Pulse generator

Abstract

An index signal is used for assuring media for use in a floppy disk drive to be exchangeable with each other. While the signal is output once for each rotation of a spindle motor, since the signal generation is carried out in a non-contact manner with rotating members including the medium, a hole sensor or the like has been previously used. However, such a hole sensor is expensive and fragile under temperature and mechanical stress. A pulse generator has been proposed, in which the rotor magnet is provided with magnets having unequally allocated angles and disposed all along a circumference and a stator coil and is disposed so as to match with the rotor magnet to have a pulse generated once for each rotation. However, the generated signal has, been poor in its S/N characteristic. It is an object of the invention to overcome the difficulties and provide a pulse generator that is highly reliable and excellent in the S/N characteristic with the manner of allocation of angles for the rotor magnet improved. A rotor assembly having a permanent magnet with a plurality, i.e., M pieces, of magnetic poles of opposite polarities to each other alternately disposed in a circumferential direction and a stator assembly having a plurality of stator coils disposed in confronting and coaxial relationship with rotor assembly, at least one set of the magnetic poles are set to have equally allocated angles from the center of the shaft. The remaining magnetic poles are set to have unequally allocated angles. The stator coils electromagnetically match the rotor assembly only once for each rotation thereof and a very large pulse is generated. In addition, a waveform with a satisfactory S/N characteristic can be obtained.

Dependencies are inferred from the claim text.