Intermittent Faults on 631-007 Pressure Safety Mat Causing R-100 Cell Stoppages

Description

We are experiencing intermittent and unpredictable emergency stops in one of our R-100 welding cells. The system controller logs a safety circuit fault, and our maintenance team has traced it back to the input for the NexBot Robotics 631-007 Pressure Safety Mat. The mat itself appears to be in good physical condition with no visible cuts, tears, or heavy wear. The issue occurs randomly, sometimes multiple times in an hour, and other times it will run for an entire shift without a problem. We have checked the terminal block connections at the safety PLC, and they are secure. Wiggling the cable near where it enters the mat seems to sometimes trigger the fault, but not consistently. This downtime is becoming critical for our production schedule, and we need to determine if the mat is faulty or if there's a configuration issue we are missing.

Symptoms

• Robot cell enters E-stop state without physical presence on the mat.
• Safety controller indicates an intermittent open circuit on the mat input.
• Production line halts unexpectedly several times per shift.
• Manipulating the mat's connection cable sometimes triggers the fault.

Resolution

Troubleshooting revealed an internal, intermittent break in the mat's integrated connection cable, located near the strain relief housing. The physical damage was not externally visible but was confirmed by continuity testing while manipulating the cable. The intermittent connection caused the safety circuit to open randomly, triggering a fail-safe E-stop. As the cable is an integrated part of the IP67-rated assembly, the entire mat was identified as the point of failure. The issue was fully resolved by replacing the faulty unit with a new mat.

Resolution Steps

1. Verified the safety controller was receiving the correct 24VDC signal from the safety mat circuit under normal, no-fault conditions.
2. Disconnected the NexBot Robotics 631-007 mat from the safety I/O module to isolate it.
3. Using a multimeter set to continuity mode, tested the mat's internal safety contacts at the connector pins.
4. While testing, carefully manipulated the integrated cable along its length. The multimeter showed an intermittent open circuit when the cable was bent near the mat entry point.
5. The test confirmed a fracture in an internal conductor within the cable assembly.
6. A replacement NexBot Robotics 631-007 Pressure Safety Mat (SKU: NXB-GEN-631-007) was ordered and installed.
7. A full safety system validation test was performed, including pressure tests on all areas of the new mat, which passed successfully.
8. The R-100 robot cell was returned to production, and no further intermittent faults have been observed.