JPS63100628A - Optical recording and reproducing device - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording/reproducing device such as an optical disk device, and in particular to an optical recording device equipped with an optical track tracking device that utilizes diffracted light from a track. It concerns re-equipment.

[Background of the invention]

A light source (for example, He-Ne
The depth of the track groove recorded on the recording medium surface is (2n-1)λ/4 for the wavelength λ of the laser (laser, semiconductor laser)
(n=1.2.3...), there is a known device that performs track tracking by utilizing the fact that when the light beam deviates from the track, the edges of the track groove cause asymmetry in the diffracted light. (For example, JP-A-52-6203
See No. 7. ) FIG. 1 is a diagram illustrating a track tracking device using diffracted light on a reflective optical disc. A light beam emitted from a light source 1 is focused by a lens 2, and a prism 3 passes through a ruba mirror 4 and a converging lens 5 and is focused onto a reflective disk 6 into a spot of about 1 μm. An information track 61 is provided on the surface of the disk 6, the optical depth of which deviates from (2n-1)λ/4 (n-1, 2, . . .) with respect to the laser wavelength λ. When the spot is located within the track, a diffracted light pattern containing track information is generated in the reflected light. This reflected light is collected again by the collecting lens 5. Pass through galvanometer mirror 4 and prism 3
The light path is separated by the light beam, and the light is guided to the photodetector 7 which is divided into two parts. 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 (indicated by diagonal lines) at this time is shown in FIG. FIG. 2(a) shows a case where the light beam is located on the left side with respect to 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 where the positions are at the center, and the left and right sides are equal. FIG. 2(c) shows the case where it is located on the right side, and it becomes stronger on the right side 7b. In this way, depending on the positional relationship between the light beam and the track, the photodetector 7
Since the upper diffracted light component changes, by subtracting the difference between the two outputs of the detector 7 using the differential amplifier 8 shown in FIG. 1, a deviation signal for track tracking as shown in FIG. 3 can be obtained. By feeding this signal to the servo circuit 9 and performing feedback control on the galvanometer mirror 4, the light beam can always be positioned at the center of the track 61. However, in the optical track tracking device with such a configuration, since the photodetector 7 is located away from the conjugate point C of the converging lens 5, when the galvanometer mirror 4 is swung for track tracking, the surface of the photodetector 7 is It has been found that there is a problem in that the optical beam of the optical system deflects correspondingly, and this deflection is included in the track deviation signal, so that track tracking cannot be performed normally.

Converting this deflection into numerical values, if each component is positioned as shown in FIG. 1, the deflection X of the light beam on the photodetector surface is expressed by the following equation.

m - d - Q - However, m: Magnification of the converging lens 5 d: Deflection amount of the light beam on the disk 6 surface Q = Distance L between the converging lens 5 and galvanometer mirror 4: From the conjugate point C of the converging lens 5 Distance T to photodetector 7 Distance from galvanometer mirror 4 to conjugate point C For example, d=0.2 mm, m=20. (1=30+m.

If L=10mm, T=150+u+, x=
It becomes 0.044+am.

The diameter of the light beam on the surface of the photodetector 7 is =0.25 mm+, assuming that the aperture of the converging lens is 4.5 m.

Therefore, as a guide, the deviation will be approximately 20% of the optical beam diameter, and from this, the track deviation signal will be approximately 20% of the track width.
A deviation (error) equivalent to 0% will be superimposed,
The deviation signal due to beam deflection on the detector surface is of a size that cannot be ignored compared to the track deviation signal.

[Purpose of the invention]

The present invention was developed in view of this point, and is an optical system that corrects the deviation signal caused by the deflection of the light beam on the photodetector surface that occurs during track tracking, thereby achieving more accurate track tracking. The purpose is to provide a track tracking device.

[Summary of the invention]

In order to achieve such an object, the present invention corrects deviation signals caused by beam deflection by providing a separate servo circuit capable of correcting mainly low frequency components such as the fundamental frequency of eccentricity in a normal tracking control circuit system. It is.

[Embodiments of the invention]

Figure 4 is a diagram showing the positional relationship between a photodetector and a light spot for detecting a tracking control signal.When the six light spots move from the position of the solid line to the position of the dotted line in a direction that causes an imbalance of diffracted light, , tracking control signal TR
FIG. 5 shows what the offset component looks like.

The relationship between the spot movement amount Δ and the offset of the tracking control signal differs depending on the distribution shape of the spot on the photodetector surface, but if the movement amount Δ is sufficiently small compared to the spot size, it can be approximated as a proportional relationship. You may do so. Further, as described in the above embodiment, there is a proportional relationship between the movement signal of the actuator that moves the galver mirror and the lens in a direction perpendicular to the optical axis and the amount of spot movement. Therefore, the offset can be canceled by separating the low frequency component of the active signal using a low-pass filter and driving it with another actuator.

An embodiment of the present invention will be described using FIG. 6.

Looking at the frequency spectrum of the eccentricity that must be controlled by tracking, the frequency component (fundamental frequency component) that is almost identical to the rotational frequency of the disk is the largest. Therefore,
If only this frequency component is followed in advance by another actuator, the higher-order frequency component of the eccentricity will be further reduced, so that the above-mentioned shadow W can be ignored.

Therefore, as shown in FIG. 6, the entire optical head 140 is moved by using an actuator with poor frequency characteristics, such as a linear motor 41, for low frequency components. Here, the optical head 140 is connected to the linear motor 4 via the frame 142.
1 and rolls on rails 144 by rotating rollers 143. The actuator 145, which moves in response to high-order frequency components, moves the objective lens 5 in a direction perpendicular to the above-mentioned direction (tracking direction). Light emitted from a light source 1 is converted into parallel light by a coupling lens 2, is reflected by a semi-transparent mirror 3', and enters an objective lens 5 to form a spot on a disk 6. The reflected light is reflected by objective lens 5.
through the translucent tA3' again to the photodetectors 7a, 7.
incident on b.

FIG. 7 is a diagram illustrating the electric circuit system of the embodiment of FIG. 6. The tracking control signal TR is sent to the buffer amplifier 110.
This signal is first input to the Kaesjo filter 118, and then input to the drive circuit 116 that excites the linear motor 141 via an appropriate phase compensation circuit 117. Make the whole thing follow. Further, the output from the buffer amplifier 110 is passed through a high-pass filter or a band-pass filter 111 to extract eccentric high-order frequency components, and the output is passed through a phase compensation circuit 112 to an actuator that moves the objective lens 5 in a direction perpendicular to the optical axis. The light spot is input to the drive circuit 113 that drives the light beam 145 to make the light spot follow the track.

FIG. 8 is a diagram illustrating an embodiment further improved from FIG. 7. Components having the same functions as those in FIG. 7 are indicated by the same numbers. The average value of the higher-order frequency is detected by an integrating circuit 119, and the output of this integrating circuit 119 is sent to an adder 12.
0, the output from the phase compensation circuit 117 and the adder 120 are added, and the output is input to the drive circuit 116. in this way.

By superimposing the average value of high-order frequencies on the low-frequency components in a control system loop that tracks the low-frequency components,
Tracking performance for low frequency components can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a conventional optical track tracking device.
Figure 2 is a diagram explaining the principle of tracking signal detection using the unbalance of diffracted light, Figure 3 is a diagram showing the waveform of the output of the differential amplifier with respect to the amount of track deviation, and Figure 4 is the photodetector surface. FIG. 5 is a diagram showing the relationship between the amount of tracking signal offset and the amount of movement of the spot, FIG. 6 is a diagram illustrating an embodiment of the present invention, and FIG. A diagram explaining the circuit of the embodiment shown in FIG. 6, No. 8
This figure is a diagram illustrating another circuit of the embodiment of FIG. 6.悌 ne Figure half 5 B 6th

Claims (1)

[Claims] 1. A recording medium having a track, and a light irradiation unit that irradiates a light beam for recording and reproducing information on the recording medium;
a photodetector that outputs an electrical signal in response to the reflection of the light beam; a track deviation detection means for obtaining a track tracking signal indicating a deviation of the light beam with respect to the track based on the electrical signal; a first position control means for controlling the irradiation position of the light beam so that the light beam tracks the track; a means for receiving the track tracking signal and extracting a low frequency component thereof; and a first position control means responsive to the low frequency component. and a second controlling the irradiation position of the light beam so as to reduce the movement of the first position control means required for the light beam to follow the track.
1. An optical recording/reproducing device comprising: position control means. 2. The optical system according to claim 1, further comprising means for receiving the track tracking signal and obtaining an average value thereof, and driving the second position control means by the output of this means. Recording and playback device.