What are the common servo faults of four-axis CNC machining centers

Common servo faults in four-axis CNC machining centers mainly include servo alarms, motor overheating, abnormal vibration and noise, inaccurate positioning, and out-of-control runaway. Combined with system parameters and mechanical matching issues, the following are specific classifications and cause analysis.

I. Servo system alarm faults

Such faults are usually caused by incorrect parameter Settings or abnormal communication. The system will display specific alarm codes for quick location.

SV0417 alarm (servo parameters illegal) ‌ : Parameters 2020, 2022, 2023, and 2024 are set beyond the allowable range or are illegal values, which is commonly seen during the debugging process of the 4th axis due to incorrect parameter input.

SV0401 alarm (servo ready signal off) ‌ : The servo ready signal (VRDY) is not connected, which may be caused by the emergency stop not being released, the MCC contactor not being engaged, or abnormal power supply.

SV1067 alarm (FSSB configuration error) ‌ : The type of amplifier connected by the optical cable does not match the system Settings. The FSSB initialization Settings need to be checked.

ALM401 alarm ‌ : The servo driver is not ready. Common causes include a blown main circuit fuse or a phase loss in the power supply.

Ⅱ. Abnormal motor operation faults

1. The servo motor is overheating

Possible cause ‌ :

The load exceeds the motor's rated value

The cooling fan is faulty or the vent is blocked

Insufficient lubrication leads to increased friction of the bearings

Solution ‌ : Clean the cooling system, check the load current, and replenish or replace the lubricant.

2. Excessive vibration and noise

Possible cause ‌ :

The mechanical installation is unstable, the coupling is loose or the bearing is worn

The servo gain parameter does not match the mechanical rigidity, causing resonance

The encoder signal is interfered with

Solution ‌ : Tighten mechanical components, adjust servo rigidity parameters, and inspect shielded cables.

3. The motor fails to start or suddenly stops

Possible cause ‌ :

Abnormal power supply voltage or phase loss

The encoder signal is interrupted or the power line is loose

Mechanical jamming (such as damage to lead screws or bearings)

Solution ‌ : Check the power input, test the encoder connection, and manually turn the machine to confirm the mechanical status.

Ⅲ. Control Accuracy and Feedback Faults

1. Inaccurate positioning or positional deviation

Possible cause ‌ :

Encoder failure or loss of feedback signal

The backlash of the lead screw is too large

The electronic gear ratio and origin offset parameters have not been calibrated

Solution ‌ : Clean the encoder grating, measure and adjust the backlash using a dial indicator, and recalibrate the parameters.

2. Runaway phenomenon (out of control)

Possible cause ‌ :

The speed/position feedback signal is reversed to form a positive feedback

The encoder line is disconnected or not connected

CNC or servo control board failure

Solution ‌ : Check the signal polarity, confirm the integrity of the wiring, and inspect the status of the control board.

3. The speed is unstable during operation

Possible cause ‌ :

Poor contact of the tachogenerator

The gain setting of the speed loop is improper

External interference affects the feedback signal

Solution ‌ : Clean the commutator, adjust the VR3 potentiometer, and enhance signal shielding.

Iv. System-level and communication-related faults

Abnormal servo preparation signal ‌ : Three conditions, namely pulse enable, driver enable, and axis enable, must be met. The absence of any one of them will result in the inability to operate.

Absolute position loss (APC alarm) ‌ : low battery voltage, poor cable contact or incomplete FSSB initialization.

Measurement system failure ‌ : Manifested as inaccurate zeroing and dimensional drift during processing, it is usually caused by loose encoder connection or position control board failure.