JPH11308846A - Linear motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of a motor by increasing the space factor of a coil and reducing a current applied to the motor, in a linear motor. SOLUTION: This linear motor is composed of a coil 1, where a ring shape is formed by a plurality of number of windings in the circumferencial direction, and divided outer yokes 2a, 2b, 2c, 2d provided with insertion trenches 3a, 3a into which the coil 1 can be inserted on the inner peripheral side. An outer yoke 2 is installed which is formed into a cylindrical shape by combining a plurality of the divided outer yokes 2a, 2b, 2c, 2d, while the coil 1 is inserted in the insertion trenches 3a, 3a. Thereby an applied current to the motor can be reduced, and efficiency of the motor can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear motor, and more particularly to an improvement in motor efficiency.

[0002]

2. Description of the Related Art In recent years, SUNPOWER has developed a movable magnet type linear motor for a compressor used in a general environment (Nicholas R. van de).
r Walt, Reuven Unger: Linea
r compressors-amaturing t
technology, International A
appliance Technical Confer
ence, pp1-6, 1994).

FIG. 11 is a schematic view of a conventional linear motor. The linear motor 100 includes a cylindrical inner yoke 10.
1, an outer yoke 104 having two magnetic poles 102 and 103, and a coil 106 wound around a central axis 105.
And a mover 108 having a cylindrical permanent magnet 107.

When an alternating current is supplied to the coil 106, different magnetic poles are alternately formed in the magnetic poles 102 and 103 in the axial direction, and the movable element 108 is magnetically attracted to and repelled from the permanent magnet 107 by the coil. A thrust proportional to the magnitude of the current 106 and the magnetic flux density of the permanent magnet 107 is generated, and the mover 108 reciprocates.

[0005]

However, in the above-mentioned conventional configuration, the coil 104 is wound a plurality of times while pressing the inner yoke 104 from the inner peripheral side to the outer peripheral side, that is, from the outer peripheral side of the cylindrical shape. Since the coil 104 is sequentially wound around the inner periphery (outer winding), the coil 104 cannot be wound with tension.

Therefore, the coil 104 cannot be wound tightly, and the coil 104 is moved from the inner peripheral side to the outer peripheral side of the cylindrical shape.
The number of turns of the coil 104 is smaller and the space factor is lower as compared with a general winding method (inner winding) in which a coil is wound while applying tension.

As a result, in order to obtain the same motor thrust, it is necessary to supply more current for the smaller number of turns, and in that case, copper loss proportional to the square of the current value increases, and the motor efficiency may deteriorate. There was sex. Conversely, when the same current is applied, the number of turns is small, and there is a possibility that the thrust of the motor decreases.

The present invention solves the conventional problem. The present invention solves the problem by combining a coil 104 wound tightly with a high space factor by applying a tension while a plurality of divided outer yokes are sandwiched from the outer peripheral side. Thus, the applied current to the motor is reduced to improve the motor efficiency.

Further, in the above-mentioned conventional construction, since the yoke member is formed of an iron-based block material, the thickness is large, and the eddy current loss is proportional to the square of the thickness of the yoke member. Therefore, the eddy current loss becomes very large, and the motor efficiency may be reduced.

When a plurality of yoke members are combined using a metal having high magnetic permeability such as iron and integrated as a yoke, magnetic flux leakage occurs between the yoke members and iron loss increases. May decrease,
Further, there is a possibility that manufacturing and assembly for integrating the yoke member as a yoke may be difficult.

The present invention solves the conventional problems.
By using the first yoke member in which a number of thin plates having high magnetic permeability are stacked in a substantially circumferential direction, eddy current loss is reduced,
Improve motor efficiency.

The first and second yoke members are integrally formed by impregnating the second yoke member and the third yoke member, which are made of a material having a low magnetic permeability and a high resistance, into contact with both sides of the first yoke member. It is possible to combine the plurality of divided yokes into a cylindrical shape by joining the joining portions provided on the second and third yoke members. Therefore, by preventing the leakage of the magnetic flux between the yoke members and reducing the iron loss, the efficiency of the motor is improved, and the manufacture and assembly of the yoke become very easy.

Further, when a plurality of yoke members are combined by using other members and integrated as a yoke, if the gap between the yoke members is filled with other members, heat dissipation and cooling of the yoke members are insufficient, There was a possibility that the motor temperature would increase and the reliability would decrease.

Another object of the present invention is to secure a gap between the yoke members so that the yoke, that is, the linear motor is constantly cooled by a refrigerant or the like to reduce a temperature rise, thereby improving reliability.

[0015]

In order to achieve the above object, a linear motor according to the present invention comprises a coil formed into a ring shape by being wound a plurality of times in a circumferential direction, and an insertion groove in which the coil can be inserted on an inner peripheral side. And a cylindrical outer yoke formed by combining a plurality of divided outer yokes while inserting a coil into the insertion groove.

[0016] With this arrangement, a plurality of split outer yokes are sandwiched from the outer peripheral side while being coiled with a high space factor by winding while applying tension, thereby reducing the applied current of the motor and improving the motor efficiency. Plan.

A plurality of thin plates having a high magnetic permeability are stacked in a substantially circumferential direction to form a substantially rectangular prism. On both sides of the first yoke member, a substantially triangular prism formed of a material having a low magnetic permeability and a high resistance is provided. A plurality of divided yokes integrated by impregnating the resin with the second yoke member and the third yoke member in contact with each other, and joining the second yoke member and the joint provided on the third yoke member to form a divided yoke; And an outer yoke or an innerk formed by combining the two in a cylindrical shape.

Thus, since the first yoke member in which a number of thin plates having high magnetic permeability are stacked substantially in the circumferential direction is used, the eddy current loss is reduced, and the motor efficiency is improved. Further, by preventing magnetic flux leakage between the yoke members and reducing iron loss, motor efficiency is improved, and manufacture and assembly of the yoke become very easy.

Also, a plurality of thin plates having high magnetic permeability are stacked in a substantially circumferential direction to form a substantially quadrangular prism-shaped fourth yoke member, and the plurality of fourth yoke members form a substantially cylindrical shape while securing a gap. And a fixing band disposed on the outer peripheral portion of the fourth yoke member. The fixing band connects the fitting members to be fitted to the fourth yoke member, and connects the fitting members to each other. And a connection band formed of a material having high resistance.

Thus, by securing a gap between the yoke members, the yoke, that is, the linear motor is constantly cooled by the refrigerant or the like, so that the temperature rise is reduced, and the reliability is improved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a divided coil having a ring shape formed by being wound a plurality of times in the circumferential direction, and an insertion groove on the inner peripheral side for inserting the coil. It is composed of an outer yoke and an outer yoke formed into a cylindrical shape by combining a plurality of divided outer yokes while inserting a coil into the insertion groove.The space factor is increased by winding while applying tension. Combining tightly wound coils while sandwiching a plurality of split outer yokes from the outer periphery has the effect of reducing the applied current to the motor and improving motor efficiency.

According to a second aspect of the present invention, thin plates having a high magnetic permeability are stacked in a substantially circumferential direction and formed on both sides of a first yoke member having a substantially quadrangular prism shape with a material having a low magnetic permeability and a high resistance. A plurality of divided yokes which are integrated by impregnating the second yoke member and the third yoke member having a substantially triangular prism shape in contact with each other.
An outer yoke formed by combining the divided yokes into a cylindrical shape by joining the joining portions provided on the yoke member,
Or, it is composed of an inner ring, which reduces eddy current loss and improves motor efficiency, and also prevents leakage of magnetic flux between yoke members to reduce iron loss, thereby improving motor efficiency. In addition, there is an effect that the manufacture and assembly of the yoke become very easy.

According to a third aspect of the present invention, a plurality of thin plates having a high magnetic permeability are stacked in a substantially circumferential direction to form a substantially quadrangular prism-shaped fourth yoke member, and the plurality of fourth yoke members secure a gap. A fixing band disposed on an outer peripheral portion of the fourth yoke member so as to form a substantially cylindrical shape; the fixing band connects a fitting member fitted with the fourth yoke member and the fitting members; And a connecting band formed of a material that is bendable, has low magnetic permeability, and has a high resistance.
That is, it has the effect of cooling the linear motor to reduce the temperature rise and improving reliability.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a top view of an outer yoke according to Embodiment 1 of the present invention, and FIG. 2 is a sectional view taken along line AA in FIG. FIG. 3 is an external view of a coil constituting the linear motor, and FIG. 4 is an external view of a divided outer yoke constituting the linear motor.

In FIGS. 1, 2, 3, and 4, reference numeral 1 denotes a coil, which has a ring shape. An outer yoke 2 has a cylindrical shape formed by combining the divided outer yokes 2a, 2b, 2c and 2d. 3a,
Reference numeral 3b denotes a coil insertion groove provided on the inner peripheral side of each of the divided yokes 2a and 2b.

First, a method of manufacturing the coil 1 will be described. The coil 1 is wound around a jig or the like while applying tension, and a ring shape is formed while repeating stacking. At this time, since the coil 1 is constantly being tensioned, the coil 1 is wound with a small space as much as possible. In other words, since the coil 1 is wound while filling the gap, the coil 1 is wound with a high space factor.
When the winding is completed and the coil 1 is removed from the jig or the like, an integrated product in which the coil 1 is densely wound is completed. At this time, the coil 1 may be impregnated with a resin or the like for the purpose of preventing the coil 1 from being deformed or protecting the coil 1.

Therefore, since the coil 1 is wound while being tensioned, the coil 1 has a higher space factor than the case where the coil 1 is wound outwardly from the outer peripheral portion to the inner peripheral portion without tension, and is wound in the same volume. , Many turns.

Therefore, to obtain the same motor thrust,
Since the current value applied to the motor can be small, the copper loss proportional to the square of the current value can be reduced, and the motor efficiency is improved.

Next, a method of manufacturing an outer yoke incorporating the coil 1 will be described. Coil 1 and 4 described above
It is produced using the divided outer yokes 2a, 2b, 2c, 2d. Four divided outer yokes 2a, 2b, 2
Insert grooves 3a, 3b, 3c, and 3d that match the shape of the coil 1 are provided on the inner peripheral sides of c and 2d, respectively.

In assembling, while the coil 1 is inserted into the insertion grooves 3a, 3b, 3c and 3d, a cylindrical shape is formed by the four divided outer yokes 2a, 2b, 2c and 2d. Then, the joining surface 4 of the adjacent divided outer yokes
For a, 4b, 4c, and 4d, some fixing such as welding is performed so as not to separate or shift.

As described above, the linear motor of this embodiment is
Coil 1 formed in a ring shape by winding multiple times in the circumferential direction
And insertion grooves 3a, 3b, 3c, 3 into which the coil 1 can be inserted.
outer yoke 2a, 2b, 2
c, 2d, and the insertion grooves 3a, 3b, 3c, 3
d while the coil 1 is inserted into the outer yoke 2a,
b, 2c, and 2d, the outer yoke 2 is formed in a cylindrical shape by combining a plurality of coils. Therefore, the coil 1 can be wound at a high space factor, so that the applied current of the motor can be reduced and the motor efficiency can be reduced. Improvement can be achieved.

In this embodiment, the outer yoke 2 has four identically shaped divided outer yokes 2a, 2b,
2c and 2d are combined to form a cylindrical shape.
As long as the number is equal to or larger than the number, the embodiment can be similarly performed.

(Embodiment 2) FIG. 5 shows Embodiment 2 of the present invention.
And FIG. 6 is a side view of the outer yoke. FIG. 7 is an external view of a divided yoke constituting the outer yoke.

5, 6, and 7, reference numeral 5 denotes an outer yoke, which is formed by combining twelve divided yokes 6 into a cylindrical shape. The divided yoke 6 includes a first yoke member 8 formed by stacking a large number of thin plates 7 having a high magnetic permeability in a substantially circumferential direction to form a substantially quadrangular prism, and a substantially triangular prism formed of a material having a low magnetic permeability and a high resistance. The second yoke member 9 and the third yoke member 1 are provided on both sides of the first yoke member 8.
It is integrally molded by impregnating the resin in a state where 0 is in contact therewith. Here, all twelve divided yokes 6 have the same shape and the same dimensions.

The second yoke member 9 and the third yoke member 10 are provided with joints 11 and 12 which are fitted to each other. The joint 11 is concave, and the joint 12 is convex. is there.

Regarding the assembly, in the split yoke 6,
A cylindrical portion is formed by fitting a joint portion 11 (concave portion) of a certain divided yoke 6 and a joint portion 12 (convex portion) of another divided yoke 6 from the axial direction, and repeating this process for all twelve divided yokes 6. If the outer yoke 5 is formed and processed by the divided yoke 6, post-processing is unnecessary.

Therefore, the outer yoke 5 can be formed only by producing the divided yokes 6 having the same shape and the same dimensions, and by simply combining them, so that the manufacture and assembly are extremely easy. Further, also in the production of the divided yoke 6, since the first yoke member 8, the second yoke member 9 and the third yoke member 10 are integrally molded by resin impregnation, the production is extremely easy.

In the linear motor configured as described above, the eddy current loss has a characteristic proportional to the square of the plate thickness of the yoke member. Since a large number of such members are stacked, eddy current loss is extremely reduced, and motor efficiency can be improved.

Further, since the second yoke member 9 and the third yoke member 10 made of a material having low magnetic permeability and high resistance such as resin are combined on both sides of the first yoke member 8, the divided yoke 6 is formed. Using a cylindrical outer yoke 5
Is assembled, the second yoke member 9 and the third yoke member 10 are interposed between the adjacent first yoke members 8.

Therefore, the first yoke member 8 separates the first
Since the magnetic flux can be prevented from leaking to the yoke member 8,
Iron loss can be reduced and motor efficiency can be improved.

As described above, the linear motor of this embodiment is
A substantially triangular prism-shaped second yoke member formed of a material having a low magnetic permeability and a high resistance is provided on both sides of a first yoke member 8 having a substantially rectangular prism shape formed by stacking a plurality of thin plates 7 having a high magnetic permeability in a substantially circumferential direction. A plurality of divided yokes 6 are integrated by impregnating the resin with the third yoke member 9 and the third yoke member 10 in contact with each other, and the joining portions 11 and 12 provided on the second yoke member 9 and third yoke member 10 are joined. Thus, since the outer yoke 5 is formed by combining the divided yokes 6 in a cylindrical shape, the eddy current loss is extremely reduced, and the motor efficiency can be improved.

Further, since the magnetic flux can be prevented from leaking from the first yoke member 8 through which the magnetic flux flows to the other first yoke members 8, iron loss can be reduced and motor efficiency can be improved.

Further, the production of the split yoke 6 is extremely easy because the first yoke member 8, the second yoke member 9 and the third yoke member 10 are integrally molded by impregnation with a resin. As for the assembly, the cylindrical outer yoke 5 can be formed by simply fitting the joints 11 and 12 of the divided yoke 6 which are the same parts, and no post-processing is required. Therefore, the manufacture and assembly of the outer yoke 5 become extremely easy, and the cost can be reduced.

In this embodiment, the outer yoke 5 has been described. However, the present invention can be similarly applied to the inner yoke 13 disposed inside the outer yoke 5. Further, in the present embodiment, the outer yoke 5 is formed into a cylindrical shape by combining twelve identical divided yokes 6, but the outer yoke 5 can be similarly implemented as long as it is plural.

Further, in this embodiment, no coil is mounted on the outer yoke 5, but the present invention can be similarly applied to an outer yoke on which a coil is mounted. In this embodiment, the joints 11 and 12 of the divided yoke 6 have concave and convex shapes. However, other shapes may be used as long as they fit.

(Embodiment 3) FIG. 8 shows Embodiment 3 of the present invention.
FIG. 9 is an external view of a fourth yoke member constituting the outer yoke. FIG. 10 is an external view of a fixed band constituting the outer yoke.

In FIGS. 8, 9, and 10, reference numeral 14 denotes an outer yoke, and twelve fourth yoke members 15 and twelve fourth yoke members 15 form a substantially cylindrical shape while securing a gap. And a fixing band 16 disposed on the outer peripheral portion of the fourth yoke member 15.

The fourth yoke member 15 has a substantially quadrangular prism shape formed by stacking a large number of thin plates 17 having high magnetic permeability in a substantially circumferential direction. The fixing band 16 connects the fitting member 18 fitted to the fourth yoke member 15 and the plurality of fitting members 18 and is formed of a material that can be bent and has low magnetic permeability and high resistance, such as resin. And a belt 19.

In the linear motor configured as described above, the eddy current loss has a characteristic proportional to the square of the plate thickness of the yoke member, but the fourth yoke member 15 is made of a thin plate 17 having a high magnetic permeability. Since a large number of such members are stacked, eddy current loss is extremely reduced, and motor efficiency can be improved.

The twelve fourth yoke members 15 are formed in a cylindrical shape by the fixing band 16. The connecting band 19, which is a component of the fixing band 16, is made of a material having a low magnetic permeability and a high resistance. So that the adjacent fourth yoke member 1
At 5, no magnetic flux leaks through the fixed band 16. Therefore, iron loss can be reduced and motor efficiency can be improved.

Further, since the gap 20 can be secured between the adjacent fourth yoke members 15, the surface area of the motor increases, the cooling of the motor is promoted, the temperature rise can be reduced, and the reliability of the motor is improved. improves.

Further, with regard to the production, the outer yoke 14 can be constituted only by forming the same fourth yoke member 15 in a cylindrical shape with the fixing band 16, and post-processing is not required. Therefore, the manufacture and assembly of the outer yoke 14 become extremely easy, and the cost can be reduced.

As described above, the linear motor of this embodiment is
A plurality of thin plates 17 having high magnetic permeability are stacked in a substantially circumferential direction to form a substantially quadrangular prism-shaped fourth yoke member 15, and a plurality of fourth yoke members 15 are formed so as to form a substantially cylindrical shape while securing a gap. Fixed band 1 arranged on the outer periphery of four yoke member 15
6, the fixing band 16 is connected to a fitting member 18 to be fitted to the fourth yoke member 15 and to the fitting members 18 and formed of a material that is bendable, has low magnetic permeability and high resistance. Outer yoke 14 composed of band 19
The fourth yoke member 15 adjacent to the fourth yoke member 15.
Since the gap 20 can be secured between them, the surface area of the motor increases, cooling of the motor is promoted, the temperature rise can be reduced, and the reliability of the motor improves.

Further, since the fourth yoke member 15 is formed by stacking a large number of thin plates 17 having high magnetic permeability, eddy current loss is extremely reduced, and motor efficiency can be improved.

Further, the outer yoke 1 is formed simply by forming the same fourth yoke member 15 into a cylindrical shape with the fixing band 16.
Since the outer yoke 14 can be formed and no post-processing is required, the manufacture and assembly of the outer yoke 14 become extremely easy, and the cost can be reduced.

In this embodiment, the outer yoke 14 has been described. However, the present invention can be similarly applied to the inner yoke 21 provided inside the outer yoke 14.

In this embodiment, the outer yoke 14
Is formed in a cylindrical shape by combining twelve identical fourth yoke members 15, but the same can be implemented with a plurality of fourth yoke members.

In this embodiment, no coil is mounted on the outer yoke 5. However, the present invention can be similarly applied to an outer yoke on which a coil is mounted.

[0059]

As described above, according to the first aspect of the present invention, there is provided a coil having a ring shape formed by winding a plurality of times in the circumferential direction, and a split outer provided with an insertion groove in which the coil can be inserted on the inner peripheral side. Since it is composed of a yoke and an outer yoke formed in a cylindrical shape by combining a plurality of divided outer yokes while inserting a coil in the insertion groove, the coil can be wound at a high space factor, The current applied to the motor can be reduced, and the efficiency of the motor can be improved.

The invention according to claim 2 is characterized in that a large number of thin plates having a high magnetic permeability are stacked in a substantially circumferential direction and a material having a low magnetic permeability and a high resistance is formed on both sides of the first yoke member having a substantially quadrangular prism shape. A plurality of divided yokes are provided by impregnating the resin with the formed substantially triangular prism-shaped second yoke member and third yoke member in contact with each other, and a joint provided on the second yoke member and the third yoke member Since the outer yoke is formed by joining the parts to form a cylindrical combination of the divided yokes, the eddy current loss is extremely reduced, and the motor efficiency can be improved.

Further, since the magnetic flux can be prevented from leaking from the first yoke member through which the magnetic flux flows to the other first yoke members, iron loss can be reduced and motor efficiency can be improved.

Further, the split yoke includes a first yoke member,
Since the second yoke member and the third yoke member are integrally formed by resin impregnation, production is extremely easy. Also, as for assembling, a cylindrical outer yoke can be formed by simply fitting the joints of the divided yokes, which are the same parts, and no post-processing is required. Therefore, the manufacture and assembly of the outer yoke are extremely easy, and the cost can be reduced.

According to a third aspect of the present invention, a plurality of thin plates having high magnetic permeability are stacked in a substantially circumferential direction so as to form a substantially quadrangular prism, and a plurality of fourth yoke members secure a gap. And a fixing band arranged on the outer peripheral portion of the fourth yoke member so as to form a substantially cylindrical shape. The fixing band connects the fitting member fitted to the fourth yoke member and the fitting members. And a connecting band formed of a material that is bendable, has low magnetic permeability, and has a high resistance, and thus has an outer yoke. Therefore, it is possible to secure a gap between adjacent fourth yoke members. Therefore, the surface area of the motor is increased, cooling of the motor is promoted, the temperature rise can be reduced, and the reliability of the motor is improved.

Further, since the fourth yoke member is formed by stacking a large number of thin plates having high magnetic permeability, the eddy current loss is extremely small, and the motor efficiency can be improved.

Further, the outer yoke can be formed simply by forming the same fourth yoke member into a cylindrical shape with the fixing band, and no post-processing is required.
Assembly becomes extremely easy and costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a top view of an outer yoke of a linear motor according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is an external view of the coil of the embodiment.

FIG. 4 is an external view of a divided outer yoke of the embodiment.

FIG. 5 is a top view of an outer yoke according to a second embodiment of the linear motor according to the present invention;

FIG. 6 is a side view of the outer yoke according to the embodiment.

FIG. 7 is an external view of a divided yoke constituting the outer yoke of the embodiment.

FIG. 8 is a top view of an outer yoke according to a third embodiment of the linear motor according to the present invention.

FIG. 9 is an external view of a fourth yoke member constituting the outer yoke of the embodiment.

FIG. 10 is an external view of a fixing band constituting the outer yoke of the embodiment.

FIG. 11 is a schematic view of a conventional linear motor.

[Explanation of symbols]

 Reference Signs List 1 coil 2 outer yokes 2a, 2b, 2c split outer yokes 3a, 3b insertion groove 5 outer yoke 6 split yoke 7 thin plate 8 first yoke member 9 second yoke member 10 third yoke member 11, 12 joint 13 inner yoke 14 Outer yoke 15 Fourth yoke member 16 Fixed band 17 Thin plate 18 Fitting member 19 Connecting band 20 Gap 21 Inner yoke

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Makoto Katayama 4-2-5 Takaida Hondori, Higashiosaka City, Osaka Inside Matsushita Refrigeration Co., Ltd.

Claims (3)

[Claims] 1. A coil formed by winding a plurality of turns in a circumferential direction to form a ring, and a divided outer yoke having an insertion groove on the inner peripheral side into which the coil can be inserted. A linear motor comprising an outer yoke formed into a cylindrical shape by combining a plurality of the divided outer yokes while inserting the outer yoke. 2. A thin steel plate having a high magnetic permeability is stacked in a substantially circumferential direction on both sides of a first yoke member having a substantially quadrangular prism shape.
The second yoke includes a plurality of divided yokes that are integrally formed by impregnating a resin in a state where the second yoke member and the third yoke member having a substantially triangular prism shape and made of a material having a low magnetic permeability and a high resistance are in contact with each other. A linear motor comprising an outer yoke or an innerk formed by joining a member and a joint provided on the third yoke member to form a cylindrical combination of the divided yokes. 3. A fourth yoke member having a substantially quadrangular prism shape formed by stacking a large number of thin plates having high magnetic permeability in a substantially circumferential direction, and a plurality of the fourth yoke members forming a substantially cylindrical shape while securing a gap. And a fixed band disposed on the outer peripheral portion of the fourth yoke member, and the fixed band is capable of connecting the fitting member to the fourth yoke member and connecting the fitting members together and bending the fitting member. And a connecting band formed of a material having a low magnetic permeability and a high resistance.