Patent ID: 7040025

Claim:
A rotation-angle detecting device for detecting a rotation angle of a rotation detecting axle, the rotation-angle detecting device comprising: an abnormality evaluation mechanism including: first rotator and a second rotator, the first rotator and the second rotator having a same number of teeth and being adapted to engage with a gear fixed on the rotation detecting axle; a first angle-detector and a second angle-detector operable to detect a rotation angle of the first rotator and a rotation angle of the second rotator, respectively; and a controller operable to perform a calculation based on outputs from the first and second detectors and storing a result of the calculation, wherein the controller is operable to: convert the outputs from the first and the second detectors into a first periodic waveform and a second periodic waveform, respectively, the first periodic waveform and the second periodic waveform having a same crest value “A”, store a phase difference between the first and second periodic waveforms at a time of initial setting as an initial phase difference value “C”, and determine that an abnormal condition occurs if an evaluation value “X” calculated with reference to the initial phase difference value “C” exceeds a predetermined abnormality-evaluation threshold “D”.