Precision MotionAugust 14, 20266 min read

Absolute Encoder Zero-Point Alignment on Mitsubishi MR-J4 Servo Motors

IASBD Senior Automation Engineering Desk

Restoring machine mechanical homing after backup battery discharge (AL.25) or high-speed collision without losing master CNC coordinates.

1. What Causes Alarm AL.25 (Absolute Position Erased)?

Mitsubishi MELSERVO MR-J4 and MR-J3 servo systems feature multi-turn 22-bit high-resolution absolute encoders. During normal plant shutdowns, an external 3.6V lithium battery (MR-BAT6V1SET) preserves multi-turn shaft revolutions.

When this battery drops below 3.0V while power is off, the amplifier generates an AL.25 error upon startup. The servo amplifier locks into protective stop mode because it no longer knows the physical coordinates of the machine axis.

2. Field Recovery Procedure Using MR Configurator2

To restore operation, connect your laptop to the MR-J4 mini-USB front communication port running MR Configurator2 software.

Diagnostic Action Protocol:

→Step 1: Replace the exhausted battery with a fresh genuine 3.6V lithium cell (MR-BAT6V1) while the amplifier control power (L11/L21) is energized to prevent redundant memory loss.

→Step 2: In MR Configurator2, navigate to [Diagnostics] -> [Alarm Display] -> click [Alarm Reset]. Power cycle the main input line.

→Step 3: Move the physical axis to its designated mechanical home index notch using JOG mode or manual ballscrew rotation.

→Step 4: Go to [Parameter] -> [Axis Position Setup] -> select [Absolute Position Detection System (PA03 = 0001)].

→Step 5: Execute [Origin Setting (Homing)]: Choose Origin Data Set method and click [Write to Drive]. The current position is recorded as permanent Zero.

→Step 6: Power cycle the entire control cabinet. Verify the display shows "d0" or "Ab" indicating ready-state servo positioning.

3. Important Precautions Against Mechanical Collision

Before executing full-speed automated production cycles, always perform a low-speed manual jog test to confirm limit switches (LSP/LSN) respond correctly and that software overtravel limits match CAD clearances.

At IASBD, our engineers provide onsite laser calibration and servo tuning for CNC routers, wire cutting, and flying shear machines throughout Bangladesh.

Referenced Equipment in IASBD Stock

Motion Controller & CNCDigital Dream UC300 Motion Control Card

SensorsLinear Position Sensor KTC-350mm 5 Ohm

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