Potent brew

Mixing an Allen-Bradley ControlLogix controller with DeviceNet communications helps Lipton reduce downtime and engineering costs

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Known to botanists as camellia sinensis, the tea plant bears no resemblance to the leaves you steep in boiling water and serve with crumpets, jam and sympathy. Five to six feet tall, the tea plant is an evergreen with small, apple blossom-esque buds. To turn this shrub into a steaming cup of Earl Grey is a complex process that involves harvesting, withering, rolling, fermenting and drying the plant's leaves. And that's just the beginning.

 

Most commercial teas are a blend of leaves from various plants, and also include other dried herbs, fruits, etc. Mixing complementary flavors allows companies to create teas that are aromatic and delicious. This is where Lipton has made its mark. Owned by Unilever, Lipton produces the world's most popular and widely sipped teas. Its products can be found on store shelves in more than 100 countries.

 

To keep up with customer demand, Lipton recently upgraded a conveyor chassis at its manufacturing facility in Suffolk, Va. Featuring equipment from Rockwell Automation and its encompass partner SMC Corp., the new conveyor system cost significantly less than a traditional, hardwired installation, and it took less time to bring online. Most importantly, it's a vast improvement over the tangle of wires and conduit that was previously in place.

 

"Since start-up, there have been no snags," says Keith Rock, lead engineer at the Lipton plant in Suffolk. "The new system has been so effective we're using it as a blueprint for upgrading three similar applications."

 

In the bag

Saying that you drink tea is as nebulous as saying you live on Earth. That's because there are several varieties of tea -- black, green, herbal and instant -- and thousands of options within each category. This is the reason behind Lipton's vast catalog, which ranges from blackberry-infused leaves to lemon ginseng green tea. And it helps give Lipton a global turnover of almost $2 billion.

 

The Suffolk facility primarily packages black teas. And since tea bags don't grow on trees, Lipton has a multi-step process in place to make sure its customers' cups are always full. To start, trucks arrive at the Lipton facility to deliver dried and shredded leaves from tea plantations around the world. The leaves are then blended, depending on the production run and specific recipe. Next, the tea blend is transferred to the plant's packaging machines that produce double chamber tea bags.

 

Feed the machines

Although the process begins and ends on the bed of a truck, there are many activities in- between that Lipton employees must coordinate so the tea can make the trek from one end of the facility to the other. Problems in any area can make the entire operation resemble a Los Angeles freeway during rush hour. Unfortunately, due to a matrix of canvas-belt conveyors, this was becoming an all-too-common occurrence.

 

These conveyors (a conveyor chassis collectively) transport empty boxes to the machines and transport full boxes from the machines for further processing.  This can include a complex assortment of carton sizes.

 

 "That's why it's a matrix of conveyors rather than one belt spitting boxes onto 40 machines," Rock says. "We have to make sure no machine is starving."

 

The challenge is to get the right box to the right packaging machine at the right time. Otherwise, the packaging machines sit idle, throughput lags and orders are delayed.

 

Break it down

Along with the conveyor track, the old system was comprised of metal diverters that pushed empty boxes to the appropriate machines and brake paddles that controlled the flow of boxes. Lipton also placed photo eyes before each diverter or brake. These eyes would sense cartons traveling through the chassis and manage the flow of cartons to individual machines.

 

This architecture had a number of problems. First, it was hardwired, resulting in large volumes of wire with intermediate connections, making installation and maintenance a time-consuming nuisance.

 

In addition, the system had evolved significantly over time, making it unwieldy. "If we had to add a brake or gate, a technician would just wire it in with a photo eye," Rock explains. "But the electrical schemes were not well documented. Soon, it was impossible to know how loaded individual circuits were. All in all, it was a sprawling, hardwired mess."

 

As documentation slipped, so did other practices. Many of the photo eyes were connected in the conveyor trough with wire nuts or similar hardware -- not an ideal, textbook routine. And the photo eyes themselves were problematic. Because they were of the "timed" variety, each eye had a dial that technicians could set to manipulate the time between it seeing a carton and sending a message. Essentially, all the logic was contained in the individual eyes. That made adjustments easy , sometimes too easy. Over time, the photo eye settings were neither consistent nor well documented. 

 

All of these factors lead to an increasingly unstable system. Downtime was on the rise. And when equipment did malfunction, troubleshooting was anything but trouble-free. A maintenance person would head to the plant floor, locate the affected area, pinpoint the problem and deduce the cause. "At this point, we had to hope that the problem wasn't in the 120 volt circuit, because the wiring was so intertwined," Rock recalls. One failed sensor could exhibit symptoms in multiple places."

 

Because of the hardwired snarl, the time it took to get the conveyor back in working order varied wildly. A technician could locate and fix the problem in five minutes. Or it could take well over an hour. There was no consistency and Lipton confronted problems with fingers crossed.

 

"There never was a breaking point, just an accumulation of recurring headaches," Rock says. "We knew it shouldn't take more than an hour to find and solve problems. And this was occurring on a weekly basis."

 

With the obstacles defined, Lipton set several goals for the project. In brief, the company wanted to simplify the wiring scheme, centralize the logic and control for the field devices, and, in the process, reduce downtime.

 

Simplify, centralize

Before the upgrade was underway, Lipton knew it wanted to build the new conveyor system around a programmable controller and digital communications. So Rock set his sights on technologies that were modern, but proven.

 

"We didn't want hardware with single-digit serial numbers installed in the plant." Rock adds. "At the same time, legacy equipment was out of the question." After considerable research, Lipton found the necessary balance with an Allen-Bradley ControlLogix programmable controller and open DeviceNet networks.

 

Today, individual SMC solenoid blocks contain 12 to 20 photo eyes (inputs) and eight to 16 outputs, each controlling conveyors supporting two machines. The solenoid blocks feature several input adapters that allow Lipton to connect the photo eyes using simple twist-on cords. When a block receives a signal from one of the attached eyes, it turns on a stream of air that drives a nearby cylinder , connected to the block with poly-flow tubing. In turn, the cylinder pushes a squeeze brake (similar to an automobile brake) that holds and/or directs the boxes from the carton former.

 

Lipton ties the solenoid blocks to the ControlLogix controller with a DeviceNet network. Because of its open, digital design, DeviceNet can link more than 60 blocks to the controller. And the controller can support multiple DeviceNet connections. Along with the twist cords and poly tubing, DeviceNet has eliminated traditional wiring from this section of the facility. There are power supply cabinets and one cabinet for the controller. That's it.

 

"DeviceNet makes the system incredibly flexible," Rock says. "Adding components only takes a few hours, and the cost per input is less than $50. That's at least 50 percent less than a traditional I/O solution." The network also is a boon to troubleshooting because Lipton can use it to gather diagnostic information and isolate problems. Pinpointing and swapping a faulty device now takes minutes.

 

Another benefit is that Lipton can manage the system exclusively from the ControlLogix controller. Programmed using RSLogix 5000 software from Rockwell Software, all the logic for the photo eyes and solenoid blocks is stored in the controller. As a result, technicians make adjustments and monitor all network activity from a central platform. They have the ability to restrict access to parts of the system as well. This gives the company an accurate record of what changes are made, by whom and for what reason.

 

"Basically, the system is self-documenting. ControlLogix makes it easy to keep track of what's happening in the field," Rock says.

 

In addition, the ControlLogix controller is networked , via an EtherNet/IP connection and Ethernet switch from Nortel , to the 40 Allen-Bradley SLC 5/05 controllers that run the packaging machines. The main purpose of this link is to enable and disable the flow of empty cartons. There are times, for example, when Lipton must take a machine off-line, which means it can't receive cartons. To make sure this occurs (or doesn't, to be precise), the SLC controller for that particular machine communicates its status to the ControlLogix unit.

 

In addition, the Allen-Bradley PanelView 600 operator terminals tied to each SLC 5/05 now double as an interface to the conveyor system. This helps leverage the investment in PanelView technology already made at each machine.

 

"Although the Ethernet handshake wasn't essential, it has proven very beneficial," Rock says. "And it's a feature that wouldn't have been possible with many of the other control options we explored."

 

and reduce downtime

The ControlLogix system has been in place more than six months, and there have been no problems aside from typical start-up bugs. And "no problems" equals "no downtime" -- a dramatic shift from the previous conveyor chassis. "Everyone has confidence that when we encounter difficulties, the system can be repaired and brought back online quickly," Rock adds.

 

Along with negligible downtime, Lipton saved time and money assembling the system. Compared to traditional hard-wired installations, Lipton saw a 50 percent savings in labor. This ultimately helped the company reduce the cost of commissioning and assembling a control system by one-third. 

 

Given the favorable outcome, Lipton plans to duplicate the ControlLogix-DeviceNet architecture for three similar conveyors. Because of the efforts made in specifying the right equipment, Lipton will be able to duplicate the existing system.

 

"The design is there. We just have to copy and massage it to fit the other lines," Rock says. As a result, he estimates that the cloned systems will cost 60 to 70 percent less than the original due to reuse engineering. And that will give Rock and Lipton's technical staff ample time make their tea and sample it too.

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