Research On Reliability Allocation Method Of CNC Servo Turret Based On Fault Tree Analysis

CNC servo turret is one of the core components of the CNC machine tool,its reliability directly affects the reliability level of the whole machine.Studying on the reliability of CNC servo turret,finding out the weakness;giving a reasonable allocation scheme of parts In the improvement of reliability optimization design,which not only provides important guiding significance to enhance the professional level of production and reliability of China's CNC servo turret,but also provides a solid basis for the reliability enhancement of CNC lathe machine.However,the difficulty of obtaining the failure data of CNC servo turret,the disadvantages such as high cost and long design cycle in the process of traditional reliability design depending on fault data obtained by mathematical statistics,as well as the structural complexity of CNC servo turrey is contribute to the result that distribution of reliability index is only to subsystem.In order to solve these problems,this paper presented a reliability allocation method based on Fault Tree Analysis.The research worked in this paper can be summarized as follows.(1)Carried out the structural analysis of SFW series CNC servo turrets,using FMECA(Failure Mode,Effects and Criticality Analysis)method,obtained all possible failure modes,failure causes,and found the weakness of CNC servo turret,The improvement and compensation measures were given for each fault,which provided the basis for the reliability design and the establishment of the fault tree model.(2)Though the FTA(Fault Tree Analysis)method,established the fault tree model and carry out the qualitative analysis,aiming at the problems of the long cycle the fault data acquisition and the problems of less data,used the method of expert evaluation combined with the fuzzy set theory,then experience of experts will be eventually transformed into fuzzy failure probability of basic events of the fault tree,and caculate the probability of occurrence of intermediate events and the probability of top events and the importance degree of basic events for top events.(3)Combined with the fault tree model,this paper put forward the CNC servo tool reliability allocation method based on fault tree.The overall reliability index of the CNC servo turret system was assigned to the parts:Firstly,based on the method of probability importance degree,the general reliability index was assigned to the first intermediate event.Secondly,the reliability index of the first intermediate events was assigned to the second level intermediate events by the method of reliability redistribution.Finally,the reliability index of the second intermediate events which was changed is assigned to the basic events by the analytic hierarchy process.Above all,the reliability allocation of CNC servo turret was completed.(4)Based on the MATLAB-GUI(graphical user interface),the reliability allocation software of CNC servo tool rest was compiled.The software realizes the weight calculation based on the analytic hierarchy process,the transformation of expert language into the fuzzy probability for basic events,the calculation of the probability of the intermediate event and the top event and the calculation of the probability importance degree,the calculation of top event probability distribution based on probability importance degree,the calculation of the probability distribution of intermediate events based on the reliability redistribution method,the calculation of probability distribution of second level intermediate events based on Analytic Hierarchy Process,all the above results can be shown and outputed.The software is powerful,simple operation and high computational efficiency.