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.

During the operation of a servo motor, when the load feeds energy back to the motor (e.g., during braking or deceleration), the rotor speed decreases, and a reverse electromotive force (back-EMF) is generated, returning energy to the motor in a process known as "regeneration." If the energy fed back to the system exceeds the driving energy supplied to the motor, issues such as overloading and voltage spikes may occur. To address this, a regenerative resistor is used to dissipate the excess electrical energy as heat. Thus, the regenerative resistor serves to protect both the motor and the system.

2. Applicable Scenarios

However, not all servo motors require a regenerative resistor. The necessity depends on the motor model, specifications, and specific application conditions. Below are some typical scenarios:

Servo motors with built-in regenerative resistors-Some servo motors already incorporate an integrated regenerative resistor, eliminating the need for an external one.

High-inertia or frequently decelerating loads-Systems with significant inertial loads or frequent deceleration are more prone to regenerative energy, making an external regenerative resistor necessary for protection.

External braking support-If the motor controller supports external braking (e.g., via a separate brake or another motor to halt the rotor), a regenerative resistor may not be required.

3. Conclusion

It is important to note that if a regenerative resistor is required, it must be selected based on the motor and system specifications. An improperly chosen resistor may lead to overheating or malfunctions. Additionally, regular maintenance and inspection of the regenerative resistor are essential to ensure proper operation.

The above discussion clarifies whether a regenerative resistor is mandatory for servo motors. A case-specific analysis is necessary to ensure stable motor operation and system reliability.