A Tolerance Design Method for Electronic Circuits Based on Performance Degradation

Due to the effects of manufacturing tolerances and environmental conditions, component parameters vary and degrade with time. This may cause performance measures of electronic circuits to deviate from design specifications. Therefore, a tolerance design method based on performance degradation is proposed for electronic circuits, so as to improve the robustness of output characteristics. First, sensitive components causing output fluctuation are determined via orthogonal experiment and PSpice simulation. Then, degradation path models are established to describe the degradation process of sensitive components. The predicted values worked out by the degradation path models are substituted into the simulation model for Monte Carlo analysis. Besides, output characteristics and performance reliability are evaluated according to Monte Carlo simulation. Finally, optimum allocation is carried out for component tolerances as per minimum life cycle cost. The proposed method is illustrated by a case study of light‐emitting diode (LED) driver. Copyright © 2013 John Wiley & Sons, Ltd.     

Accelerated Degradation Tests: Modeling and Analysis

High reliability systems generally require individual system components having extremely high reliability over long periods of time. Short product development times require reliability tests to be conducted with severe time constraints. Frequently few or no failures occur during such tests, even with acceleration. Thus, it is difficult to assess reliability with traditional life tests that record only failure times. For some components, degradation measures can be taken over time. A relationship between component failure and amount of degradation makes it possible to use degradation models and data to make inferences and predictions about a failure-time distribution. This article describes degradation reliability models that correspond to physical-failure mechanisms. We explain the connection between degradation reliability models and failure-time reliability models. Acceleration is modeled by having an acceleration model that describes the effect that temperature (or another accelerating variable) has on the rate of a failure-causing chemical reaction. Approximate maximum likelihood estimation is used to estimate model parameters from the underlying mixed-effects nonlinear regression model. Simulation-based methods are used to compute confidence intervals for quantities of interest (e.g., failure probabilities). Finally we use a numerical example to compare the results of accelerated degradation analysis and traditional accelerated life-test failure-time analysis.     

基于模糊学习算法的空调机组性能模拟

基于模糊熵准则和误差平方和准则建立了模糊学习算法,基于该模糊学习算法,应用BP神经网络对柜式空调机组的性能进行了模拟.结果表明,与传统的基于误差平方和准则的学习算法相比,采用模糊学习算法可以大大简化网络结构,有效提高模拟精度和效率.     

一种被动式微混合器的宏微建模方法与实验

建立了可用于被动式微混合器设计的宏微建模方法,利用分离变量法建立用于求解直通道内样品浓度分布的宏模型,采用宏模型计算微混合器的各段直通道内样品的浓度分布.运用有限元方法数值求解复杂的混合单元内样品的浓度分布,通过数值拟合和插值,交换宏模型与数值求解的计算结果.经过反复迭代,实现被动式微混合器的系统级求解.采用数控铣削在聚甲基丙烯酸甲脂(PMMA)平板上加工微通道,用热键合的方法实现微混合器盖片与基片的封装.在微混合器入口,输入3种不同浓度的荧光素钠盐溶液,形成样品浓度的准正态分布.采用激光诱导荧光观察和分析样品的混合效果.通过对比数值仿真和实验测试结果,验证了宏微建模计算方法的准确性.     

基于电子产品板级加速退化数据的可靠性分析

以某24 V-2 A稳压电源板在80 C,100 C,120 C下进行恒加加速退化试验为例,观测到电源板输出电压随温度变化的退化过程,由B-S模型采用回归方法进行了可靠性统计推断,并与其它评估结果比较.结论表明,基于加速性能退化数据进行板级电子产品可靠性评估方法可行、结果可信,且更节约试验成本和时间,无继往数据和无失效数据情况下仍能适用.     

空调换热器长期运行性能衰减的加速实验研究

为研究长期积尘对空调室外机性能衰减的影响,本文采用对空调室外换热器进行加速测试方法,在高粉尘浓度环境下短时间积尘模拟实际空调在低粉尘浓度下长期运行时的积尘效果,从而加快换热器的积尘进程以达到加速测试的目的。基于上述方法搭建了换热器加速测试实验台,对具有不同翅片结构与管排数的3种换热器样件进行2～10 h的加速积尘测试,预测其在室外运行1～5年后的性能衰减效果。测试结果表明:空调换热器使用5年后,1排管波纹翅片换热器、2排管波纹翅片换热器和2排管平直翅片换热器的压降增幅分别为21.8%、29.5%和25.0%,换热量衰减率分别为11.2%、19.3%和18.0%。     

Experimental Design for a Class of Accelerated Degradation Tests

Traditionally, reliability assessment of new devices has been based on accelerated life tests. This approach is not practical for highly reliable devices, such as lasers, which are not likely to fail in experiments of reasonable length. An alternative approach is to monitor the devices for a period of time and assess their reliability from the changes in performance (degradation) observed during the experiment. In this article, we propose a methodology for designing experiments for degradation processes in which the amount of degradation over time levels off toward a plateau (maximum degradation) that is a function of stress. We provide (a) the stress levels for the experiment, (b) the proportion of devices to test at each stress level, (c) the times at which to measure the devices, and (d) the total number of devices to test. We apply the proposed methodology to an actual example.     

用人工加速老化法比较聚氨酯面漆和丙烯酸磁漆的性能

涂料在天然曝晒的条件下进行老化,需要很长的时间,不能快速比较其性能优劣,采用人工加速老化试验(氙灯老化法)对丙烯酸磁漆和聚氨酯面漆分6个周期(1周期:200 h UV和50 h盐雾)进行老化,用FTIR,SEM和光泽仪对老化的涂层进行分析表征,用交流阻抗(EIS)法来测试两种涂层抗渗水性能的强弱.结果表明,聚氨酯面漆抗紫外线的能力要比丙烯酸磁漆强;聚氨酯面漆的抗渗水性能强于丙烯酸磁漆.聚氨酯的综合性能强于丙烯酸磁漆.     

Semiparametric Models for Accelerated Destructive Degradation Test Data Analysis

Accelerated destructive degradation tests (ADDT) are widely used in industry to evaluate materials’ long-term properties. Even though there has been tremendous statistical research in nonparametric methods, the current industrial practice is still to use application-specific parametric models to describe ADDT data. The challenge of using a nonparametric approach comes from the need to retain the physical meaning of degradation mechanisms and also perform extrapolation for predictions at the use condition. Motivated by this challenge, we propose a semiparametric model to describe ADDT data. We use monotonic B-splines to model the degradation path, which not only provides flexible models with few assumptions, but also retains the physical meaning of degradation mechanisms (e.g., the degradation path is monotonic). Parametric models, such as the Arrhenius model, are used for modeling the relationship between the degradation and the accelerating variable, allowing for extrapolation to the use condition. We develop an efficient procedure to estimate model parameters. We also use simulations to validate the developed procedures and demonstrate the robustness of the semiparametric model under model misspecification. Finally, the proposed method is illustrated by multiple industrial applications. This article has online supplementary materials.     

A Degradation Feature Extraction Method for Hydraulic Pumps Based Upon MUWDF and MF-DFA

Hydraulic pump degradation feature extraction is a key step of condition-based maintenance. Since vibration signals of hydraulic pumps during degradation are strongly nonlinear and the feature information is too weak to be effectively extracted, a method based upon MUWDF and MF-DFA is proposed. Initially, the MUWDF is presented to reduce disturbances and improve feature information. Approximate signals of various decomposition layers are selected by feature energy factor and fused according to the presented fusion rules. On this basis, the fused signal is further processed by MF-DFA with a sliding window. Multi-fractal spectrum sensitive factors are selected to be the degradation feature vector of the hydraulic pump. The proposed method is verified by vibration signals sampled in a hydraulic pump degradation experiment.     

基于系统相似方法的叠堆型压电驱动器非线性动力学建模及实验研究

根据机械系统与电气系统的相似方法,将叠堆型压电驱动器的非线性电-机械耦合模型完全转换到电气域内,建立了其非线性相似电路模型;给出了非线性相似电路模型中迟滞因子的辨识方法,并对某款商用叠堆型压电驱动器进行了迟滞因子的辨识试验;基于非线性相似电路模型和迟滞因子的辨识结果,对该款叠堆型压电驱动器的非线性特性进行了仿真分析,得到了其非线性位移迟滞回线;仿真结果与试验结果吻合,证明了该建模过程与辨识方法的正确性。该建模方法在电气域内对叠堆型压电驱动器电-机械耦合特性及非线性迟滞特性进行描述,建模过程物理意义清晰且简单实用,对于研究压电驱动器的动态特性及控制算法具有实际意义。     

Optimum Allocation Rule for Accelerated Degradation Tests With a Class of Exponential-Dispersion Degradation Models

Optimum allocation problem in accelerated degradation tests (ADTs) is an important task for reliability analysts. Several researchers have attempted to address this decision problem, but their results have been based only on specific degradation models. Therefore, they lack a unified approach toward general degradation models. This study proposes a class of exponential dispersion (ED) degradation models to overcome this difficulty. Assuming that the underlying degradation path comes from the ED class, we analytically derive the optimum allocation rules (by minimizing the asymptotic variance of the estimated q quantile of product's lifetime) for two-level and three-level ADT allocation problems whether the testing stress levels are prefixed or not. For a three-level allocation problem, we show that all test units should be allocated into two out of three stresses, depending on certain specific conditions. Two examples are used to illustrate the proposed procedure. Furthermore, the penalties of using nonoptimum allocation rules are also addressed. This study demonstrates that a three-level compromise plan with small proportion allocation in the middle stress, in general, is a good strategy for ADT allocation. Supplementary materials for this article are available online.     

Geometric-Structural Study of the Accelerated Degradation of Mold Cavities for HDPE Injection

In this work, we present the case of a series of injection cavities that showed accelerated degradation. A combination of computer-aided engineering design (CAED) techniques contributed to deduce the failure origin, which may be used to increase the lifetime of the studied product. The failure in the metallic material of the injection cavity was due to degradation in the quality of the final product that was made of high-density polyethylene. The failure generated non-expected protuberances in the final product. The study was complemented by scanning electron microscopy that confirmed the initial failure hypothesis. Using the finite element method (FEM), a series of load scenarios was carried out that gave further support to understand the origin of the failure. Due to the appearance of microcracks at the surface of the injection cavity, thermal and mechanical stresses were shown to be the responsible of plastic deformation at the injection cavity. We also propose a redesign of the piece to avoid the existence of the detected damage in the injection cavity and the final product.     

一种基于子结构界面动刚度的模态综合法

针对传统模态综合法中由于高阶截断模态带来的计算误差问题,本文将子结构界面动刚度进行级数展开,用子结构的固定界面主模态表示,并利用位移协调和力平衡条件对子结构界面动刚度进行模态综合,发展了一种新的模态综合方法。该方法保留了截断模态高阶项的贡献,界面力高阶平衡条件的利用减少了界面自由度的引入。推导过程不必引入质量矩阵为对角块的假设,比现有改进方法更具普适性。数值算例的结果表明在相同自由度的前提下,本文提出的方法能获得更高的模态综合精度。     

A Relation-Based Modeling Method for Workshop Reconfiguration

To respond to the changes in the market rapidly, the workshop has become an ever-changing dynamic environment in regard to personnel change and organization alternation, etc. Therefore it is necessary to reconfigure the workshop system. In this paper, we present the point of view that the closer the relations are among elements in the system, the closer they should be connected with each other when they are integrated in designing and structural modeling of the workshop system. At first, this paper discusses the relationship among elements in the workshop system and events describing the relationship, and provides a technical overview of the expression, definition and classification of relationship. This paper focuses on the steps and algorithm to evaluate the degree of closeness of relations among elements in systems, and emphasizes the modeling methods for workshop reconfiguration by use of a fuzzy cluster. In light of the above steps and methods, types and contents of basic relationships among elements should be determined, and a standard relation tree should be set up. Then, correlation coefficients are calculated by the standard relation tree, and a fuzzy relation matrix is built up. After that, the structure modeling of the workshop equipment system can be completed through a fuzzy cluster. The paper ends with an application of a FMS( Flexible Manufactuing System) function system modeling. Results of the modeling and calculations are presented.     

基于模糊推理的数据手套传感器建模方法

分析了应用于数据手套CA SGlove上的传感器的性能和特点，提出了一种基于模糊推理的传感器建模方法：首先利用模糊推理建立传感器的模型，然后利用采样数据进行离线学习确定模型中的参数。实验证明该方法在只获取传感器最小和最大两个标定值的情况下，能够取得和分段线性插值相近似的结果。     

一种基于粘性耗散的动态黏度计算方法

基于剪切功率的耗散机理,提出了一种计算振动剪切流场中聚合物熔体动态黏度的粘性耗散法,并建立了理论模型。运用粘性耗散法,计算了简单振动剪切流场中Maxwell流体的动态黏度,得到了与传统方法相一致的结果,从而验证了理论模型的正确性。通过讨论振动叠加流场中Maxwell流体的动态黏度,分析了粘性耗散法的应用局限性。最后,通过动态流变实验,发现粘性耗散法对于小振幅范围的振动剪切流具有较好的预测能力。     

基于真实场景的大规模虚拟人群的快速生成方法

利用Poser的三维人体建模功能和3DS MAX强大的修改功能,结合MAXScript脚本语言,实现了对三维人体模型骨架的自动生成、匹配和蒙皮.通过对人物动作的建立与分解,实现了连续多个人体三维模型的生成与导出,并由此建立了一个包含不同人体及动作姿态的角色库.通过调用库中的角色,并将由图像信息获得的人群分布参数赋予这些虚拟个体人,实现了基于真实场景的虚拟人群快速生成.     

A Performance Fault Diagnosis Method for SaaS Software Based on GBDT Algorithm

SaaS software that provides services through cloud platform has been more widely used nowadays. However, when SaaS software is running, it will suffer from performance fault due to factors such as the software structural design or complex environments. It is a major challenge that how to diagnose software quickly and accurately when the performance fault occurs. For this challenge, we propose a novel performance fault diagnosis method for SaaS software based on GBDT (Gradient Boosting Decision Tree) algorithm. In particular, we leverage the monitoring mean to obtain the performance log and warning log when the SaaS software system runs, and establish the performance fault type set and determine performance log feature. We also perform performance fault type annotation for the performance log combined with the analysis result of the warning log. Moreover, we deal with the incomplete performance log and the type non-equalization problem by using the mean filling for the same type and combination of SMOTE (Synthetic Minority Oversampling Technique) and undersampling methods. Finally, we conduct an empirical study combined with the disaster reduction system deployed on the cloud platform, and it demonstrates that the proposed method has high efficiency and accuracy for the performance diagnosis when SaaS software system runs.     

针对多重退化因素的印刷图像复原方法

目的对于由多种因素所导致的印刷图像退化问题,文中提出一种针对椒盐噪声、高斯噪声和模糊退化等多重退化因素的图像复原方法。方法首先针对印刷图像椒盐噪声密度不高的特点,设计一种基于灰度范围准则和局部差别准则的椒盐噪声二级检测和滤除方法,并通过评价实验得出合适的阈值参数设置。在去除高斯噪声和图像模糊的过程中,利用边缘保持平滑滤波的原理和特性,将双边滤波器和引导滤波器应用于图像复原中,又在此基础上设计和应用图像细节增强的二次引导滤波器。结果在椒盐噪声去除方面,新方法对大部分图像都能取得较好的复原效果,尤其对细微边缘不多的图像效果最佳,复原后的PSNR值能达到40以上。二次引导滤波器对高斯噪声和图像模糊的复原效果最好。结论通过对不同图像复原方法的效果进行评价和分析,验证了文中方法的性能,为今后图像复原技术的应用提供了指导。