Mitsubishi MR-J4 Servo Alarm AL.52 Diagnostic Manual

Mathematical breakdown of position deviation errors, servo loop gain tuning, and machine resonance suppression notch filters.

1. Mathematical Foundation of the Deviation Counter

Alarm AL.52 (Error Excessive / Position Deviation Counter Overflow) on Mitsubishi MELSERVO-J4 drives (MR-J4-A and MR-J4-B) triggers when the accumulated position error in the drive's internal deviation counter exceeds the threshold set in parameter `PC01` (or nominal speed default thresholds). In closed-loop position control architecture: $$e(t) = \theta_{\text{cmd}}(t) - \theta_{\text{fb}}(t)$$ where $\theta_{\text{cmd}}$ denotes the pulse train command received from the CNC/PLC and $\theta_{\text{fb}}$ represents real-time position feedback from the 22-bit high-resolution optical encoder (4,194,304 pulses/rev). When mechanical friction, severe inertia mismatch, or torque limits prevent the motor shaft from keeping pace with input command vectors, the cumulative error $e(t)$ spikes, provoking an emergency hardware shutdown to prevent structural collision.

2. Root Cause Classification Matrix

Failure Mode	Observed Physical Symptom	Technical Diagnostic Check	Corrective Action
Mechanical Binding / Seizure	AL.52 trips immediately at motion start or at specific stroke points	Rotate ballscrew manually with Servo OFF; check for high rotational torque	Lubricate linear guideways, flush contaminated ballscrew nuts, replace thrust bearings
Excessive Acceleration Demand	AL.52 occurs exclusively during rapid traverse (G00) acceleration bursts	Current profile clamps at 300% Peak Torque limit in MR Configurator2 monitor	Lengthen acceleration/deceleration S-curve filter in PLC, or reduce rapid feed by 15-20%
Insufficient Servo Loop Gain	Smooth operation but axis lags position commands progressively until AL.52 trip	Model Loop Gain (PB01) and Position Loop Gain (PB06) set too low for machine mass	Increment PB01 and PB06 proportionally, or execute automated One-Touch Tuning
Reversed Motor Power Phasing	Servo ON causes motor shaft to violently jerk once and trip AL.52 within 50ms	Verify phase rotation and connector pinout on terminals U, V, and W	Reconnect U, V, W leads in strict sequence; never swap leads like an induction motor
Mechanical Resonance / Hunting	Loud high-frequency squealing (1,000 - 3,000 Hz) during stand-still or slow feeds	Inspect Bode Plot frequency response spectrum using MR Configurator2 analyzer	Enable Machine Resonance Suppression Filter (Notch Filter) at detected resonance peak

3. Tuning Machine Resonance Suppression Notch Filters

When an industrial axis operates with high load-to-motor inertia ratios ($J_L / J_M > 10$), the structural compliance of belts, couplings, and ballscrews excites natural mechanical resonance. This induces rapid velocity oscillations (hunting) that traditional PID gains cannot suppress without sacrificing stiffness. Mitsubishi MR-J4 servo drives feature 5 independent Machine Resonance Suppression Filters capable of automatic frequency tracking:

Connect PC to the MR-J4 USB interface and launch MR Configurator2
Navigate to `Tuning > One-Touch Tuning` and select machine rigidity class (Standard, High, or Low Rigidity)
Click `Start Tuning`; the drive injects swept sine-wave test signals to identify peak resonance frequencies across the drive train
The algorithm automatically calculates and writes anti-resonance frequency values into parameters `PB13` (Filter 1) and `PB15` (Filter 2)
Configure Notch Depth between -18dB to -24dB to eliminate acoustic oscillation while preserving phase margin

4. Essential MR-J4 Parameters Governing AL.52

text

// --- Crucial MR-J4 Control & Anti-Resonance Parameters ---
PB01: Model Loop Gain (rad/s)               -> Command tracking responsiveness (Typical: 50 - 120)
PB06: Position Loop Gain (1/s)              -> Position error stiffness (Typical: 30 - 80)
PB07: Speed Loop Gain (rad/s)               -> Velocity loop response (Typical: 300 - 800)
PB08: Speed Integral Compensation (ms)      -> Integral reset time constant
PB13: Machine Resonance Suppression Filter 1 -> Notch center frequency (10 to 4500 Hz)
PB14: Notch Depth 1                         -> Signal attenuation depth (dB)
PC01: Error Excessive Alarm Level (rev)     -> Deviation counter trip threshold before AL.52

Filter Depth Precaution

Avoid setting notch depth excessively deep (-40dB). Over-filtering introduces phase lag into the velocity feedback loop, degrading dynamic positioning accuracy and risking low-speed instability.

Torque Clamping Diagnostic

If AL.52 occurs intermittently during sudden acceleration, verify parameters PA11 (Forward Torque Limit) and PA12 (Reverse Torque Limit). If torque limits are clamped below 100%, the motor will stall against mechanical break-away friction, causing massive error accumulation.