JP2796240B2 - Objective lens drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object provided in an optical information recording / reproducing apparatus capable of optically recording, reproducing, or erasing information by irradiating a recording medium with a light beam. The present invention relates to a lens driving device.

[0002]

2. Description of the Related Art Conventionally, an objective which drives an objective lens in two axes to control a condensing position of a light beam applied to an information recording medium such as a magneto-optical disk through an objective lens in a focusing direction and a tracking direction. Lens driving devices are known, and various devices have been devised for the purpose of reducing the size and weight. An example of this type of apparatus is disclosed in
Japanese Patent Application Publication No. -11237. The focus coil and the tracking coil are arranged on the side opposite to the objective lens fixed side with respect to the vicinity of the support point of the lens support member, and are fixed to the lens support member. With this configuration, the movable portion is provided at the support point of the lens support member. The weight of the balancer added to balance the moment of the movable part so as to match the center of gravity can be reduced.

In Japanese Patent Application Laid-Open No. Hei 5-109094, at least a part of the elastic support member of the movable portion is located in a light beam incident on the objective lens or in a light beam emitted from the objective lens. By reducing the distance between the objective lens and a light beam substantially parallel to the surface of the optical recording medium, the apparatus can be made smaller and thinner.

Further, in Japanese Patent Application Laid-Open No. 5-205299, a corner of a surface of a permanent magnet of a magnetic circuit which faces a yoke portion is cut so as to have an opposing surface smaller than a width of the yoke portion. The magnetic flux directed toward the fan is spread in a fan shape, and a moment orbiting in the direction in which the movable portion is to be moved is obtained.

Here, the importance of reducing the weight of the movable part will be briefly described. Since the rigidity of each mechanical component decreases as the optical disk device becomes thinner and lighter, the magnetic circuit vibrates due to the reaction force generated in the magnetic circuit when the objective lens is driven, and the vibrations By transmitting the mechanical parts, the optical disk surface eventually resonates. For this reason, it is difficult to further reduce the thickness and weight of the optical disk device. In order to solve this problem, it is only necessary to reduce the reaction force generated in the magnetic circuit,
That is, it is important to reduce the weight of the movable part of the objective lens driving device. However, in a normal objective lens driving device, since the objective lens and the drive coil are separated to secure a space for optical components such as a light beam and a rising mirror, the rigidity of the lens holder of the movable portion is sufficiently maintained. If it is designed to be as light as possible, the position of the center of gravity of the movable part and the driving point will be shifted. Therefore, in order to suppress the occurrence of higher-order resonance caused by this shift, it is necessary to attach a balancer to the movable portion so as to eliminate the shift, which hinders the weight reduction of the movable portion. That is, it is important to reduce the weight of the movable part without attaching a balancer and to suppress the occurrence of higher-order resonance.

[0006]

However, among the above conventional examples, the objective lens driving device disclosed in Japanese Patent Application Laid-Open No. 4-111237 discloses an objective lens driving device in which the center of gravity of the movable part is adjusted to the supporting point of the lens supporting member. It is necessary to add a balancer corresponding to the difference between the moment of the lens support member relative to the support point and the moment of the focus coil and tracking coil relative to the support point of the lens support member, which hinders the weight reduction of the movable part.

The objective lens driving device disclosed in Japanese Patent Application Laid-Open No. 5-109,094 can achieve a reduction in the thickness of the device, but requires a balancer for the lens supporting member as in the above-described conventional example, and reduces the weight of the movable portion. Cannot be achieved.

Further, the objective lens driving device disclosed in Japanese Patent Application Laid-Open No. 5-205299 does not require a balancer to match the position of the center of gravity of the movable portion with the drive center. Since a higher moment can be obtained, higher-order resonance caused by the above-described displacement can be prevented, but even if the width of the facing surface of the permanent magnet is made smaller than the yoke width, most of the magnetic flux is straightened. In order to tilt the magnetic flux as much as necessary to balance the moment, it is necessary to make the width of the opposing surface of the permanent magnet much smaller than the yoke width. Is greatly reduced. Actually, the balance by this method is limited to the case where the deviation amount is very small, and also requires a balancer similarly to the conventional example, which hinders the weight reduction of the movable part.

The present invention is proposed to solve the above-mentioned problems, and it is possible to suppress the higher-order resonance by adding a moment balance without adding a balancer or the like, thereby reducing the weight of the movable part. It is an object of the present invention to provide a compact and thin objective lens driving device.

[0010]

According to a first aspect of the present invention, in addition to the main magnetic circuit, the driving means includes a phase compensating magnetic circuit for applying a driving force in a direction opposite to a direction in which the movable portion is to be displaced. The main tracking coil is mounted on one side of the focus coil, the phase compensation tracking coil is mounted on the other side facing the main coil, the main tracking coil side is in the main magnetic gap, and the phase compensation tracking coil side is for phase compensation This is a configuration that is arranged in a magnetic gap.

According to a second aspect of the present invention, the magnetic circuit for phase compensation comprises only a single magnet.

According to a third aspect of the present invention, the magnetic circuit for phase compensation has a configuration in which the yoke is shared with the main magnetic circuit.

According to a fourth aspect of the present invention, the tracking coil for phase compensation is mounted below the main tracking coil.

[0014]

When the center of gravity of the movable part is located closer to the objective lens than the drive center, a moment in the direction opposite to the direction in which the movable part is desired to be displaced is generated by the phase compensating magnetic circuit and the coil. By applying a driving force in the direction opposite to the direction in which the movable part is desired to be displaced, a moment in the direction in which the movable part is desired to be displaced is generated, and the above-mentioned moment is canceled to suppress higher-order resonance.

In addition, by using a single magnet as the phase compensation magnetic circuit, a simple magnetic circuit configuration can be used.
Higher-order resonance can be easily suppressed.

Further, since the phase compensation magnetic circuit shares the yoke with the main magnetic circuit, the magnetic flux density in the compensation magnetic gap becomes more uniform, and the amount of generated moment is stabilized, so that adjustment of the amount of moment is unnecessary. It is.

In addition, since the tracking coil for phase compensation is mounted below the main tracking coil, the phase can be compensated in the same manner as above even when the position of the center of gravity of the movable part is located above the drive center.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the objective lens driving device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view (a), a side view (b), and a perspective view (c) showing only the configuration of a drive coil showing the configuration of an objective lens driving device according to an embodiment of the present invention.

The objective lens 1 is fixed to a lens holder 2, and the lens holder 2 is provided on both sides of the lens holder 2.
The elastic body 3 movably supporting the lens holder 2 in two directions with respect to the base 4 is attached to the upper and lower sides, respectively.
The focusing coil 8 and the tracking coil 7 are fixed to the opening. The main magnetic circuit 12 includes a U-shaped yoke 5 attached to the fixed portion 11 and permanent magnets 6a and 6b attached inside the yoke 5. The permanent magnet may be attached to only one of the yokes. A part of the focusing coil 8 and the tracking coil 7 is disposed in a magnetic gap of the main magnetic circuit 12 and
Is wound so as to surround the one permanent magnet 6b and the yoke 5b, and the 8b portion of the focusing coil 8 is positioned outside the magnetic gap of the main magnetic circuit 12. The main tracking coil 7 is composed of two flat coils 7a and 7b having a ring shape as shown in FIG.

The magnetic circuit 13 for phase compensation includes a permanent magnet 10 directly attached to a fixed portion and a focusing coil 8.
And a tracking coil 9 for phase compensation fixed to the lens holder 2. A configuration in which a back yoke is attached to the back of the permanent magnet to increase the gap magnetic flux density may be used. 8b of the focusing coil 8
The part (corresponding to a phase compensating part) and the tracking coil 9 for phase compensation are arranged in a compensating magnetic gap constituted by the permanent magnet 10 and the yoke 5b. The phase compensation tracking coil 9 also has a ring shape 2 as shown in FIG.
It is composed of flat coils 9a and 9b.

The direction of the lines of magnetic force is assumed to be from right to left in the magnetic gap of the main magnetic circuit, and also from right to left in the compensation gap.

Referring to FIG. 2 to FIG.
The effect of the phase compensation in the focus direction will be described.

The driving force given by the main magnetic circuit is f
m, the driving force given by the phase compensation magnetic circuit is fc
And Usually, when the balancer is not mounted, the position of the center of gravity (GC) of the movable portion is located closer to the objective lens than the drive point fm of the main magnetic circuit as shown by + in the figure.

Here, when the objective lens 1 is driven in the upward direction, assuming that the directions of the magnetic flux in the main magnetic gap and the phase compensation gap are from right to left in FIG. When a current flows backward, an upward driving force fm is generated. Also, the focus coil 8
8b, a downward driving force fc is generated because a current flows upward from the back of the paper. Therefore, the upward driving force F is given by F = fm-fc. Further, the moment M around the position of the center of gravity (GC) of the movable part including the objective lens is M = lm × fm−lc × fc. Here, the moment M can be made zero by adjusting the magnetic field strength of the phase compensation magnet 10 and the distance from the focusing coil 8b so that fc = lm / lc × fm. Here, since lm <lc, it is possible to sufficiently compensate even if fc is small, and the amount of decrease in the upward driving force F due to the compensation driving force fc can be reduced.

Therefore, when the objective lens is driven, the moment generated around the center of gravity of the movable portion is canceled, so that higher-order resonance can be suppressed.

FIG. 3 shows the result of measuring the frequency characteristics of the displacement of the objective lens in the focusing direction in the objective lens driving device manufactured by the above-described configuration. From the figure, it can be seen that high-order resonance, which is a problem, is suppressed to a high frequency.

However, when the magnetic circuit for phase compensation is not provided, as shown in FIG. C. Since a moment M M = lm × fm in the direction opposite to the direction in which the objective lens is desired to be displaced is generated, a large higher-order resonance is generated as shown in the frequency characteristic of the displacement in the focusing direction in FIG. It is.

Similarly, the effect of phase compensation in the tracking direction will be described with reference to FIG. The driving force provided by the main magnetic circuit is denoted by rm, and the driving force provided by the phase compensation magnetic circuit is denoted by rc. When the objective lens 1 is driven in the upward direction in the figure, the main tracking coils 7a, 7b
When a backward current flows from the front side of the drawing to the respective coil connection sides (marked by x in the drawing), an upward driving force rm is generated. Further, when a front-facing current flows from the back of the drawing to the respective coil connection sides (marked by x in the drawing) of the phase compensation tracking coils 9a and 9b, a downward driving force rc is generated. Therefore, the downward driving force F in the figure is given by F = rm-rc. In addition, G.V.
C. The surrounding moment M is M = wm × rm−w
c × rc. Here, if rc = wm / wc × rm, the moment becomes zero. Here, the magnetic field intensity and the gap length of the phase compensating magnet 10 are already optimized during the phase compensation in the focus direction, but the compensation driving force rc in the tracking direction is determined by the phase compensation tracking coil alone. Therefore, the above conditions can be satisfied by adjusting the number of turns. Therefore, when the objective lens is driven, the moment generated around the center of gravity of the movable portion is canceled, so that higher-order resonance can be suppressed.

FIG. 7 shows the results of measuring the frequency characteristics of the displacement of the objective lens in the tracking direction in the objective lens driving device manufactured by the above configuration. From the figure, it can be seen that high-order resonance, which is a problem, is suppressed over a high frequency range.

Here, the tracking coil 9 for phase compensation
Is extremely lighter than the weight of the movable part, and can be said to be extremely lighter than the balancer weight when the balancer is used. The weight of the movable part of the objective lens driving device used for the measurement (FIGS. 3 and 7) of the present embodiment is about 200 mg, and the weight of the phase compensation tracking coil is about 10 mg, which is very light. Approximately 100 mg weight reduction compared to the case where the balancer is mounted.

In this embodiment, when the deviation between the position of the center of gravity of the movable part and the driving point is very small, the yoke 5
The thickness of the portion b may be reduced so that the magnetic flux leaks from the main magnetic circuit, and the phase compensating permanent magnet 10 may be eliminated, and the phase compensating driving force may be obtained by the leaked magnetic flux.

Next, FIG. 8 shows the configuration of an objective lens driving device according to a second embodiment of the present invention. Objective lens 21, lens holder 22, focusing coil 28, tracking coil 27, and tracking coil 29 for phase compensation
The configurations of the movable portion, the elastic body 23 supporting the movable portion, and the base 24 are the same as those of the first embodiment shown in FIG. The difference lies in the configuration of the magnetic circuit. The main magnetic circuit 32 and the phase compensation magnetic circuit 33 share a yoke 25. The main magnetic circuit 25 is composed of a horizontal E-shaped yoke 25 attached to the fixed portion 31 and 25a and 25b portions and permanent magnets 26a and 26b attached inside the yoke 25. The focusing coil 28 is connected to one permanent magnet 26b. The yoke 25b is wound so as to surround the yoke 25b, and the portion 28a is disposed in the magnetic gap of the main magnetic circuit 32 together with the tracking coil 27.

The phase compensating magnetic circuit 33 is composed of a 25b portion of the horizontal E-shaped yoke 25, 25c portion and a permanent magnet 30 attached to the side surface of the 25c portion. The tracking coil 29 is arranged in the magnetic gap of the magnetic circuit 33 for compensation. Assuming that the direction of the lines of magnetic force is from right to left in the magnetic gap of the main magnetic circuit, the direction of the compensation gap is also from right to left.

In the magnetic circuit of this configuration, since the compensating magnetic circuit can also constitute a closed-loop magnetic circuit like the main magnetic circuit, the magnetic flux density of the compensating magnetic gap becomes uniform,
Phase compensation can be performed more stably.

As in the first embodiment, the adjustment of the amount of phase compensation in the present apparatus is performed by first adjusting the magnetic flux density of the compensating magnetic gap and the magnetic field strength of the permanent magnet 30 so that the amount of compensation in the focusing direction is optimized. Adjust according to the gap length. Next, the compensation amount in the tracking direction is adjusted by adjusting the number of turns of the tracking coil.

9 to 11 show another embodiment of the magnetic circuit according to the present invention. In each case, only the magnetic circuit is described. Except for the magnetic circuit, the same as in the first and second embodiments may be considered.

First, the magnetic circuit shown in FIG. 9 will be described.
As in the second embodiment, the phase compensation magnetic circuit 33 shares the yoke with the main magnetic circuit 32, and portions corresponding to the second embodiment are denoted by the same reference numerals. The permanent magnet 35 of the phase compensation magnetic circuit is attached to the bottom of the yoke between the yokes 25b and 25c as shown. Assuming that the direction of the lines of magnetic force of the magnetic gap of the main magnetic circuit is from right to left, the magnetization direction of the permanent magnet 35 is from left to right so that the direction of the lines of magnetic force at the compensation gap is also from right to left. In the present magnetic circuit configuration, the size in the horizontal direction can be made smaller than the configuration in FIG.

Next, the configuration of the magnetic circuit shown in FIG. 10 will be described. The magnetic field of the phase compensating magnetic circuit actively utilizes the leakage magnetic flux from the main magnetic circuit.
Has no back yoke of the permanent magnet 41b. That is, since there is no need for a compensating permanent magnet, the number of components can be reduced, and the size of the magnetic circuit in the horizontal direction can be reduced.

Next, the configuration of the magnetic circuit shown in FIG. 11 will be described. This magnetic circuit is obtained by adding a permanent magnet 45 for phase compensation to the magnetic circuit of FIG. 10, and the magnetic field of the magnetic circuit for phase compensation is added to the magnetic field of the permanent magnet 45 in the same manner as in the above embodiment. This utilizes the magnetic flux leakage from the circuit. Since the leakage magnetic flux from the main magnetic circuit is added, the thickness of the compensating permanent magnet can be reduced, the lateral size of the magnetic circuit can be reduced, and the magnetic flux density of the compensating magnetic gap is stabilized.

FIG. 12 is a plan view, a sectional side view, and a perspective view showing only the configuration of a drive coil of an objective lens driving device according to another embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

The configuration of this apparatus is the same as that of the first embodiment except for the tracking coil 49 for phase compensation and the permanent magnet 50 for compensation. The compensation tracking coil is mounted below the main tracking coil, and accordingly, the length of the compensation permanent magnet 50 in the vertical direction is also increased. Note that the directions of the lines of magnetic force are from right to left for both the main magnetic gap and the compensating magnetic gap.

Here, the effect of the phase compensation in the tracking direction will be described with reference to FIG. 13 which simply shows the relationship between the driving force generated by each magnetic circuit and the position of the center of gravity of the movable part.

The driving force provided by the main magnetic circuit is represented by r
m, the driving force given by the phase compensation magnetic circuit is rc
Then, when the objective lens 1 is driven in the right direction in the figure, when a current is applied to the main tracking coils 7a and 7b in the direction shown in the figure, a rightward driving force rm is generated. Also,
When a current is applied to the phase compensation tracking coils 49a and 49b in the direction shown in the figure, a leftward driving force rc is generated. Therefore, the rightward driving force F is: F = rm
-Rc. In addition, G.V.
C. The surrounding moment M is M = hm × rm−hc × rc. Here, if rc = hm / hc × rm, the moment becomes zero. Here, when the position of the center of gravity of the movable part and the driving point of the main magnetic circuit coincide in the left-right direction, if hc or the magnetic flux density of the compensation gap is adjusted so as to satisfy the above equation, G. C. The surrounding moment becomes zero, and the occurrence of higher-order resonance can be suppressed.

As shown in FIGS. 2 and 6, when the position of the center of gravity (GC) of the movable portion is located closer to the objective lens than the driving point of the main magnetic circuit, the first embodiment is performed. As described in the above, the driving force rc by the magnetic circuit for phase compensation
Is already optimized by the magnetic field strength of the compensating permanent magnet 50 and the number of turns of the compensating tracking coil 49, so that hm in the above equation is adjusted, that is, the vertical mounting position of the compensating tracking coil is adjusted. As a result, G. C. It can offset the surrounding moment.

Therefore, even if the position of the center of gravity of the movable part and the driving point are three-dimensionally shifted, phase compensation can be performed at the same time.

The magnetic circuit for phase compensation in this embodiment may have a configuration in which the main magnetic circuit and the yoke are shared, as described in the second and subsequent embodiments. However, the clearance between the compensation coil and the bottom of the yoke is reduced.

[0048]

According to the objective lens driving device of the present invention, since the position of the center of gravity of the movable portion is located closer to the objective lens than the driving center, a moment in the direction opposite to the direction in which the movable portion is desired to be displaced is generated. By applying a driving force in the direction opposite to the direction in which the movable part is to be displaced by the phase compensation magnetic circuit and the coil, a moment is generated in the direction in which the movable part is to be displaced, and the above-mentioned moment is canceled to achieve a higher order. Resonance can be suppressed.

In addition, since a single magnet is used as the phase compensation magnetic circuit, a simple magnetic circuit configuration is used.
Higher-order resonance can be easily suppressed.

Further, since the phase compensating magnetic circuit shares the yoke with the main magnetic circuit, the magnetic flux density in the compensating magnetic gap becomes more uniform and the amount of generated moment is stabilized, so that the amount of moment can be easily adjusted. It is.

Further, since the phase compensation tracking coil is mounted below the main tracking coil, the position of the center of gravity of the movable portion is located above the driving point, and even if the position of the center of gravity is three-dimensionally shifted, the same as above. Phase compensation is possible, and high-order resonance can be suppressed. Therefore, in any of the above cases, the occurrence of high-order resonance can be suppressed, and the weight of the movable portion can be reduced, so that a small and thin objective lens driving device can be obtained. Weight and weight can be achieved.

[Brief description of the drawings]

FIG. 1 is a plan view (a), a side sectional view (b), and a perspective view (c) showing a configuration of a drive coil according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating the effect of the phase compensation of the present invention.

FIG. 3 is a graph of frequency versus gain and frequency versus phase, respectively.

FIG. 4 is a schematic view of a conventional example.

FIG. 5 is a graph of frequency versus gain and frequency versus phase, respectively.

FIG. 6 is a schematic diagram showing the effect of the phase compensation of the present invention.

FIG. 7 is a graph of frequency versus gain and frequency versus phase, respectively.

FIG. 8 is a plan view (a) and a side sectional view (b) of a second embodiment of the present invention.

FIG. 9 is a plan view (a) and a side sectional view (b) of a magnetic circuit portion according to a third embodiment of the present invention.

FIG. 10 is a plan view (a) and a side sectional view (b) of a magnetic circuit portion according to a fourth embodiment of the present invention.

FIG. 11 is a plan view (a) and a side sectional view (b) of a magnetic circuit portion according to a fifth embodiment of the present invention.

FIG. 12 is a plan view (a), a side sectional view (b), and a perspective view (c) showing a configuration of a drive coil according to a sixth embodiment of the present invention.

FIG. 13 is a schematic diagram simply showing the relationship between each driving force point and the position of the center of gravity of the movable part in the sixth embodiment of the present invention.

[Description of Signs] 1 Objective lens 2 Lens holder 3 Elastic body 4 Base 5 Yoke 6 Permanent magnet 7 Tracking coil 8 Focusing coil 9 Phase compensation tracking coil 10 Phase compensation permanent magnet 11 Fixed part 12 Main magnetic circuit 13 Phase compensation Magnetic circuit

Claims (4)

(57) [Claims] An optical element (objective lens) for converging and irradiating a recording medium with a light beam, a movable part including a holding means (lens holder) for holding the optical element, In an objective lens driving device comprising a driving means having a magnetic circuit composed of a coil, a yoke and a permanent magnet, which is displaced in a focusing direction and a tracking direction, the magnetic circuit as the driving means is provided in a direction in which the movable part is to be displaced. It comprises a main magnetic circuit for providing a driving force and a magnetic circuit for phase compensation for providing a driving force in a direction opposite to that of the main magnetic circuit, each of which has a single magnetic gap. The coil is composed of a focus coil whose central axis is parallel to the optical axis of the optical element, a vertical main tracking coil, and a tracking coil for phase compensation. An objective lens which is disposed in the main magnetic gap together with the coil, and the tracking coil for phase compensation is mounted on the other opposite side surface, and is disposed in the magnetic gap for compensation together with the focus coil of the mounting part. Drive. 2. The objective lens driving device according to claim 1, wherein the phase compensation magnetic circuit is constituted by only a single magnet. 3. The objective lens driving device according to claim 1, wherein the magnetic circuit for phase compensation shares a yoke with a main magnetic circuit. 4. The tracking coil for phase compensation,
2. The objective lens driving device according to claim 1, wherein the objective lens driving device is mounted below a mounting position of the main tracking coil.