How to Choose the Right AC Servo Motor for Your System

AC servo motors are specialized electric motors designed for precise position, velocity, and acceleration control. Unlike standard motors, servo motors operate in a closed-loop system, using feedback devices like encoders to adjust motion accurately. They typically offer high torque-to-inertia ratios, rapid acceleration/deceleration, smooth rotation, and efficient power usage.

• 1. Torque Requirements: Torque is the rotational force the motor must provide to move the load. Properly sizing torque is fundamental:
• Continuous Torque: The steady torque the motor must supply during normal operation.
• Peak Torque: The maximum torque needed for acceleration, load changes, or starting.
• Load Inertia: The inertia of the load affects how much torque is needed to accelerate or decelerate quickly; high load inertia requires motors with higher torque capacity.

Always add a safety margin (typically 20–30%) above calculated torque to ensure reliability and handle unexpected load peaks.

• 2. Speed and Acceleration: Speed, typically measured in RPM, must match your application needs. Consider maximum operating speed and acceleration/deceleration rates. Higher speed can reduce torque, so balance speed requirements with torque capabilities. Proper selection avoids overheating and ensures efficient cycle times.
• 3. Size and Weight Constraints: In applications like robotics or aerospace, physical size and weight matter. Choose a motor that fits within mechanical design constraints. Smaller motors may save space but must still meet torque and speed requirements.
• 4. Voltage and Current Ratings: Ensure motor voltage matches your power supply system (e.g., 100V, 200V, 400V AC). Current ratings should be within your power source and driver capabilities to prevent overload. Higher voltage motors may provide more power but might need specialized controllers.
• 5. Feedback and Control Type: Most servo motors rely on feedback devices such as encoders or potentiometers. Choose a feedback mechanism compatible with your controller or PLC system.
• 6. Environmental Conditions: Consider the motor’s operating environment—temperature, humidity, dust, and vibration levels affect motor selection. Motors with appropriate IP (Ingress Protection) ratings ensure durability in harsh environments. For outdoor or industrial settings, choose ruggedized or sealed motors to avoid contamination.
• 7. Application-Specific Requirements: Some applications require high acceleration or smooth positioning (e.g., robotics, CNC machinery). Multi-axis systems may use different motor series optimized for each axis’s needs:
  • High response motors for rapid acceleration.
  • General-purpose motors for balanced speed and torque.
  • Low ripple motors for precision feeding.
• 8. Cost and Availability: Balance budget with performance needs. Consider availability of spare parts and after-sales support. Investing in quality may reduce downtime and maintenance costs.

• Calculate the load characteristics: weight, inertia, required speed, and cycle times.
• Use motor sizing tools or consult manufacturer datasheets for torque-speed curves.
• Avoid over-sizing to save cost but ensure the motor is not undersized to prevent premature failures.
• Verify compatibility with your drive/controller’s power and control signals.
• Factor in the duty cycle—continuous vs. intermittent operation—and select accordingly.

Choosing the right AC servo motor requires thorough understanding of your mechanical load, motion profile, electrical system, and operating environment. By carefully evaluating torque, speed, size, control type, and environmental factors, you can select a motor that optimizes system performance, energy efficiency, and longevity. Manufacturers often provide detailed selection guides and software tools to aid in sizing, which can be invaluable for complex applications.