Abstract:In response to the requirements for automatic positioning and scanning of component curved surfaces during aircraft assembly, relevant research was conducted using the Leica ATS600 laser tracker. Based on the SpatialAnalyzer (SA) software, secondary development was carried out using Measure Plan and SA SDK, and a research method for automatic positioning and scanning technology of laser trackers was proposed. The research process is as follows: first, connect the measurement equipment and import the curved surface digital model and theoretical positioning point information; then, measure the positioning features and curved surfaces; subsequently, perform digital model alignment and relationship matching between the actual measured information of the curved surface and the theoretical information, and automatically generate a report based on the matching results. Finally, a set of automatic positioning and scanning system for curved surface measurement was built, and a large-scale curved surface standard device was used as the experimental object for measurement. The results show that the program runs stably, effectively addresses the inherent shortcomings of SA, and significantly improves the efficiency and automation level of curved surface scanning.

Abstract:Accurate acquisition of time of flight (TOF) is essential for high-precision ultrasonic thickness measurement. A time delay estimation method for ultrasonic thickness measurement signal based on fuzzy variable-step least mean square (LMS) was proposed, addressing the issues that the inherent contradiction between the convergence speed and the steady-state error of the fixed-step LMS algorithm in the traditional ultrasonic signal time delay estimation, and the poor adaptability of the existing variable-step algorithm under non-stationary echo signals due to the dependence on the fixed function model. The time-varying characteristics of ultrasonic echo signal were analyzed, and the single error feedback mechanism was abandoned. The local correlation coefficient error and its variation between the output signal and the desired signal were extracted as the dual input characteristics of the fuzzy controller. The zero-order Sugeno fuzzy inference system was designed, and the nonlinear mapping rule between the input feature and the step size factor was established to realize the adaptive dynamic adjustment of the step size factor. The simulated echo signals were used to carry out simulation tests under different signal-to-noise ratios. The results show that compared with the fixed step size LMS algorithm, the hyperbolic tangent function variable step size LMS algorithm and the fuzzy variable step size LMS algorithm based on instantaneous error, the comprehensive performance of the proposed method is better. The steady-state offset error is significantly reduced while ensuring rapid convergence, with higher measurement accuracy and anti-noise performance. The experimental platform of ultrasonic thickness measurement was built, and the thickness measurement experiments were performed on gauge blocks. The results show that the relative errors of the proposed method for different thickness gauge blocks are all smaller than that of the other three LMS algorithms, and the maximum relative error is 0.71 %. The fuzzy variable step size LMS time delay estimation method can provide feasible scheme selection and technical support for high-precision ultrasonic TOF calculation, which is conducive to promoting the development of ultrasonic nondestructive testing technology and has certain engineering application value.

Abstract:As a key mechanical property index of materials, hardness directly affects the service performance, operational safety, service life and comprehensive quality of core products in advanced manufacturing fields including aerospace, high-end equipment, precision instruments and the automotive industry. Given the inherent drawbacks of traditional laboratory hardness testing, such as random sampling, delayed data feedback and independent data silos, this paper proposes and develops a digital on-line Brinell hardness testing method for complex components represented by aero-engine blades. The proposed method overcomes key technical bottlenecks, including precise positioning of irregular workpieces under dynamic conditions, adaptive constant-force surface grinding, and high-precision recognition of low-quality industrial indentation images. Relying on the above technologies, a digital on-line hardness testing production line is constructed, which supports full-coverage hardness data collection and real-time traceable result evaluation. Experimental results show that the established system achieves four times higher testing efficiency, with the GRR% of measurement system analysis (MSA) reaching 17.42%. Long-term industrial application and verification on tens of thousands of workpieces demonstrate the effectiveness and technical advantages of this method in realizing in-situ, real-time, fully automated and traceable hardness quality control. This study provides a viable technical route for promoting the integration of metrology and testing under the background of intelligent manufacturing.

Abstract:Lidar point cloud and visible image fusion technology, by integrating three-dimensional point clouds with two-dimensional texture and color information, can provide a richer and more accurate data foundation for environmental perception. Compared to conventional LiDAR, single-photon LiDAR offers advantages such as photon-level sensitivity and picosecond-level timing precision, enabling high-precision three-dimensional point cloud imaging over long distances and in low-observability scenarios. The fusion technology of single-photon LiDAR with visible images provides a new pathway for addressing target recognition and localization challenges in complex environments. This paper introduces the fundamental principles of conventional/single-photon LiDAR systems and image fusion technology, analyzes the feature differences between conventional/single-photon LiDAR and visible images as well as the issue of image registration, elaborates on the research and application status of fusion technology between conventional/single-photon LiDAR and visible images, and finally summarizes and prospects the current state of conventional/single-photon LiDAR and visible image fusion technology.

Abstract:The application of high-precision spherical coordinate scanning measurement systems can significantly improve the efficiency of contour measurement for components with complex curved features, such as aircraft wings and fuselages, rocket cabins, and wind turbine blades. However, the metrology of such systems and the evaluation of contour parameters based on their scanned point clouds pose a major challenge in the industry. To address the traceability issues associated with high-precision spherical coordinate scanning measurement systems, this paper proposes a calibration scheme and related requirements based on large-scale physical surfaces. Theoretical and experimental studies were conducted on the structural design, structural mechanics simulation, and panel alignment of the standard device, along with system calibration verification experiments. The experimental results demonstrate that this method can control the assembly error tolerance within 0.05 mm and reduce the RMS error to less than 0.01 mm, effectively supporting the establishment of traceability for the measurement system's accuracy.

Abstract:Silicon-based piezoresistive pressure sensors suffer from insufficient reliability and reduced service life due to issues such as output drift and sensitivity degradation in harsh environments. This study aims to systematically elucidate the physical mechanisms behind their stability degradation and to develop a high-precision life prediction model. Utilizing the physics of failure analysis theory, the research employed variable-amplitude cyclic loading and accelerated fatigue testing. Accelerated tests were conducted by applying alternating pressure with different amplitudes. A dataset of sensor failure degradation was established through microscopic examination and performance monitoring. This approach overcame the challenge of analyzing the coupled effects of multiple mechanisms, including diaphragm cracking, piezoresistor creep, and packaging stress failure, ultimately enabling the construction of a life prediction model under uniaxial pressure loading conditions. Accelerated life testing demonstrated that under a pressure load of 140% of the full-scale range, the sensor's linearity increased by over 50% after approximately 2.2 million cycles, which was defined as failure. The developed model achieved an error of less than 15% between the predicted and measured lifespan, enabling effective prediction of the sensor's failure cycle. The fatigue experiments conducted and the life prediction model developed in this study effectively meet the engineering requirements for reliability assessment and life extension of pressure sensors. This work holds significant theoretical and practical application value, providing crucial support for advancing the design optimization and lifetime prediction of highly reliable silicon-based pressure sensors.

Abstract:In atomic clocks, the uniformity of the static magnetic field generated by the C-field coil directly influences the measurement accuracy of atomic energy level transition frequencies and the stability of the clock. To address the issue of insufficient field uniformity in finite-length solenoids under spatial constraints, this paper conducts a parametric modeling and optimization study on a multi-segment C-field coil structure placed inside a magnetic shielding tube, based on the COMSOL Multiphysics simulation software. The results demonstrate that by adopting a multi-segment coil structure and optimizing winding parameters such as the number of segments and turns density, the magnetic field uniformity within the target region along the central axis can be significantly improved. Specifically, under optimal parameters, a five-segment coil reduces the magnetic field non-uniformity to 0.078% over a 40 mm range, while a seven-segment coil further optimizes the magnetic field non-uniformity to 0.033% over the same range. In this research, a compact multi-segment coil structure is optimally designed for the high-uniformity C-field of rubidium atomic optical clock in a limited space, and an efficient parameter determination method is provided.

Abstract:The chilled mirror precision dew point meter is a device for measuring the dew point temperature of gas, and it plays an important role in the humidity measurement system. However, the important parameter for measuring the dew point, the photoelectric signal, is insensitive to the change of the mirror temperature of the chilled mirror precision dew point meter, which makes it difficult to determine the optimal voltage change value at different dew point temperatures, resulting in low accuracy of the dew point temperature finally measured. In order to determine the optimal voltage change value at different dew point temperatures, solve the problem that the photoelectric signal is insensitive to the change of mirror temperature, and find the mirror state closest to the dew point moment, a mirror image feature analysis test based on the growth law of mirror condensation was designed. The test studies the relationship between the voltage change value of the photoelectric signal and different dew point temperatures, and analyzes the law under different dew point temperatures. At the same time, an electron microscope was used to analyze the mirror image at different voltage change values. The image features were extracted by calculating the number and density of condensates. The growth law of mirror condensate at the same dew point temperature and different voltage change values was summarized, and the selection range of the optimal voltage change value for different dew point temperatures was clarified. The problem that the photoelectric signal of the chilled mirror precision dew point meter is insensitive to the mirror temperature change is solved, and the accuracy of dew point measurement of the chilled mirror precision dew point meter is improved.

Abstract:For the precise ammonia (NH3) measurement, an ammonia measurement technique using femtosecond laser filament-triggered discharge is proposed. Discharge is triggered by long filaments formed in air by femtosecond laser pulses. The plasma emission spectra of NH3 under different conditions were obtained by using a spectral acquisition system. The calibration curve for NH3 concentration was obtained by utilizing the ratio of peak areas of characteristic spectral lines in the emission spectra. The one-dimensional spatial distribution of spectral line intensity was analyzed. Experimental results demonstrate that the ratio of characteristic spectral line peak areas exhibits excellent linear response to NH3 concentration. The one-dimensional spatial distribution of characteristic spectral line intensities exhibits good stability. Femtosecond laser filament-triggered discharge for NH3 concentration measurement enables real-time quantitative NH3 detection with one-dimensional measurement capability. This technique provides a novel approach for real-time in situ measurement of NH3.

Abstract:The accurate measurement of boundary flow field is very important for hydrodynamics research and aerospace applications. To this end, we propose a femtosecond laser-induced cyano chemiluminescence (FLICC) technique. The femtosecond laser was used to generate optical filaments in methane/nitrogen mixed flow field and induce CN (B-X) fluorescence with high intensity and long lifetime, thus realizing high spatial and temporal resolution flow field velocity measurement. Experimental results show that FLICC technique can be effectively used in complex flow and high spatial and temporal resolution measurement of boundary layer velocity is successfully achieved.