| The spindle of CNC machine tool is the key functional component of CNC machine tool,and its reliability level of which affects the reliability level of CNC machine tool directly.In recent years,some achievements have been made in the development of the spindle of CNC machine tool.However,due to the lack of scientific and technological innovation of CNC machine tool and the poor basic experimental conditions,there is still a certain gap between China and world advanced level in terms of the reliability.Some problems gradually appear during use process,such as high maintenance costs,frequent early faults and poor quality stability.Therefore,the reliability analysis of the spindle of CNC machine tool is needed urgently.In this paper,the spindle of CNC machine tool are analyzed in four aspects of the reliability modeling,fault analysis,reliability allocation and the measurements to improve the reliability by using the captured fault data of the spindle.The following analysis and calculation have been done actually:(1)By using Bootstrap-Bayes method to model the reliability of the spindle system of CNC machine tool based on small sample data and fusing the historical fault data,first,Weibull prior distribution has been obtained by Bootstrap method,then,the posterior distribution of the parameters of the reliability model of the spindle system has been calculated by the Win BUGS software,thus the reliability model of the spindle system has been established,and the reliability index has been evaluated,the Mean Time Between Failures(MTBF)of CNC machine tool has been calculated also.(2)In order to prove the correctness of the improved-Bootstrap reliability modeling,the reliability information and fault data of the similar machine tools have been collected,and the small sample data are used in the improved-Bootstrap sampling method and the direct application of classical statistical method respectively.The results of comparative analysis showed that the relative error of the improved-Bootstrap sampling method is smaller than that of the classical modeling method obviously,which proves the improved-Bootstrap sampling method is feasible in small sample reliability modeling.Finally,the improved-Bootstrap method is used to model the reliability of the fault data of small sample spindle system collected in the field and calculate the Mean Time Between Failures(MTBF).By discussing the applicability of the Bootstrap-Bayes method and the improved-Bootstrap method in reliability modeling,that the modeling method based on the Bootstrap-Bayes theory is more extensive,but based on the current spindle level of reliability technology,if the improved-Bootstrap method is used to model,the calculation process of which would be simpler.(3)The fault tree model of the spindle system of CNC machine tool has been established by fault tree analysis(FTA)method,and the qualitative analysis of the fault tree has been implemented by Boolean logic operation to obtain the minimum cut set of poor lubrication,claw failure and many more.In addition,through the quantitative analysis of the fault tree of the spindle system,the failure rate of each bottom event is taken as the basic condition,and the failure rate of the other events which belongs to the different layers is calculated.Finally,the probabilistic importance of each event in the fault tree is calculated to complete the quantitative analysis of the fault tree.(4)Based on the reliability allocation method of the spindle system of CNC machine tool of the fault tree and the fault tree model,the reliability allocation model of spindle system combined with the fault tree has been established.The overall failure rate of the spindle system of CNC machine tool is allocated to basic events hierarchically by using failure rate as allocation index combined with probability importance degree,reliability reassignment method and analytic hierarchy process.As a result,the distribution outcomes is more reasonable and improvement measures for events with lower reliability could be put forward,so that the reliability of spindle of CNC machine tool would be improved. |
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