JP2976677B2 - Speed detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotational speed detector using a magnetic bubble, and more particularly to an improvement in a magnetic shield structure.

[0002]

2. Description of the Related Art The present application is an improvement of Japanese Utility Model Application No. 62-126991, entitled "Rotation Speed Detector" (hereinafter referred to as the prior application).

[0003] The applicant of the present invention discloses a rotational speed detector using a magnetic bubble, as disclosed in Japanese Patent Application No. 61-81901 (referred to as Prior Art 1).
And Japanese Patent Application No. 62-212208 (hereinafter referred to as Precedent Example 2), and the principle thereof is widely known. 2 is a diagram illustrating the operation principle of a rotation speed detector using magnetic bubbles, FIG. 3 is a diagram illustrating a pattern example of a transfer element loop provided on the magnetic bubble element in FIG. 2, and FIG. 4 is a stretcher of the transfer element loop in FIG. It is the figure which expanded the part.

In FIG. 2, reference numeral 1 denotes a magnetic bubble element, which is made of a material that generates magnetic bubbles. More specifically, a magnetic bubble is generated in a cylindrical shape in a perpendicular magnetic film epitaxially grown by several μm on GGG (gadolinium-gallium-garnet) by applying a perpendicular magnetic field of an appropriate strength. The magnetic bubble element 1 includes:
Magnetic bubble detection elements 12, 13 and aluminum wiring patterns 14, 15, 16 are formed (see FIG. 4). Each of the magnetic bubble detection elements 12 and 13 is constituted by a magnetoresistive element (for example, permalloy). Further, the magnetic bubble element 1 includes
The transfer element 11 made of a thin-film permalloy is formed in a loop shape, and the magnetic bubbles are transferred along the loop (see FIGS. 3 and 4). FIG. 3 shows one transfer element loop, but a plurality of transfer element loops are provided on the actual magnetic bubble element 1. Magnetic bubbles are written on each transfer element loop in a bit pattern based on the “memory wheel principle” as known in the preceding example 2. Note that the plane on which the magnetic bubble element 1 is arranged is referred to as x for convenience.
-Called y surface.

Reference numeral 2 denotes a pair of bias magnets (see FIG. 2).
), And has a function of applying a constant vertical magnetic field (bias magnetic field) to the magnetic bubble element 1 to maintain a bubble-like magnetic domain.

[0006] Reference numerals 3 and 4 denote read coils, which are arranged around the magnetic bubble element 1 as shown in FIG. The read coils 3 and 4 are used when reading the number of rotations of the ring magnet 5, and generate a rotating magnetic field by passing an alternating current through the coils to transfer the magnetic bubbles 17, 18 and 19.
The read coils 3 and 4 are described in detail in Prior Examples 1 and 2.

Reference numeral 5 denotes a ring magnet, which is a permanent magnet attached to a rotating shaft (not shown). The ring magnet 5 applies a parallel in-plane magnetic field to the magnetic bubble element 1, and the in-plane magnetic field is rotated by the rotation of the rotating shaft. The magnetic bubble circulates around the transfer element loop with one step / one rotating magnetic field. FIG. 2 shows an example of a ring magnet magnetized with eight poles. In this case, when the rotating shaft makes one rotation, the magnetic bubbles move four transfer elements 11.

In each transfer element loop shown in FIG. 3, magnetic bubbles having a special arrangement pattern based on the “principle of the memory wheel” described in the preceding example 2 are written. The special arrangement pattern is a pattern having a feature that a continuous bit pattern cut out from a certain position in all bit patterns is not the same as a pattern having the same number of bits cut out from any other position. Therefore, by reading out a pattern of several consecutive bits from a certain position of the transfer element loop, the transfer shift amount of the bit pattern in the loop can be known.

The magnetic bubble is detected by the magnetic bubble detector 10 arranged at the certain position. The magnetic bubble detector 10 includes magnetic bubble detection elements 12 and 13 shown in FIG. A constant current is passed through the magnetic bubble detecting elements 12 and 13 via aluminum wiring patterns 14, 15 and 16 in advance (the aluminum wiring pattern 16 is at ground potential). When the magnetic bubbles 17, 18, 19 move to the magnetic bubble detecting elements 12, 13, the resistance value changes, so that the potential of the aluminum wiring patterns 14, 15 changes. The differential signal of the potential signals of the two aluminum wiring patterns 14 and 15 is calculated by a differential amplifier (not shown) to obtain a magnetic bubble detection signal.

In the magnetic bubble element 1 as described above,
On the transfer element loop, for example, a bit pattern (01110100) of 8 bits per loop determined by the “principle of the memory wheel” is formed depending on the presence or absence of a magnetic bubble. In the embodiment shown in FIG. 3, the number of bits is more (for example, around 49 bits), but here, 8 bits will be described to make the invention easier to understand. When the ring magnet 5 rotates, the 8-digit bit pattern circulates on the transfer element loop according to the rotation. The circulating operation is normally performed even if the device in FIG. 2 stops its operation in an electric circuit due to a power failure or the like. For example, if the ring magnet 5 rotates ten times while the operation of the rotation speed detector shown in FIG.
The 8-bit magnetic bubble has moved to a position corresponding to zero rotation. When the power is restored, the read coils 3 and 4 are operated to generate a rotating magnetic field to measure how many rotations of the ring magnet 5, and the position of the magnetic bubble is sequentially moved by, for example, three transfer elements. (See Prior Example 2). Accordingly, three time-series bit patterns are read from the magnetic bubble detector 10, and the cumulative number of rotations of the ring magnet 5 can be known from the patterns based on the principle of the memory wheel. After detection, the read coils 3 and 4 apply a rotating magnetic field in the opposite direction to the magnetic bubble element 1 to move the magnetic bubbles by three transfer elements and return to the original position.

FIG. 5 is a conceptual block diagram of a specific example of FIG.
2 are given the same reference numerals. That is, the ring magnet 5 is attached to the end of the shaft 20 of the object to be measured. A disk-shaped base 21 is rotatably mounted on a portion of the shaft 20 via a bearing such as a bearing. The base 21 has a U-shaped magnetic bubble unit 22 having a magnetic bubble element 1 and a pair of bias magnets 2 incorporated therein so as to sandwich the magnetic bubble element 1 on the inner surface. It is mounted so as to face the magnet 5.

In such a configuration, the bias magnet 2
To apply an optimal bias magnetic field to the magnetic bubble element 1,
Always generate stable magnetic bubbles. On the other hand, the ring magnet 5 applies an optimal rotating magnetic field according to the rotation of the shaft 20 to the magnetic bubble element 1, and moves the magnetic bubble stably by the rotating magnetic field. By detecting the movement of the magnetic bubble, the cumulative rotation speed of the shaft 20 can be measured.

At this time, if the external magnetic field changes, the bias magnetic field and the rotating magnetic field applied to the magnetic bubble element 1 change, causing a problem that stable movement of the magnetic bubble is hindered.

Therefore, conventionally, a double magnetic shield structure comprising a cylindrical outer magnetic shield case 23 and an inner magnetic shield case 24 as shown in FIG. 6 has been adopted.

Here, the external magnetic shield case 23 also has a function of an external case that covers the outside of the rotational speed detector, and soft iron (SUY) is used as a material. Due to the external magnetic shield case 23, the external magnetic field fluctuation value 200
A magnetic shielding effect that reduces the leakage magnetic field to about 5 Gauss with respect to Gauss can be obtained.

On the other hand, the inner magnetic shield case 24 has a shape slightly smaller than the outer magnetic shield case 23, and is required to have a function of reducing the leakage magnetic field of the outer magnetic shield to about 2 gauss. For example, Permalloy is used because it is necessary.

[0017]

However, such a double magnetic shield structure has a problem that the structure is complicated.

Further, since a very expensive material, Permalloy, must be used in a considerably large amount, there is a problem that the cost of the rotational speed detector is increased. SUMMARY OF THE INVENTION An object of the present invention is to provide a rotation speed detector having a magnetic shield structure capable of obtaining a sufficient magnetic shield effect with a simple structure and capable of performing stable rotation speed detection.

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a shaft connected to an object to be measured, a ring magnet attached to an end of the shaft, and an intermediate portion of the shaft. A disk-shaped base rotatably mounted, a U-shaped magnetic bubble element, and a pair of bias magnets incorporated therein so as to sandwich the magnetic bubble element on the inner surface, and the U-shaped opening is formed by the ring magnet. A magnetic bubble unit attached to the base so as to oppose, an external magnetic shield case formed in a cylindrical shape so as to include these ring magnets and the magnetic bubble unit and attached to the base, and a high magnetic permeability material. A local magnetic shield formed in a U-shape and attached so as to cover an outer surface of the magnetic bubble unit. That.

[0020]

The local magnetic shield locally shields the magnetic bubble unit in the direction of the bias magnetic field.

Thus, the influence of an external magnetic field change on the magnetic bubble element can be greatly reduced by the external magnetic shield case and the local magnetic shield, and an optimum bias magnetic field is always applied to the magnetic bubble element by the bias magnet. In addition to generating a stable magnetic bubble, the ring magnet can stably move the magnetic bubble by applying an optimum rotating magnetic field to the magnetic bubble element according to the rotation of the shaft.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, and portions common to FIG. 5 are denoted by the same reference numerals. FIG. 1 is different from FIG. 5 in that an external magnetic shield case 25 formed in a cylindrical shape so as to include the ring magnet 5 and the magnetic bubble unit 22 is attached to the base 21, and the outer surface of the magnetic bubble unit 22. A local magnetic shield 26 formed in a U-shape from a material having high magnetic permeability is attached so as to cover the magnetic shield 26.

The external magnetic shield case 25 also has a function of an external case that covers the outside of the rotation speed detector, similarly to the external magnetic shield case 23 of FIG. 6, and is made of a material having a thickness of, for example, 1.5 mm. Soft iron (SUY) is used. The external magnetic shield case 25 achieves a magnetic shield effect of reducing a leakage magnetic field to about 4 gauss with respect to an external magnetic field fluctuation value of 200 gauss.

On the other hand, the local magnetic shield 26 is required to have a function of reducing the leakage magnetic field of the external magnetic shield to about 2 gauss. Since a high magnetic permeability material is required, for example, a permalloy plate having a thickness of 1 mm is used. Used.

In such a configuration, the local magnetic shield 26 locally magnetically shields the magnetic bubble unit 22 in the direction of the bias magnetic field. The bias magnetic field is set to an optimum value for the magnetic bubble element 1 by the two bias magnets 2 as described above.

Therefore, only a part around the bias magnetic field is internally shielded, so that the magnetic bubble
Can be reduced to a sufficiently small value, and the magnetic bubbles can be moved stably.

[0027]

As described above, according to the present invention, the following effects can be obtained. With the simple configuration of attaching a U-shaped local shield member to the magnetic bubble unit, the magnetic bubble element can always receive a constant magnetic field even if the external magnetic field of the magnetic bubble unit changes, and stable rotation speed detection is possible. realizable.

Further, the magnetic shield member can be reduced in size, simplified, and reduced in cost.

[Brief description of the drawings]

FIG. 1 is a structural example of a main part of a rotational speed detector according to the present invention.

FIG. 2 is an operation principle diagram of a rotation speed detector using magnetic bubbles.

FIG. 3 is a pattern example diagram of a transfer element loop provided on the magnetic bubble element of FIG. 2;

FIG. 4 is an enlarged view of a stretcher section of the transfer element loop of FIG. 3;

FIG. 5 is a conceptual configuration diagram of a specific example of FIG. 2;

FIG. 6 is a diagram illustrating a configuration example of a magnetic shield in a conventional rotation speed detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic bubble element 2 Bias magnet 5 Ring magnet 20 Shaft 21 Base 22 Magnetic bubble unit 25 External magnetic shield case 26 Local magnetic shield

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-212016 (JP, A) JP-A-3-125973 (JP, A) JP-A-3-70319 (JP, A) 115396 (JP, U) Japanese Utility Model 3-29593 (JP, U) Japanese Utility Model 3-27376 (JP, U) Japanese Utility Model 2-128596 (JP, U) Japanese Utility Model 5-55020 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) G01D 5/245

Claims (1)

(57) [Claims] 1. A shaft connected to an object to be measured, a ring magnet attached to an end of the shaft, a disk-shaped base rotatably attached to an intermediate portion of the shaft, and a U-shape. A magnetic bubble element, and a pair of bias magnets built therein so as to sandwich the magnetic bubble element, and a magnetic bubble unit attached to the base such that a U-shaped opening faces the ring magnet; A local magnetic shield formed in a U-shape from a high magnetic permeability material and attached so as to cover an outer surface of the magnetic bubble unit; and a cylindrical shape formed so as to include these ring magnets and the magnetic bubble unit and attached to the base. An external magnetic shield case, and a rotational speed detector.