For numerically controlled machines, digital drives offer maximum precision and speeds while minimizing equipment costs. High performance digital interface is required to make use of these advantages. In the interest of product choice, optimum configuration, and standardization, in order to simplify procurement and operational maintenance, a digital drive interface not only has to meet the functional requirements of different applications, but it must also ensure, through openness and standardization, problem-free operation between various controllers and drives from different manufacturers. The digital drive interface Sercos (SErial Real-time COmmunication System) meets all these requirements and was accepted as International standard (IEC 61491) in 1995 and as European standard (EN 61491) in 1998 for drives on production machines. Since the beginning of the 1990s, the digital drive interface has become a worldwide accepted real-time networking standard for demanding motion control applications. The Sercos technology is particularly interesting due to its outstanding technical features like real time capabilities, performance, noise immunity, and last but not least a very large variety of products and suppliers.
The origin of Sercos
Sercos was developed as a digital drive interface in the mid 1980s by an industry consortium supported by the "Verein Deutscher Werkzeugmaschinenfabriken e.V. (VDW) and the "Zentralverband Elektrotechnik- und Elektroindustrie e. V." (ZVEI). The first generation of Sercos supported transmission rates of 2 and 4 Mbit/s and was mainly used in advanced machine tool applications. In the following years Sercos became more and more accepted worldwide and has been used in all kinds of different servo-driven applications. In 1995 Sercos was established as IEC standard 61491. In 1999 the second generation of the technology was launched. The transmission rate was increased to 8 and 16 Mbit/s and the service channel for the transmission of asynchronous data was extended. This new technology has been available since 2001 based on the SERCON816 ASIC, while downward compatibility to the first generation was maintained. Sercos offers an outstanding performance due to collision free transmissions based on time slot mechanisms and a highly efficient protocol, combined with an absolutely deterministic time behaviour. Example: Up to 40 axis can be synchronized exactly with a cycle time of 1ms and a jitter of <1µs. The optic fibres provide a maximum of noise immunity and robustness of the transmission.
Thanks to its technical abilities and its widespread use, Sercos has become the de-facto standard in many branches, especially for highly dynamic servo applications with many axes. The hardware-based synchronization is the indispensable prerequisite for the reliable implementation of challenging motion applications, such as electronic line shafts in printing machines, packaging machines or multi-axis machine tools.
Although Sercos was initially designed as a dedicated drive interface, it has since then mutated to a universally applicable motion control interface. Sercos not only defines a real time communication system but also specifies more than 500 standardized parameters which provide a vendor-neutral semantics for the interoperability of controls and drives. Further to drives, also I/O stations are being connected to the bus, so that most standalone machines do not require an additional fieldbus.
Worldwide more than 50 control manufacturers and 30 drive manufacturers offer Sercos compatible devices. Up to now more than 3,0 Million Sercos nodes are used world-wide in over 500 thousand applications. The user organization Sercos International (SI) with its head office in Suessen close to Stuttgart, Germany, has more than 60 member companies worldwide and is represented in North America and Japan with branch organizations.