| 1.Purpose Based on the subject of Hi-Tech Research and Development Program of China --The research and development on the key reliability-technology of Computer Numerical Control(CNC) equipment and system , put forward the scientific research of this thesis. The thesis aims to study the reliability of CNC system, construct the reasonable study method and standard system info according to the characteristic of CNC system, and establish the fault analysis method.2.The sample selection method of CNC system The general analysis procedure of reliability is that choose some products based on the amount of this set. The sample has been proceeding the relevant experiment before leave factory. The fault data of this paper are all come from working environment. Assess and analyze the faulty data by using statistic theory . In general, the experiment of reliability adopt time-limit or quantity-limit test. To the test on reliability of CNC machine tool mainly adopt time-limit experiment. This method will take long time, use a mount of manpower and material, it is not very fit the practical manufacture. The CNC system is belong to electronic products, it's reliable level is very high, as the limit of experimental condition, it can not take for a long time. In the period of test, there are several case will be take place, such as below:The test equipment at least occurred two failure.There is one or more test equipment has no failure.The all test equipments have no failure. According the reliability assess of CNC machine tool, to the case of (2) and (3), we must delete the corresponding data, that will make the result be lower than factual reliability level. To the experiment of CNC system, these cases will often take place, adopt the method that using in machine tool will have more error, so in this thesis, we discuss a better technic that integrate the characteristic of time-limit and amount-limit experiment, based on the amount of failure products, select the reasonable deadline of test, so as to make the result exact and reasonable. 3. The assess method of CNC system reliability index According to the sample theory, in the cases of less sample and lower failure rate, the general statistic method has some deficiency. So in the thesis apply total failure time method to build up the failure probability function λ(t), then calculate the other reliability function and index. Based upon the comprehensive evaluation index system constructed, this thesis uses entropy method to do a comprehensive valuation of CNC system reliability index. This method overcome the shortcoming of frequently used method which gives weight subjectively. The entropy method integrated the reliability index and failure effect, it makes the evaluation reasonable and objective. Using comprehensive evaluation index , we can analyze the reliability level of the before and after reliability test, or contract reliability level of other manufacturing factory, find out the deficiency of own and improve the design, manufacturing, etc. through this method, in short period , we can assess the reliability level of CNC system, reduce the payout of reliability test.4. Build up the criteria of CNC system After the fault analysis and reliability assess of CNC system, summarize the method of test, the index system, the reliable measure in design and manufacture, build up the reliability criteria of CNC system. In this criteria, add the content software reliability, constitute the reliability measure of software from requirement analysis, general design, detailed design, the carry out and test phase, and consolidate the management of software reliability. Software reliability is different from the reliability of machine tool, it is difficult to study it's reliability, as an important content of fault analysis and diagnose, it is an crucial direction in further study.5. ConclusionThrough the study of this thesis, enhance the reliability system of CNC equipment. For the case of less sample and lower failure rate, build up the correspondi...
|
PDF Full Text Request