SERCOS-III links real time and Ethernet

Introduced in the 1980s, SERCOS (SErial Real-time COmmunication System) originally provided an interface to ease the transition of electric drives from an analog to a digital world. By combining with Ethernet, the third-generation architecture—SERCOS-III—is in the process of evolving into a communication interface for all elements of a motion-control system.

By Control Engineering Staff January 29, 2004

Introduced in the 1980s, SERCOS (SErial Real-time COmmunication System) originally provided an interface to ease the transition of electric drives from an analog to a digital world. By combining with Ethernet, the third-generation architecture—SERCOS-III—is in the process of evolving into a communication interface for all elements of a motion-control system.

In SERCOS-III, any standard TCP/IP messaging will be transmitted in a non-real-time time slot, in parallel to real-time data transfer needs of motion control, according to Interests Group SERCOS (IGS). The new interface will draw on the individual strengths of SERCOS and Ethernet—real-time mechanisms and “universal communication,” respectively—for added performance and lower cost.

Reducing cost “per node” is an important goal for this next-generation network. It’s being addressed by a search for lower cost hardware options, for example, a multi-protocol controller or a controller based on field-programmable gate arrays (FPGAs). This development phase is to be completed “in the next few months.” The intent is to take hardware costs down to the level of a typical analog interface.

Among features and enhancements of SERCOS-III are:

A double-ring structure to enable redundant data transfer capability in case of cable breakage;

Direct slave-to-slave communication (not currently available); and

Half the minimum cyclic time of the current SERCOS interface (31.25

One long-standing user of SERCOS technology is Bosch Rexroth Corp . Scott Hibbard, VP of technology, for the company’s Electric Drives and Controls business unit (Hoffman Estates, IL), told Control Engineering , “By incorporating field bus connectivity under the proven synchronous SERCOS protocol, SERCOS-III will give us a single bus that achieves the motion synchronization we require, with the flexibility to access all drive information over a variety of factory protocols.”

First SERCOS-III prototypes are expected in 2004, with first chip products coming in 2005, says SERCOS North America, the promotional alliance for the interface.

—Frank J. Bartos, executive editor, fbartos@reedbusiness.com