Pneumatics make the bus connection

DN Staff

November 18, 1996

9 Min Read
Pneumatics make the bus connection

When a beer manufacturer recently opened a plant in Brazil, its first order of business was to network the manufacturing operation. Technicians installed more than a hundred "smart" pneumatic valve manifolds, then wired them to a central nervous system that ran through the plant's spine. Engineers conservatively estimate that the networking technique saved them from installing more than 2,000 separate wires. More important, it supplied them with information they'd never had previously.

"If a valve bank goes down, it's readily apparent from the control room," notes Mike Leffler, electropneumatic product manager for Schrader Bellows, the Ohio-based supplier of many of the brewery's manifolds. "The system diagnostics have the ability to tell the user, 'Node five, valve four has a shorted solenoid coil.' It drastically reduces downtime."

Such tales from the manufacturing front have grown increasingly common in recent years as manufacturers struggle with the complexities of global competition and shorter lead times. To compete, against low-cost, Third World labor, many must streamline their assembly lines, adapt quickly to product changes, and re-tool faster than ever before. In short, many firms now face an almost impossible manufacturing task.

For an increasing number, the solution to the problems lies in the plant's "central nervous system." Known as the fieldbus, it offers the ability to simplify the design and assembly of machinery employed on the factory floor. It can reduce wiring, simplify plumbing, and remove the mystery from the linkage of pneumatics and electronics.

The key to the new technology lies in the development of manifolds, sensors, and other devices that use on-board electronics for control. "This is one of the most exciting and important developments in motion control," notes Frank Latino, electronic products engineer for Festo Corp., Hauppauge, NY. "Adding communication abilities to the valve manifolds is revolutionizing industry."

Driven by new protocols. The prime driver behind the new simplicity stems from the emergence of powerful bus-networking technologies introduced by a wide array of companies. Such protocols as DeviceNet, Smart Distributed System, Actuator Sensor Interface (ASI), Seriplex(R), INTERBUS-S, and SERCOS have provided users with the ability to change the face of pneumatic motion control.

Using fieldbus technology, a valve bank can be controlled by a pair of wires connected to a personal computer or a programmable logic controller (PLC). This new design trend has vastly simplified the process of carrying out sequential operations on the factory floor. If, for example, a process requires a series of actuators to position, clamp, and weld some parts, all of the operations can be controlled by sending signals from the PC to a valve stack. Such manufacturers as Festo, Schrader Bellows (Akron, OH), SMC Pneumatics (Indianapolis, IN), Crouzet Corp. (Carrollton, TX), Parker Pneumatics (Richland, MI), Numatics Inc. (Highland, MI), and many others, make fieldbus-compatible manifolds or valves.

For now, most of the cost advantages are realized through labor and materials savings. At the Brazilian brewery, for example, conventional pneumatic manifolds would employ between 13 and 24 wires each. Those wires are replaced by two power cables and a communication wire at each manifold. That alone amounts to a 10:1 wiring reduction.

Wiring reduction, however, isn't the only issue. Many manufacturers also see reductions in such components as junction boxes, terminal strips, interconnects, wiring labels, and cable-support structures. In contrast, the fieldbus manifold incorporates only one extra component: an interface card that bolts onto the end of the manifold.

By reducing or eliminating all of those components, manufacturers say that there are also significant labor savings. "If you use conventional techniques, you have to face the reality of hiring an electrician at roughly $50 per hour to install the conduit, pull hundreds of wires through, and terminate them," Leffler says. "When you can eliminate all that conduit and labor, you can achieve amazing cost savings."

Design simplicity. For OEM engineers, the fieldbus trend also simplifies design and assembly of machinery. That's particularly true for engineers who build a machine in their plant, disassemble it for shipping, then re-assemble it at the job site. Using conventional pneumatic design techniques, each valve would be wired to its own relay, and each relay would have to be re-wired during re-assembly. On big machines, such configurations lead to wiring headaches.

By employing specially designed electronic fieldbus modules at every valve stack, however, engineers can now eliminate those wiring problems. "After a machine goes through final approval at the manufacturer, it often has to be dismantled before it is sent to the customer, and then re-assembled," explains Logan Mathis, manager of the engineering division for Ross Controls, and chairman of the National Fluid Power Association's Pneumatics Section. "That means you have to disconnect all those solenoids from the valves, then re-connect them. All of these fieldbus manifolds are prewired, so you no longer need to worry about all that."

Mathis says that machine designers also can benefit from increased flexibility by employing fieldbus technology. Using a proximity switch on a fieldbus network, they can now receive positioning feedback for their machines. "You could take the output from the proximity switch, feed it back through the fieldbus network, and then know the actuator is in the right position." Key applications for such technology include welding machinery. Using it, a welding system could "know" whether the weld material is correctly placed in its fixture.

New wrinkles. At Festo, engineers have taken fieldbus technology in another direction. Instead of ganging large banks of valves together, they have de-centralized the fieldbus concept by breaking their valve manifolds into individual modules. Festo's system, known as the Compact Performance or CP concept, disassembles the traditional manifold into a valve module, sensor I/O module, and bus interface module. Each set of modules is part of a node that is connected by the fieldbus line back to the PC or PLC. Nodes are joined by conventional twisted-pair wire. Other pneumatic component manufacturers, including Parker Hannifin, are said to be working on similar systems.

The advantage of the concept is that it enables machine designers to move control modules closer to actuators. As a result, designers no longer must run long plumbing lines from the valve manifold to the component, whether it's a cylinder, clamp, or motor. "When you put the control device close to the actuator, you simplify the system," says Lou Bruska of Parker Hannifin. "You also keep the designers on both sides happy. The control engineer has an organized way of dealing with the components, and the mechanical engineer has a way to make the machine more efficient."

The concept is particularly well-suited to assembly lines, conveyors, and process systems that employ valves at intervals. There, it not only offers convenience, but improved performance. The reason: Long airlines must exhaust air prior to performing their next assigned task. To exhaust the airline, users must either employ a larger valve with larger orifices, or accept slower performance.

Festo engineers say that the need for the decentralized concept was prompted by discussions with machine designers. "If you work with machine designers, you see that a conventional manifold structure works in many cases, but not all cases," Latino says. "It's an advantage to be able to decentralize these blocks when your actuators are spaced out all over the machine."

Some pneumatic system manufacturers have also added their own wrinkles to the growing number of pneumatic fieldbus products. Among those is IMI Norgren Inc., Littleton, CO. Using the firm's Nugget 120 valves in a configuration that the company has dubbed the "circuit islands," Norgren engineers have added a host of features to valve manifold technology. Instead of having all valves in a manifold operate at equal pressures and with identical switching functions, Norgren's circuit-island concept offers such features as multi-pressure systems, twin supply valves, double flow outlets, vacuum supply, dual-speed cylinders, and alternating forces on cylinders.

Acceptance on the rise. Among users, pneumatics manufacturers report varying levels of acceptance of the technology. Some customers are taking a wait-and-see approach, in hopes that one fieldbus protocol is selected as a standard.

Some manufacturers report that customers are trying out fieldbus systems in small increments. Numatics, for example, has installed fieldbus manifolds for spot welding of automotive frames at a General Motors plant in Baltimore. The valve manifolds supply air pressure for actuators that locate and clamp the parts. They also supply air for the weld guns.

The GM plant employs nine pneumatic manifolds, each with six to eight valves. The fieldbus units eliminate about 10 wires per manifold, but that wasn't the prime motivator behind their use. "They wanted to obtain some experience with networks and see how well they perform," says Tom Zuchowski, a product manager for Numatics. "They did it to prove the viability of networks for potentially broader application."

Zuchowski adds that the network has had almost no downtime during one year of use. He says the company also has applied the pneumatic fieldbus technology in food processing and automated assembly systems.

Cost reduction and flexibility. Whatever type of configuration is employed, industry engineers agree that fieldbus technology promotes simplicity. On big machines, which often incorporate hundreds of pneumatic valves, each valve no longer needs to be wired to its own relay. Users estimate that the technology cuts wiring costs by 30% or more. It also offers simpler assembly and better diagnostics.

Eventually, the benefits are expected to go much farther. "As bus systems become more and more intelligent, the biggest benefit will be additional information to the user," Zuchowski explains. "Ultimately, that information will help reduce downtime, prevent problems from occurring, and increase productivity."

For manufacturers, the bottom line is market competitiveness. "Today, manufacturers are not only looking for cost reduction, they are looking for flexibility," says Latino. "This technology gives them the flexibility they need to be competitive."

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