New-Tech Europe Magazine | July 2019 | Digital Edition

Deterministic Ethernet Protocols Popular industrial Ethernet protocols include PROFINET, EtherNet/IP, EtherCAT, SERCOS III, and POWERLINK. Since there are major differences in the technical approaches taken by each of these protocols, supporting every one of them would be a Herculean software effort for all but the largest manufacturers of industrial automation equipment. Each protocol offers real-time and deterministic behavior for devices and each has various supporting companies and manufacturers. However, EtherCAT is the most adopted and offers both superior performance and market acceptance, delivering real-time, deterministic responses required by industrial machine controllers using low-cost network interface cards (NICs) and Ethernet cables. (2) To support this collection of protocols, also referred to as a fieldbus, the OPC Unified Architecture (OPC UA – IEC 62451), an open standard developed by the OPC Foundation, can be used to specify the information exchange for industrial communication on computer-based machines, in-

the GenICam Standard Features Naming Convention (SFNC) providing a common set of camera features, their names, and their behavior. The Importance of Being on Time While GigE Vision and GenICam standards allow for different devices to work with each over Ethernet the issue of deterministic behaviour between devices still needs to be addressed. Business systems and office environments using Ethernet do not require precise or critical timing between devices to function properly, because it is not crucial if all data packets are correctly sent and received, or whether they are sent and received during a known period of time. However, for industrial Ethernet systems such as a machine vision system inspecting parts in a timely fashion, determinism is required. Industrial systems must be highly deterministic because any failure to transmit, receive, or act on processed data at specific times can result in data loss and delays producing an unpredictable industrial system. Determinism is therefore highly important and has been addressed by a number of specialized industrial Ethernet protocols.

between machines, and from machines to and from computers systems. With OPC UA, developers can take advantage of OPC’s data model and services that enable devices to exchange data with an agreed and shared meaning, rather than mapping data as byte streams. At the same time, the EtherCAT TechnologyGroup(ETG,Nuremberg, Germany) and the OPC Foundation’s technologies complement each other with EtherCAT being used as a real-time-Ethernet fieldbus for machine and plant controls and OPC UA as a platform for scalable communication. Making Machine Vision Systems While the collaborations above are useful, they do not specifically address the needs of developers of machine vision systems wishing to leverage Ethernet-based systems on the factory floor. To do so, the VDMA has collaborated with the OPC Foundation to form an OPC Vision Initiative to develop an OPC UA companion specification for machine vision (see “OPC UA Vision,VDMA Specification”, Draft Version November 2018).

Figure 5: The OPC UA’s Companion Specification for Machine Vision (OPC UA Vision) is an open, Ethernet-based standard that allows for non-linear communication and data exchange between components of factory networked systems.

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