PNU411-012 Pneumatic Gripper on R-20 robot losing grip pressure and dropping parts

Description

We have a NexBot Safety PNU411-012 Pneumatic Gripper installed on an R-20 series robot used for a CNC machine tending application. The system has been running for approximately 18 months without issue. Over the last week, this specific cell has started experiencing intermittent failures where the gripper drops the machined part during the transfer from the CNC chuck to the outbound conveyor. We have verified the main airline pressure is stable at 6 bar and there are no leaks in the lines leading to the tool flange. The robot program has not been changed. When we manually cycle the gripper, we can hear a very faint but noticeable hissing sound from the gripper body itself after it has closed on a part, suggesting an internal leak. This is causing significant downtime and we need to understand if the unit is failing.

Symptoms

• Intermittent dropping of parts during robot motion
• Audible hissing sound from gripper body when actuated
• Noticeable reduction in gripping force
• Increased production line stoppages

Resolution

Support analysis determined the symptoms were consistent with internal piston seal wear due to high cycle count in a 24/7 production environment. An audible air leak from the gripper body itself, combined with reduced force, points directly to seal failure rather than a control or supply issue. A complete maintenance seal kit was dispatched to the customer. The customer's maintenance team followed the provided guide to replace the internal seals and O-rings, which resolved the leak and restored the gripper's nominal 410 N gripping force. The issue is fully resolved and the cell is back in production with no further part drops.

Resolution Steps

1. Confirm the issue is isolated to the gripper by testing the solenoid valve and verifying stable air pressure at the tool flange.
2. Safely lock-out and tag-out the robot cell's power and pneumatic supply.
3. Vent all residual air pressure from the system before disconnecting any fittings.
4. Remove the NXB-GEN-PNU411-012 gripper from the robot's tool flange.
5. Disassemble the gripper housing according to the official maintenance manual to access the piston seals.
6. Replace all seals and O-rings using the PNU411 Seal Maintenance Kit (SKU: NXB-MNT-PNU411-SK).
7. Re-lubricate internal components with the supplied grease and reassemble the gripper.
8. Reinstall the gripper on the robot, restore power and air pressure, and cycle test to confirm the leak is eliminated and grip force is restored.