| 摘要 |
PURPOSE:To constitute a small-sized, inexpensive floppy disk driving device with excellent performance by incorporating a rotating speed detecting mechanism which rotates a disk type semiconductor motor at a constant speed without occupying a space. CONSTITUTION:Magnetic poles 12b for frequency detection which are magnetized into many poles (about 180 poles) are formed on the top surfaces of a field magnet 12 at outer circumferences of magnetic poles 12a for driving. The magnetic poles 12b for frequency detection may be magnetized while separated from the driving magnetic poles 12a, but in this example, eight driving magnetic poles 12a are formed in the field magnet 12 and then the magnetic poles 12b for frequency are formed by outer-circumferential part double magnetizing means on the driving magnetic poles 12a. The magnetic poles 12b for frequency detection have intense N-pole magnetized parts and weak N'-pole magnetized parts formed alternately in the N-pole driving magnetic poles 12a at fine pitch and intense S-pole magnetized parts and weak S-pole magnetized parts alternately in the S-pole driving magnetic poles 12a at fine pitch. The N' poles correspond to the S poles and the S' poles correspond to the N poles. |
