THE SERCOS trade organizations recently introduced a safety protocol extension concept that allows safe data transfer based on the
SERCOS interface. They say this safety concept is compatible with the established transmission mechanisms of the SERCOS interface and can be used for safety applications up to Safety Integrity Level (SIL) 3 according to IEC61508, even with the shortest cycle times."SERCOS safety is independent of the transport layer, so that any transmission physics can be used, meaning the extension is available for SERCOS II and SERCOS III--no special requirements for transmission components need be considered,” says Ronald Larsen, SERCOS NA’s managing director. “Due to the routing capability of the protocol, a safety network can even be extended over several subordinate SERCOS networks. The safe data container, which is embedded in the SERCOS III data telegram, can transfer up to 64 bits of safe user data.”Larsen reports that SERCOS safety achieves its best performance when used in combination with the new Ethernet-based SERCOS III. Safe data can be exchanged directly between slaves using the peer-to-peer cross-communication capabilities of SERCOS III, without collection and re-distribution of data by a central master (safety control).“In addition, when combining SERCOS safety with the fault tolerance provided by the hardware redundancy of SERCOS III, safe, highly dependable automation solutions can be implemented for both centralized and decentralized safety applications,” adds Larsen.SERCOS safety is being investigated by TÜV Rheinland, an international technical service provider that evaluates, tests and certifies the safety and quality of products. The specification could be approved by TÜV in the next two months and will be made available free of charge to all SERCOS members. The organization claims the first SERCOS safety products will be available in 2006.The SERCOS organizations also recently announced intensified activities in I/O communication. While I/O always has been a part of SERCOS, the organization’s I/O Technical Working Group now is preparing a specification for an extended device profile for I/O, based on the existing SERCOS communication protocol. Modular I/O devices with bus couplers as well as simple block I/Os will be included. “In order to minimize the costs of the bus interface, especially for simple I/O, an FPGA-based low-cost communication controller will be developed,” says Larsen. “Even in smaller quantities, the price is expected to be under $5.” Peter Lutz, managing director of Interests Group SERCOS interface, reports, “Today more and more I/O devices are being connected to SERCOS in addition to servo drives. In the future, the integration of peripheral I/O devices into SERCOS III networks will become even more simplified, occurring in combination with minimal interface costs and the support of centralized and decentralized control architectures.”Lutz adds the SERCOS I/O specification will be available by mid-2006, with first prototypes of the low-cost FPGA I/O controller, as well as corresponding product implementations, available in 2006.The SERCOS organizations announced these changes at the SPS/IPC/DRIVES 2005 show in Nurenberg, Germany, last November.
