Mitsubishi MR-J4 AL.51 during operation, what to check first?
I'm getting an AL.51 alarm on a Mitsubishi MR-J4 servo amplifier during operation. The axis seems to hit something and then faults out. What should I check first?
The AL.51 Overload 2 alarm on a Mitsubishi MR-J4 servo amplifier indicates that the maximum output current flowed continuously. This typically happens during operation if the axis collides with an obstruction or the torque saturates, or during a stop if the axis pushes against a hard stop. If AL.52 (Error excessive) also appears, the axis was blocked and couldn't follow the command.
Likely causes and checks
1Collision with the machine
- Points to it
- The most common cause for AL.51 is a physical collision, where a moving part of the machine hits an obstruction, causing the motor to draw maximum current continuously.
- Check
- Check whether a moving part collided and review the operation pattern. Look for any marks on the mechanism or if the alarm occurs at a fixed position.
2Motor power cable disconnected or U/V/W wired wrongly
- Points to it
- Incorrect or disconnected motor power cable wiring can lead to the motor not being able to generate sufficient torque, causing it to draw excessive current and trigger an overload alarm.
- Check
- Check the servo motor power cable and U/V/W wiring, especially if the alarm occurred after recent maintenance.
3Encoder cable connected wrongly
- Points to it
- An improperly connected encoder cable can lead to incorrect feedback, causing the servo amplifier to command maximum current in an attempt to achieve the desired position, resulting in an overload.
- Check
- Check the encoder cable connection, particularly if it's a multi-axis unit or if the cable was recently changed.
4Torque insufficient (saturated)
- Points to it
- If the required load exceeds the motor's capacity, the motor will continuously draw maximum current, leading to torque saturation and an AL.51 alarm.
- Check
- Check the peak load ratio. If it's at the limit during the move, consider reducing the load, reviewing the operation pattern, or using a larger motor.
Next check: Given that the axis seems to hit something, the first step should be to thoroughly inspect the machine for any signs of collision or obstruction and review the operation pattern for the axis.
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