JPH0554178B2 - - Google Patents

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 or records and reproduces information.

[Conventional technology]

Optical disk devices require a tracking servo to record or reproduce signals concentrically or spirally on an information recording medium 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 utilizes diffracted light from a signal pit or a guide groove.

The principle of the tracking servo sensor system using the pull-pull method will be explained using FIG. The information recording medium 1 has a guide groove 2 in the center of the surface on the objective lens side. The objective lens 3 is disposed facing the above-mentioned objective lens side surface of the information recording medium 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 information recording medium 1. The two-split photodetector 6 is composed of two light-receiving surfaces 6a and 6b, and is arranged on the opposite side of the convex lens 5. The differential amplifier 7 has input terminals (+) and (-) connected to the two light-receiving surfaces 6a and 6b of the two-split photodetector 6, respectively, and performs a torque control based on the outputs from the light-receiving surfaces 6a and 6b. Generates king error signal TS. When the condensing spot 4 undergoes diffraction by both edges of the guide groove 2, it produces diffracted light distributions 8 and 9, and is also projected onto the surface of the two-split photodetector 6 to produce diffracted light distributions 10 and 11. arise. When the objective lens 3 is located at the center of the guide groove 2, the intensities of the above-mentioned diffracted light distributions 8, 9 and hence the diffracted light distributions 10, 11 become equal, and the output of the differential amplifier 7 becomes zero. However, if the relative positional relationship between the objective lens 3 and the guide groove 2 deviates due to eccentricity of the information recording medium 1, etc., the diffracted light distributions 8 and 9 will no longer be uniform, so that the differential amplifier The output of 7 can 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, I will explain the problems with the push-pull method. 7th
The figure shows the neutral point of objective lens 3 (on the dashed line in the figure)
3 is a diagram showing a state in which the guide groove 2 and the objective lens 3 are displaced by a distance d. In this state, although the condensing spot 4 is located at the center of the guide groove 2, the projected diffracted light distributions 10 and 11 are divided into two light receiving surfaces 6a, 11 on the surface of the two-split photodetector 6.
6b, and as a result, the output of the differential amplifier 7 no longer becomes zero. In other words, a tracking offset occurs.
FIG. 8 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, and as a result, a wide movable range in the tracking direction cannot be achieved. There was a drawback.

Conventionally, there has been an objective lens position detecting device disclosed in Japanese Patent Application Laid-Open No. 198436/1983, for example, as a method for improving such drawbacks.

This conventional objective lens position detection device is shown in Figure 9~
FIG. 11 will be explained.

FIG. 9 is a configuration diagram of a conventional objective lens position detection device. In this objective lens position detection device, a light beam emitted from a light source 12, for example, a semiconductor laser, is made into a parallel light beam by a collimator lens 13. The emitted light beam 14 of this collimator lens 13 is split by a second beam splitter 15, and one light beam 16 is transmitted through an objective lens 17 and reflected by an information recording medium 18. The reflected light flux returns to the original optical path, is reflected by the first beam splitter 19, and is
The light enters a two-split photodetector 20 for tracking error detection, which has two light receiving surfaces 20a and 20b. The differential amplifier 21 is connected to a two-split photodetector 20 for tracking error detection, and its two light-receiving surfaces 2
A tracking error signal TS is generated based on the outputs from 0a and 20b. The other beam 22 transmitted through the second beam splitter 15 is reflected by a mirror 23 and transmitted through a slit 25 provided in a turntable 24 holding an objective lens 17. The light transmitted through the slit 25 is received by a two-split photodetector 26 for detecting the position of the objective lens, which has two light receiving surfaces 26a and 26b. The differential amplifier 27 is connected to the two-split photodetector 26 for detecting the position of the objective lens, and the two light-receiving surfaces 26a, 2
Objective lens position detection signal based on the output from 6b
Generates LPS. The differential amplifier 28 is connected to the differential amplifiers 21 and 27, and outputs a tracking error signal corrected by the tracking error signal TS obtained from the respective differential amplifiers 21 and 27 and the objective lens position detection signal LPS. Generate C-TS.

Next, the operation of the conventional objective lens position detection device configured as described above will be explained. 1st
FIG. 0 is a perspective view showing the main parts for detecting the objective lens position detection signal LPS. Objective lens 17
The turntable 24 holding the shaft 29
The tracking operation is performed by rotating in the direction of the arrow in the figure around . turntable 24
Since the slit 25 provided in the slit 25 is linked to this tracking operation, the light beam 22 incident on the slit 25 is transmitted to a two-split photodetector 26 for detecting the position of the objective lens.
By receiving the light and taking its differential output, the first
Objective lens position detection signal LPS as shown in Figure 1b
can be obtained.

Note that the tracking error signal TS by the normal push-pull method is obtained as the output of the differential amplifier 21 in FIG. 9, and produces a tracking offset with respect to the displacement d of the objective lens 17 as shown in FIG. 11a. It becomes a waveform. These two signals are
By calculating with the differential amplifier 28 shown in the figure,
As shown in FIG. 11c, regardless of the displacement of the objective lens 17 in the tracking direction, it is possible to always obtain a corrected tracking error signal C-TS without tracking offset. It becomes possible to widen the range.

[Problem that the invention seeks to solve]

In the conventional objective lens position detection device, the light flux incident on the objective lens 17 and the slit 25 is split by the second beam splitter 15, so the amount of light flux incident on the objective lens 17 is reduced. In order to prevent this, a light source with a large optical output is required, and a mirror is also required to make the light beam incident on the slit 25, resulting in problems such as an increase in the number of parts.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain an objective lens position detection device that has a simple configuration and is highly reliable.

[Means for solving problems]

The objective lens position detecting device according to the present invention includes a turntable that includes a pair of knife edge portions that are parallel to a predetermined axis, and is rotatable around the axis and movable along the axis. An objective lens that is supported at a position eccentric from the axis of the table so that its optical axis is substantially parallel to the axis, and a photodetector and a light source that are arranged above and below with the knife edge section in between. It is.

[Effect]

In this invention, the amount of rotational displacement of the objective lens can be detected based on the change in the amount of light received by the photodetector due to rotation of the turntable about the axis.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of an embodiment of the present invention, and in the figure, reference numerals 12 to 14, 16 to 21,
27 to 29 are the same as those shown in FIGS. 9 and 10 of the conventional example. The mirror 30 guides the emitted light beam 14 from the collimator lens 13 to the objective lens 17 . The turntable 31 that supports the objective lens 17 is formed with a pair of knife edge portions that are parallel to each other with respect to a predetermined axis. The turntable 31 is rotatable around the axis mentioned above and movable along the axis. To explain in detail, the objective lens 17 is a turntable 31
It is supported at a position eccentric from the above-mentioned axis so that its optical axis is substantially parallel to the axis. The objective lens position detection detector 32 and the objective lens position detection light source 33 are arranged one above the other with the knife edge portion of the turntable 31 in between. At this time, the objective lens position detection detector 32 receives a light beam 3 from the objective lens position detection light source 33 by the displacement of the turntable 31 in the tracking direction.
4 is placed at a position where the amount of light changes.

Next, an embodiment of the present invention will be described with reference to FIG. Figures a, b, and c are plan views showing the relationship between the displacement d of the objective lens 17 and the photodetector 32 for detecting the position of the objective lens when viewed from the information recording medium side. Figure a shows the case where the objective lens 17 is at the neutral point.
At this time, the objective lens position detection photodetector 32 supplies an output V, but it is desirable that the objective lens position detection signal LSP be zero when the objective lens 17 is at the neutral point. Therefore, in this example,
A voltage V equivalent to the output V of the objective lens position detection photodetector 32 when the objective lens 17 is at the neutral point.
is input to the negative side of the differential amplifier 27, and the output V from the objective lens position detection photodetector 32 is input to the positive side of the differential amplifier 27 to obtain the objective lens position detection signal LPS. Therefore, when the objective lens 17 is at the neutral point, the differential amplifier 2
The output of 7 becomes zero. Figure b shows a case where the objective lens 17 is displaced by (+d) in the tracking direction. In this case, since the objective lens position detection photodetector 32 receives more light than in the case of FIG. 2a, the output of the differential amplifier 27 becomes positive. On the other hand, Figure c shows a case where the objective lens 17 is displaced by (-d) in the tracking direction, and based on the same principle, the output of the differential amplifier 27 becomes negative. According to the above explanation, the relationship between the displacement d of the objective lens 17 and the objective lens position detection signal LPS is as shown in d of the figure.

Note that the tracking error signal TS by the normal push-pull method is generated by the differential amplifier 21 shown in FIG.
is obtained as the output of Therefore, as in the case of the conventional example shown in FIG. 10, the differential amplifier 2 in FIG.
Tracking error signal C corrected by 8
−TS can be obtained.

Although the above example shows a photodetector for detecting the position of the objective lens with only one light-receiving surface, this is an example that can be realized when the incident light to the photodetector is a parallel light beam or a parallel light beam. It is.

As a practical matter, the light flux from the light source for detecting the objective lens position is a diverging light, and when this diverging light is directly received by a photodetector, the influence of diffraction due to the knife edge portion must be taken into consideration. This will be explained with reference to FIG. FIG. 3 is a diagram showing the relationship between the amount of light beam 35 received by the photodetector 41 from the light source 42 and the position of the knife edge portion 43. The amount of light received by the photodetector 41 is determined in the vertical direction (focusing direction) even if the knife edge portion 43 is not displaced in the horizontal direction (tracking direction) in the figure.
When it is displaced to , it changes as shown in b and c in the same figure due to diffraction. That is, the objective lens tracking position signal becomes as shown in d in the figure, making it impossible to detect the correct objective lens tracking position.

Hereinafter, an embodiment of a solution to the above-mentioned problem will be described with reference to FIGS. 4 and 5. FIG. 4 is a diagram showing the main part of an embodiment using two photodetectors 36a and 36b for detecting the position of the objective lens, and 17, 29 and 31 are the same as those shown in FIG. The objective lens position detection photodetectors 36a and 36b are arranged in the same manner as in FIG. 1 and are connected to both the adder 37 and the differential amplifier 39. The adder 37 takes the sum signal of the objective lens position detection photodetectors 36a and 36b, and monitors the displacement of the objective lens 17 in the focus direction based on this signal. The differential amplifier 39 takes the difference signal between the objective lens position detection photodetectors 36a and 36b,
This monitors the displacement of the objective lens 17 in the tracking direction. amplifier (or attenuator)
38 adjusts the level of the position signal in the focus direction obtained by the adder 37. Differential amplifier 40 includes adder 37 and an amplifier (or attenuator)
A difference signal between the position signal of the objective lens 17 in the focusing direction obtained by the differential amplifier 38 and the position signal of the objective lens 17 in the tracking direction obtained by the differential amplifier 39 is obtained.

FIG. 5a is a diagram showing the relationship between the objective lens position signal obtained by the differential amplifier 39 and the displacement of the objective lens 17 in the tracking direction. To explain this figure, first, a case will be described in which the objective lens 17 is not displaced in the focusing direction but only in the tracking direction. In this case, the fourth
At the neutral point shown in Figure a, the objective lens position detection photodetectors 36a and 36b receive light equally, so the output of the differential amplifier 39 becomes zero. Next, in the case of FIG. 4b where the objective lens 17 is displaced by (-d), the objective lens position detection detector 36a receives more light than the objective lens position detection photodetector 36b, so the differential The output of amplifier 39 becomes negative. Based on the same principle, in the case of FIG. 4c where the objective lens 17 is displaced by (+d), the output of the differential amplifier 39 becomes positive. Therefore, the displacement of the objective lens 17 and the objective lens position signal as shown in FIG. 5a are obtained. Next, a case will be described in which the objective lens 17 is also displaced in the focus direction. In this case, the objective lens 17 is connected to the photodetector 3 for detecting the objective lens position.
As the distance from 6a, 36b increases, the amount of light received by the objective lens position detecting photodetectors 36a, 36b increases, so that the image shown in FIG. 5a becomes as shown in the same figure. Conversely, when the objective lens 17 approaches the objective lens position detection photodetectors 36a, 36b, the amount of light received by the objective lens position detection photodetectors 36a, 36b decreases, as shown in the figure. As explained above, the differential amplifier 39 outputs the relationship between the displacement of the objective lens 17 and the objective lens position signal as shown in FIG. 5a.

FIG. 5b is a diagram showing the relationship between the displacement of the objective lens 17 in the focus direction and the position signal of the objective lens 17 in the focus direction, obtained by the adder 37. The relationship shown in the figure can be obtained by taking the sum signal of the objective lens position detection photodetectors 36a and 36b. Regarding the principle,
This is the same as the explanation in FIG.

The difference signal between the output of the differential amplifier 39 and the output obtained by controlling the gain of the output of the adder 37 by the amplifier (or attenuator) 38 is sent to the differential amplifier 40.
Even if the light beam incident on the photodetector is a diverging light, the correct position of the objective lens 17 in the tracking direction can be detected as shown in FIG. 5c.

In the above embodiment, the case where two photodetectors are used has been described, but it goes without saying that a two-divided photodetector may be used and the same effect will be achieved.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a turntable in which a pair of knife edge portions are formed parallel to each other with respect to a predetermined axis, and is rotatable around the axis and movable along the axis; An objective lens whose optical axis is directed to be substantially parallel to the axis is provided at a position eccentric from the axis of the turntable, and a photodetector and a light source are arranged above and below with the knife edge section in between. Therefore, the position of the objective lens can be detected with high reliability with an inexpensive and simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of the objective lens position detection device of the present invention, and FIG. 3 is a top and bottom view of the knife edge when diverging light is incident on the photodetector. 4 is an explanatory diagram of the operation of another embodiment of the present invention. FIG. 5 is a signal waveform diagram of another embodiment. Figures 6 and 7 are principle diagrams of the conventional tracking servo sensor system using the push-pull method, Figure 8 is a signal waveform diagram of the conventional tracking servo sensor system, and Figure 9 is the configuration of a conventional objective lens position detection device. Figure 10 is a detailed view of the main part of a conventional objective lens position detection device, Figure 11 is
The figure is a diagram of signal waveforms at various parts of a conventional objective lens position detection device. In the figure, 17 is an objective lens, 31 is a turntable, 32 is a photodetector, 33 is a light source, and 43 is a knife edge section. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A turntable in which a pair of knife edge portions are formed parallel to a predetermined axis, and is rotatable around the axis and movable along the axis; An objective lens supported at a position eccentric from the axis so that its optical axis is substantially parallel to the axis, and a photodetector and a light source arranged above and below with the knife edge part in between, the objective lens being rotated around the axis. An objective lens position detection device characterized in that the amount of rotational displacement of the objective lens is detected based on a change in the amount of light received by the photodetector due to rotation of the turntable about a rotation center.