All rotors are generally built in the same manner; 2 winding poles with lead wire connections to a slip ring (brush type), or diodes (brushless type).  The rotor wires are rotated within the stator core, producing an induced voltage within stator power windings.  Problem is, this type of power production, usually will have between 15%- 25% harmonic distortion of voltage sine wave for a slip ring rotor, and 30%-40% for a diode type rotor.  This is totally un-acceptable, for Gillette.  However, by using an exclusive process of precisely skewed rotor laminations and strategically placed aluminum damping bars, Gillette has been able to reproduce the voltage generated sine wave to produce an average of only 7% harmonic distortions.  To date, this is still a Gillette exclusive feature, from it's introduction year of 1994.