US Patent 8471552 Rotational angle-measurement apparatus and rotational speed-measurement apparatus

A rotational angle-measurement apparatus with high accuracy is provided through electric correction of the rotational angle-measurement apparatus by rotating the rotation shaft at a constant speed. The rotational angle-measurement apparatus includes an electric motor having a rotation shaft, a magnet mounted on one end of the rotation shaft, and a magnetic sensor with an output signal that changes in accordance with an orientation of a magnetic field surrounding the magnetic sensor. The magnetic sensor outputs an angle signal representing the rotational angle of the rotation shaft, and the correction procedure utilizes rotation of the electric motor shaft through more than one revolution at a rotational speed with a known rate of change.