Research On Step-stress Accelerated Degradation Test Optimum Design Of Motorized Spindle

As one of the key functional components of CNC machine tools,motorized spindle has been more and more widely used in CNC machine tools with the rapid development of high-speed cutting technology.China is the largest consumer and producer of machine tools in the world.However,the key functional components such as motorized spindle,tool magazine and tool holder of medium and high grade CNC machine tools mainly depend on imports.The main reasons are the low reliability of key functional components and frequent failures.At present,the reliability probability design of complex electromechanical system is still immature,and reliability test is the main technical way to improve its reliability level.The spindle is a high-reliability product,so it cannot obtain sufficient fault data through traditional reliability test within a short time.Thus,the reliability test of motorized spindle has the characteristics of long test cycle and high test cost.In order to save cost,domestic research and development companies usually do not carry out reliability test of motorized spindle,or simply replace reliability test with performance test,so it is difficult to obtain fault data of motorized spindle.In order to reduce the cost of reliability test of motorized spindle,accelerated degradation test must be used to quickly excite faults of motorized spindle,and basic data used for motorized spindle reliability assessment and failure analysis can be obtained within a short time.How to carry out accelerated degradation test of motorized spindle under limited conditions is an urgent problem to be solved faced by acceleration degradation test of motorized spindle.Taking domestic motorized spindle as the research object,based on the analysis of the structure,working principle and degradation mechanism,this paper propose an optimum design method and evaluation system for step-stress accelerated degradation test of motorized spindle.Finally,the effectiveness of the optimum method is verified by simulation evaluation.The main contents of this paper are as follow:1.Based on the basic structure and working principle of motorized spindle,the degradation mechanism of motorized spindle is analyzed.Taking speed and radial force as the stress,radial runout as the degeneration feature,the accelerated degradation model of motorized spindle is established.And the accelerated degradation test system of motorized spindle is built.2.Under the premise of not changing the failure mode and failure mechanism of motorized spindle,the step-stress accelerated degradation test method of motorized spindle is studied.This paper propose an optimization criterion based on reliability evaluation accuracy,and optimum design model of step-stress of accelerated degradation test for motorized spindle is established.The maximum likelihood estimation method is used to estimate the parameters.3.An optimum design method of accelerated degradation test based on genetic algorithm is proposed.Combined with the step-stress optimum design model of motorized spindle,the optimization design of step-stress accelerated degradation test of motorized spindle is carried out.Comprehensively considering the accuracy and robustness of the test,an improved test plan is proposed.Finally,sensitivity analysis of improved test plan is carried out.4.Taking variance and standard deviation of the reliability estimate as the evaluation index,this paper puts forward a simulation evaluation method for step-stress accelerated based on the Monte Carlo simulation method.Optimum test plans are evaluated to verify the effectiveness of the optimum design method proposed in this paper.