Methods And Applications Of Operational Reliability Estimation For CNC Equipment Based On Performance Parameters

The reliability of Made-in-China CNC equipment is one of the key problems to restrict the rapid development of CNC equipment industry. The operational reliability estimation for a CNC equipment is an indispensable approach to control the reliability level of the equipment, and its tasks are to ensure that the CNC equipment will achieve desired objectives and requirements, and to identify those underlying faults, and then to indicate the required improvements in the CNC equipment's design, manufacture, operation, maintenance and etc., in order to implement reliability growth and improve reliability level. According to current deficiency research on operational reliability estimation for CNC equipment, methods, applications and a developed prototype system for the operational reliability estimation are discussed in detail based on the inherent characteristics of CNC equipment.Firstly, this thesis provides a systematic literature review on the theories and methods for CNC equipment reliability and its related fields, and points out the limitations of traditional reliability estimation based on binary states: working or failed. Therefore, the concept of operational reliability estimation is brought forward. The reliability index and main research content of operational reliability estimation for the CNC equipment are built. And two failure modes such as catastrophic failure and drift failure are analyzed. And then, the three-tier system structure of operational reliability estimation is set up. Meanwhile, the methods of performance monitoring and machining processes' dynamic modeling in CNC equipment are presented.According to the three-tier system structure of operational reliability estimation, the operational reliability estimation for CNC equipment reliability is implemented as follows:(1) The symptoms of performance degradation related to CNC equipment are illuminated, and the methods of performance degradation modeling and analysis based on performance monitoring are proposed. The performance degradation models based on nonsteady ARIMA time series are set up, which might correctly describe performance degradation process. Furthermore, discrete hidden Markov chain model is introduced to analyze the CNC equipment reliability under conditions of several observation sequences. The result shows that the discrete hidden Markov chain model might recognize the hidden states change of degradation process.(2) After indicating the difficulties in applying traditional reliability estimation methods to the CNC equipment, it is brought forward that the approach of the operational reliability estimation for the CNC equipment with small sample are based on statistical learning theory. The reliability estimation models are built using v-SVR and AIS arithmetic. And the confidence interval of calculated reliability index is deduced by integrating the Bootstrap with v-SVR arithmetic. Furthermore, the sensitivity and importance level of calculated reliability index are counted.(3) The foregoing methods are adopted to estimate the operational reliability of a machining process in DM4600 vertical milling machining center. The nonlinear dynamics model of the machining process is built based on the dynamic characteristic testing for the DM4600 machining center. Meanwhile, the model is verified by milling testing. The result shows that the nonlinear dynamics model is feasible. Furthermore, it is discussed how the dynamic characteristics of mechanical structure and machining system impact the operational reliability for the machining center. And the effect of machining parameter varieties on machining performance is studied by means of emulation. And then, the operational reliability for this equipment within a machining cycle is estimated.(4) The prototype system of machine reliability modeling and estimation called MRME is designed and developed. Its function modules and adoptive technologies are presented. A case is given to demonstrate the operation process of MRME system.Finally, a conclusion is drawn and the trend on operational reliability estimation is anticipated.