Fanuc PLC Sensor Encoder A20B-2003-0310 A20B20030310 A2OB-2OO3-O31O

A20B-2003-0310 | FANUC MI/MIZ Sensor Pick-Up Unit PCB — A860-2100-V001 / Alpha and Alpha-i Spindle / Speed / Orientation / Rigid Tapping

MI/MIZ Sensor — Three Functions, One Sensor Assembly

The FANUC Alpha and Alpha-i spindle motor's MI sensor (Magnetic sensor with Index) or MIZ sensor (Magnetic sensor with Index and Z-phase) provides the spindle amplifier with the feedback it needs for three distinct functions:

Spindle speed regulation: Continuous speed pulse counting provides actual spindle speed. The spindle amplifier compares this against the CNC-commanded speed every few milliseconds, adjusting the motor current to maintain programmed speed under varying cutting loads.

Spindle orientation: The CNC commands the spindle to rotate to a specific angular position before a tool change. The sensor's I (index) pulse provides the absolute angular reference. The amplifier counts encoder steps from this reference to reach and hold the orientation position.

Rigid tapping: Rigid tapping requires exact phase-locked synchronisation between spindle rotation and Z-axis feedrate. The sensor's real-time angular feedback allows the CNC to compute the Z-axis position command from the spindle angle at every interpolation cycle — maintaining the precise pitch ratio required for accurate threads.

Key Product Information

Sensor PCB Failure — Symptoms

A failed A20B-2003-0310 disrupts the spindle's feedback:

SP alarm 07 (speed feedback fault): The spindle amplifier detects no or implausible speed feedback signal. This alarm fires when the spindle is commanded to run — the drive cannot regulate speed without feedback.

Orientation failure: The index pulse is absent or corrupted. The spindle rotates indefinitely searching for the orientation reference. The CNC generates an orientation timeout.

Rigid tapping errors: Phase synchronisation breaks down — incorrect thread pitch or CNC synchronisation alarms during tapping cycles.

Intermittent alarms correlating with temperature: The PCB may work correctly at cold start but fail as the spindle motor area heats up — a characteristic of thermally degraded solder joints or components in the sensor assembly.

Application Scenarios

SP-07 alarm diagnosis: A machining centre generates SP-07 on spindle start. Motor winding, cable, and amplifier feedback input all test correctly. The A860-2100-V001 pick-up unit is identified. Replacing the A20B-2003-0310 PCB inside clears the alarm.

Orientation fault on CNC lathe: A turning centre fails tool change operations — spindle cannot orient. The I-pulse from the pick-up unit is absent. A20B-2003-0310 replacement restores the orientation index.

FAQ

Q1: Is A20B-2003-0310 the complete A860-2100-V001 unit or just the PCB inside?

The A20B-2003-0310 is the PCB inside the complete unit. The A860-2100-V001 is the full assembly (housing, sensor elements, and PCB). If the mechanical housing and sensor elements are undamaged but the electronics have failed, the A20B-2003-0310 is the specific replacement component.

Q2: What is the difference between MI and MIZ sensors?

The MI sensor provides speed pulses and one index (I) pulse per revolution for orientation reference. The MIZ sensor adds a Z-phase output — a higher-resolution position reference used in applications requiring more precise absolute angular positioning. The A860-2100-V001 pick-up unit serves both; the A20B-2003-0310 PCB processes both signal types.

Q3: Does A20B-2003-0310 work with both Alpha and Alpha-i spindle motors?

Yes. The user description explicitly confirms: "FOR ALPHA & ALPHA-I SPINDLE MOTOR." Both spindle motor generations use the A860-2100-V001 pick-up unit with A20B-2003-0310 PCB for MI/MIZ feedback.

Q4: Can A20B-2003-0310 be bench tested outside the pick-up unit?

The PCB requires sensor element input signals to produce outputs — it cannot be meaningfully tested in isolation. The most practical diagnostic method is substitution: replace the pick-up unit or PCB with a known-good example and observe whether spindle alarms clear. If alarms persist after replacement, the fault lies elsewhere in the feedback chain (cable integrity, target disc condition, amplifier feedback input circuit).

Q5: What target disc condition should be checked alongside A20B-2003-0310?

Before replacing the sensor PCB, inspect the target disc on the spindle motor shaft for damage, contamination (oil buildup or metal debris), or incorrect air gap to the sensor elements. A contaminated or damaged target disc can produce irregular pulse patterns that the sensor PCB cannot correct — resulting in spindle alarms even with a functioning PCB. Clean or replace the target disc if abnormal condition is found.