Mechatronics boosts wet-wipes production

Green Bay, Wis.-based Paper Converting Machine Co. (PCMC), a builder of wet-wipes converting machines, used a mechatronic approach for the first time when it decided to increase the machines’ throughput. Wet wipes are nonwoven fabrics made by mixing fibers into liquid slurries, making the resultant paste into flat sheets using rollers, drying the sheet, and forming the sheet into long rolls of material. Converting machines fold the material into long ribbons of the familiar web shapes (which pop-up when a consumer pulls a wipe from its container). The machine cuts the ribbon into individual lengths for packaging. To boost throughput, PCMC wanted faster rotary saws that would let operators adjust lengths with the push of a button. To reach this goal, the company used design software and automation technology from Rockwell Automation Inc., Milwaukee.

A mechatronic approach in the case of the new Mako saws made sense because it combines mechanical, electrical, and control engineering, providing a collaborative, interdisciplinary way to lower design and development costs while bringing products to market faster.

Early in the design process, PCMC modeled the new application by linking SolidWorks models with controls in Rockwell Software’s RSLogix 5000 program using Allen-Bradley Motion Analyzer software. Motion Analyzer helps users size and select an optimized motion system by evaluating a variety of gear ratios, inertias, and mechanical alternatives. SolidWorks and Motion Analyzer working together let designers quickly simulate a variety of motor-drive combinations to select the one best suited for the job.

To implement the machine pushbutton capability for changing cut lengths, PCMC decoupled the shaft between the segmented support and overhead arm and installed Allen-Bradley RDD-Series Direct Drive Rotary servomotors. Designers combined the servomotors with Rockwell Kinetix servodrives. The motors precisely drive the two saw blades through the segmented support. The motors also eliminated the need for timing belts and pulleys, reducing the number of components and simplifying installation and maintenance.

PCMC also used an Allen-Bradley ControlLogix Programmable Automation Controller to control the Kinetix drives and motors. A noise-immune, fiber-optic Sercos interfaces between the controller and servodrives. Motion-control instructions embedded in both the RSLogix 5000 software and the controller provide synchronization and ease of use.

“We had already standardized on the Logix Control Platform, so it was natural for us to use Rockwell’s control technology,” says Pennings. “The direct-drive technology was a tougher choice, being the first time our company used it. But our history with Rockwell Automation inspired trust to try new things.”

According to PCMC, the Mako rotary saw is now the highest-speed saw on the market. It cuts more than 500 wipes/min as compared to the previous 300 cuts/min.

PCMC also leveraged the brownout-protection feature on Kinetix drives, which keeps saw blades and the segmented support synchronized in the event of an interruption in the electrical supply. Without such a feature, power outages could destroy the saw and create safety risks. This feature is particularly important because PCMC machines are frequently shipped to countries where brownouts are common.

In addition, the Kinetix Integrated Motion system stops the blades within milliseconds of detecting a brownout. The machines maintain power to the drives just long enough to stop the blades while also coordinating the stop as quickly as possible to avoid crashing the blades.

“The blades’ large size means there is an incredible amount of inertia when the machine is running, says Pennings. “No way would a conventional motor stop the blades as quickly as the Kinetix technology. Conventional motors would take 1 or 2 seconds, at best.”

Because the Mako application was PCMC’s first foray into mechatronics, Rockwell Automation simulated the saw using Motion Analyzer software. The simulation correlated closely with results from the test floor, so PCMC gained confidence in using the model in the future.

“Mechatronics can slash assembly times because it eliminates replacing drive and motor combinations,” says Pennings. “It will also let us test our applications in simulations before moving to the plant floor.”

© 2011 Penton Media, Inc.