Research On Reliability Modeling Of Electric Spindle Tool Clamping Mechanism Based On Step Stress Accelerated Degradation Test

CNC machine tool is very important in modern manufacturing industry,and its reliability has an important impact on the production efficiency and cost control of manufacturing industry.Motorized spindle is the core component of NC machine tool,and broach mechanism is the key subsystem of the motorized spindle,so improving the reliability of broach mechanism is of great significance to improve the reliability level of NC machine tool.Broach mechanism as a mechanical mechanism with long life and high reliability,how to evaluate the reliability of broach mechanism in a short time is an urgent problem to be solved.In this paper,the broach mechanism is taken as the research object,and the reliability model considering multiple uncertainties(nonlinear,time-varying,individual differences between elements,degradation and covariate measurement errors)is established to provide theoretical and methodological support for estimating the life and remaining useful life(RUL)of broach mechanism.The main research contents of this paper are as follows:(1)The accelerated degradation test scheme of broach mechanism based on stepping stress is designed.Firstly,by analyzing the working principle,structure and failure mechanism of broach mechanism,the performance index and acceleration stress of accelerated degradation test(ADT)were determined,and the specific test scheme of ADT was developed.Finally,the designed broach mechanism test system is briefly introduced.(2)A multi-stress stepping stress accelerated degradation model of broach mechanism considering multiple uncertainties was established.The degradation process of broach mechanism is complex.In order to accurately evaluate the reliability of broach mechanism,the influences of nonlinear,time-varying,individual differences between elements,degradation quantity and covariate measurement errors on the degradation model are considered.The degradation model and acceleration model of broiler mechanism were established based on Wiener process,and then the probability density function(PDFs)of lifetime and RUL was derived,and the parameter estimation method of MLE-GA-SIMEX was proposed.Then,the feasibility and accuracy of the proposed model are verified by a simulation example.(3)The unitary performance degradation model of broach mechanism is established.Firstly,according to the stepping stress accelerated degradation test scheme of broach mechanism,the stepping stress accelerated degradation test of broach mechanism was carried out.Secondly,the hypothesis test is carried out to determine whether the experimental data obey the model distribution proposed in this paper.The parameters of each degradation edge model were estimated by MLE-GA-SIMEX parameter estimation method,and then the MTTF and median life of broach mechanism were calculated.Then,the unitary reliability evaluation and reliability sensitivity analysis of broach mechanism are carried out.(4)Based on Copula function and Bayesian estimation method combined with Hamiltonian Monte Carlo(HMC)algorithm,a binary performance degradation model of broach mechanism was established.Firstly,four common Copula functions are used to fit the binary degradation data of broach mechanism.In order to improve the parameter estimation efficiency of Copula function,the HMC algorithm is used for Bayesian parameter estimation.The optimal Copula function was selected by BIC criterion,and based on this,the reliability evaluation of broach mechanism was completed.