30,165 research outputs found
A Periodicity Metric for Assessing Maintenance Strategies
Organised by: Cranfield UniversityThe maintenance policy in manufacturing systems is devised to reset the machines functionality
in an economical fashion in order to keep the products quality within acceptable levels. Therefore,
there is a need for a metric to evaluate and quantify function resetting due to the adopted
maintenance policy. A novel metric for measuring the functional periodicity has been developed
using the complexity theory. It is based on the rate and extent of function resetting. It can be used
as an important criterion for comparing the different maintenance policy alternatives. An industrial
example is used to illustrate the application of the new metric.Mori Seiki – The Machine Tool Company; BAE Systems; S4T – Support Service Solutions: Strategy and Transitio
Implementing intelligent asset management systems (IAMS) within an industry 4.0 manufacturing environment
9th IFAC Conference on Manufacturing Modelling, Management and Control, MIM 2019; Berlin; Germany; 28 August 2019 through 30 August 2019. Publicado en IFAC-PapersOnLine 52(13), p. 2488-2493This paper aims to define the different considerations and results obtained in the implementation in an Intelligent Maintenance System of a laboratory designed based on basic concepts of Industry 4.0. The Intelligent Maintenance System uses asset monitoring techniques that allow, on-line digital modelling and automatic decision making. The three fundamental premises used for the development of the management system are the structuring of information, value identification and risk management
Integrated production quality and condition-based maintenance optimisation for a stochastically deteriorating manufacturing system
This paper investigates the problem of optimally integrating production quality and condition-based maintenance in a stochastically deteriorating single- product, single-machine production system. Inspections are periodically performed on the system to assess its actual degradation status. The system is considered to be in ‘fail mode’ whenever its degradation level exceeds a predetermined threshold. The proportion of non-conforming items, those that are produced during the time interval where the degradation is beyond the specification threshold, are replaced either via overtime production or spot market purchases. To optimise preventive maintenance costs and at the same time reduce production of non-conforming items, the degradation of the system must be optimally monitored so that preventive maintenance is carried out at appropriate time intervals. In this paper, an integrated optimisation model is developed to determine the optimal inspection cycle and the degradation threshold level, beyond which preventive maintenance should be carried out, while minimising the sum of inspection and maintenance costs, in addition to the production of non-conforming items and inventory costs. An expression for the total expected cost rate over an infinite time horizon is developed and solution method for the resulting model is discussed. Numerical experiments are provided to illustrate the proposed approach
An overview on the obsolescence of physical assets for the defence facing the challenges of industry 4.0 and the new operating environments
Libro en Open AccessThis contribution is intended to observe special features presented in physical assets for
defence. Particularly, the management of defence assets has to consider not only the reliability, availability,
maintainability and other factors frequently used in asset management. On the contrary, such systems
should also take into account their adaptation to changing operating environments as well as their capability
to changes on the technological context. This study approaches to the current real situation where, due
to the diversity of conflicts in our international context, the same type of defence systems must be able
to provide services under different boundary conditions in different areas of the globe. At the same time,
new concepts from the Industry 4.0 provide quick changes that should be considered along the life cycle
of a defence asset. As a finding or consequence, these variations in operating conditions and in technology
may accelerate asset degradation by modifying its reliability, its up-to-date status and, in general terms, its
end-of-life estimation, depending of course on a diversity of factors. This accelerated deterioration of the
asset is often known as “obsolescence” and its implications are often evaluated (when possible), in terms
of costs from different natures. The originality of this contribution is the introduction of a discussion on
how a proper analysis may help to reduce errors and mistakes in the decision-making process regarding the
suitability or not of repairing, replacing, or modernizing the asset or system under study. In other words,
the obsolescence analysis, from a reliability and technological point of view, could be used to determine the
conservation or not of a specific asset fleet, in order to understand the effects of operational and technology
factors variation over the functionality and life cycle cost of physical assets for defence
Fleet Prognosis with Physics-informed Recurrent Neural Networks
Services and warranties of large fleets of engineering assets is a very
profitable business. The success of companies in that area is often related to
predictive maintenance driven by advanced analytics. Therefore, accurate
modeling, as a way to understand how the complex interactions between operating
conditions and component capability define useful life, is key for services
profitability. Unfortunately, building prognosis models for large fleets is a
daunting task as factors such as duty cycle variation, harsh environments,
inadequate maintenance, and problems with mass production can lead to large
discrepancies between designed and observed useful lives. This paper introduces
a novel physics-informed neural network approach to prognosis by extending
recurrent neural networks to cumulative damage models. We propose a new
recurrent neural network cell designed to merge physics-informed and
data-driven layers. With that, engineers and scientists have the chance to use
physics-informed layers to model parts that are well understood (e.g., fatigue
crack growth) and use data-driven layers to model parts that are poorly
characterized (e.g., internal loads). A simple numerical experiment is used to
present the main features of the proposed physics-informed recurrent neural
network for damage accumulation. The test problem consist of predicting fatigue
crack length for a synthetic fleet of airplanes subject to different mission
mixes. The model is trained using full observation inputs (far-field loads) and
very limited observation of outputs (crack length at inspection for only a
portion of the fleet). The results demonstrate that our proposed hybrid
physics-informed recurrent neural network is able to accurately model fatigue
crack growth even when the observed distribution of crack length does not match
with the (unobservable) fleet distribution.Comment: Data and codes (including our implementation for both the multi-layer
perceptron, the stress intensity and Paris law layers, the cumulative damage
cell, as well as python driver scripts) used in this manuscript are publicly
available on GitHub at https://github.com/PML-UCF/pinn. The data and code are
released under the MIT Licens
Condition-Based Production for Stochastically Deteriorating Systems: Optimal Policies and Learning
Production systems deteriorate stochastically due to usage and may eventually
break down, resulting in high maintenance costs at scheduled maintenance
moments. This deterioration behavior is affected by the system's production
rate. While producing at a higher rate generates more revenue, the system may
also deteriorate faster. Production should thus be controlled dynamically to
trade-off deterioration and revenue accumulation in between maintenance
moments. We study systems for which the relation between production and
deterioration is known and the same for each system as well as systems for
which this relation differs from system to system and needs to be learned
on-the-fly. The decision problem is to find the optimal production policy given
planned maintenance moments (operational) and the optimal interval length
between such maintenance moments (tactical). For systems with a known
production-deterioration relation, we cast the operational decision problem as
a continuous-time Markov decision process and prove that the optimal policy has
intuitive monotonic properties. We also present sufficient conditions for the
optimality of bang-bang policies and we partially characterize the structure of
the optimal interval length, thereby enabling efficient joint optimization of
the operational and tactical decision problem. For systems that exhibit
variability in their production-deterioration relations, we propose a Bayesian
procedure to learn the unknown deterioration rate under any production policy.
Our extensive numerical study indicates significant profit increases of our
approaches compared to the state-of-the-art
Healing Our Houses Will Cure Lead Poisoning Epidemic
Two main obstacles hinder efforts to end lead poisoning in Buffalo. One, lack of knowledge in at-risk populations about causes, symptoms, and prevention, which puts people at greater risk and makes enforcement of current system difficult. Two, the poor condition of our houses makes repairs unaffordable to homeowners and discourages outside investment
Optimal maintenance strategies for systems with partial repair options and without assuming bounded costs
We study a repairable system with Markovian deterioration and partial repair options, carried out at fixed times and look for optimal strategies under certain conditions. Two optimality criteria are considered: expected discounted cost and long-run average cost. Douer and Yechiali found conditions under which a policy in the class of generalized control limit policies is optimal. In this paper conditions are found under which an optimal policy is a control-limit policy. We explicitly explain how to derive this optimal policy; numerical examples are given, too
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A modular hybrid simulation framework for complex manufacturing system design
For complex manufacturing systems, the current hybrid Agent-Based Modelling and Discrete Event Simulation (ABM–DES) frameworks are limited to component and system levels of representation and present a degree of static complexity to study optimal resource planning. To address these limitations, a modular hybrid simulation framework for complex manufacturing system design is presented. A manufacturing system with highly regulated and manual handling processes, composed of multiple repeating modules, is considered. In this framework, the concept of modular hybrid ABM–DES technique is introduced to demonstrate a novel simulation method using a dynamic system of parallel multi-agent discrete events. In this context, to create a modular model, the stochastic finite dynamical system is extended to allow the description of discrete event states inside the agent for manufacturing repeating modules (meso level). Moreover, dynamic complexity regarding uncertain processing time and resources is considered. This framework guides the user step-by-step through the system design and modular hybrid model. A real case study in the cell and gene therapy industry is conducted to test the validity of the framework. The simulation results are compared against the data from the studied case; excellent agreement with 1.038% error margin is found in terms of the company performance. The optimal resource planning and the uncertainty of the processing time for manufacturing phases (exo level), in the presence of dynamic complexity is calculated
Review of Markov models for maintenance optimization in the context of offshore wind
The offshore environment poses a number of challenges to wind farm operators. Harsher climatic conditions typically result in lower reliability while challenges in accessibility make maintenance difficult. One of the ways to improve availability is to optimize the Operation and Maintenance (O&M) actions such as scheduled, corrective and proactive maintenance. Many authors have attempted to model or optimize O&M through the use of Markov models. Two examples of Markov models, Hidden Markov Models (HMMs) and Partially Observable Markov Decision Processes (POMDPs) are investigated in this paper. In general, Markov models are a powerful statistical tool, which has been successfully applied for component diagnostics, prognostics and maintenance optimization across a range of industries. This paper discusses the suitability of these models to the offshore wind industry. Existing models which have been created for the wind industry are critically reviewed and discussed. As there is little evidence of widespread application of these models, this paper aims to highlight the key factors required for successful application of Markov models to practical problems. From this, the paper identifies the necessary theoretical and practical gaps that must be resolved in order to gain broad acceptance of Markov models to support O&M decision making in the offshore wind industry
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