US Patent 7112956 Method of generating an index signal with reduced parts

In an index signal generator for generating an index signal for use in a direct-drive motor having a rotation axis and comprising a stator and a rotor, a particular at least one of M magnetized elements is used as an index detection magnet having magnetic force which is different from those in remaining ones of the M magnetized elements. Wound around one of a specific one of particular three cores in the stator, an index detection coil detects variations of the magnetic force generated by the ring-shaped permanent magnet to produce a detected signal. On the basis of the detected signal, the index signal is generated.