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Servo Drive Basics: Top 25 Entry-Level Interview Questions and Answers

 

1. What is a servo drive?

Answer:
A servo drive is an electronic controller used to control the position, speed, and torque of a servo motor with high accuracy. It supplies power to the motor and continuously corrects its motion using feedback.



2. What is the difference between a servo motor and a servo drive?

Answer:

  • Servo Motor: Converts electrical energy into mechanical motion
  • Servo Drive: Controls the motor by providing power and control signals
    A servo motor cannot operate without a servo drive.

3. What are the main components of a servo system?

Answer:

  1. Servo Motor
  2. Servo Drive
  3. Feedback device (Encoder / Resolver)
  4. Controller (PLC / CNC)
  5. Power Supply

 4. What is the main function of a servo drive?

Answer:
The main function of a servo drive is to:

  • Supply controlled power to the motor
  • Read feedback signals
  • Calculate error
  • Correct motor movement in real time

 5. On which principle does a servo drive work?

Answer:
A servo drive works on the closed-loop control principle, where actual motor feedback is continuously compared with the command signal to eliminate error.

 6. What is the difference between open-loop and closed-loop systems?

Answer:

  • Open-loop system: No feedback (e.g., stepper motor)
  • Closed-loop system: Uses feedback for accuracy (servo system)
    Closed-loop systems are more accurate and reliable.

 

7. What is a feedback device?

Answer:
A feedback device measures the actual position, speed, and direction of the motor and sends this information to the servo drive.

 8. What is an encoder?

Answer:
An encoder is a sensor that converts the motor shaft movement into electrical signals so the servo drive can calculate position and speed.

 

9. What is position control in a servo drive?

Answer:
Position control means moving the motor to an exact location, such as rotating to a specific angle or moving a fixed distance.

 10. What is speed control?

Answer:
Speed control ensures the motor runs at a constant RPM, even when the load changes.

 11. What is torque control?

Answer:
In torque control mode, the servo motor operates based on applied force, while position and speed become secondary.

 12. How many control loops are used in a servo drive?

Answer:
A servo drive uses three control loops:

  1. Current loop
  2. Speed loop
  3. Position loop

 13. Why is the current loop the fastest?

Answer:
Because motor torque is directly proportional to current, the current loop must respond very fast to maintain precise control.

 14. Who gives commands to a servo drive?

Answer:
Commands are provided by:

  • PLC
  • CNC controller
  • Motion controller

 15. What types of input signals are used in servo drives?

Answer:
Common input signals include:

  • Pulse / Direction
  • Analog signals (0–10 V)
  • Fieldbus communication (EtherCAT, Modbus, etc.)

 16. What are the outputs of a servo drive?

Answer:

  • Motor power output
  • Alarm signal
  • Ready signal
  • Status and feedback signals

17. What is homing in a servo system?

Answer:
Homing is the process of finding a reference or zero position to ensure accurate and repeatable positioning.

18. What is the difference between AC servo and DC servo?

Answer:

  • DC Servo: Older technology, higher maintenance
  • AC Servo: Brushless, high efficiency, long lifespan
    Most modern industries use AC servo motors.

 19. What is servo tuning?

Answer:
Servo tuning is the process of adjusting control parameters to achieve smooth motion, minimal vibration, and fast response.

 20. What is auto-tuning?

Answer:
Auto-tuning allows the servo drive to automatically adjust control parameters by detecting the load characteristics.

 21. Where are servo drives commonly used?

Answer:
Servo drives are used in:

  • CNC machines
  • Robotics
  • Packaging machines
  • Pick-and-place systems
  • Printing machines

 

22. What is the difference between a servo drive and a VFD?

Answer:

  • VFD: Controls only speed
  • Servo Drive: Controls position, speed, and torque
    Servo drives provide higher accuracy.

 23. How is accuracy achieved in a servo system?

Answer:
Accuracy is achieved using:

  • High-resolution feedback devices
  • Closed-loop control
  • Fast response control loops

24. What is the response time of a servo drive?

Answer:
Servo drives have a response time in milliseconds, making them suitable for high-speed automation.

 25. Why are servo drives important in industry?

Answer:
Servo drives improve:

  • Production speed
  • Precision and repeatability
  • Product quality
  • Automation reliability

 

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