. Simulation experiment results indicate that the DFPUA realizes a significant reduction in the sampling rate and the amount of data for low frequency vibration measurement, proposing a practical approach for high-speed and long-time measurement such as ultra-low frequency vibration calibration.

Velocity feedback control method of low-frequency electromagnetic vibration exciter based on Kalman filter estimation.

The absence of an appropriate low-frequency vibration velocity detection method to establish feedback control limits the further improvement of the low-frequency vibration performance of electromagnetic vibration exciters. In this article, a low-frequency vibration velocity feedback control method based on the Kalman filter estimation is proposed for the first time to reduce the total harmonic distortion of the vibration waveform. The rationality of establishing velocity feedback control in the velocity characteristic band of the electromagnetic vibration exciter is analyzed. Based on an identification model of the system and measured vibration displacements, the vibration velocity is estimated with high accuracy through the Kalman filter. The velocity feedback control system is established to suppress the impacts of disturbances effectively. Experimental results show that the method proposed in this paper can reduce the harmonic distortion of vibration waveform by 40%, which is 20% higher than the traditional control method, thoroughly verifying its superiority.