JP7583281B2 - Eddy Current Damper - Google Patents

Description

This disclosure relates to an eddy current damper.

Vibration control devices are used to protect buildings from vibrations caused by earthquakes and other events. Vibration control devices are attached to the pillars or beams of a building, for example, to suppress the vibration of the building. One type of such vibration control device is the eddy current damper.

Patent Document 1 discloses an eddy current damper including a cylindrical conductive member, a cylindrical magnet holding member, and a number of permanent magnets. In the eddy current damper of Patent Document 1, the magnet holding member is, for example, disposed inside the conductive member. The permanent magnets are held by the magnet holding member and face the conductive member with a gap between them. A ball screw nut is fixed to one axial end of the magnet holding member. The screw shaft of the ball screw passes through the nut and extends into the magnet holding member. The screw shaft and conductive member are each attached to a pillar or beam of a building via an attachment member.

When a building vibrates due to an earthquake or the like and the vibration is input to the eddy current damper of Patent Document 1, the screw shaft of the ball screw moves along its axial direction. As a result, the nut and magnet holding member of the ball screw rotate around the screw shaft. As a result, the permanent magnet held by the magnet holding member rotates relative to the conductive member, generating eddy currents in the conductive member. The interaction between this eddy current and the magnetic field formed by the permanent magnet generates a resistance force (Lorentz force) in the opposite direction to the rotation of the nut and magnet holding member, preventing the rotation of the nut and magnet holding member. As a result, the axial movement of the screw shaft is also prevented, and the vibration of the building is damped.

International Publication No. 2019/044722

As described in Patent Document 1, in an eddy current damper using permanent magnets, multiple permanent magnets face a conductive member with a gap between them. The smaller this gap is, the more easily the magnetic field of the permanent magnets affects the conductive member. Therefore, in order to improve the resistance of the eddy current damper, it is preferable to reduce the gap between the permanent magnets and the conductive member as much as possible. However, reducing the gap between the permanent magnets and the conductive member may cause the permanent magnets to come into contact with the conductive member.

For example, when the nut of a ball screw rotates, it swings radially by the amount of the gap between the ball rolling in the screw groove. In this case, the magnet holding member that holds the permanent magnet also swings radially together with the nut. The more an eddy current damper is used, the more the balls wear and the larger the gap between the balls and the nut becomes, so the more the nut swings when it rotates. This type of nut swing can cause contact between the permanent magnet and the conductive member.

Alternatively, the magnet holding member that holds the permanent magnet may move radially by an amount equal to the gap (backlash) between the components that make up the eddy current damper. Because the magnetic force (attractive force) of the permanent magnet acts between the permanent magnet and the conductive member, the permanent magnet and the magnet holding member tend to approach the conductive member. This can lead to contact between the permanent magnet and the conductive member.

Alternatively, if vibrations from a building are input to the screw shaft of the ball screw at an angle to the axial direction, the components that make up the eddy current damper may deform or move radially. This may cause contact between the permanent magnet and the conductive material.

Thus, the rocking of the nut, the attractive force of the permanent magnet, and the input direction of vibration, or a combination of these, may cause the permanent magnet to come into contact with the conductive member while the eddy current damper is in use. If the gap between the permanent magnet and the conductive member is too small, contact between the permanent magnet and the conductive member is particularly likely to occur. If the permanent magnet comes into contact with the conductive member, there is a risk that the permanent magnet will be damaged. However, from the perspective of improving the resistance of the eddy current damper, it is necessary to reduce the gap between the permanent magnet and the conductive member.

The objective of the present disclosure is to provide an eddy current damper that can prevent contact between a permanent magnet and a conductive member while reducing the gap between the permanent magnet and the conductive member.

The eddy current damper according to the present disclosure includes a conductive member, a magnet holding member, a plurality of permanent magnets, a ball screw, a pair of first bearings, and a pair of second bearings. The conductive member has a cylindrical shape. The magnet holding member is disposed inside the conductive member. The magnet holding member has a cylindrical shape. The magnet holding member is configured to be rotatable around its central axis. The plurality of permanent magnets are arranged along the circumferential direction of the magnet holding member. The plurality of permanent magnets are held by the outer peripheral surface of the magnet holding member. The plurality of permanent magnets face the inner peripheral surface of the conductive member with a gap therebetween. The ball screw includes a nut and a screw shaft. The nut is fixed to one end of the magnet holding member in the axial direction. The screw shaft passes through the nut. The pair of first bearings are provided outside the magnet holding member in the axial direction of the magnet holding member. The pair of first bearings support the magnet holding member in the axial direction. The pair of second bearings are provided on both sides of the permanent magnet, inside the first bearings in the axial direction. The pair of second bearings support the magnet holding member in the radial direction.

The eddy current damper disclosed herein can prevent contact between the permanent magnet and the conductive member while reducing the gap between the permanent magnet and the conductive member.

FIG. 1 is a vertical cross-sectional view of an eddy current damper according to a first embodiment. FIG. 2 is a cross-sectional view of the eddy current damper according to the first embodiment. FIG. 3 is a partially enlarged vertical cross-sectional view of the eddy current damper shown in FIG. FIG. 4 is a vertical cross-sectional view of the eddy current damper according to the second embodiment, showing an enlarged portion of the eddy current damper.

The eddy current damper according to the embodiment includes a conductive member, a magnet holding member, a plurality of permanent magnets, a ball screw, a pair of first bearings, and a pair of second bearings. The conductive member has a cylindrical shape. The magnet holding member is disposed inside the conductive member. The magnet holding member has a cylindrical shape. The magnet holding member is configured to be rotatable around its central axis. The plurality of permanent magnets are arranged along the circumferential direction of the magnet holding member. The plurality of permanent magnets are held by the outer peripheral surface of the magnet holding member. The plurality of permanent magnets face the inner peripheral surface of the conductive member with a gap therebetween. The ball screw includes a nut and a screw shaft. The nut is fixed to one end of the magnet holding member in the axial direction. The screw shaft passes through the nut. The pair of first bearings are provided outside the magnet holding member in the axial direction of the magnet holding member. The pair of first bearings support the magnet holding member in the axial direction. The pair of second bearings are provided on both sides of the permanent magnet, inside the first bearings in the axial direction. A pair of second bearings support the magnet holding member in its radial direction (first configuration).

A conventional eddy current damper is provided with a first bearing that supports the magnet holding member in the axial direction, and a second bearing that supports the magnet holding member in the radial direction. The first bearing supports the axial load, and is therefore positioned outside the magnet holding member in the axial direction. In a conventional eddy current damper, the second bearing is positioned further outside the first bearing in the axial direction. That is, in a conventional eddy current damper, the second bearing is positioned axially away from the permanent magnet held by the magnet holding member.

On the other hand, in the eddy current damper according to the first configuration, the second bearing is provided inside the first bearing in the axial direction of the magnet holding member. That is, in the eddy current damper according to the first configuration, the second bearing is arranged closer to the permanent magnet than in a conventional eddy current damper. As a result, even if the permanent magnet held by the magnet holding member moves toward the conductive member for some reason, the movement of the permanent magnet can be restricted by the second bearing. Therefore, contact between the permanent magnet and the conductive member can be prevented. Furthermore, since there is no contact between the permanent magnet and the conductive member, the gap between the permanent magnet and the conductive member can be reduced. As a result, the resistance of the eddy current damper can be improved.

In the eddy current damper of the first configuration, the second bearing is provided inside the first bearing in the axial direction of the magnet holding member. Therefore, the eddy current damper can be made smaller in the axial direction compared to the conventional case in which the second bearing is provided outside the first bearing in the axial direction.

The second bearing may be made of a magnetic material. In this case, it is preferable that the shortest distance in the axial direction between the second bearing and the permanent magnet is equal to or greater than the distance between adjacent permanent magnets in the circumferential direction among the multiple permanent magnets (second configuration).

If the second bearing is made of a magnetic material and the second bearing and the permanent magnet are too close to each other in the axial direction of the magnet holding member, the magnetic flux from the permanent magnet will flow into the second bearing. If the magnetic flux from the permanent magnet flows into the second bearing and relative motion occurs between the permanent magnet and the second bearing, eddy currents will be generated in the second bearing, which may cause the second bearing to heat up.

In contrast, in the second configuration, the shortest distance in the axial direction between the second bearing and the permanent magnet is ensured to be equal to or greater than the distance between adjacent permanent magnets in the circumferential direction of the magnet holding member. This allows the magnetic flux from each permanent magnet to preferentially reach the adjacent permanent magnet and is less likely to wrap around the second bearing. Therefore, even if the second bearing is made of a magnetic material, the generation of eddy currents in the second bearing and the associated heat generation in the second bearing can be suppressed.

The second bearing may be made of a non-magnetic material (third configuration).

In the third configuration, the second bearing is made of a non-magnetic material. In this case, there is essentially no intrusion of magnetic flux from the permanent magnet to the second bearing, and the problem of heat generation in the second bearing does not occur. Therefore, the second bearing can be positioned close to the permanent magnet in the axial direction of the magnet holding member. As a result, it becomes easier for the second bearing to restrict the movement of the permanent magnet, and contact between the permanent magnet and the conductive member can be more effectively prevented.

One of the pair of second bearings may be arranged in the axial direction between the fixed portion of the nut relative to one end of the magnet holding member and the permanent magnet (fourth configuration). Alternatively, the fixed portion of the nut relative to one end of the magnet holding member may be arranged in the axial direction between one of the pair of second bearings and the permanent magnet (fifth configuration).

Embodiments of the present disclosure will be described below with reference to the drawings. In each drawing, the same or equivalent components are given the same reference numerals, and the same description will not be repeated.

First Embodiment
[Overall configuration of eddy current damper]
1 is a vertical cross-sectional view showing a schematic configuration of an eddy current damper 10 according to a first embodiment. The eddy current damper 10 is attached to a pillar or beam of a building by mounting members 20a, 20b, for example, to suppress vibrations of the building.

Referring to FIG. 1, the eddy current damper 10 includes a conductive member 1, a magnet holding member 2, a plurality of permanent magnets 3, a pair of first bearings 41, 42, a pair of second bearings 51, 52, and a ball screw 6.

(Conductive member)
The conductive member 1 has a tubular shape with its central axis coincident with the dashed dotted line X shown in Fig. 1. The conductive member 1 has, for example, a substantially cylindrical shape. Hereinafter, with regard to the eddy current damper 10 and its components, the direction in which the central axis X of the conductive member 1 extends will be referred to as the axial direction, and the radial direction of the circle or cylinder around the central axis X will be simply referred to as the radial direction.

The conductive member 1 is supported at both axial ends by support members 71 and 72. Each of the support members 71 and 72 has a cylindrical shape. In this embodiment, the portions of the support members 71 and 72 on the conductive member 1 side are formed in a conical cylindrical shape, and the other portions are formed in a cylindrical shape. The support members 71 and 72 are each disposed substantially coaxially with the conductive member 1. One support member 71 is connected to one axial end of the conductive member 1. The other support member 72 is connected to the other axial end of the conductive member 1. The support member 72 is attached to a pillar or beam of a building via the attachment member 20b. This fixes the conductive member 1 to the building.

In the example of FIG. 1, the support members 71 and 72 are separate from the conductive member 1. In this case, the support members 71 and 72 can be connected to the conductive member 1 using, for example, a bolt. However, the support members 71 and 72 may also be formed integrally with the conductive member 1.

The conductive member 1 is made of a material having electrical conductivity. The material of the conductive member 1 is, for example, a ferromagnetic material such as carbon steel or cast iron. The material of the conductive member 1 may be a weakly magnetic material such as ferritic stainless steel, or a non-magnetic material such as an aluminum alloy, an austenitic stainless steel, or a copper alloy.

(Magnet holding member)
The magnet holding member 2 has a cylindrical shape. The magnet holding member 2 has, for example, a substantially cylindrical shape. The magnet holding member 2 has a common central axis X with the conductive member 1, and is disposed inside the conductive member 1. In other words, the magnet holding member 2 is disposed substantially coaxially with the conductive member 1 inside the conductive member 1 in the radial direction. The magnet holding member 2 is configured to be rotatable around the central axis X.

The axial ends of the magnet holding member 2 are supported by support members 81 and 82. The support members 81 and 82 are disposed radially inside the support members 71 and 72 of the conductive member 1, respectively.

One of the support members 81 includes, for example, an annular flange portion 811 and a cylindrical portion 812. The flange portion 811 and the cylindrical portion 812 are arranged substantially coaxially with the magnet holding member 2. The flange portion 811 is fixed to one axial end of the magnet holding member 2 via a ball screw 6. The cylindrical portion 812 extends from the flange portion 811 toward the mounting member 20a. The cylindrical portion 812 is inserted into the cylindrical portion of the support member 71 of the conductive member 1.

The other support member 82 includes, for example, an annular flange portion 821 and a tubular portion 822. The flange portion 821 and the tubular portion 822 are arranged substantially coaxially with the magnet holding member 2. The flange portion 821 is connected to the other axial end of the magnet holding member 2. The tubular portion 822 extends from the flange portion 821 toward the mounting member 20b. The tubular portion 822 is inserted into the cylindrical portion of the support member 72 of the conductive member 1.

In the example of FIG. 1, the support member 82 is formed integrally with the magnet holding member 2. However, the support member 82 may be separate from the magnet holding member 2. If the support member 82 is separate from the magnet holding member 2, the support member 82 can be connected to the magnet holding member 2 using, for example, a bolt or the like.

In this embodiment, the magnet holding member 2 is made of a magnetic material. It is preferable that the material of the magnet holding member 2 has high magnetic permeability. Examples of materials with high magnetic permeability include ferromagnetic materials such as carbon steel and cast iron.

(Permanent magnet)
The multiple permanent magnets 3 are held by the outer circumferential surface of the magnet holding member 2. Each of the permanent magnets 3 is fixed to the outer circumferential surface of the magnet holding member 2, for example, by an adhesive. Each of the permanent magnets 3 may also be fixed to the outer circumferential surface of the magnet holding member 2 by a bolt or the like. The permanent magnets 3 face the inner circumferential surface of the conductive member 1 with a gap therebetween.

Figure 2 is a cross-sectional view (horizontal cross-sectional view) of the eddy current damper 10 cut along a plane perpendicular to the central axis X. In Figure 2, only a portion of the conductive member 1, the magnet holding member 2, and the multiple permanent magnets 3 are shown.

Referring to FIG. 2, the permanent magnets 3 are arranged on the outer peripheral surface of the magnet holding member 2 along the circumferential direction of the magnet holding member 2. These permanent magnets 3 are arranged at intervals A around the entire circumference of the magnet holding member 2. The interval A between adjacent permanent magnets 3 in the circumferential direction is the circumferential distance between the permanent magnets 3. If the circumferential distance between the permanent magnets 3 is not constant (if it changes along the radial direction), the interval A is the maximum circumferential distance between the permanent magnets 3.

In this embodiment, the magnetic poles (north and south poles) of the permanent magnets 3 are aligned in the radial direction. The permanent magnets 3 are provided on the magnet holding member 2 such that the magnetic poles of adjacent permanent magnets 3 in the circumferential direction of the magnet holding member 2 are reversed. In other words, if the north pole of a certain permanent magnet 3 is arranged on the radial outside and the south pole on the radial inside, the permanent magnets 3 on either side of this permanent magnet 3 have their south poles arranged on the radial outside and their north poles arranged on the radial inside.

(Bearings)
1 , the pair of first bearings 41, 42 are bearings for supporting the axial load of the magnet holding member 2 rotating around the central axis X. The first bearings 41, 42 are configured to support the magnet holding member 2 in the axial direction.

The first bearings 41, 42 are provided on the outside of the magnet holding member 2 in the axial direction. The first bearings 41, 42 are arranged to sandwich the magnet holding member 2 and support both axial ends of the magnet holding member 2. In the example of this embodiment, the first bearings 41, 42 are arranged between the support members 71, 72 of the conductive member 1 and the support members 81, 82 of the magnet holding member 2, and indirectly support both axial ends of the magnet holding member 2. One of the first bearings 41 is arranged between the cylindrical portion of the support member 71 and the flange portion 811 of the support member 81 in the axial direction. The other first bearing 42 is arranged between the cylindrical portion of the support member 72 and the flange portion 821 of the support member 82 in the axial direction.

The pair of second bearings 51, 52 are bearings for supporting the radial load of the magnet holding member 2 rotating around the central axis X. The second bearings 51, 52 are configured to support the magnet holding member 2 in the radial direction.

The second bearings 51, 52 are provided on both sides of the permanent magnet 3, axially inside the first bearings 41, 42. That is, one second bearing 51 is arranged between one first bearing 41 and the permanent magnet 3 in the axial direction, and the other second bearing 52 is arranged between the other first bearing 42 and the permanent magnet 3 in the axial direction. In this embodiment, the second bearings 51, 52 are arranged on the outer circumferential surface of the magnet holding member 2 so as to sandwich the row of permanent magnets 3 arranged in the circumferential direction. The second bearings 51, 52 directly support the outer circumferential surface of the magnet holding member 2.

As the first bearings 41, 42 and the second bearings 51, 52, known bearings can be appropriately selected and used. The first bearings 41, 42 may be rolling bearings such as ball bearings and roller bearings, or may be plain bearings. Similarly, the second bearings 51, 52 may be rolling bearings such as ball bearings and roller bearings, or may be plain bearings. When rolling bearings are used as the second bearings 51, 52, the second bearings 51, 52 may be, for example, needle roller bearings.

(Ball screw)
The ball screw 6 includes a nut 61 and a screw shaft 62 .

The nut 61 includes an annular flange portion 611 and a cylindrical portion 612. The flange portion 611 and the cylindrical portion 612 are arranged substantially coaxially with the magnet holding member 2. The flange portion 611 is arranged between the magnet holding member 2 and the support member 81. More specifically, the flange portion 611 is arranged between one axial end of the magnet holding member 2 and the flange portion 811 of the support member 81. The cylindrical portion 612 extends from the flange portion 611 into the magnet holding member 2.

The nut 61 is fixed to the magnet holding member 2. More specifically, the nut 61 is fixed to one axial end of the magnet holding member 2 by a flange portion 611. The nut 61 is also fixed to the support member 81 of the magnet holding member 2. More specifically, the nut 61 is fixed to the flange portion 811 of the support member 81 by the flange portion 611. The nut 61 is fixed to the magnet holding member 2 and the support member 81 by, for example, a bolt or the like.

The screw shaft 62 passes through the nut 61. The screw shaft 62 is movable in the axial direction relative to the nut 61, and is configured to rotate the nut 61 around the screw shaft 62 (central axis X) as the screw shaft 62 moves in the axial direction. As the nut 61 rotates, the magnet holding member 2 rotates around the central axis X.

Balls are interposed between the outer peripheral surface of the screw shaft 62 and the inner peripheral surface of the nut 61. When the screw shaft 62 moves in the axial direction, the balls roll along the thread grooves provided on the outer peripheral surface of the screw shaft 62 and the inner peripheral surface of the nut 61. One axial end of the screw shaft 62 is attached to a pillar or beam of a building via an attachment member 20a. In other words, the screw shaft 62 is fixed to the building.

[Detailed configuration of eddy current damper]
3 is a partially enlarged view of the vertical cross section (FIG. 1) of the eddy current damper 10. Hereinafter, the second bearings 51 and 52 in particular will be described in more detail with reference to FIG.

Referring to FIG. 3, of the pair of second bearings 51, 52, one second bearing 51 is disposed near a flange portion 611 of the nut 61. The flange portion 611 is a fixing portion of the nut 61 to one end of the magnet holding member 2. The second bearing 51 is disposed between the flange portion 611 and the permanent magnet 3 in the axial direction. The other second bearing 52 is disposed on the opposite side of the second bearing 51, sandwiching the permanent magnet 3. The second bearings 51, 52 are disposed between the inner peripheral surface of the conductive member 1 and the outer peripheral surface of the magnet holding member 2.

The inner circumferential surface of the conductive member 1 has a step formed between the portion where the second bearings 51, 52 are arranged and the other portion, or a groove formed in the portion where the second bearings 51, 52 are arranged. In other words, the portion of the inner circumferential surface of the conductive member 1 where the second bearings 51, 52 are arranged is positioned radially outward compared to the other portion. In the example shown in FIG. 3, a groove is formed in the inner circumferential surface of the conductive member 1, and a portion of the second bearings 51, 52 is embedded in this groove.

Similarly, the outer peripheral surface of the magnet holding member 2 has a step formed between the portion where the second bearings 51, 52 are arranged and other portions, or a groove formed in the portion where the second bearings 51, 52 are arranged. In other words, the portion of the outer peripheral surface of the magnet holding member 2 where the second bearings 51, 52 are arranged is positioned radially inward compared to the other portions. In the example shown in FIG. 3, a step is formed on the outer peripheral surface of the magnet holding member 2.

The size of the step or groove on the inner circumferential surface of the conductive member 1 and the outer circumferential surface of the magnet holding member 2 is determined according to the dimension (thickness) of the second bearings 51, 52 in the radial direction of the eddy current damper 10. For example, when the second bearings 51, 52 are needle roller bearings, the dimension (thickness) of the second bearings 51, 52 in the radial direction of the eddy current damper 10 is smaller than that of deep groove ball bearings, etc., so the step or groove on the inner circumferential surface of the conductive member 1 and the outer circumferential surface of the magnet holding member 2 can be made shallow. Therefore, the conductive member 1 and the magnet holding member 2 can be made thinner.

The second bearings 51, 52 are arranged in contact with the conductive member 1 and the magnet holding member 2. There is substantially no radial gap between the second bearings 51, 52 and the conductive member 1, and between the second bearings 51, 52 and the magnet holding member 2.

When the second bearings 51, 52 are rolling bearings, the magnet holding member 2 is pressed into the inner ring of the second bearings 51, 52, so there is no radial gap between the second bearings 51, 52 and the magnet holding member 2. Also, the outer ring of the second bearings 51, 52 is fixed to the inner circumferential surface of the conductive member 1, so there is no radial gap between the second bearings 51, 52 and the conductive member 1, or if there is a radial gap, it is very small. When the second bearings 51, 52 are rolling bearings, there are rolling elements between the inner ring and the outer ring, but the rolling elements roll on raceways formed in the inner ring and the outer ring, so the radial gap between the inner ring and the outer ring and the rolling elements is very small.

When the second bearings 51, 52 are sliding bearings having an outer ring and an inner ring, the magnet holding member 2 is pressed into the inner ring of the second bearings 51, 52, so there is no radial gap between the second bearings 51, 52 and the magnet holding member 2. In addition, the outer ring of the second bearings 51, 52 is fixed to the inner peripheral surface of the conductive member 1, so there is no radial gap between the second bearings 51, 52 and the conductive member 1, or if there is, it is very small. Furthermore, since the outer ring and the inner ring are configured to be in contact almost all the time, the radial gap between the outer ring and the inner ring is very small. When the second bearings 51, 52 are sliding bearings consisting of a single annular member, this annular member is attached to one of the conductive member 1 and the magnet holding member 2, and is configured to be in contact with the other of the conductive member 1 and the magnet holding member 2 almost all the time. Therefore, there is no radial gap between the annular member and the conductive member 1 and the magnet holding member 2, or if there is, it is very small.

The second bearings 51, 52 may be made of a magnetic material or may be made of a non-magnetic material. When the second bearings 51, 52 are made of a magnetic material, it is preferable that the intervals B1, B2 between the second bearings 51, 52 and the permanent magnet 3 are equal to or greater than the interval A (FIG. 2) between the permanent magnets 3 adjacent to each other in the circumferential direction. When the second bearings 51, 52 are made of a magnetic material, the intervals B1, B2 between the second bearings 51, 52 and the permanent magnet 3 can be, for example, 5 times or more the gap G between the inner circumferential surface of the conductive member 1 and the permanent magnet 3. When the second bearings 51, 52 are made of a non-magnetic material, the intervals B1, B2 between the second bearings 51, 52 and the permanent magnet 3 may be equal to or greater than the interval A between the permanent magnets 3, or may be less than the interval A. When the second bearings 51, 52 are made of a non-magnetic material, the permanent magnet 3 and the second bearings 51, 52 can be arranged adjacent to each other in the axial direction. The intervals B1 and B2 are the shortest distance in the axial direction between the second bearings 51 and 52 and the permanent magnet 3. The gap G is the shortest distance in the radial direction from the surface of the permanent magnet 3 to the inner surface of the conductive member 1.

[Operation of eddy current damper]
Referring again to FIG. 1, when the building vibrates due to an earthquake or the like and the vibration is input to the eddy current damper 10, the screw shaft 62 of the ball screw 6 moves along the axial direction. Accordingly, the nut 61 of the ball screw 6 rotates around the central axis X. The magnet holding member 2 and the permanent magnet 3 rotate together with the nut 61 around the central axis X. As a result, the permanent magnet 3 rotates relative to the conductive member 1 fixed to the building, and an eddy current is generated in the conductive member 1. The interaction between the eddy current and the magnetic field formed by the permanent magnet 3 generates a resistance force (Lorentz force) in the opposite direction to the rotation direction of the nut 61 and the magnet holding member 2, preventing the rotation of the nut 61 and the magnet holding member 2. As a result, the axial movement of the screw shaft 62 is also prevented, and the vibration of the building is damped.

[effect]
In the eddy current damper 10 according to this embodiment, the second bearings 51, 52 that support the magnet holding member 2 in the radial direction are provided axially inward of the first bearings 41, 42 that support the magnet holding member 2 in the axial direction. This allows the second bearings 51, 52 to be brought closer to the permanent magnet 3 in the axial direction. There is substantially no radial gap between the second bearings 51, 52 and the conductive member 1, and between the second bearings 51, 52 and the magnet holding member 2. Therefore, even if the permanent magnet 3 held by the magnet holding member 2 attempts to move toward the conductive member 1 (toward the radial outside) due to some factor, the movement of the permanent magnet 3 is restricted by the second bearings 51, 52 before the permanent magnet 3 comes into contact with the inner peripheral surface of the conductive member 1. This makes it possible to prevent contact between the permanent magnet 3 and the conductive member 1. In addition, since the second bearings 51, 52 prevent contact between the permanent magnet 3 and the conductive member 1, the gap G between the permanent magnet 3 and the conductive member 1 can be reduced. As a result, the resistance of the eddy current damper 10 can be improved.

The first bearings 41, 42 support the magnet holding member 2 in the axial direction, and are therefore arranged outside the magnet holding member 2 in the axial direction. In a conventional eddy current damper, the second bearings 51, 52 are arranged further outward in the axial direction than the first bearings 41, 42. In contrast, in the eddy current damper 10 according to this embodiment, the second bearings 51, 52 are arranged inside the axial direction than the first bearings 41, 42. Therefore, in addition to preventing contact between the permanent magnet 3 and the conductive member 1 while reducing the gap G between the permanent magnet 3 and the conductive member 1, the eddy current damper 10 can also be made smaller in the axial direction.

The first bearings 41, 42 are disposed between the support members 71, 72 of the conductive member 1 and the support members 81, 82 of the magnet holding member 2. If the second bearings 51, 52 were disposed further outboard in the axial direction than the first bearings 41, 42, each of the support members 71, 72 would need to be constructed from two members. However, in this embodiment, since the second bearings 51, 52 are disposed axially inboard of the first bearings 41, 42, each of the support members 71, 72 can be constructed from a single member. This allows the eddy current damper 10 to be made smaller, and also reduces the number of parts in the eddy current damper 10.

In the eddy current damper 10 according to this embodiment, the second bearings 51 and 52 may be made of a magnetic material. In this case, it is preferable that the intervals B1 and B2 between the second bearings 51 and 52 and the permanent magnet 3 are equal to or greater than the interval A between the permanent magnets 3 adjacent to each other in the circumferential direction. This makes it easier for the magnetic flux from each permanent magnet 3 to reach the adjacent permanent magnet 3 and makes it difficult for it to flow around the second bearings 51 and 52. Therefore, even if the second bearings 51 and 52 are made of a magnetic material, the generation of eddy currents in the second bearings 51 and 52 and the associated heat generation in the second bearings 51 and 52 can be suppressed. From the viewpoint of miniaturization of the eddy current damper 10, the intervals B1 and B2 between the second bearings 51 and 52 and the permanent magnet 3 can be set to, for example, 1.5 times or less the interval A between the permanent magnets 3.

In the eddy current damper 10 according to this embodiment, when the second bearings 51, 52 are made of a magnetic material, the distances B1, B2 between the second bearings 51, 52 and the permanent magnet 3 can be, for example, 5 times or more the gap G between the inner circumferential surface of the conductive member 1 and the permanent magnet 3. In this case, too, it becomes difficult for the magnetic flux from the permanent magnet 3 to flow around the second bearings 51, 52. Therefore, the generation of eddy currents in the second bearings 51, 52 and the associated heat generation in the second bearings 51, 52 can be suppressed.

In the eddy current damper 10 according to this embodiment, the second bearings 51 and 52 may be made of a non-magnetic material. In this case, the magnetic flux from the permanent magnet 3 does not substantially flow around the second bearings 51 and 52, and the problem of heat generation in the second bearings 51 and 52 does not occur. Therefore, the second bearings 51 and 52 can be arranged close to the permanent magnet 3 in the axial direction. The intervals B1 and B2 between the second bearings 51 and 52 and the permanent magnet 3 may be less than the interval A between the permanent magnets 3. By placing the second bearings 51 and 52 close to the permanent magnet 3, the movement of the permanent magnet 3 can be more easily restricted by the second bearings 51 and 52. Therefore, contact between the permanent magnet 3 and the conductive member 1 can be more effectively prevented.

Second Embodiment
Fig. 4 is a vertical cross-sectional view of the eddy current damper 10A according to the second embodiment, and is an enlarged view of a portion of the eddy current damper 10A. As shown in Fig. 4, the eddy current damper 10A according to this embodiment differs from the eddy current damper 10 according to the first embodiment in the positions of the second bearings 51, 52.

In the eddy current damper 10 according to the first embodiment, the second bearings 51, 52 are disposed between the inner peripheral surface of the conductive member 1 and the outer peripheral surface of the magnet holding member 2 (Fig. 3). On the other hand, in the eddy current damper 10A according to the present embodiment, as shown in Fig. 4, the second bearings 51, 52 are disposed between the inner peripheral surface of the conductive member 1 and the outer peripheral surfaces of the support members 81, 82 of the magnet holding member 2. The second bearings 51, 52 are disposed outside the magnet holding member 2 in the axial direction.

One of the second bearings 51 is positioned outside the flange portion 611 of the nut 61 in the axial direction. In other words, the flange portion 611 of the nut is positioned between the second bearing 51 and the permanent magnet 3 in the axial direction. The other second bearing 52 is positioned on the opposite side of the second bearing 51, sandwiching the permanent magnet 3.

The eddy current damper 10A according to this embodiment has the same effect as the eddy current damper 10 according to the first embodiment. That is, even if the magnet holding member 2 and the permanent magnet 3 try to move toward the conductive member 1 during operation of the eddy current damper 10A, the movement of the permanent magnet 3 is restricted by the second bearings 51, 52 before the permanent magnet 3 comes into contact with the inner peripheral surface of the conductive member 1. This makes it possible to prevent contact between the permanent magnet 3 and the conductive member 1, and to reduce the gap G between the permanent magnet 3 and the conductive member 1. In addition, since the second bearings 51, 52 are disposed axially inward of the first bearings 41, 42, the eddy current damper 10A can be made smaller in the axial direction.

In this embodiment, the second bearings 51, 52 are arranged axially outward from the magnet holding member 2. In this case, space for arranging the second bearings 51, 52 can be secured without machining the conductive member 1 and the magnet holding member 2. That is, it is not necessary to form a step or groove for arranging the second bearings 51, 52 on the outer peripheral surface of the magnet holding member 2. Similarly, it is not necessary to form a step or groove for arranging the second bearings 51, 52 on the inner peripheral surface of the conductive member 1. Therefore, the structure of the conductive member 1 and the magnet holding member 2 can be simplified. In addition, since it is not necessary to secure a thickness sufficient to form a step or groove in the conductive member 1 and the magnet holding member 2, the conductive member 1 and the magnet holding member 2 can be thin-walled.

Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

In the above embodiment, two examples of the arrangement of the second bearings 51, 52 are shown, but the arrangement of the second bearings 51, 52 is not limited to the examples in the above embodiment. The second bearings 51, 52 only need to be arranged on both sides of the permanent magnet 3 inside the first bearings 41, 42 in the axial direction, and their positions can be changed as appropriate.

In the above embodiment, a row of permanent magnets 3 arranged in the circumferential direction is provided on the outer peripheral surface of the magnet holding member 2. However, multiple rows of permanent magnets 3 may be provided on the outer peripheral surface of the magnet holding member 2. In this case, the second bearings 51, 52 are provided on both sides of the multiple rows of permanent magnets 3 in the axial direction. In other words, the multiple rows of permanent magnets 3 are arranged between one second bearing 51 and the other second bearing 52 in the axial direction.

In the above embodiment, the magnetic poles (north and south poles) of the permanent magnets 3 are aligned in the radial direction of the magnet holding member 2. However, the magnetic poles (north and south poles) of the permanent magnets 3 may be aligned in the circumferential direction of the magnet holding member 2. In this case, it is preferable that a pole piece is disposed between the permanent magnets 3 adjacent in the circumferential direction, and it is preferable that the magnet holding member 2 is made of a non-magnetic material.

10, 10A: Eddy current damper 1: Conductive member 2: Magnet holding member 3: Permanent magnet 41, 42: First bearing 51, 52: Second bearing 6: Ball screw 61: Nut 62: Screw shaft

Claims (4)

An eddy current damper,
A conductive member having a cylindrical shape;
a magnet holding member arranged inside the conductive member, having a cylindrical shape, and configured to be rotatable around a central axis;
a plurality of permanent magnets arranged along a circumferential direction of the magnet holding member, held by an outer circumferential surface of the magnet holding member, and facing an inner circumferential surface of the conductive member with a gap therebetween;
a ball screw including a nut fixed to one axial end of the magnet holding member and a screw shaft passing through the nut;
a pair of first bearings provided outside the magnet holding member in the axial direction and supporting the magnet holding member in the axial direction;
a pair of second bearings provided on both sides of the permanent magnet and inward of the first bearing in the axial direction, the second bearings supporting the magnet holding member in a radial direction;
Equipped with
The second bearing is made of a magnetic material,
a shortest distance between the second bearing and the permanent magnet in the axial direction is equal to or greater than a distance between adjacent permanent magnets in the circumferential direction among the plurality of permanent magnets . An eddy current damper,
A conductive member having a cylindrical shape;
a magnet holding member arranged inside the conductive member, having a cylindrical shape, and configured to be rotatable around a central axis;
a plurality of permanent magnets arranged along a circumferential direction of the magnet holding member, held by an outer circumferential surface of the magnet holding member, and facing an inner circumferential surface of the conductive member with a gap therebetween;
a ball screw including a nut fixed to one axial end of the magnet holding member and a screw shaft passing through the nut;
a pair of first bearings provided outside the magnet holding member in the axial direction and supporting the magnet holding member in the axial direction;
a pair of second bearings provided on both sides of the permanent magnet and inward of the first bearing in the axial direction, the second bearings supporting the magnet holding member in a radial direction;
Equipped with
The second bearing is made of a non-magnetic material. 3. The eddy current damper according to claim 1 or 2 ,
A damper, wherein one of the pair of second bearings is disposed in the axial direction between the permanent magnet and a fixed portion of the nut relative to the one end of the magnet holding member. 3. The eddy current damper according to claim 1 or 2 ,
A damper, wherein a fixing portion of the nut relative to the one end of the magnet holding member is positioned between one of the pair of second bearings and the permanent magnet in the axial direction.

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