KR20010060784A - Optical Pickup Apparatus and Method of Detecting and Compensating Tilt - Google Patents

Abstract

PURPOSE: An optical pickup apparatus and tilt detection and compensation method using this is provided to compensate a tilt error by driving an actuator depending on the detected tilt error after detecting the detected tilt error using a binary wavelength light source module. CONSTITUTION: An optical pickup apparatus is composed of a light source generating part which generates the first and the second light beam to have each different wavelength and a tilt detection part to detect a tilt of an optical disk(100) based on any one defocus value of the first(1a) and the second light beam(1b). An optical disk apparatus is composed of an optical pickup(50) which generates light beams(1a,1b) having each different wavelength simultaneously, a defocus detecting part(60) to detect defocus value of light beams(1a,1b), a controller(62) to calculate tilt error value of a disk based on defocus value and a tilt compensation part(64) to compensate a tilt depending on a tilt error value.

Description

Optical Pickup Apparatus and Method of Detecting and Compensating Tilt

The present invention relates to an optical pickup apparatus which detects the tilt of an optical disc by using the defocus amount of the light beam. The present invention also relates to a tilt detection and compensation method using an optical pickup device.

In general, optical discs have been commercialized by commercially available compact discs (CDs) and commercially available DVDs (Digital Versatile Discs) with improved recording capacity. As such optical discs become denser, recording marks and track pitches become smaller. In addition, the denser the optical disk, the shorter the distance from the surface of the optical disk to the information recording surface.

In order to accurately record and reproduce data on the recording surface of the disk, the optical axis of the light beam 1 condensed from the objective lens 2 to the optical disk 100 must be perpendicular to the optical disk surface as shown in FIG. When the light beam 1 is incident perpendicularly to the optical disc 100, the reflected light beam reflecting from the optical disc 100 and returning to the optical path is accurately incident on the photo diode. On the other hand, if a tilt exists in the optical disc, the optical axis of the light beam 1 incident on the optical disc 100 from the objective lens 2 as shown in FIG. 2 may have an arbitrary inclination angle that is not perpendicular to the plane of the optical disc. In this case, since the reflected light beam reflected from the optical disc 100 is eccentrically incident on either side of the photodiode, data cannot be reproduced accurately.

An ideal optical disc has an angular deviation of the optical disc surface, that is, its bending angle is '0', but the eccentricity of the optical disc itself generated during the manufacture of the optical disc, the mechanical mechanism of the turntable or spindle motor of the spindle motor, and the surface supporting the optical pickup. Because tolerances exist realistically, some degree of tolerance is acknowledged. For example, in the case of DVD-RAM, angular division allows up to ± 0.7 ° in the radial direction (R) of the optical disc and ± 0.3 ° in the tangential direction (T). However, even in the optical disc 100 within such a tolerance, since the rotational speed of the optical disc 100 increases, the amount of vibration increases, so that the tilt changes in the radial direction R, and the amount of the optical disc 100 increases. Moreover, since the pit becomes smaller as the optical disc 100 becomes higher in density, in the case of the high density optical disc, the optical adverse effect due to the tilt becomes larger.

In order to detect the tilt of the disk, the conventional optical disk apparatus includes two tilt sensors 102 and 104 installed in the radial direction of the optical disk 100 as shown in FIG. Each of the inner circumferential side tilt sensor 104 and the outer circumferential side tilt sensor 102 irradiates the optical disc 100 with infrared rays in a direction of an optical axis perpendicular to the optical disc surface. At this time, when the difference between the reflected light beams reflected from the inner circumference side and the outer circumference side of the optical disc 100 is calculated, the tilt amount of the optical disc, that is, the inclination of the optical disc 100 is detected. However, such a tilt detection method requires a tilt sensor (102, 104) and a detector (not shown) for detecting the reflected light beams, and a circuit for driving them. This not only causes the cost of the optical disk device to rise, but also constrains the space inside the thinning optical disk device.

It is therefore an object of the present invention to provide an optical pickup apparatus which detects the tilt of an optical disc by using the defocus amount of the light beam.

Another object of the present invention is to provide a tilt detection and compensation method using an optical pickup device.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view schematically showing that a light beam is vertically incident on a disk surface from an objective lens.

FIG. 2 is a view schematically showing a light beam incident when a tilt occurs in the disk shown in FIG.

3 is a view showing a conventional tilt sensor.

4 illustrates an optical disk device according to an embodiment of the present invention.

5 is a cross-sectional view showing in detail the two-wavelength light source module in the optical pickup device shown in FIG.

FIG. 6 is a view showing a two-wavelength light beam incident on an optical disk from the optical pickup device shown in FIG. 4; FIG.

7 is a flow chart showing step by step the control procedure of the tilt detection and compensation method according to an embodiment of the present invention.

<Brief description of symbols for the main parts of the drawings>

1a, 1b: light beam 2: objective lens

4 collimating lens 6,8 beam splitter

10: 45 ° reflector 12: two wavelength light source

12a, 12b: LD chip 14, 18: sensor lens

16,20: photodetector 60: defocus detector

62: control unit 64: tilt compensation unit

100: optical disk 102,104: tilt sensor

In order to achieve the above object, the optical pickup device according to the present invention is based on a light source generator for generating the first and second light beams having different wavelengths, and the defocus value of any one of the first and second light beams; Tilt detection means for detecting the tilt of the optical disc is provided.

The tilt detection and compensation method using the optical pickup device according to the present invention comprises the steps of irradiating the optical disk with the first and second light beams, and detecting the tilt of the optical disk based on the defocus value of any one of the first and second light beams And compensating the tilt according to the detected tilt.

Other objects and advantages of the present invention in addition to the above object will become apparent from the description of the preferred embodiment of the present invention with reference to the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 4 to 13.

Referring to FIG. 4, an optical disk apparatus according to the present invention is used to detect an optical pickup 50 that simultaneously generates light beams 1a and 1b of different wavelengths and a defocus value of light beams 1a and 1b. The defocus detection unit 60, a control unit 62 for calculating the tilt error value of the disc based on the defocus value, and a tilt compensation unit 64 for compensating the tilt in accordance with the tilt error value.

The optical pickup 50 includes a two-wavelength light source module 12 having a first and a second laser diode chip (hereinafter referred to as an “LD chip”) and a second wave light source module 12. An objective lens 2 for condensing the first and second light beams 1a, 1b on each of the first recording surface 100a and the second recording surface 100b of the optical disc 100, the two-wavelength light source module 12, and the objective A first beam splitter 6, a second beam splitter 8, and a 45 ° reflector 10 arranged side by side between the lenses 2, and light for converting the light beam reflected from the optical disc 100 into an electrical signal. With detectors 16,20. Each of the first and second LD chips 12a and 12b embedded in the two wavelength light source module 12 generates the first and second light beams 1a and 1b having wavelengths corresponding to different types of optical disks. The spacing between these first and second LD chips 12a and 12b is approximately 100 μm, as shown in FIG. 5. Thus, since the first and second LD chips 12a and 12b are separated, the first and second light beams 1a and 1b are incident at predetermined intervals in the radial direction of the optical disc 100. The first LD chip 12a generates a first light beam 1a having a wavelength of 635 to 650 nm corresponding to the DVD-based optical disc as shown in FIG. 5, and the second LD chip 12b has a 780-nm wavelength corresponding to the CD-based optical disc. Generates a second light beam 1b. The first and second light beams 1a and 1b in the form of diverging beams generated from the two-wavelength light source module 12 are converted into parallel light beams by the collimating lens 4, and then the first and second beam splitters 6 and 8. ) Is incident on the 45 ° reflector 10. The first and second light beams 1a and 1b incident on the 45 ° reflector 10 are reflected toward the objective lens 2. The objective lens 2 focuses the first and second light beams 1a and 1b incident through the 45 ° reflector 10 on the recording surfaces 100a and 22b of the optical disc 100 in the form of spots. Since the light beams 1a and 1b emitted at the same time have different focal lengths, respective defocus amounts are different. In the case of accessing the CD-based optical disc, as shown in FIG. 6, the second light beam 12b corresponding to the CD series is focused on the optical disc surface, and the first light beam 12a corresponding to the DVD series is on the optical disc surface. Defocused. On the contrary, when the DVD-based optical disc is accessed, the second light beam 12b corresponding to the CD series is focused on the optical disc surface, and the first light beam 12a corresponding to the DVD series defocuses on the optical disc surface. Will be concluded. The reflected light beam of the first light beam 1a reflected from the optical disc 100 is reflected by the second beam splitter 8 and is incident on the photodetector 16 for DVD via the first sensor lens 14. Similarly, the reflected light beam of the second light beam 1b is reflected by the first beam splitter 6 and is incident on the photodetector 20 for CD via the second sensor lens 18. The reflected light beams incident on the photodetectors 16 are converted by the photodetectors 16, 20 into electrical signals.

The defocus detection unit 60 processes the output signals of the photodetectors 16 and 20 to detect defocus values of each of the light beams 1a and 1b focused on the optical disc 100.

The controller 62 generates a tilt error signal by comparing the defocus value of each of the detected light beams 1a and 1b with a reference value. The reference value is that when there is no tilt in the optical disc 100, that is, the optical axis of the optical disc 100 and the objective lens 2 are horizontal and the optical axes of the light beams 1a and 1b condensed from the objective lens 2 are perpendicular to the plane of the optical disc. At this time, the defocus difference between the light beams 1a and 1b incident on the optical disc is set. The controller 62 compares the defocus value of each of the light beams 1a and 1b supplied from the defocus detector 60 with a reference value and generates a tilt error signal corresponding to the difference.

The tilt compensator 64 drives the actuator 24 according to the tilt error signal supplied from the controller 62. The actuator 24 inclines the objective lens 24 with the same tilt as the tilt direction of the optical disc 100. Meanwhile, the tilt compensator 64 may optically compensate the tilt by adjusting the optical paths of the light beams 1a and 1b, and adjust the tilt of the turntable on which the optical pickup 50 or the optical disc 100 is seated. You can also compensate. As a result of the tilt compensation in real time, the optical disc 100 and the objective lens 2 are always parallel to each other, and the optical axes of the light beams 1a and 1b condensed from the objective lens 2 to the optical disc 100 are changed to the optical disc ( Incident perpendicularly to 100).

The operations of the defocus detector 60, the controller 62, and the tilt compensator 64 for tilt detection and compensation during CD or DVD-based optical disc access will be described with reference to FIG. 7.

First, the optical disc device of the CD series or the DVD series is loaded into the optical disc apparatus. (Step S1) If the currently loaded optical disc is the CD series, the controller 62 controls a servo system (not shown) to control the second optical beam having a wavelength of 780 nm. The focus servo for (1b) is driven (step S2). The defocus detector 60 detects the defocus value of the first light beam 1a having a wavelength of 635 to 650 nm. The controller 62 generates a tilt error signal by comparing the defocus value of the first light beam 1a input from the defocus detector 60 with a preset reference value (steps S6 and S7). If the optical disk is a DVD series, the controller 62 controls a servo system (not shown) to drive the focus servo for the first light beam 1a. (Step S4) The defocus detection unit 60 performs a second light beam ( Defocus value of 1b) is detected (step S5). The unit 62 generates a tilt error signal by comparing the defocus value of the second light beam 1a input from the defocus detection unit 60 with a preset reference value (steps S6 and S7). The tilt compensator 64 compensates for the tilt by driving the actuator 24.

As described above, the optical pickup apparatus according to the present invention uses a two-wavelength light source module for optically accessing heterogeneous optical disks without using a separate tilt sensor, and any one of these wavelength light sources is used for optical disk access. One is used for defocus detection, and the tilt is detected by comparing the defocus value of the detected light beam with a preset reference value. In the tilt detection and compensation method according to the present invention, the tilt error is detected using the two-wavelength light source module and the actuator can be compensated by driving the actuator according to the detected tilt error.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (6)

A light source generator for generating first and second light beams having different wavelengths; And tilt detection means for detecting the tilt of the optical disk based on the defocus value of any one of the first and second light beams. The method of claim 1, And the light sources generating the first and second light beams are modularized into one package at predetermined intervals. The method of claim 2, And the tilt detecting means generates the tilt error signal by comparing a predetermined reference value with the detected defocus value. The method of claim 3, wherein And said reference value is a defocus difference between first and second light beams when the light beam is incident perpendicularly to the optical disc. Irradiating the optical disk with the first and second light beams, Detecting the tilt of the optical disk based on a defocus value of any one of the first and second light beams; And detecting the tilt according to the detected tilt. The method of claim 3, wherein The tilt detection and compensation method, characterized in that for compensating the tilt by driving the actuator mounted to the objective lens in accordance with the detected tilt.