Actuators solve baffling bagging application

Dec. 1, 2008
In the diverse bulk-materials processing industries, systems must be designed to measure, fill, and seal bags containing anything from pet food to salt,

In the diverse bulk-materials processing industries, systems must be designed to measure, fill, and seal bags containing anything from pet food to salt, sugar to dirt, and fertilizer to animal feed. And because the bags themselves are one area where processors can cut corners, many are sourcing their bags from China. However, low-cost bags often mean irregular dimensions, making them challenging for automated machinery to handle. Packaging equipment manufacturer Thiele Technologies Inc., Minneapolis, recently faced this dilemma — how to compensate for inconsistent bag dimensions on its modular bag filling and sealing system. Many of Thiele's customers had recently switched to cheaper bags, and the irregular bags were slowing production processes.

Because repeatability is critical to filling and sealing, Thiele engineers needed a solution that would increase accuracy and flexibility for packagers. They found their answer in four custom electric screw linear actuators from Tolomatic Inc., Hamel, Minn., which precisely position incoming empty bags. The bagging system now automatically compensates for variations in bag dimensions and eliminates manual setup when changing bag sizes.

The original version of the bagging system was automated except for a tray that positioned bags prior to pickup and insertion into the filling line. When using high-quality bags with consistent dimensions, the trays required only a simple manual adjustment at the start of a run. However, when customers began switching to low-cost bags, some were not positioned accurately, resulting in improper filling and sealing. With bag lengths varying by as much as 3/4 of an inch, bag-handling issues were becoming commonplace. To solve the problem, the company developed a “bag top reference” mechanism to compensate for varying lengths.

The new mechanism uses four modified-standard B3S10 rodless electric screw actuators to precisely position incoming bags before they are inserted into the filling/sealing line. Two of the actuators, each one operated by a separate servomotor, adjust the vertical position of the bags. As bags are loaded into the staging trays, vertical actuators catch them and lower the bag tops to a precise reference point determined by two video cameras controlled by the system's PLC.

At the same time, bags are centered in their trays by two horizontal B3S10 actuators that have been extensively modified. Each actuator has two carriers riding on a screw with right-hand threads on one half, and left-hand threads on the other half. As the screw turns, each pair of carriers moves toward each other to center the bag in the tray. The two actuators are joined by a coupler and are operated by one servomotor connected by a compact 180° belt drive. Once bags are vertically aligned and centered, they're picked up by a pneumatic arm and inserted into the filling/sealing line. The new design automatically compensates for variations in bag length and width and eliminates filling and sealing problems. For more information, visit

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