Fanuc Alarm Code 31

Alarm Code 31 – ALPHA Spindle Amplifier
The motor does not rotate as commanded. Either it does not rotate at all or rotates slowly.

The AL. 31 is another common fault on ALPHA & ai series spindle drives. Caused by usually one of four issues, namely the speed sensor, parameters in the CNC associated to the setup of the speed sensor, the cable(s) between the speed sensory and the amplifier and the amplifier. However there can be others which are less common causes.

(1) If the motor rotates at a very low speed and this alarm is issued

• The Sensor is physically damaged or obstructed or moved.
• The feedback cable of the motor has a problem.
• The setting of a parameter is incorrect.
• The motor phase sequence is incorrect.

(2) If the motor does not rotate at all and this alarm is issued

• The Sensor is physically damaged, obstructed or moved.
• The feedback cable of the motor is faulty.
• Internal feedback cable between sensor & terminal box is faulty.
• The power line is faulty.
• The sequence for locking the spindle is incorrect.
• The SPM is faulty. Replace the SPM.

CNC Tip: When AL. 31 code presents on the twin seven segment display on your ALPHA series spindle amplifier module and aiSP modules is too make sure the sensor is not obstructed and has not moved.

We can test most ALPHA and ai spindle amplifiers, and models of AC spindle motors at our location in Virginia. We also supply servo drives, motors and system axis cards.

We always recommend using the services of a trained CNC service engineer whom has the electronic and mechanical training, experience and knowledge to deal with the Fanuc side of your machine tool.

The alarm above cover ALPHA 6078, 6082, 6088, 6092, 6012, 6104 and ALPHA i series 6111, 6112, 6121, 6122, 6141, 6142, 6151, 6152 and later aiSP modules.