Servo Motors vs. AC Motors

An AC (as well as many DC) motor just turns.

A servo motor has some sort of feedback scheme that synchronizes with a partner servo, or gives actual position data to its controller.

AC motor is build for converting AC electric power to mechanic power with minimum power loss.

Servo motors are not built for power output purposes. They are adjustment motors.

Their use is remotely control and adjust anything.

Application for servo motors are in millions. Adjusting temperature by varying the set of valves, adjusting the position of a projector, and tons of examples.

The servomotor torque requirement and acceleration requirements are a bit different from the normal AC motor.

To have high accelaretion (and hence speed of response) the servo are with smaller/lighter rotor.

These need torque- theoritically (linearly) proportional to the applied voltage. To approach this type of characteristics, these are with high resistance rotor coils.

next feature is that these have a fixed winding - excited by a constant voltage source and a control winding excited by the control voltage.

Further details will be available in any electrical machines/ drives book.