Solving Slip Ring Hassles

The application of wireless technology to packaging is still in its infancy, but some success stories have emerged from among the early adopters.

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One that Milwaukee-based vendor Rockwell Automation Inc. likes to point to concerns a 16-station rotary powder filler and an electrical slip ring. Control for this filling machine is provided by 16 Rockwell CompactLogix controllers, one for each of the net-weigh filling stations, with overall supervision provided by a central ControLogix controller.

An electrical slip ring provided the electromechanical connection needed to allow the ControLogix supervisor to communicate with the 16 CompactLogix controllers. The slip ring consisted of a shaft-mounted conductive ring. Fixed contacts or brushes contacted the ring, transferring the electrical signals. Signals were then transferred via Ethernet connection.

“Slip rings are good candidates for replacement by wireless technology,” says Cliff Whitehead, manager, strategic applications, for Rockwell. “These are expensive, costing as much as $20,000 to $30,000 each, and because they are mechanical devices subject to constant movement, they are susceptible to failure. If the slip ring fails, the machine stops, and chances are you don’t have another one in stock, so there can be a significant delay in getting the device replaced.” In addition, packets of data were sometimes dropped, requiring retransmission that consumed time and bandwidth.

The packager addressed the problem by switching to wireless. The company replaced the slip ring with 17 RadioLinx Industrial Hotspot Ethernet radios from ProSoft Technology Inc., Bakersfield, Calif. One radio was placed at each of the 16 filling stations and one at the central ControLogix controller. The data is now transmitted wirelessly between the central controller and the remote controllers. Results have included better, more reliable throughput, thanks to fewer dropped data packets; reduced maintenance; less wiring; and, of course, that expensive slip ring will not need to be replaced.

 In the future, says Whitehead, we are going to see more rotary filler slip rings eliminated by having their communications functionality replaced by wireless technology. This, he says, is part of a trend in which “wireless technology is being pushed out further and further toward the end node devices, such as a sensor, a temperature probe, or perhaps someday even an actuator—probably not a high-speed application because latency is one of the technical challenges that faces wireless right now,” Whitehead concedes. “However,” he adds. “I can foresee an application in packaging where you’ve got a photo sensor or some sort of mechanical switch on a carton manifold to sense low content, let’s say, and wirelessly send a replenishment signal.”

Related Feature - Wireless Technology in Packaging: The Art of the Possible?
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