The present invention relates to a structure of a pulse motor, in particular, relates to a pulse motor in which a permanent magnet is mounted in a magnetic path.
First, a prior pulse motor is described in accordance with FIGS. 1,2A and 2B to facilitate understanding of the present invention. FIG. 1 is a cross sectional view of a prior pulse motor, FIG. 2A is a cross sectional view at the line A--A of FIG. 1, and FIG. 2B is a perspective view of the stator. In those figures, the reference numeral 1 is a stator assembly, and 2 is a stator. The stator 2 has a plurality of magnetic poles 3a-3h on the internal surface of the stator 2. Each magnetic poles 3a-3h has a winding 4a through 4h.
The reference numeral 12 is a rotor assembly, 13 is a first rotor, and 14 is a second rotor. 15 is a permanent magnet secured between the first rotor 13 and the second rotor 14. On the outer surface of the rotors 13 and 14, a plurality of magnetic poles 16 are provided. Each magnetic pole 16 runs parallel to the axis of the rotor assembly 12, and confronts the magnetic poles 3a through 3h on the stator assembly 2. The magnetic pole 16 of the second rotor 14 is positioned at a different angle from that of the first rotor 13 by half the pitch of the magnetic poles.
The operation of the pulse motor in FIGS. 1,2A and 2B is as follows. As apparent from FIG. 1, the first rotor 13 is magnetized as an N-pole, and the second rotor 14 is magnetized as an S-pole by the permanent magnet 15. Supposing that the stator magnetic poles 3d and 3h are magnetized as N-poles by flowing an electrical current in the windings 4d and 4h, and that the stator magnetic poles 3b and 3f are magnetized as S-poles by the electrical current in the windings 4b and 4f, the magnetic pole 16 on the second rotor 14 is attracted by the N-pole of the stator magnetic poles 3d and 3h, thus, the rotor assembly rotates so that the rotor magnetic poles of the second rotor confront the N-poles of the stator magnetic poles. Next, supposing that the stator magnetic poles 3c and 3g are magnetized as N-poles by the windings 4c and 4g, and that the stator magnetic poles 3a and 3e are magnetized as S-poles by the windings 4a and 4e, then the second rotor 14 has the rotor assembly rotate in the clock-wise direction in FIG. 2A. Further, supposing that the stator magnetic poles 3b and 3f are magnetized as N-poles by the windings 4b and 4f and that the stator magnetic poles 3d and 3h are magnetized as S-poles by the windings 4d and 4h, then the second rotor 14 continues to have the rotor assembly rotate in the clock-wise direction. Similarly, by shifting the N-pole and S-pole on the stator magnetic poles, the second rotor continues to have the rotor assembly rotate.
Similarly, the first rotor 13 has the rotor assembly rotate in the clock-wise direction. That is to say, as the first rotor 13 is magnetized as N-pole by the permanent magnet 15, the first rotor 13 has the rotor assembly rotate when the corresponding stator magnetic poles are magnetized as S-poles. As mentioned before, the rotor magnetic poles 16 of the first rotor 13 are positioned on the axis of the rotor assembly at half pitch angle from these of the second rotor 14, the first rotor and the second rotor apply the rotational power to the rotor assembly alternately.
However, the prior pulse motor disclosed in FIGS. 1 and 2 has the disadvantages as follows. First, the prior pulse motor has rectangular stator magnetic poles, and thus, the windings are rectangular. So, the coil-winding operation is very difficult. Further, eight windings are necessary, and it takes a long time to insert each coil in the spaces around the magnetic poles.
Further, since the structure of the stator windings is complicated, some portion of the windings becomes shortcircuited or suffer from a loss of insulation. In some case, each coil has 500 turns, and the diameter of the stator assembly is only 4 mm, so it should be appreciated that the coil-winding work is very difficult.