Search

In order to solve the problem of small high-speed precision cylindrical roller, which is difficult to drive and the surface is easily damaged when doing dynamic unbalance detection due to the small size and light mass of the roller, this paper proposes a new drive method, using air flotation non-destructive support instead of V-block or cylindrical surface of the roller and other lossy contact support and air flotation electric spindle combined with vacuum suction cup instead of belt friction drive; establish a mathematical model of cylindrical roller force to study the force of cylindrical roller in the air flotation sleeve during the drive, and through the force analysis, it is shown that under the condition that the structural parameters and material parameters of the drive remain unchanged, the start-up speed of the drive depends on the load-bearing capacity of the air film on the cylindrical roller; the mathematical model of the air film load-bearing capacity and the thickness of the air film is established to study the changing characteristics of the air film load-bearing capacity in the air flotation sleeve, and the correctness of the mathematical model is verified through numerical calculation combined with simulation analysis; the test platform of the drive device based on the non destructive detection of cylindrical roller dynamic unbalance is built to further verify the feasibility of high-speed non-destructive drive of cylindrical rollers and to create favorable conditions for the development of the non-destructive detection instrument for small mass cylindrical rollers dynamic unbalance.

This study presents a method for measuring the imbalance in a small-sized cylindrical roller. The roller imbalance was calibrated on the built static-pressure-air flotation measurement machine. The impact of the roller imbalance on the dynamic characteristics of a cage were then studied on the aero-bearing test rig. The displacement spectrums with different roller imbalance of the obtained cage orbits under various bearing speed and radial load were used to evaluate the cage stability. The results show that the cage cannot form a stable operating state at a lower bearing speed with or without the unbalanced rollers. The cage with balanced rollers gradually develops stable motion with the increase of the bearing speed. The existence of a small roller imbalance causes the stability of the cage to deteriorate. With an increase in the bearing speed and radial load, the cage with the unbalanced rollers runs unsteadily accompanied by a high-frequency vibration when the roller imbalance is large enough. The vibration amplitude of the cage in the horizontal direction is greater than that in the vertical direction during an unstable operation, which is similar in the stable status.

With the increase in the intelligence of the production process and the increase in reliability requirements, the monitoring of the bearing life status after the event has been unable to meet the needs of industrial production. Performance degradation assessment and life monitoring have attracted more attention as intelligent methods based on condition maintenance. Hidden Markov model is a statistical probability model based on time series, which is very suitable for modeling the performance degradation process of equipment. Therefore, this paper proposes a life monitoring algorithm based on hidden Markov model. First, the continuous wavelet transform is introduced to obtain the optimal value of the shape factor or the stretch factor. Secondly, a hidden Markov model of multi-channel information fusion is proposed. The algorithm significantly improves the effectiveness and robustness of life monitoring. The hidden Markov model explicitly expresses the state duration distribution, making the model more suitable for life monitoring.

The angular misalignment of cylindrical rollers causes the stress edge effect at roller ends to be aggravated, which would affect bearing capacity and fatigue life of bearings. Therefore, based on the roller angular misalignment, the geometric interference model of the cylindrical contact pair was established in this paper. Thereafter, two types of logarithmic crowning models were theoretically deduced, in which design redundancy was considered through special treatment of pre-pressure. Taking the aero-engine main shaft bearing as an example, contact characteristics of the cylindrical roller with these two logarithmic profiles were studied by the DC-FFT method and the conjugate gradient method (CGM). The results show that two profiles can effectively eliminate the stress edge effect, improve contact pressure distribution and subsurface stress field of the roller in misalignment state, and at the same time ensure fine contact characteristics in alignment state. The research can provide a theoretical basis and reference for finite line contact pairs under angular misalignment.

Since the manual extraction of features is not sufficient to accurately characterize the health status of rolling bearings, machine learning algorithms are gradually being used for fault diagnosis of bearings, which can adaptively learn the required features from the input data. In this paper, k -nearest neighbor, support vector machines, and convolutional neural networks are successfully applied to the fault diagnosis of bearings, for the benefit of achieving the detection and early warning of bearing fatigue damage. The original samples are segmented into semioverlapping samples. When using k -nearest neighbor and support vector machines as early warning models, we searched their hyperparameters with random search and grid search, and the results showed that support vector machines could achieve 87.1% of bearing detection accuracy and k -nearest neighbor could achieve 100% of detection accuracy. When convolutional neural networks are used as the early warning model, the accuracy can reach 99.75%.

Purpose The purpose of this paper is to study the influence of the cage dynamic unbalance on the dynamic performances in cylindrical roller bearings. Design/methodology/approach The dynamic analysis model which considering cage dynamic unbalance is presented, and the relationship between the cage dynamic unbalance and the cage stability, the cage slip ratio and the cage skew angle is investigated. Findings Cage dynamic unbalance has a great effect on the cage stability. The cage dynamic unbalance which in an axial excursion affects the cage characteristics is greater than that only in the radial direction. The cage slip ratio and the cage skew increases with the cage dynamic unbalance, especially with the axial excursion. The non-metal cage is more sensitive to the cage dynamic unbalance than that of the metal cage. Originality/value The analytical method and model can be applied by the bearing engineering designers.

Tapered roller bearings (TRBs) are applied extensively in the field of high-speed trains, machine tools, automobiles, etc. The motion prediction of main components of TRBs under grease lubrication will be beneficial to the design of bearings and the selection of lubricating grease. In this study, considering the dynamic contact relationship among the cage, rollers, and raceways, a multibody contact dynamic model of the TRB was established based on the geometric interaction models and grease lubrication theories. The impacts of load, grease rheological properties, and temperature on the roller tilt and skew and the bearing slip were simulated by using the fourth-order Runge–Kutta method. The results show that the roller tilt angle in the unloaded zone is obviously larger than that in the loaded zone, while the roller skew angle in the unloaded zone is smaller than that in the loaded zone. As the speed increases, the roller tilt and skew and the bearing slip become more serious. Bearing preload can effectively reduce the bearing slip but will make the roller tilt and skew angle increase. The roller skew angle and the bearing slip decrease with the increase of the grease plastic viscosity. The roller tilt angle increases with the increase of the plastic viscosity. The yield stress of the grease has little effect on motions of the roller and cage. The influence of temperature on the roller and cage motions varies with the type of grease used.

This paper presents a nonlinear dynamic differential equations of high-speed cylindrical roller bearing considering the impact of roller dynamic unbalance. The cage vibration characteristics are investigated as a function of roller dynamic unbalance, structure parameters and working conditions. The fast Fourier transformation, cage orbit and vibration acceleration level are used to evaluate the vibration magnitude of the cage. The results show that: (1) Roller dynamic unbalance can affect the state of the cage motion and cause the cage's vibration acceleration level to increase. Once the roller dynamic unbalance exceeds a threshold, the cage will produce a high frequency vibration; (2) The most significant impact on the cage vibration is roller dynamic unbalance in angular direction of roller axis, followed by radial and axial direction; (3) A smaller radial clearance and a reasonable pocket clearance are beneficial to reducing the effect of roller dynamic unbalance on the cage vibration. It is recommended to take a larger cage-race guide clearance within a certain range to lower the cage vibration; (4) The cage vibration due to the roller dynamic unbalance increases with the bearing speed, and is greater than that of the cage with ideal roller. The effect of roller dynamic unbalance on the vibration of cage under high-speed condition is greater than that of the low-speed condition. The increase of the radial load of the bearing, to a certain extent, can reduce the vibration of cage considering the roller dynamic unbalance.

Purpose The purpose of this study is to investigate the effect of roller dynamic unbalance on cage stress. Design/methodology/approach Considering the impact of roller dynamic unbalance, the dynamic analysis model of high-speed cylindrical roller bearing is established. And then the results of dynamic model are used as the boundary conditions for the finite element analysis model of roller and cage to obtain the cage stress. Findings Roller dynamic unbalance affects the contact status between roller and cage pocket and causes the overall increase in cage stress. The most significant impact on cage stress is roller dynamic unbalance in angular direction of roller axis, followed by radial and axial directions. Smaller radial clearance of bearing and a reasonable range of pocket clearance are beneficial to reduce the impact of roller dynamic unbalance on cage stress; the larger cage guide clearance is a disadvantage to decrease cage stress. The impact of roller dynamic unbalance on cage stress under high-speed condition is greater than that in low-speed conditions. Originality/value The research can provide some theoretical guidance for the design and manufacture of bearing in high-speed cylindrical roller bearing.

Based on dynamic analysis of rolling bearings, the nonlinear dynamic differential equations of a cylindrical roller bearing with a trilobe-raceway were established and solved by the GSTIFF (gear stiff) integer algorithm with a variable step. The influences of structural parameters and the tolerance of the trilobe-raceway, working conditions of the bearing, and the outer ring installation method on cage slip characteristics were investigated. The results show that: (i) The cage slip ratio and bearing rating life of a cylindrical roller bearing with a trilobe-raceway would reduce when the low-radius (radius of the outer raceway contour at the lowest point) and D-value (difference value between the high and low points of the outer raceway contour) decrease, and the former (low-radius) contributes more significantly. (ii) The cage slip ratio of a cylindrical roller bearing with a trilobe-raceway rises with the increase of the bearing speed, and decreases with the increase of the radial force; the variation range increases with the increase of the low-radius. (iii) When the installation angle of the outer ring increases in a period, the cage slip ratio remains unchanged while the bearing rating life rises up a little. Therefore, when installing a cylindrical roller bearing with a trilobe-raceway, the location of the maximum radius shall be under that of the radial force to improve the bearing rating life. (iv) With the increase of the roundness of the base circle where the radius of the lowest points of the trilobe-raceway contour locates, the cage slip ratio rises gradually and the bearing rating life decreases. Keywords: Bearing rating life, Cage slip ratio, Dynamics, Raceway contour, Trilobe-raceway

This paper presents dynamics differential equations of high-speed cylindrical roller bearing considering the impact of roller convexity excursion on mass center of roller, which are solved by GSTIFF (Gear Stiff) integer algorithm with variable step. The impact of roller convexity excursion on roller's dynamic characteristics is investigated theoretically, and the accuracy of dynamic model of high-speed cylindrical roller bearing and the computation results are demonstrated via Caba3D. The findings are as following: 1) Roller convexity excursion has tiny impact on tilting angle of roller but great impact on skewing angle, and the bigger convexity excursion the bigger skewing angle; 2) For PCRC(partially crowned roller with the center of crowned profile locating at the center line of roller), PCRE(partially crowned roller with the center of crowned profile locating at the ends of roller), fully crowned roller and logarithmic crowned roller, the amounts of roller convexity excursion are less than 0.6 mm, 0.4 mm, 0.4 mm and 0.4 mm, respectively; 3) The sensitivity to roller convexity excursion for four types of rollers is different, and the sensitivity level of roller from small to large is logarithmic crowned roller, PCRE, PCRC, fully crowned roller. 4) Among four types of crowned rollers, anti-speed capability and anti-load capability of logarithmic crowned roller are the most excellent, followed by PCRE and PCRC, and fully crowned roller is the worst one in both aspects.

In the present dissertation, series of Al–Mg-Ga-In-Sn alloys were prepared by using arc melting and melt-spinning techniques. Their microstructures were characterized by X-ray diffraction (XRD) and scanning electron microscope with energy dispersed X-ray (SEM/EDX). The generated hydrogen volume of Al splitting water reaction was measured using a water displacement method. The morphology and microstructure of the reaction by-products were also characterized using XRD. The results show that from the comparison of microstructures and Al-water reactions between the as-cast and the rapidly solidified alloys, it was found that the effect of Mg on Al-water reaction was attributed to the induction of segregation of In and Sn and formation of intermetallic compounds on Al surfaces. However, Mg dissolved in Al grains hardly had any effect on the Al-water reaction. The reaction rate and hydrogen yield of the rapidly solidified alloys are significantly enhanced due to the refinement of Al grain.

In this paper, the formulas of elastohydrodynamic traction coefficients of four Chinese aviation lubricating oils, namely, 4109, 4106, 4050, and 4010, were obtained by a great number of elastohydrodynamic traction tests. The nonlinear dynamics differential equations of high-speed cylindrical roller bearing were built on the basis of dynamic theory of rolling bearings and solved by Hilber–Hughes–Taylor (HHT) integer algorithm with variable step. The influence of lubricant traction coefficient on cage's nonlinear dynamic behavior was investigated, and Poincaré map was used to analyze the influence of four types of aviation lubricating oils on the nonlinear dynamic response of cage's mass center. The period of nonlinear dynamic response of cage's mass center was used to assess cage's stability. The results of this paper provide the theoretical basis for selection of aviation lubricating oil.

To investigate the cage stability of high-speed oil-lubricated angular contact ball bearings, a dynamic model of cages is developed on the basis of Gupta’s and Meeks’ work. The model can simulate the cage motion under oil lubrication with all six degrees of freedom. Particularly, the model introduces oil-film damping and hysteresis damping, and deals with the collision contact as imperfect elastic contact. In addition, the effects of inner ring rotational speed, the ratio of pocket clearance to guiding clearance and applied load on the cage stability are investigated by simulating the cage motion with the model. The results can provide a theoretical basis for the design of ball bearing parameters.

Cage rotating and whirling inside rolling bearings involve conical motion and easily lead to excessive wear if the cage exists unexpected unbalances. In this study, the cage motions affected by its...

The control of acceleration and deceleration of stepper motor is one of the most key technologies of CNC system development. Acceleration is discontinuous in linear acceleration and decleration, which caused impact in NC machining. The exponential algorithm has a strong tracking capability but weak stability at higher speed. The questions could be overcome by conventional S-curve acceleration and deceleration implementation method, but the algorithm is too complex. So a new method was proposed to implement S-curve acceleration and deceleration. This paper presents five-stage model of S curve acceleration and deceleration algorithm to satisfy the actual roller polishing machine needs. The algorithm consists of five kinematic stages: increasing acceleration stage, decreasing acceleration stage, constant-speed stage, increasing deceleration stage and decreasing deceleration stage. At the starting point and the ending point, the velocity is zero and the jerk is absolutely the maximum value J. Analysis shows that: the acceleration curve of the algorithm is a continuous curve, and there is a first-order continuous relationship between time and speed, a smooth velocity and acceleration can be obtained, which is to avoid the impact when the CNC system accelerates and decelerates or reverses. The application on roller polishing machine shows that : compared with the traditional S-curve, the algorithm can make sure the acceleration is continuous, the speed changes smoothly, the flexibility is improved and the algorithm is easy to implement.

Due to the high demands for productivity and quality of bearing and the shortage of traditional detection methods, this paper proposes an automatic detection system based on machine vision technique. The detection system uses digital image processing technology to process the images collected by CCD camera and finish identification for the surfaces of bearing quickly and accurately. Firstly, least squares fitting and annulus scan are used to locate the bearing and the regions which will be detected. Secondly, contrast enhancement and low-pass filtering are used to improve the quality of images. Next, object inspection is applied to determine whether defects exist. Finally, the shape feature is used to finish recognition of defects. Experiments show that the detection system has the features of high efficiency, high accuracy and ease of use. This research has a certain practical value.

This paper develops a five degrees of freedom (5-DOF) model for aeroengine spindle dual-rotor system dynamic analysis. In this system, the dual rotors are supported on two angular contact ball bearings and two deep groove ball bearings, one of the latter-mentioned bearings works as the inter-shaft bearing. Driven by respective motors, the dual rotors have different co-rotating speeds. The proposed model mathematically formulates the nonlinear displacements, elastic deflections and contact forces of bearings with consideration of 5-DOF and coupling of dual rotors. The nonlinear equations of motions of dual rotors with 5-DOF are solved using Runge-Kutta-Fehlberg algorithm. In order to investigate the effect of the introduced 5-DOF and nonlinear dynamic bearing model, we compare the proposed model with two models: the 3-DOF model of this system only considering three translational degrees of freedom (Gupta,1993, rotational freedom is neglected); the 5-DOF model where the deep groove ball bearings are simplified as linear elastic spring (Guskov, 2007). The simulation results verify Gupta's prediction (1993) and show that the rotational freedom of rotors and nonlinear dynamic model of bearings have great effect on the system dynamic simulation. The quantitative results are given as well.