Customer Challenge

Inteplast Group is a multi-billion dollar company with a focus and specialization in plastics. One of the company's core product lines is the t-shirt bag. These low-cost bags are widely used by retailers including Wal-Mart and Target, as well as in supermarkets and drug stores.

Inteplast was employing an antiquated system to stack and pack the t-shirt bags. The system relied on the labor of three persons per line and produced a substantial number of boxes that were either under- or over-filled. This inconsistency greatly reduced customer satisfaction, throughput efficiency and overall profitability.  

Inteplast asked RT to design a machine that would increase the number of bags per box and ensure standardization and accuracy. Additionally, Inteplast aspired to reduce the number of operators per packing line from three to one.

RT Engineering's Solution

Scope of Supply:  The Autopacker RT built for Inteplast moves stacks of bags through a total of six conveyors, which are controlled by variable frequency drives. The system also features two servo axes—one to rotate paddles that hold bags above a box, and one to rotate the box in 90-degree increments. When the first servo axis rotates its corresponding paddles the bags drop into the box.  This allows for more uniform and flat packing, and by overfilling the box prior to its conveyance to the stomper station, the system increases the total number of bags per box by 15%. The stomper removes all air between the bags, increasing density.  Once the air is removed, the box is sealed, labeled, weighed for accuracy, and moved to a manual palletizing station.

The variable frequency drives are Allen Bradley Power Flex 525 models, and the servo drive is Yaskawa Sigma 5 M2600iec. The system also utilizes an Allen Bradley Compact Logix PLC for machine control and a Red Lion Human Machine Interface unit for operator interaction.

The system is equipped with a safety light curtain to allow the operator to gain safe access to the machine to fix potential jams. A safety rated Category 2 circuit is employed with a dual channel E-Stop circuit. Inteplast and RT Engineering completed a risk analysis to guarantee that the system meets all safety requirements.

The system houses electrical components in an enclosure mounted to the machine frame. While one main disconnect electrically isolates the entire machine, the stomper section contains a secondary isolation disconnect so that it may be shut down for maintenance while the packer section continues to run. The stomper section has its own E-Stop zone circuit so the operator can fix issues there while the rest of the Autopacker maintains functionality.

Remote I/O junction boxes are deployed at strategic locations across the machine. These junction boxes contain Allen Bradley Point I/O modules to accept field device wiring. The remote I/O data communicate with the PLC via the Ethernet/IP protocol.

Upper Autopacker: The Autopacker machine integrates to the end of a bag fabrication machine conveyor, which introduces “hands” of bags to the Autopacker’s ramp conveyor. The ramp conveyor is at an incline and transfers the hands of bags to a QC conveyor for processing.

The ramp conveyor is actuated pneumatically out of the way to be able to accommodate functionality independent of the Autopacker. This allows the Lemo bag line to open and the Greenbelt to slide under so the operator can service the seal section of the line.

The QC conveyor is perpendicular to the ramp conveyor. While the ramp conveyor runs it introduces an air blanket under the hands of bags as they are being transferred. There is a small guarding section at the transfer point to discourage the operator from interfering in this critical area.

Once the first transfer is complete, the QC conveyor transfers the hands of bags to a stacking (takeaway) conveyor. The stacking conveyor runs at a faster rate, which creates space between each hand of bags. The stacking conveyor transports the hands of bags directly to the drop paddles station.

Both the QC and stacking conveyor speeds are independent and can be adjusted to maximize product transfer times.

In the drop paddles station the paddles rotate 90 degrees, guiding the hand of bags into a box directly below, which resides on the turntable station. After the paddles have completely released the hand of bags into the box, a pre-stomp cylinder is actuated to compress the bags in the box and relieve any trapped, residual air.

Lower Autopacker: The first section of the lower Autopacker is the box feed conveyor. The operator manually loads the box feed conveyor with pre-erected boxes that are left open at the top. Although the operator pre-folds the bottom of the boxes when placing them in the conveyor, the box is not sealed until later in the process. The operator will continue to load pre-erected boxes onto the conveyor until it is fully populated.

As the operator places boxes onto the conveyor they move to the box holdback/box pusher station.

The box holdback/box pusher station is where the box is pneumatically transferred to the turntable station. Because there are other boxes in the queue, a box holdback station is pneumatically engaged to hold the rest of the boxes in place until the box pusher has completed its cycle, at which point the holdback will retract and allow the next box to transfer into the station.

Once a box is introduced to the turntable, a hand of bags is dropped into the box from the drop paddle station directly above. The turntable then rotates and another hand of bags is dropped into the box. This continues until the box is full, at which point the box pusher moves the next empty box into the turntable station. While this box is being transferred it will push the full box onto a box conveyor. There is a safety light curtain at the exit area of the turntable for operator safety. This light curtain is active throughout all machine operation and is muted only when a box is being transferred from the turntable to the box conveyor. 

RT designed a direct drive servo indexing unit which allows for complete control of turntable motions. Instead of having fixed moves, the turntable will be able to rotate in any number of increments with a simple programming change.

Stomper/Taper: The stomper/taper section is where the full boxes get weighed, sealed and offloaded.

Once the box reaches the end of the box conveyor it is transferred to the stomper/taper conveyor, where it is weighed before it moves forward. The scale is located under the conveyor and is pneumatically actuated. Two arms press the box up from the sides and weigh the box. Then the scale retracts and the box is conveyed to a box pusher/stomper station.At this point, the stomper cylinder pneumatically extends down and presses against the hands of bags to ascertain complete compression. Once this cycle is complete the box pusher pneumatically transfers the box to the upper/lower seal machine.

The gravity conveyor acts as the finished product queue area. An operator will manually unload the conveyor.

Solution Highlights


  • The Autopacker frame is welded tubular, spray-painted steel. It includes two safety doors for machine access with mesh inlays. All other guarding includes item framing with mesh inlays, as well.
  • The stacking conveyor station is equipped with a safety access door with mesh inlay.

  • The box infeed conveyor is a flat belt conveyor, which solves issues that arise from roller conveyors.

  • The drop paddles are designed to require only one servo motor.

  • The pre-stomper is installed to the drop paddles section of the machine to help eliminate trapped air.

  • The turntable utilizes a user-friendly direct drive servo motor instead of pneumatics to streamline and simplify the unit.

  • A safety light curtain is situated in exit area of the turntable to enhance operator safety.

  • An Ethernet-controlled pneumatics manifold enhances the pneumatics section of the Autopacker.


  • The stomper/taper frame was constructed with Item aluminum extrusion with mesh inlays. It includes two safety doors for machine access with mesh inlays.

  • The stomper/taper conveyor is a flat belt conveyor to replace the problematic roller conveyor.

  • The box pusher was designed to ensure that transferring boxes is not an issue.

  • The scale is positioned under the new stomper/taper conveyor.

  • An Ethernet-controlled pneumatics manifold enhances the pneumatics section of the stomper/taper.

The Result

  • Production increase of 30-40% over semi-manual operation for two product types
  • Eliminate operator manual/repetitive tasks
  • Improved product quality by automating key assembly operations
  • Improved safety and updated electrical control standards

To find out how performance monitoring systems could help your business, please contact RT Engineering today to learn how we can improve your company’s manufacturing processes.

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