STO Relay Fault

When error [5.7122] occurs, the robot decelerates and stops, then switches to STO (servo off).

• Servo on fails, or the robot stops again shortly after servo on.
• The error often appears together with other error codes. Which codes appear with it is the most useful clue to the cause.
• It may start after a power outage, a collision, or work on the controller.

[5.7122] Safety controller category

STO relay fault occurred.
Param 1: CPU Number
Param 2: Expected value
Param 3: Measured feedback value

STO (Safe Torque Off) is the safety function that cuts power to the motors. The safety controller checks that the STO relay switches exactly as commanded. This error means the relay's feedback did not match what was expected, so the robot stays stopped for safety.

• Power supply in the controller — the motor power supply does not reach the right voltage, often after a power outage or an unstable mains supply. In this case 5.7114 usually appears as well.
• A fault in a joint — a problem in one joint, often reported together with joint torque sensor errors, stops the robot abruptly and the STO check fails as a result.
• Temporary disturbance — static discharge, a poor contact, a power surge, or conductive dust inside the controller.
• Safety controller board — damage from shock, vibration or overheating.

These checks need no tools and do not require opening the controller.

• Write down every error code shown with 5.7122, with the Param values. Support will ask for them.
• Turn the controller off, wait about a minute, and turn it on again. Note whether the error returns.
• Check that the controller's power comes from a stable supply, and whether there was a power outage or voltage drop just before the error.
• Check that the robot arm cable and the power cable are firmly connected.
• Check that the controller is not in a hot, dusty or damp place, that its fan is running, and that nothing is resting on it.
• Check whether the robot collided with something shortly before the error first appeared.

If the error returns after a restart, contact your distributor. Do not keep resetting it — the STO function is a safety function and must be confirmed to work correctly.

Prepare the following so the problem can be diagnosed quickly:

• Robot model and serial number
• Software version of the controller
• All error codes shown with 5.7122, their Param values, and the date and time
• What happened just before — power outage, collision, maintenance work
• The controller log exported right after the error
• A photo of the error message

• 5.7114 Under-voltage occurred on precharge voltage
• 5.7130 Watchdog fault occurred
• 4.1040 Abnormal Torque of the JTS #2
• 4.1044 JTS #2 value does not change
• 5.7059 Joint torque has exceeded user limit in at least one joint
• 5.7023 Joint torque sensor data sequence number error occurred on Inverter board