| 摘要 |
PURPOSE:To lower the detection of a leakage flux to an FG coil, and to improve the accuracy of an FG signal by setting the FG coil to a position where the direction of the leakage flux from a main magnet is parallel to the rotation center direction of the magnet. CONSTITUTION:A main magnet 4 is rotated by receiving a rotating magnetic field by a main coil 2 on a stator 1. In this case, a magnetic flux of the main magnet 4 leaks to the inside diameter part of a magnet yoke 6. The leakage flux quantity of this main magnet 4 becomes the largest at the same height part as the end face part of the main magnet 4, and the smallest at the part being a little near the end face of a magnet case of a mechanical center height of the main magnet 4, namely, a magnetic center height. An FG coil 8 detects an FG signal magnetized by an FG magnet 9, but a device is installed at the almost same height as the magnetic center in the height direction of the main magnet 4, therefore, it is not influenced by a leakage flux by the main magnet 4.
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