Manufacturing Accuracy Research Articles

Фотонные кристаллы: оптимизация характеристик и перспективы оптических приложений

Background: Photonic crystals (PCs) have emerged as a new material for light manipulation, providing unprecedented control over light-matter interaction. This unique capacity is due to their periodic dielectric structure, which may produce photonic band gaps that impact photon transmission. Objective: The article summarizes current advances in photonic crystal design and use, focusing on their significance in creating next-generation optical systems. Methods: The article performed a complete literature analysis, concentrating on the most recent PC production and characterization approaches. Innovative techniques like 3D printing, nanoimprint lithography, self-assembly, and advanced computational modelling were studied in depth to optimize their optical characteristics. Results: Recent studies show that PC manufacturing accuracy has increased significantly, allowing for more effective light manipulation and enhanced optical device functioning. Applications such as ultrasensitive sensors, improved optical fibers, and innovative laser designs demonstrate PCs' rising value. Conclusion: The ongoing advancement of photonic crystal technology is laying a solid basis for the next generation of optical devices. These developments improve existing applications and provide opportunities to investigate new functionality in optical and other electromagnetic systems. Incorporating PCs into numerous technical sectors holds the prospect of significant advances in both commercial and scientific fields.

Fabrication of Circular Defects in 2-Dimensional Photonic Crystal Lasers with Convex Edge Structure

We have developed circular defects in 2-dimensional photonic crystal lasers that allow current injection for interconnected optical communications. However, when cleaving the sample to measure the output light, the output light intensity changes due to the cleaving position. In a previous study, we proposed a new end face structure called a convex edge structure. In this paper, we design the electron beam lithography patterns to fabricate this structure. With this design, it is possible to eliminate the effect of different cleaving positions and ensure that the cleavage tolerance is larger than the cleavage position error. We also develop the fabrication technology for this structure, fabricate samples, and measure the output light experimentally. The optical properties of the fabricated sample are similar to well-fabricated samples with normal cleavage edge faces. We are assured that these results contribute to future work such as accurate manufacturing and improving the end face configuration to obtain higher outputs.

In vitro comparison of guide planes for removable partial dentures prepared with CAD-CAM-assisted templates, guiding rod templates, and freehand

ObjectivesThis study aimed to evaluate the accuracy of computer-aided design and computer-aided manufacturing (CAD-CAM)-assisted templates (CCAT), guiding rod templates (GRT), and freehand (FH) preparation of guide planes. MethodsForty-five identical maxillary resin casts were divided into three groups, in which the guide planes of the two abutment teeth were prepared using a CCAT (n=15), GRT (n=15), and FH (n=15). The CCAT and GRT were digitally designed on a digital cast of virtually prepared guide planes and fabricated using three-dimensional printing (3DP) technology. To assess the 3D trueness, the prepared guide planes were digitally scanned and compared to the virtually designed guide planes. The angle deviation was measured to assess the trueness of the direction of the guide plane preparation. Shapiro–Wilk and Levene's tests were used to check the normality and equivalence of the variance of the data. The data were compared by using the Kruskal‒Wallis H test (α=0.05). ResultsThe CCAT group exhibited significantly better 3D trueness (78.5±19.8 μm) than the GRT group (211.3±42.4 μm, p<0.05) and the FH group (198.9±44.3 μm, p<0.05). Additionally, the CCAT group (1.31±0.50°) showed significantly smaller direction trueness compared to the GRT (4.65±0.72°, p<0.05) and FH (5.64±0.70°, p<0.05) groups. ConclusionsThe novel CAD-CAM-assisted template significantly improved the quality of the guide planes compared with the GRT and FH procedures. This enhancement suggests that removable partial dentures can be predictably inserted immediately after guide plane preparation. Clinical SignificanceCAD-CAM-assisted templates improve the quality of guide plane preparation.

Analysis and Verification on Buckling Mechanism of Spatial Tow Steering in Automated Fiber Placement

Automated fiber placement (AFP) enables the efficient and precise fabrication of complex-shaped aerospace composite structures with lightweight and high-performance properties. However, due to the excessive compression on the inner edge of the tow placed along the curved trajectory, the resulting defects represented by buckling and wrinkles in spatial tow steering can induce poor manufacturing accuracy and quality degradation of products. In this paper, a theoretical model of tow buckling based on the first-order shear deformation laminate theory, linear elastic adhesion interface and Hertz compaction contact theory is proposed to analyze the formation mechanism of the wrinkles and predict the formation of defects by solving the critical radius of the trajectory, and finite element analysis involving the cohesive zone modeling (CZM) is innovated to simulate the local buckling state of the steered tow in AFP. Additionally, numerical parametric studies and experimental results indicate that mechanical properties and geometric parameters of the prepreg, the curvature of the placement trajectory and critical process parameters have a significant impact on buckling formation, and optimization of process parameters can achieve effective suppression of placement defects. This research proposes a theoretical modeling method for tow buckling, and conducts in-depth research on defect formation and suppression methods based on finite element simulation and placement experiments.

Maschinelles Lernen als modernes Werkzeug für Additive Fertigung

Abstract In modern manufacturing systems, quality monitoring is crucial for efficient and cost-effective production. Conventional systems rely on thresholds and process windows, but machine learning (ML) techniques promise greater accuracy and efficiency. However, pre-processing the data is still timeconsuming. This paper presents an approach to visually verify two Variational Autoencoders (VAEs) using contextual information such as print job numbers and timestamps, with the aim of predicting time series data from image data to optimize additive manufacturing processes in time. The approach focuses on the Digital Light Processing (DLP) printing process and emphasizes the importance of accurate data pre-processing and contextual visualization. The approach utilizes VAE-generated latent spaces to improve prediction accuracy in additive manufacturing and implement quality monitoring without thresholds and process windows.

FreeArcs Knife: a Novel Stereotactic Radiosurgery System

This paper describes the design of an innovative linear accelerator image-guided radiosurgery (IGRS) device, which is based on a composite twofold rotary gantry structure. The paper discusses five aspects of the innovative device: its overall composition, the safety net space created by the accelerator radiation head as it rotates around the patient's longitudinal axis, the non-coplanar spherical coverage in the direction of the incidence angle for quasi-4π delivery, the structural features of the composite twofold rotary gantry, and the processes of treatment planning and implementation. It elaborates on the device's manufacturing feasibility, safety, effectiveness, accuracy, and efficiency. The conclusion is that this innovative device design holds significant development value and market promotion potential.

Trueness and precision of digital light processing fabricated 3D printed monolithic zirconia crowns

ObjectivesThe present study aimed to evaluate the trueness and precision of monolithic zirconia crowns (MZCs) fabricated by 3D printing and milling techniques. MethodsA premolar crown was designed after scanning a prepared typodont. Twenty MZCs were fabricated using milling and 3D-printing techniques (n = 10). All the specimens were scanned with an industrial scanner, and the scanned data were analyzed using 3D measurement software to evaluate the trueness and precision of each group. Root mean square (RMS) deviations were measured and statistically analyzed (One-way ANOVA, Tukey's, p ≤ 0.05). ResultsThe trueness of the printed MZC group (140 ± 14 μm) showed a significantly higher RMS value compared to the milled MZCs (96 ± 27 μm,p < 0.001). At the same time, the precision of the milled MZCs (61 ± 17 μm) showed a significantly higher RMS value compared to that of the printed MZCs (31 ± 5 μm,p < 0.001). ConclusionsThe Fabrication techniques had a significant impact on the accuracy of the MZCs. Milled MZCs showed the highest trueness, while printed MZCs showed the highest precision. All the results were within the clinically acceptable error values. Clinical SignificanceAlthough the trueness of the milled MZCs is higher, the manufacturing accuracy of the 3D-printed MZCs showed clinically acceptable results in terms of trueness and precision. However, additional clinical studies are recommended. Furthermore, the volumetric changes of the material should be considered.

Testing of spherical mirrors with extremely large R numbers using a quasi-autocollimation method

Spherical mirrors with large R numbers have extreme advantages in optical systems with large apertures and long focus lengths for improving imaging resolution and field of view. Their manufacturing and testing accuracy directly affects the final wavefront aberration of the systems. However, due to the influence of airflow disturbance in the long optical path, testing large R number spherical mirrors with high precision is difficult for the direct testing method. In this paper, a quasi-autocollimation test (QACT) method is proposed based on the consistency and reverse compensation between sphere and paraboloid with large R numbers. In QACT, the length of the testing path is reduced to half, and the test sensitivity of the surface figure error is doubled. According to the Kolmogorov turbulence theory, the suppressed degree of QACT to airflow disturbance is quantitatively evaluated, and QACT can suppress the random error in test to 35%. A comparative experiment between direct test and QACT method is carried out on a ∅100 spherical mirror with 8-meter radius of curvature. Airflow disturbance in the testing environment is calculated by mathematical fitting and the repeated accuracy is improved from 4 nm to 1.4 nm in a single test using the QACT method, which is consistent with theoretical analysis. The research results will provide a new strategy for ultra-precision and efficiency tests of large R number spherical mirrors.

Process development and validation of next generation 3D calibration standards for application in optical microscopy

Abstract A scalable wafer-based fabrication process for a new generation of 3D standards enabling the 3D calibration of optical microscopes is presented and validated. The 3D standards are based on step pyramids with several layers in the µm range and a system of cylindrical knops distributed across the layers as marks for coordinate based calibration. This enables calibration for the three coordinate axes and the orthogonality error between them in a single measurement step. The requirements necessary for such a calibration, as optical non-transparency, reproducible flatness of the pyramid step heights and the lowest possible deviations of the lateral marks coordinates, are met by optimizing the manufacturing process: The deviation of the height steps distributed over the wafer is ±3.6 nm and is primarily caused by the layer deposition processes. The lateral manufacturing accuracy was determined using calibrated scanning electron microscope (SEM) and show a mean deviation of 20 or 60 nm, depending on the lateral size of the structures. The electron beam lithography process and the level of inaccuracy of the SEM standard have an influence on the lateral scaling accuracy. Based on the tactilely generated height values and the coordinates of the mark determined by a calibrated SEM, an example calibration of a confocal laser scanning microscope was successfully performed and showed good conformity to conventional calibration techniques.

Remote sensing monitoring of changes in forest cover in the Volyn region: a cross section for the first two decades of the 21st century

The aim of the article. This article highlights the significance of forest cover as an important indicator of the state of the environment. It discusses the findings of the Food and Agriculture Organization of the United Nations (FAO) Forest Resources Assessment (FRA) 2020 report, which states that the world's forest area has decreased by 178 million hectares since 1990. The case study of Volyn region shows how cloud processing and vegetation classification can help quantify forest dynamics from 2000 to 2020, allowing local authorities and decision makers to monitor and analyze trends in near real time. Overall, this work provides insights into the importance of monitoring forest dynamics and the potential for remote sensing technology to facilitate this process. Data &amp; Methods. Remote sensing is an effective tool for monitoring forest ecology and management, and Google Earth Engine (GEE) is an online platform that combines data from various agencies to analyze environmental data. The article presents a case study of the Volyn region and how cloud processing and vegetation classification were used to assess forest dynamics from 2000 to 2020. The study used data from Landsat 7 Collection 1 Tier 1 composites and the CART algorithm for binary decision tree building. The study was based on information provided by the Main Department of Statistics in the Volyn region on the area of forests and areas where logging was carried out during the specified period. Research results. It is interesting to note that despite the decrease in logging activities, there is an increase in forest cover loss within forest ranges. This could be due to various reasons, such as illegal logging or natural disturbances like fires or disease outbreaks. The use of machine learning methods like CART classification can help to identify and monitor these changes, which can then be used to inform policy decisions and management practices to reduce forest cover loss. In general, in the Volyn region, there is a gradual decrease in the areas where various kinds of logging are carried out from 524 km2 in 2003 to 239 km2 in 2020. In contrast, forest cover loss within forest ranges increased rapidly from 37.85 km2 in 2015 to 84.01 km2 in 2017 and beyond from 5.53 km2 to 10.80 km2 in 2015 and 2017 respectively. In this study, the accuracy assessment was performed using 30% of the control points obtained initially, based on data on the reliability of the land cover. The manufacturer's accuracy and user accuracy were calculated to evaluate error omissions and possibilities of a pixel being categorized in a certain category. The spatial resolution of Landsat 7 data used in this study was 30 m, with a minimum calculation area of 0.337 hectares. The overall accuracy and the coefficient κ are the most representative measures of accuracy, with an average accuracy of classification of OAav=98.82% and κav=0.9764.

Computer model for detecting tsunami wave hazard on built-up land using machine learning and sentinel 2A satellite imagery

&lt;p&gt;The aim of this research is to compile a tsunami wave hazard scale based on built-up land density extracted and classified by machine learning from Sentinel 2A satellite and digital elevation model (DEM) imageries. This research was carried out in 5 stages, namely: (i) pre-processing of Sentinel 2A and DEM images, (ii) Classification of VI data using the machine learning algorithms, (iii) Spatial prediction using the ordinary kriging method, (iv) Field testing using the confusion matrix method, (v) Preparation of decision matrix for tsunami wave hazard. The results of the study show that the most accurate classification algorithm for classifying built-up indices data is the k-nearest neighbor (k-NN) algorithm. The results of the statistical accuracy test show that the most accurate is normalized difference built-up index (NDBI) with a mean of square error (MSE) value of 0.073 and a mean of absolute error (MAE) of 0.003. DEM analysis shows that the research area is at an altitude of 0–15 meters above sea level so it is in the high vulnerability to medium vulnerability category. Field testing showed user accuracy of 91.11%, manufacturer accuracy of 92.16%, and overall average accuracy of 91%.&lt;/p&gt;

A Flexible and Accurate Additive Manufacturing Data Retrieval Method Based on Probabilistic Modeling and Transformation-Invariant Feature Learning

A Flexible and Accurate Additive Manufacturing Data Retrieval Method Based on Probabilistic Modeling and Transformation-Invariant Feature Learning

Secondary ion mass spectrometry helps semiconductor manufacturing

Adapting SIMS to monitor rapid thermal anneal enables more accurate and reliable semiconductor device manufacturing.

Influence of Machine Tool Operating Conditions on the Resulting Circularity and Positioning Accuracy

The operating conditions of the production process significantly influence the resulting dimensional and form accuracy of the workpiece. The operating conditions include the position of the workpiece location, with internal and external heat sources influenced not only by the machine location but also by its operation. In addition, there are the cutting conditions and the feed rate requirements of CNC machine tools. These changes, such as workpiece position, feed rates, and machine heat load, are further reflected in the ability of the machine to run at the position required and interpolate within the given tolerances of circularity. For the accuracy and repeatability of positioning, the machine was set up according to ISO 230-2 and for the circular interpolation tests according to ISO 230-4. The obtained results show the importance of attention to the appropriate setting of the operating conditions of the production process, where the knowledge of the geometric accuracy of the CNC machine tool in its working space can systematically increase the manufacturing accuracy itself or be another tool suitable for predicting the dimensional and form accuracy of workpieces.

The rotation stability of the tapered rollers in a novel ring-type lapping process

This work introduces a novel ring-type lapping method for precision machining of tapered rollers. In contrast to the conventional centerless grinding, this method allows for the simultaneous machining of a group of tapered rollers. The stable rotation of the tapered rollers during the lapping process is a prerequisite for achieving a high manufacturing accuracy. Therefore, an investigation is conducted to examine the criteria for achieving a stable rotation of the tapered rollers. First, the equilibrium equation for the tapered rollers in the lapping process was established. The stable rotation region for the tapered rollers was determined according to the stable rotation criteria. The impacts of the included angle of straight groove and the contact force of lapping sleeve on the stable rotation region were examined. The results demonstrated that the tapered roller's stable rotation can only be realized when a specific parameter combination was satisfied. Subsequently, to expand the stable rotation region, the electromagnetic driving force was introduced to enhance the lapping process. An electromagnetic lapping sleeve structure was designed according to the critical electromagnetic force required for the tapered roller's lapping process. Furthermore, the structure of the electromagnetic lapping sleeve was optimized by electromagnetic simulation in order to improve the uniformity of the electromagnetic driving force exerted on each tapered roller. Finally, the rotation movement of the tapered rollers and the critical electromagnetic forces exerted on the tapered rollers were validated on a ring-type tapered roller lapping platform. The results demonstrated that the stable rotation of the bearing rollers in the lapping process can be achieved throughout a wide range of processing parameters. The roundness of the tapered rollers was significantly improved from 0.83 μm to 0.47 μm on the stable rotation condition. This study established a solid foundation for the precision machining of tapered rollers.

Results of round robin form measurements of optical aspheres and freeform surfaces

High-quality aspherical and freeform surfaces are in high demand, and the high-accuracy form measurement of such surfaces is a challenging task. To explore the current status of form measurement systems for complex surfaces such as aspheres and freeforms, interlaboratory comparison measurements are performed. This study presents the pseudonymized results obtained using three different surfaces (metal asphere, glass asphere, toroidal surface) in a total of six different round robins. These results were taken from a total of 13 different measurement instruments based on 9 different measurement principles and operated at 12 different laboratories. They were analyzed using a sophisticated procedure that was first developed in 2018 and then refined and tested on simulated data in 2022 to address the challenges of such a comparison at this level of accuracy. In the current study, we applied these refined methods to data acquired from tactile and optical point measurements as well as from optical areal measurements. As there are no absolutely measured and very well characterized reference standard aspherical and freeform surfaces available at the accuracy level of a few tens of nanometers root-mean-square, the approximated true forms of the surfaces were derived from the measurements and indicate the manufacturing accuracy of the surface forms. Then, the measurement’s differences to the approximated true forms were analyzed, which directly indicate the systematic measurement errors of the instruments. By also comparing the approximated true forms from the two different round robins for each surface, additional insights into the reliability and stability of these so-called virtual reference topographies were gained.

Fast and accurate Zero-defect manufacturing using collaborative real-time photogrammetry

Abstract. For the machining of industrial components, their accurate alignment on operative machines is a crucial step with significant impacts on the whole process, especially when dealing with large-scale elements. To achieve this alignment, a trained operator is needed along with expensive equipment, such as laser trackers, whose correct use requires the measurements of many significant points and is time-consuming. The lack of a precise alignment comes with possible incorrect parts machining, resulting in quality concerns and potentially expensive rework. To face this problem, collaborative real-time photogrammetry is an effective solution for guiding untrained users in correctly positioning various measured and codified components to generate the best solution for machining high-volume parts. The solution proposed in this contribution is part of the TACCO project, co-financed by EIT Manufacturing (co-funded by the EU). It takes advantage of the TACCO system, where auxiliary components (scale bars, dome-shaped components, coded targets and a cross-reference system) are placed on the object to be measured for their correct positioning in order to obtain an optimal photogrammetric reconstruction. This allows the reduction of the error ellipsoids on several uncoded targets, which are calculated through an iterative simulation carried out in a MATLAB environment. Unskilled operators are then guided through an Augmented Reality headset for their correct placement on the real-world object and for defining the positions and orientations from which to acquire images. This methodology will lead to an accurate measurement of the target points to be machined and, thus, a precise alignment process for the subsequent machining operations.

Imperfections for the calculation of steel structures by the finite element method. Part 1

It is well known that imperfections are always present in structural elements. Imperfections can significantly affect the behavior and bearing capacity of steel structures, especially in the case of stability-related tasks. Therefore, inconsistencies must be taken into account in the loadbearing capacity model and their correct application (setting the shape and value) is a key point in the numerical analysis process. In recent decades, much attention has been paid in the domestic scientific space to updating imperfection models for use in numerical models, including taking into account modern more accurate manufacturing and installation technologies for steel structures. The purpose of this study is an analytical review and analysis of scientific research and technical literature, followed by synthesis and elaboration of recommendations on imperfections in relation to the calculation of steel structures using computer modeling technology, including the finite element method. The results of the study contain instructions on how to set the shapes and values of imperfections for different groups of imperfections. The article consists of two parts. The first part is devoted to the study of geometric imperfections, residual stresses and rules for the combination of imperfections, the second part of the article is devoted to equivalent imperfections.

Influence of base designs on the manufacturing accuracy of vat-polymerized diagnostic casts using two different technologies

Statement of problemDiagnostic casts can incorporate different base designs and be manufactured using different vat-polymerization technologies. However, the influence of the interrelation between the base design and the 3D printing technology on the casts' final accuracy remains unclear. PurposeThe purpose of this in vitro study was to assess the influence of different base designs of 3D printed casts on the accuracy of 2 vat-polymerization technologies. Material and methodsA digital maxillary cast was obtained and used to generate 3 different base designs: solid (S group), honeycombed (HC group), and hollow (H group). The HC and H groups were subdivided based on the wall thickness of the cast design, resulting in 2 subgroups with thicknesses of 1 mm (HC1 and H1) and 2 mm (HC2 and H2) (N=100, n=10). Eleven reference cubes were added to each specimen for subsequent measurements. Specimens were manufactured by using 2 vat-polymerization 3D printers: Nextdent 5100 (ND group) and Sonic Mini 4K (SM4K group) and a resin material suitable for both 3D printers (Nextdent Model 2.0). A coordinate measuring machine quantified the linear and 3-dimensional discrepancies between the digital cast and each reference specimen. Trueness was defined as the average absolute dimensional discrepancy between the virtual cast and the specimens produced through additive manufacturing (AM), while precision was delineated as the standard deviation in dimensional discrepancies between the digital cast and the AM specimens. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U pairwise comparison tests (α=.05). ResultsFor the NextDent group the trueness ranged from 21.83 µm to 28.35 µm, and the precision ranged from 17.82 µm to 37.70 µm. For the Phrozen group, the trueness ranged from 45.15 µm to 64.51 µm, and the precision ranged from 33.51 µm to 48.92 µm. The Kruskal-Wallis test showed significant differences on the x-, y-, and z-axes and in the 3D discrepancy (all P<.001). On the x-axis, the Mann-Whitney U test showed significant differences for the Phrozen group between the H-2 and H-1 groups (P=.001), H-2 and S groups (P<.001), and HC-2 and S groups (P=.012). On the y-axis, significant differences were found in the Phrozen group between the H-2 and H-1 groups (P=.001), the H-2 and S, H-1 and HC-1, and HC-1 and S groups (P<.001), the H-1 and HC-2 groups (P=.007), and the HC-2 and S groups (P=.009). The NextDent group exhibited significant differences, particularly among the HC-1 and H-2 groups (P=.004), H-1 (P=.020), and HC-2 (P=.001) groups; and on the z-axis significant differences were found in the Phrozen group between the H-2 and H-1 and S groups and the HC-2 group and H-1 and S groups (both P<.001). In the NextDent group, significant differences were found between the H-2 and HC-2 (P=.047) and HC-1 (P=.028) groups. For the 3D discrepancy analysis, significant differences were found in the Phrozen group between the H-2 and H-1 and S groups (P<.001), the H-1 and HC-2 groups (P=.001), the S and HC-1 and HC-2 groups (P<.001), and the H-1 and HC-1 groups (P=.002). In the NextDent group, significant differences were observed between the H-2 and HC-1 groups (P=.012). ConclusionsThe accuracy of digital casts depends on the manufacturing trinomial and base design of the casts. The honeycomb and hollow based designs provided the highest accuracy in the NextDent and Phrozen groups respectively for the material polymer tested. All specimens fell in the clinically acceptable range.

Efficient Method for Identifying Key Errors Based on 21-Geometric-Error Measurement of Three Linear Axes of Machine Tools

Key errors of machine tools have a significant impact on their accuracy, however accurately and quickly measuring the geometric errors of machine tools is essential for key error identification. Fortunately, a quick and direct laser measurement method and system for 21 geometric errors of three linear axes of machine tools were proposed previously, which enables the measurement of all 21 geometric errors via a one-step installation and a three-step automated measurement process. Based on this, to efficiently identify the key error factors, this paper first utilizes the 21 geometric errors obtained from the proposed measurement system to evaluate the contribution of each error to the volumetric errors of machine tools, leading to the building of a 21-geometric-error sensitivity analysis model. Then, experiments are carried out on the vertical machining tool TH5656, and all 21 geometric errors are obtained in 5 min. After this, the volumetric error distribution in the machining workspace is mapped according to the relationship between the geometric errors and the machining errors, and the key error factors affecting the manufacturing and machining accuracy of the TH5656 are ultimately determined. Thus, this new method provides a way to quickly identify key errors of the three linear axes of machine tools, and offers guidance for the machine tool configuration design, machining technology determination, and geometric error compensation.