Which type of servo motor is used for rapid positioning in industrial applications where low inertia is present?

• A. AC servo motor
• B. DC servo motor
• C. Stepper motor
• D. Induction motor

Answer: (A)

Rapid positioning with low inertia requires a motor that can respond quickly and be precisely controlled. AC servo motors fit this need because, when used with a servo drive and encoder feedback, they offer high dynamic response, strong torque at speed, and accurate position tracking. The closed-loop control continuously adjusts motor torque to minimize position error, which reduces overshoot and settling time during quick moves. With low inertia, the load can accelerate and decelerate rapidly, and the AC servo’s fast response and good high‑speed torque make those moves achievable and repeatable. DC servo motors can also perform well but rely on brushes and typically require more maintenance, making AC servo motors the more common choice in modern industrial systems. Stepper motors are great for simple, open-loop positioning but can struggle with rapid moves due to torque ripple and potential missed steps, and induction motors generally lack the precise speed/position control needed without additional feedback hardware.