JPH02278526A - Magnetic driving structure - Google Patents

Abstract

PURPOSE:To obtain the magnet of low height and small outer diameter by using a magnet member composed of a circular arc-shaped sintered magnet. CONSTITUTION:Magnet members 25a and 25b are magnetized so that a magnetic flux can be generated from an outer circumferential surface toward an inner circumferential surface. Then, a pair of these magnet members 25a and 25b are coupled and a magnet 25 for focusing, which is C-shaped as a whole, is formed. Thus, since the circular arc-shaped magnet members 25a and 25b, for which the sintered magnet is used, can be respectively magnetized so that the magnetic flux can be generated in a direction passing through the inner and outer circumferential surfaces, the magnetic flux can be generated in an almost radial direction toward a guide shaft 2 by the C-shaped magnet 25 for focusing. Accordingly, by using the sintered magnet of large magnetic force, the magnetic flux to be generated in the radial direction can be obtained without overlapping ring-shaped yoke members and the dimension in the height direction can be lowered. Further, since the magnetic flux can be generated in the radial direction without using a plastic magnet, the outer diameter of the magnet 25 for focusing can be made small.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) The present invention relates to a magnet provided to surround a coil in order to supply magnetic flux in the radial direction of the coil provided in a movable body. The present invention relates to a magnetic drive structure having a magnetic drive structure.

<Prior Art> Various actuators for driving the objective lens of an optical head used in an optical disk drive etc. have been proposed. The holder is supported by a guide shaft so as to be rotatable around the axis and slidable in the axial direction, and is wound around the outer periphery of a cylindrical coil bobbin that is integral with the holder and coaxial with the guide shaft. The holding body is driven in both focusing and tracking directions by the magnetic action between the focusing drive coil, the tracking drive coil attached to the coil, and fixed magnetic units such as permanent magnets corresponding to both drive coils. A shaft-sliding actuator is disclosed.

By the way, when a sintered magnet is formed into an annular shape, it is magnetized so that a magnetic flux is generated in the axial direction, and in order to supply magnetic flux in the radial direction of the coil, as shown in the above publication, , an annular yoke member is coaxially superimposed on an annular magnet, and the inner peripheral surface of the annular yoke member is used as a magnetic pole surface.

Therefore, there is a problem in that the size of the annular magnet in the axial direction, that is, the height direction increases, and the actuator becomes larger.

Furthermore, when a plastic magnet is formed into an annular shape, it can be magnetized so that magnetic flux is generated in the radial direction. However, due to its magnetized structure, plastic magnets cannot be formed with relatively small inner diameters, and the magnetic force is smaller than that of sintered magnets, so there is a problem that the outer diameter of the magnets becomes large.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the main object of the present invention is to provide a magnet having a large magnetic force and a small outer diameter for an annular or C-shaped magnet. The object of the present invention is to provide a magnetic drive structure that can be made small.

[Structure of the Invention] <Means for Solving the Problems> According to the present invention, the movable body is guided movably in the axial direction of the guide shaft and in at least one direction around the axis; A coil provided on a movable body and a plurality of arc-shaped magnet members are coupled in the circumferential direction so as to form an annular or C-shape surrounding the coil in order to supply magnetic flux in the radial direction of the coil. This is achieved by providing a magnetic drive structure characterized by having a magnet.

In this way, the magnet member made of an arc-shaped sintered magnet can be magnetized in the direction in which the magnetic flux passes through its inner and outer circumferential surfaces, and they can be coupled in the circumferential direction. hand,
By forming the magnet into an annular or C-shape, magnetic flux can be generated generally in the radial direction, so a small-diameter magnet can be formed using a sintered magnet with a large magnetic force.

<Embodiments> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 to 4 show the structure of an actuator for an optical head based on the present invention. A guide shaft 2 made of a round bar-shaped magnetic material is erected at the center of a bottom wall 1a of a base yoke 1 made of a magnetic material and serving as a bottomed cylindrical lower casing. The guide shaft 2 has a holder 4 which has a deformed elliptical shape long in the diameter direction and supports the objective lens 3 at one free end thereof, and a holder 4 in the center thereof in the vertical direction in FIG. The fittingly formed bearing is supported by the hole 5 so as to be rotatable around the axis of the guide shaft 2 and slidable in the axial direction. The holding body 4 is made of, for example, pps resin, which is a material having a large specific modulus of elasticity, which is the magnitude of bending elasticity with respect to specific gravity, in order to improve the natural frequency.

A cylindrical portion 6 coaxial with the bearing hole 5 is provided at the lower center of the holder 4 and protrudes downward, and the lower end surface 6 of the cylindrical portion 6
A focusing drive coil 7 wound annularly is provided so as to surround the guide shaft 2 . A predetermined gap is defined between the inner peripheral surface of the focusing drive coil 7 and the guide shaft 2.

A support portion 9 for integrally supporting the objective lens 3 is formed at the left free end in the longitudinal direction of the holder 4 in FIG. A support hole 11 is formed in this support portion 9, and a support hole 11 is formed in the bearing hole 5, and a cylindrical lens holder 8 having a cylindrical shape having an objective lens 3 coaxially and integrally therein is formed therein. It is fixed. An annular rib 12 is formed on the outer periphery of the support hole 11 on the upper end surface of the support portion 9 so as to surround the second portion of the lens holder 8 .

As clearly shown in FIG. 2, the annular rib 12 extends from the middle of the support portion 9 to the farthest left side in FIG. It is cut off with a cutting surface facing diagonally downward at the end. still,
The lower portion of the support portion 9 is similarly cut off with a cut surface facing diagonally upward at the farthest end.

A counterweight 13 for balancing the weight of the objective lens 3 is attached to the other longitudinal end of the holder 4, that is, the right end in FIG.

The counterweight 13 has a cylindrical shape with a bottom,
The bottom wall thereof has a slit 14 formed in a direction perpendicular to the rotating direction of the holder 4. Further, a light emitting diode 16 fixed to the lower surface of the top plate portion 15a of the cover yoke 15 and a photodiode 17 as a light receiving sensor fixed to the bottom wall 1a of the base yoke 1 are connected through the slit 14. They are arranged so as to face each other.

The light emitted from the light emitting diode 16 is irradiated onto the photodiode 17 through the slit 14, and this photodiode 17 is made up of two photodiode elements equally divided in the tracking direction, and is placed at the neutral position of the holder 4. The irradiation pattern through the slit 14 is divided into two equal parts at the dividing line "2". Therefore, when the holder 4 rotates in the tracking direction, a difference in light amount occurs between both photodiode elements, so that deviation from the neutral position can be easily detected. By doing so, it is possible to control the objective lens 3 so that it is always held at a neutral position with respect to the tracking direction.

As shown in FIG. 3, a skirt portion 4a having a surface continuous with the outer peripheral surface of the support portion 9 is formed in a portion of the outer peripheral portion of the holder 4 adjacent to the support portion 9 described above. A tracking drive coil 18a having a rectangular annular shape is attached to a flat support surface formed on the outer wall surface of the skirt portion 4a. A similar tracking drive coil 18b is attached. Further, the bearing of the holder 4 has a through hole in a portion between the hole 5 and the tracking drive coils 18a and 18b that penetrates downward along the axis of the bearing hole 5 and has a generally fan-shaped cross section. 19 are provided respectively.

Between the supporting part 9 of the holding body 4 and the skirt part 4a adjacent to each other in the clockwise direction of the guide shaft 2 in FIG. A concave portion 21 is formed between the matching skirt portion 4b and the concave portion 21, which opens toward the outer peripheral surface and lower side of the holder 4 in order to reduce the weight of the holder 4. Engagement pieces 22 are stepped downwardly on the top plate portions of these biconcave crotch portions 21, respectively. The engagement pieces 22 and locking pieces 23 provided on corresponding parts of the peripheral wall 1b of the base yoke 1 are connected to each other via an annular rubber body 24, and the base yoke 1
The holder 4 is elastically supported by. Here, the annular rubber body 24 is for maintaining the neutral position of the holder 4, and is preferably made of silicone rubber that has a relatively large damping effect and good temperature characteristics.

The above-mentioned through hole 19 is formed integrally with the base yoke 1 and rises from the bottom wall 1a side thereof, and the through hole 19
An inner yoke 27 having an arcuate cross section having a generally complementary shape to 9 is received.

The peripheral wall portion 1b of the base yoke 1 is open on the side facing the inner yoke 27, and the top plate portion 15a of the cover yoke 15 is open.
On the inner circumferential surface of the outer yoke 28, which is formed so as to fall from the yoke and substantially fill the opening thereof, a pair of magnet members 29a having a shape substantially complementary to that of the inner yoke 27 are provided.
A trafking magnet 29 is provided in which magnetic poles 29b are arranged so that opposite magnetic poles are adjacent to each other.

Note that a yoke member 2 is provided between the lower part of the inner yoke 27 and the lower part of the outer yoke 28 for magnetically bridging the two.
0 is set.

A cover yoke 15 made of a magnetic material and serving as an upper casing for covering the upper opening surface of the base yoke 1 is integrally attached to the second part of the base yoke 1. The top plate portion 15a of the cover yoke 15 is provided with a mirror body 31 for passing the laser light passing through the objective lens 3 in the vertical direction, and the bottom wall 1a of the base yoke 1 is provided with a mirror body 31 for passing the laser light passing through the objective lens 3 in the vertical direction. A mirror body 31 is provided to bend the optical axis of the laser beam at right angles and guide it to the outside.

Further, the upper end surface of the guide shaft 2 is fixed to the top plate portion 15a of the cover yoke 15, and the guide shaft 2 is fixedly supported at both ends by the base yoke 1 and the cover yoke 15.

As clearly shown in FIG. 5, a C-shaped focusing magnet 25 is arranged around the outer periphery of the focusing drive coil 7 so as to avoid the hole 30 provided in the bottom wall 1a of the base yoke 1. It is set up. This focusing magnet 25 is formed by connecting a pair of arc-shaped magnet members 25a and 25b that are symmetrical to each other in the circumferential direction, and includes the above-mentioned focusing drive coil 7.
is fixed to the inner circumferential surface of a circumferential wall 26 made of a C-shaped magnetic material, which is erected on the bottom wall 1a of the base yoke 1 so as to surround it with a predetermined gap. has been done.

By the way, in general, when a sintered magnet is formed in a closed ring shape, it cannot be magnetized to generate magnetic flux in the radial direction. A magnetic flux is generated in the radial direction via the circumferential surface. Therefore, since the yoke is stacked on top of the magnet, it tends to increase in height. Also, by forming a plastic magnet into an annular shape, it can be magnetized to generate magnetic flux in the radial direction.
The magnetic force is weak and the inner diameter is relatively large due to the magnetization conditions, making it difficult to downsize the actuator.

In this embodiment, as shown in FIG. 6, a pair of magnet members 25a and 25b, which are magnetized so that magnetic flux is generated from the outer peripheral surface to the inner peripheral surface, are combined to form a C-shape as a whole. A focusing magnet 25 is formed. By doing so, the arc-shaped magnet members 25a and 25b using sintered magnets can be magnetized so as to generate magnetic flux in a direction passing through the inner and outer peripheral surfaces thereof. Therefore, the C-shaped focusing magnet 25 generates a generally radial magnetic flux toward the guide shaft 2.

Therefore, by using a sintered magnet with a large magnetic force and without overlapping the annular yoke members, a magnetic flux generated in the radial direction can be obtained, and the dimension in the height direction can be reduced. Further, since a radial magnetic flux can be generated without using a plastic magnet, the outer diameter of the focusing magnet 25 can be reduced.

Further, in the above embodiment □, the focusing magnet 25 is divided into two parts, but as shown in FIG.
A three-part structure formed by combining 5c to 25e may also be used.

In this case, the magnetic flux can be made more uniform in the radial direction than in a two-part structure. Furthermore, although it is possible to divide it into four or more parts, it is appropriate to divide it into three to four parts depending on the ease of manufacturing and assembly. In addition, in the embodiment, the focusing magnet 25 was formed in a C-shape.
It may be formed into a ring shape.

In the optical head actuator constructed in this manner, the guide shaft 2 is made of a magnetic material with a high saturation magnetic flux density such as silicon steel, and is a part of the yoke of the magnetic circuit for driving in the focusing direction. The magnetic flux formed in the magnetic gear pump between the guide shaft 2 and the focusing magnet 25 passes through the focusing drive coil 7. Therefore, by appropriately adjusting the direction and strength of the current supplied to the focusing drive coil 7, the holder 4 can be controlled to be driven in the axial direction of the guide shaft 2.

On the other hand, as described above, the tracking magnet 29 is provided such that the opposite magnetic poles of both the magnet members 29a and 29b are adjacent to each other, that is, the sides forming a pair in the rotational direction of the tracking drive coil 18a118b. The magnetic flux is made to penetrate in opposite directions to each other. Therefore, by appropriately adjusting the direction and strength of the current supplied to the tracking drive coils 18a, 18b, the pair of sides of the tracking drive coils 18a, 18b are subjected to magnetic action in the same direction. This results in efficient drive control of the holder 4 in the tracking direction around the axis.

[Effects of the Invention] As described above, according to the present invention, by using a magnet member made of arc-shaped sintered magnets, the approximate radius of the annular or C-shaped magnet formed by connecting them in the circumferential direction Since it is possible to generate magnetic flux in the direction, 1
Compared to the case where a sintered magnet consisting of two annular bodies is used, there is no need to overlap the annular yoke members, so the height dimension can be reduced, and there is no need to use plastic magnets (to increase the magnetic flux in the radial direction). This has extremely great effects, such as making it possible to reduce the outer diameter and downsizing the device using the magnet according to the present invention.

[Brief explanation of drawings]

FIG. 1 is a plan view showing two sides of a casing of an actuator for an optical head according to the present invention. FIG. 2 is a side sectional view taken along the line ■--■ in FIG. 1. FIG. 3 is a side sectional view taken along the line ■--■ in FIG. 1. FIG. 4 is a side sectional view taken along the line IV--IV in FIG. 1. FIG. 5 is a sectional view taken along the line ■--■ in FIG. 2. FIG. 6 is an explanatory diagram showing the direction of the magnetic flux of the focusing magnet yh. FIG. 7 is a diagram similar to FIG. 6 showing another embodiment. 1...Base yoke 1a...Bottom wall 1b...Peripheral wall part 2...Guide shaft 3...Objective lens
4... Holder 4a, 4b... Skirt part 5... Bearing is hole 6... Cylindrical part 6a... Lower end surface 7... Focusing drive coil 8... Lens holder 9... - Support part 11... Support hole 12... Annular rib 13... Counter weight 14... Slit 15... Cover yoke 15
a...Top plate part 16...Light emitting diode 17.
...Photodiodes 18a, 18b...Tracking drive coil 19.
...Through hole 20...Yoke member 21...Concave portion 22...Engagement piece 3...Locking piece
24... Annular rubber body 5... Focusing magnets 5a to 25e... Magnet member 6... Circumferential wall 27... Inner yoke 8...
Outer yoke 9...Tracking magnets 9a, 29b...Magnetic member

Claims (1)

[Claims] (1) A movable body guided so as to be movable in at least one direction of the axis of the guide shaft and around the axis; a coil provided on the movable body; annular or C to surround
1. A magnetic drive structure comprising a magnet formed by connecting a plurality of arc-shaped magnet members in the circumferential direction so as to form a letter shape.