How to Palletize Bags with the Robotiq Palletizing Solution

Bags are a flexible, deformable load and behave very differently from rigid boxes. The Robotiq Palletizing Solution can palletize bags, but because the Configurator, the collision model, and the payload transition are all designed around a rigid box, a bag application requires specific hardware choices and configuration techniques.

This article gathers the practices that work well for bag palletizing. Because bag materials vary widely, Robotiq recommends testing on customer-supplied bags before confirming a setup. The techniques below have been validated on bags with a plastic liner inside.

Before you start

• Bag type. The guidance here applies to bags that have a plastic liner inside. For other materials (paper, woven sacks, porous or fabric bags), grip reliability depends on the surface, so send representative samples to Robotiq for evaluation first. See the related article on the Piab Kenos KSG gripper for bag handling.
• Bag flattener. A bag flattener is strongly recommended. It creates a repeatable grip surface, which improves both pick reliability and placement accuracy. The benefit depends on the bag type.
• Plan for testing. Bag palletizing is an application that benefits from on-site validation. Expect to tune the settings below for your specific bag and product.
• Plan for new bag formats. Bag palletizing involves more manual configuration than rigid boxes. Each new bag format needs to be set up and tuned (placement pattern, collision model, payload transition). If you introduce new bag formats often, plan for the in-house skills or Robotiq support to re-tune each one. A small, stable set of bag formats is easier to maintain.

Step 1: Select and maintain the gripper

• A foam-based vacuum gripper such as the Piab Kenos KSG is a proven choice for lifting plastic-lined bags and provides a strong grip.
• Account for the gripper weight in your payload budget. A bag gripper can be heavy (a typical KSG setup is around 10 kg). Add the gripper weight to the bag weight, then confirm the total against your robot's payload curve at the working reach. A heavy gripper reduces the available bag weight and may require a larger robot.
• Treat the foam as a consumable. Foam wears with use. Inspect it regularly, plan a replacement interval, and keep spares on hand. If foam wear or adhesion is an issue, ask Robotiq or Piab about a different foam grade or adjusting the internal plate height.

Step 2: Configure the placement pattern in the Configurator

The Configurator places bags as if they were rigid boxes, so a few configuration techniques help keep the bags inside the pallet footprint and stacked correctly.

• Control the placement order with additional software layers. Bag placement order is important to keep every bag within the pallet footprint. A practical method is to define 2 or 3 software layers for a single real layer (the count depends on the bag size). The first software layer uses the real bag thickness, and the additional layers use a 1 mm thickness. This lets you set the exact placement sequence you want inside one physical layer.
• Orient the bags with Label Orientation. Use the Label Orientation feature to keep the closed end (the "butt") of each bag facing outward on the pallet, which produces a cleaner and more stable stack.

Step 3: Drop the bags from slightly higher

Dropping bags from a bit higher helps them settle into place, similar to how an operator palletizes bags by hand. For a row of three bags placed side by side, place the two outer bags first, then let the middle bag drop down between them.

To achieve this, increase the pallet height value in the Palletizer node rather than using the "adjust pallet height" feature.

Step 4: Protect the bag in the collision model

When you pick a bag by its filled end, the other end is often empty and extends beyond the modeled box dimensions. Without adjustment, the robot can collide with the empty end of the bag and trigger a protective stop (P-stop).

To prevent this, define a larger gripper model in the collision model so that it covers most of the bag. The software then plans trajectories that keep the entire bag clear of obstacles. For how to customize the gripper model, see the related articles on defining the gripper in the collision model and adding a bounding box.

Step 5: Tune the payload transition

Because a bag deforms as it is lifted, its weight and center of gravity shift during the pick. This is the most common source of protective stops on bag applications, so the payload transition deserves careful tuning.

• Use a longer payload transition. Giving the transition more time greatly reduces position deviation and protective stops. As a reference from a tested setup, a 0.5 second transition caused protective stops, 1 second produced noticeable deviation, and 2 seconds kept deviation consistently low. Budget cycle time accordingly.
• On an AX series (linear axis), lift with Force Control. Lifting the bag off the conveyor with a linear-axis move inside a Force Control node works better than a standard MoveL.
• Measure the deviation while you tune. You can add position_deviation_warning(True, 0.2) together with textmsg() at each step of the pick sequence to see which step creates the most deviation and to measure the effect of each change. Aim to keep the deviation low (below roughly 20%).

For more background, see the related article on payload transition strategies for palletizing.

Handling overhang

Depending on the bag size and the product inside, some overhang on the pallet is often necessary. Make sure your pallet specification allows it, and configure the overhang in the Configurator as needed.

Summary of best practices

• Validate the bag and add a bag flattener for a repeatable grip surface.
• Size the robot for the bag weight plus the gripper weight, and plan foam maintenance.
• Build the placement sequence with additional thin software layers, and use Label Orientation.
• Drop bags from slightly higher by increasing the pallet height value.
• Enlarge the gripper collision model so it protects the full bag.
• Use a longer payload transition (1 to 2 seconds), prefer a Force Control lift on AX series, and measure deviation while tuning.

Conclusion

The Robotiq Palletizing Solution can palletize flexible, plastic-lined bags when the gripper, the placement pattern, the collision model, and the payload transition are set up for a deformable load. Because bag materials and products vary, validate your specific bags with Robotiq before finalizing the setup. For help getting started or to arrange bag testing, contact the Robotiq support team.