考虑缓冲区库存的退化系统最优维修更换策略

为提高生产过程的连续性,在设备间设置缓冲区,假设上游设备不能修复如新的条件下,以缓冲区库存控制K和设备更换前故障次数N为决策变量,运用几何过程建立了退化系统维修更换模型。以最小化系统运行成本为目标,利用更新过程理论求得系统平均费用率C(N,K),并给出求解最优联合策略的演化算法。借助数值算例演示了本模型,通过灵敏度分析确定了最优策略和相关参数的关系。     

Optimal periodic replacement policy for a two-unit system with failure rate interaction

In this paper, an economic periodic replacement model for a two-unit system with failure rate interaction between units is presented. In this model, whenever unit 1 fails, it causes a certain amount of damage to unit 2 by increasing the failure rate of unit 2 by a certain degree, while each unit 2 failure induces unit 1 into instantaneous failure. Without failure interaction between units, the failure rates of two units also increase with through an ageing process. The two-unit system is all replaced at age T, or on failure, whichever occurs first. The aim of this paper is to derive the long-run expected cost per unit time by introducing relative costs as a criterion of optimality. The optimal period T^* that minimizes that cost is also discussed. A numerical example is given to illustrate the method.     

随机产出与需求条件下的响应性定价策略

为了应对供需不确定带来的问题,构建了供应商产出和市场需求均不确定情况下的两级供应链定价模型。通过三阶段Stackelberg博弈分析,探讨了响应性定价策略下零售商的最优订货量和产品定价决策以及供应商的最优分销价格,分析了响应性定价策略与清仓定价策略的差别以及随机产出率和潜在市场需求对响应性定价策略价值的影响。研究结果表明,响应性定价能提高零售商的利润,但有可能降低供应商的利润;产出率越大、潜在市场需求越小时响应性定价对供应商和零售商的价值越大,而产出率和潜在市场需求的不确定性对响应性定价策略价值的影响具有非单调性。     

基于期量折扣的变质产品订货策略

针对多频次、小批量的变质产品订货模式,提出期量折扣策略,并将其划分为时间全数量折扣和时间增量折扣两种。考虑零售商在订货过程中的机会损失成本,分别研究了两种折扣策略下的变质产品订货策略。结果表明,时间全数量折扣较时间增量折扣更能激励零售商增加订货,折扣时间限制越宽松越有利于零售商降低成本。     

Optimal production run length and maintenance schedule for a deteriorating production system

This study considers manufacturing cost, inventory holding cost, system setup and maintenance costs, restoration cost, and warranty cost to a deteriorating production system whose state can be classified into in-control or out-of-control state at any time. This study develops a framework of simultaneous determination of optimal production run length and maintenance schedule and shows that there exists a unique optimal production run length and scheduled maintenance policy that minimize the expected total cost per item. The mathematical conditions to the optimal production run length and scheduled maintenance policy for a production cycle are deduced.     

Reliability assessment and replacement for machine tools under wear deterioration

This paper considers a problem of reliability assessment and determination of optimal replacement time for a machine tool under wear deterioration. Traditional models classifying a tool’s condition use binary states, with working (success) or failure (1 or 0), to evaluate its reliability and decide its optimal replacement time; however, as most machine tools deteriorate over time, a multi-state discrete model is reported as a more realistic classification for quantifying the tool wear condition. In this paper, we propose a nonhomogeneous continuous-time Markov process (NHCTMP) for modeling the tool wear process, representing the length of time the tool stays in a certain state, which depends not only on its current state but also on how long it has remained in the current state. According to this model, we first develop reliability assessment for the tool with the multi-state deterioration. Then, we derive an average expected cost function of the tool operating over the manufacturing period and optimize it to find the optimal replacement time of the tool. The optimization of the average value of the expected cost over tool replacement time emerges as a classical tradeoff idea, balancing between increasing the average cost of tool replacement and decreasing the average cost of tool deterioration. A real application is illustrated throughout the paper.     

多值属性系统的故障诊断策略最优化方法

针对过程工业系统故障诊断的检测次序问题,其检测属性存在多个取值.为了降低此类系统的故障诊断费用,提出使用人工智能的搜索剪枝技术来生成最优故障诊断策略.根据多值属性系统及其诊断策略问题的描述,给出了穷举诊断策路的生成树剪枝方法.根据此方法,形成2种故障诊断策略最优化的算法:广度优先生成树深度优先剪枝算法(BFS-DFC)和启发广度优先生成树动态规划剪枝算法(HBFS-DPC).算法分析和实例结果表明此方法适用于小系统的最优故障诊断策略设计,并通过例子展示了两种算法的差异.     

A study of “mode selecting stochastic controller” for a dynamic system under random vibration

This paper presents a new stochastic controller applied on the vibration control system under irregular disturbances based on the mode selection scheme. Measured displacement and frequency characteristics are simultaneously used in designing a mode selecting controller. This technique is validated by applying to the suppression problem of a flexible beam with randomly vibrated circumstances. The presented method, called Mode Selecting Stochastic Controller, uses the frequency measurement of the flexible system based on a Fast-Fourier transformation algorithm. This controller is constructed by combining mode selection method with previous known Stochastic Controller in real time. Numerical simulations and several experiments are conducted to validate the proposed method. The performance of the proposed method is compared with a stochastic controller developed recently. This method was improved compared with previous one.     

Optimal pricing and replenishment policies of an EOQ model for non-instantaneous deteriorating items with shortages

This paper discusses the optimal pricing and replenishment policies of an economic order quantity model for non-instantaneous deteriorating items with partial backlogging over an infinite time horizon. The model is studied under the replenishment policy starting with no shortages. The backlogging rate is any non-increasing function of the waiting time up to the next replenishment. The objective of this model is to maximize the total profit which includes the sales revenue, purchasing cost, set up cost, holding cost, shortage cost, and opportunity cost due to lost sales. Here, the selling price, replenishment quantity, replenishment cycle length, and the time duration of the positive inventory level are taken as decision variables to maximize the profit of the inventory system. The existence and the uniqueness of the solution of the proposed inventory system are examined. We suggest a solution procedure to find the optimal solution of the described model. Numerical examples are presented to determine the developed model and the solution procedure. Sensitivity analysis of the optimal solution with respect to major parameters is carried out and some useful managerial results are obtained.     

Dynamic response analysis of closed-loop control system for random intelligent truss structure under random forces

Considering the randomness of structural damping, physical parameters of structural materials, geometric dimensions of active bars and passive bars, applied loads and control forces simultaneously, the problems of dynamic response analysis of closed-loop control system based on probability for the random intelligent truss structures are studied in this paper. The computational expressions of numerical characteristics of structural dynamic response of closed-loop control system are derived by means of the mode superposition method. Through the engineering examples, the influences of the randomness of them on structural dynamic response are inspected and some significant conclusions are obtained.     

Purchasing model for deteriorating items with time-varying demand under inflation and time discounting

The study proposes a purchasing model, which considers a case of time-varying deterioration, partial back-ordering that depends on the waiting time for backlogging, and time value of money over a finite horizon. The model integrates all possible real-world situations that may happen in dealing with an order quantity. We derive the lower bound of the replenishment for a specific planning horizon and propose a procedure to solve the problem.     

Optimal pro-rata warranty decision with consideration of the marketing strategy under insufficient historical reliability data

Warranties play an important role in the market, not only safeguarding the rights and interests of consumers, but also promoting the sales and reputation of manufacturers. Due to their impacts on the market, manufacturers should take their warranty policies into consideration in developing an integrated marketing strategy which can promote a product by simultaneously considering pricing, production, and related post-sale services. Most of the studies regarding the issue of pro-rata warranties (PRW) only focus on cost analysis with the reliability estimation, and few consider how marketing strategies can be integrated in the warranty decision. Moreover, the manufacturer may not have sufficient historical data to estimate the deterioration of a newly developed product, and therefore, the results obtained from analytical models may not be reliable. A Bayesian analysis should be a reasonable approach in order to deal with such a problem for the situation of insufficient historical data because it can effectively assess the deterioration based on experts’ opinions and possibly few relevant data. Accordingly, this paper proposes a Bayesian decision-making model which considers the PRW policy with the pricing and the production strategy. Moreover, in order to deal with the complexity of computation of the proposed model, a heuristic algorithm is also provided, and finally, a practical application case is used to demonstrate its usefulness.     

The efficiency range of economical cutting conditions for a multistage transfer machine under a failure replacement strategy

This paper presents models for calculating the optimal cutting feed rate and spindle speed at each stage in a multistage transfer machine. The optimal cutting conditions are determined by taking into account the cutting constraints for three objective functions, which are: minimum expected cycle time, minimum expected cost per unit, and maximum expected profit rate, using a one-dimensional search procedure. The efficiency range in which the optimal solutions for the three objective functions can be found is also analyzed. In addition, the optimal cutting conditions at each stage are compared to those of a stand-alone cutting machine.     

Optimal production policy for a manufacturing system with volume flexibility in a supply chain under lumpy demand

A batch production system with volume flexibility in a supply chain where a manufacturer procures raw materials and/or component parts from multiple suppliers in a lot and processes them into a single product, is considered in this research. First of all, a decision-making model is developed for an optimal production rate selection in the volume-flexibility production system, where a single type of finished products is delivered periodically in fixed quantities within a fixed interval of time. In this model, the production rate is perceived as a decision variable and unit production cost becomes a function of production rate. This model takes into account not only inventory costs of raw materials and finished goods, but production costs as well. Then, a pragmatic computation approach is presented to solve the proposed model for special unit-production-cost functions. It is used to determine an optimal production rate, and thus to decide an optimal ordering policy for procurement of raw materials from suppliers and an optimal manufacturing batch size. Some observations are made for optimal production rate analysis. Finally, a numerical study is conducted to illustrate the solution and a set of data with ten problems is tested and compared.     

Tuning of an optimal fuzzy PID controller with stochastic algorithms for networked control systems with random time delay

An optimal PID and an optimal fuzzy PID have been tuned by minimizing the Integral of Time multiplied Absolute Error (ITAE) and squared controller output for a networked control system (NCS). The tuning is attempted for a higher order and a time delay system using two stochastic algorithms viz. the Genetic Algorithm (GA) and two variants of Particle Swarm Optimization (PSO) and the closed loop performances are compared. The paper shows that random variation in network delay can be handled efficiently with fuzzy logic based PID controllers over conventional PID controllers.     

Estimation for fatigue limit reliability of a metal with inhomogeneities under stress ratio

In this paper, by using statistical characteristics of hardness in a small region and statistical characteristics of mechanical condition in a small region based on a defect size distribution and a certain stress which is applied to a defect, a quantitative prediction method for fatigue limit reliability of a metal with inhomogeneities is proposed. Also rotating bending and push–pull fatigue tests under R=-1 are carried out on quenched-tempered 0.5% carbon steels, whose average hardness is about H_V600. Comparing a predicted fatigue limit reliability with experimental data, the applicability of the present proposed method is examined and confirmed.     

A queueing model for a two-stage stochastic manufacturing system with overlapping operations

This paper presents analytical expressions for estimating average process batch flow times through a stochastic manufacturing system with overlapping operations. It is shown that the traditional queueing methodology cannot be directly applied to this setting, as the use of the overlapping operations principle causes the arrival process of sublots at the second stage to be a non-renewal process. An embedded queueing model is then proposed, which provides a tool to estimate the flow time reductions caused by the use of overlapping operations. Moreover, we provide expressions to estimate the production disruptions occurring at the second stage. The results of our research confirm the general intuition that the overlapping operations principle leads to less congestion, and hence a smoother flow of work through the system. On the other hand however, lot splitting inevitably requires more material handling on the shop floor. The expressions provided in this paper allow the quantification of the trade-off between these two effects, e.g., by gauging them within the scope of a cost model.