SV0468 Hi-Speed 1-Rev Signal Error fault in Fanuc drive

SV0468 Hi-Speed 1-Rev Signal Error fault in Fanuc drive

Description

SV0468 is a specific alarm related to the "One Rotation Signal" (Z-pulse) of the encoder. This signal is critical for operations that require synchronizing the axis to a specific angle, such as rigid tapping, screw threading on a lathe, or tool changing orientation. The alarm triggers if the drive rotates the motor but fails to detect the index pulse once per revolution, or if the pulse width is incorrect. It means the drive has lost track of the "Top Dead Center" of the motor shaft.

Cause

• Encoder Failure: The specific sensor track on the encoder disk responsible for the Z-pulse is damaged or dirty.
• Cable Wire Break: The specific wire pair carrying the 1-rev signal is broken, while the regular position A/B signals are fine.
• Coupling Slip: If the motor is used as a spindle (C-axis), a slipping belt can confuse the relationship between the motor commutation and the separate spindle position sensor.
• Noise: A noise spike masquerading as a Z-pulse at the wrong time.

Solution

1. Continuity Test: Check the continuity of the specific pins for the 1-rev signal in the feedback cable (Consult pinout diagram).
2. Swap Motor/Sensor: Since this is usually an internal optical failure of the pulse coder, swapping the motor is the primary diagnostic step.
3. Check Alignment: If using an external proximity switch as the 1-rev signal (common in some spindle setups), ensure the gap is tight and the target bolt is present.