Motion Control-in-a-Box

Lee Stephens calls motion control and logic on a motor the “extreme end of distributed intelligence.”

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But the Radford, Va.-based motion-control engineer with vendor Danaher Motion (www.danahermotion.com), of Wood Dale, Ill., sees one real benefit of this combination that he labels motion control-in-a-box: reduced power and feedback cabling. This is particularly important with moving applications such as motors located on moving members of a robot, he says. “With a typical distributed-intelligence system, at least 60 percent of the cable volume would be reduced,” he estimates.

 

And less cable equals smaller footprint. For example, Bosch-Rexroth Corp.’s (www.boschrexroth-us.com) IndraDrive Mi product combines control electronics and servo motor into a single, highly compact drive unit. This reduces the drive’s size by 50 percent, compared to traditional servo solutions, says Rami Al-Ashqar, product manager in Bosch Rexroth’s Electric Drives and Controls Group in Hoffman Estates, Ill. “The unit’s design also combines the power and SERCOS (Serial Real-time Communication System) communication links into a single cable.”

Get outta there

In addition, cabinet space is also reduced, points out Carl Owens, application engineer with the Production Machines/Drive Technologies Group within vendor Siemens Energy & Automation Inc. (www.sea.siemens.com), in Norcross, Ga. “Our end-users are typically used to large control cabinets, which sometimes are mounted next to the machine,” Owens observes. But he’s seen demand increase in the past two years for decentralized systems, Owens adds, because “people realize there’s a cost savings” due getting out of the cabinet.

“We want to reduce panel size and floor space—and take as much of the motor control as possible and put it near to, or on the motor,” adds Darlene Acklin, a product manager for Lyman, S.C.-based SEW-Eurodrive USA’s (www.seweurodrive.com) decentralized products group, another vendor in the space. That means taking overload, brake control and variable-frequency drives, as well as communications for any fieldbus, out of the control cabinet.

These decentralized systems also provide more potential input/output (I/O). Jan Lindholm, SEW-Eurodrive industry account manager, adds that with his company’s current generation of Movofit field distributors—or decentralized control units—up to 16 I/O are possible with each unit.

End-users “see that equipment costs and capital costs are less. They also see that installation time is shorter,” Lindholm observes. For example, for a line of 50 motors and a 600-foot conveyor belt, he estimates that a centralized system would need approximately 9,700 feet of power cable. “But if you have a decentralized system, you need only about 1,200 feet.” To install the centralized drives would require almost 300 hours of labor, he approximates. “But for the decentralized system, you’d need about 40 hours.”

Putting motion control and logic on a motor also enables original equipment manufacturers to pre-commission the motors in the warehouse, Lindholm points out.

But at least one potential downside exists for motion control-in-a-box: reliability and maintenance. “You [may] have heat sources—the motion controller and the motor—coupled in the same housing. So, temperature becomes a critical parameter,” warns Matheus Bulho, product marketing manager in Rockwell Automation Inc.’s (www.rockwellautomation.com) Kinetix Motion Control Group, in Mequon, Wis. To overcome that problem, the motor-plus-motion-control-in-a-box unit may have to be a few times larger in volume than just a motor tethered to a central, air-conditioned control cabinet. And because of the excessive heat potential in the decentralized instance, mean time between failure (MTBF) is “typically higher than for the cabinet,” Bulho states.

Regardless, outside of the automotive industry, U.S. companies in industries such as food and beverage, as well as materials handling, are just beginning to adopt decentralized technology, Lindholm says. 

C. Kenna Amos, ckamosjr@earthlink.net, is an Automation World Contributing Editor

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