Age Replacement Research Articles

Age replacement policies for discrete and continuous heterogeneous k-out-of-n systems

Age replacement policies for discrete and continuous heterogeneous k-out-of-n systems

Antimicrobial Combinations as Novel Indicators for Clostridioides difficile infection development: Population-Based, Nested Case-Controlled Study in Japan—The Shizuoka Kokuho Database Study

BackgroundClostridioides difficile is a major cause of antimicrobial-associated colitis. While antimicrobial stewardship has reduced the incidence of C. difficile infection (CDI), managing CDI is challenging because knowledge about preventing it is limited among healthcare professionals. To address this, we examined associations between antimicrobial use and CDI development. MethodsThis observational, nested case-controlled study was conducted using the Shizuoka Kokuho Database (SKDB). Individuals with no record of CDI or antimicrobial-associated enterocolitis within 1 year after SKDB enrolment, but who subsequently developed CDI, were included as the Case group. The Control group comprised individuals selected via 1:4 matching sampling without replacement for sex, age, and month of CDI onset. Conditional logistic regression analysis was performed to assess associations between antimicrobial use (number and combination) and CDI development, controlling for matched variables, background factors, and underlying conditions. ResultsOf the 2,398,393 individuals, 4917 were assigned to the Case group and 19,668 to the Control group. The adjusted odds ratios (ORs) for CDI were 3.65 for one antimicrobial and 8.58, 17.3, and 38.9 for combinations of two, three, or four or more agents (all p < 0.001). Penicillins, fourth-generation cephems, and carbapenems exhibited high ORs. Similar results were observed in certain demographic and comorbidity-free subgroups. Several combinations (penicillins + carbapenems, penicillins + cephems + carbapenems, cephems + fluoroquinolones, and penicillins + cephems + carbapenems) were notably associated with CDI development. ConclusionCDI prevalence increased with the number of antimicrobial classes used in combination. Certain types or combinations of antimicrobials may increase the OR for CDI.

Optimal maintenance policies for a k-out-of-n system with replacement bias costs

In this paper, the issue of determining an optimal age replacement is explored by incorporating minimal repair, preventive replacement, and corrective replacement into a k-out-of-n system subject to shocks. The k-out-of-n system in question consists of n identical components, and functions if at least k components function. Each shock causes the failure of a random number of components; if at least n-k + 1 components fail, the system fails and implements corrective replacement, otherwise the system is minimally repaired. The system is scheduled to implement preventive replacement before failure at age T or at the complement of a random working cycle, whichever occurs first or last. In order to balance the bias time between preventive replacement and corrective replacement, a replacement bias cost is also taken into account for planning replacement policies. The present paper develops a two-phase maintenance methodology and determines the optimal number of components and preventive replacement age that minimize the expected cost rate functions. For each model, the expected cost rate function is formulated analytically and optimized theoretically, and a numerical example is given to illustrate the applicability of the proposed methodology.

Optimal age replacement in parallel systems with random components

Optimal age replacement in parallel systems with random components

Unlocking Global Efficiency with Enhanced Milling Machines Worldwide

This study investigates the effectiveness of six milling machines at PT. INKA, a railroad car manufacturing company, focusing on CNC Plano 133 and Horizontal Milling 142. Utilizing Overall Equipment Effectiveness (OEE) and Age Replacement methods, the research aims to optimize machine performance and propose preventive maintenance strategies. Data spanning from January 2021 to December 2022 were collected and analyzed. Results indicate that both CNC Plano 133 and Horizontal Milling 142 exhibit suboptimal OEE values, primarily due to breakdown losses. Applying Age Replacement within 10 days significantly enhances reliability, with post-replacement reliability reaching 100%. The findings underscore the importance of preventive maintenance in improving milling machine reliability and overall productivity, thereby enhancing competitiveness and sustainability in the manufacturing sector. Highlight: Improved productivity: Preventive maintenance boosts milling machines' reliability and effectiveness. Resource efficiency: Analyzing OEE minimizes downtime, optimizes production output. Competitive edge: Enhanced performance sustains competitiveness, strengthens manufacturing sector's sustainability. Keyword: Milling machines, Overall Equipment Effectiveness (OEE), Preventive maintenance, Age Replacement, Manufacturing industry

A Net Present Value Analysis of Opportunity-Based Age Replacement Models in Discrete Time

Two important opportunistic age replacement models, under replacement first and last disciplines, are generalized in discrete time. The net present value (NPV) is applied to formulate the expected total costs. The priority of multiple replacement options is considered to classify the cost model with discounting into six cases. Since the NPV method accurately calculates the expected replacement costs over an infinite horizon in an unstable economic environment, we discuss some optimal opportunistic age replacement policies which minimize the expected total discounted costs over an infinite time horizon. Furthermore, we formulate a unified model under each discipline, merging six discrete time replacement models with probabilistic priority. Finally, a case study on optimal replacement first and last policies for pole air switches in a Japanese power company is presented.

Optimal age replacement time for coherent systems under Geometric Point Process

In spatial context, the understanding of event dynamics and point distributions is a fundamental requirement. This study addresses a critical need by introducing the Geometric Point Process (GPP) and explaining its potential impact on optimizing the determination of optimal replacement ages for coherent systems. Our paper has three overarching aims: firstly, to bridge the gap by presenting the novel GPP model that effectively captures the geometric distribution of points, filling a void in point process theory. Secondly, we calculate the optimal replacement age for the coherent system based on the principles of GPP. This involves employing the Infinitesimal-Look Ahead stopping rule within the framework of Smooth Semi-Martingale (SSM) decomposition. A comprehensive comparative analysis is conducted to assess the distinct features and advantages of the GPP in relation to other point processes, offering valuable insights into its applicability and performance. Lastly, we extend the practical application of GPP by examining optimal replacement strategies for components in coherent systems, offering a bridge between theory and real-world practices, especially in the context of aircraft and wind turbine component deterioration. Additionally, we conduct reliability and sensitivity analyses, providing management suggestions, and present Monte Carlo simulations as an alternative method for validating optimal solutions. This research invites the industrial community to utilize the proposed replacement policy, paving the way for exploring geometric characteristics in stochastic processes. The timeliness and significance of this work are underscored by the relatively unexplored field of smooth semi-martingales, with the most recent publication dating back to 2015 by Bueno.

Optimal opportunity-based age replacement policies in discrete time

Optimal opportunity-based age replacement policies in discrete time

Determining Preventive Maintenance Schedule on Press Machine Components using Age Replacement Methods

To minimize severe damage and reduce maintenance costs, it is essential to monitor and control the performance decline of machines periodically. Implementing regular preventive maintenance on the machines used in production activities is a key approach to achieve this goal. By performing scheduled maintenance on a regular basis, the strength of the machines can be maintained, ensuring their stability, and facilitating smooth production processes. Notably, the press machine serves as the primary printing equipment for the company’s product manufacturing. Any breakdown in this machine can significantly disrupt production and lead to losses for the company. Frequent production interruptions due to sudden inspections and repairs are among the challenges faced by the company. To address this issue, it is recommended for the company to establish a specific preventive maintenance schedule for the press machine to ensure its stability. The Age Replacement method can be employed in creating this preventive maintenance schedule, as it determines the optimal replacement interval based on the component’s age. By utilizing the Age Replacement method, the company can generate the most effective proposed scheduling required for maintaining the press machine in optimal condition.

On the point process with finite memory and its application to optimal age replacement

There has been extensive study of various repair models in the literature, mostly under the assumption that these repairs are minimal or imperfect/better than minimal. Although this is often a realistic assumption, it may not be sufficient to model instances where the repair is worse than minimal. The generalized Polya process (GPP) that has been used to describe this type of repair takes into account all previous events/repairs, which is not often the case in practice. Therefore, in this paper, we define a new process with finite memory that starts as the GPP but, after a certain number of events or elapsed time, becomes the non-homogeneous Poisson process of repairs (minimal repairs). The corresponding age replacement policy is defined and the optimal solutions that minimize the long-run expected cost rate are analyzed. The detailed numerical examples illustrate our findings.

Development of Methods for an Overhead Cable Health Index Evaluation That Considers Economic Feasibility

To supply stable and high-quality power according to the advancement of industrial growth, electric power companies have performed maintenance of power facilities using various methods. In the case of domestic power distribution facilities, there are limitations in performing diagnostic management on all facilities owing to the large number of facilities; therefore, old facilities are managed using the health index assessment method. The health index assessment comprises only facility operation data and external environmental data and is managed only for four types of distribution facilities including overhead/underground transformers and switchgears. In the case of high voltage overhead lines, there are a large number of wires such as transformers and switchgears connected to the lines, and the ripple effect of power outages is large. However, in Korea, there is no overhead line health index standard. In overseas cases, a health index for overhead lines was developed, but only the material characteristics and surrounding environment of the overhead lines were considered and economic feasibility was not considered. Therefore, in this paper, we developed a health index evaluation methodology for ultra-high voltage overhead lines that considers economic feasibility. In this paper, unlike the existing health index evaluation method that uses only operational data and external environmental data to determine facility performance evaluation and aging replacement standards, we developed an economic health index evaluation methodology that additionally considers failure probability and risk costs. Using the health index assessment methodology developed in this paper, it is possible to expect a reduction in facility operating costs and investment costs from the perspective of the electric power companies through the replacement of old extra-high voltage overhead cables. In addition, from the perspective of consumers, it is expected to increase power reliability and reduce the ripple effect of failure by preferentially replacing equipment with a high probability of failure.

Determination of Maintenance Intervals Using Multi-Criteria Approach to Increase Machine Availability at a Cement Company

A downtime will decrease machine availability that will affect reliability and maintainability. If interval time between two consecutive machine failures is approach to zero, it shows that the machine reliability is low, and so the availability. In the other hand, if interval time between is high, the machine availability and reliability are high. However, the procuring cost of the machine components is expensive. The problem is what is the maintenance interval time in order to optimize machine availability and reliability. In this study, the downtime is minimized by determining maintenance intervals using a multicriteria, i.e. reliability, availability, and maintainability (RAM). The model used in this research is the Age Replacement Model. A case study of a cement company is taken to show the determination of the maintenance interval. The observation shows that the Kiln Division has the longest total downtime of 1,846 hours/year although the Kiln Division has implemented overhaul during 15 days and maintenance one times. The total downtime of the Kiln Division was caused by failure to the Grate Cooler machine by 56.582%. A maintenance interval is proposed, and the result shows that the proposed maintenance intervals reduce total downtime by 86.6% and improve machine availability by 1,8%.

Age replacement policy for heterogeneous parallel systems

The optimization policy on age replacement mostly focuses on systems comprised of identical components. In this paper, both discrete and continuous time age replacement policies are considered by relaxing the assumption of identical components and working with heterogeneous parallel system, i.e. system with not necessarily identical components. In particular, necessary conditions are obtained for the existence and uniqueness of optimal replacement cycle/time for the parallel system with two nonidentical components under the proposed policy. The extension of the results to a system with more than two components is also presented.

Analisa Pemeliharaan Mesin Produksi dengan Metode Reliability Centered Maintenance (RCM) dan Age Replacement

Maintenance is needed to keep a machine operating under normal conditions for a certain period of time. PT. Daesang Ingredients Indonesia produces its packaging at a printing plant with the help of rotogravure printing, laminating and slitting machines. A total downtime of 21,100 minutes was obtained from March 2021 to March 2023, resulting in a decrease in production and an increase in costs due to corrective machine maintenance. This study aims to provide preventive maintenance proposals by identifying critical components and optimal maintenance actions using the Reliability Centered Maintenance (RCM) method and formulating component replacement intervals to minimize downtime with Age Replacement. Based on the research results, it is known that the critical components are the bearing, vanbelt and slitting blade components with time direct optimal maintenance measures, while the hose components and impression rollers are condition direct. The formulation of the replacement interval for the bearing, vanbelt and impression roller printing machine components is 23,000 minutes, 49,000 minutes and 47,000 minutes. For bearing components, hoses and vanbelt laminating machines for 28,000 minutes, 35,000 minutes and 44,000 minutes. As for the components of the slitting blade, bearing and vanbelt slitting machine 80,000 minutes, 120,000 minutes and 150,000 minutes

An optimal screening policy for heterogeneous items with minimal repairs

This article proposes a screening policy for heterogeneous repairable items, where each item is minimally repaired at failure and a limited number of minimal repairs is available. The item is replaced when the predetermined age is reached, the number of minimal repairs exceeds the upper limit, or the number of minimal repairs at the screening time exceeds the screening threshold, whichever occurs first. We show that the proposed screening policy is superior to the age replacement policy with repair number limit in terms of probability. The corresponding cost model is derived and an illustrative example is also presented.

Age replacement and inspection models for estimating optimal maintenance cost: numerical performance comparisons with a case study from chemical industries

Age replacement and inspection models for estimating optimal maintenance cost: numerical performance comparisons with a case study from chemical industries

Customizing Random Replacement Model and Flexible Warranty Model from the Perspective of Screening Reliability

In the present academic and engineering fields, every measure function of product reliability is modeled and estimated from the statistical perspective. These indicate that there universally exist differences in the reliabilities of new identical products that survive the burn-in test. On the basis of the differences in the reliabilities of new identical products, designing through-life maintenance models for managing the different reliabilities is a very practical topic for engineering fields. In this study, a random warranty model and a random maintenance model are designed by screening product reliabilities to manage the through-life reliabilities of products. In the random warranty model, the coverage areas of the warranty are set as the different areas for applying flexibility to them to control the warranty costs of new identical products with different reliabilities, and thus this warranty is called a flexible random free repair warranty (FRFRW) model. In the random maintenance model, two random replacement actions are customized by setting different replacement ranges for controlling maintenance costs and lengthening service life. This random maintenance model is called a customized random replacement (CRR), which is used to manage product reliabilities after the FRFRW expiration. These two random models are characterized from the mathematical perspective, and some derivatives of both are provided to model other maintenance problems. The characteristics of every model and the performance of the CRR are explored and illustrated through numerical experiments. The results show that the CRR is superior to random age replacement.

Optimal age replacement policies of mission-oriented systems with discounting

The instability of global economic would affect us in many aspects. For some important mission-oriented systems, if the decision-makers does not make the adequate budget preventively, the systems could not undergo the maintenance in time and then unimaginable disasters would occur. Therefore, we firstly consider the discount rate of cost, and extend the age replacement policies of mission-oriented systems with discounting. To balance the maintainability and cost, the replacement first and replacement last are analyzed respectively. Furthermore, the effectiveness of the suggested policies are verified via the numerical examples. Finally, we illustrate the suggested policies in maintaining the electronic radar system of warning aircraft based on the assumed data. It can provide a better guidance for the engineers to maintain the mission-oriented systems when the economic is changed a lot.

A Revisit of Age-Based Replacement Models With Exponential Failure Distributions

This article revisits the optimization problems of age-based replacement models for exponential failure distributions. First, we show the steps how an age replacement time goes to an infinite value when the lifetime of a unit has an exponential distribution, and then, we give two discussions of possible replacement times, by introducing a new concept of cost named as deviation cost per unit of time between replacement and failure. Second, similar discussion is given for a random replacement model when the age replacement time is a random variable with a uniform distribution. Third, the models of age-based replacement first and last with deviation costs are discussed when a random replacement is taken into account for an age replacement model. Numerical examples are illustrated to show the results of the analytical discussions. Finally, necessary proofs are provided in the Appendixes.

하이브리드 고장률을 이용한 태양광 발전 시스템의 설비 유지보수 시점 결정에 관한 연구

Recently, the PV(Photovoltaic) penetration has increased rapidly in Republic of Korea. And quite a lot of PV systems has been installed in small capacity. And the PV systems have difficult to have its own maintenance planning system due to difficulties in securing economic feasibility. Therefore the maintenance planning method for PV systems that can be generally applied are attracting considerable. Although the age replacement policy, one of the traditional RCM(Reliability Centered Maintenance) methodology, is excellent for determining the replacement cycle of facilities. But It evaluates that the facilities as good as new after maintenance. In this paper, the maintenance planning method for PV system facilities based on RCM has been proposed. To evaluate the failure rate after the imperfective maintenance, hybrid model has been applied. In addition, the economic feasibility of maintenance has been compared by considering investment cost and loss of the implementation for preventive maintenance policy.