Patent ID: 8319493

Claim:
A rotation detecting device comprising: a plurality of magnetic encoders of a ring shape arranged coaxially and having different numbers of magnetic poles; a plurality of magnetic sensors each operable to detect the magnetic field of the corresponding magnetic encoder and having a function of detecting positional information within a single magnetic pole of the corresponding magnetic encoder; a phase difference detector to determine the phase difference of magnetic field signals detected respectively by the magnetic sensors; an angle calculator to calculate an absolute rotation angle of the magnetic encoders based on the detected phase difference; and a correcting unit to correct an initial phase difference occurring in the magnetic field signals, detected respectively by the magnetic sensors, due to positions at which the magnetic encoders are fitted, wherein each of the magnetic sensors comprises a line sensor, in which sensor elements are lined up in a direction conforming to the direction, in which the magnetic poles of the corresponding magnetic encoder are arranged and is operable to generate two phase signal outputs descriptive of sine and cosine curves by means of calculation to thereby detect the position within the magnetic poles by interpolation of the two phase signal outputs.