4,178 research outputs found
Intelligent maintenance management in a reconfigurable manufacturing environment using multi-agent systems
Thesis (M. Tech.) -- Central University of Technology, Free State, 2010Traditional corrective maintenance is both costly and ineffective. In some situations it is more cost effective to replace a device than to maintain it; however it is far more likely that the cost of the device far outweighs the cost of performing routine maintenance. These device related costs coupled with the profit loss due to reduced production levels, makes this reactive maintenance approach unacceptably inefficient in many situations. Blind predictive maintenance without considering the actual physical state of the hardware is an improvement, but is still far from ideal. Simply maintaining devices on a schedule without taking into account the operational hours and workload can be a costly mistake.
The inefficiencies associated with these approaches have contributed to the development of proactive maintenance strategies. These approaches take the device health state into account. For this reason, proactive maintenance strategies are inherently more efficient compared to the aforementioned traditional approaches. Predicting the health degradation of devices allows for easier anticipation of the required maintenance resources and costs. Maintenance can also be scheduled to accommodate production needs.
This work represents the design and simulation of an intelligent maintenance management system that incorporates device health prognosis with maintenance schedule generation. The simulation scenario provided prognostic data to be used to schedule devices for maintenance. A production rule engine was provided with a feasible starting schedule. This schedule was then improved and the process was determined by adhering to a set of criteria. Benchmarks were conducted to show the benefit of optimising the starting schedule and the results were presented as proof.
Improving on existing maintenance approaches will result in several benefits for an organisation. Eliminating the need to address unexpected failures or perform maintenance prematurely will ensure that the relevant resources are available when they are required. This will in turn reduce the expenditure related to wasted maintenance resources without compromising the health of devices or systems in the organisation
Context-Aware Composition of Agent Policies by Markov Decision Process Entity Embeddings and Agent Ensembles
Computational agents support humans in many areas of life and are therefore
found in heterogeneous contexts. This means they operate in rapidly changing
environments and can be confronted with huge state and action spaces. In order
to perform services and carry out activities in a goal-oriented manner, agents
require prior knowledge and therefore have to develop and pursue
context-dependent policies. However, prescribing policies in advance is limited
and inflexible, especially in dynamically changing environments. Moreover, the
context of an agent determines its choice of actions. Since the environments
can be stochastic and complex in terms of the number of states and feasible
actions, activities are usually modelled in a simplified way by Markov decision
processes so that, e.g., agents with reinforcement learning are able to learn
policies, that help to capture the context and act accordingly to optimally
perform activities. However, training policies for all possible contexts using
reinforcement learning is time-consuming. A requirement and challenge for
agents is to learn strategies quickly and respond immediately in cross-context
environments and applications, e.g., the Internet, service robotics,
cyber-physical systems. In this work, we propose a novel simulation-based
approach that enables a) the representation of heterogeneous contexts through
knowledge graphs and entity embeddings and b) the context-aware composition of
policies on demand by ensembles of agents running in parallel. The evaluation
we conducted with the "Virtual Home" dataset indicates that agents with a need
to switch seamlessly between different contexts, can request on-demand composed
policies that lead to the successful completion of context-appropriate
activities without having to learn these policies in lengthy training steps and
episodes, in contrast to agents that use reinforcement learning.Comment: 30 pages, 11 figures, 9 tables, 3 listings, Re-submitted to Semantic
Web Journal, Currently, under revie
Pattern Operators for Grid Environments
The definition and programming of distributed applications has become a major research
issue due to the increasing availability of (large scale) distributed platforms
and the requirements posed by the economical globalization. However, such a task
requires a huge effort due to the complexity of the distributed environments: large
amount of users may communicate and share information across different authority
domains; moreover, the “execution environment” or “computations” are dynamic
since the number of users and the computational infrastructure change in time. Grid
environments, in particular, promise to be an answer to deal with such complexity, by
providing high performance execution support to large amount of users, and resource
sharing across different organizations. Nevertheless, programming in Grid environments
is still a difficult task. There is a lack of high level programming paradigms
and support tools that may guide the application developer and allow reusability of
state-of-the-art solutions.
Specifically, the main goal of the work presented in this thesis is to contribute to
the simplification of the development cycle of applications for Grid environments by
bringing structure and flexibility to three stages of that cycle through a commonmodel.
The stages are: the design phase, the execution phase, and the reconfiguration phase.
The common model is based on the manipulation of patterns through pattern operators,
and the division of both patterns and operators into two categories, namely
structural and behavioural. Moreover, both structural and behavioural patterns are
first class entities at each of the aforesaid stages. At the design phase, patterns can
be manipulated like other first class entities such as components. This allows a more
structured way to build applications by reusing and composing state-of-the-art patterns.
At the execution phase, patterns are units of execution control: it is possible, for
example, to start or stop and to resume the execution of a pattern as a single entity. At
the reconfiguration phase, patterns can also be manipulated as single entities with the
additional advantage that it is possible to perform a structural reconfiguration while
keeping some of the behavioural constraints, and vice-versa. For example, it is possible
to replace a behavioural pattern, which was applied to some structural pattern,
with another behavioural pattern.
In this thesis, besides the proposal of the methodology for distributed application
development, as sketched above, a definition of a relevant set of pattern operators
was made. The methodology and the expressivity of the pattern operators were assessed
through the development of several representative distributed applications. To
support this validation, a prototype was designed and implemented, encompassing
some relevant patterns and a significant part of the patterns operators defined. This
prototype was based in the Triana environment; Triana supports the development and
deployment of distributed applications in the Grid through a dataflow-based programming
model. Additionally, this thesis also presents the analysis of a mapping of some
operators for execution control onto the Distributed Resource Management Application
API (DRMAA).
This assessment confirmed the suitability of the proposed model, as well as the
generality and flexibility of the defined pattern operatorsDepartamento de Informática and Faculdade de Ciências e Tecnologia of the Universidade
Nova de Lisboa;
Centro de Informática e Tecnologias da Informação of the FCT/UNL;
Reitoria da Universidade Nova de Lisboa;
Distributed Collaborative Computing Group, Cardiff University, United Kingdom;
Fundação para a Ciência e Tecnologia;
Instituto de Cooperação Científica e Tecnológica Internacional;
French Embassy in Portugal;
European Union Commission through the Agentcities.NET and Coordina projects;
and the European Science Foundation, EURESCO
Pattern operators for grid
The definition and programming of distributed applications has become a major research
issue due to the increasing availability of (large scale) distributed platforms
and the requirements posed by the economical globalization. However, such a task
requires a huge effort due to the complexity of the distributed environments: large
amount of users may communicate and share information across different authority
domains; moreover, the “execution environment” or “computations” are dynamic
since the number of users and the computational infrastructure change in time. Grid
environments, in particular, promise to be an answer to deal with such complexity, by
providing high performance execution support to large amount of users, and resource
sharing across different organizations. Nevertheless, programming in Grid environments
is still a difficult task. There is a lack of high level programming paradigms
and support tools that may guide the application developer and allow reusability of
state-of-the-art solutions.
Specifically, the main goal of the work presented in this thesis is to contribute to
the simplification of the development cycle of applications for Grid environments by
bringing structure and flexibility to three stages of that cycle through a commonmodel.
The stages are: the design phase, the execution phase, and the reconfiguration phase.
The common model is based on the manipulation of patterns through pattern operators,
and the division of both patterns and operators into two categories, namely
structural and behavioural. Moreover, both structural and behavioural patterns are
first class entities at each of the aforesaid stages. At the design phase, patterns can
be manipulated like other first class entities such as components. This allows a more
structured way to build applications by reusing and composing state-of-the-art patterns.
At the execution phase, patterns are units of execution control: it is possible, for
example, to start or stop and to resume the execution of a pattern as a single entity. At
the reconfiguration phase, patterns can also be manipulated as single entities with the
additional advantage that it is possible to perform a structural reconfiguration while
keeping some of the behavioural constraints, and vice-versa. For example, it is possible
to replace a behavioural pattern, which was applied to some structural pattern,
with another behavioural pattern.
In this thesis, besides the proposal of the methodology for distributed application
development, as sketched above, a definition of a relevant set of pattern operators
was made. The methodology and the expressivity of the pattern operators were assessed
through the development of several representative distributed applications. To
support this validation, a prototype was designed and implemented, encompassing
some relevant patterns and a significant part of the patterns operators defined. This
prototype was based in the Triana environment; Triana supports the development and
deployment of distributed applications in the Grid through a dataflow-based programming
model. Additionally, this thesis also presents the analysis of a mapping of some
operators for execution control onto the Distributed Resource Management Application
API (DRMAA).
This assessment confirmed the suitability of the proposed model, as well as the
generality and flexibility of the defined pattern operatorsDepartamento de Informática and Faculdade de Ciências e Tecnologia of the Universidade
Nova de Lisboa;
Centro de Informática e Tecnologias da Informação of the FCT/UNL;
Reitoria da Universidade Nova de Lisboa;
Distributed Collaborative Computing Group, Cardiff University, United Kingdom;
Fundação para a Ciência e Tecnologia;
Instituto de Cooperação Científica e Tecnológica Internacional;
French Embassy in Portugal;
European Union Commission through the Agentcities.NET and Coordina projects;
and the European Science Foundation, EURESCO
Multi-Agent Systems
A multi-agent system (MAS) is a system composed of multiple interacting intelligent agents. Multi-agent systems can be used to solve problems which are difficult or impossible for an individual agent or monolithic system to solve. Agent systems are open and extensible systems that allow for the deployment of autonomous and proactive software components. Multi-agent systems have been brought up and used in several application domains
Hybrid modelling methodology for system design
In the face of rapid development in information technology coupled with a growing
dynamism in global markets, manufacturing systems have to be re-constructed for
short term or long term goal. Such innovations promise to lead to a new competitive
stage, which typically involve design of function, information and behaviour of
systems. In order to design the system, simulation has often been chosen. However,
simulation has proved limited and fails to aid design of such a complex systems
because of consuming much computing time and cost, especially when modelling
larger systems. Thus, there is a need to seek a new approach, in a way that results in
simulating such a large manufacturing system with less demand on computing time and
cost.
This study researches into a hybrid modelling approach to minimise these limitations. It
includes proposing a hybrid modelling methodology and developing a hybrid modelling
tool. The methodology integrates simulation and metamodelling techniques. The
metamodel employed in the study possesses, not only characteristics of conventional
metamodels in terms of representing relationships in quantity, but also in time lapse.
This is the originality of the study and the significant distinction between this research
and application of metamodelling in conventional ways. The hybrid modelling tool is
developed to support and demonstrate the identified hybrid methodology. LISP has
been used as the software language for the hybrid modelling tool. The result of this
work concludes that the hybrid modelling approach is capable of simulating a complex
manufacturing system with less demands on the computer.
The work reported in this thesis has been carried out in conjunction with the EPSRC
research project, Hierarchical Manufacturing System Modelling (HMSM)
(GR/F96549), to produce an Integrated Design and Modelling Methodology (IDEM).
The project was initially a collaborative research program including Loughborough
University of Technology (LUT), Morris Crane Ltd., of Loughborough and GEC
Large Machine, of Rugby. The experience of these collaborators has proved most
valuable in supporting the research, and have provided a cross section of views and
comments. The research reported in this thesis is set in the context of the HMSM
Research group at Loughborough
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