In the field of
Industrial Control Systems
An industrial control system (ICS) is an electronic control system and associated instrumentation used for industrial process control. Control systems can range in size from a few modular panel-mounted controllers to large interconnected and i ...
, 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 control
Motion control is a sub-field of automation, encompassing the systems or sub-systems involved in moving parts of machines in a controlled manner. Motion control systems are extensively used in a variety of fields for automation purposes, includi ...
s, where directing the movement of individual axes of motion must be precisely coordinated so that the motion of the entire system follows a desired path. Types of equipment requiring such coordination include 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 standardized in 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
Real-time computing (RTC) is the computer science term for hardware and software systems subject to a "real-time constraint", for example from event to system response. Real-time programs must guarantee response within specified time constrai ...
, high performance communications between industrial
motion control
Motion control is a sub-field of automation, encompassing the systems or sub-systems involved in moving parts of machines in a controlled manner. Motion control systems are extensively used in a variety of fields for automation purposes, includi ...
s and digital
servo drive
A servo drive is an electronic amplifier used to power electric servomechanisms.
A servo drive monitors the feedback signal from the servomechanism and continually adjusts for deviation from expected behavior.
Function
A servo drive receives a c ...
s.
History
Until the early 1980s the majority of servo drive systems used to control motion in industrial machinery were based upon
analog electronics
Analogue electronics ( en-US, analog electronics) are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two levels. The term "analogue" describes the proportional relat ...
. 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 appropriate for digital-drive systems. The resulting specification, entitled "Sercos (serial real-time communication system) interface, was released and later submitted to the
IEC
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
, which in 1995 released it as IEC 61491. After the release of the original standard, original working group member companies including
ABB
ABB Ltd. is a Swedish- Swiss multinational corporation headquartered in Zürich, Switzerland. The company was formed in 1988 when Sweden's Allmänna Svenska Elektriska Aktiebolaget (ASEA) and Switzerland's Brown, Boveri & Cie merged to crea ...
,
AEG, AMK,
Robert Bosch
Robert Bosch (23 September 1861 – 12 March 1942) was a German industrialist, engineer and inventor, founder of Robert Bosch GmbH.
Biography
Bosch was born in Albeck, a village to the northeast of Ulm in southern Germany as the eleventh of ...
,
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.
Versions
Sercos I was released in 1991. The transmission medium used is optical fiber. The data rates supported are 2 and 4 Mbit/s, and cyclic update rates as low as 62.5 microseconds. A ring topology is used. Sercos I also supports a "Service Channel" which allows asynchronous communication with slaves for less time-critical data.
Sercos II was introduced in 1999. It expanded the data rates supported to 2, 4, 8 and 16 Mbit/s.
Sercos III was introduced in 2003. It merges the hard-real-time aspects of Sercos with the
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...
standard.
Features of Sercos Automation Bus
Important features of Sercos include:
*Collision-free communication through the use of a time-slot mechanism.
*Highly efficient communication protocol (little overhead).
*Extremely low telegram
jitter (specified at less than 1 microsecond, in practice as low as 35 nanoseconds).
*Highly developed standardized profiles agreed upon by multi-vendor technical working groups for dependable interoperability of devices from different manufacturers.
*Ability to control, for example, 60 axes of motion at an update of 250 microseconds for each and every drive (Sercos III).
Support
Sercos is supported globally b
Sercos International e.V.(SI) in Germany. Regional support is provided b
Sercos North AmericaUSA)
Sercos Japanand Sercos China. These organizations provide a forum for the continued development of the standard, as well as user support.
Conformance Testing and Interoperability
An important aspect of an open,
interoperable
Interoperability is a characteristic of a product or system to work with other products or systems. While the term was initially defined for information technology or systems engineering services to allow for information exchange, a broader def ...
communications system is rigorous testing of products for adherence to the standard and their ability to operate in networks of products from multiple vendors.
Sercos International e.V.supports
Conformance Laboratoryat the University of Stuttgart's Institute for Control Engineering of Machine Tools and Manufacturing Units (ISW). Products successfully passing conformance testing may display a mark indicating they are conformance tested. Conformance-tested Sercos I and II products are publicized in a
index of certified products, Sercos I and II Conformance-tested Sercos III products are publicized in
index of certified products, Sercos III
External links
Sercos International e.V.Open Source Sercos Master APIOpen Source Sercos internet protocol servicesSercos North AmericaSercos Japan
References
{{Automation protocols
Industrial Ethernet
Industrial computing