Accurate Shape Research Articles

Machinability Measurements in Milling and Recurrence Analysis of Thin-Walled Elements Made of Polymer Composites

The milling of polymer composites is a process that ensures dimensional and shape accuracy and appropriate surface quality. The shaping of thin-walled elements is a challenge owing to their deformation. This article presents the results of milling polymer composites made of glass and carbon fibers saturated with epoxy resin. The milling of each material was conducted using different tools (tools with polycrystalline diamond inserts, physically coated carbide inserts with titanium nitride and uncoated carbide inserts) to show differences in feed force and deformation after the machining of individual thin-walled samples. In addition, the study used recurrence analysis to determine the most appropriate quantifications sensitive to changes occurring in milling different materials with the use of different tools. The study showed that the highest forces occurred in milling thin-walled carbon-fiber-reinforced plastics using uncoated tools and the highest feeds per revolution and cutting speeds. The use of a high feed per revolution (0.8 mm/rev) in carbon-fiber-reinforced plastics machining by uncoated tools resulted in a maximum feed force of 1185 N. A cutting speed of 400 m/min resulted in a force of 754 N. The largest permanent deformation occurred in the milling of glass-fiber-reinforced composite samples with uncoated tools. The permanent deformation value of this material was 0.88 mm. Low feed per revolution (0.1 mm/rev) resulted in permanent deformations of less than 0.30 mm for both types of materials. A change in feed per revolution had the most significant effect on the deformations of thin-walled polymer composites. The analysis of forces and deformation made it possible to conclude that high feed per revolution were not recommended in composite milling. In addition to the analysis of machining thin-walled composites, the novelty of this study was also the use of recurrence methods. Recurrence methods were used to determine the most appropriate quantifications. Determinism, averaged diagonal length and entropy have been shown to be suitable quantifications for determining the type of machined material and the tools used.

3D Information Guided Motion Transfer via Sequential Image Based Human Model Refinement and Face-Attention GAN

Image and video based human motions can be regarded as the deformation processes of person appearances, so motion transfer is usually treated as a pose guided image generation task and implemented in the 2D image plane. However, the 2D plane image generation lacks guidance of the original 3D motion information, which results in blur and shape distortions of the generated motion images. Therefore, we propose to simulate the generation process of real motion images by projecting the 3D human models, which are reconstructed from the training motion images and driven with target poses, into the 2D plane. We then take the 2D projections as the pose representations and input them into the generation model as they naturally inherit the 3D information from the original motions. Considering the unreliability on the invisible surface of the single image based human model reconstruction, we propose a sequential image based human model refinement module which exploits the complementary information between adjacent motion frames to refine the 3D human model. Furthermore, we propose a face-attention GAN model to conduct the final motion transfer, in which we use the Gaussian distribution to match the elliptical face region and design a face enhancement loss function since the faces in the generated motion images influence the performances very much. The generated motion images with reliable depth information, accurate shapes and clear faces demonstrate the effectiveness of the proposed method.

Research on Plastic Deformation of Rolled Pieces of Four-power rolling Mill Based on Deform

Aiming at the problems of large cross-section size change and low shape and position accuracy of the workpiece rolled by the four-power rolling mill, based on analyzing the plastic deformation mechanism of metal crystals, the rolling simulation was carried out by deform software to analyze the variation of section plastic deformation height and equivalent stress distribution of the rolled workpiece section. The results show that under the action of mutual vertical rolling force, the large plastic deformation with a length of about 2mm occurs in the local area of 45 ° diagonal at the end of the section, and the maximum height dimension increases by 4.5% relative to the blank height dimension. Its equivalent stress at the ends of both sides of the section is also the largest, and then gradually decreases and tends to be stable.

2D shape reconstruction of submillimetric irregular rough particles from speckle pattern in interferometric particle imaging measurement

Particle shape is a significant feature of irregular particles. The interferometric particle imaging (IPI) technique has been introduced to retrieve submillimetric irregular rough particle shapes, while inevitable experimental noises hinder the convergence of two-dimensional (2D) particle shapes from single speckle patterns. In this work, a hybrid input–output algorithm with shrink-wrap support and oversampling smoothness constraints is utilized to suppress the Poisson noise in IPI measurement and recover accurate 2D shapes of particles. Our method is tested in numerical simulations on ice crystal shapes and actual IPI measurements on four different types of irregular, rough particles. The shape similarity of the reconstructed 2D shape has reached an average Jaccard Index score of 0.927, and the relative deviation of the reconstructed size is within 7% for all 60 tested irregular particles at the maximum shot noise level of 7.4%. Furthermore, our method has obviously reduced the uncertainty in the 3D shape reconstruction of irregular, rough particles.

Full-Coverage Path Planning and Stable Interaction Control for Automated Robotic Breast Ultrasound Scanning

Ultrasound examination is widely used for diagnosis of breast cancer, which requires a full-coverage scan of the whole organ and stable probe–breast interaction for high-quality image acquisition. In this study, a robotic system for automated breast ultrasound scanning is proposed. To avoid occlusion, point cloud of the breast is obtained from multiple angles and registered together for accurate tissue shape reconstruction, then scan path planning is performed with isometric 3-D point cloud searching algorithm for full and uniform coverage. To reduce the adverse influence of large tissue deformation during ultrasound scanning, a contact force–strain regression model is built for tissue deformation estimation and used as a feedforward to correct the planned scanning path, and a probe–tissue interaction model with scanning resistance is built for normal probe orientation adjustment. To maintain normal probe orientation and stable contact force during robotic ultrasound scanning, a hybrid force–velocity control framework is proposed based on admittance control algorithm. Experiment results show that the robotic system can successfully maintain a constant contact force and keep the probe's posture along the normal orientation of probe–breast interaction both in in-plane direction and out-of-plane direction.

Parameters Optimization of Laser-Grinding Chain for Processing Groove of 2.5-Dimensional C/SiC Composites.

Aiming at problems such as poor precision of laser processing C/SiC composites, low efficiency of grinding C/SiC composites, and serious wear of grinding wheel, a method of laser-grinding chain processing C/SiC composite groove was proposed in this paper. The method combined the high efficiency characteristic of laser ablating and the high precision characteristic of grinding. The relationship between laser processing parameters and the characteristics of ablative grooves was investigated, and the appropriate laser processing parameters were optimized, and then, to further improve the processing quality of the grooves, the grinding parameters optimization experiments of the grooves of C/SiC composites were carried out. The results showed that the C/SiC composites could be quickly removed by laser processing, and the grooves with relatively good size and shape accuracy could be obtained by laser parameters optimization experiments, but the side wall of the groove still had a certain inclination and the surface quality of the groove was yet poor; meanwhile, the size accuracy, shape accuracy, and surface quality of the grooves were greatly improved by further grinding. In addition, then, through the laser and grinding optimization experiments, the optimized parameters were obtained, where the laser power was 80 W, the scanning speed was 300 mm/s, the scanning frequency was 50 kHz, the scanning spacing was 25 μm, the depth of cut was 30 μm, the liner speed of wheel was 62.832 m/min, and the feed speed was 10 mm/min. With these parameters, the time used to process the groove with the laser-grinding chain was about 23/40 of the grinding process, and the quality of grooves could be guaranteed. Therefore, combined with the optimized process parameters, the laser-grinding chain processing scheme could be used to achieve high efficiency and precision grinding of C/SiC composite grooves.

Study of Biomass Composite Workpiece Support Structure Based on Selective Laser Sintering Technology

When using selective laser sintering to print parts with thin-walled structures, the thermal action of the laser can cause thermal stresses that lead to plastic deformation, resulting in large warpage and dimensional deviations. To address this issue, this study proposes a bottom support method for selective laser sintering. The impact of lattice-type, concentric-type, and cross-type support structures with varying filling densities and thicknesses on the suppression of warpage and dimensional errors was investigated. The optimal process parameters for each support structure were then determined through optimization. The findings of this study demonstrated a reduction in Z-axis dimensional errors of the workpiece following the addition of supports. The reduction amounted to 33.809%, 86.160%, and 66.214%, respectively, compared to the original workpiece. Moreover, the corresponding warpage was reduced by 35.673%, 46.189%, and 46.059% for each respective case, showcasing an improvement in the printing precision. Therefore, the bottom support effectively reduces dimensional and shape errors in thin-walled parts printed by selective laser sintering. Specifically, the results obtained indicated that the concentric type of support is more effective in reducing dimensional errors and enhancing the shape accuracy of the printed workpiece. Conversely, the cross type of support demonstrated superior capabilities in minimizing the consumption of printing materials while still delivering satisfactory results. Thus, this study holds promise for contributing to the advancement of thin-walled part quality using selective laser sintering technology. This research can contribute to achieving greater accuracy in the fabrication of parts through 3D printing.

Numerical Simulation and Experiment of Stress Relief and Processing Deformation of 2219 Aluminum Alloy Ring

Large aluminum alloy ring forgings are the core components of heavy-duty rocket fuel storage tanks, and the large residual stress inside the rings leads to poor shape accuracy of large thin-walled parts. The initial stress of the 2219 aluminum alloy ring blank was tested using the drilling method, and the creep constitutive coefficient of the 2219 aluminum alloy was determined through stress relaxation tests. The numerical simulation processes of thermal stress relief (TSR), vibration stress relief (VSR), and thermal–vibration stress relief (TVSR) were compared and established. Through the correlation analysis between the actual measurement results of residual stress and the simulation results, it can be seen that the strong correlation in three directions at each measurement point accounts for over 37.5%, and the moderate correlation accounts for over 62.5%. This indicates that the numerical simulation model of 2219 aluminum alloy ring containing initial residual stress can accurately reflect the size and distribution of residual stress inside the actual ring. The simulation results show that the derived constitutive model can describe the stress relaxation process of TVSR by combining a single thermal time effect stress relaxation constitutive theory with a VSR plastic deformation material model. The simulation models established above were used to calculate the residual stress homogenization ability of three types of aging. The results showed that VSR, TSR, and TVSR can homogenize and reduce the residual stress field inside the ring, improve the distribution of residual stress inside the ring, and have a better overall homogenization ability of TVSR. The VSR control has a certain effect on reducing and homogenizing residual stress, but compared with TSR and TVSR, the reduction and homogenization ability of residual stress control is limited. The homogenization control effect TVSR > TSR > VSR, and the maximum equivalent stress homogenization rates of VSR, TSR, and TVSR are 52.8%, 80.6%, and 82.2%, respectively. Then, numerical simulation technology was used to study how the initial residual stress in the blank causes the deformation of the ring during the thin-walled machining process. The roundness error theory of the minimum containment area method was applied to evaluate the deformation degree during the thin-walled numerical machining process, and the TVSR method was used for stress regulation. The deformation law of the thin-walled machining of the ring under different aging parameters was studied.

Pretension design for mesh reflector antennas with flexible trusses and hinges based on the equilibrium matrix method

In the current pretension design of mesh reflector antennas based on the equilibrium matrix method (EMM), the truss and hinge deformation cannot be accurately captured, which will deteriorate the shape accuracy of the antenna. To solve this problem, this paper proposes a new EMM-based pretension design method. In this method, the rod of the truss is modeled as Euler-Bernoulli beam, and the joint of the hinge is treated as the spring with six degrees of freedom. Based on the beams and springs, the systematic equilibrium equation of the mesh reflector antenna is established considering the flexibility of rods and hinges. Then, the mesh reflector antenna is divided into the inner cable network and boundary cable-truss-hinge assembly. The equilibrium equation of the boundary cable-truss-hinge assembly is solved by the force density method to calculate the truss and hinge deformation. The equilibrium equation of the inner cable network is solved by the EMM to fix all free nodes at desired positions. Combined with the active-set optimization algorithm, the required cable tensions are obtained by taking the mean tension ratio of the cable network as the objective function, thus ensuring high shape accuracy. Lastly, the proposed method is applied to the mesh reflector antenna and verified by ABAQUS.

Optimization Design of Large-Aperture Primary Mirror for a Space Remote Camera

Lightweight, high stability, and high-temperature adaptability are the primary considerations when designing the primary mirror of a micro/nano satellite remote sensing camera. In this paper, the optimized design and experimental verification of the large-aperture primary mirror of the space camera with a diameter of Φ610 mm is carried out. First, the design performance index of the primary mirror was determined according to the coaxial tri-reflective optical imaging system. Then, SiC, with excellent comprehensive performance, was selected as the primary mirror material. The initial structural parameters of the primary mirror were obtained using the traditional empirical design method. Due to the improvement of SiC material casting complex structure reflector technology level, the initial structure of the primary mirror was improved by integrating the flange with the primary mirror body design. The support force acts directly on the flange, changing the transmission path of the traditional back plate support force, and has the advantage that the primary mirror surface shape accuracy can be maintained for a long time when subjected to shock, vibration, and temperature changes. Then, a parametric optimization algorithm based on the mathematical method of compromise programming was used to optimize the design of the initial structural parameters of the improved primary mirror and the flexible hinge, and finite element simulation was conducted on the optimally designed primary mirror assembly. Simulation results show that the root mean square (RMS) surface error is less than λ/50 (λ = 632.8 nm) under gravity, 4 °C temperature rise, and 0.01 mm assembly error. The mass of the primary mirror is 8.66 kg. The maximum displacement of the primary mirror assembly is less than 10 μm, and the maximum inclination angle is less than 5″. The fundamental frequency is 203.74 Hz. Finally, after the primary mirror assembly was precision manufactured and assembled, the surface shape accuracy of the primary mirror was tested by ZYGO interferometer, and the test value was 0.02 λ. The vibration test of the primary mirror assembly was conducted at a fundamental frequency of 208.25 Hz. This simulation and experimental results show that the optimized design of the primary mirror assembly meets the design requirements of the space camera.

The Design and Development of a Foot-Detection Approach Based on Seven-Foot Dimensions: A Case Study of a Virtual Try-On Shoe System Using Augmented Reality Techniques

Unsuitable shoe shapes and sizes are a critical reason for unhealthy feet, may severely contribute to chronic injuries such as foot ulcers in susceptible people (e.g., diabetes patients), and thus need accurate measurements in the manner of expert-based procedures. However, the manual measure of such accurate shapes and sizes is labor-intensive, time-consuming, and impractical to apply in a real-time system. This research proposes a foot-detection approach using expert-like measurements to address this concern. It combines the seven-foot dimensions model and the light detection and ranging sensor to encode foot shapes and sizes and detect the dimension surfaces. The graph-based algorithms are developed to present seven-foot dimensions and visualize the shoe’s model based on the augmented reality (AR) technique. The results show that our approach can detect shapes and sizes more effectively than the traditional approach, helps the system imitate expert-like measurements accurately, and can be employed in intelligent applications for susceptible people-based feet measurements.

Assessing the technological quality of abrasive water jet and laser cutting processes by geometrical errors and a multiplicative indicator

Technological quality is an important factor in industry processes. In this study an original index for assessing the technological quality for laser and abrasive water jet cutting was proposed. Developed MCTQ index links the most important features of quality assessment. The carried out tests allowed for the determination of the technological quality assessment based on the evaluation of dimensional and shape accuracy, analysis of the perpendicularity error of the cut edge, measurements of the surface texture parameters, and analysis of microscopic images. The results for both cutting technologies showed that the magnitude of the deviation of the analyzed geometric features increases with the thickness of the sheet. In the case of the laser jet cutting, the occurrence of surface defects were mainly affected by the molten material blow out from the kerf by the associated gas through the upper cutting zone. Straightness deviation, is mainly shape errors in case of the abrasive water jet cutting process. A proposed multiplicative indicator of cutting technological quality provides a relative measure for comparing the results of the cutting process among themselves.

Lie Group Formulation and Sensitivity Analysis for Shape Sensing of Variable Curvature Continuum Robots With General String Encoder Routing

This article considers a combination of actuation tendons and measurement strings to achieve accurate shape sensing and direct kinematics of continuum robots. Assuming general string routing, a methodical Lie group formulation for the shape sensing of these robots is presented. The shape kinematics is expressed using arc-length-dependent curvature distributions parameterized by modal functions, and the Magnus expansion for Lie group integration is used to express the shape as a product of exponentials. The tendon and string length kinematic constraints are solved for the modal coefficients and the configuration space and body Jacobian are derived. The noise amplification index for the shape reconstruction problem is defined and used for optimizing the string/tendon routing paths, and a planar simulation study shows the minimal number of strings/tendons needed for accurate shape reconstruction. A torsionally stiff continuum segment is used for experimental evaluation, demonstrating mean (maximal) end-effector absolute position error of less than 2% (5%) of total length. Finally, a simulation study of a torsionally compliant segment demonstrates the approach for general deflections and string routings. We believe that the methods of this article can benefit the design process, sensing, and control of continuum and soft robots.

PneuPrint: 3D printing on inflatables

This research investigated the feasibility of thermoplastic 3D printing on inflatable membranes. Five experiments were performed in an iterative process through design and manufacture (1), computational simulation and 3D scanning (2), and robotic fabrication on the pneumatic formwork (3). These experiments ranged from small to large-scale 3D printing. Experiment 1 demonstrated the small-scale feasibility of the process and the need to integrate an air-pressure control loop. Experiment 2 investigated the technique transfer from small to large-scale. Experiment 3 analyzed the deviation and shape accuracy of the inflatable membrane. Experiment 4 identified the required fabrication settings and compatibility between the membrane and the 3D printing material. Finally, Experiment 5 demonstrated the design and fabrication potential of large-scale 3D printed elements on pneumatic formworks. The results proved high potential for building freeform design elements for architectural applications on pneumatic formworks.

3-D Crosswell electromagnetic inversion based on IRLS norm sparse optimization algorithms

Due to the complexity of underground reservoir distribution and the non-uniqueness of geophysical inverse problems, there is still a lack of practical and effective cross-well electromagnetic inversion methods. Our goal is to develop an efficient method to reduce the non-uniqueness of the physical property model recovered in the inversion. Based on a defined framework, we propose a 3-D crosswell electromagnetic sparse inversion based on iterative reweighted least squares (IRLS) method. We perform the inversion using a hybrid norm formulation, where the lp-norm (0 ≤ p ≤ 1) sparse optimization problem can be transformed into a series of weighted l2-norm optimization problems. Compared with the traditional norm inversion method, the sparse inversion method can make more effective use of the known physical information and obtain more accurate abnormal body position and shape. Finally, the effectiveness of sparse inversion method is verified by model test and inversion of measured data in mining area.

Constitutive modelling of coupled creep deformation and age hardening behavior of aluminum alloys under various thermal and mechanical loadings

A new theoretical-based constitutive model has been proposed in this study to concurrently predict the ageing and coupled creep-ageing behavior in both micro and macro ways of aluminum alloys under complex thermal and mechanical loading histories. The nucleation, growth and coarsening theories for age strengthening of aluminum alloys have been modified with the integration of dislocation-based theories raised by plastic or creep deformation to form the new theoretical-based creep-ageing modelling framework. Both the key microstructures (precipitates, solid solutes and dislocations) and macro properties (creep/stress-relaxation, yield strength and strengthening components) under various thermal and loading histories (e.g., single-step/multi-step isothermal and non-isothermal, pre-strain loaded) of a typical Al–Zn–Mg alloy have been effectively predicted and validated by the same set model. Furthermore, the capability of the developed model to reveal the detailed deformation and strengthening mechanisms with complex thermal and loading histories, and to assist the design of complex non-isothermal creep-ageing processes with optimization objectives of accurate shape and high strength in the formed alloys has been discussed and demonstrated.

Spectral optimization-based modal identification: A novel operational modal analysis technique

In this work, we introduce a novel method, namely Spectral Optimization-based Modal Identification (SOMI) for estimating the modal parameters of structures. SOMI is developed to estimate highly accurate modal damping ratios and mode shapes using the Frequency Domain Decomposition (FDD) principles. The FDD method (and most of the present modal identification techniques), encounters some problems such as modal complexity, lack of accuracy in the case of large damping ratios, and noticeable error in mode shape estimation. In the FDD formulation, the Singular Value Decomposition (SVD) estimation is precise only for lightly damped structures for obtaining the mode shapes and the Power Spectral Density (PSD) function of the modal coordinates. Moreover, the complexity of the mode shapes obtained from the FDD method is significantly biased and should not be used for physical interpretations. The main idea behind the proposed SOMI method is the elimination of the SVD estimation and obtaining the PSD function of the modal coordinates and the mode shapes with the least approximations. Moreover, the modal damping ratio is directly estimated in the frequency domain without any transformation into time domain using two equations derived in this paper. SOMI method uses optimization to make the PSD function of the modal coordinates follow the theoretical equations and estimates highly accurate mode shapes. In this work, the derivations are given for the displacement, velocity, and acceleration signals. The detailed formulation of the proposed method is presented, it is validated with some examples, and its competitive accuracy is compared with the FDD method. The accuracy and robustness of SOMI in noisy conditions are also assessed, with results indicating its effectiveness in handling noise and maintaining accuracy.

Practical work for exploring the capabilities and benefits of CNC technology

Computer Numerical Control (CNC) technology's precision and complexity in design are two of its greatest strengths. CNC machines can make consistent and accurate cuts, drills, and shapes because they are controlled by computer programs. This precision is especially useful in sectors where producing complex components is mission-critical, such as the aerospace, medical, and automotive industries. The capacity to automate mundane processes is another benefit of CNC technology. CNC machines, once programmed, can mass-produce parts with little to no human intervention, greatly boosting efficiency and lowering production costs. By eliminating the potential for human error, this automation also increases the reliability and consistency of the final output. In addition, CNC machinery can facilitate quicker production runs and shorter setup times, both of which boost productivity. Enhanced productivity has the potential to boost a company's bottom line. Overall, CNC technology has the potential to revolutionize manufacturing by facilitating the rapid, precise, and cost-effective fabrication of intricate parts and components. Since this is a hotspot for innovation, new uses and capabilities appear frequently.

A strategy for improving negative-Poisson's-ratio constraint effect and shape accuracy of metamaterials by regulating mechanical properties of elastomer with facile filler incorporation

Negative Poisson's ratio (NPR) metamaterials are widely used for their light weight and good shear resistance. However, the essential concave hollow structures in NPR materials may easily distort irregularly when the constraint effect of their solid materials is weak, especially for elastomer-based materials. Here, we introduced nano-scale carbon black (CB) particles into the NPR material based on thermoplastic polyurethane (TPU) elastomers to control the static and dynamic mechanical deformation behavior of the material, improving their constraint effect on the NPR structure. The results show that the modulus of the NPR structure is improved by 269% by adjusting the unit and rigid particle load. The Poisson's ratio of the NPR structure reaches as great as −1.3 via controlling the thickness/width ratio (TWR) of the unit. Meanwhile, finite element analysis verifies that when TWR is less than 0.5, increasing the modulus and yield strength of the composites can enhance the constraint on the NPR unit. Theoretical calculation shows that CB introduced into TPU can improve the shape accuracy of NPR structure. Therefore, the work could offer a new mechanical enhancing strategy for NPR materials, and its application potential is verified as a form of exoskeletons.

Towards Accurate Reconstruction of 3D Scene Shape From A Single Monocular Image.

Despite significant progress made in the past few years, challenges remain for depth estimation using a single monocular image. First, it is nontrivial to train a metric-depth prediction model that can generalize well to diverse scenes mainly due to limited training data. Thus, researchers have built large-scale relative depth datasets that are much easier to collect. However, existing relative depth estimation models often fail to recover accurate 3D scene shapes due to the unknown depth shift caused by training with the relative depth data. We tackle this problem here and attempt to estimate accurate scene shapes by training on large-scale relative depth data, and estimating the depth shift. To do so, we propose a two-stage framework that first predicts depth up to an unknown scale and shift from a single monocular image, and then exploits 3D point cloud data to predict the depth shift and the camera's focal length that allow us to recover 3D scene shapes. As the two modules are trained separately, we do not need strictly paired training data. In addition, we propose an image-level normalized regression loss and a normal-based geometry loss to improve training with relative depth annotation. We test our depth model on nine unseen datasets and achieve state-of-the-art performance on zero-shot evaluation. Code is available at: https://github.com/aim-uofa/depth/.