Intermittent E-Stop Fault on C-5 Robot Cell Using NXB-GEN-622-015

Description

We are experiencing intermittent and random emergency stop faults on our C-5 series robot in cell 3B. The controller throws an E-4110 error, indicating an external E-Stop circuit fault. The operator confirms that no one has activated the E-Stop button when the fault occurs. The button in question is the NexBot Vision 622-015 Emergency Stop Device. We've inspected the wiring between the button and the safety I/O module, and all connections appear secure with no visible damage to the conduit. The fault happens maybe once or twice per shift, causing significant downtime as we have to reset the entire line. After a reset, the system runs fine for several hours before it happens again. We suspect the NXB-GEN-622-015 E-stop device itself may have an internal intermittent failure, but we want to confirm before replacing it.

Symptoms

• Robot unexpectedly enters emergency stop state during operation.
• Controller displays error E-4110 (External E-Stop Circuit Fault).
• The physical E-Stop button (NXB-GEN-622-015) is not depressed when the fault occurs.
• The issue is intermittent and temporarily clears after a full system reset.

Resolution

The customer was guided through a diagnostic procedure to test the internal contacts of the E-Stop device. Using a multimeter in continuity mode, they tested the normally closed (NC) contacts of the NXB-GEN-622-015. While monitoring the connection, slight vibration and wiggling of the button assembly caused the continuity to break intermittently, confirming an internal mechanical fault. The intermittent open circuit was tricking the robot's safety controller into thinking the E-Stop had been pressed. The customer was advised to replace the faulty unit. After installing a new NXB-GEN-622-015 device, the intermittent faults were eliminated and the robot cell has been operating without issue for 48 hours.

Resolution Steps

1. Ensure the robot controller and related machinery are powered down using proper lock-out/tag-out (LOTO) procedures.
2. Disconnect the two wires from the normally closed (NC) contact terminals on the back of the suspect NXB-GEN-622-015 E-Stop device.
3. Set a digital multimeter to the continuity test setting (the one that beeps).
4. Connect the multimeter probes to the two NC terminals on the E-Stop device. The meter should indicate a closed circuit (beep).
5. While the probes are connected, gently tap and wiggle the red mushroom head of the E-Stop button without pushing it in. Observe the multimeter.
6. If continuity is lost at any point (the beeping stops), the device has an internal fault and must be replaced.
7. Replace the faulty unit with a new NXB-GEN-622-015 E-Stop device.
8. Reconnect wiring, remove LOTO, and power on the system to verify normal operation.