Fast and Accurate Changeovers With Servos

Whether handling cookies, toothpaste, medicine or make-up, contract packagers are always under pressure to provide quick product changeovers to meet a variety of cartoning demands for their customers. Faced with these requirements, in early 2005, contract packager Packaging Division Industries, LLC (PDI), Northlake, IL, installed a servo-driven vertical cartoner from Ultra Packaging Inc. (www.ultrapackaging.com). Ultra Packaging, an original equipment manufacturer located in Bensenville, IL, has been serving the packaging industry with cartoning equipment for more than 13 years and is familiar with the changeover challenges faced by its customers.

Traditionally, vertical cartoners have relied on mechanical line shafts and linkages to erect and move cartons through the machine. Seeking ways to improve uptime, Ultra Packaging examined the shortcomings of mechanical cartoners, including the time required for machine maintenance and troubleshooting, and more importantly, the time required to convert the cartoner to handle product changeovers. The company wanted to simplify these tasks and reduce the effort it takes to perform them.

By taking an all-servo, GEN III packaging automation approach in its latest machine design, Ultra Packaging successfully converted the mechanically controlled motions on its vertical cartoner to a servomotor and drive-system from the Electric Drives and Controls Technology Group of Bosch Rexroth Corp. (www.boschrexroth-us.com).

To understand the benefits of servo-controlled motion on a vertical cartoner, consider the function of Ultra Packaging's Veronica cartoner. Servomotors are used to control the critical areas of the machine by providing precise synchronization of the carton and products and the tucking and gluing of the carton flaps. Cartons are erected from flat paperboard blanks, which are moved onto the transport belt running through the machine. During the process, the minor flaps on the bottom of the carton are closed and the product is loaded into the open end of the carton from the top. The upper carton flaps are then closed and glued shut. The entire process must be tightly synchronized by servos to avoid frequent carton jams on the machine.

Within this process, seven Bosch Rexroth EcoDrive Cs drives and MSM compact, alternating-current servomotors are used to provide the synchronization, camming, and gluing functions of the machine. The servo drives are commanded through an industry-standard SERCOS digital fiber-optic network, which provides a 32-bit command signal and diagnostic feedback from each ac servo in the system.

Instead of relying on a traditional programmable-logic controller for motion control, the machine is controlled by a Bosch Rexroth high performance PPC (PowerPC) motion and logic controller. This compact, rack-based system provides all of the synchronized motion on all of the axes, as well as the logic programming for the 24 V, direct-current I/O connections on the machine. Analog I/O connects to the two ac drives that run the carton magazine and the outfeed conveyor at adjustable speeds. Ultra Packaging chose this control system because of its multi-axis synchronization capabilities, as well as its ability to return to production without the need for rehoming after a jam or an emergency stop.

For Ultra Packaging, the Veronica's servo-centric design is a first for the company and is also relatively unique within the industry. Supplying cartoning speeds from 20 to 120 cartons/min in continuous or intermittent motion, the Veronica is adjustable for a broad range of cartons, from small 2 x 3/4 x 41/2-in. cartons, to large 10 x 4 x 12-in. cartons. But its most dominating feature is said to be the capability for quick, easy changeovers.

"For contract packagers or any cartoning operation that requires frequent changeovers, the Veronica's typical 10-min changeover time is a welcome savings compared to the usual 30- to 90-min break for mechanical changes," says Bob Stockus, Ultra Packaging's vice president.

According to Stockus, if an operator changes from a cereal carton with a pitch (left-to-right dimension) of 71/2 in. to a toothpaste carton with a pitch of 13/4 in., it would only take about 3 sec compared to 10-12 min on a mechanical cartoner. Likewise, a vertical dimension (depth) change would take about 3 sec, compared to 5 min on a mechanical cartoner.

Through the human/machine interface panel, the Veronica's operator can access up to 50 carton size presets. Ultra Packaging also added a feature in which the individual products are represented on the HMI screens by images of the product as opposed to a product code or number. This allows faster visual identification and adds to the simplicity of the changeover action.

"The Rexroth servo and PPC combination allows the Veronica operator to simply touch an icon on the HMI screen to change a dimension," says Stockus. "This represents a significant reduction in downtime, as well as more product changeup capabilities, for contract-packaging customers. Greater capabilities mean greater profits."

While designing the Veronica, Stockus says motion-control synchronization was the greatest challenge. The first servo system Ultra Packaging used was from another supplier and was configured as five independent servos drives, which had problems achieving precision and synchronization. The company then evaluated multiple technologies from other suppliers. They considered technology, price, application-knowledge within the food and packaging industry and the level of support they could expect from the supplier. Stockus said the company chose Bosch Rexroth because of its experience in the packaging industry, as well as the multi-axis synchronization capability of its servo/PPC package. Another feature that influenced Ultra Packaging's decision was that Rexroth servos do not require rehoming after a jam or emergency stop. The system remembers where the motor shafts were positioned, which speeds machine recovery by as much as 80%.

An example of this speedy recovery is found in the cartoner's servo-controlled flap-folding feature, which is relatively unique in the industry because it's usually a mechanical operation. "The benefit of converting this motion to servo control is that, if a carton flap fails and causes a jam, the machine is programmed to stop before damage occurs," says Stockus. "In addition, a stack light alerts the operator of the jam. The HMI touch screen identifies the jam location, and the machine quickly resets to the appropriate position."

Conversely, a jam on a mechanical flap folder will damage the carton (and likely consecutive cartons) and requires a wrench and other tools to retime the machine's product position. The Rexroth servomotor, drive, and PPC work together to automatically reset the position, remembering "home" and performing corrective action, so no cartons are lost. Time spent resolving this type of jam is also reduced significantly. On average, servos require less than 2 min to resolve a jam; mechanical counterparts require up to 10 min.

Another benefit of servo control is that intermittent-motion profiles are automatically calculated to maintain the desired fill-time dwell over a broad range of production speeds and corresponding product dimensions. Likewise, an electronic cam profile for the carton-erector axis enables precise product positioning that is synchronous with the speed of the conveyor belts, while a high-speed retract of the vacuum cups avoids interference with moving machine components.

Stockus says the servos and machine design:

PDI was one of the first Ultra Packaging customers to add the Veronica vertical cartoner to its production line. Rey Interian, PDI maintenance manager, says the cartoner was purchased to expand the capacity of the company's 540,000-sq-ft facility. PDI primarily serves retail and warehouse clubs that want 48 two-count packages of cookies or other products in multiple quantities, so it's not surprising that Interian identified PDI's biggest challenges as quick changeovers coupled with quick startups and overall product-handling versatility.

For PDI, the elimination of manual adjustments for the length and depth of cartons during changeover is a major advantage of the servo-driven design. Interian also cites other benefits of the cartoner, including production speed, product-positioning accuracy, carton-size versatility and reduced maintenance. "The cartoner has allowed PDI to increase productivity about 15%, depending on the product we are running," says Interian. "The typical changeover time has been reduced from nearly six hours on a comparable mechanical cartoner to as little as 30 minutes on the Veronica."

He also notes that the quick identification of trouble spots allows the operator to quickly resolve jams or other problems and return the cartoner to production in a fraction of the time of its mechanical counterpart. Interian also included the use of timing belts as a key benefit because they drastically reduce the noise level previously generated by the roller chains riding on guides. "It is also safer for the personnel," says Interian, since metal roller chains and lugs are much less forgiving than the Veronica's timing belts.

"Keeping the cartoner up and running is obviously vital to a business like ours, that handles a number of product sizes and configurations with shorter runs," says Interian. "The servo control of the Veronica allows us to spend much more uptime in production and much less downtime on changeovers, troubleshooting and maintenance. Naturally this translates into greater capacity for PDI to handle a variety of products and more efficient service for our customers."