Importance

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Abstract

A brushless motor comprises a stator and a rotor fixed to a rotary shaft. A first magnetic poles row is formed on an inner peripheral surface of an annular magnet included in the rotor. A second magnetic poles row having magnetic poles of a number larger than that of magnetic poles included in the first magnetic poles row is formed on the bottom end surface of the annular magnet, which is magnetized in an axial direction of the rotary shaft and is magnetized in an alternately opposite polarity in a circumferential direction of the annular magnet. A third magnetic poles row which is magnetized in the axial direction and is magnetized in alternately opposite polarity in the radial direction is formed at a predetermined position of the second magnetic poles row. A frequency signal generating coil and a pulse signal generating coil which can respectively face the second magnetic poles row and the third magnetic poles row are formed on a printed board of the stator facing the bottom end surface of the annular magnet with an interval kept inbetween. A signal having a frequency responding to a rotation of the brushless motor is outputted from the frequency signal generating coil, and one or more pulse signals are outputted from the pulse signal generating coil for each rotation of the brushless motor.

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First Claim