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Air control takes the bus
Operating valves through a network brings productivity gains.
Paul Sharke -- Design News, February 6, 2006
Field bus-based pneumatic controls from Bosch Rexroth are helping RRR Development Co.’s tire making machines to confirm valve function and pressures critical to tire building, according to RRR sales and engineering vp, Bob Irwin. The company recently adapted the controls system and produced a machine from it that no longer resembles a “50 arm octopus” with cabling and air lines running everywhere, Irwin says.
Dubbed DDL for Drive and Diagnostic Link, the pneumatic controls “know when a valve coil is starting to lose its magnetic field,” says Ed Bickel, a B-R district sales manager. By sensing minute changes in a coil’s energy draw, the system looks for failure “flukes” –those falling outside the realm ofpreventive maintenance predictions—which could throw the quality of a product run into question.
Most buyers of RRR machines wouldn’t pay for feedback from a pressure regulator any more than they’d pay an operator to stand around all day watching the gauge, Irwin says. But the field bus controls deliver that for nothing, he says.
“Say a header supplying a machine has a dip,” he suggests. “The product may have quality defects” as a result, he says.
The system drops modules onto the field bus, each supporting up to 128 inputs and outputs depending on bus protocol, Bickel explains. Those inputs and outputs can be spread out among 13 participants, including the master. A huge benefit is the system’s ability to handle analog signals (4 in and 4 out) to accommodate sensors from load cells to thermostats that give gradient feedback.
The system takes advantage of the extra bits that certain bus protocols like Profibus, Ethernet, and Controlnet have to carry more “boxcars” of data on their serial string “trains,” as Bickel puts it.
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| Tire making equipment uses pneumatic valves controlled over the field bus. |
“We told the operators that the Ethernet system was similar to email,”Irwin says. “Our ISO 1 valves could only receive commands. The Ethernet ISO 2 valves can receive commands and immediately send back feedback concerning their health,” he says. “On the networked system, valve health is interrogated prior to the initiation of each critical operation,” Irwin explains. Maintenance can be scheduled during downtime, rather than allowing production to be interrupted unexpectedly.
Another place where the system is seeing play is food and beverage operations where clean in place, or CIP, is the rule of the day. The system can monitor the actuation of three-way valves to make sure they close upstream outlets fast enough to prevent cleaning solutions from migrating “into the marinara vats,” for instance.
Web resources
To read more about the DDL system from Bosch Rexroth, click here
Learn more about RRR Development by visiting the company’s website at http://www.rrrdev.com
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