Fanuc Series 0i Error Code 407

Fanuc PLC & VFD Minor Servo

Model: Series 0i | Code: 407

Applicable Systems
Series 0i Series 16/18/21 Alpha Beta

Symptoms

The CNC system displays alarm 407: SERVO ALARM: EXCESS ERROR. The position deviation between the commanded position and actual position during synchronous axis control has exceeded the set limit. This occurs in machines with dual-axis synchronization (e.g., gantry mills).

Possible Causes

  • Mechanical mismatch between the two synchronized axes (one axis is lagging)
  • Ball screw or coupling backlash difference between the two axes
  • One servo motor or amplifier is weaker or slower than the other
  • Synchronous control parameter settings are incorrect

Troubleshooting Steps

  1. Step 1: Inspect the mechanical coupling and ball screw on both synchronized axes
    Both axes should have similar backlash and friction; check for wear or looseness
  2. Step 2: Verify both servo motors and amplifiers are the same model and rating
    Mismatched motor or amplifier sizes can cause synchronization errors
  3. Step 3: Check the synchronous axis error limit parameter (No. 2031)
    The limit should be set appropriately for the application; if too tight, even normal operation may trip
  4. Step 4: Run a test program that moves both axes simultaneously and monitor the position deviation on the diagnostic screen
    The deviation should stay within the set limit; if one axis consistently lags, investigate its mechanical or electrical condition

How to Reset

To reset: 1) Press RESET on the CNC. 2) Fix the mechanical or electrical mismatch. 3) Re-run. Caution: Excess error in synchronous control can cause mechanical twisting if the axes are rigidly connected. Always investigate the root cause.

Frequently Asked Questions

  • Q: What is synchronous axis control?

    In gantry-type machines, two servo motors drive the same mechanical axis (e.g., a bridge) to keep it level. The CNC synchronizes their positions. Alarm 407 occurs when the position difference between the two motors exceeds the allowed limit.

  • Q: How do I adjust the excess error limit?

    Parameter No. 2031 sets the maximum allowable position deviation. Increasing it allows more tolerance but reduces safety. The correct value depends on the mechanical stiffness and application. Always consult the machine tool builder's documentation.

Related Fanuc Fault Codes

Source: FANUC Series 0i-Mate Maintenance Manual, B-64115EN

Category: PLC & VFD