5 Causes of Servo Motor Failure & How to Prevent Them

Servo motors, also known as AC synchronous motors, are flexible solutions for machine builders. They pair incredible energy efficiency with compact size, producing up to 60% higher torque capacity vs. equivalent-sized induction motors.

Like any tool, servos are not foolproof: failures can occur with these motors, impacting productivity and safety. This is why it’s essential to understand the typical causes of servo motor failure. Keeping tabs on these largely preventable problems will help limit downtime and ensure you get the best performance from these motors across their lifespan. 

1. Bearing Failure

Bearing failure in servo motors is highly common and has multiple causes. Of course, bearings naturally wear out over time with repeated use. Incorrect installation or reinstallation of the motor can also misalign these bearings. A telltale sign of bearing failure is abnormal sound, including growling or screaming while the motor is running at high speeds. 

Predictive maintenance is the best method to prevent bearing failure. Consistently checking the motor to swap out bad bearings will significantly improve the lifespan of the motor—and allow you to schedule repairs at convenient times that won’t impact productivity. It’s crucial to work with a trusted repair partner to ensure bearings are replaced properly. Critical applications might also consider using motor-mounted vibration sensors which can help detect a bearing failure early. 

2. Brake Failure

Servo motor brakes are used to hold a load in place when the drive is deactivated or shut down. Most servo motor brakes are intended for holding only and not for dynamic stopping.  Using the brake for repetitive stopping or multiple e-stops could cause the brake to wear to the point that it needs to be replaced.

Since many servo motors are designed with IP65 protection, the brake is often enclosed in the housing and is not easily checked or replaced.  A best practice is to always engage the motor brake at standstill.  After the brake has engaged, then the drive current to the motor can be disabled.  

If a brake is needed for occasional e-stops and dynamic stopping, the machine should use a separate brake like KEB’s Double C-Face or Spring-Set Brakes which are capable of repetitive dynamic stopping. 

3. Winding & Cable Failures

Bad winding is a common cause of servo motor failure. These copper coils within the motor can be compromised due to water contamination—or more slowly over time thanks to natural vibration as the motor runs. Similarly, the system’s power, control, or feedback cables can lose integrity over time, causing failure or voltage spikes that shut down the motor. 

It’s key to check for winding failure if the servo motor is exposed to any contaminant, including coolant or water. (We’ll touch on this point more below.) Even uncontaminated windings should also be checked because they do wear down naturally. Rewinding the defunct coils will keep the motor in good operating condition and maximize its lifespan.

One of the best ways to prevent cabling malfunctions is to invest in reliable cables. A high-quality feedback cable will boost the entire performance of the system, enabling fast, error-free connections. Regardless of quality, cables should be regularly tested as part of your troubleshooting efforts. 

4. Contamination

Contamination is a root cause behind many motor issues we’ve touched on so far. Despite their general hardiness, servos can be harshly compromised by certain substances, including coolant, oil, and even common debris like dirt. The latter can block up system-critical parts, including fans, which causes overheating. Liquid contaminants can impact the motor’s bearings, encoder, windings, and more.

Diligence is key in avoiding servo contamination, as are regular inspections and cleanings. Fully closed motor systems and sealing the motor windings can help prevent these harmful substances from entering and affecting the system, especially for those running in harsh environmental conditions. 

5. Overheating

Overheating is a critical threat for most machines, including servo motors. Excessive heat may damage parts within the motor and connected systems, incurring costly downtime. Frequent causes of heat damage in servos include blockage in the motor, high environmental temperatures, and extended operating times. 

Heat damage is often insidious: an overheated servo may not show obvious signs of damage but will eventually fail because of it. Thankfully, most servo motors include a failsafe to shut down the system when the temperature exceeds a safe threshold.

Old, worn-down parts are a common cause of overheating in older motors, which can be addressed by simply replacing them. Ideally, servo motors will operate in climate-controlled environments to limit excessive heat, but this is not always possible. Proper ventilation will help manage the threat of overheating servos—as will allow the stressed system enough time to cool off before continuing operation. 

Servo Motor Solutions at KEB

KEB’s line of versatile servo motors and servo drives allows you to take full advantage of this powerful technology. Contact a KEB Application Engineer today to learn about our cutting-edge servo solutions and how they can unlock new efficiencies in your application.