AC servomotors

  These are basically two-phase, reversible,induction motors modified for servo operation. They are used in applications requiring rapid and accurate response characteristics. To achieve these characteristics, these induction motors have small diameter, high resistance rotors. The small diameter provides low inertia for fast starts, stops, and reversals. High resistance provides nearly linear speedtorque characteristics for accurate control.

  

 An induction motor designed forservo use is wound with two phases physically at right angles or in space quadrature. A fixed or reference winding is excited by a fixed voltage source, while the control winding is excited by an adjustable or variable control voltage, usually from a servoamplifier. The windings are often designed with the same voltage/turns ratio, so that power inputs at maximum fixed phase excitation, and at maximum control phase signal, are in

balance.

  The inherent damping of servomotors decreases as ratings increase, and the motors are designed to have a reasonable efficiency at the sacrifice of speed-torque linearity. Induction type servomotors are available in fractional and integral

horsepower sizes.