Under normal conditions, a protective stop is typically caused by the robot software (e.g. Hardware protection, limited joint angles or speed limits). With MIRAI, we have seen users unexpectedly encounter this error when trying to run a program or trying to use the toolbar for UR+ on polyscope. This has been reported during initial setup and even after successfully running several cycles of a skill.
To resolve, we recommend the following troubleshooting steps:
Check if a different URCap is using the Real-time Data Exchange (RTDE) feature. Some URCaps you have installed may be using RTDE which is considered a field-bus. If their processes stop, it can cause a disconnect issue.
To troubleshoot, try removing other URCaps off Polyscope, does the issue continue? If it does, try doing a cold restart on the robot using the following service manual procedure: Complete Rebooting Sequence.
Check the fieldbus connections (RTDE, ModBus, EtherNet/IP and Profinet) or disable the fieldbus from the installation tab on Polyscope. Also, verify that the Profinet adapter is disabled as well.
In many cases, disabling all settings in the installation tab (Ethernet/IP Adapter, MODBUS, PROFINET Onrobot FT Setup, gripper) solves the issue. Make sure to save your settings, then reboot the robot.
Check for an RTDE watchdog.
A watchdog is a timer which must be reset regularly before it times out, or it will cause the PLC or microcontroller to fault or reset. In a microcontroller, your program would explicitly reset the watchdog. In a PLC, the watchdog is automatically reset during the I/O update (between program scans).
A watchdog switches to fault mode and stops the program if the scan time of the PLC goes over specified limits. If your PLC supports loops or jumps, you can test this by programming an infinite loop. The PLC should fault and either go into stop mode or perform whatever other fault action.
The protective stop may actually be an authentic error and should be investigated further from the robot-side. For a detailed breakdown of possible protective stop factors, see the Protective Stop Service Note from Universal Robots.