Several efforts in Ethernet development, plus add-on technologies to the standard, are making it possible for Ethernet gear to be deployed in factory networks, where LAN gear controls the precise movements and actions of machine tools, and a dropped packet or network delay can be costly.
One emerging standard is IEEE 1588, which lets networked Ethernet gear synchronise internal clocks according to a network master clock. Another multivendor technology effort, called Ethernet Powerlink, uses a standard Layer 2 Ethernet protocol along with a time stamp that operates similarly to TDM technology, where data flows are allotted specific, microsecond time slots for transmission. This type of technology eliminates packet collisions, which can cause data to be resent on shared Ethernet LANs; it also solves network latency involved with packet buffering in switched Ethernet.
Manufacturers are looking at control protocols that run on Ethernet networks to cut costs and bring the management of factory processes into the domain of an overall enterprise IP network.
"If everything has an IP address, then you know the status of any piece of machinery or a system" across a manufacturing enterprise, says Bob Parker, an analyst with IDC who tracks IT trends in manufacturing. "Looking at standard, off-the-shelf devices makes sense," for deploying in factory networks. "It's like owning a boat; anything you buy for the boat that has 'marine' in front of the name costs twice as much. It's the same with industrial [IT products]. Buying something 'industrial' will cost twice as much."
Although Ethernet latencies are measured in fractions of a second, they are unacceptable to precision industrial processes, where machines can receive hundreds of control instructions in seconds. Missing one command could be disastrous, says Markus Sandhoefner, a marketer with B&R Industrial Automation, which makes an Ethernet Powerlink software stack for standard network gear.
"Ethernet is a great, low-cost technology," Sandhoefner says, "but it's not the most deterministic. If you have two real-time messages waiting in an [Ethernet] switch queue, you'll be in trouble if you're running applications such as motion control."
B&R is part of the Ethernet Powerlink Standards Group, which includes 165 vendors of automation and control products. The group's aim is to migrate legacy protocols such as ModBus used in factory floors to Ethernet-based technology.
Eagle Manufacturing recently deployed Ethernet Powerlink gear from B&R to control its line of machine tool equipment used to manufacture automobile components - specifically, car window frames and seals.
Machines on this line can change components on the fly to process materials for several vehicle types, says Brent Short, president of the company. This process lets the small component maker create a range of products without stopping production to refit equipment.
Time-sensitive applications, such as VoIP or video, can falter when packet delays rise above 100ms. With Eagle's machines cutting materials at precisely eight thousandths of a second and running at 50 feet per second, the delay of control messages sent to the equipment must be about 800 microsec (800 millionths of a second). The Ethernet Powerlink network provides preciseness.
Another factor in plant networks is time synchronisation of network- and computer-controlled machinery. Like Ethernet Powerlink, IEEE 1588 uses time-stamping protocols to ensure that clocks are synchronised.
One vendor driving IEEE 1588 is Intel, which makes network processors with integrated time-stamping technology into Ethernet controllers and switch silicon. The use of IEEE 1588 in standards-based network gear in factories will help manufactures cut costs by eliminating expensive, custom-made or proprietary industrial automation communication technologies, says Puneet Sharma, technical marketing engineer for Intel's Digital Enterprise Group. But to gain the reliability of the network technologies that Ethernet may replace, something extra must be added.
"Time-synchronisation protocols, such as Network Time Protocol, are not reliable enough and do not provide sufficient resolution to be useful for industrial automation applications," Sharma writes in an IEEE 1588 application report.
That means IEEE 1588 defined technology would need to run in network gear along with standard 802.3 Ethernet and a TCP/IP stack. This combination would let a Layer 2/3 Ethernet LAN act as a precision-control network, where factory floor machines can be controlled. Ethernet Powerlink Version 3 is set to be released later this year.
Find your next job with techworld jobs