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7 Troubleshooting
MITSUBISHI CNC
Alarm No.
31
Overspeed
The motor was detected to rotate at a speed exceeding the allowable speed (In the case of linear motor, it was detected to move
at a speed exceeding the allowable speed).
Investigation details Investigation results Remedies SV SP
1
Check if the unit in which the alarm was detected is
servo or spindle.
The alarm was detected in servo. Check the investigation item No. 2.
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The alarm was detected in spindle. Check the investigation item No. 3.
2
Check the servo parameters SV001 (PC1), SV002
(PC2), SV018 (PIT) and SV025 (MTYP) settings.
The settings are incorrect. Correctly set.
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Correctly set. Check the investigation item No. 5.
3 Check the spindle parameter SP026 (TSP) setting.
The setting is incorrect.
The alarm is detected at 115% of SP026.
Correctly set.
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Correctly set. Check the investigation item No. 4.
4 Check the PLG output waveform.
There is a problem. Adjust the PLG output waveform.
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Normal. Check the investigation item No. 5.
5
Check whether the speed waveform is
overshooting.
The waveform is overshooting.
Increase the acceleration/ deceleration time
constant.
Lower the load inertia.
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The waveform is not overshooting.
Check if there is any abnormality in the unit's
ambient environment.
(Ex.: Ambient temperature, noise, grounding)
Check the investigation item No. 6.
6 Check the repeatability.
[1] The alarm occurs when the motor is
stopped.
[2] The rotation speed displayed on the drive
monitor varies when the motor is stopped.
Replace the encoder or encoder cable.
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The alarm occurs at all time. Replace the drive unit.
Alarm No.
32
Power module overcurrent
Overcurrent protection function in the power module has started its operation.
Investigation details Investigation results Remedies SV SP
1
Disconnect the power cable (U, V, W) from the
unit’s terminal block and motor, and check whether
a short-circuit between the power cable or whether
conduction at both end of wiring occurs with a
tester.
[1] Before disconnecting the power cable, the
cable connector or screw has been
loosened.
[2] The short-circuit condition persists even
after disconnecting the cable from the unit
and motor.
[1] Tighten it.
[2] Check the motor wiring.
[3] Replace the power cable.
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There is no problem. Check the investigation item No. 2.
2
Check the motor insulation with a (megger) tester.
-Between motor power and ground earth
Less than 1MΩ. (Grounding) Replace the motor.
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1MΩ or more. (Normal) Check the investigation item No. 3.
Check the unit capacity.
[1] The same size but smaller than the selected
capacity.
[2] The combination of the motor and axis is
alternated in a 2-axis unit.
The capacity is small.
The smaller capacity side was used in 2-axis
unit.
Replace to the unit of the selected capacity or
change the axis.
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The motor meets the selected capacity. Check the investigation item No. 3.
3 Check the current loop gain parameters.
Different from the standard parameter
settings.
Adjust the value to the standard setting.
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Equivalent to the standard parameter
settings.
Check the investigation item No. 4.
4
Jiggle the encoder connectors (drive unit side and
encoder side) and check if they are disconnected.
The connector is disconnected (or loose). Correctly install.
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The connector is not disconnected. Check the investigation item No. 5.
5
Turn the power OFF, and check the encoder cable
connection with a tester.
Connection is faulty. Replace the encoder cable.
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Connection is normal. Check the investigation item No. 6.
6 Check the repeatability.
The state returns to normal once, but occurs
sometimes thereafter.
Check the investigation item No. 8.
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The error is always repeated. Check the investigation item No. 7.
7
Replace with another unit, and check whether the
fault is on the drive unit side or encoder side.
The alarm is on the drive unit side. Replace the drive unit.
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The alarm is on the encoder side. Replace the encoder.
8
Check for any abnormalities in the unit's ambient
environment.
(Ex.: Ambient temperature, noise, grounding)
Take remedies according to the causes of the abnormality in the ambient environment.
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