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Haas Controller
Overtravel/Limit · Basic · 1-2.5 hours
Overtravel Positive Z
Alarm 24 Fourth Axis Servo Fault occurs when the NGC control detects a communication or feedback error between the fourth axis servo amplifier and motor assembly. This typically results from encoder signal degradation, servo amplifier malfunction, or motor winding issues that prevent proper servo loop closure.
24
Overtravel Positive Z
Fourth Axis Servo Fault
This alarm indicates the IOCON board has detected a fault condition from the A-axis servo amplifier during operation or attempted motion. The servo amp monitors motor current, encoder feedback, temperature, and DC bus voltage and will fault if any parameter exceeds safe limits or if encoder communication is lost. The machine will stop all motion and require a reset before the A-axis can be re-enabled.
Root Cause Summary
Alarm 24 Fourth Axis Servo Fault occurs when the NGC control detects a communication or feedback error between the fourth axis servo amplifier and motor assembly. This typically results from encoder signal degradation, servo amplifier malfunction, or motor winding issues that prevent proper servo loop closure.
Safety
- Do not manually rotate fourth axis continuously during diagnosis, servo encoder may reset improperly
- Ensure spindle is stopped before rotating fourth axis to prevent cutting tool damage
- Mechanical rotation of fourth axis may release stored energy in brake or clutch systems
Causes and Fixes
- 1
Check Fourth Axis Encoder Cable
Power down machine and inspect the fourth axis encoder cable from motor to servo amplifier. Look for cuts, pinch points, or damaged connectors at both ends.
Ensure main power is OFF and LOTO procedures are followed before inspecting cables.
- 2
Verify Encoder Signals in Diagnostics
Navigate to CURRENT COMMANDS > DIAGNOSTICS > ENCODER and check fourth axis encoder counts. Values should change smoothly when manually rotating the axis.
Erratic or missing encoder counts confirm encoder system failure.
- 3
Test Encoder Connector Integrity
Disconnect and reconnect the encoder connector at the servo amplifier. Clean contacts with electrical contact cleaner if corrosion is present.
Apply dielectric grease to prevent future corrosion in harsh environments.
- 4
Replace Encoder Cable if Damaged
If cable damage is found, replace with genuine Haas encoder cable. Ensure proper routing away from high-voltage cables and moving components.
Call a technician if:
- ·Servo amplifier replacement required
- ·Motor replacement needed
- ·Multiple servo faults present
- ·Electrical measurements show dangerous conditions
Prevention
- Regular encoder cable inspection
- Maintain proper fourth axis lubrication
- Monitor servo motor operating temperature
- Keep electrical cabinet clean and dry
- Perform periodic parameter backup
Common Mistakes
- Ignoring encoder cable routing requirements
- Mixing servo amplifier models between axes
- Skipping servo tuning after repairs
- Not checking motor coupling alignment
- Failing to verify encoder phasing after motor replacement
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