JPH07182669A - Apparatus for driving objective lens - Google Patents

Abstract

PURPOSE:To restrict a resonance of higher order without adding a balancer or the like and to make a movable part light-weight and an apparatus compact and thin, by providing a magnetic circuit for compensation of a phase in addition to a main magnetic circuit as a driving means. CONSTITUTION:A main magnetic circuit 12 is constituted of a U-shaped yoke 5 fitted at a fixed part 11, and permanent magnets 6a, 6b mounted inside the yoke 5. A focusing coil 8 is wound in a manner to surround the permanent magnet 6b and yoke 5b. A main tracking coil 7 consists of two rings of flat coils 7a, 7b. A magnetic circuit 13 for compensation of a phase comprises a permanent magnet 10 directly set at the fixed part, and a tracking coil 9 for compensation of a phase which is secured to a side face of the focusing coil 8 and a lens holder 2, and impresses a driving force opposite to that of the main magnetic circuit 12 to a movable part of the lens holder 2. A phase- compensating part 8b of the focusing coil 8 and the tracking coil 9 are arranged in a compensation magnetic gap defined by the permanent magnet 10 and yoke 5b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective 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 lens is biaxially driven in order to control a focusing position of a light beam irradiated on an information recording medium such as a magneto-optical disk through the objective lens in a focusing direction and a tracking direction. Lens drive devices are known, and various devices have been devised for the purpose of size reduction and weight reduction. As an example of this type of apparatus, Japanese Patent Laid-Open No.
-111237 is available. The focus coil and the tracking coil are arranged on the opposite side of the objective lens fixed side with respect to the vicinity of the support point of the lens support member and fixed to the lens support member. With this configuration, the movable portion is fixed to the support point of the lens support member. It is possible to reduce the weight of the balancer added to balance the moments of the movable parts so as to match the center of gravity.

In Japanese Patent Laid-Open No. 5-109094, at least a part of the elastic supporting member of the movable portion is located in the light beam entering the objective lens and / or in the light beam exiting from the objective lens. By making the objective lens and the light flux substantially parallel to the surface of the optical recording medium close to each other, the device can be made compact and thin.

Further, in Japanese Patent Laid-Open No. 5-205299, the corner of the permanent magnet of the magnetic circuit on the side facing the yoke is cut off to make the facing side smaller than the width of the yoke. The magnetic flux directed toward the fan is spread in a fan shape so as to obtain a moment around the movable portion in the direction of movement.

Now, the importance of reducing the weight of the movable portion will be briefly described. As the optical disk device body becomes thinner and lighter, the rigidity of each mechanical component decreases overall.Therefore, the reaction force generated in the magnetic circuit when driving the objective lens causes the magnetic circuit to vibrate and the vibration to occur. The mechanical parts are transmitted, and finally the optical disk surface resonates. Therefore, it is difficult to make the optical disc device thinner and lighter. To solve this problem, the reaction force generated in the magnetic circuit should be reduced.
That is, it is important to reduce the weight of the movable portion of the objective lens driving device. However, in an ordinary objective lens driving device, the objective lens and the driving coil are separated from each other in order to secure a space for optical components such as a light beam and a rising mirror. If the weight is designed to be as light as possible, the position of the center of gravity of the movable portion and the driving point will deviate. Therefore, in order to suppress the occurrence of higher-order resonance due to this deviation, it is necessary to attach the balancer to the movable part so as to eliminate the above-mentioned deviation, which is an obstacle to reducing the weight of the movable part. 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-mentioned conventional examples, the objective lens driving device disclosed in Japanese Patent Laid-Open No. 4-111237 discloses an objective lens driving device for aligning the center of gravity of the movable portion with the supporting point of the lens supporting member. It is necessary to add a balancer corresponding to the difference between the moment with respect to the support point of the lens support member and the moment with respect to the support point of the lens support member of the focus coil and the tracking coil, which hinders the weight reduction of the movable portion.

The objective lens driving device disclosed in Japanese Patent Laid-Open No. 5-109094 can achieve a thin device, but requires a balancer for the lens supporting member, which reduces the weight of the movable part, as in the conventional example. Can not be achieved.

Further, the objective lens driving device disclosed in Japanese Patent Laid-Open No. 5-205299 does not require a balancer for matching the center of gravity of the movable portion with the driving center, but the movable portion is moved in the direction in which the movable portion is moved. Since it is possible to obtain a moment, the higher-order resonance that occurs due to the above-mentioned 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 remains straight. In order to tilt the magnetic flux as much as necessary to balance the moment, it is necessary to make the width of the facing surface of the permanent magnet much smaller than the yoke width. Will be greatly reduced. Actually, balancing by this method is limited to the case where the shift amount is minute, and a balancer is required as in the conventional example, which hinders reduction in weight of the movable portion.

The present invention has been proposed to solve the above problems, and since higher order resonance can be suppressed by balancing moments without adding a balancer or the like, the weight of the movable part can be reduced. 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 as a driving means, a phase compensating magnetic circuit for applying a driving force in a direction opposite to the direction in which the movable portion is desired to be displaced is provided. The main tracking coil is attached to one side of the focus coil, the tracking coil for phase compensation is attached to the other side facing the focus coil, the main tracking coil side is in the main magnetic gap, and the tracking coil side for phase compensation is for phase compensation. It is arranged in the magnetic gap.

According to a second aspect of the invention, the phase compensating magnetic circuit is constituted by only a single magnet.

According to a third aspect of the invention, the phase compensating magnetic circuit shares the yoke with the main magnetic circuit.

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

[0014]

When the center of gravity of the movable portion is located closer to the objective lens than the driving center, a moment is generated in a direction opposite to the direction in which the movable portion is to be displaced. By applying a driving force in a direction opposite to the direction in which the movable portion is desired to be displaced, a moment in the direction in which the movable portion is desired to be displaced is generated, and the moment is offset to suppress higher-order resonance.

Further, by constructing the magnetic circuit for phase compensation with a single magnet, a simple magnetic circuit configuration is provided.
Higher-order resonance can be easily suppressed.

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

Further, since the phase compensation tracking coil is attached below the main tracking coil, even if the position of the center of gravity of the movable portion is above the drive center, phase compensation can be performed in the same manner as above.

[0018]

Embodiments of the objective lens driving device of the present invention will be described below with reference to the drawings.

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

The objective lens 1 is fixed to the lens holder 2, and the lens holder 2 is provided on both side surfaces of the lens holder 2.
The elastic bodies 3 for movably supporting the base 4 in two directions are attached to the upper and lower sides, respectively.
The focusing coil 8 and the tracking coil 7 are fixed to the opening of the. The main magnetic circuit 12 is composed of a U-shaped yoke 5 attached to the fixed portion 11 and permanent magnets 6a and 6b attached inside thereof. 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 arranged in the magnetic gap of the main magnetic circuit 12, and the focusing coil 8 and
Is wound so as to surround one permanent magnet 6b and one yoke 5b portion, and the 8b portion of the focusing coil 8 is located outside the magnetic gap of the main magnetic circuit 12. Further, the main tracking coil 7 is composed of two ring-shaped flat coils 7a and 7b as shown in FIG.

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

The direction of the lines of magnetic force is from right to left when the magnetic gap of the main magnetic circuit is from right to left.

2 to 5, in the above embodiment,
The effect of phase compensation in the focus direction will be described.

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

Here, when the objective lens 1 is driven in the upward direction, assuming that the directions of the magnetic fluxes in the main magnetic gap and the phase compensation gap are from right to left in the figure, the 8a portion of the focus coil 8 is viewed from the front of the paper. When the current is passed in the downward direction, the upward driving force fm is generated. Also, the focus coil 8
In the portion 8b, a current flows from the back side of the paper to the front, so that the downward driving force fc is generated. Therefore, the upward driving force F is given by F = fm-fc. In addition, the moment M around 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 set to 0 by adjusting the magnetic field strength of the phase compensating magnet 10 and the distance to 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 it is possible to reduce the amount of decrease in the upward driving force F due to the compensation driving force fc.

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

FIG. 3 shows the result of measuring the frequency characteristic of the displacement of the objective lens in the focus direction in the objective lens driving device manufactured by the above-mentioned structure. From the figure, it can be seen that the problematic higher-order resonance is suppressed up to high frequencies.

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 high-order resonance is generated as shown in the frequency characteristic of displacement in the focusing direction in FIG. Is.

Similarly, the effect of phase compensation in the tracking direction will be described with reference to FIG. The driving force given by the main magnetic circuit is rm, and the driving force given by the phase compensating magnetic circuit is rc. When the objective lens 1 is driven upward in the figure, the main tracking coils 7a and 7b
When a backward current is applied to each coil connection side (marked with X in the figure) from the front side of the paper, an upward driving force rm is generated. Further, when a frontward current is passed from the back side of the drawing to the coil connection side (marked by X in the drawing) of each 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, the G.V. of the movable part including the objective lens.
C. The surrounding moment M is M = wm × rm−w
It becomes c × rc. Here, if rc = wm / wc × rm, then the moment becomes zero. Here, the magnetic field strength 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 condition can be satisfied by adjusting the number of turns. Therefore, when the objective lens is driven, the moments generated around the center of gravity of the movable portion are canceled out, so that higher-order resonance can be suppressed.

FIG. 7 shows the result of measuring the frequency characteristic of the displacement of the objective lens in the tracking direction in the objective lens driving device manufactured by the above structure. From the figure, it can be seen that the problematic higher-order resonance is suppressed over a high range.

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

In this embodiment, if the amount of displacement between the center of gravity of the movable portion and the driving point is very small, 5 of the yoke 5 is used.
It is also possible to reduce the thickness of the b portion so that the magnetic flux leaks from the main magnetic circuit, eliminate the permanent magnet 10 for phase compensation, and obtain the driving force for phase compensation by the leaked magnetic flux.

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

The phase compensating magnetic circuit 33 is constituted by the permanent magnets 30 attached to the side surfaces of the 25b portion, 25c portion and 25c portion of the horizontal E-shaped yoke 25, and the 28b portion of the focusing coil 28 and the phase compensating circuit. The tracking coil 29 is arranged in the magnetic gap of the compensating magnetic circuit 33. The direction of the magnetic force lines is from right to left when the magnetic gap of the main magnetic circuit is from right to left.

In the magnetic circuit of this structure, the compensating magnetic circuit can form a closed loop magnetic circuit as well as the main magnetic circuit, so that the magnetic flux density in the compensating magnetic gap becomes uniform,
More stable phase compensation can be performed.

In the adjustment of the phase compensation amount in this apparatus, the magnetic flux density of the compensating magnetic gap, the magnetic field strength of the permanent magnet 30, and the magnetic field strength of the permanent magnet 30 are first adjusted so that the compensation amount in the focusing direction is optimized, as in the first embodiment. 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. Only the magnetic circuit is described in each case. Except for the magnetic circuit, it may be considered as in the first and second embodiments.

First, the magnetic circuit of FIG. 9 will be described.
The phase compensating magnetic circuit 33 is of a type that shares the yoke with the main magnetic circuit 32 as in the case of the second embodiment, and the portions corresponding to those of the second embodiment are designated by the same reference numerals. The permanent magnet 35 of the magnetic circuit for phase compensation is attached to the bottom of the yoke between the yokes 25b and 25c as shown in the figure. The magnetization direction of the permanent magnet 35 is from left to right so that the direction of the magnetic force lines in the magnetic gap of the main magnetic circuit is from right to left, so that the direction of the magnetic force lines in the compensation gap is also from right to left. With this magnetic circuit configuration, the size in the lateral direction can be made smaller than that of the configuration of FIG.

Next, the magnetic circuit configuration of FIG. 10 will be described. The magnetic field of the phase compensating magnetic circuit positively utilizes the leakage magnetic flux from the main magnetic circuit.
The permanent magnet 41b has no back yoke. In other words, since a permanent magnet for compensation is not required, the number of parts can be reduced and the lateral size of the magnetic circuit can be reduced.

Next, the magnetic circuit configuration of 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 the magnetic field of the permanent magnet 45 plus the main magnetic field as in the above embodiment. It uses the leakage flux from the circuit. Since the leakage magnetic flux from the main magnetic circuit is added, the thickness of the permanent magnet for compensation can be reduced, the lateral size of the magnetic circuit can be reduced, and the magnetic flux density of the compensation magnetic gap is stabilized.

FIG. 12 shows a plan view, a side sectional view and a perspective view showing only the structure of the 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 designated by the same reference numerals, and the duplicated description will be omitted.

This device has the same structure as the device 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 attached below the main tracking coil, and the vertical length of the compensation permanent magnet 50 is also increased accordingly. The direction of the lines of magnetic force is from right to left for both the main magnetic gap and the compensating magnetic gap.

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

The driving force given by the main magnetic circuit is r
m, the driving force given by the magnetic circuit for phase compensation is rc
Then, when the objective lens 1 is driven in the right direction in the figure, when a current is passed through 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 passed through the phase compensation tracking coils 49a and 49b in the direction shown in the drawing, a leftward driving force rc is generated. Therefore, the driving force F to the right is: F = rm
Given by -rc. In addition, the G.V.
C. The surrounding moment M is M = hm × rm−hc × rc. Here, if rc = hm / hc × rm, then the moment becomes zero. If the position of the center of gravity of the movable portion and the driving point of the main magnetic circuit are aligned in the left-right direction, the magnetic flux density of hc or the compensation gap should be adjusted so as to satisfy the above equation. C. The surrounding moment becomes 0, and the occurrence of higher-order resonance can be suppressed.

As shown in FIGS. 2 and 6, when 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 used. As described above, the driving force rc by the magnetic circuit for phase compensation
Has already been optimized depending on the magnetic field strength of the compensation permanent magnet 50 and the number of turns of the compensation tracking coil 49. Therefore, hm of the above equation is adjusted, that is, the vertical mounting position of the compensation tracking coil is adjusted. By this, G. C. The surrounding moments can be offset.

Therefore, even if the position of the center of gravity of the movable portion and the driving point are three-dimensionally displaced, the phase can be compensated at the same time.

The phase compensating magnetic circuit in this embodiment may have a structure in which the main magnetic circuit and the yoke are shared, as in the second and subsequent embodiments. However, the clearance between the compensation coil and the bottom of the yoke becomes small.

[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 side than the drive center, a moment is generated in a direction opposite to the direction in which the movable portion is desired to be displaced. By applying a driving force in the direction opposite to the direction in which the moving part is to be displaced by the magnetic circuit for phase compensation and the coil, a moment is generated in the direction in which the moving part is to be displaced, and by canceling the moment, a higher order Resonance can be suppressed.

Further, by constructing the phase compensating magnetic circuit with a single magnet, a simple magnetic circuit configuration
Higher-order resonance can be easily suppressed.

Further, in the phase compensating magnetic circuit, by sharing the yoke with the main magnetic circuit, the magnetic flux density in the compensating magnetic gap becomes more uniform and the generated moment amount becomes stable, so that the moment amount can be easily adjusted. Is.

Further, since the phase compensation tracking coil is mounted below the main tracking coil, the center of gravity of the movable portion is located above the driving point, and even when the position is three-dimensionally displaced, the same as above. Phase compensation is possible and high-order resonance can be suppressed. Therefore, in any of the above cases, it is possible to suppress the occurrence of high-order resonance and to reduce the weight of the movable portion, so that it is possible to obtain a compact and thin objective lens driving device, which in turn reduces the thickness of the optical disk device body. And weight reduction can be achieved.

[Brief description of 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 showing an effect of 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 an effect of 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 of 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 of a sixth embodiment of the present invention.

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

[Explanation of symbols]

 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)

[Claims] 1. A movable part including an optical element (objective lens) that focuses a light beam and irradiates the recording medium, a holding unit (lens holder) that holds the optical element, and the optical element with respect to the recording medium. In the objective lens driving device including a driving unit having a magnetic circuit composed of a coil, a yoke, and a permanent magnet, which are displaced in the focusing direction and the tracking direction, the magnetic circuit serving as the driving unit is arranged in a direction in which the movable portion is to be displaced. It is composed of a main magnetic circuit for giving a driving force and a phase compensating magnetic circuit for giving a driving force in a direction opposite to the main magnetic circuit, and each has a single magnetic gap. The coil is composed of a focus coil whose center axis is parallel to the optical axis of the optical element, a main tracking coil and a tracking coil for phase compensation which are perpendicular to each other. The objective lens is arranged in the main magnetic gap together with the coil, the phase compensation tracking coil is attached to the other side surface facing the coil, and is arranged in the compensation magnetic gap together with the focus coil of the attachment portion. Drive. 2. The objective lens driving device according to claim 1, wherein the magnetic circuit for phase compensation is composed of only a single magnet. 3. The objective lens driving device according to claim 1, wherein the phase compensating magnetic circuit shares a yoke with the main magnetic circuit. 4. The phase compensation tracking coil comprises:
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.