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Short note: Servo motor

Short answer

A servo motor is a small motor designed for closed-loop position/speed control, requiring low inertia, linear torque, and no drift at zero signal. AC types are two-phase induction; DC types are separately excited or permanent magnet. Common applications include robots, CNC, and radar positioning.

Write a short note on servo motor.

A servo motor is a small motor designed for use in a closed-loop control system, in which its shaft position or speed follows a command signal accurately and quickly.

Requirements

  • Torque proportional to control signal, linear torque-speed characteristics.
  • Low inertia (small diameter, long rotor) for quick start, stop and reversal.
  • Stable operation; no running when the control signal is zero.

Types

AC servo motorDC servo motor
Two-phase induction motorSeparately excited / PM DC motor
Reference + control winding at 90∘90^\circArmature or field control
High-resistance cage or drag-cup rotorLow-inertia armature
Low power (few W to ~100 W)Higher power
No brushes, ruggedBrushes need maintenance

Working (closed loop)

 Ref -->(+)--> [Amplifier] --> [Servo motor] --> Load
        (-)                          |
         ^------[Feedback sensor]<---+
  • The error between the command and the feedback (from a potentiometer, encoder or tachogenerator) is amplified and applied to the motor.
  • The motor turns until the error becomes zero; the direction of the error decides the direction of rotation.

Applications

Robots, CNC machine tools, radar and antenna positioning, aircraft control surfaces, camera auto-focus, printers and instrument servos.

✓ Answer checked by Claude Sonnet 5.5

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