| NC machine tool is the key equipment in manufacturing industry, and NC manufacturing technology is one of advanced manufacturing technology. The developing state of NC manufacturing technology can directly show the manufacturing ability of a country. And the manufacturing industry is also the pillar industry related to people’s livelihood and national defense security.Ball screw pair (BSP) is the key part of NC machine tool, and its performance states directly affects machining quality and production efficiency of NC machine tool. To research the performance degradation (PD) mechanism of BSP is extremely important for improving the performance of BSP, realizing fault prediction and intelligent maintenance of machine tools.The service life of BSP may be10years. During its working condition, performance of BSP declines gradually, so that the precision of transmission is reduced gradually and BSP faults occur, or even scrapped in the end. In order to accurately evaluate the performance of BSP on time, intelligent maintenance plan and spare parts plan, the PD mechanism of BSP is firstly studied in this thesis. And then, the influence factors of wear, vibration and impact and so on are analyzed. Based on above researches, the BSP performance evaluation system is established. Main contents of this thesis are following:Force analysis of BSP. Firstly, aimed at BSP with different structures, the contact load characteristic between ball and its rollaway nest, the curvature change of rollaway nest, the friction characteristic of contact area and the loading features of the ball are analyzed. The characteristics of loading and motion between balls and its raceway are also studied. Then, the effects of wear, fatigue and vibration due to contact stress and friction torque are studied and the kinematic analysis of the ball is also carried out. The PD mechanism of BSP is uncovered by above researches.On the bases of the structure, PD characteristic and working process of BSP, evaluation goal and evaluation principle on PD of BSP are proposed. Based on sufficiently analysis of whole system PD processing, on time performance evaluation of the BSP is carried out by means of combination of qualitative analysis and quantitative analysis.PD evaluation index set of the BSP is set up by correspondence analysis between the performance and the accuracy parameters of BSP. The performance evaluation system structure and the PD evaluating system of BSP are established by means of three layers classification evaluation. Test program of BSP PD is built up based on VMC1500and other type NC machine tools.In order to realize the mapping relationship of signal characters and performance states, PD evaluating model of BSP is established by dynamic fuzzy neural network. Because the prediction accuracy of network is seriously affected by sample distribution, the test method of orthogonal test conjunted with performance index test is employed.The study is shown that the PD of BSP is a gradually reducing process, well the BSP degenerated curve is continuously, the degradation curve of ball screw, therefore, is continuous. In order to obtain PD character and solve the massive data problem, data simplification algorithm with dynamic clustering is established. Evaluation precision and dynamic response characteristics can be adjusted by adjusting the threshold of dynamic clustering.The vibration signal of energy spectruml and the energy distribution of current signal are taken as input parameters of PD evaluation model by means of time domain analysis, frequency domain analysis and wavelet analysis for the signals. PD evaluation precision is improved by qualitative analysis of some indexes at the same time.In order to solve the difficult problem that the friction torque can not be meassured in real time in NC machine tool working conditions, the hypothes is taken as that the output torque of drive motor is completely used to overcome friction torque while BSP is in no load condition. In this way, mapping relationships between current signals and friction torque is built and PD evaluation precision is also improved by taking friction torque as the input index.Intelligent practical model used for NC machine tool preserving and maintenance is proposed according to the BSP evaluation results of PD and attrition rate. On the basis of this model, intelligent maintenance schedules of NC machine tool key parts such as BSP can be confirmed and the spare parts planning can be set out reasonably. These are in favor of reducing the cost of maintenance and the cost of spare parts, and also increasing service efficiency of NC machine tools effectively.Above research results have important theoretical significance and engineering practical value for enhancing BSP performance, reducing costs of maintenance and spare parts, and effectively increasing the processability and processing efficiency of NC machine tool. |
PDF Full Text Request