Reliability Evaluation Of Grating Encoder Based On Step-stress Accelerated Degradation Test

Grating encoders,as an important part of motion control in CNC equipment such as CNC machine tools and industrial robots,play a key role in the normal and reliable operation of equipment.Understanding its reliability can provide a theoretical basis for reliability evaluation of raster encoder and reliability allocation during design of raster encoder.However,raster encoder is characterized by high reliability and long life,and it is difficult to obtain failure data for reliability evaluation in limited time.Therefore,the research purpose of this paper is: How to evaluate the reliability of grating encoder reasonably and effectively in a short time.In order to evaluate reliability,a multi-stress accelerated degradation model considering multi-source variability was established based on performance degradation data obtained from laboratory bench tests.The main research work of this paper is as follows:Firstly,from the working principle of the grating encoder,the key performance indexes that need to be measured in the process of accelerated degradation test are determined,and the failure modes,failure causes and sensitive stress of the internal components are analyzed from bottom to top,and the sensitive stress of the grating encoder is summarized.On this basis,the accelerated degradation test scheme is formulated with reference to relevant standards,and the design scheme of hardware system and data acquisition system in the test system is described in detail.Then,the performance degradation model of Wiener process with nonlinear random effect considering the measurement error was established to solve the problems of the difference between individual encoders,the measurement error and the nonlinear change of degradation with time,and the dual-stress acceleration model was established according to the temperature and humidity acceleration stress.In usually assume that performance degradation model under the premise of drift parameter depends on the acceleration model,combined with performance degradation model and acceleration model,get the grating encoder accelerated degradation model,and presents a two-stage maximum likelihood estimation method,to solve the accelerated the degradation of unknown parameters in the model,finally through a simulation example proved the validity and the correctness of the method.Finally,the reliability of the grating encoder is evaluated by using experimental data and accelerated degradation model.The experimental data are preprocessed to obtain the available performance degradation data and to estimate the parameters.Then check whether the data comply with the performance degradation model and accelerated degradation model established in this paper.Then the constant stress reliability was extrapolated,and the reliability evaluation and reliability sensitivity analysis of the grating encoder were carried out.In the end,the binary reliability function was established by Copula function to evaluate the binary reliability of the grating encoder.