JP2000184679A - Vcm magnetic circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the leakage magnetic field of upper and lower parts of a magnetic circuit by installing two permanent magnet thin plates while the plates are brought into contact with an end face, so that the direction of magnetization is different by specified degrees, and at the same time are brought into contact with the outside of each magnetic body yoke with polarity opposite to that of a flat permanent magnet. SOLUTION: A thin-plate permanent magnet 44 (a counter magnet) is provided on the external surface of upper/lower up yokes 41a and 41b in a VCM magnetic circuit. However, in the counter magnet 44, two permanent magnet thin plates are brought into contact each other on an end face, so that the directions of magnetization are different by 180 degrees and are magnetized with polarity opposite to that of a permanent magnet 40 opposing while sandwiching the up yokes 41s and 41b. Also, in the case of magnet one-side arrangement, two permanent magnet thin plates are brought into contact each other on an end face so that the directions of magnetization are different by 180 degrees and are magnetized with polarity opposite to that of a permanent magnet 40. More specifically, the counter magnet 44 is arranged on the upper surface of the upper up yoke 41a and the lower surface of the lower up yoke 41b, thus achieving high flux density and miniaturization, and reducing a leakage magnetic field without increasing costs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magnetic circuit of a voice coil motor used for head access of a hard disk drive as a storage device of a computer.

[0002]

2. Description of the Related Art As shown in a plan view in FIG. 1, a hard disk drive as a storage device of a computer has a rotating media disk 15 coated with a recording medium.
In addition, a magnetic head 14 is provided at the tip of a movable arm 13 that rotates about a pivot 12, and the magnetic head 14 is positioned to write or read data.
The positioning of the magnetic head is performed by a voice coil motor (hereinafter referred to as VCM) magnetic circuit 1 that generates a two-pole magnetic field in the air gap.
This is performed by supplying a current to the coil 11 in the zero position and controlling the current. The size of a media disk is 2.5 inches or 3.5 inches.

FIG. 2 is a schematic view of the magnetic circuit 10 shown in FIG. A magnetic circuit of a VCM used for magnetic head access is provided with two plate-like magnetic yokes, ie, up yokes (hereinafter referred to as up yokes) 21a and 21b, as shown in FIG. Plate permanent magnets (hereinafter referred to as “permanent magnets”) 20a, 20 which are arranged in a single plate shape with two permanent magnets being in contact with each other at their end faces so that the directions of magnetization are different by 180 °.
b is in contact with the opposing surface side of the up yoke, and the two-sided magnet arrangement structure provided with a gap therebetween, and two plate-like up yokes 21a and 21b face each other as shown in FIG. The two permanent magnets are arranged in contact with each other at their end faces so that the directions of magnetization are different by 180 degrees. There is a one-sided magnet arrangement structure provided in contact with one surface. FIGS. 2A and 2B are side views. A coil 23 is arranged in the gap, and two up yokes 21a,
21 b are connected by a side plate 22.

[0004]

In recent years, higher capacity and higher speed have been desired for hard disk drives.
There is a need to increase the magnetic flux density in the air gap of the magnetic circuit. In order to increase the magnetic flux density, there are methods of narrowing the air gap, increasing the thickness of the permanent magnet, or improving the magnetic properties of the permanent magnet. Since the coil is arranged in the air gap, there is a limit in the dimensions. Generally, the performance is increased by increasing the performance and thickness of the permanent magnet. However, with the demand for miniaturization of equipment, especially the thinning of notebook personal computers, even if the thickness of the permanent magnet is increased, the overall height of the magnetic circuit cannot be increased. Accordingly, the thickness of the up yoke in contact with the permanent magnet is reduced.

[0005] Since the up yoke has a function of efficiently flowing the magnetic flux of the permanent magnet into the air gap, when the up yoke becomes thinner, the magnetic flux leaking out of the air gap increases. The magnetic flux leaking out of the magnetic circuit is called a leakage magnetic field (leakage magnetic flux). If the leakage magnetic field is large in the VCM magnetic circuit, it affects the magnetic head and the media disk, causing an error when writing or reading data, and causing the VCM magnetic circuit to fail. It adversely affects substrates disposed above and below and media disks other than hard disks, for example, floppy (registered trademark) disks. The specific value of the leakage magnetic field is 2 at the magnetic head 14 in FIG.
It is considered that the G is preferably 100 G or less from the VCM magnetic circuit of the media disk 15, and 100 G or less at each of 10 mm above and below the outer surface of the VCM magnetic circuit 10. In many VCM magnetic circuits, since the thickness of the up yoke cannot be made sufficiently large, the leakage magnetic field above and below the VCM magnetic circuit is large, which is a problem. The leakage magnetic field of the magnetic head portion and the media disk portion rarely causes a problem.

Here, the leakage magnetic field generated above and below the VCM magnetic circuit will be described with reference to FIG. Note that a direction perpendicular to the up yoke facing surface is hereinafter referred to as a vertical direction. The leakage magnetic field above the up yoke is maximum immediately above the reversal of the magnetic pole of the permanent magnet of the VCM magnetic circuit, and its direction is a horizontal component due to the symmetry of the magnetic circuit. As shown in FIG. 3A, the magnetization 30 of the permanent magnet 35 is changed to M01, M02, M0.
3, M04, and magnetization 3 of the up yokes 36a, 36b
1 is modeled as M11 and M12. Since the side plate (not shown) is also a magnetic material, magnetization occurs, but the side plate (not shown) is thinner than the up yoke and thus has a small degree of influence. The leakage magnetic field (H) 32 above the upper up yoke 36a is a magnetic field due to the magnetization of the upper up yoke and the magnetization of the permanent magnet, and the magnetization (M) of the permanent magnet
01 to M04) 30 and weakened by the magnetization (M11) of the upper up yoke 36a. Further, the influence of the magnetization (M12) of the lower up yoke 36b on the leakage magnetic field 32 above the up yoke is ignored because the distance is far and small. As shown in FIG. 3B, the magnetic field is obtained by superimposing the magnetization of the magnetic material of each part, which can be calculated by Coulomb's law. According to Coulomb's law, the leakage magnetic field (Hx) 32 on the up yoke shown in FIGS.
The distance r (r01, r01) is proportional to the magnitude (M01 to M04) of the magnetization M of the permanent magnet, the cosine of the angle θ between the magnetization vector (vector m) and the direction vector (vector r), and the volume V of the magnetic material. r11). Note that r01 is the distance between the permanent magnet and the leakage magnetic field, and r11 is the distance between the up yoke and the leakage magnetic field. In other words, in order to increase the magnetic flux density in the air gap of the VCM magnetic circuit, increasing the magnetization of the permanent magnet, increasing the volume of the permanent magnet, and further reducing the volume of the up yoke require the leakage magnetic field 32 above the up yoke.
Will increase. Usually, since the up yoke does not have a sufficient thickness, the effect of the magnetization of the permanent magnet is stronger than the effect of the magnetization of the up yoke, and the leakage magnetic field 32 has the same direction as the magnetization of the up yoke. . The present invention
VCM at low cost while realizing high magnetic flux density and miniaturization
It is an object to reduce a leakage magnetic field above and below a magnetic circuit.

[0007]

According to the present invention, two plate-shaped magnetic yokes are disposed to face each other, and two permanent magnets are provided.
Contact each other at the end faces so that the magnetization directions differ by 180 degrees.
A magnetic circuit having a structure in which two permanent magnets are provided, wherein two permanent magnet thin plates are provided in such a manner that two plate-shaped permanent magnets arranged in the form of two plates are in contact with the opposing surface of the magnetic yoke and provided with a gap therebetween. Are arranged in contact with each other so that the directions of magnetization are 180 degrees different from each other at the end faces, and are in contact with the outer surface of each magnetic yoke with the polarity opposite to the polarity of the flat permanent magnet opposed to the magnetic yoke. A VCM magnetic circuit characterized in that: Alternatively, two plate-shaped magnetic yokes are disposed to face each other, and two permanent magnets are disposed in one plate in contact with each other at their end faces so that the directions of magnetization are different by 180 degrees. A magnetic circuit having a magnet one-sided structure in which a plate-shaped permanent magnet is provided in contact with one of the opposing surfaces of the magnetic yoke,
The two permanent magnet thin plates are placed in contact with each other at their end faces so that the directions of magnetization are different by 180 degrees, and are installed in contact with the outer surface of each magnetic yoke with the polarity opposite to that of the flat permanent magnet. It is a VCM magnetic circuit that is a feature.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS The invention is explained in more detail by means of the drawings. FIG. 4A shows a case where the magnets of the VCM magnetic circuit are arranged on both sides of the magnet, and FIG. 4B shows a case where the magnets of the VCM magnetic circuit are arranged on one side of the magnet. In order to reduce the leakage magnetic field above and below the up yoke, in the VCM magnetic circuit of the present invention, thin permanent magnets 44 are disposed on the outer surfaces of the upper and lower up yokes 41a and 41b, respectively. Hereinafter, the thin plate-shaped permanent magnet 44 is referred to as a counter magnet 44. As shown in FIG. 4 (a), the counter magnet 44 is composed of two permanent magnet thin plates which are in contact with each other at their end faces so that the directions of magnetization are different by 180 degrees, and which face each other with the up yokes 41a and 41b interposed therebetween. It is magnetized to the polarity opposite to the polarity of 40. Further, in the one-sided magnet arrangement shown in FIG. 4B, the counter magnet 44 is formed by two permanent magnet thin plates having a magnetization direction of 180 °.
The magnets are in contact with each other at their end faces so as to be different from each other, and are magnetized to the polarity opposite to the polarity of the permanent magnet 40. The counter magnets are disposed on the outer surfaces of the upper and lower up yokes 41a and 41b regardless of the arrangement of the permanent magnets on both sides and on one side. That is, the counter magnets 44 are arranged on the upper surface of the upper up yoke 41a and on the lower surface of the lower up yoke 41b.

FIG. 5A and FIG. 5B show the V of the present invention.
The operation of the counter magnet in the CM magnetic circuit will be described. As described above, conventionally, a leakage magnetic field (H) 52 is generated above the up yoke in the same direction as the magnetization (M11) 51 of the up yoke (see FIG. 5A). FIG. 5 (b)
In the VCM magnetic circuit of the present invention shown in FIG.
a, the counter magnet 58 disposed outside the
In the direction opposite to the leakage magnetic field 52 of the M magnetic circuit, Hcm
By generating the magnetic field 55 indicated by, and superposing the magnetic field 55 and the leakage magnetic field 52, the leakage magnetic field 52 can be canceled out and reduced. The counter magnet 58 has two magnetization directions of 18
The permanent magnets 56 are provided in contact with each other at the end faces so as to differ by 0 degrees, and are magnetized in the M41 and M42 directions opposite to the magnetization directions M01, M02, M03, and M04 of the permanent magnet 56. Since the magnetic field 54 created by the counter magnet may be a magnetic field weak enough to offset the leakage magnetic field 52, the thickness of the counter magnet is 0.5
mm, and the total height of the VCM magnetic circuit is 1 mm.
Since the number of magnetic circuits is increased only, the problem that the magnetic circuit becomes large does not need to be considered. The upper up yoke 57
Although the leakage magnetic field above a has been described, the leakage magnetic field below the lower up yoke 57b can be similarly reduced by the counter magnet 58. The material of the counter magnet is Nd rolled into a plate
-Fe-B-based bonded magnets, Sm-Co-based bonded magnets, ferrite-based bonded magnets, and the like. Further, the counter magnet may be fixed to the outer surface of the up yoke with an adhesive.

[0010]

Next, examples of the present invention will be described. (Embodiment) In a VCM magnetic circuit in which magnets are arranged on both sides, as shown in FIG. 5B, a counter magnet 58 is arranged on the outer surface side of the upper and lower up yokes 57a and 57b, and the VCM magnetic circuit of the present invention is assembled. 5A and the one assembled in a conventional manner as shown in FIG.
The leakage magnetic field at the position of mm was measured. As a result, the leakage magnetic field of the VCM magnetic circuit of the present invention was 5 G, and the leakage magnetic field of the conventional one was 110 G.

The material of the up yoke was low carbon steel (residual magnetization of 12,000 G, coercive force of 4 Oe), the permanent magnet of the VCM magnetic circuit was an Nd-Fe-B sintered magnet, and the maximum energy product was 45 MGOe. . The size of the magnetic circuit is 3.5 m.
m, magnet thickness 4.5mm, up yoke thickness 4mm,
For 2.5 inch hard disk drive. Also,
The material of the counter magnet was Nd-Fe-B based magnetic powder, which was rolled into a plate using rubber as a binder, and had a maximum energy product of 6MGOe. The size of the counter magnet is a thin plate having a width of 30 mm, a depth of 15 mm, and a thickness of 0.5 mm, and is magnetized with two poles whose magnetization direction is inverted by 180 degrees so as to divide the width into two. The upper and lower counter magnets were attached to the outer surfaces of the upper and lower up yokes, respectively, so that the surfaces where the magnetic poles of the counter magnet were reversed and the surfaces where the magnetic poles of the permanent magnets were reversed were matched.

[0012]

According to the present invention, the leakage magnetic field can be reduced to zero theoretically. Moreover, since a permanent magnet is used, there is almost no increase in the cost of the process. Higher magnetic flux density and miniaturization of VCM magnetic circuits due to higher capacity, higher speed, and smaller size of hard disk drives in the future. It is.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing a hard disk drive.

2A and 2B are schematic cross-sectional views illustrating a conventional VCM magnetic circuit for a hard disk, wherein FIG. 2A shows a case where magnets are arranged on both sides, and FIG. 2B shows a case where magnets are arranged on one side.

FIG. 3 is a diagram illustrating a conventional VCM magnetic circuit;
(A) is a schematic sectional view for explaining a magnetization distribution of a VCM magnetic circuit, and (b) is a schematic view for explaining a magnetic field generated by a magnetic dipole.

FIG. 4 is a schematic sectional view of a VCM magnetic circuit of the present invention;
(A) shows a case where magnets are arranged on both sides, and (b) shows a case where magnets are arranged on one side.

FIG. 5A is a schematic cross-sectional view illustrating a leakage magnetic field of a conventional VCM magnetic circuit. (B) It is an outline sectional view explaining an operation of a counter magnet in the present invention.

[Explanation of symbols]

10 VCM magnetic circuit 11 Coil 12 Pivot 13 Movable arm 14 Magnetic head 15 {Media disks 20a, 20b, 35, 40, 56} Permanent magnets 21a, 21b, 36a, 36b, 41a, 41b, 5
7a, 57b {up yoke 22, 42} side plate 23, 43} coil 30, 50 {permanent magnet magnetization 31, 51} up yoke magnetization 32, 52} yoke Upper leakage magnetic field (magnetic field due to magnetization of upper up yoke and magnetization of permanent magnet) 44, 58 ° Counter magnet (thin plate-shaped permanent magnet) 54 ° Magnetization of counter magnet 55 ° Magnetic field due to magnetization of counter magnet r01 {Distance between permanent magnet and leakage magnetic field r11} Distance between up yoke and leakage magnetic field

Claims (2)

[Claims] 1. Two plate-shaped magnetic yokes are arranged to face each other, and two permanent magnets are arranged in a single plate-like shape in contact with each other at their end faces so that the directions of magnetization differ by 180 degrees. A magnetic circuit provided with a plate-shaped permanent magnet provided in contact with the opposing surface side of the magnetic yoke and provided with an air gap between the two permanent magnet thin plates so that the magnetization directions are different by 180 degrees. A VCM magnetic circuit, wherein the VCM magnetic circuits are provided so as to be in contact with each other at the end faces and in contact with the outer surface of each magnetic yoke with a polarity opposite to the polarity of the plate-shaped permanent magnet facing the magnetic yoke. 2. A two plate-shaped magnetic yoke is disposed facing each other, and two permanent magnets are disposed in a single plate shape in contact with each other at their end faces so that the directions of magnetization are different by 180 degrees. A magnetic circuit provided with the provided plate-shaped permanent magnet in contact with one of the opposing surfaces of the magnetic yoke, wherein the two permanent magnet thin plates have end faces that are different from each other so that the magnetization directions are different by 180 degrees. A VCM magnetic circuit, wherein the VCM magnetic circuit is disposed in contact with the outer surface of each magnetic yoke with a polarity opposite to that of the plate-shaped permanent magnet.