The industrial wireless automation sector exhibitsa huge market growth in the last years. Today, many applicationsalready use wireless technologies. However, the existingwireless solutions do not yet offer sufficient performance withrespect to real-time and reliability requirements, particularlyfor closed-loop control applications. As a result, low latencywireless communication technologies will bridge the gap andcan become a key factor for the wide-spread penetration ofwireless in industrial communication systems. It is therefore themain goal of this paper to provide a comprehensive overviewon requirements, current solutions, and challenges as well asopportunities for future wireless industrial systems. Thereby,presented requirement figures, analysis results, and performanceevaluations are based on numerous practical examples fromindustry
Abstract. In the context of the Industry 4.0 initiative, Cyber-Physical Production Systems (CPPS) or Cyber Manufacturing Systems (CMS) can be characterized as advanced networked mechatronic production systems gaining their added value by interaction with the ambient Industrial Internet of Things (IIoT). In this context appropriate communication technologies and standards play a vital role to realize the manifold potential improvements in the production process. One of these standards is IO-Link. In 2016 more than 5 million IO-Link nodes have been produced and delivered, still gaining increasing acceptance for the communication between sensors, actuators and the control level. The steadily increasing demand for more flexibility in automation solutions can be fulfilled using wireless technologies. With the wireless extension for the IO-Link standard, which will be presented in this article, maximum cycle times of 5 ms can be achieved with a probability that this limit will be exceeded to be at maximum one part per billion. Also roaming capabilities, wireless coexistence mechanisms and the possibility to include battery-powered or energy-harvesting sensors with very limited energy resources in the realtime network were defined. For system planning, setup, operation and maintenance, the standard engineering tools of IO-Link can be employed so that the backward compatibility with wired IO-Link solutions can be guaranteed. Interoperability between manufacturers is a key requirement for any communication standard, thus a procedure for IO-Link Wireless testing is also suggested.
The "Parallel Redundancy Protocol" (PRP) according to IEC 62439-3 realizes active network redundancy by packet duplication over two independent networks that operate in parallel. It has been specifically designed for industrial networks to meet highest availability requirements. In case of a single network failure, seamless redundancy is provided for data communication between PRP nodes that are connected to both networks. However, PRP was designed as a layer 2 Ethernet protocol that is transparent to higher protocol layers. In its current version, PRP is not able to support IP routing. This is because an IP router would change the source MAC address field of the Ethernet header which is used by a PRP receiver node for duplicate detection. In this work we propose and discuss a novel approach that keeps the PRP duplicate identification information across IP router boundaries.
WLAN according to standard IEEE 802.11 is widely regarded unsuitable as communication channel for realtime and safety applications. Non-determinism and interference liability leads to packet loss, exceeded and variable latency times due to retransmissions.This work proposes a method that compensates such consequences of stochastic channel fading by the parallel operation of diverse wireless channels, applying frequency and space diversity techniques. A fault-tolerant wireless "black channel" is achieved that is able to fulfill soft real-time availability plus providing redundancy. This is realized with standard WLAN components and the "Parallel Redundancy Protocol" (PRP) according to IEC 62439-3. Reliability and performance characteristics are derived from measurements on an experimental setup with SafetyNET p nodes.
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