Accelerated life reliability evaluation of grating ruler for CNC machine tools based on competing risk model and incomplete data

Haiji Yang,Guofa Li,Jialong He,Liding Wang,Yupeng Ma,Wei Zhang

doi:10.1007/s00170-021-07627-w

Abstract

Grating rulers are high-precision linear displacement sensors used in the servo control system of CNC machine tools. Due to the long lifetime of these rulers, evaluating their reliability level by using traditional methods takes huge amounts of time and resources. Meanwhile, some incomplete data are observed in the failure data, which will cause inaccurate evaluation results. In this study, an accelerated life reliability evaluation method of a grating ruler based on a competing risk model and incomplete data is proposed. Firstly, according to the characteristics of the grating ruler, the life distribution model based on competitive risk is established. The representation and conversion methods of failure data, considering incomplete data, are also proposed. Secondly, the accelerated life test (ALT) system is set up, and the 4500 h step stress ALT is conducted. Results indicate that the reliability level of the grating ruler is MTBFt = 8864.12 h, and that of each subsystem is MTBFt(MS) = 13,351.98 h, MTBFt(OS) = 14,283.48 h and MTBFt(ES) = 17,038.65 h. The advantages of the proposed method are that it is helpful in determining the subsystem with the highest failure rate in each stage and puts forward targeted suggestions for subsequent improvement designs.

Highlights

IntroductionGrating ruler is the high-precision linear displacement consume a lot of time and resources
The life of the grating ruler can usually reach more than 10,000 hours, and the traditional life test willGrating ruler is the high-precision linear displacement consume a lot of time and resources
Grating ruler is one of the key parts that affect the machining accuracy of CNC machine tools

Summary

Introduction

Grating ruler is the high-precision linear displacement consume a lot of time and resources It is an effective sensor which integrates mechanical, optical, electronic method to quickly evaluate the reliability level of grating technology, which is widely used in all kinds of CNC ruler by carrying out accelerated life test (ALT) to make machine tools [1,2,3]. Its essence is to stimulate the potential control system of CNC machine tools, and an failure quickly by improving the stress level of the product, important factor affecting the machining accuracy of CNC and use the acceleration model to convert the failure data machine tools [4, 5] It is of great significance under each stress level into the failure data under normal to accurately evaluate the reliability level of grating ruler stress [12]. After obtaining the failure data, how to is to drive the reading head of grating ruler to run establish an accurate reliability model according to the continuously at a certain speed until failure occurs [9]

Results

Discussion

Conclusion