Motor apparatus

A motor apparatus having a rotor placed rotatably on a stator base and provided with an FG signal for controlling the rotation of the rotor, the motor apparatus comprising:

• a driving magnet having an even number of magnetic poles evenly placed on the outer circumference of the rotor, wherein the even number is not less than 12 and not more than 32, and having a magnetic flux density pattern superposed with an “n”th (n is either one of 3 and 5) harmonic component, wherein the driving magnet is made of Nd—Fe—B system material;
• and
• an FG coil provided on the circumference of the stator base in the position opposing to each of the magnetic poles of the driving magnet with keeping a predetermined gap between the FG coil and the driving magnet, wherein the FG coil has a folding pattern of being folded alternately in the radial direction by a fold pitch angle of 1/n of a pitch angle of the driving magnet, the motor apparatus further satisfying an equation of 4≦πD/(PG)≦15 in order to suppress rotational fluctuation caused by controlling the rotation of rotor within 5%, wherein
• π is circular constant,
• D is a diameter of the driving magnet,
• P is a number of magnetic pole of the driving magnet, and
• G is a gap length between the driving magnet and the FG coil.