Wenhua Chen

Optimal Time-Censored Constant-Stress ALT Plan Based on Chord of Nonlinear Stress-Life Relationship

This paper proposes a method for designing an optimal plan for the type-I censoring constant-stress accelerated life test (ALT) with a nonlinear stress-life relationship. This method derives the optimal plan based on the line segment (the chord) that connects the highest and lowest points of the curve or surface that corresponds to the nonlinear stress-life relationship, and consequently, it transforms the problem of designing the optimal plan of an ALT with a univariate or multivariate nonlinear stress-life relationship to the problem of designing the optimal plan of an ALT with a univariate linear stress-life relationship. The theoretical analysis and examples show that compared with the methods that find the optimal plan based on the nonlinear stress-life relationship itself, the proposed method can simplify the design problem and obtain better plans.

Optimal Design of Multiple Stresses Accelerated Life Test Plan Based on Transforming the Multiple Stresses to Single Stress

For planning optimum multiple stresses accelerated life test plans, a commonly followed guiding principle is that all parameters of the life-stress relationship should be estimated, and the number of the stress level combinations must be no less than the number of parameters of the life-stress relationship. However, the general objective of an accelerated life test(ALT) is to assess the p-th quantile of the product life distribution under normal stress. For this objective, estimating all model parameters is not necessary, and this will increase the cost of test. Based on the theoretical conclusion that the stress level combinations of the optimum multiple stresses ALT plan locate on a straight line through the origin of coordinate, it is proposed that a design idea of planning the optimum multiple stresses ALT plan through transforming the problem of designing an optimum multiple stresses ALT plan to designing an optimum single stress ALT plan. Moreover, a method of planning the optimum multiple stresses ALT plan which can avoid estimating all model parameters is established. An example shows that, the proposed plan which only has two stress level combinations could achieve an accuracy no less than the traditional plan, and save the test time and cost on one stress level combination at least; when the actual product life is less than the design value, even the deviation of the model initial parameters value is up to 20%, the variance of the estimation of the p-th quantile of the proposed plan is still smaller than the traditional plans approximately 25%. A design method is provided for planning the optimum multiple stresses ALT which uses the statistical optimum degenerate test plan as the optimum multiple stresses accelerated life test plan.

Accelerated Aging Test and Study of Storage Life Prediction of NBR O-Ring

Nitrile Butadiene Rubber (NBR) is a kind of common sealing materials for the electric hydraulic servo mechanism, there exists the aging failure problem in its storage environment, which is the key factor determining the storage life of the electric hydraulic servo mechanism. Through the analysis of aging failure mechanism of the NBR o-ring, the degradation path that varies with the changes of aging time based on compression set was established. And the Arrhenius equation, which is the acceleration equation of the aging reaction velocity varies with the changes of temperature, was established as well. In order to obtain the related parameters of the model, the accelerated aging test was conducted and its data were processed by applying the approximation standards and least square method. Also through the test the prediction of storage life of NBR o-ring under special storage conditions was made, and its predicted results were basically identical with the actual storage life.

Electronic Tension Control of High-Speed and Active Sending Line Based on Fuzzy PID Control

In the case of small diameter( 10000 r/min)winding, high-speed initiative electronic tension control for sending line was designed to solve the problem that the winding motor speed changes at the start and down state and increasing the size of the coil wound level lead to tension fluctuation. The structure, working principle and the factors that affect the tension fluctuation were discussed in detail. The transfer function of this system was deduced, and the Fuzzy PID control algorithm was also introduced to the system. The model of the Fuzzy PID control algorithm and the conventional PID control algorithm were established using MATLAB/SIMULINK tool, The simulation results show that the fuzzy PID control is better than the conventional PID control in improving the dynamic response of the tension controller, furthermore, the control precision and in terms of robustness is showed.

Research on Vector Blending Algorithm of Velocity for Acceleration and Deceleration of High Speed Machining

To guarantee the efficiency and accuracy of machining in high speed machining, a novel vector blending algorithm for velocity smooth link is proposed. Based on efficient acceleration/deceleration technique for a single distance movement, the desired acceleration/deceleration characteristics can be selected. According to acceleration/deceleration characteristics, two different acceleration/deceleration profiles for two corresponding distance movements are constructed respectively. Under the condition of length of movement, highest velocity and direction of motion, two different acceleration/deceleration profiles are blended. On-line implementation results show that the proposed approach makes velocity link smoothly and efficiency and accuracy of machining can be guaranteed.

Statistical Analysis on Accelerated Degradation Test Data Based on Multiple Performance Parameters

In view of the multiple performance parameters accelerated degradation and need to consider its dependence, we should know how to statistical analysis on the data of testing, establish multiple performance parameters degradation path model and its distribution model and the accelerated model of degradation rate. The multiple performance parameters degradation data’s statistics has two different situations which are independent and dependent. So, A method is proposed which is multiple performance parameters of reliability comprehensive evaluation method based on least squares parameters estimation. This method can achieve rapid and effective assessment of their reliability by using an efficient Monte-Carlo simulation method to get the performance parameters degradation data.