JPS605431A - Tilt detecting system of information recording medium - Google Patents

Abstract

PURPOSE:To detect the tilt angle of a recording medium with high accuracy by irradiating the tilt detecting beam obliquely to a flat part of the recording medium and leading the reflected light of the detecting beam to a position detector set at a rear focal position of a condenser lens so that the photodetecting surface is set nearly vertical to the optical axis of the condenser lens after transmitting said reflected light through the condenser lens. CONSTITUTION:A detecting beam 201 for tilt of a recording medium 202 is made incident obliquely to a flat part of the medium 202. The reflected light of the beam 201 is led to a condenser lens 203 set so that its optical axis is paralle to the reflected light. Then the reflected light is received by a position detector 204 which is set approximately at a rear focal position of the lens 203 so that the photodetecting surface is set nearly vertical to the optical axis of the lens 203. Here the medium 202 has a tilt by DELTAtheta as shown by a broken line in the figure. In such a case, the reflecting angle of the beam 201 has a displacement by 2DELTAtheta and the photodetecting point moves by DELTAx on the detector 204. Then DELTAx=2fDELTAtheta is satisfied, where (f) shows the focal distance of the lens 203. Thus the tilt angle DELTAtheta of the medium 202 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for detecting the inclination of an information recording medium in an optical information recording/reproducing apparatus.

[Technical background of the invention and its problems]

In recent years, optical disk devices have become popular as high-density, large-capacity news recording and playback devices, and video disks (VDs) and digital audio disks (DADs) have become popular as information playback devices.
) is attracting attention and is capable of recording and reproducing zero information.In optical disk devices capable of recording and reproducing zero information, a laser beam is focused to a diameter of about 1 μm and irradiated onto an information recording medium called an optical disk.
Width: 046-1 μm.

Information signals are recorded by forming pits with a length of about 1 to 2 μm on the information recording medium. Information is also reproduced by detecting reflected diffracted light from the information recording medium using a similar laser beam. In such a large-capacity, high-density information recording and reproducing device capable of recording and reproducing, it is essential to perform stable tracking and focusing. Therefore, a tracking guide groove called a burr group is formed in advance on the substrate of the information recording medium. Usually, these guide grooves are formed concentrically or spirally on the information recording medium with a track pitch of about 1.6 to 2 μm. Then, information is recorded or reproduced while stable tracking is performed using a dragging signal detected from this guide groove.

On the other hand, the information reproducing device VD-? Although DAD does not have a guide groove for tracking, it reproduces information signals by accurately tracking pits that are about the same size as the above-mentioned optical disk device.

By the way, as a method of detecting a tracking signal, conventionally, a so-called two-split photodetector in which unit detectors are arranged in parallel in the recording track width direction is placed at a position sufficiently far field from the information recording medium. Output 11 of each unit detector and I! A method is used to obtain the above-mentioned dragging signal by calculation between . That is, the tracking signal ITRK is TRK "IS"! Tracking control is performed to obtain ITRK-0. This method has the advantage of simplifying the optical system because the signal detection position is in the far field, but if the information recording medium is tilted, the reflected and diffracted light from the information recording medium will move on the photodetector. Therefore, even though there is no track shift, there is one tracking word I? R.K.
The value of is not 0, and there is a drawback that tracking control results in substantial track deviation. Especially when the information recording medium is tilted in the width direction of the information recording track, the reflected and diffracted light from the information recording medium moves on the photodetector in the width direction of the information recording track, so the value of the tracking signal ITRK becomes very large. Furthermore, if the signal detection position is set at the position of the imaging point with respect to the information recording medium, a conjugate image on the information recording medium is formed, so that even if the information recording medium is tilted, there is little effect on the tracking signal. However, since there are a plurality of stable points where the tracking signal I TRK = 0 for track deviation, the imaging position is not appropriate as the tracking signal detection position.

In addition, with respect to the focusing signal, as in the case of the tracking signal, as the information recording medium is tilted, reflected diffracted light from the information recording medium moves on the photodetector, causing a focus shift.

From the above points, there is no track deviation or focus deviation.
That is, in order to record or reproduce an information signal with a high S/N ratio, it is necessary to detect the tilt of the information recording medium and correct the tracking signal or focusing signal.

The conventional tilt detection method for information recording media is shown in Figure 1 fa.
), a beam 101 for detecting the inclination of the information recording medium
is made obliquely incident on the flat part of the information recording medium 102, and the reflected light is guided to a position detector 104 arranged parallel to and facing the information recording medium, as shown by solid lines and broken lines in the figure, respectively. The tilt angle of the information recording medium was determined by detecting the shift in the receiving position of the reflected light on the position detector when the information recording medium was not tilted and when the information recording medium was tilted by 7 degrees. That is, when the incident angle of the #4 detection beam on the information recording medium is θ, the inclination angle of the information recording medium is Δθ, and the distance M between the information recording medium and the position detector is l, the position detector The r difference △X of the receiving position of the reflected light on the upper side is Δx=/・(tan(θ+2Δθ
)−1anθ]tan2Δθ(1+tan”θ) =7・□ (1) It is given by 1−tanθ−1an2Δθ.Here, θ and l are known, so if we detect the shift ΔX of the receiving position of the reflected light, ( The tilt angle Δθ of the information recording medium can be calculated from equation 1). However, in such a method, the above-mentioned problem may occur due to surface wobbling of the information recording medium, etc. as shown by the dashed line and dashed line in FIG. 1(b). If the information recording medium moves upward F, that is, if there is a focus shift, the receiving position of the reflected light on the position detector changes, causing a problem similar to that of causing an error in the tilt angle of the information recording medium. Furthermore, if the incident angle θ of the tilt detection beam with respect to the information recording medium is not accurately known, an error will similarly be mixed into the tilt angle of the information recording medium.

[Purpose of the invention]

The present invention has been made in view of the above points, and provides optical information that enables accurate detection of the tilt angle of the information recording medium regardless of the angle of incidence of the tilt detection beam on the information recording medium and the focus r. It is an object of the present invention to provide a method for detecting the inclination of an information recording medium in a recording/reproducing apparatus.

[Summary of the invention]

In this invention, an M detection beam of an information recording medium is incident on a flat part between information recording tracks or between recording pits of the information recording medium obliquely with respect to the information recording medium.
When the information recording medium is not tilted, the reflected light is passed through a condenser lens arranged so that the reflected light is parallel to the optical axis of the lens, and then the light is received at approximately the rear focal position of the condenser lens. By using four position detectors arranged so that their surfaces are substantially perpendicular to the optical axis of the condensing lens, the tilt of the information recording medium can be detected regardless of the angle of incidence of the tilt detection beam on the information recording medium and the focus shift. This makes it possible to accurately detect corners.

〔Effect of the invention〕

According to the present invention, it is possible to accurately detect the tilt angle of the information recording medium without being affected by the incident angle of the tilt detection beam on the information recording medium and the focus shift.
By correcting the information signal, it is possible to perform more stable tracking control, focusing control, and jitter control than in the past. Therefore, information signals can be recorded or reproduced with a higher S than before. Furthermore, since there is no need to adjust the angle of incidence of the beam for detecting the inclination of the information recording medium, assembly of the optical system becomes easier.

[Embodiments of the invention]

The present invention will be explained in detail below with reference to the drawings.

FIG. 2 shows the principle of detecting the tilt angle of an information recording medium. As shown by the solid line in FIG. 2(a), the beam 2 for detecting the inclination of the information recording medium is obliquely incident on the flat part of the information recording medium 202, and the optical axis of the lens reflects the reflected light 1 as described above. Condensing lens 2 arranged parallel to the light
03, the light is received by a position detector 204 disposed approximately at the rear focal position of the condenser lens so that its light receiving surface is substantially perpendicular to the optical axis of the condenser lens. Here, if the information recording medium 202 is deformed by a pressure Δθ as shown by the broken line in the figure, the reflection angle of the tilt detection beam is 2Δθ, and the position of the light receiving point on the position detector 204 is ΔX $! #do. Here, if the focal length of the condensing lens 203 is f, the movement amount ΔX is given by Δx,=2f80 (2). Since the focal length f of the condensing lens is known, the r difference ΔX of the receiving position of the reflected light on the position detector
If it is detected, the tendency/propensity Δ of the information recording medium can be determined from equation (2).
θ can be set. As is clear from equation (2), in this method, the angle of incidence of the tilt detection beam on the information recording medium is irrelevant to the calculation of the tilt angle of the information recording medium.

Furthermore, when the information recording medium i 202 moves up and down as shown by the dashed line and broken line in FIG.
Since the light is parallel to the light beam 3, there is no change in the light receiving position on the position detector 204, which is placed approximately at the rear focal position of the focusing lens. Therefore, even if there is a focus shift, no error occurs in the determined tilt angle of the information recording medium. As described above, according to this method, IIJ on the information recording medium is
I @ It is important to accurately detect the declination angle of the information recording medium regardless of the incident angle of the detection beam and the 7 orcus deviation.

FIG. 3 is a schematic diagram of an embodiment of an optical disk device equipped with an information recording medium tilt detection method according to the present invention. In the figure, 301 is an information signal/tracking signal 7
A semiconductor laser is used as a laser beam light source for detecting an excusing signal, and the wavelength of the laser light is λ. A laser beam emitted from a semiconductor laser 301 is turned into a parallel beam by a collimating lens 302, passes through a polarizing beam splitter 303 and a λ/4 plate 304, and enters an objective lens 305.
The i light is emitted from K onto an information recording track 307 of an optical disk 306 which is an information recording medium. Here optical f isk 30
6 has a guide groove for tracking, and the cross-sectional shape in the radial direction is shown in the figure. It is also assumed that the objective lens 305 moves in the radial direction of the optical disk 306 perpendicular to the light IN direction and the optical axis by a focus servo mechanism and a tracking servo mechanism, respectively. The reflected and diffracted light from the information recording track 307 of the optical disc passes through the objective lens 305, the λ/4 plate 304, the polarizing beam splitter 303, the focusing lens 308, and the cylindrical lens 309, and is directed in the width direction of the information recording track 307 of the optical disc 306. and a so-called 4-split photodetector 310 in which unit detectors are arranged side by side in the length direction,
An information signal/tracking signal; focusing signal is detected by calculating the outputs from the four unit detectors. The tilt of the optical disc is determined by the tilt detection beam light source 3]1
．． (7) The laser beam from the semi-quartet laser is made into parallel light by the collimating lens 312, and the optical disc is placed on the flat part between the information recording tracks 307 near the focal point of the laser beam which is narrowed down by the objective lens 305. Irradiate obliquely to 306K. Then, after passing the reflected light through a condenser lens 313 arranged so that the reflected light is parallel to the optical axis of the lens when the optical disc has no slope, the light receiving surface is located approximately at the rear focal position of the condenser lens. A semiconductor device detector (P
A position detector 314 such as 8D) or a single charge coupling element (C'CD) detects the deviation of the receiving position of the reflected light due to the tilt of the guide tube and the optical disk. Here, the semiconductor laser 3
11, collimating lens 312, condensing lens 313,
The position detector 314 is perpendicular to the optical axis of the objective lens 305 and located in the radial direction of the optical disk 306 (information recording track 3
07 width direction). In the optical disc device shown in the figure, the tilting of the optical disc in the radial direction can be detected, and the tracking signal can be corrected based on this.

[Other embodiments of the invention]

This invention can be implemented with various modifications. For example, in optical discs such as video discs and digital audio discs that do not have guide grooves for tracking and information is recorded as a concave and convex pattern, a beam for detecting disc inclination is applied to the flat area between the pits of the information track. If the inclination of the disk is detected based on the inclination detection principle according to the present invention, it is possible to perform jitter correction. Furthermore, by providing a plurality of sets of beams for detecting the inclination of the information recording medium, condensing lenses, and position detectors, it is also possible to detect the inclination angles of the information recording medium in various directions.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the ode detection method of a conventional information recording medium.
FIG. 2 is a diagram showing an information recording medium tilt detection method according to the present invention, and FIG. 3 is a schematic diagram of an optical disk device equipped with an information recording medium tilt detection function according to an embodiment of the present invention. . 101.201... Beam for tilt detection 102.202... Information recording medium (optical disk) 20
3. ...Condensing lens

Claims (1)

[Claims] In an optical information recording/reproducing device that optically records or reproduces information, a beam for detecting the inclination of an information recording medium is incident on a flat part of the information recording medium obliquely to the information recording medium, and its reflection is detected. When the light is not tilted to the upper information recording medium, the reflected light passes through a condensing lens arranged parallel to the optical axis of the lens, and then the light receiving surface is located approximately at the rear focal point of the condensing lens. A tilt detection method for an information recording medium, characterized in that the information is guided to a position detector arranged substantially perpendicular to the optical axis of the condenser lens.