JPS5832476Y2 - Voice coil motor - Google Patents

Description

[Detailed description of the invention] The present invention relates to a voice coil motor, and more particularly to a voice coil motor equipped with a magnetic circuit that can contribute to improved and stable output by increasing the air gap magnetic flux density passing through a moving coil. .

Voice coil motors have a wide range of applications, such as head positioning motors for magnetic disk drives, motors for driving speakers and vibration exciters, and linear motors for various types of movement. A typical example of a motor has the structure shown in FIGS. 1A and 1H.

That is, for example, it consists of a magnetic head device 10 that can be positioned and moved with respect to a magnetic disk (not shown), a moving coil 12 mechanically connected to it, and a fixed magnetic circuit section 14, and this fixed magnetic circuit section 14 is connected to an iron core 16. It includes a side yoke 18 provided around the yoke, a rear yoke 20, a permanent magnet 22 attached to the side yoke 18, and a magnetic pole piece 24.
A gap 26 is formed between the iron core 16 and the iron core 16, and the movable coil 12 is movable within the gap.

In such a structure, in the fixed magnetic circuit section 14, the magnetic flux flow emitted from the permanent magnet 22 having the illustrated N-8 complement array interlinks with the moving coil 26 in the air gap 26, passes through the iron core 16, and reaches the rear joint. After passing iron 20 and side yoke 18, permanent magnet 2
A magnetic circuit is formed that returns to step 2.

Therefore, by passing a current through the moving coil 12 connected to the magnetic head device 10, the interaction with the magnetic flux passing through the air gap 26 causes the moving coil 12 and the magnetic head device 10 to
The movable coil 12 receives a moving force in the direction of the center line of the movable coil 12.

At this time, by appropriately controlling the amount and direction of the current flowing through the movable coil 12, the magnetic head device 10 can be positioned at the target position on the magnetic disk.

In the magnetic circuit section 14 of the conventional voice coil type motor shown in FIG. It is inserted in the direction along the center line.

That is, if permanent magnets are made of ferrite material, it is possible to have a thin structure, so they are placed around the moving coil 12 in order to reduce the overall dimensions of the voice coil motor as much as possible. be.

However, in general, in order to improve the high-speed performance of the motor, it is necessary to make the magnetic flux density passing through the air gap 26 as high as possible, and for this purpose, according to the structure shown in FIG. The width dimension W (see FIG. 1B) and the wall thickness dimension t (also see FIG. 1B) must be increased.

On the other hand, increasing these dimensions W and t inevitably increases the shape and dimensions of the fixed magnetic circuit section 14, especially the dimensions and shape of the front part of the fixed magnetic circuit section 14 in which the permanent magnet 22 is inserted. Therefore, when the voice coil type motor is assembled and installed in various devices according to various uses, a disadvantage arises in that a large installation space is required.

Furthermore, according to the structure of the conventional fixed magnetic circuit section 14 shown in FIG. 1, the magnetic flux distribution in the moving direction of the moving coil 12 (arrow S in FIG. 1A) is caused by magnetic flux leakage at the front and rear ends of the permanent magnet 24, i.e. As a result, the relationship between the coil position and the air gap magnetic flux distribution shown in FIG. As such, flatness characteristics are lacking.

For this purpose, the length dimension t1 (
(see FIG. 1A) must be formed to a size that is the sum of the moving distance of the moving coil 12 and the length of the coil 12 in the axial direction, plus a certain length α that takes into account the non-flat characteristics of the magnetic flux distribution.

The length 11 of the permanent magnetic flux 22 in the center line direction is selected based on the design principle of compensating for magnetic flux leakage, and the length 11 of the permanent magnetic flux 22 is
There is a disadvantage that the magnetic flux density inside cannot be used as a factor for increasing the density.

That is, as a result, with the structure of the magnetic circuit section 14 in the conventional voice coil motor, it is impossible to avoid increasing the size and shape of the motor itself in order to increase the magnetic flux density. There are certain limits to adopting the structure shown in FIG. 1 when achieving high speed and high output.

Therefore, the purpose of the present invention is to easily increase the magnetic flux density in the air gap in the fixed magnetic circuit while using magnetic materials such as ferrite that are inexpensive and have high coercive force, which are used in conventional voice coil motors. It is an object of the present invention to provide a voice coil type motor having a magnetic circuit structure that can perform the following steps.

That is, in the voice coil type motor according to the present invention, the arrangement of the permanent magnets that generate magnetic flux in the fixed magnetic circuit section is completely different from the conventional structure, and is removed from the air gap and placed in a part of the iron core, that is, as described above. It has a structure in which it is placed in close contact with the rear part of the core located at the rear stage of the gap.

According to the present invention, in a voice coil type motor comprising a moving coil and a fixed magnetic circuit, a columnar iron core consisting of a front part and a rear part, and a yoke provided around the outside of the columnar iron core are provided. an external yoke which holds a magnetic pole surface on the inner surface of a tapered front part facing the front part of the columnar iron core with a certain gap therebetween; The fixed magnetic circuit is formed by a permanent magnet that is tightly held and generates a magnetic flux flow in a direction perpendicular to the center line of the columnar core, and the movable coil is connected between the front part of the columnar core and the external yoke. A voice coil type motor is provided, which is characterized in that the motor is disposed within a constant gap between magnetic pole faces.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

Figures 3A and 3B show one example of a voice coil type motor according to the present invention.
FIG. 3 is a sectional view showing main parts in an example.

In FIGS. 3A and 3B, 12 is a moving coil similar to the conventional one, and 14' is a fixed magnetic circuit section according to the present invention.

The fixed magnetic circuit section 14' has a front section 36a and a rear section 3.
6b, a yoke part 38 provided around the core 36 and having a magnetic pole surface 38a facing the front part 36a of the core 36 through the air gap 26, and a yoke part 38 that is connected to the rear part 36b of the core 36. A permanent magnet 22' is held between the iron part 38 and a non-magnetic holding plate 40 provided on the rear surface of the iron core 36.

The permanent magnet 22' in this embodiment is formed of a high coercive force material such as ferrite material and has an annular shape, and is made of a N
- It has an 8-complement sequence.

Therefore, the magnetic flux generated from the permanent magnet 22' flows perpendicularly to the center line of the iron core 36 into the rear part 36b of the iron core 36, and then flows through the iron core toward the front part 36aK, and then passes through the air gap 26. It flows into the yoke 38 from the magnetic pole face 38a, and then returns to the permanent magnet 22' via the yoke 38.

When passing through the air gap 26, electromagnetic interaction occurs with the current flowing through the movable coil 12, thereby moving the movable coil 12 in the axial direction.

The arrows in FIG. 3A indicate the circulation path of the magnetic flux.

4A and 4B are cross-sectional views showing other embodiments of the voice coil type motor according to the present invention;

Compared to the embodiment shown in Figure B, the overall shape of the motor is square.

That is, the embodiment shown in FIGS. 4A and 4B is composed of a moving coil 12 and a fixed magnetic circuit section 14'', and the fixed magnetic circuit section 14'' has an iron core 36' (front section 36'a, rear section 36'). 'b), rectangular yoke part 38', iron core 36'
It is formed by four plate-shaped magnet pieces 22'' held between the rear part 36'b of the yoke part 38' and the rear part of the yoke part 38', and a non-magnetic holding plate 40'.

In the embodiment shown in Figs. 4A and 4B, the overall shape of the motor is square as described above, and the axial length of each magnet piece 22'' is different from that in the embodiment shown in Figs. 3A and 3B.
From the axial length L2 of the rear portion 36'b of the iron core 36',
It is formed to be longer by lengths m and n at the front and rear ends, respectively, as shown in the figure.

However, the magnetic flux flow of the magnetic circuit section 14'' according to this embodiment also exits from each magnet piece 22'', flows into the iron core 36' in a direction perpendicular to the center line, and then flows through the iron core 36'. From the magnetic pole face 38'a through the air gap 26 to the yoke 38'
and then passes through the yoke 38' to the permanent magnet 22.
This embodiment is similar to the embodiment shown in FIGS. 3A and 3B in that it forms a magnetic flux flow that returns to ".".

As mentioned above, according to the present invention, a structure is adopted in which the permanent magnets 22' or 22'' that generate magnetic flux are arranged at the rear part 36b or 36'b of the iron core 36 or 36'. The following advantageous effects can be obtained.

That is, (1) In any of the embodiments shown in FIGS. 3A, B and 4A, B, in the fixed magnetic circuit 14' or 14", the permanent magnet 22' or 22" is excluded from the front portion having the air gap 26. Because of this, it is possible to create a compact shape with the outer shape and dimensions narrowed toward the front, and this allows for greater freedom of installation when assembling and installing the voice coil motor according to the present invention into various devices. Sufficient space can be secured,
Increased installation flexibility.

(2) Factors that increase the density of magnetic flux passing through the air gap 26 can be increased.

That is, this point can be explained in the conventional example shown in Figures 1A and B and in the conventional example shown in Figures 4A and B.
In the case of the structure according to the present invention shown in FIG. 1, when the gap formation conditions and the magnetic flux leakage conditions are compared and examined under the same conditions, the following equation is obtained.

(Conventional example)... (Present invention)... In both of the above equations, the contents of each symbol are as follows.

Bg, Bg'; Magnetic flux density passing through the air gap 26.

K, K/: Constants related to the operating point and leakage coefficient of the permanent magnets 22, 22''.

W: Width dimension of permanent magnets 22 and 22''.

t1=L1! The axial length dimension of the cavity 26.

L2: Axial length of permanent magnet 22''.

D: Average diameter of voids.

In both of the above equations, if the gap formation conditions and magnetic flux leakage conditions are the same, then is equal to a constant.

Therefore, in the case of the fixed magnetic circuit section 14'' according to the present invention, the axial length dimension of the permanent magnet 22'' as seen from the punched hole also affects the magnetic flux density passing through the air gap 26, compared to the conventional case. It can be understood that L2/L1 contributes to increasing the magnetic flux density.

(3) The distribution characteristics of the magnetic flux density passing through the air gap 26 are flattened according to the present invention.

That is, the configuration of the magnetic circuit section in the conventional voice coil type motor has non-flat characteristics as shown by the arcuate curve C1, as already described with reference to FIG.

For this reason, it was necessary to ensure a sufficient axial dimension of the permanent magnet 22 in consideration of this non-flat characteristic.

However, according to the present invention, since the permanent magnet 22' or 22'' is removed from the air gap 26, leakage magnetic flux from these permanent magnets directly passes through the air gap 26, which affects the magnetic flux density distribution characteristic. Therefore, a magnetic flux density distribution having sufficiently flat characteristics as shown by curve C2 in FIG. 2 can be obtained.

As a result, the dimension corresponding to the dimension α in the conventional example described above can be made sufficiently small, and conversely, by allowing the same dimension α as in the conventional example, it is possible to obtain the advantage that the magnetic flux density in the air gap 26 is increased. It becomes possible to obtain.

(4) Furthermore, according to the embodiment of the present invention shown in FIGS. 4A and 4B, the length of the permanent magnet 22'' in the same direction is determined from the length L2 in the axial direction at the rear portion 36'b of the iron core 36', as described above. By increasing the length by the dimensions m and n, it is possible to reduce the leakage magnetic flux, which has the effect of effectively concentrating the magnetic flux passing through the air gap 26.

(5) Generally, the temperature of the permanent magnet in the fixed magnetic circuit increases due to the heat generated by the moving coil, and as a result, the density of magnetic flux passing through the air gap 26 decreases.

In particular, when the permanent magnet is made of a ferrite material, the effect is significant because the ferrite material has a large temperature coefficient.

However, according to the structure of the fixed magnetic circuit section according to the present invention, since the permanent magnets 22' and 22'' are spaced apart from the moving coil 12, the influence of heat generated by the moving coil can be reduced.

According to the present invention, in order to compensate for the decrease in magnetic flux density due to temperature rise, the non-magnetic holding plate 40,40' provided on the rear surface of the iron core 36 or 36' is made of a magnetic shunt alloy or the like having a relatively large temperature coefficient. The temperature compensation described above can be achieved when formed using

On this point, 1A. With the structure of the fixed magnetic circuit in the conventional voice coil type motor shown in FIG. B, it is completely impossible to provide such a correction means.

As is clear from the above explanation, the voice coil motor according to the present invention can skillfully achieve high speed and high output by increasing the magnetic flux density.

[Brief Description of the Drawings] Figures 1A and 1B are cross-sectional views showing structural examples of conventional voice coil motors, and Figure 2 is magnetic flux distribution in the conventional voice coil motor and the voice coil motor according to the present invention. Graphs showing the characteristics, FIGS. 3A and 3 and 3B are cross-sectional views showing the structure of a voice coil motor according to an embodiment of the present invention, and FIGS. 4A and 4B are according to another embodiment of the present invention. FIG. 2 is a cross-sectional view showing the structure of a voice coil motor. In the figure, 12... moving coil, 14', 14''
...Fixed magnetic circuit section, 22', 22"...
... Permanent magnet and permanent magnet piece, 26 ... Air gap, 36 , 36' ... Iron core, 36 a ,
36'a"-"core forward section, 36b. 36'b... Core rear part, 38, 38'...
...Yoke, 38a, 38'a...Magnetic pole surface, 4
0,40'...Nonmagnetic holding plate.

Claims (2)

[Scope of utility model registration request] (1) In a voice coil type motor comprising a moving coil and a fixed magnetic circuit, there is provided a columnar iron core consisting of a front part and a rear part, and a yoke provided around the outside of the columnar iron core, and a yoke provided at the front of the columnar iron core. an external yoke holding a magnetic pole surface on the inner surface of a tapered front part facing the columnar core with a certain gap therebetween; a rear part of the columnar iron core; a permanent magnet that generates a magnetic flux flow in a direction perpendicular to the centerline of the iron core; A voice coil type motor characterized by being placed within a gap. (2) Utility Model Registration The voice coil motor according to claim 1, wherein the permanent magnet is composed of a plurality of permanent magnet pieces, both of which are oriented in the same polar direction with respect to the iron core.