JPH02192029A - Optical head - Google Patents

Abstract

PURPOSE:To allow the correction of the sensor offset generated by the inclination of a disk or the positional deviation thereof with age by adjusting the position of a photodetector according to an offset quantity. CONSTITUTION:This optical head has the offset detecting circuit which detects the sensor offset by searching the disk surface while displacing a condensing means at a specified frequency in an optical axis direction by means of an actuator just prior to the execution of a focus control operation. The head has also the offset detecting circuit which detects the sensor offset by searching tracks while displacing the condensing means at a specified frequency in the direction orthogonal with the tracks by means of the actuator just prior to the execution of a tracking control operation. A correcting means which displaces the position of a photodetector according to the offset quantity detected by the detecting circuit is provided. Namely, the offset is detected at the time of the operation start and the position of the photodetector is adequately adjusted according to this offset quantity, by which the influence by the inclination of the disk and the positional deviation with age is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an optical head in an optical disk recording/reproducing device that optically reads information on a disk, and more particularly relates to an optical head for optically reading information on a disk. The present invention relates to improving the characteristics of a focus sensor that detects misalignment and a tracking sensor that detects track misalignment of a light spot with respect to an information track on a disk.

[Prior Art] FIG. 7 is a diagram showing an optical path of a conventional optical head for a magneto-optical disk. In the figure, (1) is a laser beam, (2) is a semiconductor laser, (3) is a collimator lens, (4) is a half prism, (5) is a reflecting mirror, (6) is an objective lens,
(7) is a λ/2 plate, (8) is a polarizing beam splitter, (
9) is a condensing lens, (lO) is a photodetector for tracking detection, (11) is a condensing lens, (12) is a wedge prism, (13) is a magnifying lens, and (14) is a photodetector for focusing detection. It is.

FIG. 8 shows a side view of the reflecting mirror (5) and objective lens (6) in FIG. 7, and (15) is a disk.

Figure 9 shows the tracking detection photodetector (10
), in which (21) is a photodetector plate for tracking detection, (22) is two photodetector elements (22).
a) In the photodetector section consisting of (22b), (30)
is the light spot received on the photodetector section (22), (3
2) is a differential amplifier that takes the difference between the outputs of the respective light receiving elements (2za) and (22b).

Figure 10 shows the focusing detection photodetector (
14), in which (23) is a photodetector plate for focusing detection, and (24) is the four light receiving elements (24a), (24b), (24c), (
(24d), a photodetector section consisting of (31a), (
31b) is the light spot received on the photodetector section (24), (33) is the light receiving element (24a), (24d)
This is a differential amplifier that takes the difference between the outputs of the light receiving elements (24b) and (24c).

Next, the operation will be explained.

The laser beam (1) emitted from the semiconductor laser (2) becomes parallel light by the collimator lens (3), is reflected by the half prism (4) and the reflection mirror (5), and is reflected by the objective lens (
6). The light spot focused by the objective lens (6) is irradiated onto the disk (15), and the reflected light travels in the opposite direction to the incident light, causing a reflection mirror (5) and a half prism (4).
, a λ/2 plate (7), and a polarizing beam splitter (8).
) is divided into transmitted light and reflected light.

The transmitted laser light is received by a tracking detection photodetector (10) through a condensing lens (9). Further, the reflected laser beam is condensed by a condensing lens (11), divided into two beams by a wedge prism (12), and each beam is received by a focusing detection photodetector (14).

The tracking detection photodetector (10) is connected to the disk (1
5) When the light spot is located at the center of the upper track,
The two light receiving elements (22a) and (22
The positional relationship in b) is initially adjusted so that the outputs are equal. In addition, the focusing detection photodetector (14) detects the first
Of the four light receiving elements shown in Figure 0, (24a),
The positional relationship is initially adjusted so that the outputs of (24b), (24c), and (24d) are equal.

Therefore, when track deviation occurs, the light spot (
30) changes and the differential amplifier (32) takes the differential output of the light receiving elements (22a) and (22b), a tracking detection characteristic as shown in FIG. 11 is obtained. In Figure 11, the horizontal axis represents the amount of deviation of the optical spot from the track center, and the vertical axis represents the differential amplifier (3
2) represents the output.

In addition, when a focus shift occurs, the light spot (31a)
, (31b) change, the differential output ((31b) of the light receiving element is changed by the differential amplifier (33).
24a) + (24d) )−((24b) +
(24c)), a focusing detection characteristic as shown in FIG. 12 is obtained. In Fig. 12, the horizontal axis represents the focus shift amount, and the vertical axis represents the differential amplifier (33
) represents the output of

Of the two types of detection signals mentioned above, the objective lens (6) is driven and controlled in the direction of arrow a in FIG. 7 according to the former tracking detection signal to perform tracking control. In addition, the objective lens (6) is adjusted according to the latter focusing detection signal.
is driven in the direction of the arrow in FIG. 8 to perform focusing control.

[Problems to be Solved by the Invention] However, in the conventional optical head as described above, changes in the tilt when replacing the disk (15) and aging of the photodetectors (10) and (14) occur. If a significant positional shift occurs, as shown in FIG. 13, even when the light spot is located at the center of the track, the two light receiving elements (
In 22a) and (2)'b), a light spot (30) may occur at a position where the output is not evenly obtained. When a deviation occurs in the optical spot in this way, as shown in FIG. 14, the target position P to which tracking control is to be performed does not coincide with the track center, that is, the point PO where the reproduction output signal is largest, resulting in an offset deviation δ, which causes the reproduction There was a problem that the characteristics deteriorated. On the other hand, the focusing system also has the same problem as described above, in that an offset shift occurs in the target position to which focusing control is to be performed, resulting in deterioration of reproduction characteristics.

This invention was made to solve the above-mentioned problems, and it is an optical system that improves playback characteristics by correcting the offset shift caused by the tilt of the disk and the positional shift of the photodetector over time. The purpose is to provide the head.

[Means for Solving the Problems] In the present invention, first, the focusing system searches the disk surface while displacing the focusing means in the optical axis direction at a constant frequency by the actuator immediately before performing the focus control operation, and calculates the sensor offset. An offset detection circuit for detecting the amount of offset detected by the detection circuit and a correction means for displacing the position of the light receiving element according to the amount of offset detected by the detection circuit are provided.

Regarding the tracking system, there is also an offset detection circuit that detects sensor offset by searching the track while displacing the light focusing means at a constant frequency in a direction perpendicular to the track using an actuator immediately before performing a tracking control operation, and this detection circuit. A correction means for displacing the position of the light-receiving element according to the offset amount detected in is provided.

Furthermore, the correction means is composed of a laminated piezoelectric element.

[Function] In the optical head of the present invention, the sensor offset is detected at the start of operation, and the position of the light receiving element is adjusted appropriately according to the amount of offset, so that the influence of disk inclination and positional shift over time can be avoided. It can be corrected.

Furthermore, by using a laminated piezoelectric element, it is possible to eliminate adverse effects caused by vibrations and the like.

[Embodiments of the invention] Embodiments of the present invention will be described below with reference to the drawings.

First, a method for detecting the relative positional deviation between the received light spot and the light receiving element will be described. Figures 1 and 2 show the relationship between the focus shift of the objective lens (6), the focus detection signal, and the reproduced output signal.When the focal point is at the focused position shown in Figure 1(b), the reproduced output signal is at its maximum. The focus detection signal is adjusted to zero at this position. When a focus shift occurs, the reproduced output signal decreases.

Based on this relationship, in order to detect the deviation between the focus detection signal and the re-main output signal, the operation at the time of initial retraction of the objective lens (6) is used. Since the position of the objective lens (6) relative to the disk (15) is not known when the power is turned on and the objective lens (6) starts operating, it performs a retracting operation as shown in FIG. That is, by applying a triangular wave input to an actuator (not shown) that drives the objective lens (6) and moving the objective lens (6) up and down, the disk (
15) Detect the position.

During this operation, as shown in FIG. 4, the objective lens (6) is driven with a triangular wave+AC component (for example, 30 flz), and at the same time, the reproduced output signal and the focus detection signal are monitored. That is, the amount and direction of deviation between the zero point of the focus detection signal and the maximum point of the reproduced output signal can be detected from the level change and phase of the output signal due to movement of the objective lens (6).

To explain this in more detail, if the light spot is passed through the disk surface while being slightly displaced in an AC manner, the fourth
At the maximum point of the reproduced output signal in the figure, the frequency is twice the minute displacement, and when it deviates from this maximum point to either side, it is the same frequency as the minute displacement frequency, but in the region (A) in FIG. The phase differs by 180 degrees in the Bl region, and outputs with different amplitudes are obtained depending on the amount of shift.By phase-detecting this output and the AC output that drives the optical spot, the maximum point of the reproduced output signal can be detected. Can be detected.

The sensor offset can be detected by detecting the deviation between the maximum point of the reproduced output signal and the zero point of the focus detection signal.

Next, a means for correcting the relative position of the light spot and the photodetector will be described. FIG. 5 shows an example of this correction mechanism,
A recess (
A photodetector section (24) is held on the negative side of 23a) via a laminated piezoelectric element (40).

Since the piezoelectric element (40) expands and contracts in the stacking direction by applying a voltage, the piezoelectric element (40) is driven with a voltage value corresponding to the above-mentioned sensor offset amount, and the position of the photodetector section (24) is adjusted as shown in FIG. The light receiving element (24a) is displaced in the left and right direction.
The offset can be corrected by optimizing the positional relationship between (24d) and (24d).

FIG. 6 shows another embodiment of the correction mechanism.

In this embodiment, a notch (23b) is provided in a part of the photodetector plate (23), and the notch (23b) is configured to be plastically deformed by expansion and contraction of the piezoelectric element (40). . In this case, both ends of the photodetector section (24) are supported by the inner wall of the recess (23a) of the photodetector plate (23), which is advantageous in terms of vibration resistance and the like.

The above has explained the correction in the focusing system shown in FIG. 10, but the tracking system shown in FIG. Correction can be performed by holding the offset, detecting the offset while driving the objective lens (6) in the tracking direction at a constant frequency during servo retraction, and displacing the piezoelectric element according to the offset amount.

In this way, according to the embodiment described above, the sensor offset is detected and corrected at the start of the operation, so it can be realized by simply adding a simple circuit to the conventional servo circuit. Furthermore, since a solid laminated piezoelectric element is used as the correction means, there is no adverse effect due to vibration or the like.

Note that the correction can be performed once when replacing the disk or turning on the power, and can sufficiently cope with the influence of the disk and changes over time. Furthermore, the precision of delicate adjustment of the positional relationship between the photodetector and the received light spot, which is essential when manufacturing an optical head, can be relaxed in accordance with the amount of correction.

[Effects of the Invention] As described above, according to the present invention, the position of the photodetector is adjusted according to the amount of offset, so that sensor offset caused by disk inclination or positional shift over time can be corrected. This has the effect of providing an optical head with significantly improved reliability.

Further, by using a laminated piezoelectric element as the correction means, it is possible to eliminate the adverse effects caused by vibrations and the like.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the positional relationship between the objective lens and the disk, Figure 2 is a diagram showing the sensor output characteristics and playback output characteristics corresponding to the above positional relationship, and Figure 3 is for explaining the initial retraction operation of the objective lens. , FIG. 4 is a diagram for explaining the initial retracting operation according to the present invention, FIG. 5 is a diagram showing an example of the correction mechanism in the optical head of the invention, and FIG. 6 is a diagram showing another embodiment of the correction mechanism. 7 is a diagram showing the optical path of a conventional optical head for a magneto-optical disk, FIG. 8 is a side view of the reflecting mirror and objective lens portion of FIG. 7, and FIG. 9 is a diagram showing a conventional tracking light Figure 10 shows a conventional focusing photodetector, Figure 11 shows tracking detection characteristics, Figure 12 shows focusing detection characteristics, and Figure 13 shows how light is received. FIG. 14 is a diagram showing the relative positional relationship between the light spot and the photodetector, and FIG. 14 is a diagram showing the characteristics of the output of the tracking detection photodetector and the reproduced output signal corresponding to the above-mentioned relative positional deviation. (1)...Laser light, (2)...Semiconductor laser, (
3)...Collimator lens, (4)...Half prism, (5)...Reflection mirror (6)...Objective lens, (7)...λ/2 plate, (8)...・Polarizing beam splitter, (9)...Condensing lens, (10)...Photodetector for tracking detection, (11)...Condensing lens, (12)...Wedge prism, (13) ... Magnifying lens, (14) ... Photodetector for focusing detection, (15) ... Disk, (22) ... Photodetector section, (24) ... Photodetector section, ( 32), (33
)...Differential amplifier, (4o)...Piezoelectric element. In addition, the same symbols in the figures indicate the same or equivalent parts.

Claims (4)

[Claims] (1) A light source, an optical member that guides the light beam emitted from the light source onto the disk, a condensing means that forms a light spot on the disk, and a light source that receives reflected light from the disk to correct defocus and track. In an optical head, the optical head includes a light-receiving element that obtains a deviation and a reproduction signal, and an actuator that drives the focusing means in a predetermined direction according to the focal deviation and track deviation. An offset detection circuit that detects a sensor offset by searching the disk surface while displacing the optical means in the optical axis direction at a constant frequency, and a correction that displaces the position of the light receiving element according to the amount of offset detected by this detection circuit. An optical head characterized by comprising: means. (2) a light source, an optical member that guides the light beam emitted from the light source onto the disk, a condensing means that forms a light spot on the disk, and a light source that receives reflected light from the disk to correct defocus and track. In an optical head that includes a light receiving element that obtains a deviation and a reproduction signal, and an actuator that drives the focusing means in a predetermined direction according to the focal deviation and track deviation, the actuator drives the focusing means immediately before performing a tracking control operation. an offset detection circuit that searches the track and detects a sensor offset while displacing the optical means in a direction perpendicular to the track at a constant frequency; and a position of the light receiving element is displaced in accordance with the amount of offset detected by the detection circuit. An optical head characterized in that it is provided with a correction means. (3) a light source, an optical member that guides the light beam emitted from the light source onto the disk, a condensing means that forms a light spot on the disk, and a light source that receives the reflected light from the disk to prevent defocusing and tracking. A focus control operation is performed in an optical head that includes a light receiving element that obtains a deviation and a reproduction signal, and an actuator that drives the focusing means in an optical axis direction and a direction perpendicular to the track in accordance with the focal deviation and track deviation. A first offset detection circuit detects a sensor offset by searching the disk surface while displacing the light focusing means in the optical axis direction at a constant frequency by the actuator immediately before, and an offset detected by the first detection circuit. a first correction means for displacing the position of the light-receiving element according to the amount of the light receiving element; and a second offset detection circuit for detecting a sensor offset, and a second correction means for displacing the position of the light receiving element according to the amount of offset detected by the second detection circuit. light head. (4) The optical head according to claim 1, 2, or 3, wherein the correction means is composed of a laminated piezoelectric element.