Using a Mechanical Gripper on the Robotiq Palletizing Workcell: Tips and Best Practices

Configure the collision model, payloads, pick angles and grip/release sequences so a jaw gripper runs reliably and at full speed.

The Robotiq Palletizing Workcell (PE Series, AX Series and PAL Ready) generates the robot trajectories from your recipe. The gripper itself is not part of that calculation: the software only knows what you tell it through the collision model, the TCP, the payloads, and the instructions you place in the Grip and Release folders of the Palletizer node.

The standard end effector is a PowerPick Vacuum Gripper. Some applications call for a mechanical gripper instead: two jaws that clamp the box from the sides. Because the jaws reach down beside the box, and one of them moves when the gripper opens, a mechanical gripper needs a few settings that a vacuum gripper does not.

This article covers grippers with one static jaw and one moving jaw. Grippers where both jaws move toward the center need free space on both sides of the box at every placement and are not covered here.

1. Start with one static jaw

• Use a gripper where one jaw stays fixed and only the other one moves. The static jaw is your reference: the box always sits at the same place relative to the TCP, and only one side of the box needs free space when the gripper opens on the pallet.
• Define the TCP at the center of the top face of the box as it sits in the gripper. This is the reference the Palletizer node uses for box positions.
• Enter the gripper mass and center of gravity as the installation payload. The box mass goes in the box type of the recipe, never in the installation payload.

2. Check the gripper against the collision model

By default, the software represents the gripper as a simple block above the box. Its dimensions follow the box size (PE20 user manual, section "Other Grippers"):

A mechanical gripper rarely fits in that block: the jaws sit outside the box footprint and reach down along its sides. If the real gripper is larger than its model, the software cannot guarantee a collision-free path.

• Use the custom gripper model option of the Palletizer node so that the model covers the whole gripper with the jaws closed, or load a simplified 3D mesh. See Defining the gripper in the Palletizer Collision Model.
• Keep the model simple: a coarse shape computes faster than a detailed one.

3. Make the moving jaw always open toward free space

When the gripper opens on the pallet, the moving jaw sweeps sideways. If a box already sits on that side, the jaw hits it. The solution is to declare that sweep as an obstacle attached to the gripper, so the software only chooses placements where the moving side faces free space.

1. In the Before Start section of the program, register a bounding box attached to the tool flange (referential 9) with the documented function:

rq_register_bounding_box(9, p[X, Y, Z, 0, 0, 0], [length, width, height], "movingJaw")

Size it to cover the moving jaw over its full opening travel, and position it on the moving side of the gripper. Because the referential is the flange, the volume travels with the gripper. Parameter details: Adding a bounding box to the palletizing collision model. To plan its size and position: Creating Bounding Boxes with the Online Configurator.

1. Keep the 180-degree pick option enabled (see section 4). It is the rotation that lets the software turn the gripper around so that the moving jaw faces the free side.
2. Build the patterns so that every box has a free side at the moment it is placed: fill each row away from the boxes already placed, and avoid closing a box between two placed boxes.
3. Check in the collision model viewer that the volume is where you expect, at the pick position as well as on the pallet: How to consult Collision model for Palletizing Solution.

4. Tell the software how the gripper can pick

In the Settings menu of the Palletizer node:

• Allow gripper to pick the box at different angles. The two options let the software pick a box as if the wrist had turned 90 or 180 degrees. A jaw gripper set for the box width usually cannot take the box across its length, so untick the 90-degree option in that case. Keep the 180-degree option: the moving-jaw rule of section 3 depends on it. Only remove what the gripper physically cannot do. Every option removed leaves fewer trajectory candidates, and the software then falls back more often to longer approach paths.
• Define conveyor to avoid collisions. Tick it and enter the conveyor geometry. With jaws that go down beside the box, the conveyor rails and end stop are the first things they meet.
• Add virtual planes around pallet(s). Robotiq recommends at least 50 mm around each pallet side. With a jaw gripper, include the travel of the open moving jaw when you choose that distance.

5. Leave room for the jaws on the pallet

• Gaps in the pattern. At release, the jaws are between the box and its neighbours. Leave a gap at least equal to the jaw thickness on the static side, and equal to the jaw thickness plus the opening travel on the moving side. Use the pattern editor (movement step or box coordinates) to set those gaps precisely.
• Place the box before opening. Enable the contact detection option before releasing the box on the pallet. A box held by its sides and released too high falls and tilts into the gap you left for the jaws.
• When boxes must touch. The "Use of force sensing for heavy payloads" feature moves the box horizontally toward its position until it touches the adjacent boxes, then lowers it. It is off by default and reduces throughput, so keep it for the recipes that need it.
• Open fully, then retract vertically. Wait for the open confirmation of the gripper before any retract move, and retract straight up first: the jaws are still between boxes.

6. Program the Grip and Release folders for speed

Everything you put in the Grip and Release folders is added to every cycle. When you estimate the cycle time in the online configurator, enter your real grip and release times. Without measured values, Robotiq uses 2 s for the pick and 2.5 s for the release with a mechanical gripper (see Understanding Cycle Time Estimates in the Online Simulator).

• Wait on the gripper feedback, not on timers. Close, then wait for the grip signal (or width reading) of the gripper before continuing. Do the same at release with the open signal.
• Switch the payload at the right moment, and let it finish. In the Grip folder, once the grip is confirmed, apply the box payload with rq_use_payload_with_box(). In the Release folder, once the box is released, call rq_use_payload_no_box(). If you use a transition time, set the blocking parameter to True: the Advanced Script sheet warns that a transition must be complete before the next robot trajectory. Details and alternatives: Payload transition strategies for palletizing.
• Add wait is_steady() before opening. The robot should be still when the load leaves the gripper. See Guidelines for Managing Protective Stops on Robotiq Palletizing Solutions.
• Keep custom moves short and relative. If you add a retract after release, define it relative to the current pose rather than to a fixed height above the floor. A fixed height makes the retract longer at each lower layer, and the cycle time changes from layer to layer.
• Set speed and acceleration on every custom move. The Tool speed and Tool acceleration values of the node do not apply to your own moves. A short retract commanded at a low acceleration never reaches its speed and can cost more than the whole gap you are trying to close.
• Measure before tuning. Recent versions of the Copilot URCap provide rq_get_last_completed_pallet_execution_stats(is_pallet_left), which returns the box count, the total, execution, wait and pause times, and the actual and optimal boxes per minute of the last pallet. It tells you whether the time goes to robot motion or to waiting for boxes. The function list is in the Advanced Script sheet: Where to find advanced script sheet for palletizer.

7. Clear the conveyor and the next box

• At pick, the jaws go down on both sides of the box. Check the clearance to the conveyor rails, to the end stop and to the next box waiting behind the gate: the gap between staged boxes must exceed the jaw thickness plus the opening travel of the moving jaw.
• Trajectories are computed for each box against the current collision model, which includes the conveyor you defined. When the direct exit path is predicted to collide, the software uses a higher one. Consistent staging on the conveyor therefore gives consistent trajectories and cycle times.
• To force a repeatable vertical exit and return above the conveyor, use rq_set_conveyor_clearance(is_left_pallet, height). The height is measured from the top of the box on the conveyor. Procedure from the Advanced Script sheet: define the conveyor in the node settings, run the first layer of each pallet without boxes, and increase the clearance only if the software reports a collision.

Conclusion

A mechanical gripper works well on the Palletizing Workcell when the software sees the same gripper you see: a collision model that includes the jaws, a bounding box on the moving side so the gripper always opens toward free space, correct payloads switched at the right moment, pick options that match what the jaws can do, and Grip and Release folders that wait on real feedback instead of timers. Validate each change one at a time, in the collision model viewer and with the execution statistics, before moving to the next.

Related articles:

• Defining the gripper in the Palletizer Collision Model
• Adding a bounding box to the palletizing collision model
• Payload transition strategies for palletizing
• Guidelines for Managing Protective Stops on Robotiq Palletizing Solutions
• Understanding Cycle Time Estimates in the Online Simulator
• Where to find advanced script sheet for palletizer

Need help with your gripper integration? Contact Robotiq Support.