Networking Factories: Peripheral Vision

Cameras and other peripherals are beginning to use Ethernet and TCP/IP protocol, accelerating the move toward flat, single-network architectures in factories.

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Packaging glass wool insulation is not an easy task. The material is difficult to handle and there are many packaging styles, so several steps must be performed with a high degree of precision. With the growing interest in energy conservation, Norway’s Askim Mek Verksted (AMV) needed to improve the efficiency of its glass wool packaging lines.

When AMV upgraded its Battpacker control architecture in 2008, it needed a good networking architecture to ensure that the many sensors and valves on an eight-stage system all worked in harmony. EtherNet/IP, a protocol promulgated by ODVA (previously known as the Open DeviceNet Vendors Association), provided the necessary level of performance, along with the ability to link to a number of peripherals.

For example, plug-in pneumatic valves from components supplier Festo and some motors use Internet Protocols, operating without having to maintain constant contact with controllers. Allen-Bradley PanelView Plus human-machine interfaces (HMIs) and ControlLogix programmable logic controllers (PLCs), all from Milwaukee automation supplier Rockwell Automation Inc., are linked to the same network, keeping efficiency high.

That’s a growing trend as Ethernet takes over the industrial world. Peripherals as diverse as vision systems, bar code readers, printers, and radio frequency identification (RFID) scanners now often run transmission control protocol/Internet protocol (TCP/IP), once used only for backbone communications. Ethernet is expanding its reach by moving to higher speeds for products such as cameras, while trimming costs to pull in more low-cost products.

At the high end, the emergence of gigabit (Gbit) and 10 Gbit Ethernet lets a single network carry large volumes of video data without compromising the delivery of data packets needed for control and other functions. At the low end, the shift away from fieldbuses and other simple connections is driven in part because Ethernet connectivity is common on microcontrollers, which are being used in more products as the chips become less expensive.

“Most peripherals connected to Ethernet are intelligent. They need some intelligence to handle Ethernet communications, so they have enough for sensing process functions,” says Dan Holste, applications engineer at Banner Engineering Corp., a Minneapolis automation components supplier. “Vision systems and high-content sensors like those used for laser gauging have a lot of intelligence, either microprocessors or DSPs (digital signal processors).”

There’s high likelihood that a constantly growing number of peripherals will use Ethernet and TCP/IP instead of fieldbuses and other alternatives. A recent survey by automation supplier Turck Inc.’s Minneapolis-based network division found that 100 percent of the responding companies either use Ethernet or plan to adopt it this year. “I never thought I’d see 100 percent on any survey of industrial companies,” says Karie Daudt, senior product manager at Turck.

Speeding up

A fast network is critical for AMV as it transforms glass wool into palletized products that are ready to ship. Its Battpacker system has eight separate stages, each using several sensors and valves to move the raw materials through each step. Accuracy and repeatability are vital to minimize waste and maximize throughput. The network also helps make the machinery flexible enough to adapt to the many products and recipes used for Europe’s diverse markets.

AMV is hardly the only packager that’s adopted Ethernet for all of its hardware. This field is among the leaders in moving to flat architectures that eschew alternative communication schemes. “Packaging is one of the areas that has seen the value of moving the entire plant to one network,” says Mike Hannah, marketing manager for Rockwell Automation, in Mayfield Heights, Ohio.

Cameras are among the high-end peripherals taking advantage of Gigabit Ethernet and the GigE Vision variation developed by the Automated Imaging Association. It’s possible to link them to controllers using older versions of Ethernet, depending on the volume of data that goes onto the network. But whether cameras send raw video streams or simple pass-fail messages, Ethernet and IP protocols are gaining market share. “IP cameras are gaining popularity. There’s a strong advantage in linking them to Ethernet,” Hannah says.

As cameras see more use, the large volumes of video data often mean that system architects must look at the network schemes closely before setting them up. Video networks may have to be segmented so they don’t consume all the bandwidth. While engineers need to ensure that video arrives in time to be useful, they must also ensure that these video streams don’t degrade performance for important system commands. “If you’re going to do straight video, you don’t want it interfering with mission critical tasks,” says Carl Henning, deputy director at the Profibus Trade Organization, based in Scottsdale, Ariz.

Meeting demands

Ensuring that all commands arrive in a timely fashion can be a significant issue when Ethernet comes to the plant floor. Engineers must avoid the collisions that are no big deal in commercial applications but can skew equipment efficiency when they cause even brief delays on the plant floor.

Determining how long it will take messages to arrive is the key to creating systems that demand high precision. Some designers focus on high speed to get what’s called real-time performance, but true real-time performance is rarely needed and seldom achieved. “Outside of aerospace and the military, most people don’t truly achieve real time, they throw speed at the problem and hope it’s fast enough,” says Banner Engineering’s Holste.

There are a number of techniques for providing determinism in Ethernet, which wasn’t designed for time-sensitive applications. Several vendors have developed compatible variations that provide near-real-time performance or determinism with extremely short delays.

In applications that don’t have extremely tight timing requirements, adding more intelligence to the network can help reduce delay times. “There are a lot of ways to get determinism. One that we use is distributed control,” Daudt says. “Dumb I/O (input/output) nodes become smart nodes, hosting the I/O and reporting to PLCs. No matter what form of Ethernet you use, distributed control gives you complete control of the network and guarantees that you won’t lose data.”

For more demanding applications, plant managers can employ technologies that leverage Ethernet but upgrade its performance. Among them is the Common Industrial Protocol (CIP), which ensures that often-used industrial commands are run efficiently without hindering compatibility at any level of enterprise communications.

CIP, developed and managed by ODVA, has been enhanced for specific requirements such as safety. It also provides extensions for synchronization and motion, letting engineers quickly set up high-performance networks. Even fairly complex motion control applications can be run on Ethernet.

“With CIP Motion, all axes know where they need to be at a given time,” says Joe Lee, Rockwell’s product manager for EtherNet/IP. “CIP measures the delay that data packets see as they go through switches, for example, and the system compensates for delays. That keeps everyone on the same time base.”

Correctly configured networks can even handle two demanding tasks such as motion and vision simultaneously. “Some people say Ethernet is not deterministic enough for motion control, but we have applications where they’re doing motion and video on the same network without degradation,” Hannah says.

Not so fast

While some developers push the limits of Ethernet’s capability to ensure the prompt delivery of data, observers note that many industrial networks don’t really come close to those limits. Ethernet was designed to transmit large blocks of data, but most industrial systems send a large number of small data packets. That means many network segments don’t need the newer versions of Ethernet.
 
“Engineers always like technology, so they say they need gigabit speeds, but a lot of applications work better with 10-megabit (Mbit) Ethernet,” says Turck’s Daudt. “Industrial applications, especially peripherals, often transmit small packets that don’t need much bandwidth. 10/100 Ethernet is sufficient for 90 percent of industrial applications.”

Though many industrial devices are limited to 10 or 100 Mbit, she notes that companies that need Gbit data rates in some areas won’t suffer any penalties. All versions of Ethernet are backward compatible, so slower equipment can easily be attached to fast versions of Ethernet.

Though Ethernet’s performance can be improved by adding switches, some observers say that isn’t necessarily the best route to take. Switches make a lot of decisions and help prevent collisions on the network. But they also add complexity and cost, factors that most installers like to avoid. “The fewer switches you use, the better off you are,” Holste says.

While Ethernet can handle vision’s high-bandwidth requirements, running video on a common network isn’t always the best solution. Video files can easily total hundreds of Mbytes of data, so transferring a full image can consume a lot of bandwidth. Some developers say that if companies want to keep every image without using data compression, they may want to set up dedicated links. “If you want to store all the images in full resolution, you should probably look at a point-to-point Ethernet connection,” Holste says.

Not ubiquitous

Though more peripherals are moving to Ethernet, it’s nowhere near achieving a 100 percent takeover that eliminates any other communication scheme. Fieldbuses still offer lower costs for simple devices that don’t need much onboard intelligence. Many sensors, valves and other low-cost products don’t have Ethernet compatibility, so these lower-level architectures won’t fade away any time soon.

Another downside for Ethernet is that many factory-floor personnel are more comfortable with established industrial networks than with Ethernet. “One of the biggest issues is still that a lot of control engineers don’t have Ethernet backgrounds, so they’re not sure how to lay out networks to get the best performance,” Daudt says.

Fieldbuses such as Profibus, Modbus and DeviceNet have been upgraded with Ethernet versions, but the original versions are still seeing widespread usage. Low-cost solutions such as AS-Interface, which offers simplified wiring, are also maintaining solid market acceptance.

Another alternative comes from the personal computer world that made Ethernet a high-volume standard technology. Some vendors are starting to use the Universal Serial Bus (USB) to link sensors and other gear to controllers. The simplicity that made it sell at a clip of two billion units per year in the consumer world is also its lure in industrial environments.

USB 3.0, which is now shipping in consumer markets, pushes the data rate up to 3.2 Gbits per second. That’s far above the 480 Mbits/second for USB 2.0, which dominates current shipments. The slower rate will often be sufficient for industrial products, while the higher speed provides a path to the future. “USB’s data rates are increasing, and it has much better plug-and-play characteristics than Ethernet,” Holste says. “There’s a lot of confusion about getting Ethernet installed, there’s confusion about hubs, gateways and IP addresses. With USB, you just plug it in.”

Holste predicts that USB will see growing acceptance for sensor configuration, with less usage for communications. However, he notes that one limitation for USB is its cable lengths.

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