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
Minneapolis (Vocus) March 17, 2009
Thiele Technologies, a leader in packaging technology and equipment, recently faced the problem of how to compensate for inconsistent bag dimensions on its popular modular bag filling and sealing system. Thiele serves customers in the diverse bulk-materials processing industries, and the bagging system is designed to measure, fill and seal bags containing anything from pet food to salt, sugar, dirt, seed, fertilizer or animal feed. Many of Thiele's customers had switched to low-cost bags with irregular dimensions. These irregularly sized bags were slowing the production process, which requires high-speed accuracy to meet manufacturing goals.
Since repeatability is critical to the filling and sealing operation, Thiele engineers sought a solution that would increase accuracy, flexibility and productivity for packagers. They found their solution in 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 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 would not be positioned accurately, resulting in improper filling and sealing.
"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 lower cost has come lower quality, however. 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."
Improvement features rodless actuators
Thiele's new 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 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-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.
Improving repeatability was key objective
"This new design meets our criteria for repeatability because it automatically compensates for variations in bag length and width and eliminates filling and sealing problems," says Gifford. "The design tolerance for positioning the tops of the bags is only +/- 0.031 inches, and now we can maintain that precision even when bag dimensions vary."
To download the complete case study and high resolution photos, go to: http://www.cccinc.com/pr/tolomatic/thiele .