JP2009213210A - Vibrating motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce only restoring force, without causing reduction in the thrust increasing effect of a secondary main magnet, and thereby enabling reduction in the size and the price and enhancement of efficiency. <P>SOLUTION: The vibrating motor includes a movable part and two leg parts, opposed to the movable part with a void part in-between. The movable part includes: a substantially cylindrical first main magnet comprised of a permanent magnet magnetized in the radial direction; a substantially cylindrical sub-magnet comprising a permanent magnet magnetized in the axial direction; and a substantially cylindrical second main magnet comprising a permanent magnet magnetized in a polarity opposite that of the first main magnet. The sub-magnet and the second main magnet are coaxially and disposed symmetrically, with respect to the first main magnet. The motor further includes an excitation yoke disposed coaxially with the movable part; an exciting coil that is wound on the excitation yoke and produces magnetic flux at the leg parts; and a cylindrical back yoke, placed so as to oppose the excitation yoke, with the movable part in-between. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vibration type motor that can be used in a vibration type compressor of a Stirling refrigerator.

Conventionally, a movable magnet type linear motor (hereinafter also simply referred to as a movable magnet type motor) has been used as this type of vibration type motor.
FIG. 5 and FIG. 6 are schematic configuration diagrams for explaining the driving principle of the movable magnet type motor, and all show a part of a sectional view along the central axis C of the substantially cylindrical motor. .
In FIG. 5, 101 is an exciting yoke, 102 is an exciting coil, 103 is a back yoke, 104 is disposed in a gap between the exciting yoke 101 and the back yoke 103, and the inner and outer peripheral sides are magnetized to have different polarities. The movable part 110 made of a cylindrical permanent magnet is a magnetic flux generated by the movable part 104. The arrow written inside the movable portion 104 indicates the magnetization direction (the arrow tip is the N pole, and the arrow rear end is the S pole). The casing that supports the movable portion 104 is not shown.
In many movable magnet type motors, a single permanent magnet magnetized as the movable part 104 is used as shown in the figure, and this movable part 104 is integrally connected to a piston (not shown). In addition, both end portions in the axial direction of the movable portion 104 are accommodated within the leg width of the excitation yoke 101.
As shown in FIG. 5, when the outer peripheral side of the movable part 104 is an N pole and the inner peripheral side is an S pole, the magnetic flux 110 generated from the outer peripheral side goes around the outer side of the movable part 104 and returns to the inner peripheral side. For this reason, at the both ends in the axial direction of the movable portion 104, the magnetic flux 110 is equivalent to the magnetic flux generated when current flows in the opposite direction in the direction perpendicular to the paper surface. This is called the equivalent current I _M of the permanent magnet.

As shown in FIG. 6, when an alternating current is applied to the exciting coil 102 to generate a magnetic flux Φ and this magnetic flux Φ is linked to the gap G where the equivalent current I _M exists, the movable part disposed in the gap G In accordance with Fleming's left-hand rule, 104 reciprocates in response to a horizontal force (thrust) in the figure.
The thrust F can be simply calculated by Equation 1.

ここで、Ｂは空隙部Ｇに発生させた磁束Φの磁束密度、Ｌ_Mは可動部１０４の周方向の平均長さである。
数式１において、通常のＢ・Ｉ・Ｌ則と異なって等価電流Ｉ_Mが２倍されているのは、本モデルでは可動部１０４の軸方向両端部の２箇所に等価電流Ｉ_Mが存在するためである。
一方、可動部１０４は、図示していない軸方向に適正なばね力を持つ機械ばね（例えば、コイルばねや板ばね）を設置している（特許文献２参照）。これは、機械振動の共振点で運転させることで、入力電力を抑えることができるからである。一般的には、スターリング冷凍機では、40〜80Hzの比較的低周波数で運転される。
単純なばね質量系の固有周波数ｆは、ばね定数ｋ、可動質量ｍとして次式で与えられる。

Here, B is the magnetic flux density of the magnetic flux Φ generated in the gap G, and L _M is the average length in the circumferential direction of the movable portion 104.
In Equation 1, the equivalent current I _M is doubled unlike the normal B · I · L rule. In this model, the equivalent current I _M exists at two positions on both ends of the movable portion 104 in the axial direction. Because.
On the other hand, the movable part 104 is provided with a mechanical spring (for example, a coil spring or a leaf spring) having an appropriate spring force in the axial direction (not shown) (see Patent Document 2). This is because the input power can be suppressed by operating at the resonance point of mechanical vibration. Generally, a Stirling refrigerator is operated at a relatively low frequency of 40 to 80 Hz.
The natural frequency f of a simple spring mass system is given by the following equation as a spring constant k and a movable mass m.

また、本発明の振動型モータを圧縮機として使用する場合、ばね定数ｋは以下のように表される。

When the vibration type motor of the present invention is used as a compressor, the spring constant k is expressed as follows.

ここで、
ｋ_spは機械ばねによるばね定数、
ｋ_magは可動部磁石の復元力によるばね定数、
ｋ_gasは圧縮ガスによるばね定数である。
そのうち、ｋ_gasは要求される冷凍出力により、作動ガスの封入圧力と圧縮比でほぼ決まってしまうため、意図的に調整することは困難である。図５，図６のように、可動部１０４が単極着磁された単一の永久磁石の場合には、磁石の復元力は可動領域においてほとんど作用しないため、実用上ｋ_magを考慮する必要は無い。したがって、機械ばね定数ｋ_spの調整可能範囲が広く、設計が比較的容易である。
ところで、モータの体格を変えずに（Ｌ_M＝一定）、推力Ｆを大きくするためには、数式１から明らかなように、空隙部の磁束密度Ｂまたは等価電流Ｉ_Mを増加させればよい。
まず、磁束密度Ｂを増加させるには、空隙部のギャップ長を短くするか、励磁コイル１０２を流れる励磁電流を増加させる必要がある。しかし、前者の方法は、可動部１０４及びそれを支える部材が薄くなるため強度不足や加工コストの上昇を招き易く、後者の方法はジュール熱損失（Ｉ²Ｒ）が増大して性能の低下を招くという問題がある。

here,
k _sp is a spring constant by a mechanical spring,
k _mag is the spring constant due to the restoring force of the moving part magnet,
k _gas is a spring constant by compressed gas.
Of these, k _gas is almost determined by the pressure and compression ratio of the working gas depending on the required refrigeration output, so it is difficult to adjust it intentionally. As shown in FIGS. 5 and 6, in the case where the movable part 104 is a single permanent magnet magnetized with a single pole, the restoring force of the magnet hardly acts in the movable region, so it is necessary to consider k _mag practically. There is no. Therefore, the adjustable range of the mechanical spring constant _ksp is wide and the design is relatively easy.
By the way, in order to increase the thrust F without changing the physique of the motor (L _M = constant), it is sufficient to increase the magnetic flux density B or the equivalent current I _M in the air gap as is apparent from Equation 1. .
First, in order to increase the magnetic flux density B, it is necessary to shorten the gap length of the gap or increase the exciting current flowing through the exciting coil 102. However, in the former method, the movable part 104 and the member supporting it are thinned, so that the strength is insufficient and the processing cost is likely to increase. The latter method increases Joule heat loss (I ² R) and decreases performance. There is a problem of inviting.

On the other hand, in order to increase the equivalent current I _M , it is conceivable to use a permanent magnet having a larger magnetic force in addition to changing the thickness of the permanent magnet as the movable portion 104. However, both of them cause an increase in cost.
Therefore, as another method for increasing the thrust F, a structure as shown in FIG. 7 can be considered. In this movable magnet type motor, a pair of cylindrical secondary main magnets 107 magnetized in the opposite direction to the primary main magnet 105 are coaxially and integrally formed at both axial ends of the cylindrical primary main magnet 105. Are joined to each other to form a movable portion 104A, and the equivalent current I _M is virtually increased.
According to the structure of FIG. 7, the magnetic flux cancels out at the joint portion between the primary main magnet 105 and the secondary main magnet 107 in the non-excited state, so that the neutral portion of the movable portion 104A is compared with the structures of FIGS. There is also an advantage that the holding force at the position becomes strong and so-called automatic neutral positioning (self-centering) becomes easy.
As shown in FIG. 7, a movable magnet type motor described in Patent Document 1 is known as a prior art provided with a movable portion including a primary main magnet and a pair of secondary main magnets.
FIG. 8 is a configuration diagram of the movable magnet type motor described in Patent Document 1. In FIG. In FIG. 8, 201 is a back yoke, 202 is an excitation coil, 203 is an excitation yoke, 204 is a movable part, 205 is a primary main magnet, 207 is a secondary main magnet, 300 is a Stirling engine, 301 is a casing, 302 is a piston, Reference numeral 303 denotes a display server. Reference numeral 210 denotes a neutral position of the movable unit 204.
US Pat. No. 5,148,066 (FIG. 1) Japanese Patent Laid-Open No. 2005-9397

According to the prior art shown in FIG. 8, when the movable part 204 is displaced in the axial direction, a large restoring force acts on the movable part 204, so that a sufficient piston stroke may not be ensured.
As a measure for alleviating the restoring force, FIG. 7A and 8A disclose that the shape and structure are changed by a method such as forming the secondary main magnet into a triangle or reducing the thickness, but in order to design these shapes to the optimum values. Has a problem that the number of parameters becomes very large and the design of the secondary main magnet becomes difficult. Further, when a method such as making the secondary main magnet into a triangle is adopted, there is a problem that the equivalent current I _M is reduced, and not only the restoring force but also the thrust increasing effect is reduced.
On the other hand, when no measures are taken to mitigate the restoring force, a large restoring force acts on the primary main magnet and the secondary main magnet, so the k _mag shown in Equation 3 must be considered. As is clear from Equations 2 and 3, when k _mag is increased, the design requirement range of the mechanical spring for adjusting the resonance of the mechanical vibration becomes narrow, and the design of the low frequency resonance becomes difficult.
In this case, it is conceivable that the holding force in the radial direction of the support spring (mechanical spring) is reduced to weaken the overall spring force, or the movable mass m in Formula 2 is increased. However, these measures have problems that the piston and the cylinder cannot be supported in a non-contact manner, and that the overall weight increases and the size increases.

Further, when there is a secondary main magnet, since the magnetic flux passing through the back yoke increases, it is necessary to increase the cross-sectional area of the back yoke in the magnetic flux passing direction, resulting in a problem that the size is increased. Furthermore, since the change in magnetic flux in the back yoke during reciprocating motion in the axial direction also increases, there is a problem in that the efficiency decreases due to eddy currents generated in the back yoke.
Therefore, the problem to be solved by the present invention is to make the resonance design of the vibration type motor easy by reducing only the restoring force without reducing the thrust increase effect by the secondary main magnet, and to reduce the eddy current generated in the back yoke. An object of the present invention is to provide a vibration type motor that can reduce the thrust, increase the size, and reduce the size and increase the efficiency.

In order to solve the above-mentioned problems, the invention according to claim 1 is a substantially cylindrical first main magnet made of a permanent magnet magnetized in the radial direction and a substantially cylinder made of a permanent magnet magnetized in the axial direction. And a substantially cylindrical second main magnet composed of a permanent magnet magnetized in the opposite polarity to the first main magnet, the sub magnet and the second magnet centering on the first main magnet. The main magnet is provided with a movable part coaxially arranged symmetrically, and two leg parts facing the movable part via a gap, and is wound around the excitation yoke and coaxially arranged with the movable part. An excitation coil for generating a magnetic flux in the leg portion, and a cylindrical back yoke arranged to face the excitation yoke with the movable portion interposed therebetween, and an alternating current is passed through the excitation coil. The movable portion is reciprocated in the axial direction.
The invention according to claim 2 is the vibration type motor according to claim 1, wherein the magnetic flux generated by the first main magnet and the second main magnet and the magnetic flux generated by the sub magnet are the same on the excitation yoke side. Each magnet is arranged so as to be in the direction and in the opposite direction on the back yoke side.
The invention according to claim 3 is the vibration type motor according to claim 1 or 2, wherein a ratio of axial lengths of the first main magnet and the second main magnet is 2: 1. And

  According to a fourth aspect of the present invention, in the vibration type motor according to the first to third aspects, a value obtained by adding 1/2 of the axial length of the sub-magnet and the maximum displacement amount of the movable portion in the axial direction is: The excitation yoke is configured to be smaller than ½ of the axial length of the leg portion.

According to the first aspect of the present invention, the axial restoring force can be reduced while maintaining the thrust increasing effect.
According to the invention of claim 2, since the magnetic flux generated on the back yoke side can be reduced and the loss due to the eddy current in the back yoke can be reduced, high efficiency can be achieved.
According to the invention of claim 3, since the total magnetic fluxes of the first main magnet and the second main magnet coincide with each other and the passing magnetic flux of the exciting yoke can be reduced, the cross-sectional area of the outer peripheral portion of the exciting yoke can be reduced. It is possible to reduce the size. Furthermore, loss due to eddy current can be reduced by reducing the passing magnetic flux.
According to the fourth aspect of the present invention, the end portions of the first main magnet and the second main magnet are always within the leg during the reciprocating motion, so that the equivalent current I _M can be reliably used as the thrust increasing element.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a main part of the present invention, and shows a part of a sectional view along a central axis C of a substantially cylindrical motor, similarly to FIGS.
In FIG. 1, 1 is an excitation yoke, 2 is an excitation coil wound around the excitation yoke 1, 3 is a back yoke, and 4 is a cylindrical permanent arranged in a gap between the excitation yoke 1 and the back yoke 3. It is a movable part made of a magnet. In addition, the casing which supports the movable part 4 is abbreviate | omitting illustration.
The movable portion 4 includes a cylindrical primary main magnet 5 magnetized with an N pole on the outer peripheral side and an S pole on the inner peripheral side, and a pair of cylinders magnetized with an N pole on the inner side in the axial direction and an S pole on the outer side in the axial direction. A sub-magnet 6 and a pair of cylindrical secondary main magnets 7 magnetized in the opposite direction to the primary main magnet 5, with the primary main magnet 5 as the center, the sub-magnet 6 and the secondary main magnet 7. In this order, they are connected symmetrically. In addition, the arrow described inside the primary main magnet 5, the submagnet 6, and the primary main magnet 7 has shown the magnetization direction (the arrow tip is N pole and the arrow back end is S pole), and the movable part 4 is a magnetization direction. It is a Halbach magnet arranged by changing 90 degrees.
For the primary main magnet 5, the secondary main magnet 7, and the secondary magnet 6, for example, rare earth permanent magnets such as neodymium and samarium are used.

The excitation yoke 1 is formed of a block obtained by cutting a soft magnetic material, a laminate of iron plates, silicon steel plates, or the like, or a sintered soft magnetic material. When an alternating magnetic field is applied like a vibration type motor, an eddy current is generated in a direction perpendicular to the magnetic flux to deteriorate the performance. Therefore, it is preferable to insulate the direction perpendicular to the magnetic flux using a laminated steel plate or the like.
The back yoke 3 is made of a soft magnetic material, and its axial end coincides with the axial outer end of the leg 11 of the exciting yoke as shown.
Next, the effect by adopting the Halbach magnet for the movable part 4 will be described.
As shown in FIG. 1, in this invention, the magnetic flux 21 by the primary main magnet 5 and the secondary main magnet 7, and the magnetic flux 22 by the submagnet 6 generate | occur | produce. Since the magnetic flux 21 and the magnetic flux 22 are in the same direction on the exciting yoke side, the magnetic flux is strengthened, but on the back yoke side, the magnetic flux is weakened in the opposite direction, so that the magnetic flux passing through the back yoke 3 is greatly reduced. As a result, the back yoke 3 can be made thin, and the restoring force due to the magnetism in the axial direction is reduced, so that the range of resonance design of the mechanical spring can be widened. Furthermore, even when the back yoke is manufactured by a ring, the change in magnetic flux due to the reciprocating motion of the magnet is reduced, so that eddy current can be reduced.
FIG. 2 is a diagram showing the principle of operation of the present invention.

As shown in FIG. 2, when a current is passed through the coil in a direction perpendicular to the plane of the drawing, an exciting magnetic flux 31 is generated in the exciting yoke in the clockwise direction as shown in the figure, and the primary main magnet 5, submagnet 6, Due to the equivalent current I _M of the next main magnet 7, the movable part 4 receives a force in the left direction at the two legs 11 of the exciting yoke 1 in the direction of the left hand of Fleming. Since the secondary magnet 6 has an equivalent current I _{M in} both directions, the force is canceled out, and the effect of increasing the thrust obtained by comprising the primary main magnet 5 and the secondary main magnet 7 is not reduced. Further, when a current in the reverse direction (vertical upward direction in the drawing) is passed through the exciting coil 2, a force is generated on the right side. Therefore, a reciprocating motion is realized by passing a sine wave current through the exciting coil 2.
Next, in order to obtain a greater effect by employing the Halbach magnet, each permanent magnet is further configured as follows.
FIG. 3 is an enlarged view of the vicinity of the legs in the embodiment of the present invention.
As shown in FIG. 3, when the axial center of the movable part 4 and the axial center of the excitation yoke 2 coincide (excitation coil 2 is in a non-excited state), the axial center of each submagnet 6 and each excitation yoke leg. And the length La of the submagnet 6, the maximum displacement Ymax of the movable portion 4, and the axial width Ly of the exciting yoke leg 11 are Ymax + La / 2 <Ly. It is comprised so that the relationship of / 2 may be satisfy | filled. Thereby, the end portions of the primary main magnet 5 and the secondary main magnet 7 are accommodated in the leg portion 11 during the reciprocating motion, so that the equivalent current I _M can be used as a thrust increasing element.

Further, the length of the secondary main magnet 7 is such that the outermost end of the secondary main magnet 7 does not reach the inside of the excitation yoke leg 11 even when the displacement of the movable portion 4 reaches the maximum displacement amount Ymax. Have. This is because, when the length of the secondary main magnet 7 is short, a reaction force due to the equivalent current I _M (see FIG. 3) existing at the outer end of the secondary main magnet 7 is generated, and the thrust increasing effect is reduced. .
Furthermore, when the axial length of the secondary main magnet 7 is not ½ of the axial length of the primary main magnet 5 as shown in FIG. 3 passes through the magnetic flux 31 generated by the exciting coil 2 and the leakage magnetic flux 32 from the primary main magnet 5 and the secondary main magnet 7. However, since the axial length of the secondary main magnet 7 is ½ of the axial length of the primary main magnet 5, the generated magnetic fluxes of the primary main magnet 5 and the secondary main magnet 7 coincide with each other. Since the magnetic flux passing through the excitation yoke 1 and the back yoke 3 is only the magnetic flux 31 generated from the excitation coil 2 without the leakage magnetic flux 32, the sectional area of the outer periphery of the excitation yoke can be reduced, and the vibration motor can be downsized. .
In the embodiment described above, the excitation yoke 1 is arranged on the outer side in the circular radial direction of the movable part 4 and the back yoke 3 is arranged on the inner side in the circular radial direction of the movable part 4. However, the excitation yoke 1 and the back yoke 3 are arranged oppositely. May be.

  The vibration type motor according to the present invention can be applied to a vibration type compressor of a Stirling refrigerator.

Configuration diagram showing an embodiment of the present invention The figure which showed the state at the time of operation | movement of this invention The enlarged view near the leg in the embodiment of the present invention The figure showing the magnetic flux in the case where the axial length of the secondary main magnet 7 is not ½ of the axial length of the primary main magnet 5 Configuration diagram of movable magnet type motor The figure for explaining the drive principle of the movable magnet type motor Configuration diagram showing conventional technology The block diagram which shows the prior art described in patent document 1

Explanation of symbols

1, 101, 201: Excitation yoke 2, 102, 202: Excitation coil 3, 103, 203: Back yoke 4, 104, 104A, 204: Movable part 5, 105, 205: Primary main magnet 6: Sub magnet 7, 107 207: Secondary main magnet 11: Leg part

Claims (4)

A substantially cylindrical first main magnet composed of a permanent magnet magnetized in the radial direction, a pair of substantially cylindrical submagnets composed of a permanent magnet magnetized in the axial direction, and the first main magnet; A pair of substantially cylindrical second main magnets composed of permanent magnets magnetized in opposite polarities are arranged in the order of sub magnets and second main magnets at both ends of the first main magnet with the first main magnet as the center. Movable parts arranged coaxially and symmetrically at
An excitation yoke provided with two legs facing the movable part via a gap, and arranged coaxially with the movable part;
An exciting coil wound around the exciting yoke and generating magnetic flux in the leg;
A cylindrical back yoke arranged so as to face the excitation yoke with the movable part interposed therebetween,
An oscillation type motor characterized in that an alternating current is passed through the excitation coil to reciprocate the movable part in the axial direction.   The magnets are arranged so that the magnetic flux generated by the first main magnet and the second main magnet and the magnetic flux generated by the sub magnet are in the same direction on the excitation yoke side and in the opposite directions on the back yoke side. The vibration type motor according to claim 1.   3. The vibration type motor according to claim 1, wherein a ratio of axial lengths of the first main magnet and the second main magnet is 2: 1. 4. In the state where the excitation coil is not excited,
The magnets are arranged so that the axial center of each leg of the excitation yoke coincides with the axial center of the sub-magnet,
A value obtained by adding 1/2 of the axial length of the secondary magnet and the maximum axial displacement of the movable portion is smaller than 1/2 of the axial length of one leg of the excitation yoke. The vibration type motor according to claim 1, wherein the vibration type motor is configured as described above.

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