=Paper= {{Paper |id=Vol-2404/paper05 |storemode=property |title=Intelligent Agents Supporting Digital Factories |pdfUrl=https://ceur-ws.org/Vol-2404/paper05.pdf |volume=Vol-2404 |authors=Nicola Bicocchi,Giacomo Cabri,Letizia Leonardi,Giulio Salierno |dblpUrl=https://dblp.org/rec/conf/woa/BicocchiCLS19 }} ==Intelligent Agents Supporting Digital Factories== https://ceur-ws.org/Vol-2404/paper05.pdf
                                          Workshop "From Objects to Agents" (WOA 2019)


       Intelligent Agents Supporting Digital Factories
                           Nicola Bicocchi∗ , Giacomo Cabri∗ , Letizia Leonardi∗ , Giulio Salierno∗
                                              ∗ Università di Modena e Reggio Emilia, Italy,

                            {nicola.bicocchi, giacomo.cabri, letizia.leonardi, giulio.salierno}@unimore.it


   Abstract—Intelligent agents represent a widely exploited                     digital factories as a key paradigm embracing multiple aspects
paradigm of the Distributed Artificial Intelligence (DAI). They                 related to the digitialization of factories.
have been applied in many fields, and recently they have appeared                  The rest of this paper is organized as follows. Section II
also in the digital factory field. Digital factories are abstractions of
real factories, which enable high-level management of factories’                presents the existing approaches that exploit intelligent agents
processes, along with their automatization. So, the real factories              in digital factories, starting from some existing surveys re-
can dynamically adapt their processes to unexpected situations.                 lated to those topics (Section II-A). Section III discusses the
   In this paper, we survey different works at the state of the                 presented approaches and reports the advantages and limita-
art that show how intelligent agents can support digital factories,             tions of adopting agent-based technologies in digital factories.
along with the limitations of their application. A discussion about
the advantages of intelligent agents and the open issues completes
                                                                                Finally, Section IV concludes the paper and sketches future
the paper.                                                                      directions.
   Index Terms—Intelligent Agents, Digital Factory, Industrial
IoT.
                                                                                    II. I NTELLIGENT AGENTS FOR D IGITAL FACTORIES
                                                                                   This section is devoted to present the work related to
                        I. I NTRODUCTION                                        intelligent agents applied to the field of in digital factories.
                                                                                Some surveys already exist and we summarize them for
   Digital factories [1] represent a key enabling paradigm                      completeness’s sake (Subsection II-A). Then, we present the
for the next generation of smart manufacturing. Digital tech-                   existing approaches, divided into three subsections:
nologies promote the integration of traditional product design                     • Agent-based decentralized management
processes, manufacturing processes, and general collaborative                      • Agent-based data management
business processes in order to bridge the gap between design                       • Agent-based architectures
and manufacturing processes of a traditional factory [2]. To                    Of course, not all reported works fit perfectly in a category,
this end, the digital factory covers the entire product lifecycle               but we think that this can be useful to have an idea about the
ranging from the product design stage down to product plan-                     topics addressed by the existing works.
ning and realization. The new wave of technologies that could
lead to the fourth industrial revolution, the so-called Industry                A. Surveys in the Literature
4.0, is further multiplying the opportunities to get access to                     In the literature we can find some surveys of the researches
global supply and sale markets.                                                 related to the application of the AI technologies to the
   Intelligent agents [3] are decentralized software components                 manufacturing field. we think that they can be useful to
that exhibit some main features, such as autonomy, reactiv-                     readers interested in the topic; nevertheless, the rest of the
ity, proactivity and sociality, which can be enhanced with                      paper will focus on intelligent agents (which can be conceived
other ones such as mobility and learning ability; all these                     as a specific AI technology) and digital factories (which can
features lead them to be “intelligent” in a Distributed Artificial              be seen as an implementation of intelligent manufacturing).
Intelligence (DAI) fashion [4]. Thanks to these features, a
proper implementation adds flexibility to software systems and                    [7] presents a survey focusing on Multi-Agent Systems
applications thus leveraging the development of autonomous                      (MASs). As application field, it is limited to the manufacturing
systems [5], [6].                                                               production, while our survey concern digital factories in
   In this paper, we propose a survey of agent-based ap-                        general, which involve also other manufacturign aspects.
proaches in the digital factory field. Thanks to the previously                 The paper proposes a classification of the MAS into
mentioned features, intelligent agents have been considered in                  two main categories: centralized multi-agent coordination
the development of digital abstractions aiming at providing a                   and decentralized multi-agent coordination. The former
means to manage real factories and all the required interactions                exploits a coordinator agent that manages all other agents
in a flexible way.                                                              and comprises a facilitator agent, which coordinate the
   Some surveys have already been proposed [7], [8], [9] in the                 communication between agents, and a mediator agent,
field; we report about their results, but we point out that our                 which takes decisions on low-level aspects. In the latter
work is more specific on the one hand, because we focus on the                  category, agents have a high degree of autonomy, and thus
agent methodologies for the realization of digital factory tasks,               the control is spread over all agents. The paper highlights the
and more general on the other hand, because we consider                         advantages of exploiting agents in manufacturing systems,




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mainly in terms of coordination of manufacturing components.              them to sequence their plans of operation and to adjust the
                                                                          timing of those manufacturing operations cooperatively. A
   [8] presents a survey of technologies for Industry 4.0                 frequent issue in manufacturing contexts consists, in fact, of
classifying previous works into five categories:                          jobs with rigid plans. Established approaches usually perform
   • Concept and perspectives of Industry 4.0                             conflict resolution in a way that forces involved agents to wait
   • CPS-based Industry 4.0                                               until they are allowed to sequence and time the next operation.
   • Interoperability of Industry 4.0                                        The assumption behind those approaches is removed in [11],
   • Key technologies of Industry 4.0                                     thus allowing operations to be scheduled in parallel. More
   • Applications of Industry 4.0                                         specifically, the authors discuss an innovative mechanism
   The intelligent agents represent a future direction of                 enabling the emergence of manufacturer operation schedules
Cyber-Physical Systems (CPS) and also as a key technology                 from a generic collection of decentralized algorithms. This
at the base of several aspects such as products, orders,                  mechanism allows agents to independently sequence their
machine processes, controls; in addition, agents can provide              operations with regard to their constraints while enabling
interoperability among the participants in the manufacturing              cooperation.
product chain.                                                               As case studies for assessing the proposal, the MT6, MT10,
                                                                          and LA19 job scheduling problems were used. Furthermore,
    [9] discusses the use of agent-based methodologies in                 an industrial use case was detailed to provide context to
projects in the field of Cyber-Physical Production Systems                the manufacturing environment under investigation. It has
(CPPS), which can be considered part of digital factories. Two            been shown that agents could generate plans of operations
aspects are identified in order to classify the existing projects.        by executing in parallel thus reducing the computation and
The former is the CPPS type, which can be one or more of                  communications efforts 10X and 5X respectively. It has also
the following:                                                            been found that the proposed family of algorithms are capable
                                                                          of addressing disturbances such as delays and last rush jobs.
   • Demonstrators
                                                                             2) Decentralized and on-the-fly agent-based service re-
   • Smart manufacturing approaches
                                                                          configuration in manufacturing systems: The work reported
   • Electric Grid applications
                                                                          in [12] deals with the problem of service manufacturing recon-
   • Architectures
                                                                          figuration in industrial manufacturing systems. In this work,
The latter aspect considered is the ISA 95 levels [10], which             the authors examined the service reconfiguration problem in
can be:                                                                   a real-time constrained environment. In particular, concerning
   • Device Level (L1)                                                    the physical equipment of the factory which reconfiguration
   • Supervisory Control And Data Acquisition or SCADA                    is only possible when it satisfy timing requirements. To this
     Level (L2)                                                           end, the author proposes a system for identifying dynamic
   • Manufacturing Operations Management or MOM Level                     reconfiguration opportunities as well as the selection of the
     (L3)                                                                 best reconfiguration strategies to optimize productivity. The
   • Enterprise or ERP Level (L4)                                         proposed MAS consist of three-type of agents: Resource Agent
In addition, the authors define requirements for agent-based              (RA) which encapsulate the physical operation of a machine
methodologies in order to be suitable for the development of              as a service. Product Agent (PA) represents a service consumer
CPPS, as follows:                                                         and fulfill the production demand by creating new products.
   • Minimal conditions                                                   PA and RA have different services reconfiguration needs.
   • Intelligent characteristics attributes                               RA covers the changes of structure of a composed service
   • Formalized modeling terms                                            while PA focuses on changing the services catalog as well
   • Systems and human integration needs                                  as modification of their behavior. The MAS is enriched with
Starting from the above aspects, the authors classify the                 early detection of reconfiguration opportunities. To this end,
existing agent-based methodologies concluding that they have              the detection of a reconfiguring phase is performed through
several attributes to meet the CPPS requirements, but some                continuously collecting data and analyzing them to trigger
specific requirements still need attention from the developers;           a reconfiguration opportunity (i.e., changing in a service,
in particular, they mention vertical integration, human inte-             degradation of service performances, trend or pattern in a
gration, proactivity and abstraction. The lack of proactivity             service performance). When an event is triggered, a set com-
and abstraction is surprising, because they are two of the                prising possible service reconfiguration strategies is computed
main features of agents [3]. The other two features are instead           by each agent. To reduce the space of strategies generated
expected and are worth being subject of future researches.                by a single agent, a matching mechanism is proposed to
                                                                          analyze the performance of a strategy in a given context.
B. Agent-based Decentralized Management                                   The feasibility of a reconfiguration strategy is evaluated us-
  1) Knowledge and agent-based system for decentralized                   ing the JENA framework which exploits semantic reasoning
scheduling in manufacturing: In [11], authors propose an                  about the logic of a solution to assess its applicability. In
innovative group of algorithms for agent systems allowing                 the end, an optimal reconfiguration strategy is selected by




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ranking feasible solutions using a multi-criteria function which        entities. The negotiation takes place between an agent, elected
quantifies the benefit of adopting a strategy on the other.             as a manager, and the other agents (named contractors). The
For a collaborative environment comprised of multi-agents,              agent manager is capable of initiating new rounds and taking
an interaction protocol is proposed to ensure that a selected           decisions based on the received messages sent by the agent
strategy is optimal for the whole system. The proposed service          contractors.
reconfiguration approach is evaluated on a real-case scenario              A typical negotiation involves the following steps: 1) A
of a manufacturing system comprised of five workstations                manager initiates a new task. 2) Each contractor either send a
connected by a conveyor system. The results reported by the             bid message to take part in a new round or a busy message.
authors demonstrate the benefit of a service reconfiguration            Depending on received messages, the manager ranks bidders
mechanism with an increasing of the productivity. Moreover,             according to a predefined set of layered rules. As an example,
the proposed interaction protocol shows the advantage of                the task of finding a conveying path requires to determine the
distributing the service reconfiguration problem as the number          next available hop of the route. In this scenario, the agent
of generated candidate strategies increase.                             manager will select the highest-ranked bidder as the winner
   3) Potential of a Multi-Agent System Approach for Produc-            of the negotiation, and it becomes the next hop of the path.
tion Control in Smart Factories: The paper [13] presents a              Conditions of deadlock between multi-function and multi-
multi-agent framework for control, planning and scheduling              occurrence agents are further examined, and a solution based
production autonomously and adaptively. The model is built              on congestion control is presented. In contrast to other strate-
from real data of a production line of an automotive and then it        gies (i.e., functional redundancy and replication of agents)
is simulated to evaluate the performance. Six types of agents           which cannot guarantee deadlock prevention, the proposed
are defined to control the production, and in particular, the           mechanism effectively prevent deadlock even if less efficient
supervisor agent communicates real-time information about               compared to the other approaches.
the status of the product agents and machine agents. Based                 2) Data-driven decision making for supply chain networks
on the received messages, the coordinator agent selects the             with agent-based computational experiment: One of the key
machine that will perform the next job adopting a two-step              issues in supply chain networks is decision making for solv-
decision rule. The decision rule takes into consideration the           ing operational problems. Authors of [15] recognizing the
type of the task as well as the availability of a machine to            importance of business analytics based on multi-dimensional
carry out the job. MAS performances are evaluated on four               data and decision support systems, propose a data-driven
scenarios in which the model is compared with the traditional           methodology for decision support in supply chain networks.
scheduler. An enhancement common to all the experiments is              A four-dimensional-flow model is proposed to satisfy data
represented by the flexibility introduced by the MAS.                   requirements of decision-making. In this work, agents are
   Thanks to the capability of assigning a priority value to the        employed in a computational experiment to generates a com-
production of a batch and the ability to enqueue products for           prehensive operational dataset of a supply chain thus verify the
delayed manufacturing, the production becomes more flexible             solution produced in the decision making. In particular, a data-
compared to the traditional scheduling system. Additional               driven decision-making framework for supply chain networks
experiments are further described in order to evaluate the              is proposed, and two solutions based on business analytics
capabilities of the MAS to react to machines failures. The              are put forward. The framework is evaluated on a real-
real-time communication between the coordinator agent and               case scenario of a five-echelon manufacturing supply chain
the supervisor agent allows the system to be aware of machine           network. In particular, results demonstrated the effectiveness
failures and react by assigning the task to the first non-faulty        of the proposed four-dimensional-flow model in representing
machine. Finally, from a performance evaluation perspective,            operations typical of supply chain networks. The agent-based
the MAS simulation help to focus not only on the scheduling             computational experiment allowed to generate a comprehen-
efficiency but in general to the overall system performances in         sive dataset but also to verify solution of decision making. The
particular cases where machines are added or removed from               data-driven methodology presented offers a valuable tool for
the shop floor.                                                         the decision-making process into the supply chain domain.
                                                                           3) Intelligent sustainable supplier selection using multi-
C. Agent-based Data Management                                          agent technology: Theory and application for Industry 4.0
   1) A self-organized multi-agent system with big database             supply chains: Ghadimi et al. [16] analyze the problem of
feedback and coordination: Authors of [14] propose a concep-            suppliers evaluation and selection for the management of sup-
tual smart factory framework based on a multi-agent system.             ply chains (Scs) within the context of Industry 4.0. Although
The manufacturing shop floor is composed of four different              the problem has been addressed before, sustainable supplier
categories of autonomous agents, which share common knowl-              selection needs are further investigated to enhance green and
edge and communicate with each other to reach a system-wide             lean Scs concepts into Industry 4.0. To this end, the authors
goal. In order to overcome limited decision capabilities of             propose a MAS for sustainable supplier selection. The process
agents caused by poor knowledge of the environment in which             of supplier evaluation conducted in their work is divided into
they act, a Contract Net Protocol mechanism is proposed to              four steps as follows: i) Identification of components and
enhance cooperation and collaboration among the distributed             products to be supplied. ii) Definition of impact factors of




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sustainability typically defined by manufacturer requirements          agents. Each and every type of agent is focused on different
and then utilized during the supplier evaluation phase. iii)           manufacturing-related functions. Agents use the most proper
Suppliers assessment is conducted via data gathered on the             methods for communicating their internal reasoning data.
basis of manufacturer requirements. iv) Suppliers evaluation is        Furthermore, a mechanism based on the cloud network has
based on a score which permits to evaluate their capabilities          been introduced for coordinating the agents. For eliminating
in terms of sustainability.                                            eventual local optima in the case of distributed scheduling,
   The evaluation process is modeled as a MAS in which                 the cloud-assisted layer collects data from the lower layer and
negotiation takes place between a buyer (manufacturer) who             defines the optimal scheduling policy through data analysis.
collaborate with multiple sellers (suppliers). The proposed            These policies are fed back to the plants for assisted scheduling
architecture of the MAS is composed of three-layer named               in form of suggestions.
as interface layer, technical layer, and data resource layer.             Experimental results have shown that this architecture can
The interface layer allows both manufacturers and suppliers to         be deployed to build smart manufacturing system with limited
update information utilized during the evaluation process. The         efforts and can improve the capabilities of adaptation and
resource layer is comprised of the data management systems             robustness of manufacturing system when dealing with multi-
which store both information provided by the manufacturers             product problems. Finally, the results showed that the dynamic
and suppliers as well as the evaluation performance score              scheduling policy proposed has clear advantages over more
of each supplier. The technical layer mediates between other           traditional and static scheduling policies. In particular, CASOA
layers to retrieve data for the evaluation process of the sup-         showed remarkable robustness and capacity of adaption to
pliers. The MAS developed by using the JADE framework                  frequent product changes and inferences to the production
consists of one container which will be ideally hosted by              process.
a manufacturing company while other containers will be                    2) An agent-based monitoring architecture for plug and
maintained by suppliers connected to the main container.               produce based manufacturing systems: The article [18] pro-
Agents of different containers interact using a FIPA proto-            poses a MAS architecture to support the monitoring of a
col to fulfill the evaluation process following a predefined           shop floor in the case of dynamic entities join or leave
schema. Authors also introduce the designed evaluation model           the system thus changing the network topology. The pro-
used by the decision-maker agent in order to periodically              posed architecture is based on three different agents. A low-
evaluate the geographically dispersed suppliers. A FIS model           level agent is responsible for abstracting a physical resource
is proposed to deal with uncertainty and lack of magnitude             (CNC, machine, robot). At a higher level, the monitoring
of sustainability information. The evaluation of the data is           agent abstracts low-level components to represent a high-
based on fuzzy set theory. To evaluate the sustainability of           level subsystem. This agent receives data from both devices
the MAS an implementation of a real-case scenario regarding            positioned on the field and lowest-layer agents. Finally, a
the medical sector is proposed. The scenario consists of one           coordinator agent is responsible for monitoring the system
manufacturer providing electronic medical devices and nine             behavior in terms of subsystems as well as single components.
suppliers producing different components. Results had shown            A knowledge base containing a set of predefined rules allows
an improvement in terms of economic sustainability increase            each agent to determine useful events to be aware of. Inter-
the performance evaluation score of suppliers. Therefore, this         layer communication is based on CNP (Contract net Protocol)
information is propagated to the right supply chain member in          and the Foundation for Intelligent Physical Agents (FIPA)
time. In conclusion, the developed MAS promote to enhance              request protocol. The CNP protocol is used to perform task
sustainability among supply chain networks in the context of           negotiation, while the FIPA protocol is adopted to establish
industry 4.0 by enabling interconnection among Scs, Real-time          point-to-point communication between agents. This archi-
information, decentralization, and reduced human interaction.          tecture presents a benefit in terms of enhanced monitoring
                                                                       performances thanks to a decentralized analysis of the raw
D. Agent-based Architectures                                           data. External components such as remote servers are involved
   1) CASOA: An Architecture for Agent-Based Manufacturing             in incrementing the computational capabilities and therefore
System in the Context of Industry 4.0: In [17], authors present        processing a massive amount of data. The system results in
a self-organizing architecture making use of agents commu-             better and accurate monitoring.
nicating and negotiating through a cloud network. Knowl-                  3) Agent-based fault tolerant framework for manufacturing
edge is organized into representations based on ontologies             process automation: Agent-based approaches are often used
for providing the basis for decision-making. Thus, agents              for dealing with manufacturing-related disruptions regarding
can reconfigure their network in a prompt and collaborative            machine faults. disruption of manufacturing processes, in fact,
way. Because the interactions among agents in distributed              adversely affect productivity and efficiency while down times
systems are often difficult to be understood and predicted,            affect the whole chain of value.
their interaction behaviour has been modeled as a hierarchical            Widely used solutions to these issues are centralized and
structure.                                                             mostly focused on the detection and isolation of a particular
   The architecture has been assembled around agents of                disruption. Unfortunately, this kind of centralized approaches
four types: suggestion, product, machining, and conveying              suffers of time lags between the moment in which data are




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analyzed and a response is generated.                                           productivity; they cannot be disregarded by the digital
    [19] proposes an alternative approach for mitigating dis-                   counterpart, and from this point of view intelligent agents
ruptions by deploying a fault tolerant framework based on                       may be inadequate to tackle them. This aspect must be
agent technologies. The technique is adopted for handling                       further investigated and deserves appropriate solutions.
fault detection and identification and for further investing the
root cause of the disruption. Once a disruption is identified, a                      IV. C ONCLUSIONS AND F UTURE W ORK
weight is assigned to it, and the eventual corrective mechanism               In this paper, we analyzed the current trends in the im-
is executed.                                                               plementation of agent-based digital factories. As shown by
   This agent-based model has been tested on an asphalt                    the mentioned works, the adoption agent-based architectures
manufacturing plant. Results showed a reduction in downtime                optimize many of the tasks of traditional factories by exploting
around 5%. Additionally, 37% reduction in the number of                    agent characteristics. Although, the effectiveness of agents
failures has been noticed. This can lead to an increase of                 promotes a concrete support for the digitalization of traditional
about 5% in the overall productive activity. As a consequence,             manufacturing tasks, the number of implementations in the
this method offers a promising opportunity for enhancing the               industry is not significant; we think that this is due to the
overall efficiency of manufacturing plants when compared to                limitations analyzed in the paper and briefly sketched in three
more traditional approaches.                                               key points as follows:
                                                                              1) Simplicity of agent interactions is required to have
                        III. S UMMARY                                             systems easier to design and more controllable. This
   The literature presents a small number of approaches in                        prerequisite is fundamental in order to keep as simple
which intelligent agents are applied to digital factories. The                    as possible the management of complex manufacturing
concept of digital factory can be found in different shapes,                      tasks and their integration.
among which Smart manufacturing, Industry 4.0, Cyber-                         2) The involvement of humans [20] is an important aspect
Physical Production Systems, Smart factories; we consider                         when real factories are managed through digital abstrac-
them as sorts of “implementations” of the more general                            tions, thus human plays an active roles and therefore
concept of digital factory, but still very interesting also because               must be considered as part of the digital processes.
they can propose different points of view.                                    3) Real-Time constraint in a MAS, need to be further
   The survey of the approaches we have proposed highlights                       examined in order to fulfill timing requirements of
the advantages of applying intelligent agents in digital facto-                   tasks and services of IoT based digital factories. The
ries; the main ones turn out to be:                                               enablement of a digital twin models in a digital factory
   • Autonomy. Agents can manage the real factory reducing
                                                                                  requires real-time data exchange among the virtual and
      the need for human intervention.                                            the real factory. In this scenario, legacy manufacturing
   • Adaptation. Agents can rely on different plans in order
                                                                                  systems must be integrated with high end manufacturing
      to flexibly adapt to different situations.                                  equipments IoT devices, robotic arms, and robots to en-
   • Decentralization. Agents allow for scalable decentralized
                                                                                  able a flexible and transparent real-time communication.
      solutions with neither bottlenecks nor single points of                 On the other side, the advantages of the application of agents
      failure.                                                             in a digital factory are mainly related to autonomy, adaptation,
   • Robustness. Agents can react to an unpredicted situation              decentralization, and robustness. These advantages enable the
      in a flexible way and grant reduction in the process                 applicability of the agent paradigm to the digital factory field
      downtime.                                                            in order to fulfill various manufacturing tasks related to digital
                                                                           factory lifecycle. With regard to future work, we point out
   From our survey emerges that there are also some limi-
                                                                           interoperability issues intra- and inter-factories since it is
tations; in particular, agent-based approaches can be further
                                                                           a key issue that not only leverage the adoption of digital
improved in the following directions:
                                                                           factories and its effectiveness [21], but also promotes the
   • Simplicity. The autonomy of the agents leads to complex
                                                                           enablement of new form of collaborations between enterprises.
      interactions that could be difficult to define and manage;           The interoperability challenges between digital factories can
      this calls for a simpler means to enable the management              be tackled through the adoption of agent-based systems.
      of interactions, possible customized to the digital factories
      field. This can increase the acceptance of intelligent                                      ACKNOWLEDGMENT
      agents in digital factories.                                            This work has been supported by the European Commission
   • Human integration. Despite the decreasing of human
                                                                           through the H2020 project FIRST virtual Factories: Inter-
      intervention, what emerges is that humans’ contribution              operation suppoRting buSiness innovaTion (grant agreement
      is still an important part of real factories, and their              #734599).
      involvement in the system (usually called “human in the
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