| Cageless ball bearings have the characteristics of a large number of rolling elements,high rigidity,and high load-bearing capacity.As a protective bearing for magnetic levitation bearings,When the magnetic levitation bearing fails,the rotor that falls due to the disappearance of magnetic force is supported to complete the rotational motion,protecting the magnetic levitation bearing stator and motor stator from damage.Scholars have found that the main reason for the failure of cageless bearings protection is due to the uncontrollable movement behavior of the isolated rolling element without cage,which leads to sliding phenomenon of the rolling element,friction and collision between the rolling element and the raceway or between the rolling element.In addition,compared to the consistency of the motion posture of the traditional bearing rolling element,the motion of rolling element about cageless bearing is stochastic.There is a lack of corresponding bearing theory research and non-contact method,which poses great challenges for controlling the motion of rolling elements about the cageless bearing.This article takes ceramic cageless ball bearings as the research object,and conducts research on the dynamic characteristics and automatic discretization dynamics of rolling elements of cageless ball bearings.The aim is to provide a general theory and experimental research method for automatic discretization of rolling elements of cageless bearings under variable operating conditions,and to provide theoretical reference and technical support for the application of protective bearings.The specific research content is as follows:Aiming at the random friction problem during the motion of rolling elements,a friction force excitation model for random gaps of rolling elements is established based on the collision impact between adjacent rolling elements and the continuous friction contact form.Based on the spatial relative position of rolling elements and combined with the motion and mechanical characteristics,the nonlinear contact force model between bearing parts is established.Taking into account the random friction and nonlinear contact forces of rolling elements,a dynamic model for the random friction excitation of cageless bearings is established.A predictive correction algorithm is proposed to solve the problem of difficulty in convergence caused by continuous contact between rolling elements of cageless bearings.This algorithm improves computational accuracy and reduces computational time for solving the dynamic model of cageless bearings.The above research provides a basis for the subsequent design of variable diameter raceways.Based on the distribution law of random friction between rolling elements,the automatic discretization mechanism of rolling element speed change without cage bearing is studied,and a local variable diameter raceway is designed to control the micro speed change of rolling elements.A contact trajectory model between rolling elements and variable diameter raceways is established based on spatial geometric relationship theory.Based on the variable diameter raceway model and the relative position between the rolling element and raceway space,establish an instantaneous velocity model of the rolling element.Analyze the changes in revolution and rotation of rolling elements in conventional and variable diameter raceways,and establish a discrete model of rolling elements in variable diameter raceway bearings.Considering the effect of alternating stress on rolling elements passing through variable diameter raceways,the three-dimensional contact stress state between rolling elements and variable diameter raceways is studied.A numerical solution method for determining the three-dimensional contact stress of variable diameter raceway bearings is proposed.The variable diameter raceway structure by combining variable speed,discrete effect,and stress is determined.The time-varying characteristics caused by changes in contact points and contact forms caused by variable diameter raceway,a time-varying displacement model of the rolling element and a time-varying contact stiffness model of the variable diameter raceway bearing are established.The nonlinear contact force model between rolling elements and raceway based on time-varying characteristics is established.Consider the random collision force generated by the rolling element entering and exiting the variable diameter raceway,an impact collision force model between the rolling element and the raceway based on additional excitation is established.The transient dynamic model of a locally variable diameter raceway cageless bearing by comprehensively considering time-varying characteristics and additional excitation is established.Study the transient contact variable step algorithm and develop corresponding solution programs.Determine the variable diameter raceway structure and analyze the dynamic characteristics of bearings based on this structure.In response to the random differences in the motion state of rolling elements in cageless bearings,the acquisition principle of high-speed photography combined with image processing for the motion state of rolling elements is studied,and a coordinate correction model for reflective points on the surface of rolling elements is established.The test scheme is proposed to determine the rotational speed of the rolling element,the discretization of the rolling element,and the vibration of the bearing.An empirical mode decomposition combined with spectral kurtosis method is proposed to filter and preprocess the vibration signal.Build a monitoring platform for the motion status of rolling elements and conduct bearing vibration tests under variable operating conditions,and compare and analyze the characteristics of rolling element friction,dispersion,and bearing vibration with and without variable diameter raceways.Verify the correctness of the theoretical research in this paper and the rationality of the design of local variable diameter raceway automatic discrete bearings. |
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