JPH0744880A - Objective lens actuator - Google Patents

Abstract

PURPOSE:To provide an objective lens actuator preventing the inconvenience such as the lowering of the thrust of the actuator and the harmful resonance easily generated by the clearance between the pointed tip part of a thin inner yoke and an upper yoke and capable of obtaining stable magnetic field when the actuator is manufactured by press-working a base, inner and outer yokes made of a sheet of a metal plate. CONSTITUTION:The objective lens actuator comprises a pair of inner yokes 6 parallelly protruded from the surface of an actuator base 5 seperated by a prescribed interval apart, an outer yoke 7 projected in parallel with the relevant inner yokes on the position a prescribed interval apart outward from the respective inner yokes, an upper yoke 9 fixed on the upper part of the outer yoke, an objective lens 2 supported in a space between the relevant pair of inner yokes, a coil for moving the relevant objective lens forwards and backwards and a permanent magnet 8 fixed on the inner wall of the relevant outer yoke. The upper yoke 9 has a central hole 20 for exposing the objective lens 2, slits 21 on both sides of the central hole 20 and the inner surface of the outer yoke 7 is supported in the state of pressurized contact with the inner wall of the respective slits.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an objective lens actuator of an optical disk drive device, and in particular solves various problems that occur when a yoke and a base forming the actuator are produced by press working from one sheet metal. The present invention relates to an objective lens actuator.

[0002]

2. Description of the Related Art An optical disk drive device is a device that optically records, reproduces, and erases information on a mounted recording medium such as an optical disk by an optical pickup.
The optical pickup includes an objective lens actuator unit for freely moving the objective lens in both the focusing direction and the tracking direction. Figure 7
(a) is a longitudinal sectional view showing a structure of a conventional objective lens actuator. In this actuator 1, a bobbin 3 carrying an objective lens 2 is wound with a focusing coil 4 and a tracking coil is further provided. It is adhesively fixed and constitutes a linear motor. The bobbin 3 is supported by a leaf spring that is deformable in both the focusing direction and the tracking direction.
By controlling the current flowing in each tracking coil, the magnetic circuit drives and controls the focusing direction and the tracking direction by the electromagnetic action with a constant magnetic field.
The actuator base 5 is integrally provided with an inner yoke 6 and an outer yoke 7 which is slightly shorter than the inner yoke, and a permanent magnet 8 is bonded to the inner side surface of the outer yoke 7. The upper yoke 9 is fixed so as to connect the upper ends of the inner and outer yokes 6 and 7, and the upper yoke 9, the inner yoke 6, the outer yoke 7, the actuator base 5, and the permanent magnet 8 form a magnetic circuit. Since the magnetic flux generated by the permanent magnet 8 flows through the upper yoke 9 and the actuator base 5, the yoke is prevented from being saturated. The base 5 and the inner and outer yokes 6 and 7 are integrally formed by pressing from one sheet metal. It should be noted that description of specific configurations other than the above is omitted.

Next, problems that occur when the base 5 and the inner and outer yokes 6 and 7 are integrally formed by pressing from one sheet metal will be described with reference to FIGS. 7 (b) and 7 (c). That is, the objective lens actuator 1 is mounted on a carriage or the like that moves in the radial direction of the disc in order to make the recording surface of the disc loaded in the optical disc drive device accessible, but shortens the access time. Therefore, it is highly necessary to reduce the size and weight of the movable part in order to meet such requirements. In other words, there is a strong demand for miniaturization of the objective lens actuator itself. Based on this request, in order to reduce the size in the X direction of the actuator as shown in FIG. 7 (b), the wall thickness t1 of the inner yoke 6 that bends and extends upward from the base is larger than the wall thickness t2 of other portions. Is also thinning. The pair of inner yokes 6 are formed by dividing a plate portion corresponding to the center hole 5a of the base 5 into two and bending each of the divided pieces upward. As shown in FIG. Since 'is short, its tip does not reach the upper end of the outer yoke 7 when it is bent. Therefore, the jig 1
The inner yoke 6 is rolled by using Nos. 5 and 16 to reduce the wall thickness and extend the height. As a result, the tip shape of the inner yoke 6 is formed in a tapered shape in which the side of the objective lens optical axis a is higher and the side of the outer yoke is lower, as shown in FIG. 7B.

When the upper yoke 9 is assembled in this state, a gap S is formed between the upper yoke 9 and the inner yoke 6, causing variations in the magnetic field generated by the magnetic circuit, resulting in fluctuations in actuator thrust. Alternatively, unnecessary force may act to cause harmful resonance for the operation of the actuator. Specifically, when external vibration or shock is applied to the actuator base, the inner yoke vibrates, and the generated magnetic field fluctuates. In particular, when the inner yoke is displaced in the X direction, the distance between the magnet and the inner yoke fluctuates, and the magnetic resistance increases, which causes problems such as fluctuations in actuator thrust and harmful resonance.

In order to eliminate such a problem, it is possible to secure a sufficient height of the inner yoke 6 (extend the height of the outer side surface of the inner yoke to a level exceeding the upper surface of the upper yoke). With such a configuration, it is possible to reduce the gap S and reduce the adverse effects of the presence of the gap. However, since a disc (not shown) is located directly above the upper yoke, in order to eliminate the risk of interference with the disc, The height limit of the inner yoke 6 is the same as the upper surface of the upper yoke 9. Under these circumstances, conventionally, the above-mentioned gap S must be left between the tip of the inner yoke having a sharp tip and the upper yoke, and therefore a stable magnetic field can be obtained when the actuator base is used as a magnetic circuit. There was a problem that I could not do it.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and when an actuator is produced by forming a base and an inner and outer yoke by pressing one sheet metal, a thin inner yoke has a sharp point. Aiming to provide an objective lens actuator capable of obtaining a stable magnetic field by preventing problems such as reduction in actuator thrust, harmful resonance, etc., which are likely to occur as a result of a gap between the tip portion and the upper yoke, and a stable magnetic field. There is.

[0007]

To achieve the above object, the present invention provides a pair of plate-shaped inner yokes protruding in parallel on an actuator base surface at predetermined intervals, and a predetermined interval outward from each inner yoke. An outer yoke projecting parallel to the inner yoke at a fixed position, an upper yoke fixed to the upper end of the outer yoke lower than the inner yoke, and an objective supported in a space between the pair of inner yokes. In an objective lens actuator including a lens, a coil for moving the objective lens forward and backward in a focusing direction and a tracking direction, and a permanent magnet fixed to an inner wall of the outer yoke, the upper yoke exposes the objective lens. And a slit on both sides of the central hole, and the inner side wall of each slit presses and supports the inner side surface of the inner yoke. The central hole formed in the hole and the slits are communicated with each other, and a bent portion is provided at a portion of the inner wall of the slit that is in pressure contact with the inner yoke to increase the contact area with the inner yoke, On the base surface, a pair of plate-shaped inner yokes protruding in parallel at a predetermined interval, and an outer yoke projecting parallel to the inner yoke at a position spaced a predetermined distance outward from each inner yoke,
An upper yoke fixed to an upper end portion of an outer yoke lower than the inner yoke, an objective lens supported in a space between the pair of inner yokes, and for moving the objective lens forward and backward in a focusing direction and a tracking direction. An objective lens actuator having a coil and a permanent magnet fixed to the inner wall of the outer yoke, the upper yoke has a central hole for exposing the objective lens, and the inner walls of the central hole facing each other. The side end surface of the inner yoke is held under pressure by means of the above, and a bent portion is provided in a portion of the inner wall of the central hole that comes into pressure contact with the side end surface of the inner yoke to increase the contact area with the inner yoke. I am trying.

The present invention will be described in detail below with reference to the embodiments shown in the drawings. 1 (a), (b) and (c) are an exploded perspective view showing a structure of an actuator of an embodiment of the present invention, a front vertical sectional view thereof, and a structure example of an inner yoke. Also, FIG.
(a) And (b) is the top view and front vertical cross-sectional view which show the flow of a magnetic flux. An inner yoke 6 and an outer yoke 7 are integrally provided on the actuator base 5, and a permanent magnet 8 is bonded to the inner surface of the outer yoke 7. The upper yoke 9 is fixed so as to connect the upper ends of the inner and outer yokes 6 and 7, and the upper yoke 9, the inner yoke 6, the outer yoke 7, the actuator base 5, and the permanent magnet 8 form a magnetic circuit. Since the magnetic flux generated by the permanent magnet 8 flows through the upper yoke 9 and the actuator base 5, the yoke is prevented from being saturated. As described above, the base 5 and the inner and outer yokes 6 and 7 are integrally formed by pressing from one sheet metal, and as a result, the tip end portion of the inner yoke 6 is tapered.

In the present embodiment, the tip of each inner yoke 6 is tapered, and in order to solve the problem caused by forming a gap between the inner yoke 6 and the upper yoke, the central hole 20 of the upper yoke is formed. Slits 21 each having a predetermined length extending in the Y direction are punched and formed at positions on both sides in the X direction, and when the upper yoke is fixed on the outer yoke 7, the inner inner walls 21a (objective lens optical axis side surfaces) of the respective slits 21 cause the inner yokes. A characteristic is that the inner surface 6a of the tip is supported in a surface contact state. That is, this slit 21 is a slit for inserting the tip of the inner yoke, and is formed separately from the central hole 20 for exposing the objective lens. Since the tip portion of the inner yoke 6 is tapered, the wall thickness of the tip portion is not constant, but the inner side surface 6a of the inner yoke 6 is precisely flat when the inner yoke 6 is rolled (FIG. 7 (c)). Is maintained. Therefore, the flow of magnetic flux in the magnetic circuit (the flow of magnetic flux entering the upper yoke 9 from the inner yoke 6 as shown in FIGS. 2 (a) and 2 (b)) is
It flows from the inner surface 6a side of the tip of the inner yoke 6 to the upper yoke 9. As described above, the inner side surface 6a of the inner yoke 6
Since the flatness is maintained high, the inner yoke 6 and the upper yoke 9 can be easily positioned with respect to the slit 21, the fitting can be performed with high accuracy, and the gap between them is reduced.

Further, both inner yokes 6 immediately after press working
As shown in Fig. 1 (c), the inner yoke and the inner wall of the upper yoke are always made elastic by the inner yoke when the tip of the inner yoke is fitted into the slit 21. It is possible to secure the contact with 21a and stabilize the magnetic characteristics. Further, the inner yoke is firmly supported by the upper yoke at the tip portion due to the pressure contact between the inner yoke tip and the slit inner wall, so that the inner yoke does not vibrate due to disturbance or the like. Further, the positioning in the X direction shown in FIG. 1 (a) can be performed at the component level (the inner yoke 6 and the upper yoke 9), which is effective in improving the assembling accuracy. Further, the upper yoke can be fixed to the inner yoke by press-fitting the inner yoke into the slit.

Next, the size in the X direction of the actuator shown in the above embodiment can be further reduced. Figure 3
(a) and (b) show a method therefor. Here, in order to reduce the dimension in the X direction, consideration is given to shortening the distance between the inner yoke 6 and the objective lens located in the central hole 20. Has been done. Therefore, in this embodiment, the slit 21 of the upper yoke 9 is brought as close as possible to the central hole 20, and the central portion of each slit 21 is communicated with the central hole 20. Therefore, the inner inner wall 21a of each slit 21 is divided at the center, and the inner side surface 6a of the inner yoke 6 comes into pressure contact with the divided inner wall 21a. Even with this structure, since the magnetic flux is distributed and flows over the entire surface of the inner yoke, a region where the magnetic flux flows can be secured in a portion other than the slit central portion as shown in FIG. 3 (b). The first while reducing the size in the direction
The same effect as the embodiment can be obtained.

Next, FIGS. 4 (a) and 4 (b) are a front sectional view and a plan view showing the structure of the essential part of a third embodiment of the present invention, and the same reference numerals are given to the same portions as those in the above-mentioned respective embodiments. In this embodiment, the slit 2 of the upper yoke 9 is omitted, though the duplicated description will be omitted.
The inner inner wall 21a of 1 is bent downward to form a bent portion,
The characteristic is that the contact area between the inner yoke 6 and the inner wall 6a is increased. That is, in order to increase the thrust of the actuator or reduce the current flowing through the coil to reduce the power consumption, it is necessary to increase the magnetic flux flowing through the magnetic circuit. Therefore, a magnet with a large energy product is usually used. Although it has been used, since there is a problem in terms of cost reduction, compactification, in the present invention, the above problems can be solved by increasing the area of the portion through which the magnetic flux flows, without causing such problems. Has been resolved. That is, in this embodiment, since the contact area with the inner yoke 6 is increased by bending a part of the inner wall 21a, the area through which the magnetic flux passes is increased, and problems such as enlargement are not caused. In addition, the thrust of the actuator was increased and the power consumption was reduced.

Next, FIGS. 5 (a) and 5 (b) are a plan view and a sectional view taken along the line AA of the main part of the fourth embodiment of the present invention, in which the central hole 20 of the upper yoke 9 is rectangular. The configuration is characteristic in that the tip end of the inner yoke is held near both ends of the central hole 20 in the longitudinal direction. Also,
Unlike the case of each of the above embodiments, the side end surface 6b of the tip end portion of the inner yoke 6 is press-fitted and held by the inner wall of the central hole 20. Since the inner yoke 6 is sufficiently thick and has sufficient strength, there is no risk of deformation during press fitting. As a result of press fitting, the inner yoke 6 is firmly fixed by the upper yoke 9, and the inner yoke 6 does not vibrate due to disturbance. Further, since the inner yoke and the upper yoke are press-fitted in contact with each other, the adhesion between both contact surfaces is good, and their magnetic characteristics are sufficiently stable. Further, the slit for fitting the inner yoke is not formed, which is advantageous in manufacturing. However, a slit may be provided especially. In addition, the Y-direction end faces of the inner yoke are provided with holes 20
Since the positioning is performed with, the positioning in the Y direction becomes reliable.
The X-direction size can be reduced by reducing the size of the central hole 20 in the X-direction as much as possible. The flow of magnetic flux in this embodiment is as shown in FIG.
The formation of a gap due to the tapered portion at the tip of the inner yoke and the adverse effect thereof can be prevented.

FIGS. 6 (a) and 6 (b) are a plan view and a sectional view taken along the line BB of the fifth embodiment of the present invention, showing the inner wall of the central hole of the upper yoke of the embodiment of FIG. A characteristic is that a part of is bent downward to increase the contact area with the side end surface of the inner yoke. That is, of the inner wall of the rectangular center hole 20, a part of the inner wall on the side in contact with the side end surface of the inner yoke 6 is bent downward to form a bent portion 25. Since the contact area between the two is increased by supporting the end faces in a pressure contact state, the area through which the magnetic flux passes will increase, increasing the thrust of the actuator and reducing power consumption without causing problems such as size increase. can do. The bent portion 25 need not be formed over substantially the entire length of the side of the central hole 20 as shown in FIG. 6 (a), and the bent portion may be provided only at the portion where the side end surface of the inner yoke abuts. .

[0015]

As described above, according to the objective lens actuator of the present invention, slits for supporting the tip of the inner yoke are provided at both ends of the hole for exposing the objective lens provided at the center of the upper yoke. Since the inner inner wall of the slit is pressed against the inner surface of each inner yoke, it is possible to maintain a stable contact state on both sides, ensuring a stable magnetic flow path and obtaining stable magnetic characteristics. At the same time, it is possible to prevent the occurrence of resonance harmful to the operation of the actuator. Further, the positioning in the X direction shown in FIG. 1 (a) can be reliably performed at the component level. In other words, in the conventional technique, a gap is formed between the inner yoke and the upper yoke, each of which has a tapered tip, and the flow of the magnetic flux is obstructed.
Although the tip portion of the inner yoke easily vibrates, in the present invention, since the tip portion of the inner yoke is securely held by the upper yoke,
Such problems disappear. Further, since the central hole of the upper yoke and the slit are arranged close to each other and communicated with each other, the same effect as described above can be obtained and the actuator can be downsized.

Further, since the bent portion is provided on the inner wall of the slit and the inner yoke is brought into pressure contact with the surface of the bent portion, the area through which the magnetic flux passes can be expanded to allow a large magnetic flux to flow. Become. As a result, the power consumption of the actuator can be suppressed. Further, if the side walls of the inner yoke are held by the inner walls facing each other of the central hole of the upper yoke, the inner yoke can be press-fitted and fixed without deformation, and stable magnetic characteristics can be obtained. It is possible to prevent the occurrence of resonance harmful to the operation of. Further, the positioning in the Y direction is possible at the component level. Further, since the bent portion is provided in a portion of the inner wall of the central hole that holds the side end surface of the inner yoke tip at least, a large magnetic flux can be flowed and the power consumption of the actuator can be reduced. .

[Brief description of drawings]

1 (a), (b) and (c) are an exploded perspective view, a longitudinal sectional view, and an explanatory view of a modified example showing a main configuration of an actuator of an embodiment of the present invention.

2 (a) and 2 (b) are a plan view and a front sectional view showing the flow of magnetic flux in the embodiment of FIG.

3 (a) and 3 (b) are a plan view and a front view showing a main part configuration of a second embodiment of the present invention.

4 (a) and 4 (b) are a front sectional view and a plan view showing the configuration of the main part of a third embodiment of the present invention.

5 (a) and 5 (b) are a plan view and a sectional view taken along line AA of the fourth embodiment of the present invention.

6A and 6B are a plan view and a BB sectional view of a fifth embodiment of the present invention.

7 (a), (b) and (c) are explanatory views of a conventional example.

[Explanation of symbols]

1 actuator, 2 objective lens, 3 bobbin, 4
Coil, 5 actuator base, 6 inner yoke,
6a inner surface, 7 outer yoke, 8 permanent magnet, 9 upper yoke, 20 central hole, 21 slit, 21a inner inner wall,

Claims (5)

[Claims] 1. A pair of plate-shaped inner yokes protruding in parallel at a predetermined interval on an actuator base surface, and projecting in parallel to the inner yokes at a position spaced outward from each inner yoke by a predetermined interval. An outer yoke, and an upper yoke fixed to the upper end of the outer yoke lower than the inner yoke,
An objective lens supported in a space between the pair of inner yokes,
In an objective lens actuator having a coil for advancing and retracting the objective lens in a focusing direction and a tracking direction, and a permanent magnet fixed to an inner wall of the outer yoke, the upper yoke is a central portion for exposing the objective lens. An objective lens actuator comprising a hole and slits on both sides of the central hole, and an inner side wall of each slit presses and supports an inner side surface of the inner yoke. 2. The objective lens actuator according to claim 1, wherein the central hole formed in the upper yoke and the slits are communicated with each other. 3. The objective lens actuator according to claim 1, wherein a bent portion is provided in a portion of the inner wall of the slit that comes into pressure contact with the inner yoke to expand a contact area with the inner yoke. 4. A pair of plate-shaped inner yokes protruding in parallel at predetermined intervals on an actuator base surface, and projecting in parallel with the inner yokes at positions separated from each inner yoke by a predetermined interval. An outer yoke, and an upper yoke fixed to the upper end of the outer yoke lower than the inner yoke,
An objective lens supported in a space between the pair of inner yokes,
In an objective lens actuator having a coil for advancing and retracting the objective lens in a focusing direction and a tracking direction, and a permanent magnet fixed to an inner wall of the outer yoke, the upper yoke is a central portion for exposing the objective lens. An objective lens actuator having a hole, wherein side walls of the inner yoke are clamped and held by opposing inner walls of the central hole. 5. The objective lens according to claim 4, wherein a bent portion is provided in a portion of the inner wall of the central hole that is in pressure contact with the side end surface of the inner yoke to enlarge a contact area with the inner yoke. Actuator.