Unexpected servo motor failure leads to production stoppages, damaged machinery, and expensive repairs. Understanding root causes helps prevent breakdowns and extend motor life. Here’s what to watch out for.
Servo motor failures are often caused by preventable issues such as contamination, overheating, cable damage, and bearing wear. Identifying these early can reduce downtime, repair costs, and performance loss.
Explore these 12 critical failure points to protect your system.
Contamination
Contamination is one of the most common and underestimated causes of servo motor failure. It refers to the intrusion of foreign substances—such as dust, oil, coolant, metal shavings, or moisture—into the motor housing.
When contaminants penetrate motor seals:
Bearings lose lubrication and wear out faster.
Insulation resistance of windings drops, increasing risk of short circuits.
Encoders become dirty, leading to feedback errors or communication faults.
This type of damage is especially common in environments with poor sealing or where the motor operates near CNC coolant spray or unfiltered air systems. Even high-quality servo motors are vulnerable to ingress if IP ratings are ignored during setup.
Preventative measures include using sealed, IP-rated motors, proper cable glands, and regularly inspecting enclosure integrity.
Bearing Failure
Bearings are essential for smooth rotor movement, and when they fail, the entire servo motor suffers. Bearing failure is typically caused by:
Misalignment
Overloading
Contamination
Insufficient or incorrect lubrication
As bearings degrade, symptoms include increased vibration, overheating, noise, and erratic motor behavior. Over time, failed bearings can cause shaft wobble, encoder damage, and internal rotor-stator collisions.
In high-speed applications, even microscopic imperfections can accelerate bearing wear. Vibration analysis and thermal monitoring are effective predictive maintenance tools to catch bearing issues early.
Use high-quality, shielded bearings and follow the motor manufacturer’s lubrication schedule to reduce this failure risk.
Brake Failure
Some servo motors are equipped with built-in electromagnetic brakes to hold position during power-off conditions. Over time, these brakes may fail due to:
Excessive mechanical load
Coil burnout
Spring fatigue
Dust or oil contamination
Brake failure can cause drifting, dropped loads, or inability to stop at the desired position. This is particularly critical in vertical-axis applications like lift tables or robotic arms.
Proper brake selection for torque requirements, routine brake gap adjustments, and ensuring voltage specifications are met will minimize this issue. In environments with particulate or oil mist, ensure brakes are enclosed or protected.
Bad Windings
The windings in a servo motor are responsible for creating the electromagnetic fields that drive motion. Damage to these windings—due to insulation failure, thermal stress, or electrical surges—can result in:
Short circuits
Ground faults
Loss of torque or response
Insulation breakdown is often the result of overheating, voltage spikes, or contamination. Once compromised, the windings can arc internally, creating catastrophic failure.
Preventing this involves proper overload protection, using VFD-rated cables, and operating motors within specified thermal and voltage limits. Resistance and insulation resistance testing during maintenance checks can help detect winding deterioration early.
Cable Failure
Cables carry both power and feedback signals between the servo drive and the motor. Failures may occur due to:
Pinched or bent cables
Loose connectors
EMI (electromagnetic interference)
Shielding breakdown
Insulation wear
Cable failure can cause position errors, signal loss, or even complete motor shutdown. In applications involving frequent flexing or motion, improper cable routing or low-grade cable types can significantly reduce system reliability.
Use cables rated for continuous flexing (e.g., drag-chain rated), always maintain proper grounding and shielding, and regularly inspect connectors for looseness or corrosion.
Overheating
Overheating is a leading cause of premature servo motor failure. Causes include:
Excessive load
Poor ventilation
Blocked cooling fans
Ambient temperature exceeding design limits
Heat degrades insulation, reduces lubrication lifespan, and alters magnetic properties. It may also lead to thermal expansion, resulting in internal misalignment or friction.
To avoid overheating:
Monitor temperature via embedded sensors or external thermal sensors.
Ensure airflow is not restricted in enclosed panels.
Use forced-air or liquid cooling for high-demand systems.
Drive settings like soft start/stop can also help reduce sudden thermal spikes.
Demagnetization of Permanent Magnets
Servo motors rely on permanent magnets for precise control. These magnets can weaken or become demagnetized due to:
Prolonged overheating
Electrical surges
Physical shock
Exposure to strong external magnetic fields
Demagnetization reduces torque output and system accuracy, and in severe cases, the motor may fail to start or hold position.
Maintaining thermal limits and avoiding short circuits is critical to preserve magnet integrity. Once magnets are demagnetized, replacement of the rotor is typically the only remedy, making this one of the more costly types of failure.
Electrostatic Discharge (ESD)
Electrostatic discharge can damage delicate motor components like encoders, internal sensors, and PCB assemblies. ESD occurs when accumulated charge—often from human handling, tools, or nearby ungrounded equipment—suddenly transfers to the motor circuitry.
This is especially dangerous during motor installation, servicing, or transportation.
Best practices include:
Grounding personnel and tools before handling
Using anti-static packaging and mats
Ensuring motor housing and cable shielding are properly bonded
ESD-related failures are often difficult to diagnose post-damage, making prevention critical.
Vibration
Excessive or prolonged vibration can degrade bearings, loosen fasteners, and misalign internal components. Vibration is both a symptom and cause of servo motor failure.
Common vibration sources:
Unbalanced loads
Misaligned couplings
Worn-out bearings
Loose mounting
Symptoms include erratic movement, encoder errors, and mechanical noise. If unchecked, vibration can also lead to fatigue cracks in housing or breakage in fragile components like hall sensors or brake mechanisms.
Routine alignment checks, balancing rotating components, and using vibration dampers can extend motor life.
Electronic Component Fatigue
Inside every servo motor lies a network of sensitive electronics—PCBs, power transistors, feedback processors. These components degrade over time due to:
Temperature cycling
Overcurrent
Electrical noise
Voltage spikes
As capacitors dry out or solder joints fatigue, the motor may show intermittent failures, loss of torque control, or complete drive loss.
Using surge protection, ensuring proper grounding, and keeping ambient temperatures within design limits will protect electronic longevity. High-quality servo drives also include self-diagnostics to catch developing faults early.
Mechanical Faults and Failures
Beyond bearings and brakes, other mechanical failures can impact servo motors:
Shaft damage from improper coupling or shock loads
Housing cracks from mounting stress
Gearbox misalignment or wear
These often result from poor installation practices, incorrect load sizing, or unplanned impact during machine operation. Failure symptoms include abnormal noises, vibration, heat, or inability to maintain accurate position.
Following torque specs during installation, avoiding hammer fits, and conducting regular mechanical inspections helps prevent these issues.
Loss of Parameters or Setup Issue
Servo motors depend on exact parameter settings for proper operation—feedback type, motor constants, limit values, encoder resolution, etc. Loss of these parameters due to:
Power failure
Battery drain (in drives with encoders)
Improper configuration
Firmware errors
—can render the system inoperable or cause unpredictable behavior.
To mitigate this:
Backup parameters after initial commissioning
Use drives with non-volatile memory
Document setup procedures clearly
In some cases, simply reloading the correct profile can restore normal operation—assuming no physical damage has occurred.
Summary
Understanding and preventing servo motor failure ensures smoother operation, longer equipment life, and fewer unexpected shutdowns.For further questions please contact [email protected]
