JP2614043B2 - Optical pickup device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an optical pickup device, and more particularly, to a reproducing device or recording device that performs focusing and tracking of a light spot focused on an information recording surface of an optical disc. / Related to an optical pickup device of a reproducing apparatus.

2. Description of the Related Art FIGS. 2 and 3 are an exploded perspective view and a top view showing a conventional optical pickup device disclosed in, for example, Japanese Utility Model Application Laid-Open No. 62-26623. A cylindrical permanent magnet for focus control, (2a) is an outer peripheral yoke that forms a focus magnetic circuit, and (2b) is a magnetic circuit that is continuous with the outer yoke (2a) via a bottom (2c). This is a peripheral yoke, and the permanent magnet 1 is attached to the inner surface of the outer yoke (2a). The outer yoke (2a) and the inner yoke (2b) are made by cutting an iron-based base material, and then are subjected to rust-proof plating.

(3) is a focusing coil, (4) is a support shaft held at a right angle to the inner yoke (2b), and the support shaft (4) slides in the direction of arrow A with the lens holder (5). And is rotatably fitted in the direction of arrow B. An objective lens (6) is fixed to one side of the lens holder (5) at a certain distance from the support shaft (4), and the focusing coil (3) is mounted on a lower cylindrical portion of the lens holder (5). Installed.

Next, the operation will be described. By passing a servo current through the focusing coil (3), the lens holder (5) slides in the direction of arrow A depending on the polarity of the servo current,
Focusing servo is performed by changing the distance between the objective lens (6) and the optical disk (not shown). With this focusing servo, the position of the light beam incident on the objective lens (6) from the Z direction is controlled and focused on the optical disk.

[Problems to be Solved by the Invention] Since the conventional optical pickup device is configured as described above, the inner shaft yoke (2b In order to press-fit the holes, it was necessary to tighten the precision of the press-fit holes.

Therefore, in order to reduce the axial press-fitting accuracy, it is conceivable to manufacture the inner peripheral yoke by a sintering method. In addition, there is no overall advantage in terms of cost, and the yoke constituting the magnetic circuit is desirably continuous without any discontinuity except for the magnetic gap where the drive coil is inserted. It was desired to manufacture the entire magnetic yoke for focusing up to the outer peripheral yoke by sintering.

However, in order to reduce the size of the optical pickup device and ensure the required accuracy, the outer yoke (2a) and the inner yoke (2b)
Since it is impossible to change the shape and the dimensional accuracy of the above, manufacturing the outer yoke and the inner yoke by cutting the iron-based base material has a problem that the cost of the focusing magnetic circuit becomes extremely high.

Also, when manufacturing a magnetic yoke for focusing by sintering, the internal structure is more porous than that of cutting a metal base material, and the density occupied by the magnetic material is low. There was a problem that was weak. For this reason, it is necessary to reduce the size and weight of the lens holder as much as possible. However, when the distance between the objective lens (6) and the support shaft (4) is reduced to reduce the size, the light from the Z direction is not blocked. In addition, the cylindrical focus control permanent magnet (1) and the outer peripheral yoke (2a) must be formed in a modified shape in which a part of the yoke (2a) is cut away.

However, as shown in FIGS. 2 and 3, when the notch is formed so as to lack two points on the circumference forming the outer peripheral yoke, the lower portion (2c) is cut off from the support shaft (4). The distance to the end face of the portion becomes greater as it is closer to the outer peripheral yoke (2a), while the lens holder (5) rotates around the support shaft (4), so that the objective lens (6) is always supported by the support shaft (4).
Since the lens holder (5) is closer to the outer peripheral yoke (2a), the bottom (2c) and the objective lens (6) overlap with each other, so that the objective lens (6) is connected to the outer yoke (2a). Even if it is located near, the distance from the support shaft (4) must be sufficient so as not to overlap with the bottom (2c). As a result, there is a problem that the length of the lens holder (5) becomes longer and the entire optical pickup device becomes larger.

Conversely, the length of the lens holder (5) can be reduced by increasing the area of the cutout portion. However, since the length of the outer peripheral yoke (2a) in the circumferential direction is shortened accordingly, the magnetic flux density is reduced. And the driving force of the driving device is reduced.

When the outer yoke (2a) and the inner yoke (2b) are made by cutting an iron-based base material, there is no problem because a relatively large magnetic flux density can be obtained. Then, since the magnetic flux density of the yoke is smaller than that in the case of cutting, the driving force is weak, and it is not preferable from the viewpoint of securing the driving force to easily reduce the area of the outer peripheral yoke (2a) as described above. was there.

Also, if the objective lens (6) is arranged farther from the support shaft (4) in order to secure the area of the outer yoke (2a),
As described above, since the lens holder (5) itself becomes large and heavy, there is a problem that it is not preferable in the case of the sintering method having a weak driving force.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and can reduce the size and weight of the lens holder and thus the entire optical pickup device, drive the lens holder with a small driving force, and reduce the cost. An object is to obtain an optical pickup device.

[Means for Solving the Problems] An optical pickup device according to the present invention holds an objective lens on one side and is movable in an axial direction and a rotational direction around a support shaft parallel to a direction of a light beam passing through the objective lens. A lens holder, a focusing coil disposed on the lower surface of the lens holder and having a diameter smaller than the distance between the support shaft and the peripheral side of the objective lens, and an outer surface facing the inner surface of the focusing coil in which the support shaft is inserted. A cylindrical inner yoke, an outer yoke provided with a magnet facing the outer surface of the focusing coil, and a bottom surface connecting the inner yoke and the outer yoke at respective lower portions. A magnetic yoke for focusing is formed by the inner yoke, the outer yoke, and the bottom surface, and the lens holder is driven to drive the disk through at least the objective lens. In an optical pickup device having a driving device for focusing a light spot of a light beam focused on a magnetic yoke for focusing, an objective lens and a support shaft are brought close to each other, and an outer yoke is formed so as not to block a light beam passing through the objective lens. Forming a bottom from the outer yoke to the inner yoke to partially cut off and forming a fan-shaped notch through which light rays pass at least from the part where the outer yoke is missing to the lower end extension of the focusing coil as an inner end limit, In addition, a magnetic yoke for focusing is produced by sintering an iron-based powder material,
It has a fitting portion for press-fitting and fixing the support shaft to the inner peripheral yoke.

[Operation] The optical pickup device according to the present invention has a bottom portion extending from the outer yoke, which is partially missing, to the inner yoke, and extending from the missing portion of the outer yoke at least on an extension of the lower end of the focusing coil to an inner end direction. A focusing magnetic yoke having a fan-shaped notch leading to the above-mentioned shape is formed, and a light beam passes through an objective lens that is arranged in the light beam direction so as to overlap the notch portion. Further, since the outer yoke and the inner yoke are manufactured by sintering an iron-based powder material and the support shaft is supported by being pressed into the inner yoke, the magnetic yoke for focusing is made inexpensive.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a driving device for an optical pickup device according to the present invention. In FIG. 1, a focusing magnetic yoke (2) comprising an outer yoke (2a), an inner yoke (2b) and a bottom surface (2c) is shown. By the sintering method of iron-based powder material,
A part of the cylindrical shape is cut into a fan shape so as not to block the light beam. That is, a bottom (2c) is provided to connect the outer yoke (2a) to the inner yoke (2b), and a notch is formed from the portion where the outer yoke (2a) is missing to the inner yoke (2b). Further, since the inner peripheral yoke (2b) is coaxial with the support shaft (4), the distance from the support shaft (4) to the end of the notch is almost the same everywhere, and the closer the distance to the outer yoke (2a), the longer the distance. It will not be. As a result, the objective lens (6) can be brought closer to the support shaft (4) to the vicinity of the inner peripheral yoke (2b), and the lens holder (5) can be made smaller and lighter than before.

Since the lens holder (5) is reduced in weight, the magnetic flux density is reduced by integrally forming the focusing magnetic yoke including the outer yoke (2a), the inner yoke (2b) and the bottom surface (2c) by a sintering method. This contributes to the direction in which the driving force is reduced and the driving force is reduced, so that focusing can be performed as well. Therefore, even if the driving force is reduced, there is an advantage that the entire focusing magnetic yoke can be manufactured inexpensively and lightly by manufacturing the entire focusing magnetic yoke by the sintering method.

In this case, the support shaft (4) is press-fitted into the inner peripheral yoke (2b) and fixed, so that a support mechanism for supporting and fixing the support shaft (4) is not required. Moreover, the inner yoke (2
The accuracy of the press-fit hole of the support shaft (4) of b)
b) made by sintering iron-based powder material,
Since the base material is soft, the accuracy can be reduced as compared with the case where the iron-based base material is cut with the same press input as that of the conventional device. In addition, since the molding is performed by the mold, the dimensional accuracy is small and a constant focusing magnetic circuit can be formed. That is, it can be said that forming the inner peripheral yoke (2b) by the sintering method is preferable in obtaining a structure for press-fitting and fixing the support shaft (4) to the inner peripheral yoke (2b).

Further, the permanent magnet (1) can be obtained at low cost by molding a resin containing a magnetic material into a predetermined shape and magnetizing the molded product.

Furthermore, a notch is provided on the bottom surface of the magnetic yoke for focusing so as not to block the light beam passing through the objective lens from the missing portion of the outer yoke to the inner yoke, so that the distance between the objective lens and the support shaft can be reduced as much as possible. In addition, since the lens holder can be reduced in size and weight, and the outer yoke can be omitted in accordance with the rotation angle at which the objective lens moves in the rotation direction about the support shaft, the circumferential length of the outer yoke can be minimized. Since it can be secured for a long time, the magnetic flux density can be increased and the driving force can be increased.Furthermore, the shape of the lens holder is reduced in weight and the driving force for focusing can be secured as much as possible, and the magnetic yoke for focusing is sintered with iron-based powder material Therefore, even if the same size as the magnetic yoke for focusing, which was conventionally manufactured by cutting a ferrous base material, was sintered, Ltd. makes it possible to supplement the driving force for focusing the magnetic flux density is lowered smaller.

Furthermore, since the lens holder is reduced in size and weight and the yoke is manufactured by a sintering method, the entire optical pick can be reduced in size and weight and cost can be reduced.

In addition, since the yoke is manufactured by the sintering method, when inserting the support shaft into the inner peripheral yoke, if the same press input as in the past, the accuracy should be loosened compared to the case of cutting the iron base. In addition, it is easy to assemble, and it is possible to make the thickness of the inner peripheral yoke slightly thicker at the center side than in the case of the iron base material, so that the outer diameter of the inner peripheral yoke is increased. The thickness of the inner peripheral yoke can be increased without the need. With the sintering method, the inner peripheral yoke is slightly plastically deformed by the force at the time of press-fitting, but the inner peripheral yoke itself is not cut, so the absolute amount of the magnetic material contained in the inner peripheral yoke does not change. This also helps in compensating for a decrease in driving force due to the sintering method.

In the above embodiment, the permanent magnet, the outer yoke, and the inner yoke were separately manufactured and used in combination. However, the permanent magnet, the outer yoke, and the inner yoke were made of a resin material containing the same magnetic material. It is also possible to use a material formed by molding and magnetized after molding.

[Effects of the Invention] As described above, according to the present invention, a focusing coil formed to have a diameter smaller than the distance between the spindle disposed on the lower surface of the lens holder and the peripheral edge of the spindle of the objective lens, A cylindrical inner yoke in which the support shaft is fitted and the outer surface of which faces the inner surface of the focusing coil, an outer yoke provided with a magnet facing the outer surface of the focusing coil and provided opposite to the inner yoke, and an inner yoke; And the outer yoke are connected by a bottom surface at each lower portion, and a magnetic yoke for focusing is formed by the inner yoke, the outer yoke, and the bottom surface, and the lens holder is driven to collect light on the disk via at least the objective lens. In a configuration having a driving device that performs focusing of a light spot of a light beam by a magnetic yoke for focusing, an objective lens and a support shaft are brought close to each other, and A part of the outer yoke is cut off so as not to block the light beam passing through the lens, a bottom surface is formed from the outer yoke to the inner yoke, and at least the lower end extension of the focusing coil extends from the part where the outer yoke is missing to the inner end. As a limit, a fan-shaped notch through which light beams pass is formed, and the outer and inner yokes are manufactured by a sintering method of a magnetic material, and a fitting portion for press-fitting and fixing a spindle to the inner yoke is provided. In addition, there is an effect that a magnetic yoke for focusing having an irregular shape due to the miniaturization of the optical pickup device can be manufactured at low cost while maintaining the performance of the conventional device as much as possible.

[Brief description of the drawings]

FIG. 1 is a perspective view in which a part of a driving device portion of an optical pickup device according to the present invention is cut away, FIG. 2 is an exploded perspective view showing a conventional optical pickup device, and FIG. . In the figure, (1) is a permanent magnet, (2a) is a magnetic yoke (outer yoke), (2b) is a magnet yoke (inner yoke),
(2c) is the bottom, (3) is the focusing coil, (5)
Denotes a lens holder, and (6) denotes an objective lens. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A lens holder which holds an objective lens on one side and is movable in an axial direction and a rotational direction about a support shaft parallel to a direction of a light beam passing through the objective lens, and is disposed on a lower surface of the lens holder. A focusing coil formed to have a diameter smaller than the distance between the spindle and the peripheral edge of the spindle of the objective lens, and a cylindrical inner yoke in which the spindle is fitted and an outer surface faces the inner surface of the focusing coil; An outer yoke provided with a magnet facing the inner yoke and facing the outer surface of the focusing coil, and a bottom surface connecting the inner yoke and the outer yoke at respective lower portions, A magnetic yoke for focusing is formed by the inner peripheral yoke, the outer peripheral yoke, and the bottom surface, and the lens holder is driven to drive a disk through at least the objective lens. In an optical pickup device having a driving device for performing focusing of a light spot of the focused light beam by the focusing magnetic yoke, the objective lens and the support shaft are brought close to each other, and a light beam passing through the objective lens is not blocked. A part of the outer yoke is omitted, a bottom surface is formed from the outer yoke to the inner yoke, and at least the lower end extension of the focusing coil is used as an inner end from the part where the outer yoke is missing to allow the light to pass therethrough. A light, wherein a sector-shaped notch is formed, and the focusing magnetic yoke is manufactured by sintering an iron-based powder material, and has a fitting portion for press-fitting and fixing the support shaft to the inner peripheral yoke. Pickup device.