JP2702566B2 - Focus signal correction method for optical pickup - Google Patents

Description

The present invention relates to a focus signal correction method in an optical pickup.

[Prior Art] An optical pickup for recording / reproducing information or recording / reproducing / erasing information on an optical information recording medium has been widely known.

FIG. 4 shows a typical example of such an optical pickup.

The light emitted from the semiconductor laser 3 is converted into a parallel light beam by the collimating lens 4 and the polarized light beam splitter 5
Through the quarter-wave plate 6 to be converted into circularly polarized light and incident on the objective lens 2. The lens 2 causes the optical information recording medium (generally in the form of a disc) 1 to have a thickness of about 1 μm on the recording surface thereof. Focused as a light spot of diameter.

The reflected light from the recording surface enters the objective lens 2 and becomes linearly polarized again when transmitted through the quarter-wave plate 6. At this time, the polarization direction is rotated by 90 degrees from the direction when the light has passed through the polarization beam splitter 5 toward the optical information recording medium 1. Therefore, the reflected light is reflected rightward in the drawing by the polarization beam splitter 5 and is converged into a converged light beam by the condenser lens 7.

A part of the focused light flux enters the knife edge prism 8 during the focusing. The luminous flux shielding rate by the knife edge prism 8 is approximately 75%. The light beam incident on the knife edge prism 8 is reflected by the prism 8 and incident on the light receiving element 9 for track control. The light beam not blocked by the knife edge prism 8 is incident on the light receiving element 10 for focus control. The track signal for track control is constituted by the output of the light receiving element 9, and the focus signal for focus control is constituted by the output of the light receiving element 10.
The RF signal is constituted by the sum of the outputs of the light receiving elements 9 and 10.

[Problems to be Solved by the Invention] By the way, it is ideal that the light applied to the optical information recording medium 1 is incident so that its optical axis is orthogonal to the recording surface of the optical information recording medium 1, and the focus signal Is generated properly when the optical information recording medium 1 is properly irradiated with the light.

However, if the optical information recording medium 1 is tilted in the +-direction in FIG. 4, an error occurs in the focus control.

In FIG. 5, the horizontal axis represents the inclination when the recording surface of the optical information recording medium is tilted from an appropriate direction with respect to the irradiation optical axis (the direction perpendicular to the irradiation optical axis), and the vertical axis represents the above-mentioned “tilt”. Represents an error generated in the focus control, that is, a “defocus amount” which is a shift between the light spot focus position and the recording surface when the focus signal gives 0.

In a general optical pickup, the depth of focus of the objective lens is about ± 1 μm. Therefore, if the inclination of the optical information recording medium becomes large, proper focus control becomes impossible, and the optical pickup function may not be performed. There is.

The inclination of the optical information recording medium described above is caused by a mechanical error between the optical pickup and the optical information recording medium holding mechanism, a warp of the optical information recording medium, or an error due to deformation of a mechanical element such as the optical pickup due to a temperature change or the like. And the deformation of the optical information recording medium, and there is naturally a limit in preventing such an inclination of the optical information recording medium.

The present invention has been made in view of the above-described circumstances, and makes it possible to realize appropriate focus control regardless of the inclination of an optical information recording medium. An object of the present invention is to provide a focus signal correction method in an optical pickup.

[Means for Solving the Problems] Hereinafter, the present invention will be described.

The present invention relates to an optical pickup for recording / reproducing information or recording / reproducing / erasing information on or from an optical information recording medium, wherein a focus signal is generated by tilting the optical information recording medium. To correct the offset error occurring in the above.

The method according to claim 1 "detects an inclination of the optical information recording medium,
The focus signal is corrected by the correction offset signal in accordance with the detected inclination. "

The method of claim 2 is characterized in that "the inclination of the optical information recording medium is detected, and the gain in the focus signal generation system is corrected according to the detected inclination". The focus signal is generally formed by the difference between the two signals. “Correcting the gain in the focus signal generation system” means changing one of the two signals forming the focus signal and changing the relative ratio of the magnitude of the two signals.

[Operation] Here, a mechanism of an error generated in the focus control due to the inclination of the optical information recording medium will be described.

FIG. 6 (I) shows a state in which the optical axis of the irradiation light is orthogonal to the recording surface of the optical information recording medium 1, that is, a state in which the optical information recording medium has no “tilt”.

FIG. 6 (II) shows the state of the light spot converged on the recording surface when the optical information recording medium 1 has no inclination as described above. The symbol AD indicates an airy disk, and the symbol L1 indicates a primary ring. The lower part of the figure shows the light intensity distribution. There is no coma in this ideal state.

In this state, the spot SP imaged on the light receiving element 10 in FIG. 4 has an elliptical shape as shown in FIG. 6 (III). The shape of the spot SP becomes elliptical due to the effect of the knife edge prism 8. However, this elliptical spot has a substantially symmetrical shape with respect to the “dividing line that divides the light receiving surface of the light receiving element 10 into two parts”. Corresponding to the difference between the outputs of

However, when the optical information recording medium 1 is tilted as shown in FIG. 6 (IV), the light spot on the recording surface generates coma aberration as shown in FIG. As shown in FIG. 6 (VI), the spot SP on the element 10 is affected by the coma aberration, and the spot shape is a primary or secondary ring.
It becomes asymmetric with respect to the dividing line due to the influence of L1 and L2. As a result, even when the light spot is properly focused on the recording surface, the focus signal does not become 0, and an offset error occurs in the focus signal.

Since the primary and secondary rings appear on a specific side of the light spot in accordance with the direction of inclination of the optical information recording medium, the reflected light from the primary and secondary rings is reflected by the knife edge prism to the light receiving element 10. In some cases, the light does not reach the light receiving element 10 without being reflected by the knife edge prism. For this reason, as shown in FIG. The degree of occurrence varies.

FIG. 7 shows the relationship between the defocus amount and the focus signal. The solid line curve 71 shows the relationship when the optical information recording medium has no inclination. When the defocus amount is 0 (point P), the focus signal is also 0.

However, if the optical information recording medium is inclined, the focus signal does not become 0 even if the light spot is correctly focused on the recording surface and the “defocus amount” is 0. When the optical information recording medium is inclined as described above, the relationship between the focus signal and the defocus amount becomes as indicated by a broken line curve 71, and the state where the focus signal becomes 0 (point Q) is actually a defocus ΔZ. Has occurred. The difference X in the vertical axis direction between the curves 70 and 71 is the offset error.

In order to correct such an offset error caused by the inclination of the optical information recording medium, the methods of claims 1 and 2 detect the inclination of the optical information recording medium.

Then, in the method of claim 1, "the focus signal is corrected with the correction offset signal according to the detected inclination".

According to the method of claim 2, "the gain in the focus signal generation system is corrected in accordance with the detected inclination".

[Example] Hereinafter, a description will be given according to a specific example.

The configuration of the optical pickup itself is assumed to be as shown in FIG. 5 in each of the following embodiments.

Since the tilts of the optical information recording medium are both detected in the methods of the first and second aspects, "detection of tilt" of the optical information recording medium will be described first.

FIG. 3 shows one method of detecting the inclination of the optical information recording medium.
An example is shown as an explanatory diagram.

As shown in FIG. 3 (I), a light-emitting element 14 and a light-receiving element 15 are provided as a pair at a portion of the housing 13 of the optical pickup which is opposed to the optical information recording medium 1. The light emitting element 14 emits a light beam obliquely incident on the optical information recording medium 1, and the light reflected by the surface of the optical information recording medium 1 is received by the light receiving element 15.
To receive light.

The light receiving surface of the light receiving element 15 is divided into two parts in the left-right direction of the figure by a dividing line orthogonal to the figure. When the optical information recording medium 1 is not tilted, the outputs from the divided light receiving portions of the light receiving element 15 are equal. Then, assuming that the difference between the outputs from the respective light receiving sections is a tilt angle detection signal, this "tilt angle detection signal" is linear with respect to the tilt angle of the optical information recording medium 1 as shown in FIG. Changes to Therefore, if the correspondence between the tilt angle detection signal and the actual tilt angle of the optical information recording medium is calibrated in advance, the tilt of the optical information recording medium can be detected based on the tilt angle detection signal.

Further, the relationship between the “tilt” of the optical information recording medium and the offset error generated in the focus signal due to the “tilt” can be experimentally determined in advance.

There are various methods for detecting the inclination of the optical information recording medium other than the above method.

Embodiment 1 Embodiment 1 shown in FIG. 1 is an embodiment of the method of claim 1.

FIG. 1 (I) is a block diagram showing a characteristic portion of the first embodiment. As described above, the light receiving element 10 for focus control has a light receiving surface divided into two light receiving sections 10A and 10B, and outputs A and B are output from each of the light receiving sections 10A and 10B. These outputs A,
B is converted to (A−B) by the differentiator 12.

Conventionally, the output of the differentiator 12 has been used as it is as a focus signal, but if this is used as it is as a focus signal, an offset error is included due to the inclination of the optical information storage medium, and if there is an “inclination”, the focus signal For example, the relationship between the amount of defocus and the amount of defocus is represented by a curve 30 in FIG.
It becomes something like At this time, the offset error X is uniquely determined by the inclination of the optical information recording medium, and the inclination of the optical information recording medium is detected. , And the correction offset signal -X is applied as a voltage signal by the correction offset signal applying means 22, and FIG. 1 (II)
By using the signal from which the offset error X has been removed as the curve 31 as a focus signal, appropriate focus control can be realized.

Embodiment 2 Embodiment 2 shown in FIG. 2 is an embodiment of the method of claim 2.

In this embodiment, one of the outputs A and B from the light receiving sections 10A and 10B of the light receiving element 10, and in this example, the output B is changed to change the gain of the focus signal generation system.

As shown by the curve 30 in FIG.
Is generated, the outputs A and B of the light receiving element 10 are A = B +
It is X. Therefore, the size of the output B is multiplied by K, and KB =
By setting B + X, an offset error can be eliminated. Since the offset error X is uniquely determined according to the inclination of the optical information recording medium, it is possible to know in advance how to determine the gain K according to the detected “inclination”.

When the inclination of the optical information recording medium is detected, the control means 24 outputs a control voltage Vc for realizing the gain K for eliminating the offset error according to the detected inclination. This control voltage Vc is applied to the voltage control amplifier 26. The gain K of the voltage control amplifier 26 changes linearly according to the control voltage Vc as shown in FIG. 2 (III). The gain B multiplies the output B of the light receiving element 10 by K, and the relationship between the focus signal and the defocus amount changes as shown by a curve 32 in FIG. 2 (II), thereby eliminating a focus error.

Note that the correction offset signal generating means of the first embodiment and the control means of the second embodiment can be specifically realized by, for example, a microcomputer.

[Effects of the Invention] As described above, according to the present invention, a novel focus signal correction method in an optical pickup can be provided. Since this method is configured as described above, the offset error of the focus signal caused by the tilt of the optical information recording medium is effectively corrected, and good and proper focus control is performed regardless of the tilt of the optical information recording medium. realizable.

In the above description, the focus control has been described by taking the knife edge method as an example. However, the present invention can be effectively applied to other focus control methods such as the astigmatism method.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining one embodiment of the method of claim 1, FIG. 2 is a diagram for explaining one embodiment of the method of claim 2, and FIG. Media tilt detection method 1
FIG. 4 is a view for explaining an example, FIG. 4 is a view for explaining an optical pickup, and FIGS. 5 to 7 are views for explaining an offset error of a focus signal due to an inclination of an optical information recording medium. is there. 10: Light receiving element for focus control, 12: Difference device

Claims (2)

(57) [Claims] A method for correcting an offset error occurring in a focus signal due to a tilt of an optical information recording medium in an optical pickup for recording / reproducing information or recording / reproducing / erasing information on / from an optical information recording medium. A focus signal correction method for an optical pickup, comprising detecting a tilt of an optical information recording medium and correcting a focus signal with a correction offset signal in accordance with the detected tilt. 2. A method for correcting an offset error occurring in a focus signal due to a tilt of an optical information recording medium in an optical pickup for recording / reproducing information or recording / reproducing / erasing information on / from an optical information recording medium. A focus signal correction method for an optical pickup, comprising: detecting a tilt of an optical information recording medium and correcting a gain in a focus signal generation system according to the detected tilt.