•A deep literature review on DT applications in manufacturing is performed.•Rarely a DT environment offers a large set of services to the real system.•Almost never a DT share the elaborated analysis ...to the real counterpart.•A DT application is proposed in a Simulink environment to overcome these gaps.•The illustrated DT poses the basis for further improvements.
In the Industry 4.0 era, the Digital Twin (DT), virtual copies of the system that are able to interact with the physical counterparts in a bi-directional way, seem to be promising enablers to replicate production systems in real time and analyse them. A DT should be capable to guarantee well-defined services to support various activities such as monitoring, maintenance, management, optimization and safety. Through an analysis of the current picture of manufacturing and a literature review about the already existing DT environment, this paper identifies what is still missing in the implemented DT to be compliant to their description in literature. Particular focuses of this paper are the degree of integration of the proposed DT with the control of the physical system, in particular with the Manufacturing Execution Systems (MES) when the production system is based on the Automation Pyramid, and the services offered from these environments, comparing them to the reference ones.
This paper proposes also a practical implementation of a DT in a MES equipped assembly laboratory line of the School of Management of the Politecnico di Milano. The application has been created to pose the basis to overcome the missing implementation aspects found in literature. In such a way, the developed DT paves the way for future research to close the loop between the MES and the DT taking into consideration the number of services that a DT could offer in a single environment.
•We present a paradigm to integrate all the major interpretations of the Digital Twin concept.•We evidence that models and data need not only communicate but be subjected to shared consistency ...rules.•We turn the above findings in the proposal of a Digital Twin management tool integrating state-of-the-art technologies.
Digital Twins are of paramount relevance in the Industry 4.0 framework. However, the idea of Digital Twin has many different interpretations. These are tied to the intended use of a Digital Twin, thus to the viewpoint of the involved professionals (process designers, control specialists, managers, and so on). The said interpretations are often highly incompatible with one another, since they can involve as heterogeneous entities as a CAD drawing and a neural network. A convergence of Digital Twin interpretations is desirable, to take full profit of the contained knowledge. In this research we argue that this desired convergence cannot be found at the same abstraction level of the available Digital Twin interpretations, and calls for a higher one. We consequently propose a paradigm – that we name Digital Multiverse – to comprehend the major Digital Twin interpretations not only in the sense of data integration, which is the goal of promising complementary ideas like that of Asset Administration Shell, but also by establishing and enforcing consistency rules that involve both data and models. We also show some examples to support the usefulness and viability of our proposal.
Digital Twins (DTs) are enablers for the fast optimisation processes required in the Industry 4.0 context. Declarative equation-based modelling languages, in turn, enable the creation of large-scale ...simulation-based DTs, as they relieve the analyst from creating the solution code. However, most industrial assets are Cyber-Physical Systems (CPSs), the Cyber part being their digital controls. With the available technology, a precise representation of modulating and logic controls conflicts with DT simulation performance. The result is a barrier to using DTs for system-level optimisation. We analyse the problem, propose a modelling paradigm to solve it and suggest how to integrate that paradigm into equation-based language compilers. We support our proposal by presenting a Modelica/C++ library, that we release as free software, built according to the said paradigm.
Manufacturing companies are experiencing the fourth industrial revolution characterised by the introduction of new technologies into production equipment, such as the Cyber Physical Systems and the ...Digital Twin simulations. Companies are then challenged by the digitization of products and production systems information, which leads to new potentials for digital continuity – i.e. information available and continuously updated for the decision makers – along the lifecycles. A semantic data model, that structures and stores physical and operational data from the field, can support the digital continuity to be used in production system simulations in a Digital Twin paradigm. This work proposes to model specific aspects and behaviours of the production system separately from the core simulation, in order to flexibly decide whether to activate the replica of the specific behaviours only when needed. The modules interact with the main simulation run through standard interfaces, allowing an easy reusability of the single modules also in different simulation environments.
In the process control, many PID loops are primarily devoted to rejecting load disturbances, and some of them are crucial for the quality of the overall plant operation. In such a scenario, automatic ...tuning is highly desired. However, load disturbance rejection calls for strong feedback up to quite high frequencies with respect to the dominant plant dynamics, on which most tuning rules are centered. As such it is difficult for a rule to yield good and, above all, uniform results in the face of all the various process structures it can be confronted with. In this paper, we propose an explicit model-based PID tuning rule specifically targeted at the problem just evidenced. The rule minimizes the magnitude of the nominal disturbance-to-output frequency response, at the same time preventing that magnitude to exhibit a peak or a plateau around its maximum. This characteristic, together with tuning the PID derivative filter, leads to sharp disturbance rejection without incurring in an excessive control sensitivity to high-frequency measurement noise and mitigates the problems caused by heterogeneous process dynamics. The proposed approach is assessed by comparing the rule with selected counterparts, on a literature benchmark with different process structures. A laboratory experiment is finally presented to show that our rule can withstand real-world operating conditions.
In recent years, the discipline of Digital Transformation in manufacturing companies turned out to be a hot topic of research debate, which allowed the design and introduction of new technologies and ...tools able to exploit the potential of the data produced by the shop floor assets. This increased interest in data generation and management has however highlighted a crucial issue about the lack of standardised models and structures to share these data and ensure interoperability. Among the several concepts proposed by the recent initiatives devoted to solving or mitigating this issue, Asset Administration Shell (AAS) is increasing in popularity, given its potential in providing standardised and modular information about the assets and events represented. This paper deals with a demonstration of the easiness of integration of AAS in pre-existing software architecture, allowing higher flexibility and a better understanding of the ongoing processes: a production line has been indeed entirely represented with modular AAS metamodels and it has been used to feed a Digital Model representing the line configuration. The use case proposed proves the effectiveness of the obtained solution when used for virtual commissioning operations.
In Smart Manufacturing, the Internet of Things technology brings about new possibilities as for the interaction of Cyber-Physical Systems with their virtual models—in Industry 4.0 jargon, Digital ...Twins. Besides traditional roles in engineering and control design, Digital Twins cab play innovative ones by evolving together with their cyber-physical counterpart: predictive maintenance, fault detection, or fast training of data-based decision aid tools. In this paper we focus on the relevance of dynamic models in this scenario, particularly as for the co-existence of continuous-time and discrete-event models wherever control and planning are involved. We argue that in such cases, models with analysis-specific levels of detail have to co-exist, interact and maintain mutual consistency. We propose a modelling approach to address the problem, and present a supporting example based on an object-oriented modelling language.
Digital Twins (DTs for short) are a powerful aid for creating, assessing and maintaining control strategies. This use of DTs however requires that the physical entities to control be described at ...different levels of detail. For example, simple I/O models are used to compute parameters of modulating controllers, more time-accurate ones may be required to set up and assess logic controls, high-accuracy, possibly nonlinear ones may serve for overall strategy verification, and for software-in-the-loop testing, also the host computing/network architecture needs representing. In such a complex scenario, guaranteeing that all the descriptions of all elements are consistent with one another is a relevant problem. We discuss this matter and propose a solution, in the form of a modelling paradigm where as a novel contributions relationships (in a sense analogous to what the term means in database theory) can be instated and enforced. This allows to create and maintain knowledge based made of interrelate data and models, embracing all the major DT interpretations proposed so far in the literature, or said more explicitly, combining data-driven and model-driven DTs in a single framework. We also provide an illustrative example.
In the literature on control education, a minority of papers concern logic control. Out of this minority, an even smaller one addresses the problem of designing an application composed of both ...modulating and logic control functions, interacting and coordinating with one another. In the opinion of the authors this is a gap to be filled, as it easily leads to an inefficient use of the available development tools, and sometimes results in cumbersome design and poor maintainability. In this paper we discuss the matter, and propose a compact teaching activity based on the experience gathered along the last years.
PDF
