Optimal nonperiodic inspection scheme for a multicomponent repairable system with failure interaction using A * search algorithm

This paper proposes an approach for finding optimal nonperiodic inspection scheme for a multicomponent repairable system with failure interaction. Failure of one component of the system is hard, i.e., as soon as it occurs, the system stops operating. Failures of the other components are soft, namely, they do not cause the system stop, but increase the system operating costs. Soft failures are detected only if inspection is performed. Thus, the components with soft failure are all inspected at the scheduled inspection instances and are minimally repaired if found failed. When the component with hard failure fails, it is also repaired. However, its failure increases the failure rate of the other components. The system’s expected total cost associated to a given inspection scheme includes inspection costs, repair costs, and the penalty costs that are incurred due to the time delay between real occurrence of the soft failures and their detection at inspections. The objective is to determine the optimal inspection scheme that yields minimum expected total cost. In the proposed approach, the expected total cost is formulated in terms of inspection scheme. Then, A ^* search algorithm, with a proposed heuristic cost function, for calculating lower bounds, is employed to search through alternative inspection schemes to determine the optimal one. The proposed approach is illustrated through a simplified numerical example.     

Optimisation of opportunistic maintenance of a multi-component system considering the effect of failures on quality and production schedule: A case study

For a manufacturing equipment, any unplanned breakdown during the production period results into a high production loss. To keep the manufacturing facilities in good condition, preventive maintenance is planned. However, because of limited time and availability of resources, not all the system components can be or need to be repaired/replaced during a planned opportunity. Hence, the unplanned breakdowns can also be considered as an opportunity to do the maintenance activities for other components to take the advantage of economic dependency in multi-component system. However, when the system is under maintenance, it is very conservative to take the decision of maintenance actions on the components because of limited available time and resources. For such situation, this paper consider an opportunistic maintenance model for a multi-component system to take maintenance decision with a constraint on available time and the system availability requirements. The maintenance decisions for each component involves one of the three actions namely, repair, replace or do nothing to achieve the target availability with minimum maintenance cost. The model also considers the effect of component failures on the quality of product being manufactured as well as the production schedule on the machine. The cost of rejections is considered in the total failure cost along with the maintenance and downtime costs. The production schedule delay factor is considered as a constraint for the maintenance decision to account for the effect on production schedule delay. The optimal solution for the model is obtained using three solution methodologies namely simulated annealing, genetic algorithm and sequence heuristics. Using a real-life example of high pressure die casting machine, the opportunistic maintenance approach is demonstrated and results are discussed.     

Integrated laser/CMM system for the dimensional inspection of objects made of soft material

The applications of the coordinate measuring machines (CMMs) with a contact trigger probe to the dimensional inspection of manufactured products are restricted to the parts made of hard material, such as steel. By combining the laser and CMM, the applications of the CMMs can be extended to the inspection of objects made of soft materials, such as foils, plastics, wood, wax and clay materials. In this research, replacing the contact probe with an inexpensive laser sensor is attempted so as to eliminate the possible deflection of the component being measured when using contact probe. By combining a laser sensor with the existing automated inspection environment, a CAD-directed, three-dimensional coordinate sampling system which can perform non-contact dimensional inspection is developed.     

磨损故障检修决策模型及应用

建立了一种考虑潜在的故障状态的磨损故障检修间隔期决策模型，利用该模型可以根据费用最低的原则选择最优的检修间隔期。并给出了该模型在某滑动轴承检修决策中的应用实例。     

A new thermographic NDT for condition monitoring of electrical components using ANN with confidence level analysis

Infrared thermography technology is one of the most effective non-destructive testing techniques for predictive faults diagnosis of electrical components. Faults in electrical system show overheating of components which is a common indicator of poor connection, overloading, load imbalance or any defect. Thermographic inspection is employed for finding such heat related problems before eventual failure of the system. However, an automatic diagnostic system based on artificial neural network reduces operating time, human efforts and also increases the reliability of system. In the present study, statistical features and artificial neural network (ANN) with confidence level analysis are utilized for inspection of electrical components and their thermal conditions are classified into two classes namely normal and overheated. All the features extracted from images do not produce good performance. Features having low performance reduce the diagnostic performance. The study reveals the performance of each feature individually for selecting the suitable feature set. In order to find the individual feature performance, each feature of thermal image was used as input for neural network and the classification of condition types were used as output target. The multilayered perceptron network using Levenberg–Marquardt training algorithm was used as classifier. The performances were determined in terms of percentage of accuracy, specificity, sensitivity, false positive and false negative. After selecting the suitable features, the study introduces the intelligent diagnosis system using suitable features as inputs of neural network. Finally, confidence percentage and confidence level were used to find out the strength of the network outputs for condition monitoring. The experimental result shows that multilayered perceptron network produced 79.4% of testing accuracy with 43.60%, 12.60%, 21.40, 9.20% and 13.40% highest, high, moderate, low and lowest confidence level respectively.     

基于机会策略的复杂系统视情维修决策模型

针对部件间存在经济相关性的复杂系统,提出一类基于机会策略的视情维修优化模型。模型从部件本身的失效规律分析出发,确定不同失效模式下部件的维修方式及对应的预防性维修阈值。对于整个复杂系统的维修决策问题,借鉴机会维修思想,通过增加机会维修阈值,将时间和状态两类不同度量空间上的维修控制参数组合起来,解决系统层事后维修与视情维修的综合优化问题。同时利用更新过程理论,提出一类基于马氏决策过程的值迭代算法,确定系统的最优检测时间间隔与机会维修状态阈值。以某机械设备为例对机会维修决策模型和值迭代算法的有效性进行了验证。通过对比分析发现,应用模型能够降低系统的运行维护费用,如果部件级失效率之比在适当范围内,其经济相关性越强,节省费用的效率越高。     

Metaheuristic-based inspection policy for a one-shot system with two types of units

In this paper, we address an inspection policy problem for a one-shot system with two types of units, namely, Type 1 units that fail at random times and Type 2 units that degrade with time. Interval availability and life cycle cost are used as optimization criteria and estimated by simulation. We determine inspection intervals, preventive replacement ages of Type 1 units, and preventive maintenance thresholds of Type 2 units that have minimal life cycle cost and satisfy the target interval availability during inspection periods. A simulation-based optimization procedure using a hybrid genetic algorithm is proposed to find near-optimal solutions. Numerical examples are studied to investigate the effects of model parameters on optimal solutions and compare the hybrid genetic algorithm with the general genetic algorithm.     

Development of new edge-detection filter based on genetic algorithm: an application to a soldering joint inspection

This paper proposes a new technique of edge detection for inspecting edge and perfection of soldering joint in the flip-chip, which is an important part of a hard disk drive. Summation of error between the actual values and the measured values from the designed system of several data sets is formulated as the objective function. Genetic algorithm is adopted to find the optimal filter mask to enhance the accuracy of the inspection system. As the results indicated, the accuracy of a system with the proposed edge-detection technique is superior to that of a system with conventional filters.     

The weakest t-norm based intuitionistic fuzzy fault-tree analysis to evaluate system reliability

In this paper, a new approach of intuitionistic fuzzy fault-tree analysis is proposed to evaluate system reliability and to find the most critical system component that affects the system reliability. Here weakest t-norm based intuitionistic fuzzy fault tree analysis is presented to calculate fault interval of system components from integrating expert's knowledge and experience in terms of providing the possibility of failure of bottom events. It applies fault-tree analysis, α-cut of intuitionistic fuzzy set and T(ω) (the weakest t-norm) based arithmetic operations on triangular intuitionistic fuzzy sets to obtain fault interval and reliability interval of the system. This paper also modifies Tanaka et al.'s fuzzy fault-tree definition. In numerical verification, a malfunction of weapon system "automatic gun" is presented as a numerical example. The result of the proposed method is compared with the listing approaches of reliability analysis methods.     

液压系统图对仿真模型图的自动映射

针对液压系统的仿真，提出了一种根据液压系统图，将系统图中的元件和连线分别映射到模型图，组装成仿真模型，然后利用Matlab进行仿真运算的方法。映射过程中，元件制作成模型图的模板，并添加了一种虚拟的部件油口，连线与油口一起映射为模型端口。这种解决方案充分利用了Matlab的引擎函数，简单直观，方便实用。     

基于半马尔科夫决策过程的风力机状态维修优化

恶劣的工作环境、昂贵的维修成本和停机损失对风力机及其部件的维修提出挑战。以齿轮箱、叶片等风力机核心机械部件为对象,将部件退化过程离散成有限的退化状态;以长期折扣成本最低为目标,考虑风速、备件物流、停机损失等因素的影响,建立基于半马尔科夫决策过程的状态维修优化模型。分析各退化状态下的维修策略、检测间隔时间以及不同退化状态间的转移概率,并采用策略迭代算法求解模型。以某风力机齿轮箱为例,通过对等周期、非等周期检测条件下检测间隔时间和维修成本的分析,得到优化的维修决策。研究结果表明,该模型能有效描述风力机核心部件的退化过程,实现风力机维修优化。     

基于有效工作寿命的多变量动态均衡设计及其度量方法研究

针对机械产品各关键部件设计寿命差异较大,设计寿命较短的关键零部件容易发生故障,从而导致停机维修甚至停产报废的问题,定义机械产品关键零部件有效工作寿命,给出机械产品关键零部件有效工作寿命的度量方法,建立基于有效工作寿命的机械产品多变量动态均衡数学模型,提出机械产品多变量动态均衡设计方法。通过求解获得关键零部件的预防性维护措施优化方案,在故障发生之前对关键零部件实施预防性维护措施,消除或减少关键零部件故障的发生,均衡各关键部件的有效工作寿命,同时满足机械产品维护费用成本指标与整机可靠性指标约束。应用该方法对某型号空分设备透平膨胀机主机进行多变量动态均衡设计,证明该方法在工程应用中的正确性与高效性。     

Reliability Evaluation of Machine Center Components Based on Cascading Failure Analysis

In order to rectify the problems that the component reliability model exhibits deviation, and the evaluation result is low due to the overlook of failure propagation in traditional reliability evaluation of machine center components, a new reliability evaluation method based on cascading failure analysis and the failure influenced degree assessment is proposed. A direct graph model of cascading failure among components is established according to cascading failure mechanism analysis and graph theory. The failure influenced degrees of the system components are assessed by the adjacency matrix and its transposition, combined with the Pagerank algorithm. Based on the comprehensive failure probability function and total probability formula, the inherent failure probability function is determined to realize the reliability evaluation of the system components. Finally, the method is applied to a machine center, it shows the following: 1) The reliability evaluation values of the proposed method are at least 2.5% higher than those of the traditional method; 2) The difference between the comprehensive and inherent reliability of the system component presents a positive correlation with the failure influenced degree of the system component, which provides a theoretical basis for reliability allocation of machine center system.     

Condition-based spares ordering for critical components

It is widely accepted that one of the potential benefits of condition-based maintenance (CBM) is the expected decrease in inventory as the procurement of parts can be triggered by the identification of a potential failure. For this to be possible, the interval between the identification of the potential failure and the occurrence of a functional failure (P-F interval) needs to be longer than the lead time for the required part. In this paper we present a model directed to the determination of the ordering decision for a spare part when the component in operation is subject to a condition monitoring program. In our model the ordering decision depends on the remaining useful life (RUL) estimation obtained through (i) the assessment of component age and (ii) condition indicators (covariates) that are indicative of the state of health of the component, at every inspection time. We consider a random lead time for spares, and a single-component, single-spare configuration that is not uncommon for very expensive and highly critical equipment.     

多失效模式机械零件可靠性灵敏度估计

机械零件的失效往往存在多种失效模式,且这些失效模式对可靠性灵敏度均有影响,因此在进行可靠性灵敏度估计时,要充分考虑零件的各个潜在失效模式。提出一种多失效模式机械零件可靠性灵敏度分析的数值方法。运用随机摄动技术和四阶矩技术,求得各失效模式功能函数的前四阶矩及可靠性指标,解决了随机变量分布类型未知时,各失效模式的可靠度计算问题。根据机械零件失效模式较少的特点,将零件的潜在失效模式视为串联关系,则零件整体的失效即为失效模式的串联失效。结合灵敏度分析的梯度算法,推导出关于随机变量均值和方差的可靠性灵敏度的计算公式。数值算例表明所述方法可快速有效地估计多失效模式机械零件的可靠性灵敏度,且适用于非线性功能函数的情况。     

Transient pressure characteristics in a pressure regulating system by using 1-D analytic valve modeling

Typically, a Pressure Control Valve (PCV) system is constructed with 3 to 4 PCV lines in order to prepare for both a future demand increase and a continuous supply of power after an emergency shutdown of the operating line. However, some operation failure cases that do not follow the original design concepts of a PCV system have been reported in the field. In this study, an accurate 1-D PCV system numerical model was built and a 1-D compressible flow theory was introduced for analytic valve modeling to find solutions for this problem. Several numerical analyses were successfully performed to examine the generation and propagation characteristics of the transient pressure and to clarify the relationships between the transient pressure or surge wave and each factor or parameter relating to fluid dynamics behavior in a PCV system. The relationship between the transient pressure and other factors, such as the size of pipe and header linked after a PCV, the pipe size of the added components linked after the header, and the generation time of the transient pressure and influence of the Slam Shut Valve were investigated in detail. Finally, in order to reduce the strength of the transient pressure and to delay its propagation, this study demonstrates the benefit both of enlargement of the pipe linked to the component added after the PCV system, and the installation of a dissipation component between the operation line and the other lines.     

基于幂指数分布的系统共因失效新模型

假定构成系统的元件存在多种失效过程，各失效过程相互独立，并服从非齐次泊松分布。则同一失效过程的连续两次失效事件之间的时间间隔服从幂指数分布，利用条件概率，从系统中某一指定元件完好的概率推广到某指定m个元件完好的概率，将独立失效时系统可靠度表达式转化成包含共因信息的可靠度表达式。算例验证了该理论模型的正确性。     

Experimental study and evaluation methodology on hard surface integrity

The Taguchi method is adopted experimentally to investigate the surface integrity (surface roughness, residual stress, and thermal damage layer) of hardened bearing steel in hard dry turning, and the validation experiments are consequently performed. It was revealed that the value and effect sequence of optimal hard turning parameter varies with different objectives of surface integrity. However, it is quite difficult to select or determine the optimal combination of hard turning parameters. A hard-turned component performance, which reflects an integrated impact of surface integrity, should be fully recognized to resolve the inherent conflict in the selection process. Based on it, an evaluation methodology composed of four steps is proposed that surface integrity should be evaluated by the service/fatigue life of hard-turned components and therefore turning parameters. It bears significance for super-finish hard turning further application in respect that it provides an integrated approach for hard turning parameter optimization to achieve a superior surface integrity. Funded by the Ministry of Education of China- “985” of international cooperation project “Clean Manufacturing Technology”.     

基于物联网的电力机械设备巡检抢修智能决策

为了保证电网正常供电,需要定期巡检电力机械设备,确保在设备发生异常时可以及时抢修,为此提出基于物联网的电力机械设备巡检抢修智能决策方法。 利用物联网构建电力机械设备实时巡检架构,并重点设计了电力巡检机器人自动控制方案。 根据线上巡检、历史数据计算健康指数与故障率之间的关系,采用层次分析法逐层分析各层面的影响因素,整合若干种抢修方式,并划分为不同方案属性,采用模糊互补方程对影响因素重要性进行两两比较得到权重计算结果,结合权重值构建三角模糊方程,采用模糊判断矩阵计算单一因素的决策排序向量,实现最优抢修决策。 仿真实验证明了该方法的决策耗时最短、抢修费用最低、效果最好。     

Scuffing of steel under boundary lubricated conditions

This research was conducted to examine whether a relationship exists between the true elastic limit of steel and its scuffing load measured under boundary lubricated conditions. Scuffing tests were carried out on a pin-on-disc machine using steel components which were heat treated to give differeing yield points. Yield point was also altered by testing at elevated temperature. The true elastic limits of steels in the same conditions as for scuffing tests were measured by a highly sensitive technique. True yield points are reported for EN8 steel in both soft and hard condition at room temperature and at 201°C. A difference in scuffing load for soft and hard specimens was measured for certain operating conditions giving some validation of the elastic limit hypothesis. Scuffing testing at elevated temperatures produced some unexpected results which do not allow a thorough proof of the hypothesis. These findings are discussed