JPH02299453A - Voice coil motor - Google Patents

Abstract

PURPOSE:To miniaturize a magnetic circuit by a method wherein both rims of a permanent magnet along the locus of the swinging arc of a coil are provided with the centers of curvatures thereof at the side of the supporting point of the shaft of a movable member while the permanent magnet is constituted so that the radius of curvature of the inside rim thereof is smaller than the radius of curvature of the outside rim of the same. CONSTITUTION:The inside rim Mi and the outside rim Mo of a permanent magnet 16, which are along the locus of the swinging circle of a coil 20, are provided with the centers of curvatures Oi, Oo at the side of the supporting point Oc of the shaft of a movable member while the radius of curvature Ri of the inside rim Mi is designed so as to be smaller than the radius of curvature Ro of the outside rim Mo. According to this constitution, the length of the permanent magnet 16 in the orthogonal direction with respect to the locus C of the swinging circle of the coil 20 becomes short when the coil 20 is positioned at the center of the permanent magnet 16 but becomes longer when the coil 20 is positioned at the end of the permanent magnet 16. Accordingly, superposed areas Sc, Se of the coil 20 and the permanent magnet 16 are increased when the coil 20 approaches to the end of the permanent magnet 16. According to this method, the size of the permanent magnet 16 may be minimized and a magnetic circuit may be miniaturized.

Description

[Detailed description of the invention] [Industrial application field].

The present invention relates to a voice coil motor, and more particularly, to a voice coil motor in which the permanent magnets constituting the magnetic circuit have an arcuate shape with wide ends, thereby achieving flat thrust-displacement characteristics. It is something.

This voice coil motor is suitable for, for example, an actuator for positioning a magnetic head of a fixed magnetic disk drive device.

[Prior Art] Voice coil motors that perform positioning drive by combining a magnetic circuit and a moving coil are conventionally known, and various types have been developed depending on the structure of the magnetic circuit, the magnetic properties of the permanent magnet used, the shape of the moving coil, etc. has been done. One of them uses a magnetic circuit consisting of a plate-shaped central yoke that serves as the central pole, permanent magnets that face each side of the central yoke through a gap and serve as the outer poles, and a yoke that surrounds the outside of these permanent magnets. ,
There is a structure in which a solenoid-like coil is arranged so as to surround the central yoke and is pivotally supported so as to be swingable along the central yoke.

Due to the shape of the yoke and central yoke, this structure is usually
It is called a "Japanese character-shaped" voice coil motor.

In the prior art, no particular consideration is given to the shape of the permanent magnet used.

[Problem to be solved by the invention] In recent years, fixed magnetic disk drive devices have been increasing in capacity, speed,
With the demand for miniaturization, high thrust, flat thrust-displacement characteristics, and miniaturization are desired. If the thrust is small, the access time will be long, and if the thrust is not constant with respect to displacement, the access time will vary. High thrust was achieved using a borrowed M magnet. However, flattening of the thrust-displacement characteristics and miniaturization are contradictory, so a method for solving these two p problems simultaneously is required.

In the prior art, attempts have been made to solve the decrease in thrust force caused by the decrease in the strength of the magnetic field near both ends of the permanent magnet by taking the following measures. There are two methods: one is to provide a circuit in the voice coil motor drive circuit that takes into account the reduction in thrust force (compensation circuit method), and the other is to extend the permanent magnet to the outside of the required oscillation area of the coil to reduce the magnetic field within the required oscillation area. This is a method (magnet magnification method) to prevent this.

However, the former compensation circuit method has the disadvantage that the circuit is complicated by the compensation circuit, and the latter magnet enlargement method has the problem that the magnetic circuit itself becomes large.

The purpose of the present invention is to reduce the fluctuation of thrust force with respect to displacement without using a compensation circuit or a large magnet as described above.
Another object of the present invention is to provide a voice coil motor that can be miniaturized by minimizing the size of the magnet.

[Means for Solving the Problems] The voice coil motor according to the present invention basically consists of a combination of a magnetic circuit and a movable member, similar to the conventional motor. The magnetic circuit consists of a plate-shaped central yoke that serves as a central pole, permanent magnets that face each side of the central yoke with a gap therebetween and serve as outer poles, and a yoke that surrounds the outside of these.The movable member is connected to the central yoke. It has a structure in which a solenoid-shaped coil surrounding the central yoke is pivotably supported along the central yoke.

In order to achieve the above object, the present invention provides that both edges of the permanent magnet along the oscillating arc locus of the coil have centers of curvature on the fulcrum side of the movable member, and the radius of curvature of the inner edge is smaller than that of the outer edge, which is a distinctive feature.

In the present invention, the outer edge of the permanent magnet includes a case where the outer edge of the permanent magnet has a straight line shape, which is the limit where the radius of curvature is the maximum. Further, the curved surface does not necessarily have to be a circular arc, and may have a shape close to a circular arc.

[Function] As described above, if both edges of the permanent magnet have their centers of curvature on the fulcrum side of the movable member, and the radius of curvature of the inner edge is smaller than that of the outer edge, the coil and permanent The area where the coil overlaps with the magnet increases as the coil approaches the end of the permanent magnet.

That is, normally, the decrease in the strength of the magnetic field near the end of the permanent magnet is compensated for by an increase in the area where the permanent magnet and the coil overlap, and it is possible to suppress a decrease in the thrust force at the end of the permanent magnet.

Furthermore, since both edges of the permanent magnet (edges along the arcuate locus of the coil's swing) are curved in the same direction, the permanent magnet can be small, making it possible to downsize the magnetic circuit.

[Example] The overall configuration of a voice coil motor according to the present invention is shown in FIG.
Consists of a combination of 2.

The magnetic circuit 10 includes a plate-shaped central yoke I4 serving as a central pole, permanent magnets 16 facing each other via gears and magnets and serving as outer poles, and a yoke 1 surrounding the outside of the plate-shaped central yoke I4.
It consists of 8.

The movable member 12 has a structure in which a solenoid-shaped coil 20 surrounding the central yoke 14 is supported by a rotating shaft 22 so as to be swingable along the central yoke 14.

A feature of the invention is particularly the shape of the permanent magnet 16. Third
A projected view from the Y direction of the figure is shown in FIG. 1, which shows the relationship between the position of the coil 20 and the shape of the permanent magnet 16.

In the permanent magnet 16, the inner and outer edges Mi and Mo along the swing arc locus C of the coil 20 are both bent toward the axis Oc side of the movable member.

00, and the radius of curvature Ri of the inner edge M+ is set smaller than the radius of curvature Ro of the outer edge Mo (
That is, Ri < RO) m In this way, as shown in FIG. When the coil 20 and the permanent magnet 16 overlap, the area 3c and S are short.
e (shaded area) increases closer to the end of the permanent magnet 16 (Sc<Se).

As the coil 20 moves tS from the center, the strength of the magnetic field decreases, but the decrease in thrust F is compensated for by increasing the area where the coil 20 and the permanent magnet 16 overlap.

Here, the thrust force F of the voice coil motor is given by F=B I L (where ■ is the current, L is the effective length of the coil,
B is the integral along the length of the coil of the magnetic field strength perpendicular to the direction of current flow). In other words, the decrease in the strength of the magnetic field near the end of the permanent magnet 16 is compensated for by increasing the effective length of the coil 20 from Lc to Le and the area to be integrated from Sc to Se. Fluctuations in thrust force F are suppressed.

In practice, the curvatures of both edges of the permanent magnet 16 are determined so that the magnetic field strength, which decreases as it approaches the end of the permanent magnet 16, can be almost completely offset by variations in the effective length of the coil 20. .

Next, FIG. 4 shows the comparison results of the thrust force F with the case of the permanent magnet shape (comparative example) shown by the broken line in FIG. 2. In FIG. 4, the solid line shows the product of the present invention, and the broken line shows the comparative example. . Over the entire required swing range of the coil, the thrust force F of the product of the present invention is flatter than that of the comparative example. In the case of the comparative example, in order to improve this, the permanent magnet must be made larger than the required swing range of the coil.

The situation is shown in FIG. 5, and the permanent magnet 16 indicated by a solid line is a product of the present invention. On the other hand, the permanent magnet 16a shown by the imaginary line is a comparative example.

In this structure where both the outer and inner edges have the same center of curvature, the permanent magnet 16a must necessarily be large, and correspondingly, the center yoke and the outer yoke are also shaped as shown by imaginary lines. It gets bigger.

FIG. 6 is an explanatory view showing another embodiment of the present invention. In the present invention, the outer edge M of the permanent magnet 16 is shown.

includes the linear case where the radius of curvature is the maximum. The figure shows this. Even in this case, it is possible to achieve a reduction in size of the permanent magnet similar to that shown in FIG.

Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to only such a configuration.

The curved surfaces at both edges of the permanent magnet do not necessarily have to be complete circular arcs, but may have a shape close to a circular arc, for example, a part of an ellipse, or a circular arc formed by connecting a plurality of line segments.

[Effects of the Invention] As described above, in the voice coil motor according to the present invention, both edges of both permanent magnets along the swing arc locus of the coil have centers of curvature on the fulcrum side of the movable member, In addition, since the radius of curvature of the inner edge is smaller than that of the outer edge, the thrust-displacement characteristics can be flattened without using a compensation circuit as in the prior art, and the dimensions of the permanent magnet can be minimized. This has the effect of making the magnetic circuit smaller.

Furthermore, since the present invention has a central yoke and a magnetic circuit closed by the yokes on both sides, there is little magnetic flux leakage and it is difficult to have an adverse magnetic effect on the outside, and from this point of view, it is possible to miniaturize. Are suitable.

Therefore, according to the present invention, it is possible to obtain a small and lightweight magnetic head positioning actuator with high access speed and little variation.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the shape of the permanent magnet of the voice coil motor according to the present invention and the positional relationship between the coils, and Fig. 2 is an explanatory diagram showing the effective length of the coil and the overlapping relationship between the coil and the permanent magnet. , Fig. 3 is a schematic configuration diagram of a voice coil motor, Fig. 4 is a graph showing the relationship between the required coil swing range and thrust between the inventive product and a comparative example, and Fig. 5 is a graph showing the relationship between the inventive product and the comparative example. FIG. 6 is an explanatory diagram showing the dimensions of the magnetic circuit, and FIG. 6 is an explanatory diagram showing another embodiment of the present invention. 10... Magnetic circuit, 12... Movable member, 14...
Central yoke, 16... permanent magnet, 18... yoke,
20... Coil, C... Swing arc locus of coil, M
i...inner edge of permanent magnet, MO...outer edge of permanent magnet, Oj...center of curvature of inner edge, Oo・
... Center of curvature of the outer edge, Oc... Axis fulcrum of the coil. Patent Applicant Fuji Electrochemical Co., Ltd. Representative Minoru Shigemi Figure 1 ＼ '00 0 Total Figure 3 Figure 4 Maximum left angle Center Right maximum swing angle Figure 5 Figure 6

Claims (1)

[Claims] 1. Consisting of a combination of a magnetic circuit and a movable member, the magnetic circuit has a plate-shaped central yoke serving as a central pole, and opposing sides of the plate-shaped central yoke with a gap therebetween to serve as outer poles. The voice coil motor is composed of a permanent magnet and a yoke surrounding the outside thereof, and the movable member has a solenoid-like coil surrounding the central yoke and is pivotally supported along the central yoke so as to be swingable. Both edges of both permanent magnets along the oscillating arc locus of the coil have centers of curvature on the axis support side of the movable member, and the radius of curvature of the inner edge is smaller than that of the outer edge. Features a voice coil motor. 2. The voice coil motor according to claim 1, wherein the outer edge of the permanent magnet is linear.