Absolute rotational position detection device

An absolute rotational position detection device comprising:

• a rotor section having a single cylindrical member having a first pattern, disposed along the circumference of the cylindrical member, which repeats change in the circumferential direction with a predetermined pitch, and a second pattern, disposed along the circumference of the cylindrical member parallel to the first pattern, which has a change of one cycle with respect to one circumference, said first and second patterns being formed with a predetermined material, said first and second patterns being independent of each other;
• a detection head section provided in proximity to said rotor section, whose position relative to the rotor section changes along the circumferential direction of the first and second patterns and which, as a result of changing relative position of the rotor section with respect to the detection head section, produces first and second cyclic output signals representing electrical phase change whose respective cycles are constituted of one pitch of the respective patterns;
• and
• means for obtaining first absolute position data whose cycle corresponds to one pitch of the first pattern by measuring electrical phase difference between the first output signal and a predetermined reference AC signal and obtaining second absolute position data whose cycle corresponds to one pitch of the second pattern by measuring electrical phase difference between the second output signal and the reference AC signal and thereby providing, responsive to said first and second absolute position data, data specifying absolute rotational position of said rotor section with respect to said detection head section.