1. Field of the Invention
The present invention relates to a rotation angle detecting device which detects a relative rotation angle between a rotary object and a stationary object. Such a rotation angle detecting device can be used for an engine throttle valve control, a robot arm control and the like.
2. Description of the Related Art
A conventional rotation angle detecting device includes a magnetic sensor element, such as a hall element integrated with an IC chip, and a pair of semi-cylindrical permanent magnets disposed to surround the magnetic sensor element, as shown in JP-B2-3206204, JP-A-Hei 2-122205, JP-A-Hei 2-298815 and JP-A-sho 64-37607. Such a conventional rotation angle detecting device has the following problems.
(1) Magnetic leakage is significant at axial ends of the permanent magnets. If the magnetic sensor element shifts in the axial direction or along the center axis of rotation, a predetermined amount of magnetic flux is not supplied to the magnetic sensor element, so that the magnetic sensor element can not detect an accurate rotation angle when a rotary object rotates.
(2) If the magnetic sensor element shifts a little in a diametrical direction or a direction perpendicular to the rotary shaft, a predetermined amount of the magnetic flux does not pass through the magnetic sensor element, so that the magnetic sensor element can not detect an accurate rotation angle when a rotary object rotates.