Optimal Preventive Maintenance Strategy Research Articles

Optimal preventive maintenance strategy for populations of systems that generate outputs

Optimal preventive maintenance strategy for populations of systems that generate outputs

Performance evaluation and optimization model for closed-loop production lines considering preventive maintenance and rework process

Closed-loop production lines with a constant number of carriers are widely encountered in today's production systems. In this paper, a production performance evaluation and optimization model is proposed for a closed-loop production line taking into account the degradation-level-dependent quality and rework process. Based on a two-machine-one-buffer decomposition method and the system state transition, a production performance evaluation method is presented. Due to the emphasis on quality management, preventive maintenance (PM) is used to ensure the reliability of the machines in the production line, increasing the effective output at minimum cost. A hybrid particle swarm optimization and estimation of distribution algorithm (PSO-EDA) is proposed to efficiently develop the optimal PM strategy. Finally, numerical experiments are performed to verify the effectiveness of the model. With the objective of maximizing the system profit, the optimization of the machines and pallets number is also explored.

Condition-Based Multi-State-System Maintenance Models for Smart Grid System with Stochastic Power Supply and Demand

This study established power-related efficiency measures from the perspective of reliability, namely, power system availability, expected power deficiency, accumulated power deficiency, instantaneous power capacity, and accumulated power capacity for a hybrid power system (HPS) in a generic smart grid. Methodologically, a power supply–demand stochastic model that simultaneously considers the inherently stochastic nature of power supply and demand was developed to quantify their interrelationship and characterize the dynamic behavior of an HPS in a continuous-time Markov chain. Preventive maintenance (PM) models were also constructed to determine the optimal PM strategy in alignment with specific scenarios that reflect the power performance requirements and resource limitations. A sensitivity analysis was conducted using the design of experiments (DOE) scheme that simulated climate change and revealed that extreme climate worsens power-related efficiency measures. This analysis provides further insight into the extent to which extreme climate conditions diminish the engineers and designers of smart grid systems’ power-related efficiency measures. The proposed approach will potentially contribute to sustainability and maintainability in the clean energy industry.

Joint optimization of imperfect condition‐based maintenance and lot sizing via an availability‐cost hybrid factor

AbstractThis article develops a joint model of condition‐based maintenance (CBM) and economic production quantity (EPQ) for a single‐unit manufacturing system. The degradation process of the system is described by a random coefficient growth model, where the mean and variance may increase with time. The condition of the system is monitored after each lot size. Three types of actions are considered, preventive maintenance (PM), preventive replacement, and corrective maintenance (CM), which are performed according to multilevel thresholds. PM is imperfect, and the system lies between two states, that is, it is as good as new or as bad as old after PM with a certain probability. Different actions lead to different calculations to determine the optimal PM strategy based on the renewal reward theory. An availability‐cost hybrid factor is proposed to balance the cost per unit time and the availability of the system. Numerical simulations are provided to illustrate the method, and then a sensitivity analysis is conducted by a real case study. A comparison with single‐level threshold strategies demonstrates the effectiveness of the proposed approach.

Improved Preventive Maintenance Scheduling for a Photovoltaic Plant under Environmental Constraints

The supply of PV power that satisfies the needs of customers is heavily dependent on the reliability of the generating plants. However, irrespective of the robustness of the design of such physical industrial assets, they tend to depreciate with usage and/or age which, in turn, increases the allowance between the design and the operational capabilities. Therefore, to ameliorate the reliability of the system, a combination of selective and preventive maintenance actions were planned by determining the best combination (optimal preventive maintenance intervals, optimal replaced components). In this work, we developed an optimal preventive maintenance strategy with minimal repair using the iterative numerical technique for a PV plant, with and without considering the influence of environmental conditions on the system. An algorithm was developed on MATLAB to determine the optimal number of preventive maintenance actions that yields the maximum availability by selecting the components to be maintained based on the reliability threshold, without considering the environmental impact on the components. The environmental elements’ criticality was introduced, and the reliability reiterated based on the new technique. Finally, by maximizing the availability of the system, an optimal preventive maintenance for a finite horizon was established.

The Reliability-Centered Maintenance (RCM) effect on plant availability and downtime loss in the process industry

The process industry needs an optimal preventive maintenance strategy because the even breakdown of one machine can cause an unexpected shutdown for the whole production process. The case study company (CSC), one of the fertilizer companies in Indonesia implements Reliability-centered Maintenance (RCM) as their preventive maintenance strategy to decrease downtime and increase the availability of the production plants. Eversince the RCM implementation started in 2007, there is no study to evaluate the RCM implementation. Relations between the two parameters (downtime loss and availability) are analyzed using the Pearson correlation test as a statistical method to evaluate the RCM implementation. The results of the analysis show that the R-value of downtime loss and availability of K-3 Ammonia and Urea plants are increased, while the R-value of K-4 Ammonia and Urea Plants are decreased. The RCM implemented in K-4 plants should be evaluated respectively, because the decreasing of the correlation means the RCM implementation on the plant still has not met its propose and there are stills hidden factors that affect the availability and downtime loss of the plant, regardless the RCM implementation.

Optimal preventive maintenance of coherent systems: A generalized Pólya process approach

We propose optimal preventive maintenance strategies for n-component coherent systems. We assume that in the early time of the system operation all failed components are repaired, such that the state of a failed component gets back to a working state, worse than that of prior to failure. To model this repair action, we utilize a counting process on the interval known as the generalized Pólya process (which subsumes the non-homogeneous Poisson process as a special case). Two generalized Pólya process-based repair strategies are proposed. The criteria to be optimized are the cost function formulated based on the repair costs of the components/system, and the system availability, to obtain the optimal time of preventive maintenance of the system. To illustrate the theoretical results, two coherent systems are studied for which the optimal preventive maintenance times are explored under different conditions.

Availability Analysis and Preventive Maintenance Planning for Systems with General Time Distributions

Steady-state availability is one of the most important performance measures for repairable systems. To improve the steady-state availability of such systems, preventive maintenance (PM) models have been extensively studied. However, these models assume that the distributions of the system lifetime and maintenance duration are exponential. In practice, the probabilistic characteristics of different systems and maintenance actions are so broad making the exponential distribution an inappropriate model. This paper seeks to determine the optimal PM strategy that maximizes the steady-state availability of a system involving general probability distributions. Specifically, PM is scheduled periodically, and a certain number of imperfect maintenance (IM) actions are carried out before each replacement. We develop state-transition equations involving general probability distributions using a supplementary variable method. The stationary distribution is calculated by solving the system of linear equations, through which the steady-state availability of the system is obtained. We prove the existence of the optimal combination of the number of IM actions before each replacement and the scheduled PM interval. Numerical examples are presented to illustrate the effectiveness of our proposed method in handling such practical maintenance problems.

Analysis of a two-dimensional stair-case warranty policy with preventive maintenance

Abstract We develop a mathematical model to study optimal preventive maintenance (PM) strategy under a two-dimensional stair-case warranty policy considering both age and usage of a product. During the warranty term, sellers implement preventive maintenance within the stair-case region of the warranty policy and upon failure a product is repaired minimally and immediately. Our objective is to find the optimal PM strategy that minimizes the seller’s cost of warranty while jointly considering the age and usage intervals of the PM policy and the level of PM executed. We also discuss how our results compare to those in a two-dimensional warranty policy with a rectangular region, and we find that the stair-case policy is preferable for sellers. An algorithm is provided to find the optimal solution and a numerical example is presented to illustrate how to find an optimal strategy with our proposed method. We show numerically that the expected total warranty cost is convex both in the age and the usage of the product under certain conditions.

Maintenance on leasing sales strategies for manufacturing/remanufacturing system with increasing failure rate and carbon emission

Several literature works have treated the quality question of the new and remanufactured products and its production cost and if the all returned-used products are remanufacturable. In this context, this study treated the case of returned-used products in the lease contract with/without maintenance monitoring option and its influence on the production and maintenance strategies for a manufacturing/remanufacturing system. A new integrated maintenance to production strategy studies the influence of the new and returned-used products according to its quality on the production cost and the degradation level of the manufacturing and remanufacturing units. Firstly, the objective of this study is to determine the economical production plan of manufacturing and remanufacturing units to satisfy the random demands under a given service level and during a finite horizon. Secondly, by considering the influence of the degradation on the failure and emission rates, we determine the optimal preventive maintenance strategy for each production unit, which minimise the total cost of production, maintenance and carbon emission. Numerical results are provided to show the efficiency of the proposed strategies by studying the impact of different parameters of the proposed model.

An optimal preventive maintenance strategy for the hydraulic system of platform firefighting vehicle based on the improved NSGA-II algorithm

Based on the reliability analysis, this work presents a model of the preventive maintenance for the hydraulic system of platform firefighting vehicle, considering the working age regression factor and the equivalent service life. In this model, both the equipment availability and average maintenance cost are treated as the objective functions and constrained by the equipment reliability as well as the total working time. The non-dominated sorting genetic algorithm II (NSGA-II) algorithm is adopted to solve the previous optimization problem, wherein the constrained inequality functions in the stages of initialization, mutation, and crossover are introduced to assess the solution to meet the constraints or not, through the improvements in three aspects, namely, the improvement of the algorithm’s initialization to ensure the initial variables meet the equality constraint, the utilization of the mean division of the difference values to adjust the variables after the selection, and crossover and mutation of the gene. Numerical analysis is carried out to verify the feasibility of the improved algorithm, wherefrom the Pareto-optimal solutions for the preventive maintenance of the platform firefighting vehicle are obtained to provide the optimum strategy for the service engineers with different weighted factors.

An optimal maintenance strategy for multi-state systems based on a system linear integral equation and dynamic programming

An optimal preventive maintenance strategy for multi-state systems based on an integral equation and dynamic programming is described herein. Unlike traditional preventive maintenance strategies, this maintenance strategy is formulated using an integral equation, which can capture the system dynamics and avoid the curse of dimensionality arising from complex semi-Markov processes. The linear integral equation of the system is constructed based on the system kernel. A numerical technique is applied to solve this integral equation and obtain all of the mean elapsed times from each reliable state to each unreliable state. An analytical approach to the optimal preventive maintenance strategy is proposed that maximizes the expected operational time of the system subject to the total maintenance budget based on dynamic programming in which both backward and forward search techniques are used to search for the local optimal solution. Finally, numerical examples concerning two different scales of systems are presented to demonstrate the performance of the strategy in terms of accuracy and efficiency. Moreover a sensitivity analysis is provided to evaluate the robustness of the proposed strategy.

Optimal preventive maintenance strategy for leased equipment under successive usage-based contracts

In the context of equipment leasing, maintenance service is usually bundled with the leased equipment and offered by the lessor as an integrated package under a lease contract. The lessor is then responsible to prescribe an effective maintenance policy to keep the equipment operational in an economical way. This paper investigates upgrade and preventive maintenance (PM) strategies for industrial equipment during successive usage-based lease contracts with consideration of a warranty period, from the lessor's perspective. The accelerated failure time model and age reduction model are adopted to capture the effect of usage rate and imperfect PM/upgrade on the equipment reliability, respectively. More importantly, since equipment usage rates may vary across different lease contracts, this study develops an age correspondence framework to characterise usage rate shifts between successive lease periods. The optimal upgrade degree and the optimal number and level of PM actions are progressively updated for each upcoming lease period to minimise the total expected lease servicing cost, by considering the usage rate and maintenance implementation history. Numerical studies show that under given cost structures, periodical PM activities within each lease period tends to outperform the pre-leasing upgrade actions, though both of them can reduce the lease servicing cost.

Optimization of periodic preventive maintenance policy following the expiration of two-dimensional warranty

This paper considers an optimal periodic preventive maintenance policy after the expiration of two-dimensional warranty. During the two-dimensional warranty period, both renewal warranty and nonrenewal warranty are considered and a repair time threshold is pre-specified so that the failed system is either minimally repaired or is replaced depending on whether the length of repair time exceeds the repair time threshold or not. After the warranty expires, the system undergoes the preventive maintenance periodically a fixed number of times by the user to prolong the life of the system and then the system is replaced preventively by a new one. In this study, we develop an optimal post-warranty periodic preventive maintenance strategy by minimizing the expected cost rate incurred during the life cycle of the system. From the user's perspective, the system is maintained free of charge or with prorated charge on the failed system during the warranty period. Once the warranty expires, the maintenance cost of the system is entirely charged to the user. Subject to such a cost structure, we derive the formula to evaluate the expected cost rate, which is used as an objective function for the optimality. The main goal of this paper is to determine an optimal preventive maintenance cycle after the warranty expires and thus to propose an optimal post-warranty strategy for the user. The effect of several parameters on the optimal strategy is also investigated numerically in this study. For the purpose of illustration of our proposed model, we present and discuss some numerical examples.

Periodical preventive maintenance contract for leased equipment with random failure penalties

Abstract Production decisions for leased equipment often depend on many market factors. In this study, we take the penalty of changing market environment into account for the expected total cost model of preventive maintenance (PM) to obtain an optimization PM strategy. The lessor in the proposed model will incur a penalty for overdue minimal repair time. The penalty is considered as a function of expected revenue during the period of minimal repair, and the Black-Scholes equation is used to model the penalty function for establishing the expected total cost model. An optimal PM strategy is obtained to minimize the expected total cost for lessor through an analytical optimal procedure. Numerical examples for Weibull lifetime equipment are used to illustrate the applications of the proposed method under different scenarios.

Optimal hybrid imperfect preventive maintenance policy for leased equipment

This paper presents a mathematical model for a sequential hybrid imperfect preventive maintenance (PM) policy for leased equipment over a finite lease period in a context where PM actions are imperfect and minimal repairs are performed following failures. Maintenance is entrusted to the lessor. The latter incurs a penalty if the number of failures exceeds a specified threshold over the lease period. Imperfect PM is executed whenever the equipment reliability reaches a certain threshold. It simultaneously reduces the effective age and increases the failure rate of the equipment. The proposed model allows finding the number n of PM actions to be performed on the equipment together with the reliability threshold Rth minimizing the expected total cost over the lease period. And therefore obtain the optimal PM intervals durations Tj*(j* = 1, 2, …, n) corresponding to the optimal reliability threshold. The model considers the expected costs of PM, repairs and penalty during the lease period. A numerical example is presented to illustrate the use of the proposed model. The optimal PM strategy is computed for a leased equipment whose time to failure follows a Weibull distribution. We investigate numerically the effect of the variation of the PM action cost and the age reduction factor on the optimal policy.

Optimal preventive maintenance strategy for repairable items under two-dimensional warranty

For repairable items under the two-dimensional warranty, the manufacturer expenses warranty costs for rectifying the failures occurring over the warranty coverage. Preventive maintenance actions reduce the occurrence intensity of item failures, and hence the warranty cost resulted from corrective maintenance, but bring additional preventive maintenance cost. In this paper, we investigate a periodic and imperfect preventive maintenance strategy for an item covered by a fixed and combined base warranty and extended warranty region from the manufacturer׳s perspective. After the base warranty expires, the buyer purchases an extended warranty service contract from the same manufacturer for extra protection. Over the whole warranty coverage, the item failures are minimally repaired by the manufacturer at no cost to the buyer. The effect of preventive maintenance action is characterized by reducing the item׳s failure intensity proportionally to the maintenance degree at each preventive maintenance action. Then a mathematical model is proposed to derive the optimal preventive maintenance strategy so as to minimize the total expected warranty servicing cost to the manufacturer. A numerical example is presented to illustrate the application of the proposed model and evaluate the impact of different model parameters on the optimal solutions and the corresponding warranty servicing costs.

On new optimal preventive maintenance strategies for navigation-information systems with penalties

A classical optimal age replacement problem of a system or its part is considered and generalized to the case when the quality of the system performance is characterized by the corresponding penalty function. This setting is applied to navigation-information systems, where the penalty is defined by the accuracy of the corresponding navigation parameters. Three optimization models are considered and discussed. Some simple examples illustrating the obtained results are given.

Performance deterioration modeling and optimal preventive maintenance strategy under scheduled servicing subject to mission time

Servicing is applied periodically in practice with the aim of restoring the system state and prolonging the lifetime. It is generally seen as an imperfect maintenance action which has a chief influence on the maintenance strategy. In order to model the maintenance effect of servicing, this study analyzes the deterioration characteristics of system under scheduled servicing. And then the deterioration model is established from the failure mechanism by compound Poisson process. On the basis of the system damage value and failure mechanism, the failure rate refresh factor is proposed to describe the maintenance effect of servicing. A maintenance strategy is developed which combines the benefits of scheduled servicing and preventive maintenance. Then the optimization model is given to determine the optimal servicing period and preventive maintenance time, with an objective to minimize the system expected life-cycle cost per unit time and a constraint on system survival probability for the duration of mission time. Subject to mission time, it can control the ability of accomplishing the mission at any time so as to ensure the high dependability. An example of water pump rotor relating to scheduled servicing is introduced to illustrate the failure rate refresh factor and the proposed maintenance strategy. Compared with traditional methods, the numerical results show that the failure rate refresh factor can describe the maintenance effect of servicing more intuitively and objectively. It also demonstrates that this maintenance strategy can prolong the lifetime, reduce the total lifetime maintenance cost and guarantee the dependability of system.

О новых оптимальных стратегиях профилактического ремонта навигационно-информационных систем со штрафами

О новых оптимальных стратегиях профилактического ремонта навигационно-информационных систем со штрафами