Step Height Research Articles

Development and evaluation of a closed-loop z-axis control strategy for wire-and-arc-additive manufacturing using the process signal

Wire-and-arc-additive manufacturing (WAAM) is an additive manufacturing technology with a high deposition rate. WAAM usually employs a layer wise build-up strategy. This makes it necessary to know the height of each deposited layer to determine the height the z-axis has to travel after each layer. Current bead geometry models (BGM) lead to variations, which can gradually accumulate over the layers. The present study focuses on the development of a closed-loop control system capable of keeping the contact tube working distance (CTWD) constant during short-circuit gas metal arc welding (GMAW) based WAAM. The algorithm calculates the CTWD based on the resistance during the short circuit. The closed-loop strategy is compared to an open-loop control strategy, which moves along a predefined height step after each layer. Using the proposed control strategy, WAAM becomes a fully automated process without the need for preliminary experiments to determine the height step. Only a short calibration slope is necessary for a complete closed-loop additive build-up. To study the influence of the control strategy on the workpiece the energy input, mechanical strength, microhardness, porosity, and microstructure were analyzed. It is shown that the CTWD of the open-loop deposited component increases slowly. Due to the novel control approach, this is prevented by the closed-loop control, while the mechanical strength and microhardness remain.

Determination of the Equivalent Thickness of a Taiko Wafer Using ANSYS Finite Element Analysis

The successful handling of large semiconductor wafers is crucial for scaling up their production. Early-stage warpage control allows the prevention of undesirable asymmetric warpage, known as wafer bifurcation or buckling. Indeed, even in a gravity-free environment, thinning an 8″ or 12″ semiconductor wafer can result in warpage and bifurcation. To mitigate this issue, the taiko method, which involves creating a thicker ring region around the rim of the wafer, has been widely used. Previous research has focused on the theoretical factors affecting the warpage of a backside metalized taiko wafer. This work extends the case to a front-side metalized taiko wafer and introduces the concept of the equivalent thickness of a taiko wafer. The equivalent thickness of a taiko wafer, influenced by the ring region, lies in between the thickness of the central region and that of the annular region. Because of the limited number of taiko wafers that can be produced on a production line, modelling can be beneficial. In this work we compared the results of a developed analytical model with those obtained from a finite element analysis (FEA) approach with ANSYSY® Mechanical Enterprise 2022/R2 software to model the equivalent thickness of a taiko wafer. We investigated the curvature as a function of the stress of the metal layer, considering key design factors such as the substrate region thickness, the thickness of the thin metal film, the step height, and the width of the ring region. By systematically varying the thickness of the central region of the taiko wafer, we explored the curvature as a function of stress induced by thermal load in the linear regime and determined the slopes in the linear region of the curvature vs. stress curves. The aim of this study is to identify regularities and similarities with the Stoney equation and investigate the validity of the analytical approach for the case of a taiko substrate. The results show that there is a good agreement between the analytical model of a taiko wafer and the numerical analysis gained by the FEA methods.

Calibration of a step height standard for dimensional metrology using phase-shift interferometry and Hamming window: band-pass filter

Calibration of a step height standard for dimensional metrology using phase-shift interferometry and Hamming window: band-pass filter

Application of Empirical Mode Decomposition and Hodrick Prescot filter for the prediction single step and multistep significant wave height with LSTM

The study discusses the application of the Empirical Model Decomposition (EMD) and Hodrick Prescot (HP) filter for significant wave height prediction. Long Short-Term Memory (LSTM) is applied for sequence predictions in Natural Language Processing (NLP). LSTM can also be modeled to time series forecasting, particularly for cyclic data since LSTM learns from experience to forecast the data. The time series signal is a combination of frequencies or spectra, when the LSTM is applied to the raw signal the prediction is lagged, to reduce the lag in the forecast the noise in the time series signal is filtered. Since, the time series consists of various frequency components, filtering the higher-frequency components is required to reduce the delay in prediction from the LSTM neural network model. The EMD is applied to the original time series wave data to split the signal into several frequencies in time series or Intrinsic Mode Functions (IMFs). Similarly, when the HP filter is applied to the original wave data or time series signal it gives a trend and cycle. The LSTM is applied to the IMFs and HP filter trend time series to predict the EMD-IMFs and Trend respectively. All the predicted IMFs are summed to compare with the original raw time series. The single step and multistep prediction or forecasting is carried out for 1-h interval, 6-h, 12-h, and 24 h interval. With the increase in forecasting interval the error values also increased and changing the lambda parameter of HP filter played a critical step for the multistep prediction. The EMD-LSTM is computationally expensive as it takes higher amount time to predict each IMF compared to HP-LSTM. Finally, the results are compared with between normal LSTM, EMD-LSTM and HP-LSTM.

Step unbunching phenomenon on 4H-SiC (0001) surface during hydrogen etching

We here report a step unbunching phenomenon, which is the inverse of the phenomenon of step bunching. When a 4H-SiC (0001) surface is annealed at a high temperature, step bunching arises due to the different velocities of the step motion in adjacent steps, resulting in steps with a height of more than several nanometers. We found that the bunched steps, thus, obtained by hydrogen etching in an Ar/H2 atmosphere were “unbunched” into lower height steps when annealed subsequently at lower temperatures. This unbunching phenomenon can be well explained by the consequence of the competition between energetics and kinetics. Our findings provide another approach for the surface smoothing of SiC by hydrogen etching and may give significant insight into the application of SiC power devices and two-dimensional materials growth techniques in general.

PMotion: an advanced markerless pose estimation approach based on novel deep learning framework used to reveal neurobehavior

Objective. The evaluation of animals’ motion behavior has played a vital role in neuromuscular biomedical research and clinical diagnostics, which reflects the changes caused by neuromodulation or neurodamage. Currently, the existing animal pose estimation methods are unreliable, unpractical, and inaccurate. Approach. Data augmentation (random scaling, random standard deviation Gaussian blur, random contrast, and random uniform color quantization) is adopted to augment image dataset. For the key points recognition, we present a novel efficient convolutional deep learning framework (PMotion), which combines modified ConvNext using multi-kernel feature fusion and self-defined stacked Hourglass block with SiLU activation function. Main results. PMotion is useful to predict the key points of dynamics of unmarked animal body joints in real time with high spatial precision. Gait quantification (step length, step height, and joint angle) was performed for the study of lateral lower limb movements with rats on a treadmill. Significance. The performance accuracy of PMotion on rat joint dataset was improved by 1.98, 1.46, and 0.55 pixels compared with deepposekit, deeplabcut, and stacked hourglass, respectively. This approach also may be applied for neurobehavioral studies of freely moving animals’ behavior in challenging environments (e.g. Drosophila melanogaster and openfield-Pranav) with a high accuracy.

Carrier phase distribution based scan step noise correction for white light interferometry topography measurements

As a type of interference microscopy, white light interferometry (WLI) is well-established measuring technique in advanced manufacturing industry and scientific research for contactless inspection of surface topographies in micro- and nanometer range. In this paper, a scan step noise correction based surface recovery algorithm is proposed for WLI precision measurement, which provides an effective solution to the inevitable scan step noise. The carrier is firstly obtained by removing the envelope in the interference signal, then the carrier phase is extracted. Based on the theoretical linearity of the phase distribution, a corrected relationship is designed in terms of scan position and phase distribution. Afterwards, the surface profiles can be precisely recovered according to the regenerated carrier after phase correction simultaneously. Simulations show that the reconstruction error is less than 5 nm when WLI is disturbed by harmonic error and random noise. In order to test the effectiveness and reliability of the proposed, a step height with nominal value 45.5 ± 1.2 nm is used to calibrate the proposed system and the new algorithm, where within 10 rounds of scanning the mean height of 44.99 nm with the repeatability of 1.39% is achieved. In the experiment, a laser marking sample is measured and the 3D shape of the marking area is successfully recovered. The repeat measurements and the comparison with the commercial profiler are also provided, which exhibits good consistence and further proves the potential of the new method in the perspective of industry applications.

Dynamic evolution law analysis of overburden separation and water flowing fracture under mining based on distributed optical fiber and information entropy theory

The water inrush from overburden separation is large and destructive, which is very easy to cause serious casualties and property losses. Therefore, a three-dimensional model of 150 cm × 150 cm × 60 cm (length × height × width) is established in the laboratory. And the dynamic development process of overburden separations and water flowing fractures in the process of coal mining in real time are analyzed based on distributed optical fiber and information entropy theory. The distributed optical fiber strain curve can well reflect the process and characteristics of overburden deformation and collapse. The strain curve of optical fiber shows a single peak or step shape at different mining stages. The separation position corresponds to the peak of the optical fiber strain curve or above the step. The change of strain value of optical fiber reflects the development, expansion and closure process of separation. The development height of the water flowing fractured zone corresponds to the lower part of the step of the strain curve. Strain information entropy realizes quantitative analysis of overburden system state. Strain information entropy can be divided into small amplitude rapid fluctuation period, sharp rapid adjustment period and stable slow fluctuation period. Water flowing fractures and separations are mainly produced during the period of the sharp rapid adjustment period. The height of the water flowing fractured zone and the height of the new separation increase step by step with the advance of the working face. The water flowing fractured zone finally develops to 86 cm of the model height. The highest position of the separation appears at the 112 cm height of the model. A new variable named growth rate of strain information entropy is defined, which can reflect the severity of the change of the overburden system state. When the key stratum breaks, the growth rate of strain information entropy increases significantly, which show that the key stratum plays a key role in controlling the overburden deformation process. In addition, the optical fiber strain curve can also reflect important information such as the change of advance support pressure, the distribution state of gangue in goaf and the breaking characteristics of key strata.

Surface morphology of polycrystalline cerium–lanthanum alloy in nanometric cutting

Molecular dynamics simulation is carried out for the nanometric cutting of polycrystalline cerium–lanthanum alloy. By adjusting different grain orientations, the effects of slip direction on the alloy's surface morphology are studied at various undeformed chip thickness. The causes of the elastic deformation of the workpiece surface are clarified by analyzing the atomic motion trajectories. The grain boundary migration found during the simulation is also illustrated. Results show that slip deformation is the main influencing factor of plastic deformation in the processing, and the number of slip lines affects the surface step height of polycrystals.

Automated extraction of interfacial dislocations and disconnections from atomistic data

We introduce Interfacial Line Defect Analysis (ILDA), a method for identifying and extracting interfacial dislocations and disconnections with little-to-no input from the user on the nature of the interface. By simply providing the orientations and coherency strains for the crystals in a coherent reference state of the interface, ILDA provides exact Burgers vectors. Alternatively, these orientations and strains can be estimated using local atomic deformation gradients, making ILDA fully automated and providing estimated Burgers vectors. ILDA also determines the step height associated with each defect line segment, in case the associated defect is a disconnection. The heart of the method is the identification of atoms residing at co-incidence sites between the two crystals and the construction of a surface mesh connecting these sites that is used to compose Burgers circuits and insert defect line segments. We demonstrate the performance of ILDA in two test cases: a twist grain boundary and a phase boundary.

Aeroacoustics of turbulent flow over a forward–backward facing step

This paper presents a combined experimental and numerical study on the aeroacoustics of low Mach number turbulent flow over a forward–backward facing step (FBS). The height of the step is fixed at 50% of the incoming boundary layer thickness. Multiple lengths of the step are considered with aspect ratios (step length to height) equal to 1,2,2.4,4, and 8. The Reynolds number based on the step height ranges from 1.2×104 to 2.8×104 in both experiments and simulations. Wall pressure measurement results show that the largest wall pressure fluctuations occur slightly downstream of the step leading edge, and the downstream flow field is influenced by the leading edge flow disturbance. Large-Eddy Simulation (LES) is performed to visualize the instantaneous and time-averaged flow field. Large-scale vortices formed at the leading edge are found to shed downstream directly when the step length is shorter than the shear layer reattachment length, which leads to lower level wall pressure fluctuations on the top surface. Spectral proper orthogonal decomposition (SPOD) is applied to identify the dynamic behaviours of coherent structures downstream of the step leading edge. Using simulation data, the fluctuating wall pressure spectra are also calculated via Poisson’s equation. The results indicate that both turbulence-mean-shear interaction and turbulence–turbulence interaction contribute to the wall pressure fluctuations in the on-step reattachment region. Aeroacoustic beamforming results show that the dominant noise source is located at the step leading edge, where the highest level of fluctuating wall pressure is recorded. Meanwhile, the integrated far-field acoustic spectra show that the levels of FBS noise are lower when there is no flow reattachment occurring on the top surface. A new scaling law for FBS sound spectra is proposed to address the influence of the step aspect ratio on noise production.

Passive vibration suppression method based on frequency domain analysis in white light vertical scanning interferometer

Vibration in manufacturing environment can significantly affects the accuracy of surface measurements, especially for the white light vertical scanning interferometry (VSI), which requires mechanical scanning for full-field measurements. This paper proposes a passive vibration suppression technique that integrates a second common-path interferometer and uses frequency domain analysis to measure vibration and reconstruct surface topography. The method is feasible for suppressing vibrations with different frequencies and amplitudes, as verified by simulation and signal recovery analysis. An in-house developed interferometer with a common optical path is used to demonstrate the measurement performance experimentally. The mathematical formula relating the vibration amplitude, the vibration frequency, the frame rate of the camera and the scanning interval is presented. The experimental results show that the precision of plane measurement decreases with increasing vibration amplitude and frequency. Moreover, the step sample signals under a maximum vibration condition of 400 nm/5 Hz are recovered, with a standard deviation of 26.07 nm for the step height measurement. As the scanning interval increases, the system can suppress higher-amplitude vibrations.

Comparing Walking-Related Everyday Life Tasks of Children with Gait Disorders in a Virtual Reality Setup With a Physical Setup: Cross-Sectional Noninferiority Study.

A frequent rehabilitation goal for children with gait disorders is to practice daily-life walking activities. Unfortunately, these are often difficult to practice in a conventional therapeutic setting. Virtual reality (VR) with head-mounted displays (HMDs) could be a promising approach in neurorehabilitation to train such activities in a safe environment. First, however, we must know whether obstacles in VR are indeed mastered as obstacles. This study aimed to provide information on whether VR is feasible and motivating to induce and practice movements needed to master real obstacles in children and adolescents with gait disorders. Furthermore, this project aims to evaluate which kinds of everyday walking activities are appropriate to be practiced in VR. In this cross-sectional study, participants stepped over a bar, crossed a gap, balanced over a beam, and circumvented stationary obstructions arranged in a course under real physical and virtual conditions wearing a VR HMD. We recorded the respective primary outcomes (step height, step length, step width, and minimal shoulder-obstacle distance) with motion capture. We then calculated the mean differences and 95% CI of the spatiotemporal parameters between the VR and physical setup and later compared them using noninferiority analysis with margins defined a priori by a clinical expert panel. Additionally, the participants responded to a standardized questionnaire while the therapists observed and evaluated their movement performance. We recruited 20 participants (mean age 12.0, range 6.6-17.8 years) with various diagnoses affecting their walking ability. At 3.77 (95% CI 1.28 to 6.26) cm, the mean difference in step height of the leading foot in the overstepping task did not exceed the predefined margin of -2 cm, thus signifying noninferiority of the VR condition compared to mastering the physical obstacles. The same was true for step length (-1.75, 95% CI -4.91 to 1.41 cm; margin -10 cm), step width (1.05, 95% CI 0.20 to -1.90 cm; margin 3 cm), and the minimal shoulder-obstacle distance (0.25, 95% CI -0.85 to 0.35 cm; margin -2 cm) in the other tasks. Only the trailing foot in the overstepping task yielded inconclusive results. Children with gait disorders perform everyday walking tasks like overstepping, crossing, balancing, or circumventing similarly in physical and VR environments, suggesting that VR could be a feasible therapeutic tool to practice everyday walking tasks.

Comparative study of experimental and CFD results for stepped planing hulls

In recent years, research has been conducted on reducing resistance by adding steps on the bottom of high-speed craft. The most significant issue in the design of multi-stepped planing craft is the selection of an appropriate step configuration, i.e., step geometry, location, and height. This requires a general knowledge of the hydrodynamic behavior of each step configuration. Although the towing tank test is an effective method to predict accurately the hydrodynamic behavior of stepped planing boats, there are restrictions in studying some details. In this study, a Computational Fluid Dynamic (CFD) method is used to investigate the hydrodynamic behavior of a stepped planing hull with eight different step configurations in detail. Comparison of the results of trim angle, resistance, sinkage, wetted surface, and ventilation length of swept-stepped planing hulls for different step configurations at various Froude numbers shows that a maximum average resistance reduction occurs at 1.9 <FrB < 4.0 with the step height of 2.73% BTC located at 48.46% L from the transom. There is also a lower resistance associated with a step height of 0.91% BTC at 48.35% L distance from the transom at FrB > 4. These results can be used to improve high-speed planing hull performances by utilizing an appropriate step configuration.

Automated pose estimation reveals walking characteristics associated with lameness in broilers

Walking ability of broilers can be improved by selective breeding, but large-scale phenotypic records are required. Currently, gait of individual broilers is scored by trained experts, however, precision phenotyping tools could offer a more objective and high-throughput alternative. We studied whether specific walking characteristics determined through pose estimation are linked to gait in broilers. We filmed male broilers from behind, walking through a 3 m×0.4 m (length×width) corridor one by one, at 3 time points during their lifetime (at 14, 21, and 33 d of age). We used a deep learning model, developed in DeepLabCut, to detect and track 8 keypoints (head, neck, left and right knees, hocks, and feet) of broilers in the recorded videos. Using the keypoints of the legs, 6 pose features were quantified during the double support phase of walking, and 1 pose feature was quantified during steps, at maximum leg lift. Gait was scored on a scale from 0 to 5 by 4 experts, using the videos recorded on d 33, and the broilers were further classified as having either good gait (mean gait score ≤2) or suboptimal gait (mean gait score >2). The relationship of pose features on d 33 with gait was analyzed using the data of 84 broilers (good gait: 57.1%, suboptimal gait: 42.9%). Birds with suboptimal gait had sharper hock joint lateral angles and lower hock-feet distance ratios during double support on d 33, on average. During steps, relative step height was lower in birds with suboptimal gait. Step height and hock-feet distance ratio showed the largest mean deviations in broilers with suboptimal gait compared to those with good gait. We demonstrate that pose estimation can be used to assess walking characteristics during a large part of the productive life of broilers, and to phenotype and monitor broiler gait. These insights can be used to understand differences in the walking patterns of lame broilers, and to build more sophisticated gait prediction models.

Atomistic simulation for initiation of crystal slip deformation from surface of nanoscale copper single-crystal nanowires

In nano/micrometer-scale materials, dislocations accounting for crystal slip deformation are introduced from the surface because of lack of pre-existing dislocations inside the materials. The dislocation emission from the surface must play an important role in the formation of dislocation network structures in the nano/micrometer-scale materials under cyclic loading, which should differ from that in macroscale materials. The purpose of this study is to investigate the effect of the atomic-level structure of surfaces on the initiation of crystal slip deformation. We create copper single-crystal nanowire models with different surface structures by varying the cross-section shape and crystal orientation. To observe the initiation of the slip deformation from the surface, we conduct atomistic simulations of tensile deformation for these models. We also discuss the effect of the surface structure on the critical shear stress for slip occurrence from the surface. Our analyses reveal that the orientation of surface steps and the normal stress on the active slip plane are important factors affecting the slip occurrence. Thus, the slip occurs in a slip system so as to reduce the height of a surface step. The active slip system is affected by the cross-section shape and crystal orientation because the slip system is dependent on the relationship between slip planes and the orientation of the surface step. Our results also suggest that the cross-section shape and crystal orientation affect the critical shear stress because of the difference of the normal stress on the active slip plane according to these factors.

Planarization profile modeling using pad bulk deformation and real contact area analysis of macro-scale device pattern

In general, the shape of the polished pattern is not flat but has a rounded curved profile. Unlike micro-patterns that have similar scales to pad asperities, macro-patterns have a very large scale compared to asperities, so bulk deformation must also be considered. To derive the pad bulk deformation, real contact area (RCA) measurements were performed in this study. Based on the preceding contact model, a semi-empirical model for RCA and bulk deformation was derived. After including the constructed pad bulk deformation function in the existing Greenwood–Williamson model, a new model that can derive the material removal rate profile according to the position in the pattern was presented. Unlike the general upper and lower removal rate behavior, this model shows a unique behavior. At the beginning of polishing, the edge shows a higher removal rate than the center, but after a specific step height, the center has a higher removal rate due to the curved shape. Analysis was performed for comparison between the proposed model equation and the experimental value. When the polishing profile in the 10 mm pattern was compared with the previous model and the proposed model, respectively, the existing model did not predict the removal rate distribution according to the position in the pattern. However, this model has the advantage of predicting both over-polishing at the edge of the pattern and high removal rate at the bottom. In addition, it was confirmed through simulation that the 4 mm and 2 mm patterns had excellent matching properties.

Numerical and experimental investigation of a large gap convergent ferrofluid seal with the stepped pole piece

To solve the problem of low pressure resistance of the conventional ferrofluid seal (FFS) under the condition of single magnetic source with large gap, which is difficult to meet the demand of vacuum sealing, the convergent FFS with stepped pole piece structure was designed. The designed structure is also compared with the conventional FFS structure. The effects of radial and axial sealing gaps (SGs), number of steps, step height on the pressure resistance and self-repairing ability of the seal were experimentally investigated. The results show that the new FFS structure can withstand 1 atm when the number of steps is 4 and the radial SG is 0.4 mm, which can provide a reference for vacuum sealing. The innovative FFS has a maximum pressure resistance 23 times higher than the conventional FFS for the same size. The self-repairing ability of the seal is negatively correlated with the radial and axial SG, the number of steps, and the height of the steps. The results of this study are important for the design of the FFS structure with single magnetic source that meets the requirements of a vacuum environment.

Dual-task walking on real-world surfaces: Adaptive changes in walking speed, step width and step height in young and older adults

ObjectivesAge-related changes in dual-task walking are well established, but research in this topic is based on evidence from laboratory rather than real-world studies. We investigated how dual-task walking on real-world surfaces affects young and older adults' gait characteristics and cognitive resource allocation. MethodSixteen young (aged 19–35, 12 female) and fifteen older adults (aged 70–85, 7 female) with no major neurological or musculoskeletal disorders walked at a self-selected speed on forty-metre outdoor paths that had asphalt or grass surface. They walked with or without a cognitive task (counting backwards). Cognitive task difficulty was individually adjusted at 80 % accuracy. Participants performed the three tasks in Single Task (ST Asphalt, ST Grass, ST Cognitive) and Dual Task context (DT Asphalt-Cognitive, DT Grass-Cognitive). ResultsThe two groups showed similar dual task effects in cognition and walking speed, both of which were slower when dual-task walking. Older adults' steps were wider overall but only young adults widened their step width when dual-task walking on grass compared to asphalt. Similarly, young adults' step height increased from single to dual-task walking when on grass, where older adults' did not. DiscussionThe lack of adaptation of step width and height when dual-task walking may leave older adults vulnerable to tripping or falling in common real-world conditions, such as while walking on grass, gravel, or uneven city sidewalks. Considering this, the built environment should be made more accessible to facilitate older adults' safe walking.

Rapid and inexpensive voltammetric detection of ochratoxin A in wheat matrices

Produced as toxic metabolites by fungi, mycotoxins, such as ochratoxin A (OTA), contaminate grain and animal feed and cause great economic losses. Herein, we report the fabrication of an electrochemical sensor consisting of an inexpensive and label-free carbon black-graphite paste electrode (CB-G-CPE), which was fully optimized to detect OTA in durum wheat matrices using differential pulse voltammetry (DPV). The effect of carbon paste composition, electrolyte pH and DPV parameters were studied to determine the optimum conditions for the electroanalytical determination of OTA. Full factorial and central composite experimental designs (FFD and CCD) were used to optimize DPV parameters, namely pulse width, pulse height, step height and step time. The developed electrochemical sensor successfully detected OTA with detection and quantification limits equal to 57.2 nM (0.023 µg mL−1) and 190.6 nM (0.077 µg mL−1), respectively. The accuracy and precision of the presented CB-G-CPE was used to successfully quantify OTA in real wheat matrices. This study presents an inexpensive and user-friendly method with potential applications in grain quality control.