Not long ago the cost of servos was prohibitive in many packaging applications. Today, with the need for higher accuracy, improved speed regulation, and flexibility for periodic profile changes, these motion control technologies can frequently be found in packaging systems.
"What's happened is that the cost of the electronics has come down so much that even open loop steppers are being replaced with closed loop servos," notes Lee Stephens, systems engineer for Danaher Motion. Equally important, implementing servo control is easier than just a few years ago. This can be quite important in the packaging industry.
"The more customers want to automate, the more it is driving them towards servos," says John Mazurkiewicz, application engineer for Baldor Electric Co. Increased accuracy and speed resulting in more output per hour are among the more compelling reasons to spend the money. Improved quality with lower rejects can complete the justification for making the move to servos. Today, the initial cost impact is less than it was just 5 years ago, but the productivity improvements from automation are much greater.
However, at least one company has changed from using servos back to stepper motors based on the servo being overkill for the application. In this case, the application did not require the torque or the speed of the servo and in a highly competitive market, the stepper provided a cost advantage. Also, with improvements in stepper motors that provide even better accuracy, the use of steppers may be the right decision. Size 34 and size 23 steppers appear to be the most common for users interested in making this switch according to Ryan Lin, director of sales and marketing at Lin Engineering.
According to Steve Lipps, Product Line ManageróHorizontal Wrappers, Bosch Doboy, servo technology has resulted in shorter development time because fewer mechanical links are required between modules and fewer mechanical parts allow the design to be split among more designers. The result is lower cost mechanics. Among the changes that have occurred is the design of these machines from the ground up for servo control to minimize costs and increase performance.
Here are five applications of motion control technology in the packaging industry.
Bosch Doboy Linium 301
Bosch Doboy designd robotic packaging, cartoning, horizontal flow wrappers, and bag closing and baggers equipment. The company has made an extensive transition from mechanical systems to servos. Its Linium 301 horizontal flow wrapper provides one such example, with servos driving the infeed, finwheels, and cutting head. "A mechanical system would have a torque limiter that would kick out if the rotating sealing jaw hit a product to be packaged," notes Steve Lipps, "It would stop the machine and require resetting." In the design when the servo drive system senses a positioning error caused by hitting a product, the PC controller reverses the direction of the drive. This allows the misplaced product to pass through, and then starts again, all without stopping the flow of incoming products.
Triangle Packaging Machinery Advantage
Triangle's packaging equipment includes cartoning machines, filling machines, form, fill and, seal machines, and packaging support with specialty equipment. Triangle's Advantage continuous motion vertical form-fill-seal (VFFS) machine uses servo controls provided by Allen-Bradley ControlLogix or Selectech iPC. However, they have direct digital dual stepper motor belt drives. "We originated with stepper motors for our back machines and we have progressed into servo motors to draw the film and to drive the jaws," says Ted Torrens, vice president of sales and marketing for Triangle. Customer requirements and impetus from the supplier of the motor controls has been one of the driving factors for Triangle. Torrens also attributes greatly improved diagnostics and reliability to today's servo driven systems. "All of our cartoners are being converted over to servo motor, which offers more torque," notes Torrens.
Supreme Plastics Reseal 460X Zipper Applicator
Supreme Plastics' zipper applicator for continuous motion form-fill-seal machinery boasts faster operation and increased precision from servo control. The units have independently servo-controlled, zipper-feed channels for high-speed application to moving film and quad-axis servo control. The dual-forcer motor attaches zippers to a continuous plastic web at 120 pouches per min. Baldor NextMove BX motion controller and four FlexDrive servo drives control the machine's four axes of motion. The control comes from two rotary servomotors and two forcers for the linear stage. According to Baldor's John Mazurkiewicz, his company is seeing greater use of servos for packaging applications. Programmable positioners with easier means of programming make the decision to go servo easier for users.
FKI Logistex Robotic Arm and Gantry System
FKI Logistex provides palletizing and depalletizing systems that can include articulated robotic arms, gantry robots, and unscramblers for packaging. The company uses multiple-axis, servo-driven systems to handle a wide variety of products. Robotic palletizers and depalletizers use 4, 5, or 6-axis jointed arm robots to provide the required accuracy and flexibility.
Lantech SW-3000 Shrink Wrap
Lantech has a different approach to motion control. Its packaging products include semiautomatic and automatic stretch wrapping, automatic case handling, automatic palletizing, shrink packaging, and pallet-load conveying systems. A system such as its continuous motion SW-3000 shrink wrapper handles up to 65 packages/ min with production speeds up to 65 ft/min. The unit uses a variable frequency drive to provide electronically controlled film collapse and product spacing. A tension controlled trim winder for the side seal only pulls on the trim when it senses slack. The system does not use a clutch to compensate for the changing diameter of the trim spool as it increases from empty to full.