Patent ID: 8278914

Claim:
A rotation angle detector for detecting a rotation angle of a detectable rotation body, comprising: a primary rotation body to be attached to the detectable rotation body and to rotate as integral with the detectable rotation body; a secondary rotation body to rotate as a predetermined rotation ratio for the primary rotation body; a primary rotation detection mechanism to output a signal to be varied periodically as corresponding to a rotation of the primary rotation body; a secondary rotation detection mechanism to output a signal to be varied periodically as corresponding to a rotation of the secondary rotation body; a signal processing unit to calculate the rotation angles of the primary rotation body and the secondary rotation body using the signals that the primary rotation detection mechanism and the secondary rotation detection mechanism output; and an operation processing unit to calculate the rotation angle of the detectable rotation body, based on the calculated rotation angle of the primary rotation body or of the secondary rotation body, and on a relative rotation angle between the primary rotation body and the secondary rotation body, wherein the operation processing unit calculates a rotation angle φ of the detectable rotation body using the following equations (1) to (4), with assuming the calculated rotation angle of the primary rotation body as θ 1 , an angle as θ 2 of which the calculated rotation angle of the secondary rotation body is multiplied by the predetermined rotation ratio, the converted cycle of the first signal of the primary rotation detection mechanism as T 1 , a cycle as T 2 (T 1 ≠T 2 ) of which the converted cycle of the second signal of the secondary rotation detection mechanism is multiplied by the predetermined rotation ratio, an absolute value |T 1 −T 2 | as d for a difference between the cycle T 1 and the T 2 ; in a case where T 1 <T 2 , and θ 2 ≦θ 1 : Φ=θ1 +T 1(θ1−θ2)/ d (1); in a case where T 1 <T 2 , and θ 2 >θ 1 : Φ=θ1+ T 1(θ1−θ2)/ d+T 1 T 2/ d (2); in a case where T 1 >T 2 , and θ 1 ≦θ 2 : Φ=θ1+ T 1(θ2−θ1)/ d (3); and in a case where T 1 >T 2 , and θ 1 >θ 2 : Φ=θ1+ T 1(θ2−θ1)/ d+T 1 T 2/ d (4).