JPH0528526A - Optical disk device - Google Patents

Abstract

PURPOSE:To make a beam shift small and to improve tracking accuracy by setting the rotational center of a galvanomirror on the virtual image face of a mobile optical part. CONSTITUTION:The galvanomirror 52 is attached to the tip side of an arm 55 pivoted by a shaft 54 on the virtual image face 38 in the case of that the mobile optical part 8 is placed to the intermediate position P0 of a moving range 9, is rotated to displace around the shaft 54 in the direction of the arrow C by the driving of an actuator 53. When the mirror is rotated and a spot 22 on an optical disk 1 is deflected by (epsilon) to the outer peripheral side, an outgoing laser beam 56 is attained to the disk 1 through an image side focus 36. Thus, a return laser beam 57 as well passes through the focus 36, coincides with the laser beam 56 and no beam shift is generated and the tracking accuracy is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device.

In the optical disk device, there is a demand for higher speed access and higher tracking accuracy.

[0003]

2. Description of the Related Art FIG. 7 shows an example of a conventional optical disk device.

An optical disc 1 is rotated by a motor 2.

Reference numeral 3 is a recording area, 4 is the outermost peripheral portion,
5 is the innermost peripheral portion.

In order to speed up access, the optical system includes a fixed optical section 7 fixed to the optical disk apparatus body 6 and a lower side of the optical disk 1 in a radial direction of the optical disk 2 (direction of arrow A).
It is separated from the movable optical unit 8 which is moved to.

The fixed optical section 7 has a laser unit 11 for emitting a laser beam 10 and a tracking actuator 12.

The tracking actuator 12 is constructed by using a galvanometer mirror, and comprises a galvanometer mirror 14 and a galvanometer mirror rotating mechanism 15 which are rotatable about an axis 13. The shaft 13 is located at the center of the galvanometer mirror 14.

The fixed optical section 7 emits a laser beam as indicated by reference numeral 16.

The movable optical unit 8 collects the raising mirror 20 for raising the laser beam 16 and the laser 21 which is raised and is directed upward so as to focus the minute spot 2 on the optical disc 1.
2 and an objective lens drive mechanism 24 that drives the objective lens 23 for focus control.
Have and.

The movable optical portion 8 is the innermost peripheral portion 5 of the recording area 3.
To move between the position P ₁ corresponding to the position P ₂ corresponding to the outermost peripheral portion 4 in. Reference numeral 9 is a moving range of the movable optical unit 8.

Reference numeral 30 denotes a push-pull type tracking error detection unit, which is provided in the fixed optical unit 7.

The tracking error detector 30 comprises a half mirror 31, photodiodes 32 and 33 symmetrically arranged with respect to the track center, and a differential amplifier 34, and a tracking error signal is taken out from an output terminal 35.

Reference numeral 36 is the image side focal point of the objective lens 23.

Reference numeral 37 is a virtual image point of the image-side focus 36 by the raising mirror 20.

Reference numeral 38 is a plane passing through the virtual image point 37, which is a virtual image plane of an image-side focal plane 39 of the objective lens 23.

For recording / reproducing on / from the optical disk 1, the movable optical unit 8 moves between P ₁ and P _{2 in the} direction of arrow A, and the galvano mirror 14 operates based on the tracking error signal from the tracking error detecting unit 30. Tracking control is performed by rotating the shaft 13 in the direction of arrow B.

Consider a case where the movable optical unit 8 is located in the middle of the moving range 9 as shown in FIG.

At this time, the axis 13 of the rotation center of the galvanometer mirror 14 is displaced from the plane 38 by a considerable distance l.

Galvano mirror 14 to start-up mirror 20
Is L, the focal length of the objective lens 23 is f, and the distance from the image-side focus 36 of the objective lens 23 to the raising mirror 20 (the distance from the virtual image point 37 to the raising mirror 20) is b.

As shown in FIG. 8, it is assumed that the galvanometer mirror 14 is rotated by a small angle and the spot 22 on the disk surface is swung by ε.

At this time, a beam shift D represented by the following equation occurs.

D = 2ε (L + b) / f As a result, the spot 40 on the photodiodes 32 and 33 is also displaced.

Therefore, in FIG. 10, the tracking error signal, which is supposed to occur as shown by the line I in FIG. 10, appears as shown by the line Ia and causes the offset S ₁ .

The distance L changes as the movable optical unit 8 moves, and L becomes maximum when the movable optical unit 8 is located at the position P ₁ .

As can be seen from the above equation, as the distance L increases, the beam shift amount D also increases as indicated by the line II in FIG.

When the movable optical unit 8 is located at P ₂ , there is already a beam shift of D ₁ . The movable optical unit 8 is P
The beam shift amount D ₂ when reaching ₁ is considerably large.

The offset S is approximately proportional to the beam shift amount D.

Therefore, the tracking error signal when the movable optical unit 8 is located at P ₁ becomes as shown by the line Ib in FIG. 10, and the offset becomes considerably large as S ₂ .

Therefore, the conventional optical disk device had poor tracking accuracy.

It is an object of the present invention to provide an optical disc device with improved tracking accuracy.

[0032]

According to a first aspect of the present invention, an optical system has a laser unit for emitting a laser beam, a tracking actuator using a galvanometer mirror, and a push-pull type tracking error detection unit, and an optical disc. In an optical disc device having a fixed optical unit fixed to the device body, a movable optical unit having a raising mirror and an objective lens, and being moved in the radial direction of the optical disc,
In the tracking actuator, the galvano-mirror is centered on a point on the virtual image plane by the raising mirror of the image-side focal plane of the objective lens when the movable optical unit is located at a predetermined position within the moving range. It is configured to rotate.

According to a second aspect of the present invention, the optical system has a laser unit for emitting a laser beam, a tracking actuator using a galvanometer mirror, and a push-pull type tracking error detection unit, and is fixed to the optical disk apparatus main body. In an optical disk device having a fixed optical section and a movable optical section that has a raising mirror and an objective lens and is moved in the radial direction of the optical disk, the tracking actuator, the galvanomirror, and the movable optical section move In the case of being positioned in the middle of the range, the objective lens is configured to rotate about a point on the virtual image plane of the image side focal plane by the raising mirror.

[0034]

According to the first aspect of the present invention, the rotation center of the galvanometer mirror is set on the virtual image plane of the movable optical unit, and the beam shift when the galvanometer mirror is turned to swing the spot on the optical disk is achieved. It works to keep it small.

According to a second aspect of the present invention, the rotation center of the galvanometer mirror is set on the virtual image plane of the movable optical section when the movable optical section is located in the middle of the movable range. At the end of each, the beam shifts when the galvano mirror is rotated to swing the spot on the optical disk are made substantially equal to each other and both are suppressed to be small.

[0036]

1 shows an optical disk device 50 according to a first embodiment of the present invention.

In the figure, parts corresponding to those shown in FIG. 7 are designated by the same reference numerals, and their description will be omitted.

Reference numeral 51 is a tracking actuator, which is composed of a galvano mirror 52, an actuator 53 and the like.

The galvanometer mirror 52 has a virtual image plane 3 when the movable optical unit 8 is located at an intermediate position P ₀ of the moving range 9.
8 is attached to the tip end side of an arm 55 that is axially supported by a shaft 54, and by driving an actuator 53,
It is rotated and displaced in the direction of arrow C about the center.

The operation when the movable optical unit 8 is located at the position P ₀ will be described.

In this case, (L + b) in the above equation becomes zero, and no beam shift occurs.

In FIG. 1, the galvano mirror 52 is denoted by reference numeral 52a.
When the spot 22 on the optical disc 1 is swung toward the outer peripheral side by ε as shown in FIG.
Reach. Since it passes through the image-side focal point 36, the returning laser beam 57 also passes through the image-side focal point 36, coincides with the laser beam 56, and no beam shift occurs.

Similarly, the galvano mirror 52 is designated by reference numeral 52b.
When the spot 22 on the optical disc 1 is swung toward the inner circumference side by ε as shown by, the going laser beam becomes as indicated by reference numeral 58 and reaches the optical disc 1 through the image side focus 36. The returning laser beam 59 coincides with the laser beam 58 and no beam shift occurs.

When the movable optical unit 8 moves from the intermediate position P ₀ , the virtual image point 37 (virtual image plane 38) moves, and the axis 54 deviates from the virtual image plane 38.

However, this deviation distance is about M ₁ and M ₂ at the maximum as shown in FIG. 2, which is considerably shorter than 1 in FIG.

Therefore, the beam shift amount D with respect to the position of the movable optical portion 8 is the position P as shown by the line IIa in FIG.
_It becomes _zero at 0, and gradually increases as it deviates from the position P ₀ . Moreover, the bias distance is short.

Therefore, the maximum beam shift Dmax is
It will be much smaller than before.

The beam shift amount D ₃ when the movable optical unit 8 reaches the position P ₁ and the beam shift amount D ₄ when the movable optical unit 8 reaches the position P ₂ are substantially the same. , Both are small.

Regarding the tracking error signal, when the movable optical unit 8 is at the intermediate position P ₀ , a signal having an offset of 0 is obtained as shown by the line I in FIG.

The movable optical unit 8 is at the end position P of the movable range 9.
Even when it is moved to ₁ or P ₂ , a tracking error signal in which the offset S ₃ is suppressed smaller than in the conventional case is obtained as shown by the line Ic.

For this reason, the tracking control is performed with higher precision than the conventional one, and with the same degree of precision over the entire recording area 3 of the optical disc 1.

Next, an optical disk device 60 according to the second embodiment of the present invention will be described with reference to FIG.

In this embodiment, the shaft 54 and the arm 55 of the galvanometer mirror 52 in the first embodiment are eliminated to miniaturize the tracking actuator.

In FIG. 5, parts corresponding to the parts shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

Reference numeral 51A is a tracking actuator.

The galvanometer mirror 52 is supported on the base 61 by a pair of spring members, which will be described later, inclined by 45 degrees.

Reference numeral 62 denotes an actuator, which comprises a magnetic circuit portion 63 fixed to the base 61 and a drive coil 64 fixed to the center of the rear surface of the galvano mirror 52.

Reference numeral 65 denotes a first spring member, which is located at a position on the lower right side of the actuator 62 and supports the end of the galvano-mirror 52 near the rotation fulcrum side.

Reference numeral 66 denotes a second spring member, which is located at a position on the upper left side of the actuator 62 and supports the end of the galvano mirror 52 opposite to the rotation fulcrum side.

The virtual axis 67 is an axis line where the extension surface 68 of the galvanometer mirror 52 intersects the plane 38.

The distance between the shaft 67 and the first spring member 65 is X ₁ , and the distance between the shaft 67 and the second spring member 66 is X.
_Set to ₂ .

Length L of the first spring member 65₁And the second ba
Length L of member 66₂Is the ratio L ₁: L₂Is the distance
X₁, X₂Ratio of₁: X₂Is set to be equal to.
That is, L₁: L₂= X₁: X₂There is.

Further, the spring constant K _{1 of} the first spring member 65 is
The spring constant K ₂ of the second spring member 66 is set so that the ratio K ₁ : K ₂ is equal to the inverse ratio X ₂ : X _{1 of the} distances X ₁ and X ₂ . That is, K ₁ : K ₂ = X ₂ : X
_{There is as 1} .

By incorporating the above-mentioned first and second spring members 65 and 66, the extension surface 69 of the base 61 is changed to the virtual shaft 6.
It goes through 7.

When the actuator 63 is energized and driven, the galvanometer mirror 52 is placed at the center of the galvanometer mirror 42.
The force F acts in the direction perpendicular to the plane of the above, and the force F / 2 acts on the first and second spring members 65 and 66, respectively. The first spring member 65 extends L1a = F / (2K ₁ ). Second
The spring member 66 of No. ₂ extends by L2a = F (2K ₂ ). Therefore, the ratio of elongations L1a and L2a, L1a: L2a, is equal to the ratio of the distances X ₁ and X ₂ . That is, L1a: L2a
= F / (2K ₁ ): F / (2K ₂ ) = K ₂ : K ₁ =
X ₁ : X ₂ .

Therefore, the total length L ₁ + of the first spring member 65
The ratio of L1a to the total length L ₂ + L2a of the second spring member 66 is equal to the ratio of the distances X ₁ and X ₂ . That is,
(L ₁ + L1a) :( L ₂ + L2a) = X ₁ : X ₂ .

Therefore, even after the displacement of the galvanometer mirror 52, the extension surface 68 of the galvanometer mirror 52 passes through the virtual axis 67.

Therefore, the galvano mirror 52 is rotationally displaced so that the extension surface 68 thereof always passes through the virtual shaft 67. That is, the galvanometer mirror 52 is rotationally displaced about the virtual axis 67.

Therefore, as in the first embodiment, a tracking control signal without offset is obtained, and tracking control is performed with high accuracy.

Since it does not actually have a central axis of rotation,
The optical disc device 60 has a small size.

Further, without the arm 55 of the first embodiment,
Since the weight is light, the tracking control is performed well.

[0072]

As described above, according to the first aspect of the invention, in the optical disc apparatus which is the separation optical system and detects the tracking error by the push-pull method, the tracking error signal whose offset is suppressed is obtained. Therefore, tracking control can be performed accurately.

According to the second aspect of the invention, when the movable optical unit reaches each end of the moving range (which is the case where the offset occurs most), the offsets can be made substantially equal and both can be suppressed to be small. Thereby, the tracking control can be performed with substantially the same accuracy over the entire recording area of the optical disc.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of an optical disk device of the present invention.

FIG. 2 is a diagram illustrating a relationship between a position of a movable optical unit and a distance between a virtual image plane and a rotation center axis.

FIG. 3 is a diagram showing a relationship between a position of a movable portion and a beam shift amount.

FIG. 4 is a diagram illustrating an offset of a tracking error signal.

FIG. 5 is a diagram showing a second embodiment of the optical disc apparatus of the present invention.

FIG. 6 is a diagram showing a state when the tracking actuator in FIG. 5 operates.

FIG. 7 is a diagram showing an example of a conventional optical disc device.

FIG. 8 is a diagram illustrating the occurrence of beam shift when the galvanometer mirror is rotated.

FIG. 9 is a diagram showing a relationship between a position of a movable part and a beam shift amount.

FIG. 10 is a diagram illustrating offset of a tracking error signal.

[Explanation of symbols]

1 Optical Disc 3 Recording Area 4 Outermost Perimeter 5 Innermost Perimeter 6 Optical Disc Device Main Body 7 Fixed Optical Section 8 Movable Optical Section 9 Moving Range of Movable Optical Section 11 Laser Unit 20 Standing Mirror 21 Laser 22 Upward Micro Spot 23 Objective Lens 24 Objective lens drive mechanism 30 Push-pull type tracking error detector 31 Half mirror 32 Photodiode 34 Differential amplifier 35 Output terminal 36 Image side focus 37 of objective lens Virtual image point 38 of image side focal point raising mirror Passing plane (virtual image plane of the image-side focal plane of the objective lens) 39 Image-side focal plane of the objective lens 40 Spots on photodiodes 50, 60 Optical disk devices 51, 51A Tracking actuator 52 Galvano mirrors 53, 62 Actuator 54 Shaft 55 Arm 56 ~ 59 61 laser beams 63 magnetic circuit 64 drives the coil 65 first spring member 66 the second spring member 67 virtual axis 68 extending surface

Claims (2)

[Claims] 1. An optical system having a laser unit (11) for emitting a laser beam, a tracking actuator using a galvanometer mirror, and a push-pull type tracking error detection unit (30), which is fixed to an optical disk apparatus main body. A fixed optical section (7), a rising mirror (20) and an objective lens (23),
In the optical disk device having a movable optical section (8) that is moved in the radial direction of the optical disk (1), the tracking actuator (51, 51A), the galvano mirror (52), the movable optical section (8).
Of the objective lens (23) on the image side focal plane (39) of the objective mirror (23) on the virtual image plane (38) by the raising mirror (20) when the lens is positioned at a predetermined position within the movement range (9). , 67) as a center of rotation. 2. The optical system has a laser unit (11) for emitting a laser beam, a tracking actuator using a galvano mirror, and a push-pull type tracking error detection unit (30), and an optical disk device main body (6). Having a fixed optical part (7) fixed to, a raising mirror (20) and an objective lens (23),
In the optical disk device having a movable optical section (8) that is moved in the radial direction of the optical disk (1), the tracking actuator (51, 51A), the galvano mirror (52), the movable optical section (8).
Of the objective lens (23) on the image side focal plane (39) on the virtual image plane (38) by the raising mirror (20) when is located in the middle (P ₀ ) of the moving range (9). 54, 67) is configured to rotate about the optical disk device.