JPH118964A - Voice coil motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it difficult for a yoke to be saturated, to reduce the loss, and to obtain good responsiveness as well. SOLUTION: A yoke 41 is composed of a square frame 47 whose opposite sides are parallel, and a center core 49 provided, stretching between one facing pair of internal side surfaces of this square frame 47. On the periphery of a part of the center core 49, a moving coil 59 is movably provided. Along with providing two permanent magnets 51, 53 so that the same poles face each other respectively between the square frame 47 and each of both ends of the center core 49, two permanent magnets 55, 57 are provided on the other facing pair of internal side surfaces of the square frame 47, so that the same poles face each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice coil motor used as a linear motion actuator, and more particularly to an improvement for preventing saturation of a magnetic path and improving followability to a change in coil current.

[0002]

2. Description of the Related Art A voice coil motor (or a linear motor) is used for positioning a magnetic head and a pickup of a magnetic disk device or an optical disk device at high speed and with high accuracy. A voice coil motor operates on the same principle as a speaker, by inserting a voice coil into a gap, forming a magnetic flux crossing the voice coil with a magnetic circuit consisting of a permanent magnet, and changing the current flowing through the voice coil. , To obtain the axial thrust of the voice coil. Japanese Patent Application Laid-Open No. 8-9849 discloses a voice coil linear motor of this type in which the generation of side force is reduced by reducing the linkage magnetic flux between the magnetic flux of the permanent magnet and the magnetic flux of the coil.
No. 6 is described with reference to FIG. York 1
Are upper and lower outer yokes 3, 3; left and right side yokes 5, 5 for closing both ends of the outer yokes 3, 3;
And a central yoke 7 connecting the central portions thereof to form a closed magnetic path. The inner surfaces of the outer yokes 3, 3 and the central yoke 7
Are provided with permanent magnets 9, 9 and 11, 11 in which the magnetic poles of an adjacent one and an opposite one are alternately exchanged. The inside of both ends of the permanent magnets 9, 9 and the permanent magnet 11,
A chamfer C1 is provided on both outer sides of 11. Chamfer C between the permanent magnets 9, 9 and 11, 11
2 are provided, and the coils 13 and 13 are connected so that currents flowing through adjacent coils are opposite. According to the voice coil type linear motor configured as described above, the magnetomotive force distribution at the ends of the permanent magnets 9 and 11 becomes smaller toward the outside in the axial direction, and the coil 1
Since the gap between the end of the outer yoke 3 and the outer yokes 3, 3 and the center yoke 7 becomes larger, the leakage magnetic flux at the end is reduced, the linkage between the magnet magnetic flux and the coil magnetic flux near the end is reduced, and the side force is reduced. Was able to be reduced. On the other hand, in the moving coil linear motor shown in FIG. 6 described in Japanese Patent Application Laid-Open No. 4-150760, upper and lower outer yokes 15, 15 and left and right side yokes 1 closing both ends of the outer yokes 15, 15 are shown.
A plurality of permanent magnets 23 that are magnetized in the thickness direction and alternately reversed in the longitudinal direction are constituted by a yoke 21 composed of the central yokes 7 and 17 and the central yoke 19 connecting the central portions of the side yokes 17 and 17. Is attached to one surface of the central yoke 19 and one surface of the lower outer yoke 15, and has a movable coil 25 that penetrates the central yoke 19 and is movable in the axial direction of the central yoke 19, and has a permanent magnet 23 attached to one surface. A plurality of short rings 27 are provided on the surface of the yoke 19. According to this moving coil type linear motor, the speed of change of the current can be increased by the short ring 27,
The response speed of the moving coil type linear motor could be improved.

[0003]

However, in the voice coil linear motor shown in FIG. 5 described in the above-mentioned Japanese Patent Application Laid-Open No. 8-98496, the yoke is saturated by the magnetic flux of the coil, so that the instantaneous maximum thrust is obtained. There was a problem that could not be enlarged. In the moving coil linear motor shown in FIG. 6 described in Japanese Patent Application Laid-Open No. 8-98496, there is a problem that an eddy current is generated by the short ring and the loss increases. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a voice coil motor in which a yoke is unlikely to be saturated, loss can be suppressed, and good responsiveness can be obtained. .

[0004]

According to a first aspect of the present invention, there is provided a voice coil motor comprising: a rectangular frame body having opposing sides parallel to each other; and a pair of opposed rectangular frame bodies. A yoke having a center core portion provided over the inner side surface of the center core, a movable coil movably provided on an outer periphery of a part of the center core portion, and a space between both ends of the center core portion and the square frame portion. And two permanent magnets provided so that the same poles face each other, and two permanent magnets provided so that the same poles face each other on the other pair of inner surfaces facing each other of the square frame portion. It was done. Further, the configuration of the voice coil motor includes a yoke having a square frame body part whose opposing sides are parallel, and a center core part provided over one pair of inner surfaces facing each other of the square frame body part; A movable coil movably provided on a part of the outer periphery of the core portion; and two permanent magnets provided between both ends of the center core portion and the square frame portion such that the same poles are opposed to each other. The shape of the center core portion is formed so that the interval between the other pair of inner side surfaces of the square frame portion and the center core portion becomes narrower as approaching the center. There may be. In the voice coil motor configured as described above, two permanent magnets are provided between both ends of the center core portion and the square frame portion, and two permanent magnets are provided on the other pair of inner surfaces facing each other of the square frame portion. A magnet is provided, and the coil magnetic flux generated by the coil current passes through the gap between the permanent magnet or the center core and the upper and lower sides or the left and right sides, thereby making it difficult for the yoke to be saturated and viewed from the movable coil. The magnetic resistance also increases, the inductance of the movable coil decreases, and the ability to follow a sudden current change is improved. Also, in a voice coil motor in which the shape of the center core portion is formed so that the distance between the other pair of inner side surfaces of the square frame portion and the center core portion becomes smaller as approaching the center, the upper and lower sides of the square frame portion are formed. The air gap between the side and the center core is shortened, and the magnetic flux distribution in the air gap is averaged.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a voice coil motor according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a first embodiment of a voice coil motor according to the present invention. The yoke 41 constituting the magnetic circuit is
Opposing parallel upper and lower sides 43, 43 and left and right sides 45,
45, and left and right side portions 45, 45, which are a pair of inner surfaces facing each other, of the square frame portion 47.
And a center core portion 49 provided over the center portion. The upper and lower sides 43, 43, the left and right sides 45 of the yoke 41,
The 45 and the center core portion 49 are made of a soft magnetic material, and may be formed by laminating thin plates having excellent magnetic properties such as a silicon steel plate. Two permanent magnets 51, 53 are provided between both ends of the center core 49 and the left and right sides 45, 45 of the square frame 47. The permanent magnets 51 and 53 are arranged so that the same poles are opposed to each other with the center core 49 interposed therebetween. In this embodiment, the N poles of the permanent magnets 51 and 53 are arranged so as to face each other. In addition, near the center of the upper and lower sides 43, 43, which are the other pair of inner surfaces facing each other, of the square frame body 47,
Two permanent magnets 55 and 57 are provided so that the same poles face each other. In this embodiment, the S poles of the permanent magnets 55 and 57 face each other. Permanent magnets 51, 53, 55, 57
As a material for the material, an NdFeB-based magnet having a high energy product, a plastic magnet having a large resistivity, or the like can be used. A movable coil 59 is provided on the outer periphery of a part of the center core 49 so as to be movable in the coil axis direction. The movable coil 59, for example, inserts a bobbin into a cored bar, winds a winding around the bobbin in a cylindrical shape, impregnates a winding portion with a reinforcing material such as a glass material or a resin material, and solidifies the winding. Can be formed by extracting the core metal from the bobbin. The voice coil motor 61 is configured by using the yoke 41, the permanent magnets 51, 53, 55, 57, and the movable coil 59 as main components. Next, the operation of the voice coil motor 61 configured as described above will be described. Permanent magnet 51,
The magnetic flux by 53 is linked to the movable coil 59, enters the upper and lower sides 43, 43 through the gap, and returns to the permanent magnets 51, 53 via the left and right sides 45, 45. The magnetic flux near the center enters the upper and lower sides 43, 43 through the permanent magnets 55, 57, and returns to the permanent magnets 51, 53 through the left and right sides 45, 45. Thus, the movable coil 59 has the permanent magnets 51, 5
The magnetic flux due to 3 interlinks. When the current I flows through the movable coil 59, a magnetic flux generated by the permanent magnets 51 and 53 and the coil current I generate a linkage flux and a thrust proportional to the coil current.
The coil magnetic flux generated by the coil current is a permanent magnet 51,
It passes through a gap between 53 or the center core portion 49 and the upper and lower sides 43, 43 or the left and right sides 45, 45. As a result, saturation of the yoke 41 hardly occurs, the magnetic resistance as viewed from the movable coil 59 increases, the inductance of the movable coil 59 decreases, and the ability to follow a sudden current change is improved. Further, since a short ring is unnecessary, resistance loss due to the short ring does not occur. FIG.
In the case of the comparative example shown in (A), if the width of the magnet is Wy and the coil length is Lc, the gap magnetic flux density Bg of the coil portion is obtained.
Can be expressed by the following equation. Bg = (Wy / Lc) × Bd where Bd; magnet operating point Therefore, it is necessary to increase Wy with respect to Lc in order to produce a thrust, and if Wy is increased, the coil end length becomes longer, so that the loss is increased. Increase. Further, in the case of the comparative example shown in FIG.
And Bd are substantially equal, and the gap magnetic flux density can be increased. On the other hand, since the core is saturated by the coil magnetic flux, a short-circuit plate is required to prevent this saturation as described in the related art, and an eddy current flows through the short-circuit plate. Loss will occur. On the other hand, in the voice coil motor 61 described above, by adding the permanent magnets 55 and 57, the variation in the gap magnetic flux distribution is reduced, and the thrust ripple is reduced. That is, in the voice coil motor 61, by appropriately adjusting the magnetic fluxes of the permanent magnets 51, 53, 55, and 57, the magnetic flux components can be easily balanced, and the gap magnetic flux distribution can be made uniform. As described above, according to the voice coil motor 61 described above, it is possible to improve the followability to a rapid current change, and no short ring is required, so that no resistance loss due to the short ring occurs and the gap magnetic flux distribution is reduced. , The thrust ripple can be reduced. Next, a second embodiment of the voice coil motor according to the present invention will be described. FIG. 3 is a schematic configuration diagram showing a second embodiment of the voice coil motor according to the present invention. The voice coil motor 71 according to this embodiment does not include the permanent magnets 55 and 57 described above. On the other hand, the shape of the center core portion 73 is formed so that the distance between the center core portion 73 and the upper and lower sides 43, 43, which are the other pair of inner surfaces facing each other, of the square frame portion 47 becomes narrower toward the center. I have. The center core portion 73 according to this example is formed in a shape shown in FIG. 3 in which the outer diameter increases toward the center from both ends. The other parts are configured in the same manner as the voice coil motor 61 described above. In the voice coil motor 71 configured as described above, since the permeance coefficient at the end of the center core 73 is large, compared to the amount of magnetic flux traveling from the center of the center core 73 to the upper and lower sides 43, 43, , The amount of magnetic flux directed to the upper and lower sides 43, 43 becomes larger. For this reason, there is no problem when the coil length is long and most of the magnetic flux links to the coil, but (magnet thickness +
In the case where (center core length)> (2 × total coil length), the generated thrust may vary depending on the position of the coil. That is, the electric load Ac is proportional to the coil distribution according to the following equation. F = Bg × Ac × L Since the gap magnetic flux density Bg changes at the position of the movable coil 59 as shown in FIG. 4, the coil distribution needs to be equal to or more than a half cycle of the Bg change in order to average the change. become. Therefore, if the coil distribution (= coil length) is X / 2 <coil length, it is considered that the magnetic flux linked to the coil is averaged with respect to the coil position. According to the voice coil motor 71, the outer diameter of the center core 73 is larger at the center than at the ends, and the gap between the upper and lower sides 43, 43 and the center core 73 is shortened, so that the magnetic flux of the gap is reduced. The distribution can be averaged.

[0006]

As described above in detail, according to the voice coil motor of the present invention, two permanent magnets are provided between both ends of the center core portion and the rectangular frame portion, and the rectangular frame portion is provided. Since two permanent magnets are provided on the other pair of inner surfaces facing each other, the followability to a sudden current change can be improved, and no resistance loss due to the short ring occurs because a short ring is unnecessary. In addition, by making the gap magnetic flux distribution uniform, the thrust ripple can be reduced. Further, according to the voice coil motor in which the shape of the center core portion is formed such that the distance between the other pair of inner side surfaces of the square frame portion and the center core portion becomes narrower as approaching the center,
By shortening the gap between the upper and lower sides of the square frame and the center core, the magnetic flux distribution in the gap can be averaged.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a voice coil motor according to the present invention.

FIG. 2 is an explanatory diagram showing a comparative example with respect to the first embodiment.

FIG. 3 is a schematic configuration diagram showing a second embodiment of the voice coil motor according to the present invention.

FIG. 4 is an explanatory diagram of a magnetic flux density distribution.

FIG. 5 is a schematic configuration diagram showing a conventional voice coil type linear motor.

FIG. 6 is a schematic configuration diagram showing a conventional moving coil type linear motor.

[Explanation of symbols]

 41 Yoke 47 Square frame part 49 Center core part 51, 53, 55, 57 Permanent magnet 59 Moving coil 61 Voice coil motor 73 Center core part

Claims (2)

[Claims] A yoke having a quadrangular frame body having opposing sides parallel to each other and a center core provided over a pair of inner surfaces facing each other of the quadrangular frame; A movable coil movably provided on the outer periphery of the portion; two permanent magnets provided so that the same poles are respectively opposed between both ends of the center core portion and the square frame portion; and the square frame portion A voice coil motor, further comprising: two permanent magnets provided so that the same poles face the other pair of inner surfaces facing each other. 2. A yoke having a square frame body part whose opposing sides are parallel and a center core part provided over one pair of inner surfaces facing each other of the square frame body part; A movable coil movably provided on the outer periphery of the portion, and two permanent magnets provided so that the same poles are respectively opposed between both ends of the center core portion and the square frame portion; A voice coil motor, wherein a shape of a core portion is formed such that a distance between the other pair of inner side surfaces of the square frame portion and the center core portion becomes smaller as approaching the center.