Keeping servo motors in optimal condition is crucial for any industrial enterprise, especially those in the robotics or CNC machine tool industries, because downtime costs due to servo motor failure can be very expensive, both financially and in terms of time.
Next, let's look at some of the most common servo motor failures and their potential causes, so we can try to avoid them.
1. Bearing failure
As the most significant wear component in a servo motor, bearing problems account for more than half of all servo motor failures. The specific manifestations are varied, ranging from minor issues like motor vibration and abnormal noises during rotation to severe problems such as the motor shaft seizing up.
It is worth noting that if bearing failure is not addressed promptly, it can often lead to secondary damage. For example, rust debris from the bearing can fly into the brake or motor encoder, causing even more serious losses.
Factors affecting the lifespan of motor bearings include: axial load acting on the bearing, radial load, motor speed, operating temperature, and bearing rated parameters. There are many causes of bearing failure, the most common being:
Inappropriate mechanical loads (such as overload, radial misalignment, axial thrust, belt tension problems)
Excessive vibration and shock
Overspeed operation
shaft current
Overheating (leading to lubrication loss)
Moisture or liquid ingress
Contaminants (e.g., use of incompatible greases, water condensation, dust/dirt contamination)
Solution:
Servo motors should not be operated beyond their rated load for extended periods.
For applications with shaft current, add conductive brushes or use a motor with insulated bearings.
Preventive maintenance of servo motors
2. Shaft seal wear
Possible reasons
Accidental damage
Normal wear and tear
Solution:
Preventive maintenance
Depending on usage, it is recommended to replace it every 3 months, and no longer than 12 months.
3. Stator and winding issues
When a winding failure occurs, a portion of the motor will short-circuit, causing the motor's internal components to burn out.
Possible reasons
Overload
overvoltage
Phase loss
Incorrect wiring
Inappropriate driver parameter settings
High ambient temperature
Cooling device malfunction
Physical damage
Solution:
Servo motors should not be operated beyond their rated load for extended periods.
Monitoring current and current accumulation over time
Monitor winding temperature
4. Rotor and shaft problems
Fault phenomenon
Shaft breakage and deformation
magnetic sheet detachment
Possible reasons
Excessive vibration (e.g., radial misalignment, axial thrust, variable duty cycle).
Too many starts or reverses, or too short intervals between starts/reverses.
Overheating (e.g., high ambient temperature, overload, or rotor lock-up operation)
Unexpected collision
Countermeasures:
Operating under rated load
Avoid accidental collisions
5. Problems with motor feedback devices (rotary transformers, encoders, etc.)
Fault phenomenon
Zero position (number of revolutions) lost
Rotary transformer or encoder wear
Glass chuck shattered
Encoder electrical fault
Possible reasons
For encoders that use backup batteries, zero-position loss may occur during use as the battery power is depleted. The battery status should be checked first.
As a secondary damage caused by the aforementioned motor bearing failure, motor bearing problems can also lead to mechanical wear on the encoder or rotary transformer.
Prolonged motor shaft current can not only affect the motor's own bearings, but also damage the encoder's internal bearings, causing them to burn and become damaged.
Shocks and vibrations during motor transportation or installation can easily cause the glass code disk of the optical encoder to shatter. Especially when adding key pins, pulleys, or couplings to the motor shaft, it is crucial to avoid striking the motor shaft.
Besides incorrect wiring, electromagnetic interference caused by improper wiring is also one of the main causes of encoder electrical failures.
Countermeasures:
Depending on the specific application, battery life is typically one year or several years. Regularly replacing the battery can reduce this risk of unexpected problems. Alternatively, a more permanent solution is to switch to a mechanical multi-turn absolute encoder.
The motor must be reliably grounded during installation. For applications with shaft current, it is necessary to consider using insulated bearings and insulated encoders, or installing a motor shaft grounding device.
During motor installation, such as when adding pulleys or couplings, if impacts are unavoidable, consider removing and storing the encoder first, and then reinstalling it after all mechanical installations are complete. In this case, the encoder's phase angle will need to be readjusted in the servo drive.
Another way to prevent code disk failure is to use metal code disk encoders, which have become increasingly popular in recent years. Compared to glass code disks, metal code disks offer significantly improved vibration and shock resistance, while their resolution and accuracy are comparable to glass code disks.
6. Braking device (holding brake) problem
The motor brake is used to brake the motor shaft and prevent rotation when the power is off; when the brake is energized, the brake is in the released state.
Fault phenomenon
Strange noise
Cannot be released
Unable to brake (locks up).
Possible reasons
Foreign object intrusion from a faulty bearing is a common cause of abnormal brake noise.
Secondly, if the brake is forced to operate in a power-off state due to a fault in the brake drive circuit, it will also lead to damage to the brake.
Countermeasures: It is worth noting that, as a stationary holding device for the motor, the brake should not be used as a motor speed reduction device while the motor is energized, as this will accelerate the wear of the brake.
7. Cooling device problem
Most small to medium power servo motors are self-cooled. For servo motors with higher power or in special applications, air cooling or liquid cooling is also common.
Fault phenomenon
Fan vibration or stalling
coolant leakage
Possible reasons
The culprit behind most fan failures is dust. This is because dust accumulates on the fan blades over time. Increased load on the blades leads to vibration and subsequent damage.
Most coolant leaks occur at joints, and seal failure is often the key to the problem.
Physical damage caused by an accidental impact.
countermeasures
Add a filter to the fan and replace it regularly.
Regularly inspect the cooling system.
8. Electrical connection devices
This includes terminal boxes and sockets.
Fault symptoms and causes
As non-wearing parts, the failures of connecting devices are mostly due to mechanical damage.
Countermeasures: Exercise extra caution when using it to avoid accidents as much as possible.
9. Couplings and pulleys
Connecting the motor shaft requires a torsional rigid coupling or a reinforced belt. After the motor has been running for a period of time, frequent acceleration and deceleration can cause the coupling or belt to loosen or slip, in which case it should be checked again.
Fault symptoms and causes
If the shaft is subjected to severe impact during the installation of couplings and pulleys, it may cause fatal damage to the motor bearings and/or encoder.
Countermeasures: Therefore, during installation or disassembly, it is strictly forbidden to use tools to strike the shaft, coupling, or pulley. When attempting to remove any equipment from the motor shaft, a hydraulic device should be used to push it out from the shaft end.
