FANUC Sensor A860-2120-V004 A8602120V004 A860-2120-V004

FANUC A860-2120-V004 | Alpha i BZ Sensor Head — Spindle Speed and Position Feedback, Without Mounting Ring

Part Number: A860-2120-V004

Cross Reference: A8602120V004

Manufacturer: FANUC Ltd. (Japan)

Product Type: Alpha i BZ Sensor Head — Spindle Encoder Sensor (AiBZ type)

Spindle Speed and Position at the Source

The A860-2120-V004 is the Alpha i BZ (AiBZ) sensor head for FANUC's built-in AC spindle motor series. This magnetic sensor detects the spindle motor's rotational speed and angular position directly from the toothed gear ring on the motor's rotor. The detected signal feeds the spindle amplifier's closed-loop control algorithm and also provides the position data that the CNC uses for spindle-orientation functions, C-axis control, and rigid tapping.

The BZ sensor operates on the Hall-effect or magnetic inductive principle. As the motor rotor turns, the gear teeth pass the sensor head and generate a pulsed signal proportional to the rotation speed and direction. The sensor assembly (V004 variant) is supplied with its cable and connector but without the mounting ring. The mounting ring is a separate component that holds the sensor head in the correct radial position relative to the gear ring — if the original mounting ring is undamaged, it can be reused with the new sensor head.

The A860-2120 series includes multiple variants (V001, V002, V003, V004, V005, V007, V013) covering different motor configurations and mounting geometries. The V004 serves a specific spindle motor variant. Confirm the installed variant from the sensor's own label before ordering.

Key Specifications

FAQ

Q1: The CNC shows spindle encoder alarm AL-24 or AL-73. Could the A860-2120-V004 be the cause?

AL-24 (speed deviation) and AL-73 (sensor fault) on the spindle axis are the most common alarms associated with a failed BZ sensor. Before replacing, check the sensor cable for damage and verify the sensor connector is fully seated at the spindle amplifier's BZ port. Magnetic dust accumulation on the gear teeth also causes detection errors — clean the gear ring with compressed air before concluding the sensor has failed.

Q2: The mounting ring is described as "not included." Is it required for installation?

The mounting ring positions the sensor head at the correct air gap above the rotor gear ring — this gap is critical for reliable signal generation. If the original mounting ring is undamaged, it can be reused with the replacement V004 sensor head. If the mounting ring is damaged or missing, it must be sourced separately from the same A860-2120 series.

Q3: How is the BZ sensor air gap set correctly after installation?

The air gap between the sensor head and the gear ring surface is set using the mounting ring's mechanical stop. After mounting, verify the sensor cable is routed without sharp bends. Power up the spindle and confirm the BZ signal is present on the spindle amplifier's diagnostic display. If the spindle amplifier shows no BZ signal, re-check the air gap and connector seating.

Q4: Magnetic dust is mentioned as a potential cause of detection errors. Is this a common problem?

Yes — built-in spindle motors in machining environments are exposed to metal swarf and coolant mist. Ferrous particles carried in the coolant can accumulate on the rotor gear ring and interfere with the sensor's magnetic detection. Periodic cleaning of the gear ring area with compressed air is a recommended preventive maintenance step on machines with significant swarf generation.

Q5: What is the difference between the A860-2120-V004 and the V001, V002, V003 variants?

The V-number suffix identifies different physical configurations — cable length, connector type, or mounting geometry differences matched to specific spindle motor variants. They all perform the same AiBZ speed and position sensing function. Always confirm the installed variant from the sensor assembly's own label before ordering — fitting an incorrect variant may result in a connector mismatch or incorrect mounting geometry.