Shape Error Analysis Research Articles

Numerical analysis of a photonic crystal fiber with elliptical air hole for supporting 80 orbital angular momentum modes

• We design photonic crystal fiber with elliptical air holes, which has good orbital angular momentum transmission performance. • The influence of elliptic air hole eccentricity on photonic crystal fiber transmission performance is analyzed. • This paper provides some ideas for new photonic crystal fiber design and air hole shape error analysis. In this paper, a new photonic crystal fiber with elliptical air hole (EAH-PCF) is designed, which can support stable transmission of 80 orbital angular momentum (OAM) modes at 1550 nm. The effective refractive index differences between vector modes are all above 0.002. Most of the modes have a confinement loss between 10 −10 dB/m and 10 −8 dB/m. The effective mode area of the vector modes are all greater than 70 μm 2 and the nonlinear coefficients are all less than 1.8 W −1 /km. These properties guarantee high quality OAM. Finally, we discuss the effect of EAH’s eccentricity on the PCF. Simulations show that increasing the EAH’s eccentricity will increase the degree of separation between the vector modes, but causes a slight decrease in the quality of OAM.

Design and surface shape error analysis of synchronous radiation focusing mirror bending mechanism

基于同步辐射聚焦镜的原理，对压弯机构进行设计，对压弯理论进行介绍, 并推导了压弯镜理论面形的计算过程；根据设计理论建立了基于柔性铰链的压弯机构的模型，并对压弯机构的参数进行计算，有效长度为84.9 mm，最大力矩为259.8×10^-3 N·m。设计并校核了压弯机构，满足了压弯机构在材料力学上的要求；最后针对压弯镜存在的理论面型误差，通过对压弯镜进行有限元仿真得到模拟值，与理论值进行对比，分析了不同的因素对面型误差的影响。

Novel distortion correction method for diffusion-weighted imaging based on non-rigid image registration between low b value image and anatomical image

PurposeThis study aimed to develop a novel technique for retrospective distortion correction based on non-rigid image registration in magnetic resonance diffusion image. MethodsA 3.0 T MRI scanner with an 18-channel dedicated breast coil and the outer shell of the original breast phantom, which provided images with non-uniform fat-suppression based on clinical data were used. The diffusion-weighted imaging with and without parallel imaging (PI) was used.The proposed study included several steps, which are FOV size matching, matrix size matching, image segmentation, edge detection, non-rigid image registration, and image wrap. We compared the results obtained using the proposed method with that obtained using TOPUP images. The correlation was assessed between T1-weighted image with fat suppression (FS-T1WI) and b1000 image with the help of cross-correlation coefficient (CCC). Shape-error analysis of tumor model and apparent diffusion coefficient (ADC) was calculated. The Steel–Dwass multiple-comparison tests were used for all comparisons and statistical analysis (P < 0.05). ResultsThe novel method of CCC showed the highest correlation between FS-T1WI and b1000 images. In the Steel–Dwass multiple-comparison test, significant differences were found (P < 0.05) except between non-correction and TOPUP (P = 0.99).The novel method was the lowest degree of error. With PI in the right breast, no significant differences, whereas in the left breast, significant differences were observed except for between novel method and TOPUP (P = 0.73). Without PI in the right breast, significant differences were observed. In the left breast, no significant differences were observed between any combinations.The ADC value, no significant differences were observed for non-correction and novel methods. ConclusionsWe developed a novel technique for retrospective distortion correction based on non-rigid image registration. The high degree of accuracy of this method combined with the lack of requirement for additional scans renders it a promising tool for application in clinical practice.

Shape Error Analysis of Functional Surface Based on Isogeometrical Approach

The construction of traditional finite element geometry (i.e., the meshing procedure) is time consuming and creates geometric errors. The drawbacks can be overcame by the Isogeometric Analysis (IGA), which integrates the computer aided design and structural analysis in a unified way. A new IGA beam element is developed by integrating the displacement field of the element, which is approximated by the NURBS basis, with the internal work formula of Euler-Bernoulli beam theory with the small deformation and elastic assumptions. Two cases of the strong coupling of IGA elements, “beam to beam” and “beam to shell”, are also discussed. The maximum relative errors of the deformation in the three directions of cantilever beam benchmark problem between analytical solutions and IGA solutions are less than 0.1%, which illustrate the good performance of the developed IGA beam element. In addition, the application of the developed IGA beam element in the Root Mean Square (RMS) error analysis of reflector antenna surface, which is a kind of typical functional surface whose precision is closely related to the product’s performance, indicates that no matter how coarse the discretization is, the IGA method is able to achieve the accurate solution with less degrees of freedom than standard Finite Element Analysis (FEA). The proposed research provides an effective alternative to standard FEA for shape error analysis of functional surface.

An Improved Edge Extraction Algorithm for Lithography Micrographs

For shape error analysis and correction of micro-structure in lithography, image edges should be extracted from micrographs of the structures. First several basic image edge detection algorithms are analyzed and compared. Then according to the unique conditions of micrographs in lithography experiments, an improved image edge extraction method is investigated. In this method Canny operator is selected as a basic algorithm, while the mathematical morphology is used in pre-processing for de-noising to reduce the uneven phenomenon. And an appropriate enhancement algorithm is used to enhance image contrast. Experimental results show that this method can extract the image edge from the micro-structure graphs effectively.

Numerical Investigation on the Process of Multi-Point Holder Forming for Titanium Mesh Sheet

Multi-point holder forming (MPHF) adopts series of coupled holder punches, arranged between forming punches, to clamp the whole sheet in the forming zone. The multi-point holder forming processes of spherical parts of titanium mesh plate were simulated by finite element code, and the results were compared with those of multi-point die forming (MPDF). The influence of holder punch load on the deformation of spherical part in multi-point holder forming was investigated. The shape error analysis of titanium mesh formed by MPHF was performed in finial. The results showed that the spherical part had more excellent performance in multi-point holder forming, and the more deformation the titanium mesh was, the larger force of holder punch would be needed. In addition, there was a small shape error for titanium mesh part formed by MPHF before springback.

Optimal shape error analysis of the matching image for a free-form surface

When using an optical non-contact scanning system to measure an object that has a large surface, large curvature, or a full 360° profile, one can acquire only one set of sectional measurement points each time. For reconstructing the entire object, every set of sectional measurement points acquired at different positions must match. Therefore, the optimal shape error analysis for the matching image of two or more sets of sectional measurement points is desired. This paper presents a measurement system that combines two CCD cameras, one line laser and a three-axis motion stage. It forms an optical non-contact scanning system in association with the mathematical method of direct shape error analysis for the use in reverse engineering. This analysis and measurement system can be used for the profile measurements of free-form objects. It analyzes the matching image of a free-form surface with high efficiency and accuracy. The validity and applicability of this system are demonstrated by two practical examples.

CAD-Directed Inspection, Error Analysis and Manufacturing Process Compensation Using Tricubic Solid Databases

This paper describes the use of a tricubic solid cell database for representing solid part geometry, generating machine motion, and compensating manufacturing processes for enhancing final part shape accuracy capability. It is shown how basic motion generation, shape error analysis, and shape fitting building blocks can be combined with the database to create systems for CAD-directed inspection, geometric error analysis, machining, and surface grinding. The integration of databases, sensors, motion generation, geometric analysis, and process compensation in these systems leads to new opportunities for producing accurate part shapes.