Gear Failure Diagnosis Function - Mitsubishi Electric MR-J5 Series User Manual

Gear failure diagnosis function

The gear diagnosis function predicts a gear malfunction by estimating the backlash amount of the gear connected to the servo
motor from the servo motor driving status. The gear diagnosis function includes the backlash estimation function and the gear
failure prediction function.
• Backlash estimation function
For the backlash estimation function, the backlash amount of the gear connected to the servo motor is estimated from the
servo amplifier internal data during the to-and-fro positioning operation. When the servo motor is at a stop, click the estimation
start button of MR Configurator2 to start. If the servo motor speed is 20 r/min or faster, the backlash estimation will not start
with the estimation start button of MR Configurator2, and an error will be displayed.
• Gear failure prediction function
The gear failure prediction function predicts the gear failure by comparing the backlash amount estimated by the backlash
estimation function with the backlash threshold set by the servo parameter. After inputting the backlash threshold with [Pr.
PF67 Backlash nominal value] and [Pr. PF68 Backlash threshold multiplication] and executing backlash estimation, gear
failure prediction is performed.
• When using a linear servo motor, the gear diagnosis function cannot be used. When the linear servo motor
is used, backlash estimation does not start as errors will occur.
• Perform backlash estimation when all the servo motors connected to the servo amplifier stop. When any of
the servo motors connected to the servo amplifier operates, backlash estimation is not performed as errors
will occur.
Precautions
• During gear diagnosis, the servo amplifier automatically generates a command to drive the servo motor. Even if the servo
motor moves by the travel distance + 1 rotation during gear diagnosis, ensure that the movable part does not collide with
the equipment, then execute backlash estimation. Use the stroke limit or EM2 during the gear diagnosis.
• The gear diagnosis function can be used for the gears with backlash amount of 0.1 degree in the servo motor shaft
conversion. If the backlash estimation is performed on the gears with the backlash amount of less than 0.1 degree, the
error between the estimated value and true value becomes large, causing an incorrect detection of [AL. 0F7 Machine
diagnosis warning]. Also, [AL. 0F7 Machine diagnosis warning] may not be detected during a gear malfunction.
• The gear diagnosis function can be used when the load to inertia ratio is two times or more. If backlash estimation is
performed when no load is applied or when the load to inertia ratio of the connected load is less than two times, the error
between the estimated value and the true value becomes large, causing an incorrect detection of [AL. 0F7 Machine
diagnosis warning]. [AL. 0F7 Machine diagnosis warning] may not be detected during a gear malfunction.
• When the backlash estimation is executed, the servo amplifier enters the test operation mode and afterwards cannot be
controlled by the command from the controller. After executing the backlash estimation, reset the communication or cycle
the power of the servo amplifier.
• If the overspeed alarm level and the torque limit value are small, the backlash estimation may fail.
• If the gear diagnosis is executed simultaneously on two or more axes in the equipment with mechanical interference, the
equipment may malfunction. Execute the gear diagnosis on one axis at a time.
• Adjust the gain before executing the backlash estimation so that the equipment does not oscillate or vibrate. The backlash
estimation estimates the backlash from the servo motor drive status during the to-and-fro operation. If the equipment
oscillates/vibrates, the error between the backlash estimate and the actual value may be large.
• If the gear ratio on the load side is large, the accuracy of the backlash estimation may deteriorate.
4 APPLICABLE FUNCTION
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4.3 Machine diagnosis