Robust Reliability Optimization Design Of Dynamic Servo Tool-holder Considering Stiffness Degradation

In this thesis,the dynamic servo tool holder is taken as the research object,based on the knowledge of reliability,the theory of stiffness degradation and the analysis method of transmission path,under the premise of considering the variable stiffness,the reliability analysis,path parameter quantitative evaluation and robust optimization design of the dynamic servo tool holder vibration transmission path system are systematically studied.As a key functional component of CNC machine tools,the power servo tool holder must be accompanied by stiffness degradation during the vibration process,by introducing the stiffness cumulative damage theory into the constructed vibration transfer path motion differential equation,combined with the stochastic finite element method and the basic theory of reliability,the mathematical model of the reliability of vibration transmission path system with random parameters and its sensitivity to the mean and variance of random parameters can be deduced considering stiffness degradation.The introduction of the stiffness cumulative damage theory also extends the frequency reliability analysis from frequency domain analysis to time domain analysis,from two-dimensional to three-dimensional,and avoids partial results of reliability analysis being submerged in the time domain.Through the numerical analysis of the servo power tool holder,the reliability of the dynamic servo tool post system at the mean of the random parameters of the transmission path and the surface sensitivity of the sensitivity of the random parameters to the excitation frequency and time are obtained.The results show that the stiffness degradation causes the reliability in the frequency domain and its sensitivity to each random parameter to shift with time,which can effectively prevent the resonance failure caused by the change of the resonance region with time.In addition,the stiffness degradation causes the system performance to change in the time domain,which causes the sensitivity peak of the reliability to fluctuate with time,and the sensitivity peak in the frequency domain at zero time is not necessarily the maximum in the time domain.By comparing and analyzing the sensitivity of the reliability to the mean value of the random parameters of each path,the dynamic optimization design of the vibration transmission path system of the power servo tool holder is carried out by optimizing the sensitive parameters,which enhances the stability of the system.