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Maintenance is one of the most important aspects in industrial and production environments. Predictive maintenance is an approach that aims to schedule maintenance tasks based on historical data in order to avoid machine failures and reduce the costs due to unnecessary maintenance actions. Approaches for the implementation of a maintenance solution often differ depending on the kind of data to be analyzed and on the techniques and models adopted for the failure forecasts and for maintenance decision-making. Nowadays, Industry 4.0 introduces a flexible and adaptable manufacturing concept to satisfy a market requiring an increasing demand for customization. The adoption of vendor-specific solutions for predictive maintenance and the heterogeneity of technologies adopted in the brownfield for the condition monitoring of machinery reduce the flexibility and interoperability required by Industry 4.0. In this paper a novel approach for the definition of a generic and technology-independent model for predictive maintenance is presented. Such model leverages on the concept of the Reference Architecture Model for Industry (RAMI) 4.0 Asset Administration Shell, as a means to achieve interoperability between different devices and to implement generic functionalities for predictive maintenance.

In the Reference Architecture Model for Industrie 4.0, the concept of Asset Administration Shell is presented as the corner stone of interoperability. Asset Administration Shell is defined as a digital representation of an asset able to provide information about the asset including documents, properties, parameters, and functionalities, all organized in a consistent way. Information provided by an Asset Administration Shell can be adopted during whole life cycle of a production system, from its development until its disposal. At the lowest level of the hierarchy of a production system, usually automation and control programs are executed by Programmable Logic Controllers, whose programming technology is based on IEC 61131-3 standard. The IEC 61131-3 programs, the Programmable Logic Controllers where they run, and the real plant controlled are closely related. Considering the life cycle of a production system, the description of IEC 61131-3 programs and the relevant relationships with the plant should be clearly defined, leading to several advantages for example regarding the definition of testing plant operations, maintenance operations at run-time and reconfiguration process of the plant. What is missing for the realization of what said so far is a standard way to realize this description. For this reason, the paper presents an Asset Administration Shell model able to represent IEC 61131-3 programs and the relevant relationships with Programmable Logic Controllers and each device of the controlled plant.

In the context of Industry 4.0, lot of effort is being put to achieve interoperability among industrial applications. As the definition and adoption of communication standards are of paramount importance for the realization of interoperability, during the last few years different organizations have developed reference architectures to align standards in the context of the fourth industrial revolution. One of the main examples is the reference architecture model for Industry 4.0, which defines the asset administration shell as the corner stone of the interoperability between applications managing manufacturing systems. Inside Industry 4.0 there is also so much interest behind the standard open platform communications unified architecture (OPC UA), which is listed as the one recommendation for realizing the communication layer of the reference architecture model. The contribution of this paper is to give some insights behind modelling techniques that should be adopted during the definition of OPC UA Information Model exposing information of the very recent metamodel defined for the asset administration shell. All the general rationales and solutions here provided are compared with the current OPC UA-based existing representation of asset administration shell provided by literature. Specifically, differences will be pointed out giving to the reader advantages and disadvantages behind each solution.

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