JPH0735365Y2 - Magnetizing yoke - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement of a magnetizing yoke for magnetizing a ring magnet used in a rotation speed detector or the like using a magnetic bubble.

<Prior Art> FIG. 3 is a perspective view showing the principle of a rotation speed detector using magnetic bubbles. Reference numeral 3 denotes a ring-shaped permanent magnet (hereinafter referred to as a ring magnet) magnetized to have different polarities (8 poles in this case) alternately in the circumferential direction. When the permanent magnet 3 rotates about the rotation axis c, the rotating magnetic field M is applied to the magnetic bubble element 4 arranged near the outer circumference thereof. When the rotating magnetic field is applied, the magnetic bubbles are transferred in the magnetic bubble element 4 and moved on the transfer pattern by the number of steps corresponding to the number of rotations of the rotating magnetic field. Therefore, if the position of the magnetic bubble on the transfer pattern is detected, the rotation speed of the rotation axis c can be known.

As shown in FIG. 4, the rotating magnetic field of the ring magnet is detected by the magnetic field sensors 5 and 6 in the x and y directions (using a Hall element or the like) located at the same distance as the magnetic bubble element 4 from the ring magnet, and It is used for compensating the magnetic field at the time of position reading.
See -247877).

5 and 6 are views showing a magnetizing yoke for magnetizing the above ring magnet. In FIG. 5, the magnetizing yoke 7
, A plurality of magnetic poles 71 are provided at equal intervals in the circumferential direction via a magnetic pole space 72. Each magnetic pole 71 has an excitation coil 73
Is wound. When a large current is applied to the coil 73, the ring magnet 8 is magnetized corresponding to the magnetizing direction of the magnetic poles. Since the number of windings of the coil can be large, there is an advantage in that the magnet can be magnetized even if the gap between the ring magnet 8 and the ring magnet 8 is relatively large, and the working accuracy of the magnetic pole 71 and the ring magnet 8 can be low.

In FIG. 6, the magnetizing yoke 9 has a thin groove 92 between a plurality of wide magnetic poles 91, and the coil 93 is housed inside the groove 92. The ring magnet 8 is magnetized by passing a large current pulse of KA order to the coil 93, but since the coil 93 is fixed in the groove 92 even when an electromagnetic force acts,
There is an advantage that the magnetic pole width is determined and the variation in the magnetization strength is reduced.

<Problems to be Solved by the Invention> However, in the case of the ring magnet magnetized by the magnetizing yoke 7 in FIG. 5, the coil 73 is moved by the electromagnetic force at the time of magnetization, so that the variation in the magnetizing strength becomes large. There is a problem.

Further, in FIG. 4, it is actually difficult to dispose the magnetic field sensors 5 and 6 at the same distance as the magnetic bubble element. That is, there is a positional shift between the magnetic sensors 5 and 6, and the distance from the ring magnet surface to the magnetic sensor is often larger than the distance from the ring magnet surface to the magnetic bubble element. Correcting. This is not a problem in the ideal case where the locus of the rotating magnetic field vector is circular regardless of the distance. However, when the locus has a square shape, that is, a harmonic component, the magnitude of the harmonic component changes depending on the distance. This is a problem because the shape of the trajectory changes. In the case of the ring magnet magnetized by the magnetizing yoke 9 shown in FIG. 6, the variation of the magnetization is small, but the adjacent polarities change discontinuously, so that the rotating magnetic field at a point separated from the ring magnet surface by a certain distance. Since the locus of is squared and its shape changes depending on the distance, there is a problem that the error in compensation by the magnetic sensors 5 and 6 becomes large.

The present invention has been made in order to solve such a problem, and provides a magnetizing yoke capable of magnetizing a ring magnet so as to generate a rotating magnetic field locus having a small magnetic fluctuation and a small number of harmonic components. Aim to achieve.

<Means for Solving the Problems> The present invention has a cylindrical shape in which a plurality of magnetic poles are provided at regular intervals in a circumferential direction inside a cylinder so that magnets inserted in the cylinder are magnetized in a radial direction. In the magnetizing yoke, the widths of the magnetic poles and the recesses are set to approximately 1: 1 and a groove narrower than the width of the recesses is provided at the bottom of the recesses so that the magnetic poles are housed in the grooves so as to wind the magnetic poles. The point is that a coil is provided and the magnetic poles adjacent to the magnet are excited to different polarities by the current flowing through the coil.

<Operation> Since the coil is fixed in the narrow groove, the variation in magnetization is small and the magnetic pole width is reduced by the recess, so that the high frequency component of the rotating magnetic field locus of the ring magnet can be reduced.

<Example> The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a top view (A) and a side view (B) showing an embodiment of a magnetizing yoke according to the present invention. Here, the case of 8 poles is shown. Reference numeral 1 is a cylindrical magnetizing yoke, and 2 is a ring magnet magnetized by the magnetizing yoke 1. In the magnetizing yoke 1, 11 is an 8-pole magnetic pole provided at equal intervals along the inner circumference forming the through hole of the magnetizing yoke 1, and 12 is a magnetic pole 11.
A recess 13 provided between the recesses 13 is a groove having a width W ₂ narrower than the surface width W _{1 of the} recess 12 provided at the bottom of the recess 12, and 14 is housed and fixed in the groove 13 to surround the magnetic pole 11. It is a coil arranged so as to be wound. Here, the recess 12 has a shape of a part of a circle. By passing a current through the coil 14, eight adjacent magnetic poles have different polarities, that is, N →
Excited as S → N → S. By inserting the ring magnet 2 to be magnetized into the through hole 15 at the center of the magnetizing yoke 1 and passing a current through the coil 14, the magnet can be magnetized to 8 poles.
At this time, the clearance between the ring magnet 2 and the end face of the magnetic pole 11 is 0.1 m by processing both with high accuracy.
It is below m.

As the width W ₁ of the recess 12 is increased in the above configuration,
The adjacent polarities of the magnetized ring magnets change gently, and the locus drawn by the tip of the vector of the rotating magnetic field generated by the ring magnet approaches a circle. Fig. 2 shows changes in spatial harmonic components of the trajectory of the rotating magnetic field corresponding to the distance from the ring magnet surface when a ring magnet with an outer diameter of φ21.4 and an inner diameter of φ18 is magnetized by the magnetizing yoke 1 described above. It is a characteristic curve figure which shows. Here, the third and higher harmonics are sufficiently small and can be ignored. As is clear from the figure, by setting the magnetic pole width W ₃ to 85% to 50% of 1/8 of the circumference, the high frequency content can be reduced by several dB. In order to sufficiently reduce the high frequency content, the magnetic pole width W ₃ is preferably 50% or less,
The actual value is determined in consideration of the magnetizing strength.

According to the magnetizing yoke having the above-mentioned structure, the coil is fixed in the narrow groove so that it does not move due to the electromagnetic force when magnetized, and the clearance between the yoke and the outer diameter of the ring magnet is reduced. And the yoke magnetic pole width is made with high accuracy, it is possible to reduce the magnetization variation of the ring magnet.

By setting the width of each magnetic pole to 50% or less of (1 / the number of magnetic poles) on the outer circumference of the magnet, the harmonic components in the rotating magnetic field generated by the magnetized ring magnet can be reduced. That is, the magnetic pole width is 100% as in the conventional magnetizing yoke of FIG.
Since the harmonic content is significantly smaller than that of the close one, the absolute value of the variation of the harmonic content corresponding to the distance from the ring magnet is also small.

As a result, it is possible to reduce the error in the magnetic field correction by the magnetic sensor (5, 6 in FIG. 4).

Although the number of poles of the magnetizing yoke is set to eight in the above embodiment, the number of poles is not limited to eight and may be any number of poles.

The shape of the recess 12 is not limited to that shown in FIG. 1, and the recess 12 and the groove 13 may be formed in a continuous shape.

Further, the above-mentioned magnetizing yoke is not limited to the ring magnet of the rotation speed detector using the magnetic bubble, but can be used for magnetizing the rotor of the motor or the like.

<Effects of the Invention> As described above, according to the present invention, a magnetizing yoke that can magnetize a ring magnet so as to generate a rotating magnetic field locus with a small magnetization variation and a small number of harmonic components is simple. It can be realized with a configuration.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a magnetizing yoke according to the present invention, FIG. 2 is a characteristic curve diagram of a ring magnet magnetized by the magnetizing yoke of FIG. 1, FIG. 3 and FIG. Is a diagram showing the principle of a rotation speed detector using magnetic bubbles, and FIGS. 5 and 6 are diagrams showing the configuration of a conventional magnetizing yoke. 1 ... Magnetizing yoke, 11 ... Magnetic pole, 12 ... Recess, 13 ...
Groove, 14 ... Coil.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuhiro Sakamaki 2-932 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Electric Co., Ltd. (56) References

Claims (1)

[Scope of utility model registration request] 1. A cylindrical magnetizing yoke in which a plurality of magnetic poles are provided at equal intervals in a circumferential direction of the inside of a cylinder to magnetize a magnet inserted in the cylinder in a radial direction. And the width of the recess is approximately 1: 1 and a groove narrower than the width of the recess is provided on the bottom of the recess, and a coil that is housed in the groove and arranged to wind the magnetic pole is provided. A magnetizing yoke, characterized in that the magnetic poles adjacent to the magnets are excited to different polarities by a flowing current.