Pick-and-place fails

1. Symptoms

• The gripper closes on nothing or off-centre.
• The object is dropped during the move.
• The arm collides or the planner fails near the object.

2. Possible causes

• Hand-eye calibration error or intrinsics error.
• Detection error or wrong object pose.
• Approach direction blocked by neighbours or the table.
• Gripper force or friction too low, or vacuum leaks.
• Planning scene incomplete.
• Timing: the object moved between detection and grasp.

3. Measurements to collect

• Offset between detected and actual object position at several places.
• Gripper width and force at each stage.
• Planner and controller errors.

4. Diagnostic commands

Commands are not executed by the site’s automated tests (they need a ROS 2 Jazzy installation or the robot).

ros2 topic echo /joint_states
ros2 topic echo /gripper/state
ros2 bag record /camera/image_raw /joint_states /gripper/state /tf

5. Step-by-step investigation

1. Locate the failing stage from the gripper signals (missed, weak, slip).
2. Check calibration with a touch test at several places.
3. Check the grasp pose and approach in RViz.
4. Check force or vacuum against the requirement with margin.
5. Check the planning scene and planner errors.
6. Check for object motion between detection and grasp.

6. Corrective actions

• Recalibrate hand-eye and intrinsics.
• Change the grasp orientation or approach.
• Increase force or change the gripper or fingers.
• Complete the planning scene.
• Detect again just before the approach.

7. Validation after the fix

• Long run with a known failure rate per type, below the requirement.

References

• See the grasp validation guide and the hand-eye calibration guide.