SERCOS interface

Sercos automation bus
Year created:	1987
Created by:	VDW/ZVEI Joint Committee
Governing Body:	sercos International e.V.
Website:	http://www.sercos.org

In the field of Industrial Control Systems, the interfacing of various control components must provide means to coordinate the signals and commands sent between control modules. While tight coordination is desirable for discrete inputs and outputs, it is especially important in motion controls, where directing the movement of individual axis of motion must be precisely coordinated so that the motion of the entire system follows a desired path. Types of equipment requiring such coordination are, for example, metal cutting machine tools, metal forming equipment, assembly machinery, packaging machinery, robotics, printing machinery and material handling equipment. The Sercos (serial real-time communication system) interface is a globally standardized open digital interface for the communication between industrial controls, motion devices (drives) and input output devices (I/O). Sercos I and II are classified as standards IEC 61491 and EN 61491. Sercos III is specified in standards IEC 61800-7; IEC 61784-1, -2, -3 and IEC 61158. Sercos is designed to provide hard real-time, high performance communications between industrial motion controls and digital servo drives.

Until the early 1980s the majority of servo drive systems used to control motion in industrial machinery were based upon analog electronics. The accepted interface to control such devices was an analog voltage signal, where polarity represented the desired direction of motion, and magnitude represented the desired speed or torque. In the 1980s, drive systems and devices based on digital technology began to emerge. A new method needed to be devised to communicate with, and control such units, as their capabilities could not be exploited with the traditional interface method used with analog drives. The earliest interfaces were either proprietary to one vendor or designed only for a single purpose, making it difficult for users of motion control systems to freely interchange motion control and drives. The membership of the VDW (German Machine Tool Builders' Association) became concerned with the implications of this trend. In response to that, in 1987 the VDW formed a joint working group with the ZVEI (German Electrical and Electronics Industry Association) to develop an open interface specification that was appropriate for digital drive systems. The resulting specification, entitled "Sercos (serial real-time communication system) interface, was released and later submitted to the IEC, which in 1995 released it as IEC 61491. After the release of the original standard, original working group member companies including ABB, AEG, AMK, Robert Bosch, Indramat, and Siemens founded the "Interest Group Sercos" to steward the standard. Over the history of Sercos, its capabilities have been enhanced to the point where today it is not only used for motion control systems, but as a universal automation bus.

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