Development Of Reliability Test Device For Grating Encoder

CNC machine tools are the industrial master machines,the manufacturing scale and development level of which reflect the national manufacturing strength and comprehensive national power.However,domestically-made CNC machine tools,especially some certain key functional components,still have a significant gap with developed countries in reliability.As angle measurement closed-loop-controlled devices of CNC machine tools and key functional components,grating encoders have a direct impact on the precision and reliability of the machine tools.Therefore,it is significant to research the reliability of grating encoders to guarantee the reliability of CNC machine tools.Reliability test is an effective means to improve the reliability of equipment.The domestic reliability test equipment mostly stay in the low-level stage of idle running and it cannot be called a complete equipment.Above all,it is practical to develop the reliability test equipment of grating encoders with the ability of condition simulation and perform reliability rest on them.The reliability test equipment of grating encoders developed in this paper make up the shortcoming that only the idle running test can be carried on existing reliability test equipment.Firstly,in this paper,the structure and principle of grating encoders are analyzed.After that,according to some principle,the typical grating encoder is divided into three subsystems: optical,mechanical,and electronic.And then,the special impact of environmental stresses,such as temperature,humidity and vibration having on the encoder is also analyzed to build fault trees.Then the MATLAB is used to view the Lissajous of original encoder output signal influenced by the DC offset in the amplitude variations and other factors and then,the overall design of the test device was determined.Next,the mechanical design of the encoder reliability test device is performed,two kinds of support schemes of encoders are designed and the optimum scheme is determined through comparing them in the difficulty of implementation,reliability,continuity of tests,accessibility of maintenance and etc.Then,different install fixtures and specific loading hardware scheme are designed.Then determine the specific scheme for stress loading and rotational speed drive and select the loading equipment.Then,this paper develop the test monitoring system plan according to the reliability test requirements,The monitored objects include stress loads and encoder output signals acting on the tested encoder.The program is divided into two parts: hardware and software.The hardware includes devices.The software is a host computer monitoring platform developed by Lab VIEW.At the same time,the specific control methods for the vibration table and the temperature and humidity box are given.Finally,based on the degradation mechanism and related experimental standards of grating encoders,a complete test plan of step-stress accelerated degradation test for grating encoders including single stress,double stress and multiple stress is established.According to the test plan,2112 hours test has been conducted to prove that the built test equipment can satisfy the request of reliability test for encoders.Through the sorting and statistical analysis on test data,the model of degenerative quantity distribution based on normal distribution is used to describe the degenerative path,and the Arrhenius accelerated equation is used to describe the relationship between the characteristic parameters of degradation quantity and stresses.The median lifetime of the grating encoder was 13817 hours.