CN105989985B

CN105989985B - Magnet, pickup device using the same, and method for manufacturing the same

Info

Publication number: CN105989985B
Application number: CN201610034649.4A
Authority: CN
Inventors: 小岛雅美; 木下佳久; 稻叶安信; 矶上慎二
Original assignee: National Institute Of Higher Education; Alpine Electronics Inc
Current assignee: National Institute Of Higher Education; Alpine Electronics Inc
Priority date: 2015-03-19
Filing date: 2016-01-19
Publication date: 2020-11-27
Anticipated expiration: 2036-01-19
Also published as: JP2016178137A; JP6536880B2; CN105989985A

Abstract

The invention provides a magnet which magnetizes one magnetic block and makes the opposite surfaces of the magnetic block have the same magnetic pole. The magnetic block (10) is a bonded block in which Sm-Fe-N or Nd-Fe-B magnetic powder is fixed by a binder resin such as a polyamide resin. A first field core (21a) is opposed to a first surface (11) of a magnetic block (10), a second magnetic core (21b) is opposed to a second surface (12), and a third magnetic core (21c) is opposed to a third surface (13). Then, by applying an excitation pulse magnetic field, the first surface (11) and the second surface (12) are magnetized to S poles, and the third surface (13) and the fourth surface (14) are magnetized to N poles. Wherein the magnetic pole of the N pole on the third surface can be stronger than that on the fourth surface (14).

Description

Magnet, pickup device using the same, and method for manufacturing the same

Technical Field

The present invention relates to a magnet magnetized in the same polarity on a surface facing in a first direction and magnetized in the opposite polarity on a surface facing in a second direction, a pickup device using the magnet, and a method for manufacturing the magnet.

Background

Patent document 1 describes a halbach magnetic circuit for a linear motor.

The Halbach magnet is composed of a first sintered magnet and two second sintered magnets located on both sides thereof. The first sintered magnets are magnetized in a direction orthogonal to the main surface, and the second sintered magnets are magnetized so that the direction of magnetization is inclined toward the main surface. This concentrates the magnetic flux in front of the main surface of the first sintered magnet, thereby generating a magnetic field generating space having a high magnetic flux density.

In the halbach magnetic circuit described in patent document 1, the second sintered magnets are fixed to both sides of the first sintered magnet by the adhesive, and the direction of magnetization of the second sintered magnets is inclined, so that when the second sintered magnets are arranged on both sides of the first sintered magnet, a force to move the second sintered magnets acts, and it is difficult to position the magnets and firmly fix the magnets by the adhesive. This necessitates the use of an expensive and strong adhesive or a fixing jig, and the bonding work is required, which lowers the production efficiency of the magnet.

Patent document 2 also discloses a permanent magnet for a linear actuator. The permanent magnet is composed of one magnet, and two opposite surfaces are magnetized to S poles, and the surface orthogonal to the two surfaces is magnetized to N poles.

The first magnetizing means for forming the permanent magnet is configured to magnetize the easy magnetization axis in advance so that the easy magnetization axis has magnetic anisotropy in accordance with the orientation of the magnetic pole in the manufacturing process of the permanent magnet, and then magnetize the permanent magnet. In the second magnetizing mechanism, an isotropic magnet that is not magnetized and is not anisotropic is used, and the magnetizing direction is oriented by magnetizing the isotropic magnet.

Documents of the prior art

Patent document

Patent document 1 japanese patent application laid-open No. 2010-50440

Japanese patent laid-open publication No. 2002-369492 of patent document 2

Problems to be solved by the invention

Unlike the permanent magnet described in patent document 1, the permanent magnet described in patent document 2 does not require an adhesive to fix a plurality of magnets.

However, in the first magnetizing mechanism, it is necessary to use a magnetic block having an easy axis of magnetization with magnetic anisotropy suitable for the orientation of the magnetic pole. Since this magnetic block is injection molded in a magnetic field, an orientation mold having a special structure for injection molding needs to be used, which increases the manufacturing cost.

In the second magnetizing mechanism, an isotropic magnet that is not magnetically anisotropic is used, and the orientations of the easy magnetization axes of the fine magnetic crystal grains in the isotropic magnet are randomly bonded, so that the residual magnetic flux density after magnetization is lower than that of an anisotropic magnet in which the easy magnetization axes of all the crystal grains are oriented in the same orientation. In general, a magnet obtained by magnetizing a magnetic material having an equivalent polarity may have a residual magnetic flux density of 1/2 or less, as compared with a magnet obtained by magnetizing a magnetic material having an anisotropic polarity.

Disclosure of Invention

The present invention has been made to solve the above conventional problems, and an object of the present invention is to provide a magnet, a pickup device using the magnet, and a method of manufacturing the magnet, which can be configured by one magnet, do not require complicated anisotropy, can use a general one-axis anisotropic magnet, and can improve the generated magnetic flux density.

Means for solving the problems

The magnet according to the present invention is a magnet in which each surface of a magnetic block is magnetized, the surfaces being a first surface and a second surface facing each other in a first direction and a third surface and a fourth surface facing each other in a second direction intersecting the first direction, wherein an axis of easy magnetization of the magnetic block is oriented in the first direction, the first surface and the second surface are magnetized to have the same polarity, and the third surface and the fourth surface are magnetized to have a polarity opposite to that of the first surface and the second surface.

In the magnet according to the present invention, the magnetic flux density of the third surface may be higher than the magnetic flux density of the fourth surface, among the magnetic flux densities of the positions at the same distance from the third surface and the fourth surface, respectively.

However, the magnet of the present invention may be: in the magnetic flux densities at positions at the same distance from the third surface and the fourth surface, the magnetic flux densities of the third surface and the fourth surface are substantially equal to each other.

In the magnet of the present invention, the magnetic body block is, for example, an adhesive block in which a powdery magnetic body is fixed by a resin material.

The pickup device of the present invention is characterized by comprising: a movable portion having the magnet and an objective lens opposed to the recording medium; a support member for movably supporting the movable portion; and a coil provided on the fixed side and facing the magnet.

Further, a pickup apparatus according to the present invention includes: a movable portion having the magnet and an objective lens opposed to the recording medium; a support member for movably supporting the movable portion; and a coil provided on a fixed side and facing the magnet, wherein a position of a support portion of the support member for supporting the movable portion is shifted toward the fourth surface side with respect to a center of gravity of the movable portion.

The pickup device of the present invention can be configured to: a first drive coil for moving the movable portion in the optical axis direction of the objective lens is opposed to at least one of the first to fourth surfaces, a current is applied to the first drive coil in a direction intersecting the optical axis direction, a second drive coil for moving the movable portion in the direction intersecting the optical axis is opposed to at least one of a plurality of corner portions formed by the intersection of the surfaces of the magnets, and a current flows in the optical axis direction in the second drive coil.

Next, a method for manufacturing a magnet according to the present invention is characterized in that a magnetic block having a first surface and a second surface opposed to each other in a first direction, a third surface and a fourth surface opposed to each other in a second direction intersecting the first direction, and an easy magnetization axis directed in the first direction is used, a first yoke is opposed to the first surface, a second yoke is opposed to the second surface, magnetizing magnetic fields for magnetization directed in opposite directions are applied from the respective yokes to the first surface and the second surface, the first surface and the second surface are magnetized to the same polarity, and the third surface and the fourth surface are magnetized to magnetic poles different from those of the first surface and the second surface.

In the method for manufacturing a magnet according to the present invention, a third yoke is opposed to the third surface, and a magnetizing field that is wound around between the first yoke and the third yoke and a magnetizing field that is wound around between the second yoke and the third yoke are formed so that the third surface has a higher magnetic flux density than the fourth surface in magnetic flux densities at positions that are at the same distance from the third surface and the fourth surface, respectively.

Effects of the invention

In the magnet of the present invention, a magnetic block having magnetic anisotropy in which an easy magnetization axis is oriented in one direction is magnetized, and the facing surfaces form the same magnetic pole. Since the magnetic block having the easy magnetization axis oriented in one direction is used, it is not necessary to mold a magnetic block having a special structure having magnetic anisotropy in the magnetization direction in a magnetic field as described in patent document 2, and a magnetic block that is a general commercially available product can be used. In addition, in the present invention, since the magnetic blocks having magnetic anisotropy are used, the magnetic force to be held can be increased as compared with a magnet obtained by magnetizing a magnetic block having magnetic anisotropy. In addition, the third surface and the fourth surface that are magnetized to the same magnetic pole may be configured such that the magnetic flux density from the third surface is high.

The pickup device of the present invention can realize a so-called moving magnet system by constituting at least a part of the movable portion with the magnet. In this aspect, since it is not necessary to connect the coil wiring to the movable portion, the structure can be simplified.

Next, in the method for manufacturing a magnet according to the present invention, since the magnetic blocks having the easy magnetization axes oriented in one direction are magnetized to have the same magnetic pole on the opposite surfaces, a high-magnetic magnet can be manufactured in a relatively simple process without using a magnetic block having a special magnetic anisotropy.

Drawings

Fig. 1 is a perspective view showing a magnet according to an embodiment of the present invention.

Fig. 2 is an end view of the magnet shown in fig. 1.

Fig. 3(a) is an explanatory diagram of a magnetizing apparatus for magnetizing the magnet shown in fig. 1, and fig. 3(b) is a conceptual diagram of an excitation pulse voltage waveform for magnetization.

Fig. 4(a) is a diagram showing the magnetic flux density perpendicularly coming out from the third and fourth surfaces of the magnet shown in fig. 1, and fig. 4(b) is a diagram showing the magnetic flux density perpendicularly coming out from the third and fourth surfaces of the magnet of the first comparative example.

Fig. 5 is a diagram showing magnetic flux densities perpendicularly emerging from the third surface and the fourth surface of the magnet of the second comparative example.

Fig. 6 is a diagram for explaining the difference in the magnetization state between the easy magnetization axis direction and the hard magnetization axis direction of the magnet having magnetic anisotropy.

Fig. 7 is a perspective view showing a pickup device according to an embodiment of the present invention.

Fig. 8 is a top view of the pickup device shown in fig. 7.

Fig. 9 is a side view showing a main part of the pickup device shown in fig. 7.

Fig. 10 is a perspective view showing a state in which a magnet of a movable portion of the pickup device shown in fig. 7 and a driving coil face each other.

In the figure:

1 magnet

10 magnetic block

11 first side

12 second side

13 third surface

14 th surface

20 magnetizing device

21 magnetizing yoke

21a first yoke

21b second yoke

21c third yoke

22a first excitation coil

22b second field coil

22c third field coil

25 drive circuit

30 pick-up device

34 sling

40 movable part

41 magnet

41a first side

41b second face

41c third surface

41d fourth surface

43 Objective lens

51 first drive coil

52 second drive coil

Easy axis of EA magnetization

Ia drive current

I1, I2 drive Current

Detailed Description

Fig. 1 and 2 show a magnet 1 according to an embodiment of the present invention. In this specification, a state before magnetization is referred to as a magnetic block 10, and a state in which the magnetic block 10 is magnetized is referred to as a magnet 1. In the embodiment of the present invention, since the magnet 1 is a bonded magnet, the magnetic block 10 before magnetization is a bonded block.

The bonded mass is obtained by fixing magnetic powder as a powdery magnetic material with a binder resin. The magnetic powder is Sm-Fe-N series (samarium-iron-nitrogen series) or Nd-Fe-B series (neodymium-iron-boron series). Alternatively, a plurality of kinds of magnetic powders may be used in combination. The binder resin is PA (polyamide resin). The magnetic blocks 10 can be called rare-earth blocks, and the finished magnet 1 is a rare-earth magnet.

The magnetic block 10 shown in FIGS. 1 and 2 is a rectangular parallelepiped, and has a planar shape with a length L of 24mm, a width W of 12mm, and a height H of 6 mm. The magnetic block 10 has a first direction in the X direction and a second direction in the Z direction. The first surface 11 and the second surface 12 face each other in the first direction (X direction), and the third surface 13 and the fourth surface 14 face each other in the second direction (Z direction).

The magnetic block 10 has magnetic anisotropy, and the easy magnetization axis EA is oriented in the X direction almost entirely in the block. The magnetic block 10 can be molded by injecting a mixture of magnetic powder and binder resin into the inside of a mold, and at this time, the magnetic block 10 having magnetic anisotropy with the easy magnetization axis EA oriented in the X direction is formed by molding in a magnetic field oriented in the X direction. Alternatively, the magnetic block 10 may be formed by so-called powder compaction in which magnetic powder mixed with a binder resin is pressed by a mold. In this case, the magnetic powder is compression molded in the Z direction in a magnetic field oriented in the X direction, whereby the magnetic anisotropic magnetic block 10 having the easy magnetization axis EA oriented in the X direction is formed.

The magnetic block 10 is an adhesive block and can be formed by injection molding using a mold, and therefore has a degree of freedom in shape. For example, the third surface 13 may be a convex surface, or a protrusion protruding in the Z direction may be formed on a part of the third surface 13, and a step may be formed so that the center portion of the third surface 13 becomes higher. This is also the same in the fourth face 14. In the present specification, even if the third surface 13 or the like has a shape having a protrusion as described above, the entirety surrounded by L × W is defined as the third surface 13 or the like.

Fig. 3(a) shows a magnetizing apparatus 20.

The magnetizing apparatus 20 has a magnetizing yoke 21. The magnetizing yoke 21 is formed of a soft magnetic material such as a Ni — Fe alloy (nickel-iron alloy). The magnetizing yoke 21 includes a first yoke 21a facing the first surface 11 of the magnetic block 10, a second yoke 21b facing the second surface 12, and a third yoke 21c facing the third surface 13. The first yoke 21a, the second yoke 21b, and the third yoke 21c are integrally formed.

As shown in fig. 3(a), the first excitation coil 22a is wound around the first yoke 21a, the second excitation coil 22b is wound around the second yoke 21b, and the third excitation coil 22c is wound around the third yoke 21 c. The

exciting coils

22a, 22b, and 22c are connected in series, and a drive circuit 25 is connected to the

exciting coils

22a, 22b, and 22 c.

The drive circuit 25 has a dc power supply 26 and a switch 27. The switch 27 is formed of an active element such as a transistor, and is switched on and off at a predetermined cycle. When the switch 27 is opened, a drive voltage having a waveform shown in fig. 3(b) is generated by a time constant determined by the capacitor C, the choke coil L, and the fixed resistor R, and the voltage is applied to the

exciting coils

22a, 22b, and 22C. The half width T of the driving voltage shown in fig. 3(b) is about 130 μ s.

At the moment when the switch 27 of the drive circuit 25 is switched from off to on, a rapidly rising excitation current flows through the

exciting coils

22a, 22b, and 22c based on the voltage waveform of fig. 3 (b). By this excitation current, the excitation magnetic flux Φ 1 is wound back between the first yoke 21a and the third yoke 21c, and the excitation magnetic flux Φ 2 is wound back between the second yoke 21b and the third yoke 21c inside the magnetizing yoke 21.

By repeatedly applying the magnetic field fluxes Φ 1 and Φ 2, as shown in fig. 2, the first surface 11 and the second surface 12 of the magnetic block 10 are magnetized to the S-pole, and the third surface 13 and the fourth surface 14 are magnetized to the N-pole, whereby the magnet 1 is completed.

The magnetic block 10 shown in fig. 1 and 2 has magnetic anisotropy, and the easy axis EA of magnetization is oriented in the first direction (X direction) in the entire block, and the second direction (Z direction) is the hard axis direction in the entire block.

FIG. 6 shows an M-H curve when a magnetic block having 5mm on one side is magnetized. The horizontal axis represents the magnitude of the excitation magnetic field externally applied to the magnetic block. (+) and (-) of the horizontal axis mean the difference in the orientation of the magnetic field. The vertical axis represents the magnetization for magnetizing the magnetic block. The solid line in fig. 6 shows the change in the magnetization of the magnetic block when an excitation field is applied in the direction of the easy axis EA, and the broken line shows the change in the magnetization of the magnetic block when an excitation field is applied in the direction of the hard axis HA.

As shown in fig. 6, when an excitation magnetic field is applied from the outside, the magnetization in the easy axis EA direction is easy, and the magnetization in the hard axis HA direction is extremely difficult inside the magnetic block.

As shown in fig. 2, since the magnetization easy axis EA of the magnetic block 10 is oriented in the first direction (X direction), when the excitation magnetic field directed from the first yoke 21a to the first face 11 and the excitation magnetic field directed from the second yoke 21b to the second face 12 are simultaneously applied, the magnetization is performed in the magnetic block 10 from the first face 11 to the left direction in the drawing and from the second face 12 to the right direction in the drawing. In the central portion of the magnetic block 10, the magnetic field from the first surface 11 and the magnetic field from the second surface 12 are trapped to form a cusped magnetic field (cusped magnetic field). At this time, the third yoke 21c is also excited at the same time, and the magnetic field is generated from the third surface 13 toward the third yoke 21c, so that the cusped magnetic field at the center inside the magnetic block 10 is oriented in the direction of the third yoke 21 c.

In the magnet thus magnetized, the first surface 11 and the second surface 12 facing each other in the first direction (X direction) are magnetized as S poles, and the third surface 13 and the fourth surface 14 facing each other in the second direction (Z direction) are magnetized as N poles. However, since the cusped magnetic field at the center inside the magnetic block 10 is attracted by the third yoke 21c, the magnetic force of the N-pole on the third surface 13 after the magnetization is stronger than the magnetic force of the N-pole on the fourth surface 14.

Fig. 4(a) is a diagram actually measuring the magnetic flux density emitted from the magnet 1 according to the embodiment of the present invention, and fig. 4(b) is a diagram actually measuring the magnetic flux density emitted from the magnet in the first comparative example. Fig. 5 is a graph in which the magnetic flux density emitted from the magnet in the second comparative example was actually measured.

In the embodiment of the present invention and the first and second comparative examples, the same magnetic block 10 was used. The magnetic powder is a mixture of Sm-Fe-N system and Nd-Fe-B system, and the adhesive resin is PA. A rectangular parallelepiped magnetic block 10 was formed by injection molding so that the length L was 24mm, the width W was 12mm, and the height H was 6 mm.

Fig. 4(a) shows that the magnetization easy axis EA of the magnetic block 10 according to the embodiment of the present invention is oriented in the first direction (X direction). The magnetization easy axis EA of comparative examples 1 and 2 is oriented in the second direction (Z direction), and the first direction (X direction) is the hard axis direction.

Fig. 4(a) shows an actual measurement value of the magnet 1 in which the magnetization is performed by using the magnet block 10 whose first direction is the easy magnetization axis EA, and the first surface 11 is opposed to the first yoke 21a, the second surface 12 is opposed to the second yoke 21b, and the third surface 13 is opposed to the third yoke 21c by using the magnetizing device 20 shown in fig. 3 (a).

Fig. 4(b) shows an actual measurement value of the magnet of the second comparative example in which the magnetization is performed using the magnet block whose second direction is the easy magnetization axis EA, and the first surface 11 is opposed to the first yoke 21a, the second surface 12 is opposed to the second yoke 21b, and the third surface 13 is opposed to the third yoke 21c using the magnetizing device 20 shown in fig. 3 (a).

Fig. 5 shows actual measurement values of a magnet of a third comparative example in which a magnetic block having the second direction (Z direction) set as the easy magnetization axis EA is magnetized in the same state as a normal magnet by applying an excitation magnetic field in the Z direction. In fig. 5, the third surface 13 is magnetized to have an N-pole, and the fourth surface 14 is magnetized to have an S-pole.

The horizontal axes in fig. 4(a), 4(b), and 5 are the midpoints in the longitudinal direction L of the magnetic block 10 shown in fig. 1, and indicate the distance from the origin (0) on the X axis. The vertical axes in fig. 4(a), 4(b), and 5 indicate the magnetic flux density, the value of (+) indicates the magnetic flux density of the magnetic flux directed upward in the figure, and the value of (-) indicates the magnetic flux density of the magnetic flux directed downward in the figure.

In each of fig. 4(a), 4(b), and 5, the line indicated by the black dots indicates the magnetic flux density measured at a position 4mm away from the third surface 13 upward in the Z direction in the magnet 1 according to the embodiment of the present invention and the magnets according to comparative examples 1 and 2. The line shown by the white dots indicates the magnetic flux density measured at a position 4mm away from the fourth face 14 downward in the Z direction.

As shown in fig. 4(a), in the magnet 1 of the embodiment, the magnetic force of the N-pole on the third surface 13 is larger than the magnetic force of the N-pole on the fourth surface 14.

When fig. 4(a) and 4(b) are compared, it is preferable that the first and

second yokes

21a and 21b apply a magnetizing field to the magnetic block 10 in the direction of the easy magnetization axis EA, and the third yoke 21c is opposed to the direction orthogonal to the easy magnetization axis EA, so that the magnetization is performed as shown in fig. 3 (a).

Further, as is clear from a comparison between fig. 4(a) and fig. 5, the magnetic force of the N pole of the third surface 13 can be increased in the embodiment of the present invention as compared with the second comparative example in which the magnetization is performed by the magnetization magnetic field in the Z direction with the Z direction as the easy magnetization axis direction.

The magnet 1 according to the embodiment of the present invention uses a general magnetic anisotropic magnetic block having the first direction as the easy magnetization axis EA, and can make the magnetic force of the third surface 13 stronger than that of the fourth surface only by facing and magnetizing the yokes from three directions. Further, since the magnet 1 is constituted by 1 magnetic block 10, it is not necessary to join a plurality of magnets, and mass productivity is excellent.

Thus, the magnet 1 of the above embodiment can be used for a small linear actuator or the like.

In fig. 2 and 3(a), the fourth yoke may be opposed to the fourth surface 14, and the third yoke 21c and the fourth yoke may generate the excitation magnetic field in the Z direction in opposite directions. In this case, if the number of turns of the fourth excitation coil wound around the fourth yoke is the same as that of the third excitation coil 22c, the magnetic force of the N pole on the third surface 13 and the magnetic force of the N pole on the fourth surface 14 can be set to the same strength.

Alternatively, the magnet block 10 may be magnetized by facing the yoke to the first surface 11 and the second surface 12 without facing the yoke to the third surface 13 and the fourth surface 14, whereby the first surface 11 and the second surface 12 are S-poles, and the third surface 13 and the fourth surface 14 are N-poles.

Further, if the winding direction of the

exciting coils

22a, 22b, and 22c of the magnetizing device 20 is reversed, it is also possible to form a magnet in which the first surface 11 and the second surface 12 are magnetized to the N pole, and the third surface 13 and the fourth surface 14 are magnetized to the S pole.

Fig. 7 to 10 show a pickup device 30 as an example of use of the magnet 1.

The pickup device 30 is opposed to a recording surface of a hard disk such as a DVD or a CD as a recording medium, and reads information recorded on the recording surface or writes information on the recording surface.

The pickup device 30 has a pickup base 31 as a fixed side. The fixed portion 32 is fixed to the pickup base 31, and the central portion of the suspension support member 33 is fixed to the rear portion thereof. Slings 34 as elastic support members are fixed to both ends of the suspension support member 33 as support members. Two slings 34 are provided at intervals in the radial direction (R direction), and four slings are provided in total.

As shown in fig. 7 and 10, a movable portion 40 is provided at the head of the sling 34. The movable part 40 includes a magnet 41, a holder 42 fixed to an upper portion of the magnet 41, and an objective lens 43 fixed to a central portion of the holder 42.

In the bracket 42, coupling portions 42a are formed by bending on both sides in the radial direction (R direction), and the heads of the four slings 34 are inserted into coupling holes of the coupling portions 42a and fixed by brazing or an adhesive. Fig. 8 and 9 show a connection part between the suspension cable 34 and the connection part 42a as the support part 42 s. The support portion 42s is located closer to the suspension support member 33 than the position where the center of gravity G of the movable portion 40 is located. Further, the center of gravity G is located on the optical axis O of the objective lens 43.

A through hole penetrating in the direction of the optical axis O of the lens is formed directly below the objective lens 43 of the magnet 41. In the pickup device 30, a tilt mirror such as a prism is provided below the movable portion 40, and the through hole is opposed to the tilt mirror. The sensing light emitted from the light emitting element is reflected by the inclined mirror, and is applied to the objective lens 43 through the inside of the through hole. The return light reflected by the recording surface of the optical disk returns in the same path, is reflected by the inclined mirror, and is received by the light receiving element.

As shown in fig. 8 and 10, the magnet 41 has first and

second surfaces

41a and 41b on both sides in the radial direction (R direction), and third and

fourth surfaces

41c and 41d on both sides in the tangential direction (T direction). The magnetic blocks forming the magnet 41 are rare earth bonded blocks similar to those used for the production of the magnet 1 shown in fig. 1 and 2, and the easy magnetization axis EA is oriented in the radial direction (R direction).

The magnetic block is magnetized by a magnetizing device 20 similar to the device shown in fig. 3 (a). The magnetic block is provided with a first surface 41a facing the first yoke 21a, a second surface 41b facing the second yoke 21b, and a third surface 41c facing the third yoke 21c, and is energized and magnetized by the

exciting coils

22a, 22b, and 22 c.

The first surface 41a and the second surface 41b of the magnetized magnet 41 are magnetized to S-poles, and the third surface 41c and the fourth surface 41d are magnetized to N-poles. However, the magnetic force of the N pole of the third surface 41c is stronger than the magnetic force of the N pole of the fourth surface 41 d.

As shown in fig. 7 and 8, a pair of first coil yokes 35 are fixed to the pickup base 31, and a first driving coil (focus driving coil) 51 is wound around each of the first coil yokes 35. The first driving coil 51 faces the third surface 41c and the fourth surface 41d of the magnet 41 of the movable portion 40, and as shown in fig. 10, the driving current Ia flows in a radial direction (R direction) which is a direction perpendicular to the optical axis O in a portion facing each of the

surfaces

41c and 41 d. The movable unit 40 is driven in the focus direction (F direction) by the driving current Ia.

The second coil yokes 36 are fixed to four positions of the pickup base 31, and the second drive coils (tracking drive coils) 52 are supported by the second coil yokes 36. The second driving coil 52 faces the corner of the magnet 41 of the movable portion 40. In the second driving coil 52 positioned before the drawing of fig. 10, the driving current I1 flowing in the optical axis O direction in the portion facing the third surface 41c and the driving current I2 flowing in the optical axis O direction in the portion facing the second surface 41b are oriented in opposite directions. The other three second driving coils 52 are also driven in the radial direction (R direction) by the movable portion 40 as a result of the same or symmetrical current flow as described above.

In the pickup device 30, the movable portion 40 is driven in the focusing direction (F direction) by the driving current Ia flowing through the first driving coil 51, and thereby the sensing light emitted from the objective lens 43 is corrected so as to be focused on the recording surface of the optical disc. The movable unit 40 is driven in the radial direction (R direction) by the drive currents I1 and I2 flowing through the second drive coil 52, and the focus of the sensing light is corrected so as to follow the recording track on the recording surface of the optical disc.

As shown in fig. 9, the support position 42s as the coupling portion between the suspension wire 34 and the coupling portion 42a is set to be shifted toward the fourth surface 41d of the magnet 41 with respect to the center of gravity G of the movable portion 40. As a result, the counterclockwise moment M generated by its own weight always acts on the movable portion 40, and when the movable portion 40 is driven in the focusing direction (F direction), a delay is likely to occur in the tracking performance of the third surface 41c with respect to the fourth surface 41d of the magnet 41. However, since the magnetic force of the N pole of the third surface 41c is stronger than the magnetic force of the N pole of the fourth surface 41d, the corrected driving force F3 generated on the third surface 41c side is larger than the corrected driving force F4 generated on the fourth surface 41d side even if the driving currents Ia flowing through the pair of first driving coils 51 are the same. This makes it possible to correct a delay in response due to a positional deviation between the center of gravity G and the support position 42 s.

When the center of gravity G is not too far away from the support position 42s, the third surface 41c and the fourth surface 41d of the magnet 41 may be magnetized so that the magnetic forces of the N poles are almost the same.

In the pickup device 30 having the above-described structure, since the coil is not provided in the movable portion 40, wiring to the movable portion 40 is not necessary, and the wiring structure can be simplified.

Claims

1. A magnet in which each face of a rectangular parallelepiped magnetic block is magnetized, the faces being a first face and a second face opposed to each other in a first direction and a third face and a fourth face opposed to each other in a second direction intersecting the first direction,

the easy axis of magnetization of the magnetic block is oriented in the first direction,

the first surface and the second surface are magnetized to have the same polarity, the third surface and the fourth surface are magnetized to have a polarity opposite to that of the first surface and the second surface,

the third surface has a higher magnetic flux density than the fourth surface in the magnetic flux densities at positions separated from the third surface and the fourth surface by the same distance, respectively.

2. The magnet according to claim 1,

the magnetic block is an adhesive block in which a powdery magnetic body is fixed by a resin material.

3. A pickup apparatus, comprising:

a movable portion having the magnet according to claim 1 and an objective lens opposed to the recording medium;

a support member for movably supporting the movable portion; and the combination of (a) and (b),

and a coil provided on the fixed side and facing the magnet.

4. The pickup device according to claim 3,

a first drive coil for moving the movable portion in the optical axis direction of the objective lens is opposed to at least one of the first surface to the fourth surface, and a current in a direction intersecting the optical axis direction is applied to the first drive coil,

a second drive coil that moves the movable portion in a direction intersecting the optical axis is opposed to at least one of a plurality of corners where the first surface to the fourth surface of the magnet intersect, and a current flows in the second drive coil in the optical axis direction.

5. A pickup apparatus, comprising:

a support member for movably supporting the movable portion; and

a coil provided on the fixed side and facing the magnet,

the position of the support portion of the support member supporting the movable portion is shifted toward the fourth surface side with respect to the center of gravity of the movable portion.

6. A method for manufacturing a magnet, characterized in that,

a rectangular parallelepiped magnetic block having a first surface and a second surface opposed to each other in a first direction, a third surface and a fourth surface opposed to each other in a second direction intersecting the first direction, and an easy magnetization axis oriented in the first direction is used,

a first yoke facing the first surface and a second yoke facing the second surface, magnetizing magnetic fields having opposite directions from each other from the first surface and the second surface from the yokes, magnetizing the first surface and the second surface to the same polarity, and magnetizing the third surface and the fourth surface to a magnetic pole different from the first surface and the second surface,

7. The method for manufacturing a magnet according to claim 6,

and a third yoke facing the third surface, the third yoke forming a magnetizing field that winds back between the first yoke and the third yoke and a magnetizing field that winds back between the second yoke and the third yoke.