JPH0419617Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a playback device for an optical recording disk, and in particular a playback device having a so-called tilt servo mechanism that controls the optical axis of the optical system to be perpendicular to the information recording surface of the disk. It is related to the device.

BACKGROUND ART In general, optical recording disks are molded parts made of resin such as polycarbonate or acrylic, and are therefore susceptible to static warpage, deformation, etc. after molding. Looking at the amount of static warpage, the maximum warpage is +1.5, -2.5mm for 30cm and 20cm optical video discs, and ±0.5mm for 12cm digital audio discs. The maximum warpage is allowed, and realistically the amount of warpage varies depending on the disk.

When such static warpage occurs, the distance between the disk pit surface in the height direction and the objective lens of the optical pick-up due to the warp changes at the inner and outer circumferences of the disk, so it is necessary to move the objective lens up and down with a focus motor. Moreover, the minimum amount of stroke required is the amount of warpage. On the other hand, since the disk pit surface is tilted due to warping, the returned light has an angle with respect to the incident light, and the optical axis is shifted, so if the shift exceeds a certain tolerance, it will deviate from the viewing angle of the objective lens, and the output of the returned light will decrease. It will end up being put away. Additionally, as the pit surface is tilted, the track pitch with adjacent tracks becomes equivalently narrower, and if the beam spot diameter on the pit surface is constant, it becomes more susceptible to the influence of pit information from adjacent tracks. This results in an increase in cross stroke.

In order to improve the performance deterioration described above, recently, the optical system body including the objective lens has been changed so that the optical axis is always perpendicular to the pit surface to follow the static warping mentioned above. A playback device having a tilt servo mechanism that rotates in a plane including the optical axis is known, and FIG. 1 shows the conventional device. 1st
In the figure, 1 is a downwardly curved optical recording disk (hereinafter simply referred to as a disk), 2 is a spindle motor, 3 is a clamper that clamps the disk 1 to the spindle motor 2, and 4 is a clamper 3.
It is the support part of. Reference numeral 5 designates an objective lens constituting a part of the optical pickup, which is mounted on the optical system body 6 so as to be movable up and down, and is driven by a focus motor (not shown). The optical system body 6 is attached to the slider base 9 so as to be freely rotatable about a rotation fulcrum 8 located on the optical axes B and B' of the objective lens 5. Reference numeral 7 denotes a tilt mechanism composed of a motor, a deceleration means, etc., which adjusts the inclination of the optical axes B and B' of the objective lens 5 with respect to the disk surface by rotating the optical system body 6 with respect to the slider base 9. . The slider base 9 is attached to the disk 1 along a guide rail (not shown).
It is movable in the radial directions C and C', and is driven by a drive mechanism (not shown) consisting of a slider motor, reduction gear, etc.

In the plane including the optical axes B and B' of the objective lens 5,
An optical sensor 10 (shown in FIG. 2) for detecting the angle of inclination of the disk 1 with respect to the optical axes B and B' is provided close to the objective lens 5. As shown in FIG. 2, this sensor 10 includes one light emitting element 11 and two light receiving elements 12a and 12b.
The reflected light from the disk 1 based on the irradiation light from the light emitting element 11 is transmitted to the light receiving elements 12a and 12b.
receives light. And two light receiving elements 12a, 12
A differential amplifier 13 obtains the difference in the amount of light received by b, and supplies this differential output as a tilt amount to the motor 15 in the tilt mechanism 7 via a drive circuit 14.

In such a configuration, when the slider base 9 moves from position a to position b in the figure and reaches the inclined portion of the outer circumference of the disk 1, the tilt mechanism 7 is operated in accordance with the output of the optical sensor 10, and the optical Rotate the system body 6 about the rotation fulcrum 8 in the clockwise direction in the figure, so that the optical axes B and B' align with the disk 1.
Stops operation at a position perpendicular to the pit surface.

In this way, the static warping of the disk 1 is followed and the optical axes B and B' are always controlled to be perpendicular to the pit surface. Since the optical axis of the irradiated light tends to shift due to the misalignment of the axes between the light source of the light emitting element 11 and the lens in the light emitting element 10, it is difficult to maintain the perpendicularity of the optical axis to the reference plane and it is difficult to prevent the inclination of the disk. The drawback was that it could not be detected accurately. Moreover, the light emitting element 11 and the light receiving element 12a,
Since the 12b is expensive, there is also the drawback that the entire device is expensive.

Summary of the Invention The present invention has been made to eliminate the above-mentioned drawbacks of the conventional devices, and aims to provide a low-cost and highly accurate optical recording disk reproducing device.

The reproducing device for an optical recording disk according to the present invention is composed of at least two independent light-receiving elements arranged symmetrically and close to each other with respect to a straight line, and the one straight line is arranged so as to correspond to the recording track direction of the recording disc. The inclination of the optical axis of the optical pickup with respect to the information recording surface of the disk is adjusted in accordance with the output difference between two light receiving elements of a photodetector that receives detection light that has passed through the information recording surface of the disk.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 3 is a block diagram showing an embodiment of the present invention, in which parts equivalent to those in FIG. 2 are designated by the same reference numerals. In the figure, 30 indicates 4 lines arranged close to each other with two orthogonal straight lines X and Y as the boundary line.
This is a so-called 4-split photodetector consisting of two independent light-receiving elements ₃₀₁ to ₃₀₄ , one of which is arranged so that the straight line X corresponds to the recording track direction of the disk, and receives the detection light that has passed through the information recording surface of the disk. do. The photodetector 30 controls the distance between the disk and the objective lens 5 (shown in the first diagram) of an optical pickup, which is always provided in a normal optical disk playback device, to be kept constant. It can also be used as a so-called focus servo system and a 4-split photodetector used for information reading.

The outputs of the light receiving elements located on the same side with respect to the straight line X of the photodetector 30, that is, the light receiving element 30 ₁
The outputs S ₁ and S ₄ of ~30 ₄ are added by an adder 32 via buffers 31 ₁ and 31 ₄ , and the outputs S 1 and S 4 of the light receiving elements 30 ₂ ~
The outputs S ₂ and S ₃ of 30 ₃ are added by an adder 33 via buffers 31 ₂ and 31 ₃ . Adders 32, 33
The respective addition outputs (S ₁ + S ₄ ) and (S ₂ + S ₃ ) are subtracted by the subtracter 34.
is subtracted by Subtraction output of the subtractor 34 [(S ₁ + S ₄ )
−(S ₂ +S ₃ )] is supplied to the sample and hold circuit 35.

Reference numeral 36 denotes a tracking servo section which determines the relative position of the information reading spot light by the optical pickup and the recording disk in the radial direction of the disk, and is always provided in a normal optical disk reproducing apparatus. This tracking servo section 30 is
For example, it is composed of two servo systems: one that moves the information reading spot light in the radial direction of the disk, and the other that moves the pick-up itself in the radial direction of the disk using a radial feed mechanism. The tracking error signal from the tracking servo section 36 is passed through the low pass filter 3.
7 to a level comparator 38. The level comparator 38 generates an output when the output level of the low-pass filter 37 is below a predetermined reference level, that is, when it is near zero. The control section 39 is connected to a sample-and-hold circuit 35 according to the comparative output of the level comparator 37, and the output of a switch circuit 40 to which the output of this sample-and-hold circuit 35 is input is connected to the motor of the tilt mechanism (shown in the first figure) via the drive circuit 14. 15.

Next, the principle and operation of the present invention will be explained.

Now, assuming that the disk is not tilted during normal operation of the playback device, the tracking servo section 3
A tracking actuator (not shown) for moving the information reading spot light in the disk radial direction at 6 tracks the eccentricity of the disk and moves the information reading spot light toward the inner circumference of the disk in the radial direction with respect to the mechanical center (reference position). Or it deviates toward the outer periphery. Due to this bias, the output of the subtracter 34 changes as shown in FIG. 4 when tracking is open. In Figure 4,
The sinusoidal change is a tracking signal, the average value of which changes approximately in proportion to the tracking actuator deflection. Therefore, even when the tracking is closed, this average value (DC component) is a signal based on the actuator bias. Further, as shown in FIG. 5, the same thing can be said about the inclination of the disk as with the deflection of the tracking actuator. As shown in FIGS. 6 and 7, the DC component of the subtracted output of the subtractor 34 changes depending on the actuator deflection and the disk inclination. This is due to the movement of the energy distribution of the spot light on the surface. In FIGS. 6 and 7, 41 is a collimator lens that guides the light reflected by the disk 1 and passed through the objective lens 5 onto the light receiving surface of the photodetector 30; This is the energy distribution of spot light.

Next, if we look at the low frequency components of the driving current of the tracking actuator over time when the disc is being played back with the tracking closed, the result will be as shown in FIG. 8. In Fig. 8, small fluctuations are steady deviations in tracking, and large sinusoidal fluctuations are fluctuations caused by following eccentricity, and change as the track feeds.The radial servo controls the position of the pickup in the radial direction of the disk. When the system operates, the output of the LPF 37, that is, the low frequency component of the tracking error signal returns to near zero. At this time, the tracking actuator is operating near the mechanical center. By repeating this process, the information reading spot light traces the track on the disk.

When the optical axes of the disk and the pickup are perpendicular and the deflection of the objective lens 5 is zero, the drive current of the tracking actuator is When becomes zero, the sixth
As shown by the solid line in the figure, since the objective lens 5 is located at the mechanical center, the energy distribution 42 of the spot light is located at the center of the light receiving surface of the photodetector 30. However, if the disk is tilted, the energy distribution 42 of the spot light moves from the center of the light receiving surface, as shown in FIG. will be done. This subtraction output indicates the tilt angle of the disk, and by driving the motor 15 of the tilt mechanism 7 based on this subtraction output, it is possible to control the optical axis of the pickup so that it is perpendicular to the information recording surface of the disk. It is.

For example, if the low frequency component of the subtracted output of the subtractor 34 is a value A in FIG. 5, then the disk is tilted by the corresponding amount a. However, if the motor 15 is driven so that the subtraction output of the subtractor 34 becomes zero at this time, the inclination of the disk with respect to the optical axis of the pickup will be canceled.

Here, when the rotational speed of the disk is, for example, 1800 rpm, the eccentric frequency is 30 Hz, so when the drive current of the tracking actuator is zero, the tilt mechanism 7 (shown in the first figure) is immediately switched to the normal closed-loop servo. It is difficult to control. Therefore, in response to the output of the level comparator 38 that detects that the tracking actuator has returned to the mechanical center, the sampling and hold circuit 35 holds the above value A, and the tilt mechanism 7 is activated based on a predetermined conversion constant. Controlled by open loop servo.

By doing this, it is possible to always measure the inclination of the disk when the tracking actuator returns to its mechanical center, and based on that measurement, the optical axis of the pick-up can be adjusted to the correct position relative to the disk. This makes it possible to correct the slope. It goes without saying that once the correction is made, the holding of the value A is reset to prepare for holding the next measured value. Further, the warp of the disk changes gradually over the entire disk, and there is no need to correct it every time the tracking actuator reaches the mechanical center. Therefore, the correction sequence may be limited to, for example, 10 times over the whole, such as once correction in a certain section.

Further, in the above embodiment, the tilt of the pickup itself is adjusted, but any configuration may be used as long as the relationship between the optical axis of the pickup and the information recording surface of the disk can be changed, for example by adjusting the tilt of the disk side.

Effects As explained above, according to the present invention, the inclination of the disc with respect to the optical axis of the pickup can be detected by a simple electronic circuit based on the output of the information reading photodetector normally provided in the disc playback device. However, since the structure is configured to adjust this inclination, there is no need to use an expensive dedicated sensor like in the past, and the adjustment work is also unnecessary, making it possible to create a low-cost and highly accurate optical information recording disk playback device. can get.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a tilt servo mechanism, Fig. 2 is a block diagram showing a conventional example of a tilt servo system, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a tracking actuator. Figure 5 is a waveform diagram of the differential output with respect to the displacement of the actuator, Figure 5 is a waveform diagram of the differential force with respect to the disk tilt, Figure 6 is an explanatory diagram of the operation of the optical system when the tracking actuator is deflected, and Figure 7 is the disk tilt. FIG. 8 is a waveform diagram showing changes in the time parameters of the driving current of the tracking actuator. Explanation of symbols of main parts, 1...disk, 5...
...Objective lens, 6...Optical system body, 7...Tilt mechanism, 30...4-split photodetector, 34...Subtractor, 35...Sample hold circuit, 36...Tracking servo unit, 37... Low pass filter, 38... Level comparator, 40... Switch circuit.

Claims (1)

[Scope of utility model registration request] An adjusting means for adjusting the inclination of the optical axis of the optical pickup with respect to the information recording surface of the recording disk, a tracking servo loop for driving the tracking actuator of the optical pickup to perform tracking adjustment, and a tracking servo loop that is symmetrical with respect to a straight line. a photodetector comprising at least two independent light-receiving elements disposed close to each other, the one straight line being provided so as to correspond to the track direction of the recording disk, and receiving the detection light that has passed through the information recording surface; a subtracter that takes an output difference between two light receiving elements of a photodetector; a detection means that detects that the tracking actuator is located near the mechanical center when the tracking servo loop is in a closed state; An optical recording disk characterized in that it comprises a sample hold circuit that samples and holds the output of the subtracter according to the detection output of the detection means, and a switch means that supplies the output of the sample hold circuit to the adjustment means. playback device.