Important trends in automation technology are the removal of the traditional separation of the universal fieldbus and the specific drive bus and the formation of new, application-optimized device structures as well as the traditional division between controls, drives and I/O periphery. Representatives of such device structures include distributed systems such as drives with separate control and power sections and a fully digital encoder connection, as well as hybrid devices that combine functions such as control, drive and I/O in one device. Both approaches can also readily be used in combination, depending on the system requirements. To consistently implement these requirements, a communication system is required that provides the necessary performance and correspondingly viable device profile specifications.
Sercos III meets these requirements and is adapted to these trends in that the well-known and tried-and-tested Sercos I/II mechanisms were combined with the advantages of the Ethernet standard. Thus the transmission speed was increased from 16 to 100 Mbit/s, providing sufficient bandwidth in order to cover the various communication requirements of a machine or system. Proven Sercos I/II communication mechanisms for real-time data exchange (RT), asynchronous data exchange via the service channel (SVC) and hardware synchronization (SYNC) were transferred to Sercos III. At the same time, new communication features based on the full duplex characteristics of Fast Ethernet were added, such as ring redundancy (RR), direct cross communication (DCC) and hot plugging (HP).
Sercos III also takes into account the increasing importance of safety technology. The safety concept – called CIP Safety on Sercos – is a protocol expansion compatible with Sercos III to allow Sercos III to be used in safety applications up to SIL3 in accordance with IEC 61508 as well, even with the smallest cycle times. Here, the safety-relevant data is transferred along with the real-time data and other standard Ethernet protocols using a single physical medium. Thus, an additional safety bus is not required, use is simplified and hardware and installation costs are reduced.
Sercos is taking a pioneering approach with the blended infrastructure for Sercos, Ethernet/IP and TCP/IP. Thus, Sercos frames, CIP messages and TCP/IP frames can all coexist in one network without extra cabling. To keep the cyclic and clocked communication of Sercos III intact, the CIP messages and TCP/IP frames are sent on the Unified Communication Channel (UCC), which is an integral part of Sercos transmission. This standard network infrastructure enables engineers and users to reduce the costs and complexity of machine integration. At the same, they can retain their preferred product suppliers and automation devices without additional cabling.
Within the course of the transmission of the drive profile to Sercos III, it has been extended and generalized, so that not only pure drive, I/O and control devices but also hybrid devices combining different applications in one device are supported.
Thanks to this evolutionary approach of Sercos III, the existing advantages are preserved and the application area of the interface is expanded significantly. The largest possible compatibility with Sercos I/II enables not only simple migration, but also the best possible investment protection for manufacturers and users.