Yujun Xue's research while affiliated with Henan University of Science and Technology and other places

Sliding electrical contact has been widely used in spacecraft such as slip ring for solar windsurfing, and its service life directly affects that of the spacecraft. Au as a sliding electrical contact material has been widely used in aerospace equipment, but poor lubricity limits its service life. To address this issue, this study introduces MoS2 into the texturing holes of the Au coating, which can improve the lubricity, and maintain the continuity of Au and thus its conductivity. Additionally, the effect of texture density on the vacuum current-carrying tribological properties of the textured Au/MoS2 coating was investigated. The results indicate that texture not only reduces the mechanical properties of the coating but also affects the amount of MoS2 that can be filled. A high texture density greatly reduced the carrying capacity, leading to serious abrasive wear. However, low texture density results in serious adhesive wear owing to insufficient lubricity. Under an appropriate texture density, excellent vacuum current-carrying tribological behaviour can be achieved depending on the formation of a transfer film of MoS2 and Au, which maintains conductivity through Au and provides lubricity through MoS2. This study is of great significance in prolonging the service life of sliding electrical contacts and provides a new idea for the design of sliding electrical contact materials.

To develop an angular contact ball bearing with low power consumption, a heat generation calculation model for angular contact ball bearings has been established based on bearing quasi dynamics, elastohydrodynamic lubrication theory, heat transfer theory, and Kirchhoff’s law of energy conservation, considering the effects of roundness error, bearing preload, centrifugal effect, and thermal expansion. The correctness of the model is verified through experiments. The influence of different operating conditions and roundness errors on the thermal characteristics of angular contact ball bearings is analyzed. The results of the calculation indicate that when the roundness error order is equal to the number of balls n/2 ± 2 (where n = 1, 2, 3, …), the overall heat generation of the bearing is lower than that without considering the roundness error. When the roundness error order is equal to (2n − 1)/4 ± 2 (where n = 1, 2, 3, …), the overall heat generation of the bearing is higher than that without considering the roundness error. At the same rotating speed, the overall heat generation fluctuates as the roundness error order changes, and the trend becomes more pronounced as the rotating speed increases. The maximum overall heat generation is achieved when the roundness error order equals (2n − 1)/4 times (where n = 1, 2, 3, …) the number of balls. When the roundness error order is equal to n/2 times the number of balls (where n = 1, 2, 3, …), the bearing’s overall heat generation is minimal. The variation in the total heat generated by the bearing is directly proportional to the amplitude of the roundness error. With the increase in roundness error harmonic order, the bearing integral heat generation shows a periodic change, and the change period has a mapping relationship with the number of balls.

Exploring the doping components of the coating is of great significance for improving the tribological properties of the MoS2-based coating. The optimization of magnetron sputtering process parameters can also improve the coating quality. In this paper, the effects of working gas flow rate on the microstructure in a vacuum chamber, nano-hardness, and tribological properties of Ce-Ti/MoS2 coatings were studied using DC and RF unbalanced co-sputtering technology. It is found that the coating structure was coarse and porous when the Ar flow rate was excessive (70 sccm), significantly affecting the mechanical properties; there are pit defects on the surface of the coating when the flow rate is just minor (30 sccm), and the coating easily falls off during the friction process. When the flow rate is 40~60 sccm, the coating grows uniformly, the hardness reaches 7.85 GPa at 50 sccm, and the wear rate is only 4.42 × 10−7 mm3 N−1 m−1 at 60 sccm. The coating doped with Ce and Ti is an approximate amorphous structure. Under appropriate gas flow rate conditions, the friction induces a transfer film with a layered structure, and the MoS2 (002) crystal plane orientation is arranged in parallel at the edge of the wear debris, effectively reducing the shear force during sliding and reducing wear. Based on rare earth doping, this study improves the tribological properties by optimizing the working gas parameters, which plays a reference role in preparing high-quality MoS2-based coatings.

During operation, angular contact ball bearings exhibit slipping behavior, which accelerates bearing wear and reduces the bearing’s overall service life. This paper focuses on studying the degree of slippage and the variation in slippage rate in the H7006C angular contact ball bearing under constant inner ring speed and angular acceleration conditions. To achieve this objective, the study defines the contact between rolling elements, inner and outer rings, and the cage as flexible. A rigid–flexible coupling slippage dynamic simulation model is then developed, which utilizes cage slippage rate as the evaluation index. The analysis method of cage slippage rate change is established through the Gaussian function fitting method. By comparing simulation and testing results, the effectiveness of the analysis method of angular contact ball bearing slip behavior is validated. On this basis, the influence law of bearing speed and acceleration conditions on the slipping behavior of angular contact ball bearings is further studied. The results of the study show that as the axial load increases at different inner ring speeds, the cage speed increases until it reaches a stable state, while the cage slip rate continuously decreases until reaching a stable state. The higher the inner ring speed, the greater the axial load required for the bearing to enter the steady state. Under different angular accelerations, the cage speed increases with time; when the cage speed increases to stable and constant, the cage slip rate decreases to a stable state, and the higher the angular acceleration, the longer it takes for the bearing to enter the stable state.

Accurate wire rope defect diagnosis is crucial for the health of whole machinery systems in various industries and practical applications. Although the loss of metallic cross-sectional area signals is the most widely used method in non-destructive wire rope evaluation methods, the weakness and scarcity of defect signals lead to poor diagnostic performance, especially in diverse conditions or those with noise interference. Thus, a new wire rope defect diagnosis method is proposed in this study. First, empirical mode decomposition and isolation forest methods are applied to eliminate noise signals and to locate the defects. Second, a convolution neural network and transformer encoder are used to design a new wire rope defect diagnosis network for the improvement of the feature extraction ability. Third, transfer learning architecture is established based on gray feature images to fine-tune the pre-trained model using a small target domain dataset. Finally, comparison experiments and a visualization analysis are conducted to verify the effectiveness of the proposed methods. The results demonstrate that the presented model can improve the performance of the wire rope defect diagnosis method under cross-domain conditions. Additionally, the transfer feasibility of transfer learning architecture is discussed for future practical applications.

The accuracy of the end-effector motion trajectory is a critical performance indicator for cable-driven parallel mechanisms. This study aims to address the problem of trajectory error during the end-effector motion in a cable-driven parallel mechanism. It proposes a comprehensive compensation method based on the simultaneous application of the improved sparrow search algorithm and the cable length space error compensation algorithm, leveraging kinematic analysis. To compensate for the motion trajectory error of the end-effector caused by the geometric parameter error, the study establishes the kinematic model of the cable-driven parallel mechanism using the vector method. It creates the end-effector position error model and motion trajectory error model using the differential kinematic theory, analyzes the impact of the geometric parameter error on the motion trajectory error, constructs the kinematic parameter identification matrix, and uses an improved sparrow search algorithm to compensate for the position error of the motion trajectory interpolation point. For the motion trajectory error of the end-effector caused by non-geometric parameter error, the study analyzes the intrinsic correlation between the adjacent position error of the end-effector and the variation of the cable length using the error similarity theory. It then compensates for the position error of the interpolation point of the trajectory using a cable length space interpolation compensation method to enhance the motion trajectory accuracy of the end-effector. The study experimentally verifies the proposed comprehensive compensation method for end-effector motion trajectory error on a 4-cable-driven 2-DOF parallel mechanism, which reduces the motion trajectory error of the end-effector by 75%.

Aiming to solve the problem of oil-air lubrication failure caused by the high working temperature of high-speed rolling bearings, this study proposes a method, based on the theory of gas-solid two-phase flow and bearing tribology, of predicting the dynamic temperature rise of nonlinear high-speed rolling bearings under oil-air lubrication conditions. The accuracy of the fluid–structure coupling model is verified by comparing the temperature rise test results of angular contact ball bearing at different speeds. The characteristics of oil-air lubrication circulation and the relationship between the lubrication parameters and the heat balance of the high-speed rolling bearings have been studied. The results show that the gas supply pressure of the system has a significant influence on the continuity and fluctuation of the oil film in the oil pipe nozzle. The initial rise in temperature of the inner and outer rings of the bearing and the fluid domain has a speed threshold value, and the temperature increases linearly with the bearing speed. With the increase in the oil supply and lube oil viscosity of the system, the temperature rise of the outer ring of the bearing increases first, then decreases, and finally increases again. There is an optimal oil supply 5.5 mL and optimize viscosity 68 cSt for the bearing in the work condition.

The traditional fault diagnosis methods generally present poor diagnosis accuracy and robustness when faced with complex conditions that involve noisy interference and domain shift. Therefore, a new weight-based dual domain adaptation transfer model for bearing fault diagnosis is proposed. First, based on continuous wavelet transform, the temporal signals are transformed into time-frequency images (TFIs) for enhancing feature representation. Second, the TFIs are used as the input of the improved network which is based on dense and residual connections to complete feature extraction. Third, the proposed transfer model uses local maximum mean discrepancy (LMMD) to adjust data distribution between different working domains and batch nuclear-norm maximization (BNM) to improve the discriminability and diversity of the output matrix. Moreover, the weight controller is used to trade off the contributions of LMMD and BNM during training. Finally, the proposed frequency domain cut can be seen as a simple moving and cutting method to adjust each frequency spectrum of TFIs. In this process, the controlled weight factor is involved to further alleviate noise interference. Case studies show that the proposed model outperforms other methods and works well even in complex conditions mixed by noise and cross-domain.

Aiming at the problem of how the thermal characteristics of cylindrical roller bearings affect the lubrication characteristics of bearings under actual working conditions, the influence of parameters such as speed and load on the lubrication characteristics of cylindrical roller bearings under thermal effects is analyzed. The numerical calculation method combining the quasi-static model of cylindrical roller bearing and the thermal elastohydrodynamic lubrication model is adopted. The effects of rotational speed, load and thermal effect on the lubrication performance of the bearing and the lubrication state under certain oil supply conditions were analyzed via numerical model calculation. The oil film thickness was measured via an immersion ultrasonic method to verify the correctness of the model. The results show that the larger the bearing speed, the larger the central film thickness and the minimum film thickness. At the same time, the thermal effect on the film thickness is more obvious; the greater the load, the greater the maximum oil film pressure. The film thickness gradient in the inlet region is greatly reduced, but the thermal effect has no obvious effect on the overall film thickness. In addition, there is a critical value of effective lubrication film thickness for each set of operating parameters. When the actual film thickness is equal to the critical value, the bearing lubrication state is at its best; the numerical simulation results are compared with the experimental values. Under the calculation conditions, the maximum error at the measuring point is within 10%, which meets the error requirements and provides a theoretical basis for revealing the bearing lubrication mechanism.