Mitsubishi Electric MELSERVO-J4 (MR-J4) alarm AL.52: Error excessive
Alarm AL.52 on a Mitsubishi MR-J4 servo amplifier is Error excessive: droop pulses (the difference between commanded and actual position) exceeded the alarm occurrence level. It is the MR-J4 following-error alarm.
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When it happens
- During acceleration when the time constant is too short
- When a torque limit is active or the axis is blocked
- At servo-on if the motor was still rotating, or at servo-off if an external force moved the axis (52.6)
Reading the subset
| Subset | What it tells you |
|---|---|
| 52.1 / 52.3 / 52.5 | Excess droop pulse 1 / 2 / 3. |
| 52.4 | Error excessive during 0 torque limit: a command was given while the torque limit was 0. |
| 52.6 | Excess droop pulse during servo-off: the shaft was turned by an external force. |
Likely causes and checks
1Motor power or encoder cable disconnected or wired wrongly
- Points to it
- First move after wiring work.
- Check
- Check the servo motor power cable, U/V/W wiring and the encoder cable connection.
2Torque limit active, or brake not released
- Points to it
- Axis moves slowly or not at all before the alarm.
- Check
- Check whether the torque limit is in effect and whether the electromagnetic brake is released.
3Collision or insufficient torque
- Points to it
- Alarm at the same position or on the heaviest move; peak load ratio saturated.
- Check
- Check for collisions and the peak load ratio; reduce the load or review the operation pattern.
4Bus voltage dropped
- Points to it
- Alarm coincides with supply dips.
- Check
- Check the bus voltage value and the supply voltage and capacity.
5Acceleration/deceleration time constant too short, or position loop gain too small
- Points to it
- Alarm only on fast moves.
- Check
- Lengthen the time constant and check repeatability; increase the position loop gain [Pr. PB08].
6Error excessive alarm level set wrongly
- Points to it
- Alarm level changed from default.
- Check
- Check [Pr. PC24]/[Pr. PC43] on [A], or [Pr. PC01]/[Pr. PC06] on [B] [WB] [RJ010] [GF].
Telling it apart
- AL.9B (Error excessive warning) can appear before AL.52 and is worth checking in the alarm history.
- AL.52 with AL.51 in the same event usually means a collision; AL.52 alone on fast moves usually means time constant or gain.
- Detail 52.6 happens at servo-off and points to the mechanism moving the axis (gravity, belt), not to tuning.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| PB08 | Position loop gain | Mitsubishi lists a small position loop gain as a cause. |
| PC24, PC43 ([A]) / PC01, PC06 ([B] [WB] [RJ010] [GF]) | Error excessive alarm level | Check these are set correctly for the application. |
Evidence to collect
- Full alarm and detail number
- Droop pulses and torque trend for the move
- Time constants and [Pr. PB08]
- Error excessive alarm level settings
- Torque limit settings and brake status
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