Extreme Changeover

No one wants to create a "me too" design for a new machine. Ultra Packaging took that notion to an extreme. For its latest line of vertical cartoners, the company replaced every bit of roller chain of an earlier design with servos and timing belts. As a result, the new all-electric machines focus on quick product changeovers, choice of continuous or intermittent motion operations and production rates as fast as 120 cartons/min.

Complete Makeover

"We knew we needed quick product changeover for the market segment we wanted to serve," says Bob Stockus, vice president for Ultra Packaging (www.ultrapackaging.com). "That prompted us immediately to explore servodrive technology for the new machine and electronic power transmission. Our goal was to eliminate all of the chains, sprockets, bearings and gears that are typical in vertical cartoners."

Stockus says the new vertical cartoner, called Veronica, eliminates the maintenance headache associated with chain stretch and backlash. Instead, the new cartoner design is equipped with eight servos and timing belts to control the carton transport conveyor and the system's power transmission components.

	In its latest line of cartoners, Ultra Packaging completely eliminates use of any roller chain, and control problems with chain stretch and backlash.

The system uses a Bosch Rexroth PPC (PowerPC) Motion and Logic Controller (www.boschrexroth.com), Ecodrive servo drives and ac servomotors with absolute feedback, along with dc drives on minor machine functions, to control the entire process. The carton transport conveyor, plus all minor flap folding and a rotary carton feed, are all servo-driven.

The new design produces a machine which runs quieter and smoother than previous chain-driven versions, and allows for much faster product changeovers. "The machine offers quick changeover due to the automatic adjustments done through the servos," says Rey Interian of Packaging Division Industries LLC (www.packdiv.com) who has used the system for the last eight months.

"Since the user can store different programs for different size cartons, we dial in a program and the machine automatically adjusts itself to the package size. That saves a lot of time compared to changeover on a regular cartoner which can take four to six hours. This machine can be changed over to an available program in less than 30 minutes."

Engineering Challenges

Designing the machine without any roller chain presented several difficulties. Stockus says they knew they could put a timing belt on the primary drive components without hardship. "But when we worked through the machine at its various levels, there were points where maybe a 1-foot strand of #40 chain would drive an ancillary component. Those points proved to be challenging, working out the details of secondary components to completely eliminate the use of chain. Sometimes we couldn't find an equivalent for a very small pitched chain or a standard timing belt that would act as a replacement."

Solving the engineering problem demanded hard work and extensive communication with vendors. Ultra engineers described the exact situation to vendors, asking them for input into how to replace roller chain and explore ways to get the same performance from timing belts. The solution took persistent trial-and-error engineering, and plenty of belt prototypes.

All along, however, they needed to stay with the same basic design of the machine. "We needed the component to perform a very specific function that had been performed by chain for many years. We had to use trial and error and be sure the function could be done by a timing belt."

Servo-Driven Synchronization

Another challenge involved motion synchronization and the complex programming required for the system's eight servos. The conveyor portion of the cartoner consists of three timing belts. One servo drives the top and bottom timing belts or pushing lugs and acts as the master position reference for synchronizing all of the motors on the machine. A second, smaller servo on the timing belt in the center completes the carton transport conveyor.

One servo controls a two-head, rotary carton feed. An optional servo can be attached to the carton feed for adjusting the width or thickness dimension of the carton. Three more servos operate the leading dust flap folder, the bottom trailing dust flap folder and the top trailing dust flap folder. All of the flaps are folded before the operator places product in each carton. Then, the flaps are tucked closed or glued so the bottom gets sealed. The product goes in and the top of the carton is sealed again either by tuck closure or glue.

Where earlier machines took physical adjusting to accommodate new product sizes, the new machine does this automatically through the servos when commanded by way of the HMI. Phase offsets for synchronizing folding operations are adjusted in this way as well.

Adjusting product length in the chain and sprocket machine, for example, required the operator to remove the guards, loosen the leading sprocket, grab the lugs and pull on a chain that might be 40 or 50 feet long. He'd then erect a carton by hand, place it between the pushing and leading lugs and tighten the bolts. Then, the operator would jog the machine to see if the chain was tight or loose, repeating the process until tension was correct. Now, the same changeover process takes two to three seconds, and the leading lug moves to the precise position required because of the accuracy of the servo system.

Both Stockus and Plant Manager Rich Peterson say developing the application software to control the complexities of the machine required both patience and persistence. Dave Stuber of Custom Control Solutions Inc., a local systems integrator, programmed the custom application. "We had to teach them about cartoning technology and the application requirements of the machine. We gave him a crash course in vertical cartoning," Peterson says.

	Bosch Rexroth PPC (PowerPC) Motion and Logic Controller.

Recovering from Jams

While software integration and motion synchronization proved to be a challenge in the application, Stockus says after you get it right, it stays right. And after the pain, they gained a wide variety of benefits through servo technology and programmable operation.

A major advantage is limiting downtime when recovering from jams. Stockus says one of the features of the servo machine is that the blade, or mechanical portion that touches the carton, can be mounted directly to the output shaft of the servomotor. "If, for some reason, timing becomes an issue or the operator doesn't push the bag of cereal all the way down into the carton, when the trailing dust flap folder on top meets resistance, we can sense the torque and automatically stop the machine. We haven't ruined any product and we can push the bag down far enough so it's no longer above the top score line of the carton, restart the machine and off we go. The time savings is invaluable for a simple operation that may take 20 seconds to accomplish."

Servos on the dust flap folders are another way servo performance improved the operation of the machine. With the mechanical machine, the operator would put a carton into the machine and jog it through to see if the timing on the folders needed to be advanced or retarded for the flaps to fold properly. Now, the operator can offset those adjustments on the fly through the HMI. If the operator moves from one skid of cartons to another, and there is variability in the cardboard, there may be intermittent folding problems. With the servo system, the timing of the folding point can be advanced or retarded half a degree or 10 degrees to help the flap fold more smoothly without crushing the box.

Absolute Positioning

Since all of the motors in the system have absolute encoders for feedback, the machine can also recover from stoppages and emergency stop conditions without losing position. The Bosch Rexroth motors used in the application provided an excellent advantage in this application during E-stop conditions. Stockus says that "even though we lose power to the drives during E-stop, we meet our safety requirements because the motor, when it is decelerating, is generating its own milli-amperage and maintains its home position signal."

He says that, with other options, the motors lost home position for one pitch of the machine, meaning that the motor had to rotate up to three times before it would find home again. "When we re-start the machine, we do not destroy any cartons because we hit the E-stop button."

Another unique use of the absolute encoders is the ability of the machine to go to "machine 0." By accessing a maintenance screen, all servos can be commanded to go back to an initial programming state. An example of where this is a valuable tool is troubleshooting. In one situation where the machine was packaging rock candy, the operator noticed that the system was dropping cartons. Operators returned the system to zero and noticed someone had dumped the suction feed arm. The mechanic adjusted the suction feed arm, set the system back into run mode, and the machine re-adjusted for the selected carton and continued production from that point.

Simpler, Clean Design

Stockus says even though they encountered challenges in the machine development, the mechanical design of the machine got much simpler with the switch to servos and timing belts. Fewer parts and linkages are used in the new machines, so instead of linkages for side flap folders, putting a motor into position eliminated many mechanical wear points.

"The fewer number of parts on the machine gave us the opportunity to create a clean-slate design," he adds. "When customers look under the machine, they call it a 'fall-through' design because there aren't a lot of nooks and crevices where food or other items can become trapped."

The machine is also significantly more accurate than its mechanical predecessor for the simple fact of chain stretching. Stockus says that chain can stretch up to 10 percent of its length over a couple of years. Timing belts will not stretch the way chain does, so the accuracy of the machine is exponentially greater than the mechanical machine.

Evolution of Packaging Machinery Sample horizontal cartoner designs     Generation I Mechanically line shafted machines Complex mechanical cams, sprockets and chains       Generation 2 Hybrid configuration machines: mechanical with a few servos in critical areas Use of servos improves flexibility and changeover No reduction in the number of parts or the overall cost of the machine       Generation 3 All electric machines: servo technology that's new from ground up Maximum flexibility and automated changeover Shorter delivery and lower cost to operate 50 percent reduction of parts and improved sanitary design   New vertical cartoner from Ultra Packaging is an example of how a clean-slate, Generation 3 design can improve product changeover and reduce machinery costs.