Machine Design

Motion Control - Sercos standard up for revision

Updates to include support for office and Fieldbus protocols.

Sercos standard up for revision

The next-generation Sercos interface is under development. The Interest Group Sercos (IGS) announced at this year's Hannover Fair in Hannover, Germany, the launch of Next Generation Sercos (NGS) which aims in the direction of using industrial Ethernet.

The IGS plans to make several improvements including simplifying integration by supporting office and fieldbus communication protocols such as TCP/IP, Profibus, and CIP; increasing data-transmission speeds; defining specific motion-control profiles to enhance interoperability of control and drive components; and reducing cost. The standard is being developed by member companies of the IGS including representatives from Bosch Rexroth AG and Rockwell Automation and will be backward compatible with previous versions of the standard.

Sercos was originally developed as a digital drive interface during the late 80s by an industrial consortium of German electrical standards associations and machine-tool builders. The first generation had speeds of 2 and 4 Mbits/sec and was mainly used in high-performance machine-tool applications. In 1995, Sercos was approved as international standard IEC 61491. In 1999, work on second-generation Sercos started which boosted transmission speeds to 8 and 16 Mbits/sec and extended the asynchronous data-service channel.

Sercos features a collision-free time-division-multiplex-access (TDMA) protocol which ensures real-time performance. For instance, up to 40 motion axes can be controlled and synchronized in real-time using a cycle time of 1 msec with jitter below 1 µsec.

Over the years, Sercos has moved beyond being a specialized drive interface to a universal motion-control interface. Not only drives but more and more decentralized I/O stations are connected to the bus. For many stand-alone machines, this eliminates the need for an additional fieldbus.

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