Cause : Encoder A/B- phase error comes when a phase error in the encoder signals. This means that the encoder's A and B phase signals are not arriving as expected, which can disrupt the servo drive's ability to accurately control motor position and speed.

"alarm 20" in panasonic servo drive indicate "Encoder A/B- phase error". This means an issue with the encoder signals, specifically with the A-phase and B-phase signals. This error suggests that there might be a problem with the encoder itself, its connections, or the signal processing within the servo drive.

Troubleshooting Steps:

1. Check Encoder Connections:

• Inspect the wiring between the encoder and the servo drive. Ensure that all connections are secure and free of damage.
• Look for any loose, frayed, or disconnected wires that might be causing intermittent signals.

2. Inspect the Encoder:

• Check the encoder for physical damage or signs of wear.
• Ensure the encoder is properly mounted and aligned. Misalignment can cause issues with signal detection.
• If possible, test the encoder on a different system to see if the problem follows the encoder or remains with the drive.

3. Check Signal Integrity:

• Use an oscilloscope to check the integrity of the A-phase and B-phase signals. These signals should be square waves with a consistent frequency and amplitude.
• Verify that there is no noise or distortion in the signals that could be causing the drive to misinterpret the encoder data.

4. Parameter Settings:

• Review the encoder-related parameters in the servo drive. Ensure that they match the specifications of the encoder you are using.
• Verify settings such as pulse count per revolution, signal type, and input filtering.

5. Inspect the Servo Drive:

• Check the servo drive for any signs of internal issues, such as overheating or component failure, that might be affecting its ability to process encoder signals.
• If possible, perform a diagnostic test on the drive to identify any potential internal faults.

6. Test with a Different Encoder:

• If available, try connecting a different encoder to the servo drive to see if the issue persists. This can help determine whether the problem lies with the encoder or the drive.

7. Error Reset and Monitor:

• After checking the potential causes, reset the error in the servo drive and monitor the system during operation to ensure the issue does not recur.