JP2595213B2 - Objective lens position adjustment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an objective lens position adjusting method, and more particularly, to an objective lens position adjusting method applicable to an optical pickup of an optical information recording / reproducing apparatus using a laser beam. is there.

(Prior Art) A configuration as shown in FIG. 3 is conventionally used as an optical system of an optical pickup in an optical information recording / reproducing apparatus for recording and reproducing information by condensing a semiconductor laser beam with an objective lens to form a minute spot. Are known.

In brief, the light beam from the semiconductor laser 2 is converted into parallel light by a coupling ring lens 4, and is passed through a deflection beam splitter 6 and a quarter-wave plate 8 to an optical disk 16 as an optical information recording medium by an objective lens 10. A minute spot of about 1 μm is formed. Then, the reflected light returns to the objective lens 1 again.
Following the 0, 1/4 wavelength plate 8, the light is split by the polarizing beam splitter 6 in a direction orthogonal to the incident light. After passing through the condenser lens 18, the reflected light is incident on a first two-part light receiving element 12 comprising two light receiving elements C and D for receiving a part of the light beam LB as shown in FIG. The remaining light flux is supplied to the detection of the track signal, and is incident on the second two-divided light receiving element 14 arranged at the condensing point thereof, and is supplied to the detection of the focus signal.

Next, a method of detecting a track control signal will be described. The track control signal is obtained as a difference signal between each of the two light receiving elements C and D of the two-divided light receiving element 12 in which the guide groove and the dividing line are parallel to each other according to the positional relationship of the converging point on the guide groove formed in advance on the optical disc 16. Can be Here, the normal track control signal shows a sine curve that is vertically symmetric about the 0v level as shown in FIG.

However, if the optical disk surface is tilted, or if each optical element moves due to temperature or aging, an offset amount a occurs in the track control signal as shown in FIG. 8 and an error x occurs, making it difficult to perform normal tracking control. May be.

In other words, conventionally, a position sensor is attached to the objective lens so that the objective lens can always perform tracking around the same location, but on the other hand, the optical disc tilts, or the temperature of each optical element, the movement over time, and There is a problem that tracking is performed with an offset occurring in the tracking control signal. Further, in the optical pickup, since the position sensor is attached to the objective lens, the mass and the size are greatly increased, and it is difficult to manufacture a small and high-performance optical pickup.

(Object) Accordingly, an object of the present invention is to remove the offset of the track control signal generated by the inclination of the optical disk or the temperature of each optical element and the movement with the passage of time by moving the objective lens in the tracking direction, and to remove the normal. An object of the present invention is to provide a method for adjusting the position of an objective lens for performing a tracking operation.

(Structure) In order to achieve the above object, the present invention first obtains an offset signal by a two-divided light receiving element, and based on the offset signal, applies a bias current to an objective lens actuator to correct an optical axis shift of the objective lens. Then, a track error signal is obtained by the two-divided light receiving element in a state where a bias current when the optical axis shift is corrected is applied, and a tracking servo is applied based on the track error signal. Here, the offset signal refers to a track control signal including an offset error, and the track error signal refers to a track control signal including no offset error.

Hereinafter, a specific description will be given based on an embodiment of the present invention.

First, the reason why the offset amount a is generated in the track control signal when the optical disk surface is tilted or when each optical element moves due to temperature or aging is considered.

For example, considering the case where there is no inclination or the like on the optical disk surface, as shown in FIG. 4, when the parallel light beam from the semiconductor laser is correctly focused on the center of the guide groove of the optical disk 16 via the objective lens 10, The reflected light is received by the light receiving elements C and D in equal amounts, respectively, with a uniform light intensity distribution on the left and right as indicated by the symbol LB1. Then, as the optical pickup is moved in the tracking direction, the converged light by the objective lens 10 shifts from the center of the guide groove, so that the reflected light LB2 from the optical disc 16 is deviated in the light intensity distribution as shown in FIG. In this example, the light receiving area of the light receiving element C is wider than the light receiving area of the light receiving element D. Accordingly, a track control signal, which is a difference signal between the light receiving elements C and D, appears as shown in FIG.

However, for example, as shown in FIG.
When the outer edge of the optical disk 16 mounted on the optical disk 16 is inclined downward due to its own weight or the like relative to the center, the laser light guided by the objective lens 10 in the optical pickup 24 is shown in FIG. Even if the light is correctly focused at the center of the guide groove as described above, the reflected light is incident on one side with respect to the division line of the light receiving element, and apparently a light intensity difference occurs between each of the light receiving elements C and D, as if guiding A track control signal is obtained as if the light were not focused at the center of the groove.

Therefore, an error x occurs in the track control signal expressed by the difference between the outputs of the light receiving elements C and D. Such a phenomenon occurs not only when the outer edge of the optical disc is tilted by its own weight, but also when the turntable is tilted with time, or when each element inside the optical pickup, for example, a mirror is tilted with time, as described above. This can also occur when the position of the light receiving element moves over time.

Therefore, in order to eliminate the error of the track control signal, the optical pickup is fixed to the state where the light is focused at the center position of the guide groove, or the optical pickup is focused to the flat part where the guide groove is not provided. With the object fixed, the objective lens itself is moved in the tracking direction to
What is necessary is just to make the difference between both outputs zero.

For the adjustment, the configuration of the tracking actuator 26 shown in FIGS. 1 and 2 can be used. That is, in the tracking actuator 26 on which the objective lens 10 is supported, the objective lens 10 is formed integrally with the coil 40 as shown in FIGS. The coil 40 is inserted into the yoke 42, is movable, and forms a kind of linear motor. Reference numeral 44 denotes a permanent magnet. The objective lens 10 is supported on a frame 48 by a leaf spring 46. These components are also part of the tracking control device.

Thus, if a required bias current is applied to the coil 40, the objective lens 10 can be forcibly moved against the elasticity of the leaf spring 46, so that the offset of the track control signal due to the inclination of the optical disk or the like can be eliminated. Can be.

 Specifically, this is performed as follows.

First, regarding an optical disk, a flat portion without a guide groove is set in an appropriate position in advance.

In addition, a circuit as shown in FIG. 1 is set. The circuits are amplifying circuits 52 and 54 that amplify the respective outputs from the light receiving elements C and D in FIG.
A difference circuit 56 that compares the outputs of the two circuits 54 and 54 to detect a difference, a switch circuit 58 that inputs a track control signal that is an output of the difference circuit 56, and a track control that is selectively switched by the switch circuit 58 The circuit includes a bias current generating circuit 60 for inputting a signal and outputting the signal to the coil 40, a tracking servo coil driving circuit 62, and the like.

In order to adjust the position of the objective lens, the bias current from the bias current generating circuit 60 is changed until the track control signal in the flat portion provided outside the guide groove of the optical disk becomes almost zero in the optical disk device. At this time, the switching state of the switch by the switch circuit 58 is a state in which conduction is provided only with the bias current generation circuit 60. When the track control signal becomes substantially zero, the bias current at that time is held until the optical disk is removed. Thus,
The objective lens 10 is forcibly moved and held in the tracking direction at the same time when the bias current suitable for the tilt of the optical disk is set and held.

Then, the switch circuit 58 is switched from a state in which only the bias current generating circuit 60 is conductive to a state in which the switch circuit 58 is conductive only with the tracking servo coil driving circuit 62, and is in a state where normal tracking operation is possible.

Thus, normal tracking can be performed by correcting each time the offset of the track control signal may change.

As described above, the case where the offset occurs is considered to be, for example, when the optical disk is changed, when the apparatus is started, when the temperature in the machine is changed, or when the tracking position is changed. Is carried out.

When the optical disk changes, the offset amount differs depending on the degree of warpage of each optical disk. Also, it differs depending on the front and back of the optical disc. Similarly, when the tracking position changes, a different offset occurs due to the radial warpage of the disk, so it is necessary to correct the offset at the flat portion closest to the tracking position.

When the apparatus is started, the change with time of each part of the apparatus, for example, the tilt of the turntable and the optical pickup, or the movement of the optical axis caused by the movement of each element inside the optical pickup,
It is necessary to correct the offset due to the movement of the light receiving element. Similarly, when the internal temperature changes, offset occurs due to expansion and contraction of each component. By the way, if the optical axis in the optical pickup is shifted by 50 μm due to aging or temperature change, it will take about 15
% Offset and a track error of about 0.04 μm. When the turntable and the optical pickup are tilted by 30 ', an offset of about 20% occurs, and a track error of about 0.05 .mu.m occurs.

In the embodiment shown in FIG. 9, when the optical disk 16 and the optical pickup 24 are tilted by 30 ', an offset of about 20% occurs in the track control signal. In such a case, the tenth
Due to the relationship between the amount of movement of the objective lens and the amount of offset shown in the figure, it is necessary to move the objective lens by 37 μm.

(Effects) According to the present invention, the offset of the track control signal can be corrected according to the state of the apparatus, for example, a change due to temperature, aging, and tracking control can be reliably performed in the best state without offset at any time. is there.

[Brief description of the drawings]

FIG. 1 is a circuit diagram suitable for carrying out the present invention, FIG. 2 is a plan view of a tracking actuator, FIG. 3 is a structural diagram of an optical pickup optical system suitable for carrying out the present invention, FIGS.
FIGS. 6A and 6B are diagrams illustrating the state of incident light on the splitting element accompanying the tracking operation of the optical pickup, FIG. 6 is a view illustrating a normal track control signal, and FIG. FIG. 8 is a view for explaining a correspondence relationship, FIG. 8 is a view for explaining a track control signal having an offset, and FIG.
FIG. 10 is a diagram for explaining a state in which the optical disk is tilted, and FIG. 10 is a diagram for explaining the relationship between the offset amount and the moving amount of the objective lens. 10 Objective lens, 16 Optical disk, 26 Tracking actuator.

Claims (1)

(57) [Claims] An offset signal is first obtained by a two-divided light receiving element, and a bias current is applied to an objective lens actuator based on the offset signal to correct an optical axis shift of the objective lens. Then, the optical axis shift is corrected. A tracking error signal is obtained by the two-divided light receiving element in a state where the bias current is applied, and a tracking servo is applied based on the tracking error signal.