Control system integrates PLCs and PACs

In this installment of What Works, a control system upgrade improves reliability and reduces maintenance costs.

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As food and beverage manufacturers adapt to meet changing consumer demands for freshness and convenience, they rely on packaging suppliers to deliver cartons and containers comprised of a variety of materials and in a range of shapes and sizes. Evergreen Packaging (www.evergreenpackaging.com) works with many manufacturers to develop fiber-based packaging for everything from juice and candy to specialty products such as liquid eggs and fabric softener.

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At its Olmsted Falls, Ohio, plant, Evergreen produces milk cartons from rolls of paperboard supplied by one of its paper mills. The plant uses eight sealers and converting machines to fold, print, die cut and seal the cardboard cartons (Figure 1). The high-speed converting operation produces cartons ranging in volume from four ounces to one-half gallon, with an average output capacity of approximately 400,000 cartons per hour.

Figure 1. An integrated control platform provides benefits for a plant that manufactures milk cartons and other converted paper products.
Figure 1. An integrated control platform provides benefits for a plant that manufactures milk cartons and other converted paper products.

After a converting machine prints the words and images on the paperboard, the same machine scores the paperboard along what will be the edges of the milk carton, where the box will fold later. A die lowers and stamps out a flat, scored and printed piece called a blank.

The blanks are loaded into a sealer, which takes the blank and folds it laterally into an overlapping side seam. The seam is heated and squeezed. The sealed and folded blanks are then loaded into corrugated cartons and shipped to the dairy. The dairy uses specialized machinery to transform the blanks into open containers, where they’re filled and top-sealed.

Challenge

Over the years, Evergreen machines have used a mix of control technologies from different suppliers. Most recently, the machines consisted of outdated drives, relay logic and PLCs running on proprietary software, which was making them increasingly difficult to operate, maintain and support. To make changes to the machines, engineers had to perform complex reprogramming for each new control function.

Access to reliable support also was a growing concern as the company was finding it increasingly difficult to find engineers with the knowledge and skills needed to support the older, diverse technologies. In addition, limited diagnostic capabilities made troubleshooting an ongoing challenge.

Another area of complexity centered on the extensive amount of wiring required with the existing control system design, which complicated maintenance and repair, and multiplied the potential points of failure.

“Some of our machines had 15 e-stop buttons wired in series, which produced a troubleshooting nightmare,” says Richard Stewart, senior project engineer, Evergreen Packaging. “Even a simple problem, such as a failed sensor, could be extremely difficult to identify and locate, putting the entire operation at risk for incurring substantial downtime losses.”

With most of the technology more than a decade old, Evergreen wanted to upgrade its production machinery with a standard control platform. This would help simplify programming and configuration, improve troubleshooting capabilities and ensure wider availability of support and replacement parts.

Solution

To make changes to the machines, engineers had to perform complex reprogramming for each new control function.

Evergreen turned to Rockwell Automation (www.rockwellautomation.com) for a standard control system that would significantly enhance the performance, reliability and ease of use of its production machinery (Figure 2). At the heart of each machine is an Allen-Bradley CompactLogix programmable automation controller (PAC), which allows Evergreen to connect machine components in an open, integrated environment. The controller tracks the sequence of machine events and allows operators to monitor variables and status information in real time to easily identify and diagnose problems.

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