JPH0152990B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present application relates to a permanent magnet type step motor whose purpose is to significantly reduce leakage magnetic flux to the outside.

Conventionally, permanent magnet step motors have been used to drive the magnetic heads of magnetic disks, and are rotated in steps by a DC power source. In order to prevent adverse effects, it has already been proposed that the brackets that are placed before and after the stator and make up the outer casing are made from a magnetic material instead of a non-magnetic material such as aluminum diegast. Also, since the bracket is simply made of magnetic material, the magnetic flux passing through the bracket is large, and as a result, magnetic flux leaks from the bracket and a sufficient shielding effect cannot be expected. When using the method of magnetizing the rotor's permanent magnets, the bracket itself is also magnetized in the same direction.
This has the disadvantage that the invalid magnetic flux passing through the bracket increases and the leakage magnetic flux to the outside also increases.

Therefore, in the present application, the bracket is made of a magnetic material, and the bracket is configured to suppress the magnetic flux passing through the bracket and reduce the leakage magnetic flux to the outside as much as possible while expecting a shielding effect from the bracket. The embodiment will be described in detail with reference to the drawings below. 1 is a rotor of a motor, a rotating shaft 2,
A pair of permanent magnets 3, which are disc-shaped and magnetized in the axial direction, with opposing surfaces magnetized to N and S poles, respectively, and a spur gear-shaped magnetic material having teeth along the circumference of the circle. The permanent magnet 3 is integrally attached to the rotating shaft 2 with the permanent magnet 3 being sandwiched between the pair of rotor yokes 4a and 4b.
5 is a concentric outer circumferential cylindrical portion 5a and an inner circumferential cylindrical portion 5
b and a disk portion 5c that closes these outer end surfaces are integrally formed from a magnetic material; 6 is a concentric outer cylindrical portion 6a and an inner cylindrical portion 6b, and their outer end surfaces. Disk portion 6c that closes
After integrally forming the bracket with magnetic material,
7 is a stator made of a laminated iron plate punched into an annular shape;
It is located between the outer circumferential cylindrical portions 5a and 6a of the front and rear brackets 5 and 6 such that its inner circumferential surface faces the outer circumferential surface of the rotor yokes 4a and 4b through a small gap and is located coaxially. It is attached integrally. 8 and 9 connect the rotating shaft 2 to the front and rear brackets 5,
A bearing 6 is rotatably supported on each inner cylindrical portion 5b, 6b, a retaining ring 10 prevents the bearings 8 and 9 from moving in the axial direction, and a rotor coil 11. A permanent magnet step motor configured in this manner is well known, and the first invention of the present application is characterized in that, in the above configuration, the front and rear brackets are magnetized in a direction opposite to the direction of magnetization of the permanent magnets. It is something to do.

That is, in the step motor having the above configuration,
When the permanent magnet 3 is magnetized to the S pole on one rotor yoke 4a side and the N pole on the other rotor yoke 4b side, the inner end of the inner circumferential cylindrical portion 5b of the front bracket 5 It is magnetized so that the side thereof becomes the S pole, the outer end thereof becomes the N pole, the inner end of the inner circumferential cylinder 6b of the rear bracket 6 becomes the N pole, and the outer end becomes the S pole. In this case, the front and rear brackets 5, The strength of the magnetic field that magnetizes the permanent magnet 6 is made smaller than the strength of the magnetic field that magnetizes the permanent magnet 3.

According to the above configuration, since the facing surfaces of the pair of rotor yokes 4a, 4b and the inner circumferential cylindrical portions 5b, 6b of the front and rear brackets 5, 6 have the same polarity, the magnetic flux from the permanent magnet 3 is is repelled between them, and the pair of rotor yokes 4a, 4b and stator 7
The number of magnetic flux passing between the permanent magnet 3 and the rotor yoke 4b, the stator 7, and the other rotor yoke 4b is rather increased compared to a case where the front and rear brackets are simply made of magnetic material. While the effective magnetic flux A reaching the rotor yoke increases, the effective magnetic flux B reaching the front bracket 5, the stator 7, the rear bracket 6, and the other rotor yoke 4b from the permanent magnet 3 decreases greatly. It also has the effect of greatly reducing leakage magnetic flux leaking from itself to the outside.

The first invention provides magnetization for the permanent magnet 3;
Although we have described a step motor in which the front and rear brackets 5 and 6 are magnetized separately, the second invention of the present application is such that after assembling the motor from the front and rear brackets 5 and 6 including the rotor 1 and stator 7, The present invention provides a step motor that is effective when applying a magnetic field in the axial direction from the outside of the motor to magnetize the magnetic poles of the permanent magnets 3.The main feature of this step motor is that the front and rear brackets are connected to the front and rear brackets of the permanent magnets in the rotor. It is characterized in that it is made of a magnetic material having a coercive force lower than that of the magnetic material, and that the front and rear brackets are magnetized in a direction opposite to that of the permanent magnet. in particular,
After configuring a step motor as shown in the figure by using a rare earth cobalt magnetic material with a high coercive force as the permanent magnet 3 and using a sintered alloy of iron with a low coercive force as the front and rear brackets 5 and 6, an external A magnetic field of, for example, 15,000 eld is applied to the permanent magnet 3 in the axial direction to magnetize the permanent magnet 3 to N and S poles. At this time, the front and rear brackets 5 and 6 are also set N and S in the same direction.
Since the poles are magnetized, the front and rear brackets 5 and 6
In order to demagnetize the magnetic poles, a magnetic field is applied in the opposite direction. In this case, the front and rear brackets 5 and 6
However, since it is made of a magnetic material having a lower coercive force than the magnetic material constituting the permanent magnet 3, only the front and rear brackets 5 and 6 are effectively demagnetized without demagnetizing the permanent magnet 3 by the magnetic field in the demagnetizing direction. be able to. After demagnetizing the front and rear brackets 5 and 6 in this way, a magnetic field of, for example, 1000 Els is applied again to the permanent magnet 3 in the same direction as the demagnetizing direction, that is, N, S.
The pole is given in the opposite direction to the magnetization direction.

Also in the case of this invention, as in the case of the first invention, the opposing surfaces of the pair of rotor yokes 4a, 4b and the inner circumferential cylindrical portions 5b, 6b of the front and rear brackets 5, 6 have the same polarity. As a result, the magnetic flux is repelled between them, and the leakage magnetic flux leaking to the outside from the front and rear brackets 5 and 6 themselves is greatly reduced. In particular, in this invention, after constructing the motor, a magnetic field is applied from the outside. Since the permanent magnet and the front and rear brackets can be magnetized with desired magnetic poles,
The magnetization operation is extremely easy, and it has an excellent effect on mass production.

Therefore, according to the present invention, the invention is extremely useful especially as a motor used for magnetic disks and the like.

[Brief explanation of drawings]

The drawing is a side sectional view showing an embodiment of the present invention. In the figure, 1 is a rotor, 2 is a rotating shaft, 3 is a permanent magnet,
4a and 4b are rotor yokes, 5 is a front bracket,
6 is a rear bracket, 7 is a stator, 8 and 9 are bearings, A is an effective magnetic flux, and B is an invalid magnetic flux.

Claims (1)

[Scope of Claims] 1. A rotor having a rotating shaft integrally provided with a permanent magnet having magnetic poles in the axial direction and a pair of rotor yokes that sandwich the permanent magnet, and an outer periphery of the pair of rotor yokes. In a permanent magnet type step motor in which a stator and a stator facing each other are coaxially held by front and rear brackets, the front and rear brackets are made of a magnetic material, and the front and rear brackets are arranged in a direction opposite to the magnetization direction of the permanent magnet. A permanent magnet step motor characterized by being magnetized with. 2. A permanent magnet type step motor according to claim 1, wherein the front and rear brackets each include a concentric outer circumferential cylindrical part and an inner circumferential cylindrical part, and a disc part closing the outer ends of these parts. 3. A rotor having a rotating shaft integrally provided with a permanent magnet having magnetic poles in the axial direction and a pair of rotor yokes that sandwich the permanent magnet, and a stator that faces the pair of rotor yokes on the outer periphery thereof. are coaxially held by front and rear brackets, the front and rear brackets are made of a magnetic material having a coercive force lower than that of the permanent magnet, and the front and rear brackets are A permanent magnet type step motor characterized by being magnetized in a direction opposite to that of the permanent magnet type step motor. 4. A permanent magnet type step motor according to claim 2, wherein the front and rear brackets each include a concentric outer circumferential cylindrical portion and an inner circumferential cylindrical portion, and a disk portion closing the outer ends of the outer circumferential cylindrical portion and the inner circumferential cylindrical portion.