Mitsubishi MR-J5 AL.052 after maintenance, what to check first?
I'm getting an AL.052 alarm on a Mitsubishi MR-J5 servo amplifier after performing maintenance on one of our machine's axes. The axis barely moves before the alarm trips. What should I check first?
The AL.052 alarm on a Mitsubishi MR-J5 servo amplifier indicates an excessive error, meaning the droop pulses exceeded the alarm occurrence level. This alarm can occur during acceleration, when an axis is blocked, or if an external force moves the axis. Given that it happened after maintenance and the axis barely moves, the most likely causes are related to wiring or a torque limit.
Likely causes and checks
1Motor power or encoder cable issue
- Points to it
- After maintenance, it's common for motor power cables (U/V/W) to be loose, incorrectly wired, or for the encoder cable to be misconnected. This directly impacts the servo's ability to follow commands.
- Check
- Inspect the U/V/W wiring for any forgotten or loose screws and incorrect connections. Also, verify the encoder cable connection is secure and correct.
2Torque limit active or brake not released
- Points to it
- If the axis barely moves before the alarm, it could be hitting a torque limit or the electromagnetic brake is not releasing properly, preventing motion.
- Check
- Check the torque limit value set in the parameters and confirm that the electromagnetic brake releases as expected during operation.
3Collision or insufficient torque
- Points to it
- A physical obstruction or the motor not having enough torque to move the load can cause an excessive error, especially if the alarm occurs at a specific position or during a heavy move.
- Check
- Look for any mechanical interference along the axis's path. Review the peak load ratio and consider reducing the load or adjusting the motion pattern.
4Acceleration time constant too short or position control gain too small
- Points to it
- If the alarm only occurs during fast movements, the acceleration time constant might be too short, or the position control gain might be set too low, making it difficult for the servo to keep up.
- Check
- Consider lengthening the acceleration/deceleration time constant. You may also need to increase the position control gain parameter [Pr. PB08].
Next check: Given the context of recent maintenance and the axis barely moving, start by thoroughly checking all motor power cable (U/V/W) and encoder cable connections for looseness, incorrect wiring, or disconnections. Then, verify the torque limit settings and ensure the electromagnetic brake is releasing correctly.
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