Index position detecting apparatus for an electromagnetic rotary machine

摘要

An electric rotary machine which prevents problems involved in leakage flux, and reduces the number of components so that it becomes thin and small in size, and inexpensive. The machine includes a first pulse generating device generating a first frequency generating signal consisting of P1 uniformly spaced pulses per one revolution of the rotor by detecting a counterelectromotive voltage induced in a rotary magnetic field generating device while a driving magnet is rotating, a magnetic body producing magnetic flux during rotation of the rotor, a second pulse generating device generating a second frequency generating signal consisting of P2 uniformly spaced pulses per one revolution of the rotor by detecting changes in the magnetic flux of the magnetic body, and an index position detecting circuit generating an index signal on the basis of a periodic phase difference between the first and second frequency generating signals. The numbers of poles of the driving magnet and the magnetic body are set so that the greatest common divisor of the pulse numbers P1 and P2 become an integer m.