More Accurate Electric Screw Actuators

When customers choose different packaging bags to keep their costs down, it can affect how packaging machines operate. Such was the case faced by Thiele Technologies, a leader in packaging technology and equipment. Its bagging systems measure, fill and seal bags containing anything from pet food to salt, sugar, dirt, seed, fertilizer or animal feed.

One of its customers recently switched to bags with irregular dimensions. But the bags slowed the production process, which requires high-speed accuracy to meet manufacturing goals. Thiele engineers needed to alter a popular modular bag filling and sealing system to compensate for the dimensional inconsistencies. 

Two ganged Tolomatic actuators center the bags in the staging trays while two other actuators adjust the vertical position.

Because repeatability was critical to the filling and sealing operation, the engineers chose four custom electric screw linear actuators from Tolomatic, Hamel, Minn., that 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 the tray that positioned the empty bags prior to them being picked up and inserted into the filling line.  When using bags with consistent dimensions, the trays required only a simple manual adjustment at the start of a run. When customers switched to other bags, some would not be positioned accurately, resulting in an improper fill and seal.

“Pet food manufacturers were forced to switch from paper bags to woven poly bags because their customers—large retail chains—would reject entire truckloads of product if there was a single ‘leaker’ bag,” says Jon Gifford, R&D manager with Thiele Technologies.  “Woven poly bags proved to be much tougher, but because of higher costs, China has become the predominant supplier. With bag lengths varying by as much as three-quarters of an inch, bag handling problems occur. To solve this problem, we developed a ‘bag top reference’ mechanism to compensate for these varying lengths.”

The standard Tolomatic B3S Series of rodless electric linear actuators handles heavy and high-moment loads with consistent, smooth operation.  It can be modified for a wide variety of special applications.

The bag top reference mechanism uses four modified-standard Tolomatic B3S10 rodless electric screw actuators to precisely position the 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, the vertical actuators catch the bags 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, the bags are centered in their trays by two horizontal B3S10 actuators that have been extensively modified. Each horizontal 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 carrier pair 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-degree Tolomatic belt drive.  Once the bags are vertically aligned and centered, they are picked up by a pneumatic arm and inserted into the filling/sealing line.

The design tolerance for positioning the tops of the bags is +/- 0.031 in. The actuators deliver the required precision despite bag variations.

Thiele’s bagging system includes a bag-handling module, a filling module and one or two sealing modules, depending on the style of bag being sealed.  The system will handle bags from 11 to 19 in. wide and 16 to 41 in. long.

Gifford wanted to use electric screw actuators for the bag trays because they are faster and more accurate, but there was no off-the-shelf system available. “Tolomatic provided a modified system that was also affordable,” he says. Their design is robust.  For example, the stainless steel band that seals the actuator as it moves protects the internal parts from dust, dirt and corrosion and reduces maintenance better than other designs.

Tolomatic Inc.
www.tolomatic.com