查看更多>>摘要：Minor debonding defects and weak adhesion impair solid propellant integrity, which may cause rocket launch failure. However, it's difficult to identify these interfacial bonding problems in-situ by the common temporal phase-shifting method due to its inaccurate phase calculation and background noises. In this work, a real-time phase processing method with high-frequency synchronizing trigger technology is proposed to improve phase map quality and anti-interference performance in the phase-shifting process. The method is applied to shearography/ESPI optical nondestructive measurement systems to detect minor debonding defects with minimum diameter of 2 mm and evaluate interfacial adhesive strengths of the bonding layers, respectively. The results show that stable and high-contrast phase maps are obtained in real-time from a large field of view, indicating that the detection capabilities of shearography/ESPI are enhanced via the application of the method. This work would contribute to the in-situ nondestructive evaluation of minor defects and weak adhesion in solid propellants.
查看更多>>摘要：On varied-mu roads, most of the current research on the estimation of tyre-road characteristic parameters and peak friction coefficient lack consideration of parameter constraints. To improve the estimation accuracy, in this study, a novel estimation scheme of tyre-road friction characteristics based on parameter constraints is proposed: based on estimating the longitudinal and lateral friction force, a data preprocessing method is proposed to obtain the constraint region of parameters. Then, the nonlinear least square method is used to preliminarily estimate the parameters. Finally, a constrained auxiliary particle filter algorithm is proposed to correct the estimated parameters. To verify the superiority of the proposed scheme, the estimation performances of friction characteristics of four schemes are compared on low/high speed varied-mu roads, respectively. The results demonstrate that the proposed scheme has the best estimation performance. Simultaneously, compared with the scheme without considering parameter constraints, the proposed scheme can significantly reduce the estimation error.
查看更多>>摘要：This study concentrates on the real-time standalone positioning that depends on single-frequency code observations with three smartphones, Xiaomi Mi 8, Google Pixel 4, and Pixel 4 XL, in the kinematic environment. For real-time positioning, two positioning approaches, which respectively employ ultra-rapid and IGS real-time service (IGS-RTS) products, are adopted in this study. Also, this study provides an advanced processing strategy that utilizes the variance component estimation method in determining the multi-GNSS observation weights. The experimental tests reveal that compared with ultra-rapid products, the use of IGS-RTS products augments the positioning accuracy of multi-GNSS solution by 5.4, 11.0, and 11.2% for Mi 8, Pixel 4, and Pixel 4XL smart phones. Also, Xiaomi Mi 8 can provide positioning accuracy of 7 m with the advanced processing strategy that improves the positioning performance of smartphones by 11.0% on average. Still, the improvement rate of the advanced processing strategy can reach 22.1% in some cases.
查看更多>>摘要：In the present investigation, an energy channelization behavior was improved while machining micro holes in the Yttria-stabilized zirconia (Y-SZ) under magneto hydrodynamic conditions. The integration of magnetic field with electrochemical spark machining (ECSM) process forms the stable and thin gas film on the tool electrode. The subsequent breakdown of this film improves the discharge frequency and increases the discharge current by 18%. The underlying process and material removal mechanisms were demonstrated by using the evidence from discharge signals, gas film images, SEM, and optical images of work material. The stirring action provided by the magnetic field in ECSM process helps to flush out the sludge and stray bubbles from the machining region. In comparison to the ECSM process, the hole depth and aspect ratio were improved by 84.37% and 120%, respectively. Thermal spalling is the leading phenomenon in the material removal process for Y-SZ instead of melting and chemical etching, as in the case of glass substrates. Energy channelization analysis is also carried out to establish the correlations between energy-based parameters and responses. The combination of higher applied energy with small pulse durations is suggested to produce deep holes. The parametric investigation, regression modeling, and optimization for the MFA-ECSM process are also carried out to explore the process behavior.
查看更多>>摘要：In the present study, we developed a torque generating machine using an electromagnetic force based on the principle of the Kibble balance method in order to realize a nano-torque traceable to the International System of Units (SI). In order to realize a nano-torque, the size and number of turns of the rectangular coil as well as the magnetic flux density must be reduced. However, when the magnetic flux density is reduced, there is concern about the influence of geomagnetism and other factors. Therefore, we first evaluated the influence of such factors on the machine using a method based on quantum mechanics. As a result, it was found that the influence of geomagnetism on the device is approximately 1 % of the magnetic field formed by the Helmholtz coil at maximum. In addition, the variation of the geomagnetic field during the time of the nano-torque experiment was found to be very small. The torque realized by an electromagnetic force was in the range of approximately 0.2 nN center dot m to 1 mN center dot m. Furthermore, the uncertainty in the realized torque was evaluated. Finally, an SI-traceable nano-torque was successfully realized using an electromagnetic force.
查看更多>>摘要：In a hand-eye collaborative measurement system, the measurement error caused by the position change of an industrial robot end can create challenges during the high-precision measurement of large-scale components. The relative instability between binocular stereo vision and robot end is discussed for the first time, and a relative instability compensation (RIC) method is proposed. Firstly, using a watershed-model based on the Gaussian mixture model clustering, and locking of the region of interest are achieved. The correction of ellipse distortion combined with camera internal parameters is employed, and the 3D coordinate is reconstructed. Subsequently, the common and link points are constructed to perceive the updating of the positions. Based on the assumption of small-angle deviation, a novel model is established for compensating the relative instability. Ultimately, the experiment results indicate that the proposed method is effective for improving the measurement precision, which is superior to 0.075 mm.
查看更多>>摘要：Pantograph slider is the critical component to provide power for the train. The friction between the slider and the contact line will lead to the continuous wear of the slider. Timely monitoring of the slider wear state is of great significance to ensure the safety of train operation. In this paper, we propose an online monitoring system based on 2D laser displacement sensors for the slider wear state. First, two 2D laser displacement sensors are employed to collect the slider data. Second, the original data are processed by algorithms including data pre-processing, data fusion, slider data correction, curve fitting, and wear curve extraction to obtain the wear curve of the slider. Then, five criteria are used to evaluate five wear states. The experimental results shown that the proposed system has good wear detection accuracy and can automatically evaluate the slider wear state, which can meet the needs of on-site maintenance.
查看更多>>摘要：In this paper, a novel eco-friendly solid bismuth microelectrode for direct tungsten quantification by cathodic stripping voltammetry (CSV) is discussed. The novelty of the proposed sensor results from the fact that the used microelectrode (o = 25 mu m) exhibits perfect long-term persistence. Moreover, on account of spherical diffusion and insensitivity to the presence of oxygen in the solution the analysis could be performed at the point of sampling. The instrumental and chemical factors influencing the sensitivity of the sensor were thoroughly investigated and their most favorable values were selected (pH = 2.88, acetic acid concentration: 0.1 M; activation potential/time:-1.8 V/1 s; accumulation potential/time:-0.5 V/20 s). Under selected conditions, the method exhibits linearity in the range of 1 x 10(-8) to 5 x 10(-6) M, while the detection boundary was calculated to be 1.3 x 10(-9) M. This method has been shown to be highly selective and insensitive to the presence of even 10 mg L-1 of humic substances due to the addition of the adsorptive Amberlite XAD-7 resin to the test solution. In keeping with the outlined procedure, the certified reference materials (SPS-SW1, SPS-WW1, NAAS-5), tap and well water samples were analyzed without any pretreatment and recovery values from 90.4 to 108.5% were obtained.
查看更多>>摘要：Benefit from high flexibility, applicability and low cost of industrial robot, robotic drilling has found its way into the field of aviation manufacturing, improving both surface quality and drilling efficiency. However, an unexpected instability, known as chatter, commonly occurs during the robotic drilling process due to relatively insufficient stiffness of robotic joints. In this paper, a monitoring approach based on concentrated velocity synchronous linear chirplet transform is proposed for robotic drilling chatter. First, for the sake of eliminating spindle speed-related components from measured acceleration signals, an optimal notch filter is designed based on the least squares method. Further, to obtain smear-free and high-resolution time-frequency representation, an enhanced concentrated velocity synchronous linear chirplet transform (CVSLCT) is proposed to process the acceleration signals. Thereafter, the acceleration signals are compartmentalized into several bands of equal frequency width. By summing coefficients of CVSLCT, sub-signals corresponding to all the frequency bands could be reconstructed effectively. Taking into account inhomogeneous change of energy and frequency distribution for acceleration signal, energy entropy is computed at regular intervals and employed as chatter monitoring indicator. Eventually, the presented CVSLCT-based approach is verified experimentally via the established robotic drilling system and making comparisons with existing chatter monitoring methods. The results verify that the CVSLCT-based approach is capable of effectively recognizing robotic drilling chatter before its full development and is superior to the existing methods.
查看更多>>摘要：The elevator is an indispensable vertical transportation tool in people's daily life. Its operation performance level is of great importance to the personal safety of passengers. However, elevator performance evaluation is carried out in accordance with some relevant standards and norms at present, and there lacks research on systematic methods for elevator performance evaluation. Therefore, it is of great practical significance and social value to evaluate the performance of elevators. Firstly, this paper establishes an elevator performance evaluation index system by fully analyzing the elevator operation mechanism. The vibration index during elevator operation, the start-stop acceleration index, the noise index, and the door opening and closing speed index are included in the evaluation index system, which can realize a comprehensive performance evaluation of elevators from various aspects. By monitoring the elevator's operation signal and extracting the time-frequency features, the performance scores of each index are calculated based on analysis of information provided by time-frequency feature parameters. In order to avoid the limitations of a single weighting method, a combination weighting method with the maximum deviation squares sum as the optimization objective is adopted to evaluate the operation performance of elevators. Finally, the effectiveness of proposed method is verified through applying to the evaluation of actual elevator systems. In this paper, an evaluation method combining objective data with subjective experiences of experts is proposed and verified through application to evaluation of elevators with different performance levels. The proposed method is expected to be applied to the actual evaluation and maintenance system to play a positive role in guiding the daily maintenance and condition monitoring of elevators.
NSTL
Elsevier