SV0410 Stop Error Exceeded (Excess Error) fault in Fanuc drive

SV0410 Stop Error Exceeded (Excess Error) fault in Fanuc drive

Description

The SV0410 alarm is arguably the most common servo alarm encountered on Fanuc CNC systems. It indicates a "Following Error" or "Excess Error" specifically while the axis is supposed to be stationary. In a closed-loop servo system, the CNC sends a command to the drive to hold a specific position. The drive uses the encoder feedback to monitor the actual position. The difference between the commanded position and the actual position is the "error." When the machine is stopped, this error should be near zero. If the error grows larger than the threshold set in the parameters (typically parameter 1829 in i-series controls), the system triggers SV0410 to prevent the machine from losing its known position or causing damage due to uncontrolled drift.

Cause

The causes for SV0410 are varied but generally fall into three categories: Mechanical, Electrical, or Parameter-based.

• Mechanical Load/Binding: If the axis is physically stuck, rusted, or binding (gibbs too tight), the motor cannot move the table to the commanded position, causing the error to spike.
• Brake Failure: On vertical axes (gravity axes), if the electromechanical brake does not release quickly enough, the motor fights the brake, causing an error. Conversely, if the brake slips while stopped, gravity pulls the axis down, creating a deviation.
• Power Issue: If the amplifier lacks one phase of power or has a blown fuse, it may not have the torque required to hold the position.
• Encoder Feedback: If the encoder coupling is loose, the motor turns but the encoder doesn't record it accurately, causing a discrepancy.

Solution

To resolve SV0410, follow this systematic approach:

1. Check Mechanics: With the machine powered off (and blocked up if vertical), try to move the axis by hand. It should move relatively smoothly. If it is stuck, check for chip buildup under way covers, lack of lubrication, or seized bearings.
2. Verify Brake Voltage: Check the 24VDC supply to the motor brake. Ensure the relay controlling the brake is functioning and that the brake physically releases when the servo is activated.
3. Inspect Power Cables: Check the U, V, W power cable going from the drive to the motor. Use a megohmmeter to check for shorts to the ground and an ohmmeter to ensure continuity between phases.
4. Check Coupling: Inspect the mechanical coupling connecting the motor to the ball screw. A cracked or slipping coupling will cause immediate position errors.