Automation engineers visiting the SPS/IPC/DRIVES show held Novemeber 25-27 in Nuremburg, Germany got their first impressions of a new fieldbus war heating up. This time it's ultra high-speed fieldbuses based on Ethernet that are in the spotlight, with promises of microsecond-level response times. Three control manufacturers—Beckhoff, B&R Automation, and Siemens A&D—made announcements.
Why the push for high speeds? Synchronizing servo drives in packaging machines and rotary presses needs that level of response, which is why SERCOS was created in the first place. "But it's not just about synchronizing servo drives," said Gerd Hoppe, VP of Beckhoff. "If you can shave milliseconds off any machine cycle in continuous production, at the end of the day, you'll have more production." Mile-long conveyor belts also will benefit from the new Ethernet buses, he says, because standard industrial fieldbuses can't extend for great distances.
One universal standard?
There are already a number of "standard" Ethernets for the factory floor, including Rockwell's EtherNet/IP, Siemens' PROFInet, Schneider Electric's Modbus/TCP, and IDA's (Interface for Distributed Automation) NDDS. And rumored at SPS: Bosch Rexroth will recast SERCOS on a 100 Mbyte Ethernet framework.
What became apparent at SPS was the competition for a new class of high-speed factory automation Ethernet: Buses capable of transmitting and receiving data in microseconds, so that dozens, or even hundreds, of servo drives could be synchronized to sub-millisecond levels. The fastest programmable controllers today work to close their operating loops in about 5-10 milliseconds, considered too slow for motion control.
If time-to-market means anything, then B&R Automation clearly has the biggest lead. After announcing Powerlink two years ago, it has installed 8,000 nodes, organized the Ethernet Powerlink Standardization Group (EPSG), and has attracted some significant players to its side, including Lenze and Baldor Electric.
"Ours is the only implementation that uses standard Ethernet hardware throughout," said Andreas Pfeiffer, the B&R member of EPSG, who was obliquely referring to the ASIC chips that the other two, Beckhoff and Siemens, will require to build their systems. "We're also the only group with a complete spec."
ESPG chose the SPS show to launch version 2 of the specification, which embraces the CANopen protocols, and makes it possible for machine builders to mix CAN networks with Powerlink segments.
If company size means anything, then Siemens A&D will likely dominate the market with its PROFInet, a completely new protocol that leverages Ethernet, XML, and Microsoft component technology. The third incarnation, PROFInet V3 introduces "hard" real-time responses (see sidebar).
But Siemens has a problem: It announced the chip architecture for its Ethernet ASIC switch at SPS, and won't have samples needed to implement V3 until late 2004 with product unlikely to be seen until 2005.
The Ethernet switches, called ERTEC (Enhanced Real-Time Ethernet Controller) will be key to Siemens' strategy. "We want to bring real-time control to standard Ethernet, but not reduce the functionality," said Antonius Boller, product manager of Simatic Net.
High Speed: Beckhoff Ultra Highspeed I/O reads and inserts data into Ethernet (EtherCat) telegrams at 100 Mbit/sec speed but requires a simple ASIC in each module.
The plan is to embed the switches into automation devices such as MMIs, PLCs, motion controllers, and drives to let them automatically connect to PROFInet. A branch of PROFInet is then constructed by chaining together the devices, with spare ports for expansion.
The automation world will also be looking at Beckhoff's EtherCAT technology which is the fastest of the three: it scans thousands of I/O in a few microseconds.
But Beckhoff is still busy signing up partners and polishing off its specification. EtherCAT will also require special I/O ASICs. "We will publish the protocol, request comments from our partners in the EtherCAT Technology Group, and publish the final specification in May of 2004," says Gerd Hoppe. "We'll have our ASICs by the end of the year." Beckhoff says it will listen to its partners, but will take responsibility and drive the process, unlike open-standard fieldbus organizations that take years to come to decisions.