The behavior of a servo motor during a sudden power loss depends on its design and the system configuration:
1. Servo Motors Without a Brake (Non-Braked Motors)
Position may shift: If the motor lacks an electromagnetic brake, it may lose holding torque when power is cut, causing the shaft to move freely due to external forces (e.g., gravity or inertia).
Back-driving risk: In vertical or high-inertia applications, the load may back-drive the motor, leading to position deviation.
2. Servo Motors with an Electromagnetic Brake (Brake-Equipped Motors)
Position maintained: Motors with integrated brakes automatically engage when power is lost, locking the shaft and preventing movement.
Common in vertical axes: Such brakes are often used in Z-axis or lifting applications to prevent unintended drops.
3. System-Level Factors
Encoder feedback: Upon power restoration, some servo systems can recover position via absolute encoders, while incremental encoders may require re-homing.
Regenerative energy: Sudden stops may generate regenerative voltage, but this does not inherently preserve position.
Conclusion
An unbraked servo motor may lose position after power loss, while a braked motor typically holds its position. The exact behavior depends on the motor type, mechanical load, and system design. For critical applications, a fail-safe brake or backup power (e.g., UPS) is recommended.