A Model for Periodic Preventive Maintenance Policy for a Series Parallel System

An exact algorithm for preventive maintenance planning of series-parallel systems

Reliability is a meaningful parameter in assessing the performance of systems such as chemical processing facilities, power plant, aircrafts, ships, etc. In the literature, reliability optimization is widely considered during the system design phase and it is carried out by an opportune selection of both system components and redundancy. On the other hand, the problem of maintaining a required level of reliability by an opportune maintenance policy has been poorly examined. The paper tackles this problem for a system whose major components can be maintained only during a planned system downtime. An exact algorithm is proposed in order to single out the set of components that must be maintai…

A new innovative cooling law for simulated annealing algorithms

The present paper proposes an original and innovative cooling law in the field of Simulated Annealing (SA) algorithms. Particularly, such a law is based on the evolution of different initial seeds on which the algorithm works in parallel. The efficiency control of the new proposal, executed on problems of different kind, shows that the convergence quickness by using such a new cooling law is considerably greater than that obtained by traditional laws. Furthermore, it is shown that the effectiveness of the SA algorithm arising from the proposed cooling law is independent of the problem type. This last feature reduces the number of parameters to be initially fixed, so simplifying the prelimin…

Optimal Selection of Maintenance Actions on a Multi-Component System

The research aims to single out the maintenance actions to perform on a series arranged components system each one constituted by elements in parallel and maintained only during some planned stops. The considered system has to periodically carry out missions during which the system failure is a critical event for their own success. That being so, the faced problem is here to assure the maximum reliability level up to the next planned stop. For this reason an exact algorithm is proposed in order to individuate the set of components on which performing maintenance actions and for each of them determining the number of elements that must be maintained so as the maximum reliability level is ach…

Optimal Maintenance For a System with Required Reliability

The effectiveness of a maintenance policy for a production system is generally measured by its availability. Nevertheless, for some production systems, the failure is a dangerous event for people or in any case too much expensive; therefore the failure probability must be maintained less than an accepted low value by a proper preventive maintenance policy. The system considered hereafter is schematized by a series of components some of them constituted by parallel-series sub-systems. The problem is to individuate the set of elements on which to operate the maintenance actions, providing the system functioning with the required reliability until the next planned maintenance instant by the mi…

A cost model for the selection of a maintenance activity in a series system

A simulated annealing-based approach for the joint optimization of production/inventory and preventive maintenance policies

Even if more reliable than the past, the performance of modern manufacturing systems is still affected by machine’s deteriorations and breakdowns. As a consequence, adequate maintenance programs must be implemented to adequately satisfy demands during manufacturing stops due to unexpected failures or preventive maintenance (PM) actions. Despite production and maintenance are closely related issues, their joint optimization has become an important research topic just during the last decade. Therefore, the present paper proposes a model for the combined optimization of production/inventory control and PM policies with the aim of minimizing the total expected cost per unit time. The model is f…

Integrated Approach to Part Scheduling and Inspection Policies for a Job Shop Manufacturing System

The quality of a product greatly depends on the quality of its components. This requires that manufacturing specifications have to be met in the manufacturing environment and as a consequence inspection stations are present in many manufacturing systems and inspection policies must be adopted. One problem, which has been widely investigated, concerns the detection of the inspection points in the hypothesis that the action to be taken is known when a defective part is detected. If different jobs are to be produced, then operation scheduling becomes yet another complex problem needing to be solved. And while the problem of scheduling has received a great amount of attention from researchers, …

An Effective Double Sampling Scheme for thecControl Chart

In the present paper is developed a statistical process control inspection procedure based on a new simple-to-implement and effective double sampling scheme for the c control chart, aimed at the minimization of the number of inspected observation units and warranting fixed levels for the type I and II error risks. In particular, the formulations of the false alarm risk α, the power P of the chart, and the expected number of inspected observation units for the developed inspection procedure are given, whereas a macro of Microsoft Excel is adopted to solve the tackled problem. In order to illustrate the application of the developed approach and to investigate on the influence of several opera…

An Effective Double Sampling Scheme for the c Control Chart

In the present paper is developed a statistical process control inspection procedure based on a new simple-to-implement and effective double sampling scheme for the c control chart, aimed at the minimization of the number of inspected observation units and warranting fixed levels for the type I and II error risks. In particular, the formulations of the false alarm risk α, the power P of the chart, and the expected number of inspected observation units for the developed inspection procedure are given, whereas a macro of Microsoft Excel is adopted to solve the tackled problem. In order to illustrate the application of the developed approach and to investigate on the influence of several opera…

MInimizing earliness and tardiness costs by ant system approach

The performance of production systems, which are more and more client oriented, strongly depends on the punctuality in the delivery of orders. However, management policies of manufacturing systems have a tendency of reducing batch dimensions which, sometimes, is reduced to a single job. The reason for this tendency is to reduce quantities of stock and to satisfy the customer’s requirements. It is the Just-in-Time approach, in which the production of a job is scheduled after the acquisition of an order, on the basis of the due date and the actual production capacity of the system. In the present paper, a manufacturing system characterized by a bottleneck station is considered. A set of jobs …

Robust Maintenance Scheduling for Reliability Maximization

The present paper aims to single out the maintenance actions to perform on a system constrained to be maintained only during some planned stops. Since system failure implies costs and risks for people and/or the environment, then it is necessary to minimize the probability of its occurrence. Thus, maintenance actions need to maximize the system reliability up to the next planned stop, in respect to some constraint. The originality of the problem discussed in the present paper lies in considering reliability values affected with uncertainty within a range of vagueness. Consequently, a further problem is added to the constrained reliability maximization, that is the search for a robust soluti…

Optimum scheduling of dual gripper robots

A multi-objective fleet routing optimization for passenger shipping among islands

In the last few years the statistical analysis on maritime freight and passenger transport highlights a positive trend of demand and for the next future, given the stressing congestion characterizing the road transport, a further increase both on the deep-sea-shipping and the short-sea-shipping is predicted. Given that, the navigation companies are called to improve their own services to assure a high quality and efficient customers transport, deriving at the same time their own benefits by minimizing the operating costs. Hence, an efficient and careful routes planning activity plays a meaningful role on navigation company productivity and income. Furthermore, the fleet deployment also cons…

Minimizing the cycle time in serial manufacturing systems with multiple dual-gripper robots

Robots are being used more and more extensively as material-handling systems for automated manufacturing systems. This is especially true for dual-gripper robots whose in-process buffer (the robot's second gripper) constitutes a further element of flexibility. When the number of stations to be served is high and the set of activities the robot must execute is great, the system throughput may depend on robot capability rather than on process times. In such conditions, the use of several robots leads to an increase in system productivity. Obviously, the design and the management of such a handling system becomes more complex: the minimum number of robots required, the work stations to be serv…

Selection of Series System Components to Maximize Reliability

The paper tackles the problem of maximizing the reliability of a series system by an opportune choice of components. Each type of component must be selected among the available alternatives for that component whereas a fixed amount of budget can not be overcome. The problem can be formulated by a binary non linear programming model and it is equivalent to a knapsack problem with multiple-choice constraints, well known to be NP-hard. An exact algorithm is proposed for solving large dimension problems to the optimum in a short time. The algorithm efficiency is finally compared with the recent heuristics proposed in literature to approach the same problem.

Handling epistemic uncertainty in the Fault Tree Analysis using interval valued expert information

Risk Analysis ( RA) is a meaningful process in every industrial context, particularly referring to major hazard plants. In such sites, input reliability data are generally poor so leading to a partial or incomplete knowledge of the failure process. As a consequence, RA is always affected by the so called epistemic uncertainty which presence makes inappropriate the classical probabilistic approach. Therefore, the present work deals with such a kind of uncertainty in the Fault Tree Analysis (FTA) and proposes a new aggregation rule to combine the interval-valued information supplied by a team of experts about each Basic Event ( BE). The aggregation leads to an interval which bounds are modell…

Handling the epistemic uncertainty in the selective maintenance problem

Abstract Nowadays, both continuous and discontinuous operating systems require higher and higher reliability levels in order to avoid the occurrence of dangerous or even disastrous consequences. Accordingly, the definition of appropriate maintenance policies and the identification of components to be maintained during the planned system’s downtimes are fundamental to ensure the reliability maximization. Therefore, the present paper proposes a mathematical programming formulation of the selective maintenance problem with the aim to maximize the system’s reliability under an uncertain environment. Specifically, the aleatory model related to the components’ failure process is well known, where…

Determination of Pareto frontier in multi-objective maintenance optimization

Abstract The objective of a maintenance policy generally is the global maintenance cost minimization that involves not only the direct costs for both the maintenance actions and the spare parts, but also those ones due to the system stop for preventive maintenance and the downtime for failure. For some operating systems, the failure event can be dangerous so that they are asked to operate assuring a very high reliability level between two consecutive fixed stops. The present paper attempts to individuate the set of elements on which performing maintenance actions so that the system can assure the required reliability level until the next fixed stop for maintenance, minimizing both the globa…