JPS63234417A - Track servo mechanism for optical disk device - Google Patents

Abstract

PURPOSE:To simplify the structure and facilitate the adjustment by feeding back the output of a track error detector and the output of a relative position detector to a lens translation actuator and a galvanomirror respectively or feeding back these outputs to the galvanomirror and the lens translating actuator respectively. CONSTITUTION:The relative position detector consists of another light source 16 (LED), a two-divided photodetector 17 which receives the emitted light from the light source 16 after reflection on a galvanomirror 9 and is provided on a mobile part of a lens translating actuator 5, and a differential amplifier 18 which operates the output difference of this photodetector 17. A difference is generated between respective quantities of reception light of the two-divided photodetector 17 even in case of shake of the galvanomirror 9 or movement of the lens translating actuator 5 because the two-divided photodetector 17 is attached to the mobile part (objective lens 4) of the lens translating actuator 5, and the output of the differential amplifier 18 is proportional to the relative position of the lens translating actuator 5 to the galvanomirror 9, and the feedback control is so performed that his output value is zero.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention provides two types of track actuators and two types of track actuators in order to solve the problem that the tracking range of the track servo is narrow due to so-called beam shift in the track servo mechanism of an optical disc device. The aim is to create a servo system with a simple mechanism and less occurrence of beam shift using a sensor that detects the relative position of the beam, and to obtain a wide tracking range.

C. Industrial Application Field] The present invention relates to a control method for an actuator used for tracking light spot control in an optical head of an optical disk device, and in particular to a method for eliminating beam shift in tracking control with high precision and good performance. This invention relates to a track servo mechanism that can be performed with follow-up characteristics.

In optical disk devices, a track servo mechanism that allows a light beam to follow a single information track in response to disk eccentricity is essential, and there is a desire to develop a track servo mechanism that is small and simple and can provide a wide tracking range. .

[Conventional technology]

A control method of an actuator used for controlling a light spot for tracking in a conventional optical head will be explained with reference to FIGS. 5 to 10. In order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures below, and repeated explanation thereof will be omitted.

FIG. 5 is a principle diagram of a conventional track servo mechanism. In the figure, light emitted from a light source 1 is reflected by a beam splitter 2, further reflected by a fixed mirror 3, and then enters an objective lens 4. Reference numeral 5 indicates a lens translation actuator that moves the objective lens 4 in parallel to the radial direction of the medium 60. The objective lens 4 is controlled by a focusing mechanism (not shown) so as to focus on an information track of the recording medium 6, and a lens translation actuator 5 causes the light beam to follow a desired track.

The reflected light reflected by the recording medium 6 travels backward along the incident path,
The signal passes through the beam splitter 2 and enters the two-split photodetector 7, where it is photoelectrically converted and is input to a tracking error detector (using a differential amplifier) 8, which generates a tracking error signal from the difference between the two types of optical signals. The output of the tracking error detector 8 is fed back to the lens translation actuator 5 to form a closed loop control system, thereby performing tracking servo.

FIG. 6 is another principle diagram of the conventional trunk servo mechanism, in which the lens translation actuator 5 in FIG.
With this structure, the light spot connected to the recording medium 6 is slightly moved in the radial direction of the recording medium 6, thereby performing tracking servo.

If the range in which the target track can be followed by the lens translation actuator 5 and the galvanometer mirror 9 is wide as in the example shown in Figs. It is desired to obtain a wide tracking range.

On the other hand, as methods for detecting tracking error signals, the pregroup method and the three-beam method are known, but the latter is not suitable, especially when the reflectance of the recording medium changes due to recording information, and the pregroup method is used exclusively. is used.

FIG. 7 is a diagram for explaining the pregroup method. As shown in the figure, λ/8 (
A groove with a depth of λ is the wavelength of the irradiated light) is provided, and the intensity distribution of the reflected light changes depending on the relative position of the groove and the light spot, as shown in the diagram above for each objective lens 4. in,
A tracking error signal can be obtained by simply receiving the reflected light with the two-split photodetector 7 and calculating the difference between the two with the differential amplifier 8.

However, since this method utilizes the intensity distribution of the light incident on the two-split photodetector 7, it is undesirable for the beam to move on the light receiving surface of the two-split one photodetector 7. In reality, the beam moves due to one rotation of the lens translation actuator 5 and the galvanometer mirror 9, as shown by the broken lines in FIGS. 5 and 6, and an offset occurs in the tracking error signal.

This movement is called a beam shift, and for this reason, even if the lens translation actuator 5 and the galvanometer mirror 9 have a wide movable range, the range that can be followed with an error below tolerance is significantly narrowed.

Therefore, the ILT method (In
ter Linked Tracking Method
d). The present invention is also based on this ILT method.

FIG. 8 is a perspective view for explaining the conventional ILT method. In the figure, the light beam emitted from the light source 1 enters the beam splinter 2 without the optical system in the middle, passes through the optical path indicated by the thick arrow, and is reflected by the galvanometer mirror 9 and the fixed mirror 3, and then is reflected by the objective lens 2. leading to.

The galvano mirror 9 is fixed to one end of a support member 9a having a galvano drive shaft 9c in the center, and a sulin) 9 at the other end.
b is bored, a drive coil 9d for swinging around a galvano drive shaft 9c is attached, and a magnetic circuit 9e corresponding to the drive coil 9d is arranged oppositely. By applying a control current to the drive coil 9d, the coil generates a drive force in the axial direction by interaction with the magnetic circuit 9e, and swings in the direction of the arrow about the galvano drive shaft 9c.

Reference numeral 10 denotes a galvano position sensor, in which the emitted light from the light emitting element 10a is received by the two-split photodetector 10b via the sensor 9b, and then sent to the differential amplifier 1) which creates a difference between the outputs of the two-split photodetector 10b. By inputting the information, the amount of deviation of the galvanometer mirror 9 itself from its reference position is detected.

The objective lens 4 is fixed to one end of a support member 5a having a lens rotation shaft 5c in the center, and has a slit 5. b is bored, a drive coil 5d for swinging around the lens rotation wheel 5c is attached, and a magnetic circuit 5e corresponding to the drive coil 5d is arranged opposite to the drive coil 5d.

Reference numeral 12 denotes an objective lens position sensor in which the light emitted from the light emitting element 12a is received by the two-split photodetector 12b via the light emitting element 12b, and is sent to the differential amplifier 1) which creates a difference between the outputs of the two-split photodetector 12b. By inputting the information, the amount of deviation of the objective lens 4 itself from the reference position is detected.

The reflected light from the recording medium (not shown) travels backward along the optical path indicated by the thick arrow, passes through the beam splitter 2, passes through the two-split photodetector 7, and obtains a tracking error signal by the track error detector 8. Feedback is provided to the drive coil 5d of the lens translation actuator 5.

Further, the output of the subtracter 14 that creates a difference between the outputs of the differential amplifier 1) and the differential amplifier 1) is fed back to the drive coil 9d of the galvano mirror 9, so that the galvano mirror 9 follows the movement of the objective lens 4. Each is controlled to always maintain its reference position.

FIG. 9 shows an explanatory diagram of a control system of the conventional ILT method. In the figure, 51 is the transfer function of the lens translation actuator;
52 is a transfer function of the galvanometer mirror, T1 is an input terminal into which a target value is input, and T2 is an output terminal of the control system. The control operation is as follows.

At point A, the target value (track center) and the tracking error signal are compared, and the residual difference moves the lens translation actuator, and at the same time targets the position of the objective lens determined at point B via the conversion coefficient K. It is compared with the position of the galvano mirror at point D and drives the galvano mirror. At point C, the amounts of movement of the objective lens and galvano mirror are added together, and feedback is applied to point A as a tracking error signal.

This method uses a lens translation actuator and a galvano mirror.
The same effect can be obtained even if the roles of are reversed and the objective lens 4 follows the movement of the galvanometer mirror 9.

FIG. 1O is a diagram for explaining a conventional beam shift countermeasure. In the figure, the galvanometer mirror 9 is controlled in conjunction with the lens translation actuator 5 so that the optical axis toward the objective lens 4 always passes through the rear focal point BP of the objective lens 4. The light that has passed through the rear focal point BP of the objective lens 4 is incident on the recording medium 6 in the perpendicular direction, and the reflected light passes through a completely reverse path, so no beam shift occurs, so a wide tracking range can be obtained.

If the focal length of the objective lens 4 is f, the distance from the reflection point of the galvano mirror 9 to the rear focal point BP is l, and the amount of track eccentricity is ε, then the amount of movement of the objective lens 4 is ε1/(1+
It is known that control should be performed so that f) is achieved.

It is also known that the influence of movement of the rear focal point BP due to focusing control of the objective lens 4 is within a negligible range.

[Problem that the invention seeks to solve]

According to the conventional ILT method, dedicated position sensors are provided for both the galvanomirror and the lens translation actuator, and the detection sensitivity and offset of each must be adjusted, which has the disadvantage of a complex structure and difficult adjustment. Ta.

The present invention has been made in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a track servo mechanism for an optical disk device that can simplify the structure and facilitate adjustment.

[Problem 71] As shown in the principle diagram of FIG. 1, the track servo mechanism of the optical disc device of the present invention directs a light beam from a light source l onto a disc-shaped recording medium G using an objective lens 4. A lens translation actuator 5 that is a track servo mechanism of an optical disk device that focuses light and optically records and reproduces information, and that moves the objective lens 4 in parallel in the radial direction of the recording medium 6.
, a galvanometer mirror 9 that rotates a reflecting surface so that the light beam from the light source I always passes through the rear focal point of the objective lens 4, and detects a track error signal from the reflected light from the recording medium 6. a track error detector 8, the lens translation actuator 5 and the galvanometer mirror 9;
a relative position detector 15 for detecting the relative position of the track error detector 8, and the output of the track error detector 8 is fed back to the lens translation actuator 5, and the output of the relative position detector 15 is fed back to the galvanometer mirror 9, respectively; Or give feedback using the opposite combination.

As shown in FIG.
6, and the light from the other light source 16 is transmitted to the galvano mirror 9.
After being reflected by the lens translation actuator 5, the light is arranged so as to be received by a two-split photodetector 17 provided on the movable part of the lens translation actuator 5, and a differential amplifier 18 that obtains the difference in the output of the two-split photodetector I7. It consists of

[Effect]

In the conventional ILT method, the positions of the objective lens 4 and the galvanometer mirror 9 are individually detected and the difference between them is calculated, but the only element actually required is the relative positional relationship between the two.

Therefore, as shown in the principle diagram of FIG. 1, a relative position detector 15 detects the relative position of the two (specifically, the emitted light of another light source 16 shown in the embodiment of FIG.
The two-split photodetector 1 provided on the two-split photodetector 17 provided on the movable part of the lens translation actuator 5
The relative position of 1J9 can be detected by setting the optical path at which the output of the optical system 7 receives light and a differential amplifier 18 that creates a difference between the respective outputs as the reference relative position. In this case the sensor can be constructed with a length of 1 m.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a configuration diagram of an embodiment of the present invention. In the figure, the only difference from the conventional ILT method explained in FIGS. 8 to 10 is the relative position detector. The relative position detector 15 shown in the principle diagram of FIG. It is composed of a two-split photodetector 17 provided in the photodetector 17 and a differential amplifier 18 that creates an output difference between the two.

It is important that the two-split photodetector I7 is attached to the movable part (objective lens 4) of the lens translation actuator 5, so that even if the galvanometer mirror 9 swings, the lens translation actuator 5 does not move. Two-split photodetector 1
There is a difference in the amount of light received by each of the components 7, and the output of the differential amplifier I8 becomes proportional to the relative position of the galvanometer mirror 9 and the lens translation actuator 5.If feedback control is applied to reduce this output value to zero, Effects equivalent to those of the conventional ILT method can be obtained.

FIG. 3 shows a block diagram of another embodiment. In the example shown in FIG. 2, the emitted light from another light source 16 is reflected by the same reflecting surface of the galvano mirror 9 as the light beam focused on the recording medium 6, but in the case of FIG. The same effect can be obtained even if the light is reflected by a dedicated reflecting surface integrally formed with -9.

Figure 4 is a reverse combination of the principle diagram of the present invention! A configuration diagram of the IJ'4n system is shown. FIG. 4 shows that the galvano mirror 9 is controlled by the tracking error signal output from the track error detector 8, and the lens translation actuator 5 is controlled by following the output of the differential amplifier 18 that outputs the position error signal of the galvano mirror 9. Although this control system has a completely opposite combination to the control system shown in FIG. 1, the effect is the same.

〔Effect of the invention〕

As explained in detail above, according to the track servo mechanism of the optical disk device of the present invention, compared to the conventional rLT method, there is only one position detector consisting of a light source LED and a two-split photodetector (with a structure that is Simplification and adjustment can be achieved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of the present invention, Fig. 2 is a block diagram of one embodiment of the present invention, Fig. 3 is a block diagram of another embodiment of the present invention, and Fig. 4 is an inverse diagram of the principle of the present invention. A configuration diagram of a combination control system, FIG. 5 is a principle diagram of a conventional track servo mechanism, FIG. 6 is a principle diagram of another conventional track servo mechanism, FIG. 7 is a diagram for explaining the pregroup method, FIG. 8 is a perspective view for explaining the conventional ILT method, FIG. 9 is a diagram for explaining the conventional control system, and FIG. 10 is a diagram for explaining the beam shift countermeasure of the conventional example. In Figures 1 and 2, 1 is a light source, 4 is an objective lens,
5 is a lens translation actuator, 6 is a recording medium, 8 is a track error detector, 9 is a galvanometer mirror (1) 5 is a relative position detector, 16 is another light source, 17 is a two-split photodetector,
Reference numeral 18 indicates a differential amplifier. Figure 1 Figure 2 O Invention 614-j++-ta IJ IW'J iJi
F"t: Figure 7 Figure 8 Jushu, s I LT Yue's embroidery P Go brown supplies Figure 9 61 example, beam shift fixed tit coin] Month 1a - Country 10th
figure

Claims (1)

[Scope of Claims] [1] A track of an optical disc device that optically records and reproduces information by condensing a light beam from a light source (1) onto a disc-shaped recording medium (6) using an objective lens (4). a servo mechanism, a lens translation actuator (5) that moves the objective lens (4) in parallel in the radial direction of the recording medium (6);
a galvanometer mirror (9) that rotates a reflective surface so that the light flux from the light source (1) always passes through the rear focal point of the objective lens (4) and enters; and reflected light from the recording medium (6). a track error detector (8) for detecting a track error signal from the lens translation actuator (5) and the galvanometer mirror (9);
), the output of the track error detector (8) is sent to the lens translation actuator (5), and the relative position detector (15)
) is fed back to the galvanometer mirror (9), or the track error detector (
A track servo mechanism for an optical disk device, characterized in that the output of step 8) is fed back to the galvanometer mirror (9), and the output of the relative position detector (15) is fed back to the lens translation actuator (5). [2] The relative position detector (15) is connected to another light source (16)
After the light from the other light source (16) is reflected by the galvanometer mirror (9), the lens translation actuator (
The two-split photodetector (17) provided on the movable part of 5) is arranged so as to receive the light, and the two-split photodetector (17)
A track servo mechanism for an optical disc device according to claim 1, characterized in that the track servo mechanism is comprised of a differential amplifier (18) for obtaining a difference in output.