Space Coordinate Transformation Research Articles

Semantic-aware hyper-space deformable neural radiance fields for facial avatar reconstruction

High-fidelity facial avatar reconstruction from monocular videos is a prominent research problem in computer graphics and computer vision. Recent advancements in the Neural Radiance Field (NeRF) have demonstrated remarkable proficiency in rendering novel views and garnered attention for its potential in facial avatar reconstruction. However, previous methodologies have overlooked the complex motion dynamics present across the head, torso, and intricate facial features. Additionally, a deficiency exists in a generalized NeRF-based framework for facial avatar reconstruction adaptable to either 3DMM coefficients or audio input. To tackle these challenges, we propose an innovative framework that leverages semantic-aware hyper-space deformable NeRF, facilitating the reconstruction of high-fidelity facial avatars from either 3DMM coefficients or audio features. Our framework effectively addresses both localized facial movements and broader head and torso motions through semantic guidance and a unified hyper-space deformation module. Specifically, we adopt a dynamic weighted ray sampling strategy to allocate varying degrees of attention to distinct semantic regions, enhancing the deformable NeRF framework with semantic guidance to capture fine-grained details across diverse facial regions. Moreover, we introduce a hyper-space deformation module that enables the transformation of observation space coordinates into canonical hyper-space coordinates, allowing for the learning of natural facial deformation and head-torso movements. Extensive experiments validate the superiority of our framework over existing state-of-the-art methods, demonstrating its effectiveness in producing realistic and expressive facial avatars. Our code is available at https://github.com/jematy/SAHS-Deformable-Nerf.

Experimental Investigation of a Rapid Calculation and Damage Diagnosis of the Quasistatic Influence Line of a Self-Anchored Suspension Bridge Based On Deflection Theory

Abstract Based on deflection theory (DT), the basic differential equations and deformation compatibility equations of self-anchored suspension bridges (SASBs) are established. The calculation formula for the stiffening girder (SG) deflection of a three-span SASB is derived, and the validity of the formula is confirmed through an example. In addition, a fast calculation method for the theoretical deflection influence line (TDIL) is proposed by using the deflection calculation formula, and a calculation method for the actual deflection influence line (ADIL) is founded on the concept of time and space coordinate transformation. By loading the bridge with a load car and using real-time monitoring of the displacement response of the bridge test section, combined with the proposed intelligent damage evaluation program, the abnormal situation of the damage of the three-span SASB can be quickly and accurately identified. The research results of this paper can provide flexible, economical and effective guidance for detecting the capacity of real bridges.

Three-dimensional simulation based on mesh modelling for warp-knitted fully-formed garments

PurposeThe warp-knitted fully-formed shorts are one kind of fully-formed garments knitted by a double-needle bar machine, which is widely used in the medical field. Because of its distinctive forming method, designers are unable to grasp the final effect of the product accurately during the design process. The purpose of this paper is to clarify a visible 3D simulation method in the design process along with the knitting method and structure characteristics, which is reflected in the final product effect.Design/methodology/approachThis study introduces a simulation process for warp-knitted fully-formed fabric from an input 3D surface model group. Stitch mesh models are established according to the garment structure and the triangle index of the garment model that swchape-controlling points belong to is calculated. The garment model group includes a 2D plate and a 3D model, between which there is a space coordinate transformation relationship. The study makes use of the 3D tubes to connect the coordinate points in order and render the tubes in real yarn colors. The effects of two parameters, radial segment and tubular segment, are analyzed and decided to obtain a fine surface within a reasonable rendering time.FindingsA stereoscopic simulation process from flat fabric to 3D product is realized using computer graphics technology. The warp-knitted fully-formed short is shown during the design process within a short time by setting the rendering parameters of tubular segments (ts = 125) and radial segments (rs = 6).Originality/valueVisual simulation for the shorts provides a time-saving and resource-saving method for structure design and parameter modification before knitting. There is no need to knit samples repeatedly to satisfy demand, which indicates that it is a saver of time and resources.

A motion characteristics modeled angular position sensor by nonlinear transfer of differential capacitance for miniaturized scanning mirrors

In this paper, an angular position sensor (APS) designed for a resonant miniaturized scanning mirror (M-SM) is presented. The APS operates based on the principle of differential variable capacitance, significantly expanding the detectable bandwidth from a few hertz to several kilohertz. By modeling the motion characteristics, the sampling rates of the biaxial scanning angles are 1473.6 times and 539.4 times higher than those of conventional sensors. Initially, the motion characteristics model is presented as a simple harmonic motion, converting sampled capacitance into continuous capacitance. Subsequently, the nonparallel state of the M-SM and sensor is transformed into a parallel state through the space coordinate system transformation. Furthermore, a 2D nonlinear angle transfer function is developed to convert the differential capacitance into an angle, thereby mitigating the nonlinear errors resulting from large angles. Achieving an accuracy better than 0.014°, the measuring range expands from ±0.5729° (±10 mrad) to ±5.026° ( ± 87 mrad). Additionally, the capturing mode and tracking mode are proposed to monitor real-time angular changes of the M-SM with an accuracy of 0.017°. High-precision APSs have enhanced beam pointing accuracy and resolution and can thereby be used to advance the development of laser components, including light detection and ranging (LiDAR).

Meshing characteristics analysis of planetary roller screw mechanism with misalignment

In this study, a meshing model for planetary roller screw mechanism (PRSM) with misalignment is established, considering misalignment angle and misalignment azimuth angle. By incorporating these misalignment variates into space coordinate transformation matrices, the meshing equations of screw-roller and nut-roller interfaces are derived to explore the meshing characteristics of PRSM with misalignment. Furtherly, the maximum misalignment angle of PRSM is obtained by the bisection method to research the limit position in misalignment. The effectiveness of the misalignment meshing model is verified by comparing with a previously published model. In addition, a typical PRSM is taken as an example to investigate the effect of misalignment angle and misalignment azimuth angle on meshing positions and axial clearances of PRSM. The results demonstrate that the meshing characteristics of PRSM with misalignment have an enormous difference from that of PRSM in an ideal state.

A fast and accurate camera-IMU calibration method for localization system

<p>Autonomous driving has spurred the development of sensor fusion techniques, which combine data from multiple sensors to improve system performance. In particular, a localization system based on sensor fusion, such as Visual Simultaneous Localization and Mapping (VSLAM), plays a crucial role in environment perception and serves as the foundation for decision-making and motion control in intelligent vehicles. The accuracy of extrinsic calibration parameters between the camera and IMU is of utmost importance for precise positioning in VSLAM systems. However, existing calibration methods are often time-consuming, rely on complex optimization techniques, and are sensitive to noise and outliers, leading to potential degradation in system performance. To address these challenges, this paper presents a fast and accurate camera-IMU calibration method based on space coordinate transformation constraints and SVD (Singular Value Decomposition) tricks. The method involves constructing constraint equations by ensuring the equality of rotation and transformation matrices between camera frames and IMU coordinates at different time instances. Subsequently, the external parameters of the camera-IMU system are solved using quaternion transformation and SVD techniques. To validate the proposed method, experiments were conducted using the ROS (Robot Operating System) platform, where camera images and velocity, acceleration, and angular velocity data from the IMU were recorded in a ROS bag file. The results demonstrate that the proposed method achieves reliable camera-IMU calibration parameters, requiring less tuning time and exhibiting reduced uncertainty.</p>

Raw Data Simulation of Spaceborne Synthetic Aperture Radar with Accurate Range Model

Simulated raw data have become an essential tool for testing and assessing system parameters and imaging performance due to the high cost and limited availability of real raw data from spaceborne synthetic aperture radar (SAR). However, with increasing resolution and higher orbit altitudes, existing simulation methods fail to generate SAR simulated raw data that closely resemble real raw data. This is due to approximations such as curved orbits, “stop-and-go” assumption, and Earth’s rotation, among other factors. To overcome these challenges, this paper presents an accurate range model with a “nonstop-and-go” configuration for raw data simulation based on existing time-domain simulation methods. We model the SAR echo signal and establish a precise space geometry for spaceborne SAR. Additionally, we precisely identify the target illumination area based on elliptical beams through space coordinate transformation. Finally, the SAR raw data were accurately simulated using high-precision time-domain simulation methods. The accuracy of the proposed model was validated by comparing it with the traditional hyperbolic model and the curved orbit model with “stop-and-go” assumption through image processing of the generated raw data. Through the analysis of point target quality parameters, the errors of various parameters in our distance model compared with the other two models are within 1%. Furthermore, this simulation method can be adapted to simulate raw data of other modes and satellite orbits by adjusting beam control and satellite orbit parameters, respectively. The proposed simulation method demonstrated high accuracy and versatility, thereby providing a valuable contribution to the development of remote sensing technology.

Wear analysis and simulation of small module gear based on Archard model

With the development of micro machining technology, small module gears are widely used in the field of high precision technology. In view of the failure problems such as tooth fracture and fatigue pitting caused by dynamic wear in the process of small module gear transmission, this paper takes a micro planetary gear reducer as the research object and establishes the analysis framework of small module gear wear calculation model based on Archard wear model and Hertz contact theory. Considering the influence of installation error and position tolerance, tooth contact analysis (TCA) model of small module gear is established based on the theory of small displacement torsor (SDT) and space coordinate transformation, and the impact of these errors on the dynamic contact trajectory, contact stress, and tooth surface wear is analyzed based on the numerical simulation. The numerical simulation results show that with the increase of the installation error, the contact trajectory will deviate significantly, which will finally result in increased contact stress and wear. Moreover, with the decrease of tolerance level, the service life of the device increases under the same reliability level. The above analysis of tooth surface wear can provide references for the design and installation of a small module gear transmission.

Applying edge artificial intelligence to closed-loop real time control and monitoring of laser based battery pack welding

The manufacturing of battery packs plays an essential role in e-mobility. In this context, laser welding of batteries has taken a considerable momentum in recent years as it can quickly adapt to different form factors and battery arrangements which is crucial for short runs and on-demand manufacturing. In this paper, we present an assisted battery pack welding system applying a novel sensor fusion strategy. The presented work introduces a multi-camera solution combining a camera in the visual range and an infrared camera in a compact scanner head that applies graphics processing unit acceleration for image processing and real-time field programmable gate array processing for process control. In order to acquire accurate temperature measurements, the infrared camera has been characterized and calibrated for the temperature ranges of the welding process. In addition, we propose a method for image space coordinate transformation based on affine transformations used to transform the coordinates of the detected battery joints into different image spaces to adapt to the welding process in real time. A single shot multibox detector Mobilenet-v2 neural network has been retrained with custom images to detect and classify a set of battery pack types allowing the extraction of the battery cell joint coordinates using image processing, which enables the application of real-time corrections to the laser aiming system and a closed-loop laser power control. Finally, we present some battery welding results using different welding strategies on the described system.

Analysis and Optimization of Suspension Spring Stiffness for Improving Frequency Response Characteristics of the Vehicle

The work puts forward a way to research the kinematics of front double wishbone suspension by virtue of analytical method. A way of discussing the kinematics of rear five-link suspension is put forward by means of space coordinate transformation. The influence of suspension spring stiffness on the suspension characteristics is analyzed. The vehicle frequency response index is deduced in view of theoretical model of equivalent handling stability. The relationship between the vehicle frequency characteristic index and the frequency of the steering wheel angle under the variation of spring stiffness is gained, and the influence mechanism of spring stiffness on the vehicle frequency characteristics is explained. The suspension spring stiffness is the optimization variable, the vehicle frequency characteristic index is the optimization objective, and genetic algorithm is used to optimize the vehicle frequency characteristic.

Geometric error modeling of the contact probe in a three-dimensional screw thread measuring machine

In this study, the influence of the geometric error of a contact probe on the accuracy of thread measurement was investigated to improve the measurement accuracy of three-dimensional (3D) screw thread measuring machines. The structure and measurement principle of the 3D thread measuring machine were studied, and the geometric error sources of the contact probe were analyzed. The principles of space coordinate transformation and the geometric theorem were used to establish a geometric model of the error sources. The experimental platform and the standard ball measurement of the three-coordinate machine were configured to verify the geometric error model. The results revealed that the measurement error was significantly reduced after compensation by the model. The proposed geometric error modeling method provides a clear theoretical basis for the accurate compensation of contact probe deviations and further improves the measurement accuracy of 3D thread measuring machines.

Analysis and optimization of vehicle handling stability with considering front and rear suspension hard point coordinates

For the front double wishbone suspension, starting from the space analytic geometry, a method of describing the movement law of the its is proposed and kinematic analysis is performed, and then the expressions of front wheel alignment parameters are derived by the vector method. Based on the theory of space coordinate transformation, a method of analyzing the kinematics of the five-link suspension is proposed, and the toe angle and camber angle of the rear wheels are derived. The virtual kingpin of the rear suspension is approximated by the instant screw axis method to obtain the expressions of the kingpin alignment parameters. The sensitivity analysis of the impact of the hard point coordinates on the suspension performance indicators is obtained, and the hard point coordinates that are most sensitive to the front and rear suspension performance indicators are obtained. And this is used as the analysis object to explore the influence of the hard point coordinate changes on the wheel alignment parameters. The frequency response index of the vehicle is derived from the vehicle dynamics model, and the change law of the frequency response index of the vehicle in the low and high frequencies is obtained based on swept-sine input simulation. Finally, the sensitivity analysis of the vehicle handling stability is carried out on the hard point coordinates, and the more sensitive hard point coordinates are selected as the optimization variables. The vehicle frequency characteristic index is used as the optimization target, and the NSGA-II algorithm is used for multi-objective optimization. After optimization, the result shows that the handing stability of the vehicle in the low frequency range has been improved.

A New Fast Matching Method for Dummy K-anonymous Location Privacy Protection in Location Based Services

This paper proposes a dummy k-anonymous location privacy protection based on a fast-matching method that adopts the space coordinate transformation algorithm. First, the 2-D coordinates are converted to binary Morton code. With the fast matching method, non-adjacent position points distributed in different grids are selected as candidate sets of dummy positions. Then, the semantic similarity of place name information of position points in the candidate sets is calculated using the edit distance, and k-1 position points with the smallest semantic similarity are selected as dummy positions. While satisfying the semantic l-diversity and physical dispersion, this method can improve the generation efficiency of dummy locations and further improve the quality of location service.

A monitoring method for car-body vibration displacement of a high-speed train in windy conditions

The long-term monitoring of car-body vibration displacement when a high-speed train passes through complex terrain sections in windy conditions has become an urgent engineering problem in China. However, few studies have focused on this topic, and an effective engineering long-term monitoring method is lacking in China. In this study, by combining the vibration characteristics and structural characteristics of railway vehicles, a real-time car-body displacement monitoring method to fulfill monitoring requirements was proposed, and a mathematical computational model based on space coordinate transformations to calculate the car-body displacements in operation was developed. Moreover, the comparison and the verification of the monitoring system accuracy were conducted using full-scale tests. The results showed that the displacement of the car-body relative to the bogie frame obtained through the system was consistent with the real vibration state of the car-body. Therefore, our monitoring system was reliable in reflecting the car-body vibration displacement changes in high-speed trains that were in motion.

Study on the Localization Method of Multi-Aperture Acoustic Array Based on TDOA

When the background noise is large or the sound source is far away from the microphone array, the localization accuracy of target sound sources will decrease dramatically. In order to solve this problem, a localization method of multi-aperture acoustic array based on time difference of arrival(TDOA) is proposed. The multi-aperture acoustic array is constructed by two small sub microphone arrays, which is supposed to surpass the performance of the equivalent large array composed of all microphones. The positions of the target sound source in two local coordinates are separately estimated by the two sub microphone arrays based on the generalized trust-region sub-problem in the modified polar representation (GTRS-MPR) method. Through the space coordinate transformation, the estimated two positions of the target sound source in the two local coordinates can be transferred into one global coordinate. To optimize the final estimated position of the target sound source by the multi-aperture acoustic array, two spatial lines are formed between the reference microphones of the two sub-arrays and the estimated two sources' positions in the global coordinate, and a search algorithm of shortest distance point based on the least-square method is proposed to fuse the localization results of the two sub-arrays. A simulation and an experimental platform are set up to verify the proposed method. The results show that the proposed method has higher localization accuracy compared with the existing methods. Especially, the accuracy of range estimation is greatly improved, which will be more suitable for the far-field sound source localization.

Using radial basis function neural network for PMSM to overcome the changing load

This paper presents a using Radial Basis Function Neural Network (RBFNN) for PMSM to overcome the changing load. Firstly, a mathematic model of the PMSM drive is derived; then, to increase the performance of the PMSM drive system, a Fuzzy PI controller in which an RBFNN adjusts its parameters is applied to the speed controller for coping with the effect of the system dynamic uncertainty and the external load. Secondly, the Very high-speed integrated circuit Hardware Description Language (VHDL) is adopted to describe the behaviour of the speed control IC which includes the circuits of space vector pulse width modulation (SVPWM), coordinate transformation, RBFNN, and Fuzzy PI. Thirdly, the simulation work is performed by MATLAB/Simulink and ModelSim co-simulation mode, provided by Electronic Design Automation (EDA) Simulator Link. The PMSM, inverter, and speed command are performed in Simulink, and the speed controller of the PMSM drive is executed in ModelSim. Finally, the co-simulation results validate the effectiveness of the proposed algorithm based speed control system

Thermal error detection and compensation technology for spindle of horizontal CNC machine tool with large torque

Titanium alloys and other difficult-to-machine materials are machined using large-torque CNC machine tools, and asymmetric mechanical spindle is employed in its spindle system. The mechanical spindle demonstrates high power and large torque. The asymmetric design makes the spindle structure more compact while reducing assembly requirements. Nevertheless, when processed, the asymmetric spindle shows complex thermal characteristics and makes it difficult to ensure real-time control, which easily results in significant errors for parts. To eliminate the uncontrollable thermal error, the efforts are made as follows. Firstly, the cold state and hot state attributes in thermal error analysis of mechanical spindle are defined, and the method to distribute the measuring position of asymmetric mechanical spindle temperature is proposed. Secondly, a three-dimensional space detection and analysis method for thermal error of six-vector eight-test based on rotation error vector and deviation error vector is suggested. Thirdly, according to the experimental results, the six-vector thermal error of the three-dimensional space is determined, and then a thermal error compensation technology based on Siemens space coordinate transformation parameters is proposed. Finally, the S specimen recommended by ISO 10791-1-annex A was used for machining verification before and after thermal error compensation. By comparing the 0.129 mm deviation before compensation and the 0.085 mm deviation after compensation, the machining accuracy of parts is discovered to improve by 34.1%. Therefore, the above research lays a theoretical foundation for the follow-up thermal error detection and compensation for the asymmetric spindle of large torque CNC machine tools of the same type.

A 3D analytical model for residual stress in flank milling process

Residual stress in metal cutting is critical due to its significant influence on the work performance of the workpiece. A 3D analytical model of residual stress appropriate for flank milling is established in this paper which takes both mechanical effect and thermal effect into consideration. Firstly, the 3D mechanical stress component is calculated considering its instantaneous and intermitted properties in the milling process. Elastic semi-infinite space contact mechanics and coordinate transformation are employed in the calculation process. Subsequently, the temperature distribution in the workpiece and corresponding thermal stress component are acquired based on the time-varying transient moving heat source model in the milling process. The plastic stress component is calculated based on the radial return method, in which all the stress components are updated during the plastic loading process. Finally, the measurement experiments for milling temperature and residual stress are performed to validate the theoretical models proposed in this work. The fine consistency between the prediction and the experiment demonstrates the accuracy of the prediction model. According to the calculation results of the proposed theoretical model, the plowing effect induced by the squeeze of the cutting edge on the work material is the major source of the residual stress.

Research on Discharging Current Distribution of Grounding Electrodes

Grounding electrodes with good current discharging performance can ensure the reliability of power system security. Discharging current is not only the reason for accelerating the corrosion, but also the key indicator of the grounding electrodes' grounding performance, which directly affects the grounding resistance, step voltage, ground potential distribution, and other macro grounding parameters. This paper focuses on the discharging current distribution of horizontal and vertical grounding electrodes. Based on the FEM of space tetrahedron and space coordinate transformation method, the calculation model of the horizontal grounding with ground lead and the vertical grounding is proposed, and distribution of discharging current on grounding electrodes with different length is analyzed. Results reveal that discharging current distribution on different location of the aforementioned grounding electrodes. Components of discharging current density on grounding electrodes surface and ground lead exhibit sinusoidal distribution along the circumference of the section on grounding electrodes, and discharging current inside the section are more concentrated on the surface of the section and less on the center. Most discharging current near the junction between horizontal grounding electrodes and ground lead is perpendicular to plane defined by grounding electrodes and ground lead.

A Rendering Engine Development for Civil Aviation Simulation

If the application software systems want to process terrain by high frame, terrain visualization is a important and spinous problem, such as the simulation of flight and synchronous sensor about ground flight test, the visualization project priority researched in this article. As far as the technology we have mastered is concerned, the main problem is the space model and coordinate transformation of visualization, which needs sufficient efficiency arithmetic and procedure to come true. Therefore, this article provides a arithmetic model and implementation to establish space construction and realize coordination transformation, which makes sure that the error rate of frame transmission is under control, and the transmission efficiency is improved.