The spindle amplifier was sent to us by the customer after strong vibrations occurred at the spindle motor over an extended period. It was noticeable that the vibrations increased significantly with higher rotational speeds. Since such symptoms in practice are very often caused by mechanical or motor-related issues, the spindle motor itself was initially suspected.

The customer commissioned a specialized service provider to measure the motor. Insulation values were checked, encoder signals were analyzed, and finally the encoder was replaced because it was heavily contaminated. Dirt and deposits had already entered the interior of the encoder housing. A positive outcome was that the motor was thoroughly cleaned during this process and the defective motor fan was replaced as it was no longer rotating. However, despite these measures, the fault pattern did not change. The spindle continued to vibrate significantly, especially at higher speeds.

Only after a recommendation did the customer contact us. During the discussion, it became clear that he had previously contacted FANUC directly. The recommendation there was to address the problem at the motor first. A replacement spindle amplifier would have cost nearly 10,000 euros, so from an economic perspective it was understandable to focus on the motor initially.

Once the spindle amplifier arrived at our facility, it was immediately tested. During the very first test on an in-house reference motor, the exact same vibration behavior occurred. This clearly showed that the cause was not the motor but unmistakably the spindle amplifier. The output power supplied by the amplifier was not clean. Current and voltage modulations occurred, which directly manifested as mechanical vibrations at the motor.

This fault pattern is well known to us from many years of experience with FANUC spindle amplifiers. Especially with older or heavily loaded units, aging effects in the power electronics and current measurement circuits occur. Precisely for this spindle drive type, we have developed a defined flat-rate repair solution many years ago. The repair is not performed only symptomatically but also preventively.

As part of the repair, the unit was completely disassembled, cleaned, and thoroughly inspected. Critical assemblies were reconditioned, thermally stressed components were renewed, and the entire cooling system was overhauled. This was followed by extensive functional testing under load on our test bench. The amplifier operated stably, the output voltage was clean and free of disturbances, and the vibrations no longer occurred.

After reinstallation at the customer’s site, the result was confirmed. The spindle ran smoothly and stably across the entire speed range. The customer was able to put the machine back into full productive operation without having to carry out a costly replacement.

Preventive Measures for the Customer

• Regular cleaning of the control cabinet and ventilation paths
• Periodic inspection and timely replacement of fans
• Early inspection of the spindle amplifier if unusual noises or vibrations occur
• Do not focus exclusively on the motor but always consider the drive as well

Conclusion

This case clearly demonstrates that speed-dependent vibrations are not necessarily caused by the motor. A proper diagnosis of the spindle amplifier saves time, costs, and unnecessary replacement actions. The professional repair and preventive overhaul of the FANUC Spindle Amplifier A06B-6122-H030#553 reliably restored full machine availability.

To mentioned Fanuc Drive: FANUC Spindle Amplifier A06B-6122-H030#553

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Device Description

Operating Environment & Compatible Devices

This spindle amplifier is typically used in CNC machine tools, including machining centers, lathes, and special-purpose machines. It operates with FANUC spindle motors of various power classes and is designed for demanding continuous operation as well as precise speed control. These units are often installed in production environments with coolant exposure, metal dust, and fluctuating thermal conditions.

Functional Description

The FANUC Spindle Amplifier A06B-6122-H030#553 converts the DC voltage supplied by the DC link into a controlled three-phase AC voltage for the spindle motor. A high-performance IGBT power stage precisely modulates the motor current to ensure stable speed control across the entire operating range. Internal monitoring continuously checks current, voltage, temperature, and fan operation. Any deviations are indicated via LED codes or reported to the CNC control.

Alarm Messages & Troubleshooting (Excerpt)

Assemblies