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Profibus promises 150-axis Ethernet-based motion control

01 April, 2003

Profibus promises 150-axis Ethernet-based motion control

Profibus International (PI) is developing a high-performance, real-time communications technology that, it claims, will be able to control motion systems of up to 150 axes, with a cycle time of 1ms and a jitter of less than 1µs. PI says that the system will cope with the most demanding motion applications, and will be more powerful than any existing technology — even motion-specific proprietary protocols — as well as being compatible with the TCP/IP standard.

But users will probably have to wait until mid-2005 to take advantage of the new technology, which PI calls "isochrone real-time" (IRT). The development will be based on the current "soft real-time" (SRT) technology incorporated in Profinet V2, runtime versions of which will be available as downloads from the Profibus Web site starting in June 2003.

Using SRT, Profinet V2 can deliver cycle times of 5—10ms. PI describes it as "the first step towards a powerful real-time solution that … completely satisfies the demands of factory automation and is fully compatible with the TCP/IP standard".

To allow simple and quick development of IRT products, PI is working on a new switching technology in the form of a four-port real-time ASIC (application-specific integrated circuit). Samples of this chip should be available by mid-2004.

The chip will allow developers to build interrupt-free, redundant designs for complex applications at a low cost. The aim is to use the Profibus motion control profile largely unchanged in the Profinet V3 implementation, thus protecting the investment of suppliers and end-users.

The IRT technology is based on 100Mb/s switched Ethernet technology, but it enhances standard Ethernet communications by splitting the capacity of an Ethernet line into two channels — an open channel, and a deterministic channel with precise time synchronisation. The open channel carries standard communications in accordance with the IEE 802.3, while the deterministic channel transfers cyclic, high-speed telegrams.

Siemens is playing a key role in developing the IRT technology. Speaking in Germany recently, Helmut Gierse, president of the company`s Automation and Drives group, hailed the technology as "a giant step forward". He said that its big advantage will be that the real-time extensions will have no effect on the Ethernet`s standard functions. It will be possible for users to access device data via standard TCP/IP communications without interfering with the clocked control.

Gierse added that there were good reasons for the long wait before the technology goes on sale. "We are entering unknown territory with this technology," he pointed out. This would mean facing the risks that can appear "whenever such ground-breaking technologies are being developed". The developers were therefore taking "a conservative approach to planning and announcing the project".

Another factor was that Siemens and PI want to send a signal to users that "it is perfectly safe for them to invest in Profinet now as they will be able to add new functions at a later date without running the risk of a technology break," Gierse said.

A third delaying factor was that because the development is a joint effort involving various Profibus supporters, it will take time to gather their ideas and to incorporate them into the new technology.

If the IRT technology lives up to Siemens` and PI`s promises, its effects could be far-reaching. PI`s claims "amount to a quantum leap in industrial Ethernet performance," says David Humphrey, a senior analyst with the ARC Advisory Group. "If PI can deliver on these claims, customers will benefit from an Ethernet-based device bus that is scalable not just from the shop-floor to the top-floor, but also has the performance depth to meet the demanding needs of motion control. The announcement will certainly give other network solutions the jitters."

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