| Gearboxes are commonly used power and motion transmission devices in mechanical equipment and are widely used in many fields such as industry,agriculture,national defense,and aerospace.The research shows that the failure rate of gearbox transmission system caused by gear fault is very large,and the gear pitting is one of the common faults in gear transmission.The gear pitting will seriously affect the reliable operation and the safety of mechanical transmission system,affect the performance of equipment and even cause serious mechanical accidents.Therefore,it is of great significance to study gear pitting fault.This paper takes gear as the research object,and focuses on the fault transmission process,dynamic modeling and fault diagnosis method of gear pitting.Firstly,the potential energy method was used to calculate time-varying mesh stiffness of the incipient micro-pitting fault,the dynamic model with the early micro-pitting fault was established.Then the response signals of the micro-pitting simulation model were analyzed in time domain and frequency domain and the influence law of early micropitting fault on the response signals of gear system was investigated.Secondly,the dynamic strain measurement method of gear root based on fiber Bragg grating sensor(FBG)was investigated and validated.Further,the dynamic strain measured by FBG was used to calculate the time-varying meshing stiffness and the gear system dynamic response of healthy and moderate pitting fault gear by the semi-analytical method,and the dynamic response was analyzed to investigate the influence of moderate gear pitting on gear system.The experimental platforms for the incipient micro-pitting fault and the moderate pitting fault were built respectively,the validity of the established gear pitting theoretical model and simulation results is verified by analyzing the experimentally measured vibration acceleration signals,meanwhile the performance of FBG sensor in the incipient micro-pitting fault diagnosis of gears is preliminarily evaluated.The main research contents are as follows:(1)In this paper,the six-degree-of-freedom nonlinear gear system dynamics model considering the influence of gear sliding friction was used to simulate the incipient micro-pitting fault of gears.The gear system dynamics simulation and analysis are conducted from three aspects: only the stiffness excitation is considered,only the friction excitation is considered,and the stiffness excitation and the friction excitation are comprehensively considered.By analyzing the dynamic characteristics of gear system response signals in time domain and frequency domain,the influence law of gear pitting fault degree on gear dynamic characteristics was investigated,which is intended to provide theoretical guidance for model-based gear fault diagnosis.(2)The semi-analytical method for calculating the time-varying meshing stiffness and the dynamic response of gear system based on experimental data is studied.a method for calculating the dynamic response of gear system based on the dynamic strain for gear tooth root by FBG sensor is proposed,the time-varying meshing stiffness and the dynamic response of healthy gear and medium pitting fault gear are calculated respectively,and the gear meshing force transmission mechanism of pitting fault is analyzed.According to the theory of potential energy and material mechanics,the relationship between the bending strain of the tooth root and the time-varying meshing stiffness is established,and the time-varying meshing stiffness of healthy gear and medium pitting fault gear are calculated by the dynamic strain for gear tooth root by FBG sensor respectively.Then the dynamic response of the gear system is analyzed and studied,and a semi-analytical method for calculating the dynamic response of gear system is presented.Finally,the semi-analytical method of gear dynamic response is validated by vibration acceleration signal.(3)The experimental platforms for the incipient micro-pitting fault was built,and the vibration acceleration sensor was used to monitor the vibration of gearboxes of different gear states(health gears and three different degrees of pitting fault gears).The gear fault diagnosis was carried out by analyzing the dynamic characteristics of the vibration acceleration signal in time domain and frequency domain,and the validity of the proposed early micro-pitting fault simulation model of the gear is verified.(4)FBG have the many advantages that they do not have electrical sensors,such as small size,anti-electromagnetic interference,distributed measurement,etc.Hence,this paper investigated the performance of FBG sensors in the incipient micro-pitting fault diagnosis of gear,and preliminarily evaluated its performance by analyzing FBG dynamic strain under different fault conditions. |
PDF Full Text Request