Effect of the Number of Rotor Magnet Poles on the Characteristics of a Direct-Drive Motor Built into a Camcorder Lens Barrel

摘要

Camcorders would be more compact, lighter, and lower-priced if their drive motors were built into their lens barrels. We propose a new direct-drive motor built into a lens barrel. The characteristics of motors with 10 rotor magnet poles reported in previous papers were studied. Analysis by the effects of the number of rotor magnet poles on characteristics of the motors is important for optimum design of these motors. The air-gap magnetic flux densities of ring magnets linked with armature windings are not increased or saturated even when the magnet pole angles are increased by more than 60 degrees (this means that there are fewer than 6 poles). On the other hand, position errors of motors with 8,10 and 14 poles are smaller than motors with 2,4 and 6 poles; hence, motors with more than 8 magnet poles are advantageous in position controls.