JPH06101131B2 - Optical recording / reproducing device - Google Patents

Description

The present invention relates to an optical recording / reproducing device such as an optical disk device, and more particularly to an optical recording / reproducing device equipped with an optical track tracking device using diffracted light from a track. It relates to the device.

[Background of the Invention]

As a track tracking device in a conventional optical information recording / reproducing device such as an optical disc, the depth of a track groove recorded on the surface of a recording medium is determined with respect to the wavelength λ of a light source (eg, He-Ne laser, semiconductor laser). (2n-1) λ / 4 (n = 1,
2, 3, ...), there is known a device for tracking a track by utilizing the fact that when the light beam deviates from the track, the asymmetry of the diffracted light occurs due to the edge of the track groove. (See, for example, JP-A-52-62037.)
It is a figure explaining the track tracking device using the diffracted light in a reflection type optical disc. A light beam emitted from a light source 1 is condensed by a lens 2, and a prism 3 passes through a Luvano mirror 4 and a converging lens 5 and is reflected by a disc 6 of a reflection type.
The spot size is narrowed down to about μm. The optical depth on the surface of the disk 6 is (2n-1) λ / 4 for the laser wavelength λ.
An information track 61 deviated from (n-1, 2, ...) Is provided, and when a light spot is located in the track, a diffracted light pattern including track information is generated in its reflected light.
This reflected light again passes through the collecting lens 5 and the galvanometer mirror 4, the optical path is separated by the prism 3, and is guided to the photodetector 7 divided into two. The photodetector 7 is located far away from the conjugate point C of the converging lens 5 in order to detect the diffracted light component of the reflected light from the track 61 on the disk 6. The relationship between the photodetector 7 and the diffracted light component (shown by diagonal lines) at this time is shown in FIG. FIG. 2A shows a case where the light beam is located on the left side of the track 61, and the diffracted light component becomes strong on the left side 7a of the photodetector 7. FIG. 2 (b) shows the case of being located at the center, and the left and right are even. FIG. 2 (c) shows the case of being located on the right side, and becomes stronger on the right side 7b. In this way, the diffracted light component on the photodetector 7 changes depending on the positional relationship between the light beam and the track, and when the two outputs of the photodetector 7 are differentiated by the differential amplifier 8 of FIG. A deviation signal for track tracking as shown can be obtained. By guiding this signal to the servo circuit 9 and performing feedback control on the galvanometer mirror 4, the light beam can be always positioned at the center of the track 61.
However, in the optical track tracking device having such a configuration, the photodetector 7 is located away from the conjugate point C of the converging lens 5, so if the galvano mirror 4 is shaken for track tracking, the photodetector 7 will be on the surface. It was found that there was a problem that the light beam of No. 1 swayed correspondingly, and the amount of this swaying was included in the track deviation signal, so that track tracking could not be performed normally. When this shake is numerically converted, the shake x of the light beam on the surface of the photodetector is expressed by the following equation when the position of each component in FIG. 1 is set as shown in FIG.

However, m: magnification of the converging lens 5 d: deflection of the light beam on the surface of the disk 6 l: distance between the converging lens 5 and the galvano mirror L: distance from the conjugate point C of the converging lens 5 to the photodetector 7 T: Distance from galvanometer mirror 4 to conjugate point C For example, d = 0.2mm, m = 20, l = 30mm, L = 10mm, T = 150mm
Then, x = 0.044 mm.

The light beam diameter D on the surface of the photodetector 7 is: Becomes

Therefore, as a guide, the deviation will be about 20% of the light beam diameter, and from this, the deviation (error) equivalent to 20% of the track width will be superimposed on the track deviation signal. The deviation signal due to the shake is of a magnitude that cannot be ignored with respect to the track deviation signal.

[Object of the Invention]

The present invention has been made in view of the above points, and an optical track capable of correcting a deviation signal due to a deflection of a light beam on a photodetector surface which occurs at the time of track tracking, thereby achieving more accurate track tracking. The purpose is to provide a tracking device.

[Outline of Invention]

In order to achieve such an object, the present invention corrects a deviation signal due to a beam shake by providing another servo circuit capable of correcting mainly low frequency components such as an eccentric fundamental frequency in a normal tracking control circuit system. Is. That is, the present invention is directed to a recording medium having a track, a light irradiating unit for irradiating a single light beam for recording and reproducing information on the recording medium, and an electric light receiving unit for receiving reflected light from the recording medium by the irradiation of the light beam. A photodetector separated into at least two parts for outputting a signal, the photodetector being arranged at a position deviated from an image forming position of an optical system for guiding reflected light to the photodetector, and the photodetector. Means for obtaining a track tracking signal indicating the deviation of the light beam with respect to the track by computing the electric signals obtained from each of the two parts of the optical beam, and the light beam so as to track the track in response to the track tracking signal. First control means for controlling the irradiation position, and controlling the irradiation position of the light beam so as to extract the rotation frequency component of the recording medium from the track tracking signal and reduce the rotation frequency component. Wherein the reducing offset included in the track following signal by and a second position control unit that.

The rotation frequency component can be extracted by extracting the low frequency component with, for example, a low pass filter. It is also a desirable example to include means for receiving the track tracking signal to obtain its average value and means for superimposing the average value on the low frequency component. Further, it is preferable that the first and second position control means have signal phase compensation means, and
It is desirable that the position control means of (1) includes a linear motor in terms of response characteristics.

Example of Invention

FIG. 4 is a diagram showing a positional relationship between a photodetector for detecting a tracking control signal and a light spot. When the light spot moves from the position of the solid line to the position of the dotted line in the direction causing the imbalance of the diffracted light, the offset component of the tracking control signal TR is shown in the fifth example.
It is a figure. The relationship between the spot movement amount Δ and the tracking control signal offset differs depending on the spot distribution shape on the photodetector surface, but if the movement amount Δ is sufficiently smaller than the spot size, it is approximated as a proportional relation. You can do it. Further, there is a proportional relationship between the drive signal of the actuator that moves the galvanic mirror and the lens in the direction perpendicular to the optical axis and the spot movement amount. Therefore, the low-frequency component of the drive signal is separated by a low-pass filter and driven by another actuator, whereby the offset can be canceled.

An embodiment of the present invention will be described with reference to FIG.

Looking at the frequency spectrum of the eccentricity that requires tracking control, the frequency component that matches the disk rotation frequency (fundamental frequency component) is the largest. Therefore,
If only this frequency component is made to follow by another actuator in advance, the higher-order frequency component of eccentricity will be further reduced, so the above-mentioned influence can be ignored.

Therefore, as shown in FIG. 6, the entire optical head 140 is moved by using an actuator having a poor frequency characteristic such as a linear motor 141 for low frequency components. Here, the optical head 140 is connected to the linear motor 141 via a frame body 142, and rolls on a rail 144 by a rotating roller 143. The actuator 145 that moves in response to the higher-order frequency component moves the objective lens 5 in a direction perpendicular to the optical axis (tracking direction).
Move to. The light emitted from the light source 1 is collimated by the coupling lens 2 and collimated by the semi-transparent mirror 3 ′ to enter the objective lens 5 to form a spot on the disc 6. The reflected light passes through the objective lens 5 again, passes through the semitransparent mirror 3 ', and enters the photodetectors 7a and 7b.

FIG. 7 is a diagram for explaining the electric circuit system of the embodiment of FIG. The tracking control signal TR is input to the buffer amplifier 110, this signal is first input to the low-pass filter 118, and then input to the drive circuit 116 that drives the linear motor 141 via the appropriate phase compensation circuit 117, thereby eccentricity is obtained. The entire optical head follows the low frequency component of. Also a buffer amplifier
Output from 110 is a high pass filter or band pass filter 1
A driving circuit 1 for extracting an eccentric high-order frequency component through 11 and driving an actuator 145 for moving the objective lens 5 in a direction perpendicular to the optical axis through a phase compensation circuit 112.
Input to 13 to make the light spot follow the track.

FIG. 8 is a diagram for explaining an embodiment in which the improvement of FIG. 7 is further added. Those having the same functions as those in FIG. 7 are indicated by the same numbers. The average value of the higher-order frequencies is detected by the integrating circuit 119, the output of the integrating circuit 119 is added by the adder 120 with the output from the phase compensation circuit 117, and the output is input to the drive circuit 116. In this way, by superimposing the average value of the high-order frequency on the low-frequency component in the loop of the control system that follows the low-frequency component, the tracking performance of the low-frequency component can be improved.

[Brief description of drawings]

FIG. 1 is a view for explaining a conventional optical track tracking device,
FIG. 2 is a diagram for explaining the principle of tracking signal detection using the dazzle light's tolerance, FIG. 3 is a diagram showing the waveform of the output of a differential amplifier with respect to the amount of track deviation, and FIG. 4 is on the photodetector surface. FIG. 5 is a diagram showing the movement of the spot in FIG. 5, FIG. 5 is a diagram showing the relationship between the amount of movement of the spot and the offset amount of the tracking signal, FIG. 6 is a diagram for explaining an embodiment of the present invention, and FIG. The figure explaining the circuit of the Example of a figure, 8th
The figure is a diagram for explaining another circuit of the embodiment shown in FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Sugiyama 5 Noguchi, Shirotori-cho, Toyokawa-shi, Aichi 5 Toyokawa factory, Hitachi Ltd. (72) Ino Motoo Uno, 1-280, Higashikoigakubo, Kokubunji, Tokyo Address: Central Research Laboratory of Hitachi, Ltd. (72) Seiji Yonezawa 1-280, Higashi Koigakubo, Kokubunji City, Tokyo Location: Central Research Laboratory of Hitachi, Ltd. (72) Inventor Tadahiko Kameyama 2880, Kozu, Odawara, Kanagawa Hitachi, Ltd. Inside the Odawara Plant (72) Inventor Tokuya Kaneda 2880 Kozu, Odawara City, Kanagawa, Ltd. Inside the Odawara Plant, Hitachi Ltd. (56) References JP-A-55-12594 (JP, A) JP-A-51-46018 (JP) , A) JP-A-55-12561 (JP, A)

Claims (5)

[Claims] 1. A recording medium having a track, a light irradiating unit for irradiating a single light beam for recording and reproducing information on the recording medium, and a reflected light from the recording medium by irradiation of the light beam. A photodetector divided into at least two parts for receiving and outputting an electric signal, the photodetector being arranged at a position deviated from an image forming position of an optical system for guiding the reflected light to the photodetector. And means for obtaining a track tracking signal indicating the deviation of the light beam with respect to the track by calculating the electric signals obtained from each of the two parts, and the light beam responding to the track tracking signal causes the light beam to scan the track. First control means for controlling the irradiation position of the light beam so as to track the rotational frequency component of the recording medium from the track tracking signal. Optical recording and reproducing apparatus characterized by reducing the offset included in the track following signal by and a second position control means for controlling the irradiation position of the light beam to reduce. 2. The optical recording / reproducing apparatus according to claim 1, wherein the rotational frequency component is extracted by extracting a low frequency component of the track tracking signal. 3. The optical recording / reproducing apparatus according to claim 2, further comprising means for receiving the track tracking signal and obtaining an average value thereof, and means for superimposing the average value on the low frequency component. 4. The optical recording / reproducing apparatus according to any one of claims 1 to 3, wherein the first and second position control means have signal phase compensating means. 5. The optical recording / reproducing apparatus according to any one of claims 1 to 4, wherein the second position control means comprises a linear motor.