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.
There is provided a stepping motor of low vibration realized by reducing cogging with a simple structure while maintaining the performances such as torque. A stepping motor of the invention is structured such that a stator unit 18 is composed of a pair of stator sub-assemblies 5, 5 attached to each other in a back to back manner, each stator sub-assembly having a plurality of pole teeth 13 formed at its inner circumference and housing a coil inside thereof, a rotor unit 19 is rotatably disposed with a small gap from the plurality of pole teeth 13 and having multiple magnetic poles formed on an circumference thereof, the multiple magnetic poles of the rotor unit 19 being formed by magnetizing the rotor unit 19 alternately with an S pole and an N pole in a circumferential direction, and that while a magnetic pole width consisting of a width of the S pole and a width of the N pole in a pair is set to a predetermined constant value, the width of the S pole and the width of the N pole in each pair are set to be different from each other.
The flux densities formed by plural electromagnet poles M1 to M12 which are arranged at a predetermined interval in a circumferential direction of a rotary body 1 at the same position in an axial direction of the rotary body 1 are gradually changed in the circumferential direction of the rotary body. Even if there is a difference between the maximum value of the flux density and the minimum value, the change of the flux densities between the adjacent electromagnet poles is small and smooth. Accordingly satisfactory detective sensitivity and detection results can be obtained.
There is provided a stepping motor of low vibration realized by reducing cogging with a simple structure while maintaining the performances such as torque. A stepping motor of the invention is structured such that a stator unit 18 is composed of a pair of stator sub-assemblies 5, 5 attached to each other in a back to back manner, each stator sub-assembly having a plurality of pole teeth 13 formed at its inner circumference and housing a coil inside thereof, a rotor unit 19 is rotatably disposed with a small gap from the plurality of pole teeth 13 and having multiple magnetic poles formed on ah circumference thereof, the multiple magnetic poles of the rotor unit 19 being formed by magnetizing the rotor unit 19 alternately with an S pole and an N pole in a circumferential direction, and that while a magnetic pole width consisting of a width of the S pole and a width of the N pole in a pair is set to a predetermined constant value, the width of the S pole and the width of the N pole in each pair are set to be different from each other.
A brushless D.C. motor assembly includes a balancing sheet made of material with magnetic conductivity, the balancing sheet having an axle hole joined together with a stator by an axle tube, a rotor rotatably received in the axle tube, the rotation thereof controlled by a controlling device, and the rotor having a annular permanent magnet with a diameter substantially the same as the diameter of the balancing sheet wherein the permanent magnet and the balancing sheet attract each other.
A position sensor, such as a rotary position sensor, includes the signal-conditioning electronics in the housing. The signal-conditioning electronics are disposed on a printed wiring board, which is assembled with another printed wiring board including the sensor windings to provide a sub-assembly. A mu-metal shield is interposed between the printed wiring boards to prevent magnetic interference. The sub-assembly is disposed in the sensor housing adjacent to an inductor board which turns on a shaft. The inductor board emanates an internally or externally generated excitation signal that induces a signal in the sensor windings. The induced signal represents the rotary position of the inductor board relative to the sensor winding board.
