Form Error Research Articles

Band-stop-filter-based repetitive control of fast tool servos for diamond turning of micro-structured functional surfaces

Fast tool servo (FTS) is a promising technique for the high-speed diamond turning of micro-structured functional surfaces due to its fast response capacity. However, the inherent actuator non-linearity, the lightly damped vibration mode and the external disturbance of the FTS would degrade its tracking performance severely and thus restrict its machining ability. To overcome this limitation, a band-stop-filter-based repetitive control (BSF-RC) scheme is proposed in this article to improve the operating performance of the FTS. Firstly, the spectra of the FTS tool paths (FTS-TPs) for machining typical micro-structured functional surfaces with the cylindrical coordinate machining method are analyzed in detail. The results reveal that the frequency components concentrate on the tiny neighborhoods of the rotational frequency of the spindle and its harmonic frequencies. Afterwards, the comb-like band-stop filter used by the BSF-RC is elaborately designed via the cascade of three comb-like notch filters to generate a comb-like band-stop loop shape for covering main spectral components of the FTS-TPs. The analytical expression of the comb-like band-stop filter amplitude as well as the stability condition of the closed-loop control system are derived to provide effective criteria for the parameter selection of the BSF-RC. The experimental validation of the developed BSF-RC scheme is conducted on a five-axis ultra-precision lathe equipped with a self-developed FTS via the diamond turning of three typical micro-structured functional surfaces. The experimental results show that good surface qualities with the maximal form error of a few hundred nanometers and the surface roughness of a several nanometers are achieved for all the obtained micro-structured surfaces by using the BSF-RC scheme under a high spindle speed.

CLIL in Spain and Vietnam

This study is based on the comparison between two Content and Language Integrated Learning (CLIL) contexts – in Madrid, Spain and in Hanoi, Vietnam – with a focus on teachers’ use of oral corrective feedback in classroom interaction at the primary school level. The model of corrective feedback (CF) developed by Lyster and Ranta (1997) and reproduced in Lyster and Mori (2006) was adapted for the analysis of teachers’ CF on errors of form and learners’ uptake. Participants of the study include three Spanish-native teachers in three bilingual schools in Madrid and four Vietnamese-native teachers in two bilingual schools in Hanoi, all at the primary school level. All classroom data was collected in CLIL natural-science classes in both settings. Results from the study showed that the overall CF patterns were very similar in both contexts with recasts as the most frequent CF type, followed by prompts and explicit correction. More specific differences were observed in the levels of uptake and repair following each type used by different teachers across the two contexts.

Influence of shape distortion on the precision of holes in parts fabricated by metal binder jetting

Metal binder jetting (MBJ) is an additive manufacturing (AM) technology split into two process steps: printing and sintering. Firstly, product is built up layer-by-layer by the selective deposition of a binder agent on a powder bed. Secondly, a thermal treatment (sintering) consolidates the metal structure. MBJ is currently becoming more and more attractive on the reason of high potential scalability, cost-effective production and wide range of available material feedstocks. However, the transition towards industrial scale production is restrained by the critical control of dimensional and geometrical precision of parts after sintering operation. In fact, product geometry is affected by anisotropic dimensional change or even shape distortion. This study aims at investigating the dimensional and geometrical precision of through holes. Three sample geometries were designed, having a through hole with axis perpendicular to the building direction and located at different levels along sample height. Samples were measured by a coordinate measuring machine before and after sintering, in order to assess the shrinkage and any shape change. Results highlight the inhomogeneous volumetric and linear shrinkage of the three geometries, which is influenced by the printing position in the building plane. A macroscopic deformation of parallelepiped geometry was also evidenced, caused by the superposition of layer shifting originated on printing, and by the frictional forces between sample surface and alumina support during sintering. Such distortion significantly affects the shrinkage and form error of holes.

Bridging the gap between design and manufacturing specifications for non-rigid parts using the influence coefficient method

The manufacturing process may lead non-rigid parts to endure large deformations which could be reduced during assembly. The manufacturing specifications of the single parts should refer to their free state or “as manufactured” state; the functional specifications should instead address the “as assembled” state. Therefore, a functional geometrical inspection requires dedicated fixtures to bring the parts in “as assembled” state. In this paper, through a linearized model that considers fixturing and elastic spring-back, we aim to correlate the functional specification to the manufacturing specifications. The model suggests a hybrid approach called “restricted skin model” that allows to reduce the degrees of freedom considering the form error when relevant. Firstly, the framework is verified in a mono-dimensional test case. Subsequently, it is verified including FEM simulation and actual measurement for two simple assemblies. The results show that the model can correctly interpret the theoretical assembly behaviour for actual applications. The use of the “restricted skin model” approach shows a negligible difference when compared to full FEM simulation with differences of 2.1 · 10−7 mm for traslations and 6.0 · 10−3 deg for rotations. The comparison with actual measurement values showed an error of ±0.2 mm at the assembly features. Furthermore, the linearized model allows a possible real-time application during production that enables to adjust manufacturing specification limits in case of process drifting.

이메일 장르 쓰기를 활용한 학문 목적 쓰기 수업 사례 연구

Objectives The purposes of this study were to identify the genre conventions of request e-mails and to analyze the international students’ e-mails based on extra-text conventions and intra-text conventions.
 Methods We designed a genre-based writing education model of e-mail and applied it to the class. Right after the class, the first task was given to the students to write an requesting e-mail and after 5 weeks, the second task was conducted on a similar topic in the midterm exam to analyze the results of the class.
 Results Students made few errors in writing appropriate content following the formal structure of the request email. However, there were many sociolinguistic errors in the customary language forms used at each stage of structure. In particular, when performing the function of requesting, it was difficult to use specific sentence patterns and honorifics used to show politeness.
 Conclusions Through email genre writing education, learners were able to recognize the importance of considering the purpose of email and the relationship with the recipient, and following sociolinguistic conventions and norms. In addition, it was found that it is effective to present grammatical items that are very closely related to the genre, not individually, but in connection with the genre.

Densi-melting effect for ultra-precision laser beam figuring with clustered overlapping technology at full-spatial-frequency.

Laser beam figuring (LBF), as a processing technology for ultra-precision figuring, is expected to be a key technology for further improving optics performance. To the best of our knowledge, we firstly demonstrated CO2 LBF for full-spatial-frequency error convergence at negligible stress. We found that controlling the subsidence and surface smoothing caused by material densification and melt under specific parameters range is an effective way to ensure both form error and roughness. Besides, an innovative "densi-melting" effect is further proposed to reveal the physical mechanism and guide the nano-precision figuring control, and the simulated results at different pulse durations fit well with the experiment results. Plus, to suppress the laser scanning ripples (mid-spatial-frequency (MSF) error) and reduce the control data volume, a clustered overlapping processing technology is proposed, where the laser processing in each sub-region is regarded as tool influence function (TIF). Through the overlapping control of TIF figuring depth, we achieved LBF experiments for the form error root mean square (RMS) reduced from 0.009λ to 0.003λ (λ=632.8 nm) without destroying microscale roughness (0.447 nm to 0.453 nm) and nanoscale roughness (0.290 nm to 0.269 nm). The establishment of the densi-melting effect and the clustered overlapping processing technology prove that LBF provides a new high-precision, low-cost manufacturing method for optics.

Improved precision of radial velocity measurements after correction for telluric absorption

Context. The detection of planets around other stars by measurement of stellar radial velocity (RV) variations benefits from improvements to dedicated spectrographs that can lead to the achievement of a precision of 1 m s−1 or better. Spectral intervals within which stellar lines are contaminated by telluric lines are classically excluded from the RV processing. Aims. We aim to estimate the potential improvement of the precision of radial velocity measurements from telluric-absorption removal and subsequent extension of the useful spectral domain. Methods. We developed a correction method based on the online web service TAPAS that allows a synthetic atmospheric transmission spectrum to be determined for the time and location of observations. This method was applied to telluric H2O and O2 absorption removal from a series of 200 consecutive ESPRESSO exposures of the K2.5V star HD40307 available in ESO archives. We calculated the radial velocity using the standard cross-correlation function (CCF) method and Gaussian fit of the CCF, with uncorrected spectra and the ESPRESSO standard stellar binary mask on one hand, and telluric-corrected spectra and an augmented binary mask with 696 additional lines on the other. Results. We find that the precision of radial velocity measurements is improved in the second case, with a reduction of the average formal error from 1.04 m s−1 down to 0.78 m s−1 in the case of these ESPRESSO data and this stellar type for the red arm. Using an estimator of the minimal error based on the photon noise limit applied to the full CCF, the error is reduced from 0.89 m s−1 down to 0.78 m s−1. This corresponds to a significant decrease (by about 35%) in the observing time required to reach the same precision in the red part.

An experimental study on out-of-roundness and material erosion rate during wire spark erosion turning of titanium cylindrical bars

This article presents an experimental investigation conducted on wire spark erosion turning of Titanium grade 5 miniature cylindrical bars. Two main output parameters i.e. roundness deviation, a type of form error, as an indicator of product quality and material erosion rate as an indicator of productivity, have been focused to measure the success of the machining process. A total of seventeen experiments with two replications based on Box-Behnken design (BBD) of the response surface methodology (RSM) were performed to identify the influence of spark duration ‘Ton’, servo voltage ‘SV’, and depth of cut ‘DOC’ on roundness deviation ‘DR’ and material erosion rate ‘MER’. Grey relational analysis (GRA) based multi-response optimization was carried out to determine the optimum turning condition of WSET with the objectives to minimize roundness deviation and maximize material erosion rate. WSET of Titanium at optimum process parameters resulted in the best values of roundness deviation 15.51 μm and material erosion rate 9.35 mm3/min. The results of validation experiments are much closer to the optimum values of DR and MER with <5% and 2% differences, respectively. Surface morphology investigation confirmed that the surface generated by WSET is fit and suitable for many applications. The results of this work are better than the previous studies and further useful to the researchers for the advanced fabrication of miniature products from difficult-to-machine materials like Titanium.

Fourier convolution-parallel neural network framework with library matching for multi-tool processing decision-making in optical fabrication.

Intelligent manufacturing of ultra-precision optical surfaces is urgently desired but rather difficult to achieve due to the complex physical interactions involved. The development of data-oriented neural networks provides a new pathway, but existing networks cannot be adapted for optical fabrication with a high number of feature dimensions and a small specific dataset. In this Letter, for the first time to the best of our knowledge, a novel Fourier convolution-parallel neural network (FCPNN) framework with library matching was proposed to realize multi-tool processing decision-making, including basically all combination processing parameters (tool size and material, slurry type and removal rate). The number of feature dimensions required to achieve supervised learning with a hundred-level dataset is reduced by 3-5 orders of magnitude. Under the guidance of the proposed network model, a 260 mm × 260 mm off-axis parabolic (OAP) fused silica mirror successfully achieved error convergence after a multi-process involving grinding, figuring, and smoothing. The peak valley (PV) of the form error for the OAP fused silica mirror decreased from 15.153λ to 0.42λ and the root mean square (RMS) decreased from 2.944λ to 0.064λ in only 25.34 hours. This network framework has the potential to push the intelligence level of optical manufacturing to a new extreme.

Chromatic confocal sensor-based on-machine measurement for microstructured optical surfaces featuring a self-aligned spiral center.

Chromatic confocal sensor-based on-machine measurement is effective for identifying and compensating for form errors of the ultra-precisely machined components. In this study, an on-machine measurement system was developed for an ultra-precision diamond turning machine to generate microstructured optical surfaces, for which the sensor probe adopts a uniform spiral scanning motion. To avoid the tedious spiral center alignment, a self-alignment method was proposed without additional equipment or artefact, which identified the deviation of the optical axis to the spindle axis by matching the measured surface points and the designed surface. The feasibility of the proposed method was demonstrated by numerical simulation with full consideration of noises and system dynamics. Practically, taking a typical microstructured surface as an example, the on-machine measured points were reconstructed after calibrating the alignment deviation, which was then verified by off-machine white light interferometry measurement. Avoiding tedious operations and special artefacts may significantly simplify the on-machine measurement process, thereby greatly improving the efficiency and flexibility for the measurement.

Exploring Lexical Errors of Indonesian EFL Students in Writing Recount Texts

&lt;p&gt;&lt;em&gt;The study aimed to examine the EFL students’ lexical errors in writing recount texts. This study employed a descriptive qualitative method involving 31 students and uses the taxonomy of James’ lexical errors in analyzing the texts. The findings revealed that there was a total of 161 lexical errors in the students’ recount writings. Likewise, it was claimed that misselection became the most frequent lexical error, with 73 errors. The next was suffix type with 35 errors and calque with 10 errors. Furthermore, the results showed that most students felt difficult to select the appropriate lexical types in writing recount texts and most of the formal errors resulted from the intralingual error. Thus, the study recommends that the teachers teach vocabulary in contexts rather than words and use English thesaurus or monolingual dictionaries to find the grammatical content, definitions, examples, spelling, or other structures. The study also recommends online lexical analyzers, drillling, and remedy as the other alternative methods of reducing lexical errors in writing.&lt;/em&gt;&lt;/p&gt;

An International Study of Factors Affecting Variability of Dosimetry Calculations, Part 2: Overall Variabilities in Absorbed Dose.

Dosimetry for personalized radiopharmaceutical therapy has gained considerable attention. Many methods, tools, and workflows have been developed to estimate absorbed dose (AD). However, standardization is still required to reduce variability of AD estimates across centers. One effort for standardization is the Society of Nuclear Medicine and Molecular Imaging 177Lu Dosimetry Challenge, which comprised 5 tasks (T1-T5) designed to assess dose estimate variability associated with the imaging protocol (T1 vs. T2 vs. T3), segmentation (T1 vs. T4), time integration (T4 vs. T5), and dose calculation (T5) steps of the dosimetry workflow. The aim of this work was to assess the overall variability in AD calculations for the different tasks. Methods: Anonymized datasets consisting of serial planar and quantitative SPECT/CT scans, organ and lesion contours, and time-integrated activity maps of 2 patients treated with 177Lu-DOTATATE were made available globally for participants to perform dosimetry calculations and submit their results in standardized submission spreadsheets. The data were carefully curated for formal mistakes and methodologic errors. General descriptive statistics for ADs were calculated, and statistical analysis was performed to compare the results of different tasks. Variability in ADs was measured using the quartile coefficient of dispersion. Results: ADs to organs estimated from planar imaging protocols (T2) were lower by about 60% than those from pure SPECT/CT (T1), and the differences were statistically significant. Importantly, the average differences in dose estimates when at least 1 SPECT/CT acquisition was available (T1, T3, T4, T5) were within ±10%, and the differences with respect to T1 were not statistically significant for most organs and lesions. When serial SPECT/CT images were used, the quartile coefficients of dispersion of ADs for organs and lesions were on average less than 20% and 26%, respectively, for T1; 20% and 18%, respectively, for T4 (segmentations provided); and 10% and 5%, respectively, for T5 (segmentation and time-integrated activity images provided). Conclusion: Variability in ADs was reduced as segmentation and time-integration data were provided to participants. Our results suggest that SPECT/CT-based imaging protocols generate more consistent and less variable results than planar imaging methods. Effort at standardizing segmentation and fitting should be made, as this may substantially reduce variability in ADs.

Accuracy of Naming Error Profiles Elicited From Adaptive Short Forms of the Philadelphia Naming Test.

The purpose of this study was to evaluate whether a short-form computerized adaptive testing (CAT) version of the Philadelphia Naming Test (PNT) provides error profiles and model-based estimates of semantic and phonological processing that agree with the full test. Twenty-four persons with aphasia took the PNT-CAT and the full version of the PNT (hereinafter referred to as the "full PNT") at least 2 weeks apart. The PNT-CAT proceeded in two stages: (a) the PNT-CAT30, in which 30 items were selected to match the evolving ability estimate with the goal of producing a 50% error rate, and (b) the PNT-CAT60, in which an additional 30 items were selected to produce a 75% error rate. Agreement was evaluated in terms of the root-mean-square deviation of the response-type proportions and, for individual response types, in terms of agreement coefficients and bias. We also evaluated agreement and bias for estimates of semantic and phonological processing derived from the semantic-phonological interactive two-step model (SP model) of word production. The results suggested that agreement was poorest for semantic, formal, mixed, and unrelated errors, all of which were underestimated by the short forms. Better agreement was observed for correct and nonword responses. SP model weights estimated by the short forms demonstrated no substantial bias but generally inadequate agreement with the full PNT, which itself showed acceptable test-retest reliability for SP model weights and all response types except for formal errors. Results suggest that the PNT-CAT30 and the PNT-CAT60 are generally inadequate for generating naming error profiles or model-derived estimates of semantic and phonological processing ability. Post hoc analyses suggested that increasing the number of stimuli available in the CAT item bank may improve the utility of adaptive short forms for generating error profiles, but the underlying theory also suggests that there are limitations to this approach based on a unidimensional measurement model. https://doi.org/10.23641/asha.22320814.

Error analysis in the middle test of Writing Post-Basic written by the third semester of English education department Universitas PGRI Madiun year 2021/2022

Writing is one of the important English skills. The process to make good writing is difficult. There were errors in the writing process. Therefore, the researcher was interested in analyzing the kinds of errors in writing. The problem of this study is to identify the errors made by the third-semester students of English education department at Universitas PGRI Madiun in the academic year 2021/2022. A descriptive qualitative method is used to analyze this research. The researcher analyzed subject-verb agreement errors, verb tense errors, verb form errors, singular/plural noun ending errors, and word form errors. The steps to finding the data are: collecting the sources of the data, understanding the content of the writing, selecting the test which contains errors, analyzing the collected data, and drawing conclusions. The result of this research, from the lowest to the highest, is as follows: singular/plural noun ending errors (3.40%), subject-verb agreement errors (12.24%), verb form errors (13.61%), verb tense errors (30.61%), and the highest error is word form errors (40.14%). The suggestion of the researcher for the next researcher, there are still many aspects that can be analyzed from other kinds of errors and analyzing other skills of English such as reading, speaking, and listening concerned in the errors aspect.

EEG Dynamics of Error Processing and Associated Behavioral Adjustments in Preschool Children.

Preschool children show neural responses and make behavioral adjustments immediately following an error. However, there is a lack of evidence regarding how neural responses to error predict subsequent behavioral adjustments during childhood. The aim of our study was to explore the neural dynamics of error processing and associated behavioral adjustments in preschool children from unsatisfied basic needs (UBN) homes. Using EEG recordings during a go/no-go task, we examined within-subject associations between the error-related negativity (ERN), frontal theta power, post-error slowing, and post-error accuracy. Post-error accuracy increased linearly with post-error slowing, and there was no association between the neural activity of error processing and post-error accuracy. However, during successful error recovery, the frontal theta power, but not the ERN amplitude, was associated positively with post-error slowing. These findings indicated that preschool children from UBN homes adjusted their behavior following an error in an adaptive form and that the error-related theta activity may be associated with the adaptive forms of post-error behavior. Furthermore, our data support the adaptive theory of post-error slowing and point to some degree of separation between the neural mechanisms represented by the ERN and theta.

Errors in Writing Among Female Students at the Tertiary Level in Saudi Arabia

Writing is regarded as the most challenging skill to acquire when learning a foreign language. Extensive research into students' writing abilities is one method for understanding the challenges they face when writing. This study aims to investigate the most frequent English writing errors made by Saudi female university students at the tertiary level. The study's population comprised forty female college students. They had 45 minutes to write paragraphs on a variety of subjects. The participants in this study were selected at random and asked to compose an essay on any of the topics provided so that errors could be identified; the results were then analyzed and explained. Based on the findings, we can conclude that all 40 paragraphs of the essays written by Saudi female university students at the tertiary level contained 192 misspellings. There were 41 plural form errors, 58 comma punctuation errors, and 52 full stop punctuation errors. There were 119 instances of incorrect grammar, syntax, or word choice. The data analysis concludes that female students make numerous punctuation, syntactic, grammatical, and lexical errors, with most errors occurring in spelling and syntax. The results of this study are significant because the identified errors will have pedagogical implications when teaching writing skills to college-level English language students. This result sheds light on the areas that should be emphasized when teaching writing skills to EFL students in Saudi Arabia.

English as a heritage language: The effects of input patterns and contact with Hebrew

Purpose: This study examines the extent to which language skills of adult speakers of heritage language (HL) English in a Hebrew-speaking society are affected by individual HL input patterns and cross-linguistic influence. Methodology: Adult HL-English speakers who grew up in families with one ( N = 22) or two ( N = 25) English-speaking parents were compared to a baseline group of native English speakers who emigrated to Israel as adults ( N = 20). Data: Proficiencies in morphosyntactic and lexical domains were measured based on formal test performance and error types and frequencies in narratives. Detailed histories of speakers’ linguistic input were documented. Findings: Results showed near-ceiling performance across the three groups in the morphosyntactic domain, while significant differences were observed between the baseline and HL groups in the lexical domain. No differences were found between HL-English speakers who grew up in families with one or two English-speaking parents. Individual HL input patterns explained a larger proportion of the variance in the lexical abilities, compared to morphosyntactic ones. Evidence of cross-linguistic influence from Hebrew was not detected in the morphosyntactic domain, but only in the lexicon, in the form of minor lexical production errors and calques. Originality: The HL examined here was English which, unlike other HLs, is heard and used in a variety of contexts outside the home. In most previous studies on HLs, English was the dominant societal language. Implications: The results suggest that morphosyntactic divergences, unlike lexical divergences, are not necessarily found in all HLs—morphosyntactic structures acquired in childhood, reinforced periodically in the societal environment, may be well-maintained because of the language’s ubiquity and relatively sparse morphology.

Numerical and experimental investigation on the effect of surface curvature and slope angle on the material removal characteristics in fluid jet polishing

Fluid jet polishing (FJP) has been extensively utilized in the ultra-precision manufacturing of freeform optical components and molds. The form accuracy is mainly improved by controlling the polishing dwell time at different positions, which is determined by the deconvolution of the initial form error and tool influence function (TIF). However, in previous studies, the erosion-induced TIF is considered constant without accounting for the freeform surfaces' curvature and slope angle variations. Due to the deviation of TIF, it is still a challenge to achieve a high form accuracy for freeform surface polishing. In this paper, the TIFs in freeform surface polishing have been modeled by computational fluid dynamics (CFD) analysis. A series of spot polishing experiments subsequently were conducted on the surfaces with different curvature radii and slope angles. The experimentally measured data including cross-section profiles of polishing spots, Peak-to-valley (PV) value, and material removal rate are found to agree well with the model simulation results, which verified the effectiveness of the CFD model. The effect of surface curvature and slope angle on the material erosion distribution was investigated and revealed by the fluid flow field distribution, abrasive impact, and abrasive trajectories. This paper not only provides a deep scientific understanding of the material erosion characteristics in FJP of freeform surfaces, but also offers a simple and cost-effective solution to build the database of TIFs on freeform surfaces under various conditions, which is beneficial for the ultra-precision form control during FJP of freeform surfaces.

The Neptunian gravity estimated from the motion of Triton based on astrometric observations

Context. Accurate gravity and ephemerides estimations for Neptune and its satellites are necessary for the forthcoming deep space exploration missions targeting its system. In addition, these estimations are also meaningful for the modeling of Neptune's interior and for solar system dynamics studies. The body of astrometric data concerning Triton has been accumulating for about two hundred years, but more accurate updates to the ephemerides of this moon and revisions to the relevant gravity parameters would be possible with more precise astrometric data. The new Gaia catalog of star positions plus observations from Voyager 2 and the Hubble Space Telescope provide such a basis for high-precision astrometry and to complement and extend the existing body of data. Aims. We aim to report integrated orbital fits for Triton based on all the available astrometric data from 1847 to 2020, including observations from Earth-based telescopes, Voyager 2, and the Hubble Space Telescope. We also estimate the Neptunian gravity using the motion of Triton. Methods. Triton’s orbital solution was determined by a weighted least-squares method to fit the model to the most complete astrometric data set to date. The DOP853 algorithm was adopted in the numerical integration calculations. For the dynamical model parameters, our orbital model for Triton is similar to the NEP081 but with an update. The perturbations from the inner satellites (Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, and Hippocamp) were considered by adding corrections to J2 and J4 for Neptune. As the gravitational oblateness coefficient of Neptune is correlated with its orientation, the pole parameters were thus kept fixed in the integration when estimating Neptunian gravity. A Monte Carlo analysis was performed, however, to obtain reliable accuracy estimations and to assess the uncertainty of pole parameters on the results’ formal error. Results. We provide a new orbit and dynamical model values for Triton. The estimated accuracy of the model we built and updated fit all the astrometric data. The RMS of the residuals was 0.074 arcsec in the right ascension and 0.071 arcsec in declination. The RMS was 0.102 arcsec for X and 0.139 arcsec for Y in differential coordinates. The RMS for the position angle was 0.834 degrees, and the angular separation distance was 0.257 arcsec for the data collected before 1960. The orbit of Triton was well determined with the orbit differences from NEP081 and NEP097 (so far the latest Triton ephemerides from Jet Propulsion Laboratory) as being less than 300 km (about 15 mas) during the observation coverage period of this study. The large body of astrometric data for Triton over a time interval from 1847 to 2020 was used to constrain its position at the initial epoch, allowing us to reduce formal uncertainty to about 3 km. Based on the most complete weighting astrometric observations of Triton, the estimated mass of the Neptune system is GMs = 6 836 525.210 ±19.526 km3 s−2. Our revised gravity model yields J2 = 3401.655 ±1.850 × 10−6 and J4 = −33.294 ±10.000 × 10−6. The astrometric observations showed little sensitivity to GMs and J4, but acted well on J2. A Monte Carlo method was used to analyze the error caused by a variation in the pole parameters and showed that J2 = 3401.655 ± 3.994 × 10−6 was a more realistic error.

Surface generation modelling and form maintenance strategy in maskless fluid jet polishing of structured array surface

Structured array surfaces are extensively utilized in the fields of functional optical components and molds. However, high surface form accuracy of these surfaces is usually needed to implement superior performance, leading to great challenges in manufacturing. In this study, fluid jet polishing (FJP) was utilized to polish the cylindrical array surface. The effect of abrasive size and jet pressure on the form maintainability was elucidated by combining computational fluid dynamics (CFD) simulation. The abrasive trajectory and abrasive impact information were analyzed to reveal the material removal process. Tool influence functions (TIF) at different positions were simulated to model the surface generation process and provide a theoretical basis for the optimization of polishing parameters. A surface form maintenance strategy was proposed to achieve high form accuracy together with excellent surface quality by controlling the feed rate of the nozzle. A series of experiments were conducted to validate the effectiveness of the form maintenance strategy. The results revealed that the form error agreed well with the requirement after polishing with the designed feed rate. This study paves a new way for the polishing of structured array surfaces with a good surface form control.