Ethernet is becoming an increasingly important networking technology in industrial applications.
In the realm of motion control, Ethernet, fieldbus, and other technologies-such as Peripheral Component Interconnect (PCI)-have historically competed to handle some of the most demanding workloads in industrial automation and control systems. Motion control applications require determinism-the guarantee that the network will deliver workloads to designated nodes in a timely manner-which is essential for ensuring position hold, which in turn ensures precise driver stops, proper acceleration/deceleration, and other tasks.
Standard IEEE 802.3 Ethernet has never met these requirements. Even though full-duplex switching and isolated collision domains have replaced the outdated CSMA/CD data link layer, the protocol still lacks predictability. Furthermore, the high complexity of TCP/IP in a typical stack is not optimized for the reliable transmission of real-time traffic. Consequently, fieldbuses and PC-based control architectures with ASIC-based PCI cards have long been common solutions for motion control.
Ethernet solutions, ranging from EtherNet/IP® to EtherCAT®, overcome these shortcomings in their own unique ways. Although Industrial Ethernet offers several other advantages over alternative technologies, it is still far from dominating the motion control market. Let's examine three reasons why it can-and will-gain increasing acceptance in the coming years.
1
Convergence Rather Than Increased Complexity
Over time, the increasing interconnection between enterprise IT and the factory floor has led to more complex systems, often involving a mix of standard Ethernet, industrial Ethernet, and fieldbus technologies. For example, a machine might utilize:
Such networks are complex, and they are expensive to set up and maintain. Each protocol requires its own implementation procedures, installation personnel, and training. In contrast, Ethernet offers the possibility of converging different networks-such as those for motion control and safety-into a cost-effective infrastructure that is easier to wire, widely supported by vendors, and adaptable to future requirements.
Ethernet offers the possibility of converging different networks.
The EtherNet/IP protocol exemplifies how convergence can be fully leveraged in practice. By using standard Ethernet technologies such as TCP/IP and UDP/IP, supplemented by features like CIP Sync (for achieving precise time protocol synchronization via the IEEE 1588 distributed clock), integrated switched systems can accommodate both commercial and industrial applications simultaneously.
2
Determinism for Motion Control Applications
Motion control relies on precise communication. This precision is supported by time-slot-based scheduling, in which each device has a schedule within the scheduling policy for communicating with other devices. These servo drives and controllers calculate their respective timing, from which the ∆T value of the control function can be derived. However, if data transmission becomes unpredictable, results may be lost; therefore, determinism is required to ensure loop stability.
Ethernet is capable of supporting demanding motion control applications in the factory.
In some cases, implementing IEEE 1588 in EtherNet/IP through accelerator circuits directly integrated into Intel® chips is just one common mechanism by which Ethernet solutions enforce determinism. EtherCAT's high-speed real-time processing is another example of how consistent, predictable performance is achieved in motion control applications. EtherCAT overcomes the strict physical limitations of PCI-based centralized communication, which requires fast communication between the machine processing unit and the servo processor while maintaining a short distance.
Jason Goerges explained in an article published in *Machine Design* in 2010:
The EtherCAT-based distributed processor architecture offers high bandwidth, synchronization, and physical flexibility, rivaling the capabilities of centralized control while offering the advantages of a distributed network.
In fact, some processors using this approach can control up to 64 highly coordinated axes-including position, speed, and current loops as well as commutation-at sampling and update rates of 20 kHz.
3
Long-Term Viability for the IIoT
Since its inception as a local area network (LAN) technology, Ethernet has undergone a series of developments. Given that traditional fieldbus components are currently produced on a small scale and that PCI risks becoming an obsolete industrial standard architecture, Ethernet has evolved to the point where it is now fully capable of serving the IP-based Industrial Internet of Things (IIoT).
Upcoming enhancements-such as time-sensitive networking, which will refine IEEE 1588 and support the possibility of network convergence-also make Ethernet an ideal choice for current and future motion control applications. This is not to say that fieldbuses and PCI will disappear; rather, as the automation industry moves toward the IIoT, the advantages of Ethernet will continue to grow.