Patent ID: 7622883

Claim:
A controller for a motor that has a first rotor, a second rotor, each of which produces a field by a permanent magnet, and an output shaft capable of rotating integrally with the first rotor of the rotors, which are coaxially disposed, said second rotor being capable of relatively rotating with respect to said first rotor, and the strength of a composite field of the fields of the permanent magnets of the rotors being capable of being changed by changing the phase difference between the rotors by the relative rotation of the second rotor, the controller comprising: phase difference changing driving means that has an actuator that produces a driving force to make said second rotor relatively rotate with respect to said first rotor; demagnetization determining means for determining whether or not demagnetization of the permanent magnets of said rotors occurs during operation of said motor; and rotor phase difference controlling means for controlling said phase difference changing driving means to change the phase difference between said rotors from a current phase difference to a phase difference that results in a higher strength of said composite field in a case where the result of determination by said demagnetization determining means is positive.