Motion Control, Networks Automate Baling Process
For most people—particularly those steeped in "heavy" industries, such as automotive—the words "manufacturing automation" don't immediately conjure up images of cotton-picking, baling, and storage. Nevertheless, the cotton industry wrestles with the same cost and efficiency pressures as any other manufacturing business.
For most people—particularly those steeped in "heavy" industries, such as automotive—the words "manufacturing automation" don't immediately conjure up images of cotton-picking, baling, and storage. Nevertheless, the cotton industry wrestles with the same cost and efficiency pressures as any other manufacturing business. With that in mind, a Kennesaw, GA, company has developed a unique cotton baling system to reduce the time and cost of the process while improving overall consistency.
The Ultra-Twist System, developed by Factory Solutions, a subsidiary of Interstate Electrical Supply, enables cotton gins to form precisely shaped bales more efficiently than other systems. The company touts Ultra-Twist's ability to fully automate the baling process with motion control using integrated components from Schneider Electric, including motion controllers, networks, and programmable logic controllers.
Developed for International Fiber Packaging—a division of cotton-gin supplier Leggett & Platt—the Ultra-Twist system is at work in approximately 15 gins in Texas and Georgia. With the recent completion of three years of testing, it is ready for full-scale deployment, says Steve Phillips, an Interstate Electric vice president.
A number of complex movements must occur to wire a bale, says James Dutton, division manager of Factory Solutions. First, a carriage that houses either three or six strapping heads is moved into place. The wire, fed from a spool, then moves through a chute around the bale and is brought back to the head, where it stops at a predetermined position. The wire is gripped, cut from the spool, and twisted into the Ultra-Twist knot a predetermined number of times. Tolerances are measured in thousandths of an inch to ensure that the cotton is held firmly, but not scored by the wire.
"The motion control system is optimized to offer maximum functionality," says Dutton. "That's important, because this solution requires controlling up to 13 different axes independently."
Cotton processing begins before the harvested plants even leave the fields. Right after picking, machines known as module makers press the cotton into blocks as much as 70-feet long. These blocks are loaded onto flatbed trucks and transported to nearby cotton gins, which typically run 24 hours a day during harvest season to give farmers quick turnaround on their crops.
At the gin, the cotton "module" is broken into individual bolls. It is then put through a number of machines that de-seed it, pull apart cotton fibers, clean the cotton, and adjust moisture levels.
Cotton fiber is transported to the baler, which uses hydraulic presses to create well-shaped blocks that weigh approximately 500 pounds each ("They're packed so densely that you'd need a hammer to drive a nail into a bale of cotton," says Phillips). Finally, the bale is weighed, bagged, and conveyed to a warehouse for storage.
A high-capacity gin can produce as many as 60 bales per hour, so Factory Solutions sought to ensure that gins could operate as efficiently and cost-effectively as possible. Use of round steel cable rather than plastic straps are among unique features applied.
Wrapping bales with steel is an old idea whose time has come, says Phillips. Prior to widespread adoption of plastic strapping, the industry used flat, steel straps to wrap bales, but they were bulky, required large strapping heads on the baling machine, and clamps on the straps to hold them in place. Development of round cables of sufficient strength to hold the bales led Factory Solutions to reintroduce steel to the process. Because the steel is recycled, the cable is as much as 50 cents-per-bale cheaper than plastic, says Phillips.
"When you consider the fact that a gin might turn out 100,000 bales during a single season, that's a substantial savings," he says.
Most baling systems wrap with plastic straps. However, varying temperatures in warehouses can cause those straps to stretch, causing the bales to become misshapen and, in some instances, they can fail altogether, says Phillips.
"It creates a real mess, but it's even worse if a bale catches fire. The plastic strap melts and the fire spreads. Metal doesn't break, so the fire can be contained to just a few bales."
In addition, Factory Solutions significantly improved handling and wiring of the bale through inclusion of advanced motion control capabilities in the Ultra-Twist System. All of the motion-control components are made by Schneider Electric, including servo drives, brushless motors, and PLCs.
Mark Olten, business development manager for Schneider Electric's motion control products, explains that the use of servo motors is key to the speed and precision of the Ultra-Twist System.
"With servo technology you're able to index the moves of the equipment rapidly and with a great deal of resolution. In other words, the system knows 'where it is' with much greater resolution than if other types of motors are used," says Olten. "These characteristics, along with fast and accurate acceleration and deceleration, improve cycle time of the strapping operation, which means that cotton can be processed faster."
The Ultra-Twist system also runs in fully automatic mode. As many as three people operated the semi-automatic and manual systems, says Olten.
Factory Solutions makes two versions of the Ultra-Twist system—a high-performance model with six strapping heads and a standard model with three heads. The high-performance model initially was controlled by a Schneider Electric TSX Premium PLC using fiber-optic-based SERCOS protocol for motion control.
"We initially used SERCOS because of the superior performance," says Olten. "This was the first automated implementation of a strapping system of this type, and we wanted to be able to address any control requirement that came up."
As the application evolved, Factory Solutions replaced SERCOS with a less-costly Modbus Plus configuration, enabling the company to reduce the price differential between Ultra-Twist system and non-servo systems on the market.
The standard version of the system features a smaller, DIN-rail-based PLC communicating via Modbus Plus. Upon commissioning, each PLC is programmed by Factory Solutions to meet the gin's particular needs. The company uses Schneider Electric software tools to develop sequential function chart, function block, and/or ladder logic programming for the Ultra-Twist's PLCs.
Individual machines typically are programmed for specific operating parameters, including wire feed speed, distance, tensioning, and cycle times, says Olten.
In addition, each machine has a Schneider-provided Magelis color touch-screen with a numeric keypad, programmed with operator screens, diagnostic displays, and engineering pages for machine setup.
Beyond enabling faster processing of bales than other machines and reducing the cost of supplies, the Ultra-Twist system is helping gins maximize uptime. Phillips notes that machines in the field are operational more than 98% of the time.
The systems are also equipped with modems, enabling technicians to bring a machine up, take it down, and perform remote diagnostics through a serial connection.
Looking ahead, Factory Solutions is working to reduce the number of servos needed and Web-enable controllers so that users of the machine, owners of the plant, and technicians can go online to communicate with the machines.
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Dan Sussman is a freelance writer based in Arizona.
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