Unifi weaves a tight system

Automatic guided vehicles and a power- and-free conveyor let this leading textile manufacturer spin a good yarn.

By -- Modern Materials Handling, 9/1/2000

Textiles is a hands-off business. While the old materials handling adage of "the less handling, the better" clearly applies, textiles require the added guideline that no human contact is even better, eliminating sources of contamination for in-process yarns.

With this in mind, Unifi, Inc. developed a materials handling system at its new extrusion and texturing facility in Yadkinville, N.C. that eliminates almost all human interaction with the product. The system additionally provides consistent quality of outgoing yarns, eliminates manual handling processes, improves ergonomics, optimizes run time, and adds flexibility.

Automatic guided vehicles (AGVs) and a power-and-free conveyor line are the heart of the handling system.

"We looked at other systems, but felt they handled the product too many times," says Kenneth Stone, services engineer at Unifi. "We wanted to handle product as little as possible and also pattern our transfers so that the product ends face the proper direction. The AGVs and robots we use help us orient the product to the position we need when it arrives at our texturing operations."

Unifi is the largest producer and processor of textured yarns in the United States, and among the leaders worldwide. The company's 17 facilities in 12 locations texture, dye, twist, and cover multi-filament polyester and nylon yarns for automotive upholstery, industrial fabrics, home furnishings, and clothing.

"We extrude the raw material and then send it to our texturing operations for other processes," says Stone.

Yarn manufacturing starts with polyester chips that are passed through extruding machines. The melted polyester is then fed into a spinnerette that combines multiple filaments from the plastic resin into yarn according to customer order specifications. The yarn is then wound onto paper tubes, known as "packages."

There are 312 separate winders, each connected to a timer. As the winder is completing a package, an attached programmable controller signals a scheduling computer that the yarn has been wound. The scheduler then dispatches an AGV to pick up the completed package, each of which is about 17 in. in diameter and weighs 42-44 lbs.

Unifi has 10 AGVs that travel between the 104 winding blocks. An AGV sitting at a dispatch station receives the order to go a specific winder. Upon arrival, mandrills on the AGV extend to receive the transfer of six packages simultaneously. Each AGV has three mandrills for transporting 18 packages at once with a total weight of 900 lbs.

Each package is also assigned a tracking number.

"As packages transfer to the AGV, a data transfer also takes place throughout the network and our location tables are updated," says Stone.

The manufacturing system uses radio frequency identification in combination with wires in the floor to direct the AGV on its 12-minute trip to a singulator station. Here a robot removes three packages at a time and transfers them onto a power-and-free conveyor carrier. Each carrier has six pegs to hold packages in a 2 by 3 array that mirrors the positions they held when transported on the AGV.

Each set of six packages also receives a radio frequency identification (RFID) tag. The data system then transfers information from the product tables onto the tag pertinent to those six packages. This includes an identification number, the date and time when each production pro-cess occurred, the batch number of the chips used to produce the yarn filaments, which winder and spinnerette were used, and the weight of each package.

"The tags have been a big advantage to us in traceability of the product and in quality issues," notes Stone.

The power-and-free carriers (Bosch Automation Products, www.boschat.com ), each about 41/2 ft. high, are floor mounted and transport the packages to an inspection station. It is here that the product is physically touched for the first time.

An inspector first removes the outer yarn, as this portion is less consistent due to the transfer process. This person also checks the quality of each package and makes certain that the yarn has wound properly. The inspector additionally ties off the tail of the yarn and examines the information recorded on the RFID tag. The package is also weighed.

"Weight variation tells us a lot of things, such as whether we may be missing some filaments, or detect other process-related issues," explains Stone.

The inspector has the option of passing the packages along the line or pulling them from the system. Some are also sent to a testing area.

The inspector determines the package's fate and records that information onto the RFID tag. The product is released on the power-and-free and immediately passes through a zone where the tag is read. Those acceptable are sent to a packaging area consisting of 26 cells in two rows of 13 each.

Two gantry robots run the length of the rows, building pallet loads upon injection-molded plastic cartons within the cells. The RFID tag is first read as the power-and-free carrier enters the packaging area. The product is identified and the robot is directed to pull off the corresponding yarn packages.

The system determines if a cell in process is already building a pallet load of that type and needs additional packages. If so, it will pick off the 2 by 3 array from the carrier and create an additional layer onto the carton until there is a total of 30 packages on the load. If that type is not currently being packed, then it will start a new load in an open cell.

Embedded into the pallet carton is an additional RFID tag. The information from the carrier tag is transferred to this tag to marry the pallet to the product it will hold.

Once a full load has been gathered, an automatic shuttle car picks up the carton and places it onto a chain conveyor where it heads to an accumulation station.

Another shuttle then places outbound product onto a roller conveyor. A hood-shaped plastic wrap comes down over the pallet carton to unify the load. It then passes through a heat zone to shrink-wrap the plastic. The complete carton is next weighed using an in-line scale and the RFID tag is updated with this information. A label is then printed and automatically applied.

As it reaches the end of the conveyor, a lift truck gathers the 1,400 lb. load and transports it to floor storage until the yarn is needed for further processing at a nearby Unifi facility.

Stone says that the materials handling system has done everything it was designed to do and more, moving nearly 85,000 packages of yarn each week.

Uptime is an important part of this, as the facility must run 24/7 because of the extrusion processes.

"Unifi has always prided itself on using the best technology that we can find," Stone says. "We've had very little downtime. It has also been very positive ergonomically for our employees. We have less injuries to wrists and backs and arms because of the system's handling and packaging."

Limited handling also helps the facility maintain a very high standard of product, with first-quality yields of 97%.

The RFID system additionally provides the ability to trace any problems that do occur down to the source. It can identify a product to the individual package within a carton, as well as trace the process back through to the individual machines that produced that yarn.

"This facility is considered the largest and most technically advanced operation of its kind in the textile industry," Stone adds.

System benefits at a glance

• Eliminates human handling

MANUFACTURER PROFILE

Unifi, Inc.
Extrusion facilityYadkinville, N.C.

Facility size:  400,000 sq. ft. on six floors

Employees: 150

Product produced: Polyester and nylon yarn

Output: 3.5 million lbs./week; 85,000 spools (packages)/week

Power and free conveyor:
Bosch Automation Products, 616-695-0151, www.boschat.com

System integrator:
Advanced Automation, 864-627-0900, www.aautomation.com

Manufacturing execution software:
Unifi Technology Group, 336-878-3400, www.unifitech.com

Automatic guided vehicles:
Munck Automation Technology, 757-887-8080, www.munck.com

Roller conveyors:
Rapistan Systems, 616-451-6525, www.rapistan.com

Industrial robots:
Adept Technology, 408-432-0888, www.adept.com

Lift trucks:
Yale Materials Handling 252-758-9253, www.yale.com

RFID tags:
Omron Electronics, 800-556-6766, www.omron.com

In-line scales:
Mettler Toledo, 614-438-4511, www.na.mt.com

Label printers:
Zebra, 847-634-6700, www.zebra.com

Plastic pallet cartons:
Technical Help in Engineering and Manufacturing (T.H.E.M.),336-855-7880, www.them-int.com