JPH03176820A - Objective lens position detector - Google Patents

Abstract

PURPOSE:To obtain a device with superior assembling capability with simple constitution by setting a light source for a bisected photodetector for position detection by separation reflected light from a disk, and providing the light source at a turntable. CONSTITUTION:Beams(LPS beam) 23, 24 for objective lens position detection are generated with a diffraction grating 22 by transmitting an objective lens 3 again with a reflected beam from the disk 1. The LPS beams 23, 24 are made incident on LPS detectors 25, 26, respectively, and are calculated with differential amplifiers 27, 28, and an adder 29, then, an objective lens position detection signal LPS is generated. Thereby, it is possible to obtain the device with superior assembling capability with simple constitution without providing the light source such as a light emitting diode, etc., on the turntable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an objective lens position detection device in an optical disk device that optically reproduces information or records and reproduces information.

[Prior Art] Optical disk devices require tracking servo to record or reproduce signals concentrically or spirally on an information recording medium (hereinafter referred to as a disk) in a non-contact manner. Various methods have been proposed for this tracking servo sensor method, and there is a method called a push-pull method that uses diffracted light from a signal bit or a guide groove.

The principle of the tracking servo sensor system using the push-pull method will be explained using FIG. The disk (1) has a guide groove (2) in the center of the surface on the objective lens side.

The objective lens (3) is arranged facing the above-mentioned objective lens side surface of the disk (1), and forms a condensing spot (4) at the center of the guide groove (2). The convex lens (5) is arranged parallel to the objective lens (3) on the side opposite to the disk (1). The two-split photodetector (6) has two light-receiving surfaces (,6
a), (6b), and a convex lens (5)
is placed on the opposite side. The differential amplifier (7) connects the knee light receiving surfaces (6a) and (6b) of the two-split photodetector (6).
It has input terminals (+) and (-) respectively connected to the light-receiving surfaces (6a) and (6b), and generates a tracking error signal TS based on the outputs from the light-receiving surfaces (6a) and (6b). Focusing spot (
4) is diffracted by both edges of the guide groove (2),
This produces diffracted light distributions (8), (9) and is also projected onto the plane of the two-split photodetector (6) to produce a diffracted light distribution (10).

(11) occurs. When the objective lens (3) is located at the center of the guide groove (2), the above-mentioned diffracted light distribution (8),
(9) Therefore, the intensities of the diffracted light distributions (10) and (11) become equal, and the output J of the differential amplifier (7) becomes zero. However, due to eccentricity of the disk (1), the objective lens (3)
If the relative positional relationship between the guide groove (2) and the guide groove (2) deviates, the diffracted light distributions (8) and (9) will no longer be uniform, and the output of the differential amplifier (7) will be positive or negative. . Therefore,
A servo operation is performed to make this output zero, and the objective lens (3) is translated in the X direction shown in the figure.

Next, problems with the push-pull method will be explained. FIG. 4 is a diagram showing a state in which the guide groove is displaced by a distance d with respect to the neutral point (on the dashed line in the figure) of the objective lens (3). In this state, although the focused spot (4) is located at the center of the guide groove (2), the projected diffracted light distributions (10), (11 ) will no longer be equally incident on the two light-receiving surfaces (6a) and (6b), and as a result, the output of the differential amplifier (7) will no longer be zero. In other words, a tracking offset occurs. FIG. 5 is a diagram showing the tracking error signal TS with respect to the displacement d of the objective lens (3), and as the displacement d increases, the amount of tracking offset also increases.

As mentioned above, the push-pull method is a simple method that uses diffracted light, but an offset occurs in the tracking error signal due to the displacement of the objective lens in the tracking direction.
For this reason, there was a drawback that a wide movable range in the tracking direction could not be achieved.

Conventionally, there has been an objective lens position detecting device shown in FIG. 6, for example, as a device for improving such drawbacks. In the figure, symbols (1), (3), and (4).

(6) and (7) are the same as in FIG. (12) is a semiconductor laser (hereinafter referred to as LD) which is a light source, and a collimator lens (13), a beam splitter (14), a reflection mirror (15), and an objective lens (3) are arranged in the emission direction of the LD (12). are arranged in sequence. The objective lens (3) is held by a turntable (16), and the turntable (16) is rotatable in the tracking direction (T) as shown in the figure by a drive mechanism (not shown) relative to the shaft (17). It is also slidable in the focus direction (F). (14) is the disk (
This is a beam splitter for guiding the reflected light from 1) to a two-split photodetector (6).

(18) is a light source, such as a light emitting diode, provided on the turntable (16). (19) has two light-receiving surfaces (19a) and (19b), and is a two-split light sensor arranged so as to equally receive the light emitted from the light source (18) at the neutral point position of the turntable (16). It is a vessel. Each light receiving surface (19a), (
The outputs of 19b) are respectively connected to two input terminals of a differential amplifier (20). (21) is a differential amplifier (
7) is connected to the addition side terminal, and the output signal LPS of the differential amplifier (20) is connected to the subtraction side terminal.

Next, the operation will be explained. When the turntable (16) is at the neutral point, the light emitted from the light source (18) is equally received by each light receiving surface (19a) and (19b) of the two-split photodetector (19), so there is no difference. The output signal LPS of the dynamic amplifier (20) becomes zero. Next, when the turntable (10) rotates due to the eccentricity of the disk (1) and the turntable (16) is at a position other than the neutral point, the light source (18)
The turntable (16) also rotates. Therefore 2
Each light receiving surface (19a) (19b) of the split photodetector (19)
Since the light emitted from the light source (18) will not be received evenly,
The output signal L P S of the differential amplifier (20) is no longer zero.

FIG. 7(a) is a diagram showing the relationship between the output signal TS of the differential amplifier (7) and the displacement d of the objective lens (3) in the tracking direction, and FIG. 2o
) a signal LPS representing the objective lens position as an output signal;
FIG. 6 is a diagram showing the relationship with the displacement d of the objective lens (3) in the tracking direction.

Since the output signal LPS in (b) of the same figure is similar to the signal obtained by extracting the DC offset signal in (a) of the same figure, the output signal LPS is subtracted from the output signal TS by the differential amplifier (21). As a result, the output signal C-TS shown in FIG. 3(c) can be obtained. The output signal C-TS is a signal whose tracking offset is always corrected regardless of the displacement of the objective lens (3), and therefore it is possible to widen the movable range of the objective lens (3) in the tracking direction.

[Problems to be Solved by the Invention] Since the conventional objective lens position detection device is configured as described above, a light source such as a light emitting diode must be provided on the turntable for position detection. A lead wire was required to supply power, and connection work was required.

Furthermore, since the light source also moves when the turntable slides in the focus direction, the amount of light incident on the two-split photodetector changes, resulting in a change in the sensitivity of the output signal LPS of the differential amplifier (20). There were problems such as the occurrence of

This invention was made in order to eliminate the above-mentioned drumming point, and provides an objective that does not require a light source such as a light emitting diode to the turntable and does not cause sensitivity changes depending on the position of the turntable in the focus direction. The purpose is to obtain a lens position detection device.

[Means for Solving the Problems] An objective lens position detection device according to the present invention uses a reflected light beam from a disk as a light source for position detection, and includes an optical element directly below the objective lens that separates the reflected light beam into three light beams. is provided, and the two separated light beams are received by two two-split photodetectors, respectively.

[Operation] In the objective lens position detection device according to the present invention, since the optical element for separating the reflected light beams works in conjunction with the objective lens, the two separated light beams are received by two two-split photodetectors. The position of the objective lens can be detected by

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
In the figure, symbols (1), (2), (3), (6), (
7), (1,2), (13), (14), (15), (
16), (17), and (21) are the same as those in the conventional example shown in FIG. (22) is an optical element that works in conjunction with the turntable (16) and separates a part of the reflected light beam to generate light beams (23) and (24) for objective lens position detection (hereinafter referred to as LPS light beam), for example. Diffraction gratings (25), (2) having flat portions with a width slightly smaller than the diameter of the reflected light beam, and grooves that are otherwise parallel to the guide grooves (2) of the disk (1);
6) has a dividing line parallel to the guide groove (2) of the disc (1), and the inner circumferential side of the disc (1) is (25a),
(26a), and (25b) and (26b) on the outer circumferential side, respectively.
) is a two-split photodetector for detecting the position of an objective lens (hereinafter referred to as an LPS detector), which has two light-receiving surfaces, and (27) connects the output of the light-receiving surface (25a) of the LPS detector (25) to the subtraction side input terminal. , a differential amplifier that inputs the output of the light receiving surface (25b) to the addition side input terminal and performs subtraction processing; (28) is an LPS detector (
26) to the output of the light receiving surface (26a) to the subtraction side input terminal,
(26b) is input to the addition side input terminal and performs subtraction processing, (29) is a differential amplifier (27) and a differential amplifier (
This is an adder that adds the outputs of 28).

The operation of one embodiment of the present invention will be described below. The emitted light flux from the light source (12) is transmitted through the collimator lens (13
), passes through the beam splitter (14), and passes through the reflecting mirror (
15), passes through the diffraction grating (22) and the objective lens (3), and is reflected by the disk (1). The reflected light beam from the disk (1) is transmitted through the objective lens (3) again, and LPS light beams (23) and (24) are generated by the diffraction grating (22). LPS luminous flux (23)
, (24) are incident on the LPS detectors (25) and (26), respectively, and are input to the differential amplifiers (27) and (28), and the adder (
29), and the objective lens position detection signal LP
Generate S. This detailed operation will be explained using FIG. 2.

Here, the LPS light flux (23), (24) incident on each light receiving surface of the LPS detector (25), (26) or the output photoelectrically converted by the LPS detector is expressed using the code of the light receiving surface.
For example, if the photoelectrically converted output of the light receiving surface (25a) of the LPS detector (25) is 1258, the LPS output I
Lps is expressed by the following formula 11, ps ”(Iz5
b +Iz6b) - (Iz+, B+l2aa) --
--■ Figure 2 (a) shows the disc (1), objective lens (3), and diffraction grating (2) when the displacement of the objective lens (3) is zero.
2), LPS luminous flux (23), (24), LPS detector (
25) and (26). At this time,
LPS detectors (25) and (26) are L5g-125b, I26b” I261+
----------1■, and the LPS output is ILPS = 0.

In FIG. 2(b), the objective lens (3) is attached to the disk (1).
This is a diagram when the LPS luminous flux (23
), (24) are also linked to the objective lens (3) in the outer peripheral direction (
(in the illustration, to the right).

Therefore, the outputs of the LPS detectors (25) and (26) are Iz
5a<I25b, I2B+1<l2eb
−−−−−−−−The relationship is as follows, and the LPS output I
LPS becomes ILPS>0. Similarly, although not shown in the figure, the objective lens (3
) moves to the inner circumference, 12sa > l2sb + l2sa > T2eb
----------12 Therefore, it is obvious that ILPS<0, and the position of the objective lens (3) can be detected.

Further, the position of the disk (1) in the focus direction changes due to surface runout due to rotation. The figure 2 (c) shows this 1 2 , and the disk (1) is displaced upward by △f, and the inside
There is no displacement on the outer periphery. At this time, objective lens (3)
is displaced along with the displacement of the disk (1), and the LPS light beams (23) and (24) are also displaced upward. LPS luminous flux (2
3), (24) are displaced upward, the LPS detector (2)
On 5) and (26), the LPS luminous fluxes (23) and (24) are
It is displaced in a direction away from the optical axis of the objective lens (3).

The outputs of the LPS detectors (25) and (26) at this time are:
Izsa = I26b+ rzsb ” I26+1
-----------The relationship 2 holds true, and when substituted into the formula 2, ILPS=0. The above equation 0 always holds true because the LPS beams (23) and (24) have exactly the same displacement around the optical axis of the objective lens (3) even if the displacement of the disk (1) is positive or negative. There is. Therefore, the objective lens position detection signal LP
S is the displacement of the objective lens (3) in the focus direction,
It doesn't change at all.

[Effects of the Invention] As described above, according to the present invention, by separating the reflected light from the disc and using it as a light source for a two-split photodetector for position detection, it is possible to eliminate the need for a separate light source on the turntable. Therefore, it is possible to obtain a device with a simple configuration and good assembly efficiency, and also to obtain an objective lens position detection device that does not depend on the displacement of the objective lens position detection signal in the focus direction.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an objective lens position detection device according to an embodiment of the present invention, Fig. 2 is a diagram explaining the operation of objective lens position detection, and Fig. 3 is a diagram of a conventional docking sensor method using a push-pull method. Figure 4 is a diagram explaining the problems of the push-pull method. Figure 5 is a signal waveform diagram of the conventional tocking servo sensor method. Figure 6 is a configuration diagram of a conventional objective lens position detection device. The figure is a diagram of signal waveforms at various parts of a conventional objective lens position detection device. In the figure, (1) is a disk, (3) is an objective lens,
(4) is a focused spot, (16) is a turntable, (
22) is a diffraction grating, (25) and (26) are LPS detectors. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] (1) An objective lens that focuses a light beam on an optical information recording medium to form a minute focused spot, a turntable that holds the objective lens, and an objective that detects the position of the objective lens. An optical head device equipped with a lens position detection device includes a separation optical element that operates in conjunction with the turntable and separates reflected light from the optical information recording medium, and separates the separated light by the separation optical element into an optical head. An objective lens position detection device characterized in that light is received by a detector.