Sten Grüner

RESTful Industrial Communication With OPC UA

Representational state transfer (REST) is a wide-spread architecture style for decentralized applications. REST proposes the use of a fixed set of service interfaces to transfer heterogeneous resource representations instead of defining custom interfaces for individual applications. This paper explores the advantages of RESTful architectures, i.e., service-oriented software architectures comprised RESTful services, in industrial settings. These include communication advantages such as reduced communication overhead and the possibility to introduce caching layers, and system design advantages including stable service interfaces across applications and the use of resource-oriented information models in cyber-physical systems. Additionally, a RESTful extension to the open platform communications (OPC) unified architecture (OPC UA) binary protocol is proposed in order to leverage these advantages. It requires only minimal modifications to the existing OPC UA stacks and is fully backward compatible with the standard protocol. Performance benchmarks on industrial hardware show a throughput increase up to a factor of eight for short-lived interactions. This reduction of overhead is especially relevant for the use of OPC UA in the emerging Industrial Internet of Things.

Open source as enabler for OPC UA in industrial automation

As a standardized communication protocol, OPC UA is the main focal point with regard to information exchange in the ongoing initiative Industrie 4.0. But there are also considerations to use it within the Internet of Things. The fact that currently no open reference implementation can be used in research for free represents a major problem in this context. The authors have the opinion that open source software can stabilize the ongoing theoretical work. Recent efforts to develop an open implementation for OPC UA were not able to meet the requirements of practical and industrial automation technology. This issue is addressed by the open62541 project which is presented in this article including an overview of its application fields and main research issues.

A RESTful extension of OPC UA

RESTful interfaces are a wide-spread architecture style for webservice implementations and are built upon the resource-oriented approach to decentralized architectures (ROA). REST postulates a set of requirements that are not covered by the OPC Unified Architecture (OPC UA) communication protocol per se. We propose a set of simple extensions to the OPC UA binary protocol that enable RESTful communication. The evaluation shows an order of magnitude improvement in the use of communication resources for sporadic service requests. Additionally, RESTful OPC UA allows applications to profit from the advantages of the resource-oriented architecture style, such as caching and loose application coupling.

A model for discrete product flows in manufacturing plants

Many tasks in factory automation can be solved with the bare knowledge of used and possible product flow paths in a plant. Unfortunately, the information about these is usually not available explicitly, but is distributed among different models and tools. We present a model that describes discrete product flow paths and aims to play a similarly important role as piping and instrumentation diagrams in process industry. The models extensibility and its CAEX representation allow a seamless integration into the established model and tool landscapes.

An engineerable procedure description method for industrial automation

Describing procedures is essential for modeling and controlling technical processes. Although various procedure description methods are available from computer science, system theory and industrial automation, they are only partially suitable as a generic method for engineering automation procedures. In order to close this gap, we propose a procedure description formalism together with a concept of its integration into existing automation systems. By utilizing of the proposed means we obtain an engineerable, generic and user accepted procedure description method.

The role of the Industry 4.0 asset administration shell and the digital twin during the life cycle of a plant

Industry 4.0 has come up with an impressive number of additional terms and definitions e.g. Asset Administration Shell or Digital Twin. Those terms stand for Industry 4.0 coreparadigms, but their meaning is not harmonized even among experts. This is a source of misunderstanding and confusion. In this paper, the mentioned terms are discussed along the life cycle of a plant. A plants life cycle comprises the whole process from its idea to its destruction. During the discussion of the terms not only the concepts, but also the visions of Industry 4.0 are clarified. Goal of this paper is not to define additional terms, but to explain and substantiate existing ones and to solve apparent contradictions. Additional outcome of the discussion are architectural recommendations for an upcoming Industry 4.0 architecture. Moreover, suggestions for device manufacturers, system integrators, plant owners and Industry 4.0 architects are given.

Rule-based engineering using declarative graph database queries

Automation of tedious engineering tasks allows for more efficient plant commissioning and reconfiguration. Usage of knowledge-based systems is one possibility to solve this challenge. We present a rule-based system that is based on declarative graph database queries which have the advantage of being comprehensible by both computer scientists and engineering domain experts. The applicability of the system is verified in two engineering use-cases: the creation of function blocks for basic control and flow path monitoring. Promising results from the first use-case reveal further application fields of the system.

Container-based architecture for flexible industrial control applications

Abstract Cyber-physical systems and the Internet-of-Things are getting more and more traction in different application areas. Boosted by initiatives such as Industrie 4.0 in Germany or the Industrial Internet Consortium in the US, they are enablers for innovation in industrial automation. To provide the advanced flexibility in production envisioned for future automation systems, Programmable Logic Controllers (PLCs), as one of their main building blocks, also need to become more flexible. However, the conservative nature of this domain prohibits changes in the controller architecture impacting the installed base. Currently there exist various approaches that evolve control architectures to the next level, but none of them address flexible function deployment at the same time with legacy support. In this paper, we present an architecture for a multi-purpose controller that is inspired by the virtualization trend in cloud systems which moves from heavyweight virtual machines to lightweight containers solutions such as LXC or Docker. Our solution includes the support for multiple PLC execution engines and adds support for the emulation of legacy engines as well. We evaluate this architecture by executing performance measurements that analyze the impact of container technologies to the real-time aspects of PLC engines.

A modular benchmark for evaluating load distribution algorithms

In the last few years, resources sharing has been one of the main focal points of the German initiative “Industrie 4.0”. Resources sharing can be properly guided by load distribution algorithms. With the availability of many load distribution algorithms, it can be an intricate decision to match the use case with the correspondent most fitting algorithm. For an easier matching process, a benchmark is introduced along with the most important quantitative and qualitative key performance indicators that cover the pivot factors that affect the performance factors in the field of engineering automation.

Model based synthesis of automation functionality

Abstract The article demonstrates the advantages of meta-model-based solutions for multi-aspect automation tasks. Multi-aspect tasks require solutions that consider information of multiple system aspects simultaneously. In todays practice, these aspects are maintained in different tools which make implicitly use of tool-driven system models. In contrast, we propose to prioritize the models in order to facilitate the handling of multi-aspect automation tasks. The article exemplifies this idea by introducing typical automation and engineering models and illustrates their utility in a use-case example.