Introduction to the SERCOS interface®
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By Ronald Larsen, Managing Director, SERCOS N.A.
SERCOS is an acronym for SErial Realtime COmmunications System, a digital motion
control bus that interconnects motion controls, drives, I/O and sensors. It is an open
controller-to-intelligent digital device interface, designed for high-speed serial
communication of standardized closed-loop data in real-time over a noise-immune, fiber
optic cable. (A third generation of the SERCOS interface, now in development, will use
industrial Ethernet as a transport mechanism—both copper and fiber optics.)
The SERCOS interface® was created in the 1980s by a group of European machine tool
builders and control/drive vendors to specify a digital open interface that would ease the
transition from analog to digital drive technology. It was originally intended to be a drive
interface for advanced machine tool applications, but today is in wide use in all servo-
controlled automation disciplines. The SERCOS interface standard covers control topics
that are common to all servo applications, as well as topics that are industry specific. It is
estimated that the majority of SERCOS interface axes in the field today are on
applications such as web-fed printing presses; packaging, converting & food processing
machines; assembly, handling and robots; semiconductor processing equipment;
metalforming and welding machines; textile processing; fiber winding; simulators and
test equipment; plastics machines and many other types of special machines.
The SERCOS interface is a real-time communication system that 1) defines a
standardized physical layer and 2) offers a rich set of more than 500 standardized
parameters (called Idents) that describe the interplay of drives and controls in terms
independent of any manufacturer. It offers advanced motion control capabilities and it
includes features for I/O control that often allow a machine builder to dispense with the
need for a separate I/O bus.
The SERCOS interface is the only internationally standardized open digital interface for
motion control and I/O with the performance required to synchronize high-performance
multi-axis motion control systems. The SERCOS interface was designed to include
mechanisms to ensure the high level of determinism required when synchronizing
multiple axes of digital drives, while some other buses attempt to ensure determinism via
brute speed. The SERCOS interface is defined with a minimum of overhead, in order to
ensure maximum throughput. A lab test has determined that a 16 Mbit/s SERCOS
interface system provides equivalent throughput to a 100 Mbit/s Ethernet system, because
of the difference in overheads.
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Much of the information in this document was adapted with permission from data published on
the SERCOS N.A. website, www.sercos.com.
Introduction to the SERCOS interface-- Page 1
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