AC servo motor stator
The stator of this motor is a laminated structure, and its two windings are wound at 90 electrical angles in space. A source of winding voltage called the primary winding (also called the reference or stationary phase) is excited. The other winding, called the control strip winding (or control phase), is powered by a variable control voltage that is 90 degrees out of phase with the voltage across the main winding. The control voltage is provided by the servo amplifier.
AC servo motor rotor
The rotor is usually a squirrel cage type with a small diameter and a long length to maintain the lowest possible mechanical inertia. In order to obtain a torque-speed characteristic that is as linear as possible, it has a high resistance. For very low power applications, the use of a drag cup rotor (Figure 2) further reduces the rotor inertia. This type of rotor is a specialized form of a squirrel-cage rotor in which the conductors are in the shape of a dragging cup and are made of a non-magnetic conductive material such as copper, aluminum or an alloy. The slotted rotor laminations are replaced by a set of fixed annular laminations, which provide a low reluctance path for the magnetic flux.