JP2000020986A - Objective lens drive - Google Patents

Abstract

(57) [Problem] To provide an objective lens driving device that does not generate unnecessary vibration even when performing high-precision control. SOLUTION: The objective lens driving device 40 according to the present invention.
Is an objective lens holder 3 capable of holding the objective lenses 1 and 2
Is provided. The objective lens holder 3 has a shaft hole 4 having an axis parallel to the optical axis of the first objective lens 1. The yoke 6 holds a sliding shaft 5 that slidably passes through the shaft hole 4. Vertical driving means 10a, 1 which can drive the objective lens holder 3 in the axial direction of the sliding shaft 5 are provided in the objective lens holder 3.
0b, and rotation driving means 7a and 7b capable of driving the objective lens holder 3 in the circumferential direction of the sliding shaft 5 are provided. The side pressure applying means 7 a, 7 b, 10 a, 10 b are connected to a straight line connecting the central axis of the sliding shaft 5 and the optical axis of the objective lens 1, the central axis of the sliding shaft 5 and the shaft hole 4 of the sliding shaft 5. Lens holder 3 so that the plane angle formed by the straight line connecting the contact points of
Is biased toward the sliding shaft 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens driving device used for recording / reproducing information on / from an information recording medium such as an optical disk.

[0002]

2. Description of the Related Art As is well known, a compact disk (C
As represented by D) and a laser disk (LD), an optical disk device for recording / reproducing information by using a laser beam is widely used. Recently, the optical disk device has also been used as a storage device of a computer.

When recording / reproducing information to / from an optical disk, the laser beam is focused on an optical disk surface using an objective lens to form a spot. The smaller the spot size, the higher the recording density on the optical disk.

On the other hand, in order to keep the above-mentioned spot size as small as possible, irradiation is performed so that the optical axis of the objective lens is as perpendicular to the optical disk surface as possible, so that coma aberration is hardly generated. It is important to do.

Further, the information recording position on the disk may move with the rotation of the disk due to the influence of the warp or eccentricity of the disk. In this case, the focal position follows the information recording position. Have to work. Therefore, it is necessary to precisely control the positioning of the objective lens. Therefore, the objective lens driving device is required to have high rigidity and high acceleration sensitivity.

As an objective lens driving device capable of performing such control, there is, for example, a shaft sliding type objective lens driving device disclosed in Japanese Patent Application Laid-Open No. 9-282885. The objective lens holder in this conventional device is slidable along a sliding shaft formed as a fixed portion, and is held rotatably around the sliding shaft.

In the conventional apparatus, a magnetic drive circuit for focusing and a magnetic drive circuit for tracking are formed between the objective lens holder and the fixed portion. In general, a focusing drive coil and a tracking drive coil are mounted on the side of the objective lens holder, and a focusing magnet and a tracking magnet are mounted on the fixed portion facing the position.
With such a configuration, by exciting the focusing driving coil, the objective lens holder slides along the sliding axis, and the focusing correction of the objective lens mounted on the objective lens holder is performed. Similarly, by exciting the tracking drive coil, the objective lens holder is driven to rotate around the sliding axis, and tracking correction of the objective lens is performed.

[0008] The shaft hole of the objective lens holder and the sliding shaft passing through the shaft hole relatively move as described above. Therefore, there is a clearance between the two. In order to prevent rattling between the two due to this clearance,
A lateral pressure (force pressing in a direction perpendicular to the sliding axis) on the sliding axis is applied to the objective lens holder. Examples of a method for applying the lateral pressure include a method using an elastic material and a magnetic method. The magnetic method is, for example, a method in which a ferromagnetic material is attached to a movable part side such as an objective lens holder, a permanent magnet is provided on a fixed part side, and a magnetic attraction force acting between the two is used.

Since the sliding shaft is usually a processed product made of a metal material or the like, the dimensional error is relatively small. However, since the objective lens holder is generally a resin molded product, the inner surface shape of the shaft hole often has irregularities in both the axial direction and the circumferential direction. In the case where the accuracy of the inner surface shape of the shaft hole is low, when the objective lens holder is displaced in the axial direction or the circumferential direction, the direction of the lateral pressure (for example, the direction of the magnetic attraction force) on the objective lens holder changes, The relationship between the frictional force between the shaft and the sliding shaft changes, the contact relationship between the shaft hole and the sliding shaft changes, and the objective lens holder tilts.

The above-mentioned publication also states that, in the case where the shaft hole has a shape that is convex near the center in the axial section, the objective lens holder remains inclined in an unstable state, which causes a problem. . As a countermeasure against such a problem, in the conventional device described in the above-mentioned publication, the shape is set such that, when the lateral pressure is applied, two points separated in the axial direction on the outer peripheral surface of the sliding shaft are set. Having a "shaft bore inner peripheral surface".

[0011]

On the other hand, in recent years, the recording density of an optical disk has been increased, and the positioning accuracy and allowable lens inclination required for an objective lens driving device have become even more severe. In order to achieve high positioning accuracy, the objective lens must be operated at a smaller amplitude. That is, the objective lens must be operated with good characteristics even with a small driving force.

However, in the above-mentioned conventional apparatus, since a frictional force is generated between the sliding shaft and the objective lens holder, the influence of the frictional force becomes relatively large as the driving force decreases. In particular, this phenomenon has a wavelength of 650 nm or less and a numerical aperture (NA) to increase the recording density of the optical disk.
This is remarkable when e) is 0.6 or more.

In particular, track control for causing the focal position to follow the movement of the track position due to eccentricity of the optical disk or the like is performed by cooperative control of an objective lens driving device and a feed mechanism (see FIG. 6) on which the objective lens driving device is mounted. In this case, a low-frequency component having a large amplitude at a low frequency is caused to follow by a feed mechanism, and a high-frequency component having a small amplitude at a high frequency is caused to follow by an objective lens driving device. in this case,
In the conventional objective lens driving device, the influence of the frictional force on the driving force cannot be ignored, and vibration due to the frictional force occurs. This vibration usually occurs from around 1 kHz to 10 kHz or less, and has a significant effect on control stability.

The present invention has been made in view of the above points, and has as its object to provide an objective lens driving device that suppresses the generation of unnecessary vibration even when performing high-precision control. .

[0015]

According to the present invention, there is provided a lens holder capable of holding an objective lens and having an axial hole having an axis parallel to the optical axis of the objective lens, and a lens holder capable of being held by a yoke. A sliding shaft that slidably penetrates through the shaft, axial driving means that can drive the lens holder in the axial direction of the sliding shaft, and that can drive the lens holder in the circumferential direction of the sliding shaft. A rotation driving unit, a straight line connecting the center axis of the sliding shaft and the optical axis of the objective lens, and a straight line connecting a center point of the sliding shaft and a contact point of the shaft hole of the sliding shaft. And a side pressure applying means for urging the lens holder toward the sliding shaft so that a plane angle formed by the lens holder is 90 ° or less.

According to the present invention, a straight line connecting the center axis of the sliding shaft and the optical axis of the objective lens, and a straight line connecting the contact point between the center axis of the sliding shaft and the shaft hole of the sliding shaft. Since the lens holder is urged toward the sliding shaft so that the plane angle formed by the lens is 90 ° or less, the generated vibration leads to a phase advance, and the control characteristics are improved.

Further, the present invention can hold an objective lens,
A lens holder having an axis parallel to the optical axis of the objective lens and having an axial hole having a cross section tapered toward a central portion of the axis, can be held by a yoke, and slidably move the axial hole. A sliding shaft that penetrates and has a diameter smaller than the minimum diameter of the shaft hole by a small amount; axial driving means capable of driving the lens holder in the axial direction of the sliding shaft; A rotation driving means that can be driven in the circumferential direction of the driving shaft,
An objective lens driving device comprising: a side pressure applying unit that urges the shaft hole toward the sliding shaft.

According to the present invention, the shaft hole is formed so that the cross section toward the central portion of the axis is tapered, and the sliding shaft has a small diameter smaller than the minimum diameter of the shaft hole, so that the sliding shaft is low. As well as obtaining a vibration frequency, a large vibration damping force is obtained, and control characteristics are improved.

The lens holder has the least optical aberration at a specific wavelength of 650 nm or less and can hold an objective lens having an aperture ratio of 0.6 or more. Also,
The lens holder can hold a plurality of objective lenses.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 are views showing an objective lens driving device according to a first embodiment of the present invention.

FIG. 1 is a plan view of an objective lens driving device according to a first embodiment of the present invention, FIG. 2 is a front sectional view of FIG.
FIG. 3 is a sectional view of the vicinity of the sliding shaft for explaining the contact state between the sliding shaft and the shaft hole, and FIG. 4 is an enlarged view of the contact portion of FIG. FIG. 5 is a front view of the objective lens holder (lens holder) showing the force generated in the tracking coil. FIG. 6 is a schematic diagram of an optical disk drive device using the objective lens driving device of the present embodiment. In addition, since each drawing is a schematic diagram, the size ratio of each part is different from the actual one.

The objective lens driving device 40 of the present embodiment
Is provided with two objective lenses 1 and 2 corresponding to respective wavelengths corresponding to reading or reading / writing of an optical disk corresponding to two wavelengths. The first objective lens 1 and the second objective lens 2 are fitted and fixed in an objective lens holder 3. A shaft hole 4 is penetrated in the center of the objective lens holder 3. The sliding shaft 5 fixed to the yoke 6 is inserted into the shaft hole 4. The first objective lens 1 has a larger NA (aperture ratio) than the second objective lens 2 and has an NA of 0.6,
It is designed so that optical aberration is minimized with respect to laser light having a wavelength of 650 nm. The objective lens 2 has the smallest optical aberration with respect to the laser light having a wavelength of 780 nm, and the NA is 0.45.

As for the two objective lenses 1 and 2, the necessary one is selected and used according to the optical disk. The objective lenses 1 and 2 receive light emitted from an optical system 21 (see FIG. 6) including a laser diode, a photodetector, various optical components, and the like through a light passage hole 13 provided on the bottom surface of the yoke 6.
a, 13b. This incident light focuses on the optical disk 20, and the reflected light enters the objective lenses 1 and 2 from opposite directions, and the light transmission holes 13a,
After passing through 13b, it returns to the optical system 21 and is received as a reproduction signal or a servo signal.

The objective lens holder 3 is made of plastic such as PPS (polyphenylenesulfide) having a good sliding property.

The shaft hole 4 has an axis parallel to the optical axes of the objective lenses 1 and 2, and as shown in FIG. 3, the cross section is tapered toward the center of the axis. The shape of the peripheral portion of the objective lens holder 3 which is not on the side of the shaft hole 4 may not be tapered.

The sliding shaft 5 slidably penetrates the shaft hole 4 and is formed to have a diameter smaller than the minimum diameter of the shaft hole 4 by a minute amount. Specifically, it is preferable that the sliding shaft 5 is a shaft having a diameter of about 2 μm to 10 μm smaller than a shaft having a maximum diameter which can be inserted into the shaft hole 4 (this diameter is substantially equal to the minimum diameter of the shaft hole). The sliding shaft 5 is coated with a lubricating film such as a fluororesin so that the friction between the shaft hole 4 and the sliding shaft 5 is reduced. Further, the sliding shaft 5 is fixed to the bottom surface of the yoke 6 by press fitting or bonding. The yoke 6 is made of a magnetic material such as iron, and has tracking permanent magnets 8a and 8b and focusing permanent magnets 9a and 9 described later.
The portion other than the portion in contact with b may be made of a composite material formed of plastic or the like. As shown in FIG.
It is fixed to 3.

The contact between the shaft hole 4 and the sliding shaft 5 is not at the upper and lower ends of the shaft hole as in the case of the conventional apparatus shown in FIG. 13, but at the center as shown in FIG. . When the actual contact surface is enlarged, it is considered that a plurality of contact points form a contact point region by fine irregularities as shown in FIG. 4, but these contact point regions are shorter than the diameter of the sliding shaft 5. Distance. Further, in the present embodiment, the center of gravity of the objective lens holder 3 holding the objective lenses 1 and 2 and the center of the contact point region substantially match both in the axial direction and in a plane perpendicular to the axis. .

In order to manufacture the shaft hole 4 which is minute and has a convex shape on the inner surface side, the center of the pin of the mold for forming the shaft hole 4 is made thinner, and the shrinkage of the resin is sufficiently considered. It is necessary to manage the mold shape and the injection molding conditions.

Further, on the side surface of the objective lens holder 3, 1
As shown in FIG. 1, each set of tracking coils 7a, 7b (rotational driving means) and one set of focus coils 10a, 10b (axial driving means) has a diameter of the objective lens holder 3 having a substantially cylindrical shape. To face each other,
They are fixed at substantially equal intervals. The tracking coils 7a, 7b and the focus coils 10a, 10b have substantially the same configuration, and their winding axes are in the radial direction of the objective lens holder 3.

The tracking coils 7a, 7b of the yoke 6
The two poles are divided into two parts in the circumferential direction of the yoke 6 so that the magnetization direction is substantially the radial direction of the objective lens holder 3 and the magnetization direction is opposite in each of the two parts. Magnetized tracking permanent magnets 8a and 8b
(Rotation driving means, side pressure applying means) are fixed. Similarly, the focus coils 10a and 10b of the yoke 6
At a position facing the object lens 2 in the axial direction of the objective lens holder 3.
The two-pole magnetized focusing permanent magnets 9a, which are divided so that the magnetizing direction is substantially the radial direction of the objective lens holder 3 and the magnetizing direction is opposite in each of the two divided portions.
9b (axial driving means, side pressure applying means) is fixed.

At a position corresponding to the back of each coil of the objective lens holder 3, a magnetic piece 11 made of an iron-based material is provided.
a, 11b, 12a, and 12b are respectively built in. Of these, the magnetic pieces 11a and 11b (side pressure applying means)
As shown in FIG. 1, the tracking permanent magnets 8a,
The position 8b is shifted to the first objective lens 1 side from the circumferential center position (magnetic pole division position) of 8b. For this reason, the magnetic piece 11
a and 11b show that the objective lens holder 3 is
A lateral pressure is generated that urges the sliding shaft 5 in the lateral direction.

On the other hand, as shown in FIG. 1, the magnetic pieces 12a and 12b (side pressure applying means)
The positions a and 9b are shifted to one side (upward in FIG. 1) from the center position in the circumferential direction. For this reason, the magnetic material pieces 12a,
Reference numeral 12b generates a side pressure that urges the objective lens holder 3 toward the sliding shaft 5 in the other direction (downward in FIG. 1).

Accordingly, the magnetic pieces 11a, 11b, 12a,
12b, the objective lens holder 3 moves the center axis of the sliding shaft 5 and the optical axis of the objective lens 1, the central axis of the sliding shaft 5 and the sliding shaft 5 Shaft hole 4
Plane angle Φ formed by a straight line connecting the contact point with
°, that is, in the direction of arrow F in FIG. 1 (the lower right direction in FIG. 1).

Here, the plane angle (side pressure action angle) Φ on which the side pressure acts is determined by the magnetic material pieces 11a, 11b, 12a, 12
changing the size and material of b, and corresponding permanent magnets 8a,
The ratio of the magnetic attraction force is adjusted by means such as changing the distance between the permanent magnets 8b, 9a, and 9b, changing the amount of deviation of these permanent magnets from the center in the circumferential direction, or changing the type of these permanent magnets. Can be easily changed. In the present embodiment, the side pressure action angle Φ is 45 °.

As shown in FIG. 2, the centers of the magnetic pieces 12a and 12b provided on the back side of the focus coils 10a and 10b are shifted downward from the axial centers of the focus coils 10a and 10b. I have. On the other hand, the magnetic pieces 11a, 11b behind the tracking coils 7a, 7b
As shown in FIG. 5, b has a center shifted upward from the center of the tracking coils 7a and 7b in the axial direction. In such an arrangement, the magnetic piece 1 facing the focusing permanent magnets 10a, 10b whose magnetization directions are different in the axial direction.
The force generated in 2a and 12b is large. Thus, the gravity acting on the objective lens holder 3 is compensated by the force acting on the magnetic pieces 12a and 12b, so that the objective lens holder 3 is held at an intermediate position in the movable range. When the objective lens holder 3 is slightly rotated, the magnetic material pieces 11a, 11b, 12a,
The resultant force acting between the permanent magnet 12b and the permanent magnets 8a, 8b, 9a, 9b is always in the opposite direction of the displacement, and the objective lens holder 3 receives a force that always returns to the position shown in FIG.

Such an objective lens driving device 40 is used by being mounted on a feeding device. An example is shown in FIG.

As shown in FIG. 6, the objective lens driving device 4
The 0 yoke 6 is fixed to the carriage 23. The carriage 23 has sliding bearings 15a, 15b, 15c,
Guide rails 14 are provided on the slide bearings 15a, 15b, and 15c.
a and 14b are inserted. Thus, the carriage 23 can freely move along the direction in which the guide rails 14a and 14b extend.

The guide rails 14a and 14b are provided with a spindle motor 1 for rotating the optical disk 20 on a base (not shown).
8 and is fixed. An optical system 21 including optical components such as a laser diode, a collimator lens, a beam splitter, and a photodetector is mounted on the base.

The carriage 23 has coils 17a, 17b
Are attached, and constitute a linear motor together with the magnetic circuit members 16a and 16b composed of magnets and yokes. Therefore, when a current flows through the coils 17a and 17b, the carriage 23 moves freely in the guide rail direction, and the objective lens driving device 40 can move substantially in the radial direction of the disk 20. The focusing positions of the objective lenses 1 and 2 on the disk 20 can be adjusted by the position of the carriage 23 and the movement of the objective lens holder 3 with respect to the carriage 23.

The mechanism for linearly moving the carriage 23 includes a linear motor as shown in FIG. 6 and a DC motor or a stepping motor as a power source.
There is a method in which a rotational force is converted into a linear force by a rack and pinion, a feed screw, or the like and driven. As the guide of the carriage 23, a ball bearing may be used in addition to the slide bearing.

As shown in FIG. 6, in this embodiment, the optical system 21 is fixed to the base.
3 may be mounted. Furthermore, only the optical system for the second objective lens 2 may be provided on the carriage 23, and the optical system for the first objective lens 1 may be provided on the base. It goes without saying that various configurations are allowed for the optical system. For example, a mode without using a collimator lens may be used.

Next, the operation of the present embodiment having the above configuration will be described.

When an electric current is applied to the focus coils 10a and 10b, the objective lens holder 3 is driven in the axial direction of the sliding shaft 5, and the positions of the objective lenses 1 and 2 in the optical axis direction change.
A so-called focus operation is achieved. When a current is applied to the tracking coils 7a and 7b, the objective lens holder 3 is driven in the circumferential direction of the sliding shaft 5, and the tracking operation is achieved.

FIGS. 7 and 8 show examples of vibration characteristic analysis when a very small current is applied to the tracking coils 7a and 7b.
This will be described with reference to FIG.

FIG. 7 shows the first objective lens 1 of the present embodiment.
FIG. 8 is a frequency response diagram of the rotation direction around the sliding shaft 5 at the time of the minute driving of FIG. 8. FIG. 8 shows the sliding at the time of the minute driving of the first objective lens when the magnetic pieces 11a and 11b are shifted to the bottom side for comparison. It is a frequency response figure of the rotation direction about a dynamic axis.

At the time of minute driving, the contact point between the sliding shaft 5 and the shaft hole 4 no longer slides, and a reaction force is generated with respect to the driving force by the tracking coils 7a and 7b. The point of contact between the sliding shaft 5 and the shaft hole 4 is on the side surface of the sliding shaft 5, whereas the center of gravity of the movable part (such as the objective lens holder 3) of this embodiment is
, The reaction force at the contact point becomes a moment force with respect to the objective lens holder 3.

In general, the objective lens driving device has a resonance mode around several kHz whose frequency is determined by the contact rigidity between the shaft hole 4 and the sliding shaft 5 and the rigidity of the sliding shaft 5, and the like. Force excites this mode.

The numerical analysis examples shown in FIGS. 7 and 8 and FIGS. 9 to 11 to be described later are calculated by approximating the contact point as a spring.

The damping term and the like are set to give priority to visibility, and since the actual phenomenon involves a sliding operation, the magnitude of the actual vibration is considered to be smaller than the analysis result shown in each figure. The tendency of the characteristics is shown in each figure, and it can be said that when driven with an extremely small current, the analysis results in each figure become closer.

As shown in FIG. 7, in the present embodiment, the generated vibration is a phase advance. This is because the present embodiment is designed to intentionally lead the phase in design and does not lead to phase lag due to other influential factors. Hereinafter, such design elements and effects will be described.

First, in order to compensate for the gravitational force acting on the objective lens holder 3, the positions of the magnetic pieces 11a and 11b should be shifted to the bottom side like the magnetic pieces 12a and 12b shown in FIG. Should be effective. However, if the magnetic pieces 11a, 11b are shifted above the tracking coils 7a, 7b, the magnetic flux passing through the tracking coils 7a, 7b is naturally affected. The arrangement of the magnetic pieces 11a and 11b in the present embodiment is determined with a greater emphasis on the influence on the magnetic flux of the tracking coils 7a and 7b than on the compensation of gravity.

FIG. 5 shows the tracking coil 7 of this embodiment.
The direction and magnitude of the force generated when a current in the direction b is passed are schematically represented by the direction and length of the arrow.

As shown in FIG. 5, the tracking coil 7
A vertical portion (b portion extending vertically) of b generates a force necessary for rotation as a whole, but at the same time, a horizontal portion (portion extending left and right) of the tracking coil 7b generates an axial force as a whole. When the magnetic pieces 11a and 11b are not provided, or when the coils are arranged symmetrically at the center of the coil, the axial force is canceled as a whole.
The above-mentioned tracking coil 7b does not cancel, and an upward force is generated as a whole.

Also, as shown in FIG.
The positions a and 11b are not axially symmetrical. When an upward force is generated in the tracking coil 7b, a downward force is generated in the tracking coil 7a. That is, the tracking coils 7a and 7b generate not only a rotational force around the sliding shaft but also a force around an axis perpendicular to the sliding shaft 5.

The phase of the rotational force about the axis perpendicular to the sliding shaft 5 and the phase of the tracking driving force determines whether the generated vibration is delayed or advanced. That is, in the present embodiment, FIG. 1, FIG.
Magnetic pieces 11a, 11b, 12a, 12b as shown in FIG.
By adopting the above arrangement, the vibration characteristic is set to the phase advance.

For comparison, FIG. 8 shows the magnetic material pieces 11a and 1a.
FIG. 7 shows a frequency response diagram of a rotation direction about a sliding axis when the first objective lens is slightly driven when the first objective lens is shifted to the bottom side. FIG.
As shown in FIG. 7, the vibration in this case is a phase lag.

Actually, not only the positions of the magnetic pieces 11a and 11b but also the dispersion of the permanent magnets 8a and 8b, the unevenness of the magnetic gap, and the fixing provided to the yoke 6 for fixing the objective lens driving device 40 are shown. For example, the magnetic material pieces 11a, 1
Even if 1b is arranged symmetrically at the center of the coils 7a, 7b, a rotational force about an axis perpendicular to the sliding axis may occur.

However, when an ideal magnetic circuit can be formed with extremely high precision, no extra force is generated.
As described above, the magnetic pieces may be arranged symmetrically with respect to the center of the coil without shifting. The magnetic pieces 11a, 11a
The arrangement of b, 12a, and 12b also depends on the allowable tilt amount of the objective lens holder 3, the accuracy of the shaft hole 4, and the like.

FIG. 9 is a frequency response diagram of the rotation direction around the sliding axis at the time of minute driving when the positions of the magnetic pieces 11a, 11b, 12a, and 12b are all shifted to the center of the coil in this embodiment. is there. In this ideal case, since no extra force is generated in the tracking coils 7a and 7b, the number of vibrations generated is smaller than in the case shown in FIG.

Next, in the present embodiment, a straight line connecting the central axis of the sliding shaft 5 and the optical axis of the first objective lens 1, the central axis of the sliding shaft 5, and the shaft hole of the sliding shaft 5. The effect that the plane angle formed by the straight line connecting the contact points with the point No. 4 is 90 ° or less will be described. For the sake of simplicity, the description will be made on the assumption that the positions of the magnetic pieces 11a, 11b, 12a, and 1b of the present embodiment are all symmetrically arranged at the center of the coil.

The vibration characteristics of the first objective lens 1 of the objective lens driving device imagined as described above are as shown in FIG.
On the other hand, the vibration characteristics of the second objective lens 2 in this virtual objective lens driving device are as shown in FIG.

In the case of FIG. 10, unlike FIG. 9, the vibration between 900 Hz and 3000 Hz has a phase delay. This difference is caused by the difference in the positional relationship between the sliding shaft 5 and the shaft hole 4 with respect to the contact point.

The virtual objective lens driving device is a magnetic piece 1
The configuration of the objective lens driving device 40 of the first embodiment is the same as that of the objective lens driving device 40 of the first embodiment except for the arrangement of 1a, 11b, 12a, and 12b. This corresponds to the case of 135 degrees. That is, when the absolute value of the plane angle Φ is 90 degrees or less, the vibration characteristic has a phase advance, and when the absolute value of the plane angle Φ exceeds 90 degrees, the vibration characteristic has a phase lag.

The first objective lens 1 has a larger NA than the second objective lens 2 and a shorter wavelength than the second objective lens 2.
Light of 50 nm or less passes. Therefore, the first objective lens 1
Can make the light condensing spot smaller than the second objective lens 2. For this reason, the use of the first objective lens 1 makes it possible to read and write finer information from the optical disc than the use of the second objective lens 2. Therefore, it is preferable that the positioning accuracy of the first objective lens 1 is high, that is, the first objective lens 1 operates with little vibration even with a small current.

The movement amount of the first objective lens 1 with respect to the optical system 21 is called a beam shift. Generally, the allowable beam shift amount becomes smaller as the spot to be generated becomes smaller. Therefore, in order to follow the eccentricity of the optical disk 20, it may be necessary to drive not only the objective lens holder 3 but also the feeder (see FIG. 6).
In such a case, it is preferable that the movement amount of the objective lens holder 3 is further controlled to be small.

When the driving current becomes small, the difference between the rotational force generated in the tracking coils 7a and 7b and the frictional force between the sliding shaft 5 and the shaft hole 4 becomes small, and the vibration shown in FIG. Will appear. On the other hand, when the second objective lens 2 is used, the allowable beam shift amount is large, the eccentricity can be followed only by the operation of the luggage lens holder 3, and the positioning accuracy is low. Therefore, the force generated in the tracking coils 7a, 7b is the second. 1
It is much larger than the case where the objective lens 1 is used, and the vibration as shown in FIG.

Therefore, in the present embodiment, by setting the plane angle Φ of the first objective lens 1 within 90 degrees, the phase is not delayed even if vibration occurs. As shown in FIG. 7, as a result of causing many vibrations to have a phase lead, there is a relatively small phase delay at 6 kHz, and all vibrations between 900 Hz and 3000 Hz have a phase lead. In the case of the present embodiment, since the servo band only needs to be about 4 kHz, there is not much problem as long as there is a small phase-lag oscillation near 6 kHz, which is beyond this. Also, since vibrations below the servo band lead the phase, it is a matter of degree, but this is much less of a problem than the phase lag, and the servo is less likely to be unstable. In general, since the control band of the objective lens driving device 40 is several kHz, the phase delay around this frequency loses the phase margin and is very problematic. On the other hand, the phase advance becomes a problem if the control band moves greatly due to the disorder of the gain.
Since a problem is less likely to occur than a phase lag, it is remarkable to make the phase lead even if vibration occurs as in the present embodiment.

The objective lens driving device 40 of the present embodiment
Performs the track control for causing the focal position to follow the movement of the track position due to the eccentricity of the optical disc 20 by the cooperative control of the objective lens driving device 40 and the feed mechanism (see FIG. 6) on which the objective lens driving device 40 is mounted. Especially suitable for. In this case, the low frequency component having a large amplitude at a low frequency can be made to follow by a feed mechanism, and the high frequency component having a small amplitude at a high frequency can be made to follow by an objective lens driving device.

On the other hand, it goes without saying that suppressing the occurrence of these vibrations is also effective for improving the vibration characteristics. The frequency of these vibrations depends on the contact rigidity between the shaft hole 4 and the sliding shaft 5. It is difficult to adjust the contact stiffness itself, but it is possible to adjust the frequency depending on the vibration mode. These vibrations are mainly vibrations in a rigid mode with respect to the sliding shaft 5 of the objective lens holder 3. The vibration in the rigid mode is a combination of vibrations in a total of six degrees of freedom, ie, three degrees of freedom in translation and three degrees of rotation.
Of these, the rigidity of the translation component is determined by the rigidity of the contact point and the weight of the objective lens holder 3, so that it is very difficult to greatly adjust the frequency.

However, the rotational rigidity can be adjusted relatively easily by the shape of the contact point. Generally, the objective lens holder 3
Is formed by injection molding of a resin, and the inner surface is formed from several microns to 10
Unevenness of micron or more is formed. In such a state, it is considered that the shaft hole 4 and the sliding shaft 5 are not in an ideal line contact but in a plurality of point contacts. Generally, the attitude of the cylindrical surface is restricted by four-point contact. However, if the shaft hole 4 is a cylinder, it is difficult to specify the contact point, and the contact point changes with the displacement of the objective lens holder 3. In this case, there arises a problem that the objective lens holder 3 is tilted due to the displacement, or that the first objective lens 1 generates an optical aberration and deteriorates the light collecting characteristics.

In the conventional device described in Japanese Patent Application Laid-Open No. 9-282885, the shape of the shaft hole is increased by increasing the inner diameter of the central portion and reducing the size of the end portion, as shown in FIG. The structure is adopted to stabilize the posture by contact with the camera. However, in such a structure, the frequency of the vibration mode in which the rigidity in the rotation direction of the objective lens holder is dominant becomes several kHz, and when this vibration is excited,
It adversely affects control stability.

In order to avoid this problem, in the present embodiment, the distance between the contact points is reduced, and the rotational rigidity of the objective lens holder 3 with respect to the sliding shaft 5 is reduced. That is, the shaft hole 4
Has an axis parallel to the optical axis of the objective lens 1 and has a cross section that tapers toward the center of the axis (see FIG. 3). Even in this case, there are a plurality of contact points as shown in FIG. Further, setting the contact point region, which is a region including all the contact points between the shaft hole 4 and the sliding shaft 5, to a distance shorter than the diameter of the sliding shaft 5 is also effective in reducing the rotational rigidity.

However, simply with such a shape,
As described in JP-A-9-282885,
There is a possibility that the objective lens holder 3 is greatly inclined. Further, the frequency of the vibration mode mainly based on translational rigidity remains at several kHz, which is also a problem.

Therefore, in this embodiment, the sliding shaft 5
The sliding shaft 5 is slidably penetrated through the shaft hole 4 and is smaller than the minimum diameter of the shaft hole 4 so that the gap between the shaft hole 4 and the shaft hole 4 is made as small as possible and small enough not to move. The diameter is reduced by the amount.

With such a small gap, an appropriate damping force is generated for the vibration generated by the contact rigidity between the objective lens holder 3 and the sliding shaft 5, and the magnitude of the vibration can be reduced.

The rigidity of the objective lens holder 3 in the direction of inclination with respect to the sliding shaft 5 is reduced by making the center portion convex and making the contact point area narrower than the diameter of the sliding shaft 5 as described above. Due to the decrease, the frequency of some vibration modes can be reduced to 1 kHz or less, the frequency can be separated from the control band of several kHz, and the adverse effect on high-precision control can be reduced.

In the present embodiment, it is preferable that the center of gravity of the objective lens holder 3 and the center position of the contact point region between the sliding shaft 5 and the shaft hole 4 be substantially equal in the axial direction. This is because the excited vibration is reduced by one. FIG. 11 shows vibration characteristics of the objective lens driving device having the characteristics shown in FIG. 9 and having the center position of the contact point region between the sliding shaft 5 and the shaft hole 4 substantially equal in the axial direction. In this case, as shown in FIG. 11, the number of generated vibrations is reduced, and the characteristics are further improved.
In this case, even if the contact points are largely separated from each other vertically as shown in FIG. 13, the same effect can be obtained because an area including all of these points can be considered as a contact point area.

Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the sliding shaft 5
The center of the contact point region between the shaft and the shaft hole 4 is
Completely with the center of gravity of the movable part consisting of
And the plane perpendicular to the sliding shaft 5 as well. When the second objective lens 2 is arranged closer to the first objective lens 1, a straight line connecting the optical axis of the second objective lens 2 and the center of the contact point region is formed by the first objective lens 1.
Is moved to a place where an angle of 90 degrees or less is formed with a straight line connecting the optical axis and the contact point region. Other configurations are the same as those of the first embodiment shown in FIGS. Second
In this embodiment, the same portions as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

According to the present embodiment, the remaining 2 kHz vibration in the characteristic shown in FIG. 11 disappears, and in principle, the vibration around several kHz is not excited at all. Further, since the angle between the contact points of the objective lenses 1 and 2 is 90 ° or less, even if vibration occurs due to imbalance of the driving force or the like, both vibrations of the objective lenses 1 and 2 lead to a phase and do not pose a problem. .

Also, when a small current is driven in the direction of the sliding shaft 5, the frictional force acts to pass through the center of gravity of the movable part, so that no rotational force is generated in the movable part, and the objective is moved in an unnecessary direction. The lens holder 3 is not moved. That is, unnecessary vibrations such as tilting of the objective lenses 1 and 2 do not occur.

However, in the second embodiment, for a rotation with a large amplitude, a rotation about the center axis of the sliding shaft 5 is generated instead of around the contact point, so that a large vibration is generated.
Therefore, the present embodiment is remarkably effective in applications in which the objective lens holder 3 is slightly rotated.

In each embodiment described above, the case where there are two objective lenses has been described. However, the same effect can be expected when there are three or more objective lenses. Of course, one case can be applied, but in this case, the wavelength is 65
The effect is particularly great when using a laser of 0 nm or less.

[0083]

According to the present invention, a straight line connecting the center axis of the sliding shaft and the optical axis of the objective lens is connected to a contact point between the center axis of the sliding shaft and the shaft hole of the sliding shaft. Since the lens holder is urged toward the sliding shaft so that the plane angle formed by the straight line is 90 ° or less, the generated vibration is advanced in phase, and the control characteristics are improved.

Further, according to the present invention, the shaft hole is formed so that the cross section toward the center of the axis is tapered, and the sliding shaft is smaller in diameter by a minute amount than the minimum diameter of the shaft hole. Accordingly, a low vibration frequency can be obtained, and a large vibration damping force can be obtained. Therefore, it is possible to provide an objective lens driving device that does not generate unnecessary vibration even when performing high-precision control.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an objective lens driving device according to a first embodiment of the present invention.

FIG. 2 is a schematic front sectional view of FIG.

FIG. 3 is an enlarged sectional view near a sliding shaft in FIG. 1;

FIG. 4 is an enlarged view showing a contact portion between a shaft hole and a sliding shaft in FIG. 3;

FIG. 5 is a front view of the objective lens holder in FIG. 1;

FIG. 6 is a schematic diagram showing an optical disk drive device on which the objective lens driving device of FIG. 1 is mounted.

FIG. 7 is a frequency response diagram of a first objective lens in FIG. 1 in a rotation direction.

FIG. 8 is a rotational frequency response diagram of the first objective lens of the objective lens driving device when the magnetic piece on the back side of the tracking coil is shifted to the bottom side.

FIG. 9 is a rotational frequency response diagram of the first objective lens of the objective lens driving device when the magnetic material pieces have the same height.

FIG. 10 is a rotational frequency response diagram of the second objective lens of the objective lens driving device when the magnetic material pieces have the same height.

FIG. 11 is a rotational frequency response diagram of the first objective lens of the objective lens driving device when the magnetic pieces are set at the same height, and the center of the contact point region and the center of gravity of the movable portion are aligned in the axial direction.

FIG. 12 is a schematic plan view showing an objective lens driving device according to a second embodiment of the present invention.

FIG. 13 is an enlarged cross-sectional view near a sliding shaft in a conventional objective lens driving device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st objective lens 2 2nd objective lens 3 Objective lens holder 4 Shaft hole 5 Sliding axis 6 Yoke 7a, 7b Tracking coil 8a, 8b Permanent magnet for tracking 9a, 9b Permanent magnet for focusing 10a, 10b Coil for focusing 11a, 11b, 12a, 12b Magnetic body 17a, 17b Coil 40 Objective lens driving device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H044 AA15 AA16 BD10 BD12 BD14 BD16 BE06 BE10 5D118 AA23 BA01 DC03 EA02 EC07 EC09 ED05 ED07 ED08 EE04 EE05 EF07 FA07 FB08 FB11

Claims (8)

[Claims] 1. A lens holder capable of holding an objective lens and having an axial hole having an axis parallel to the optical axis of the objective lens, and a slide capable of being held by a yoke and slidably penetrating the axial hole. A moving shaft; an axial driving unit capable of driving the lens holder in the axial direction of the sliding shaft; a rotary driving unit capable of driving the lens holder in a circumferential direction of the sliding shaft; A plane angle between a straight line connecting the center axis of the shaft and the optical axis of the objective lens and a straight line connecting a contact point between the center axis of the sliding shaft and the shaft hole of the sliding shaft is 90 °. An objective lens driving device, comprising: a side pressure applying unit that urges the lens holder toward the sliding shaft in order to make the following. 2. A yoke comprising: a lens holder capable of holding an objective lens, having an axis parallel to the optical axis of the objective lens, and having an axial hole having a tapered cross section toward a central portion of the axis. A sliding shaft that can be held and penetrates the shaft hole slidably, and has a diameter smaller than the minimum diameter of the shaft hole by a minute amount; and a shaft that can drive the lens holder in the axial direction of the sliding shaft. Direction driving means, rotation driving means capable of driving the lens holder in the circumferential direction of the sliding shaft, and side pressure applying means for biasing the shaft hole toward the sliding shaft. Characteristic objective lens driving device. 3. The objective lens driving device according to claim 2, wherein a length of a contact point region between the sliding shaft and the shaft hole is shorter than a diameter of the sliding shaft. 4. A center portion of a contact point region between the sliding shaft and the shaft hole coincides with the center of gravity of the entire lens holder for holding the objective lens in the sliding axis direction. The objective lens driving device according to claim 1. 5. A center portion of a contact point region between the sliding shaft and the shaft hole coincides with a center of gravity of the entire lens holder holding the objective lens with respect to a plane orthogonal to the sliding shaft. The objective lens driving device according to claim 1, wherein: 6. The side pressure applying means acts on a portion having the same axial height as the center of gravity of the objective lens holder for holding the objective lens, and applies the portion in a direction perpendicular to the sliding shaft. The objective lens driving device according to claim 1, wherein the objective lens driving device is driven. 7. The side pressure applying means is provided on the objective lens holder, and has a coil whose winding axis is in a radial direction of the optical axis, and is fixed to the yoke so as to face the coil. A permanent magnet magnetized in a radial direction, and a magnetic body attached to the lens at the same axial height with respect to the center of the winding axis of the coil or at a height higher than the axial height. Item 7. An objective lens driving device according to Item 6. 8. The side pressure applying means acts on a portion whose height in the axial direction is shifted from the center of gravity of the objective lens holder, and urges the portion in a direction perpendicular to the sliding shaft. The objective lens driving device according to any one of claims 1 to 5, wherein: