JPS6378348A - Focus error detection method - Google Patents

Abstract

PURPOSE:To detect a focus error of an optical pickup by arranging a photodetector onto an optical path of a light beam while being tilted by a prescribed angle with respect to an optical axis of the light beam and deciding the luminous quantity of the local spot light of the light beam radiated to plural photodetection parts being components of the photodetector. CONSTITUTION:The photodetector 27 arranged perpendicularly to the optical axis I is tilted by an angle alpha. An amplifier amplifying a signal photoelectric- converted in response to the irradiated state of the irradiating spot light is connected respectively to the photodetection parts A-F and a focus error signal subject to photoelectric conversion is outputted in response to the irradiation state of the light beam 2a radiated to the photodetector parts A-F. Since the focus error signal is generated in response to the facial deflection of a disk recording face 28, the signal is fed back to an actuator moving an objective lens 5 in the focus direction depending on the quantity of change. Thus, the focus error of the optical pickup (especially, of the objective lens 5) due to the facial deflection is eliminated.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a compact disc (hereinafter abbreviated as rcDJ).
The present invention relates to a detection method for detecting a focus error of an optical pickup that occurs when reproducing an optical recording medium such as the following.

(Prior Art) FIG. 7 is a diagram for explaining the principle of playing back a compact disc. In the figure, a light beam 2 emitted from a laser diode 1 passes through a half prism 3 and a collimator lens 4, and is focused by an objective lens 5.
A digital information signal is irradiated onto the aluminum evaporated film 8 located within the transparent plastic 7 constituting the D6. Aluminum vapor deposition v! 8 has a high reflectance, and the irradiated light beam 2 is reflected here,
Signals incident on the light receiving element 10 via the objective lens 5, collimator lens 4, half prism 3, and cylindrical lens 9 and photoelectrically converted there are extracted as a tracking error signal, a focus error signal, and a reproduction signal. The light-receiving surface 10a of the light-receiving element 10 receives a light beam 2 that is reflected from the recording section (aluminum film 8) of the CD 6 and reaches the light-receiving surface 10a.
It is perpendicular to the optical axis ■ of a.

Here, the above-described laser diode 1, half prism 3, collimator lens 4, objective lens 5, cylindrical lens 9, and light receiving element 10 are collectively referred to as an optical pickup.

Now, in order to faithfully reproduce the digital signal recorded on the CD 6 using a CD player, it is necessary to accurately trace the plurality of bits 11 with the light beam 2. but,
During playback, surface runout (swinging of the CD 6 in the vertical direction with respect to the recording surface) or eccentricity (swinging of the CD 6 in the radial direction) occurs. A servo technique using the output signal from the light receiving element 10 described above is essential for controlling an adjustment mechanism (for example, an actuator), not shown, which adjusts the focus or inclination of the objective lens 5 accordingly.

That is, the objective lens 5 is two-dimensional (focus direction (CD6
in the vertical direction with respect to the recording surface and in the track direction (CD6
Although not described in detail here, this adjustment IM uses an actuator similar to the voice coil of a well-known speaker so as to be movable in each direction. (not shown) is adopted. Then, use the above optical pickup as a CD
In order to swing in accordance with the surface deflection of the lens 6, it is necessary to detect a focus error signal from the light receiving element 10 and apply feedback to the actuator in accordance with the detection level.

To detect the focus error signal caused by the surface wobbling of the CD6, the following methods are mainly used: (1) Astigmatic method
method) and ■Beam size method (Beam-si method)
ze Ithod) is used.

Figure 8 is a diagram for explaining the astigmatism method.
A) is an overall view thereof, and FIG. 3(B) is a view showing the irradiation state of the light beam on the light receiving element 11. In the same figure,
11 is a light receiving element, 12 is a cylindrical lens, 13 is a collimator lens, 14 is an objective lens, 15 is a disk recording surface,
16 is an error signal amplifier.

Figure 2 is a diagram for explaining the beam size method; Figure (A) is an overall view thereof, and Figure (8) shows a photodetector 17 using a light receiving element consisting of a concentric photodiode 22. FIG. 2C is a diagram showing a photodetector 17 using a multi-division photodiode 23. In the same figure, 17
is a photodetector, 18 is a half prism, 1 is a collimator lens, 20 is an objective lens, 21 is a disk recording surface,
22 is a concentric photodiode, and 23 is a multi-division photodiode.

(1) The astigmatism method is as shown in Figure 8 (A) and (B).
Due to the combination of the cylindrical lens 12 and the convex lens (collimator lens 13 and objective lens 14), when the light beam is focused on the disk recording surface 15, a perfect circle (solid line in the figure (B)) appears on the light receiving element 11. A circle (indicated by ) will appear. Furthermore, when the focus is shifted, ellipses (two ellipses indicated by broken lines in FIG. 2B) appear on the light receiving element 11. As shown in FIG. 3B, the light receiving element 11 divided into four parts A, B, C, and D detects a focus error by obtaining a focus error signal corresponding to the shape of a perfect circle or an ellipse via an error signal amplification 316. It's a method.

Furthermore, in the beam size method, by appropriately moving the position of the objective lens 20 in the focus direction, as shown by the arrow ■ in FIG. 9 (A>), it is possible to detect changes in the beam size due to focus errors. In other words, a focus error signal is detected by calculating a photoelectrically converted signal from a concentric photodiode 22 made up of two photodiode parts E and F shown in FIG. This is a detection method in which a photoelectrically converted signal from a concentric photodiode 23 made up of a plurality of photodiode three sections G and 8.1 shown in FIG. This is a focus error detection method for detecting a focus error signal by performing zero operation.

The light-receiving surface of the light-receiving element 11 or photodetector 17 used in the above-mentioned (1) astigmatism method and (2) beam size method is perpendicular to the optical axis (2).

(Problem 5'! Ming tries to solve) In the conventional focus error detection method described above, the astigmatism method has the problem that the number of components is large and the surface is high, making adjustment troublesome. The size method has a problem in that the dynamic range of the detected IS focus error signal cannot be widened.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a focus error detection method by tilting a light receiving element at a predetermined angle with respect to the optical axis of the light beam. The focus error of the optical pickup is detected by determining the amount of partial spot light of the light beam irradiated onto a plurality of light receiving element portions forming the light receiving element.

(Example) Major features of the focus error detection method according to the present invention.

For example, the light receiving surface of the light receiving element is tilted with respect to the optical axis of the optical beam that is reflected from the recording surface of the disk and reaches the light receiving surface of the light receiving element, and this is placed on the optical path to detect the focus error signal. This is the way to do it.

FIG. 1 is a diagram for explaining the principle of the focus error detection method according to the present invention.

FIG. 2 is a diagram showing an optical image formed on the light-receiving surface 27a of the light-receiving element 27 shown in FIG. The optical image 81 in the same figure (B) shows the optical image b after the focal point Fo of the light beam 2a is on the light receiving surface 27a; the same figure (C) shows the light receiving surface 2.
FIG. 7 is a diagram showing an optical image C when a focal point F2 of the light beam 2a is behind the light beam 7a.

FIG. 3 is a diagram showing an example of light receiving element portions A to F forming the light receiving surface 27a of the light receiving element 27. In FIG.

FIG. 4 is a view showing the light receiving element 27 shown in FIG. ) is the partial spot light intensity obtained by dividing the spot light of the light beam 2a incident on the light-receiving surface 27a into six parts, and (C) is S of the light-receiving element 27 shown in (A).

FIG. 6 is a diagram showing a state in which points A and A= of the spot light shown in FIG. 3B are superimposed on one point S. FIG.

FIG. 5 is a diagram showing a state in which the optical image a appears on the light-receiving surface 27a in FIG. 2(A).

FIG. 6 is a diagram showing another embodiment of the light-receiving element portions A to F forming the light-receiving surface 27a of the light-receiving element 27 shown in FIG.

Components that are the same as those described above are given the same reference numerals, and their explanations will be omitted.

The configuration in the diagram for explaining the principle of the focus error detection method according to the present invention shown in FIG. 1 is included in the configuration of the principle for playing a compact disc shown in FIG. 7 described above.
It can be considered that the cylindrical lens 9 is removed and the light receiving element 10 installed perpendicular to the optical axis (2) is tilted by an angle α.

That is, in the principle of the present invention, the half prism 3
Since the cylindrical lens 9 is not interposed between the disc recording surface 28 and the light-receiving element 27, the light beam 2a reflected by the disk recording surface 28 can be directly introduced onto the light-receiving surface 27a of the light-receiving element 27. Furthermore, by inclining the light receiving surface 27a of the light receiving element 27 by an angle α with respect to the optical axis I of the light beam 2a, various effects can be achieved according to the conditions as shown in FIGS. Another feature is that it can receive an optical image a-C of the shape.

It goes without saying that the disk recording surface 28 refers to the information signal recording surface including bits formed on the surface of the aluminum vapor deposited film 8 of the CD 6, for example.

Now, in the light-receiving element 27 shown in FIG. 1 described above, as shown in FIG. 3, a light-receiving surface 27a is constituted by the light-receiving element portions AF. As shown in FIG. 3, the shape of the light receiving element 27 is rectangular and is composed of six light receiving element parts A to F. The light-receiving element parts A to F have a two-stage structure, upper and lower, with the upper part being A to C1 and the lower part being D-F. F)
is larger than the width of the light-receiving element portion B(E) located at the center thereof. The light receiving element 27 includes, for example, 6 photodiodes.
It is constructed by dividing it or by collecting G and T photodiodes 6@.

Each of the light receiving element portions A to F is connected to an amplifier (not shown) that amplifies a charge-converted signal according to the irradiation state of the irradiated spot light.
A focus error signal photoelectrically converted according to the irradiation state of the light beam 2a irradiated onto F is output. Since this focus 1 signal is generated in response to the vibration of the disk recording surface 28, a 7 (not shown) signal is generated that moves the objective lens 5 in the focus direction according to the amount of change. He returned to Kuche in the evening.

In this way, the focus error of the optical pickup (particularly the objective lens 5) due to surface wobbling can be eliminated.

The above-mentioned light receiving element 27 is arranged on an optical path centered on the optical axis (2) of the light beam 2a reflected from the half prism 3, as shown in FIG.

The light-receiving element 27 may be provided with an adjustment mechanism that can be adjusted as necessary to obtain a good focus error signal by means of a light-receiving surface 27a that is inclined at an angle α with respect to the optical axis (2).

In the configuration of the principle of the focus error detection method according to the present invention shown in FIG. There is a case (state ■ below) where they match. That is, if the objective lens 5 is too far away from the disk recording surface 28, then the disk recording surface 28
The focal point F1 of the light beam 2a reflected from the
), it is connected to the front of the light receiving surface 27a, and the light receiving surface 2
An optical image a (elliptical spot light extending above the optical axis ■) is formed on 7a.

■When the focus of the objective lens 5 matches the disk recording surface 28, the focus Fo' of the light beam 2a is at the second
As shown in Figure (B), the light is focused on the light-receiving surface 27a, and an optical image b (a small elliptical spot light vertically symmetrical about the optical axis I) is formed on the light-receiving surface 27a.

■If the objective lens 5 is too close to the disk recording surface 28, the focal point F2 of the light beam 2a will be as shown in Fig. 2 (C).
As shown in FIG.
An optical image C (elliptical spot light extending below the optical axis 2) is formed on a.

In this way, in the configuration shown in FIG. 1, if the focus of the objective lens 5 does not match (2) above.

The state will be either (state 2) or when the focus is in alignment (state B of state 2 above).

If the light-receiving element shown in FIG. 3 is applied to the light-receiving element 27 having the configuration shown in FIG. , as shown in FIG. 2(A), and an optical image a shown in FIG. 5 is obtained on the light-receiving surface 27a.

Moreover, if the state shown in FIG. 5 is viewed from the direction of the optical axis, it should appear as shown in FIG. 4(C). In this state, the intersection point S of the dividing line of the light-receiving surface 27a shown in FIG.
It is obtained by superimposing the splitting points A and A- of the spot light on S-.

In FIG. 4(C), the light-receiving element portion B that constitutes the light-receiving surface 27a of the light-receiving element 27 counts all the partial spot light "mouths" formed by dividing the spot light shown in FIG. 4(B). It is not possible. Conversely, the light-receiving element portion E includes all of the partial spotlights "E" and also includes parts of the partial spotlights "2" and "HE".

In the above state (2) (when the objective lens 5 is too close to the disk recording surface 28), the state shown in FIG. 2(C) occurs, and accordingly, both FIGS. The relationship is inverse to the state of .

That is, when the objective lens 5 is far from the disk recording surface 28, the output of the light-receiving element portion E is large, and when it is close, the output of the light-receiving element portion B is large.

Utilizing this fact, compare the output levels of both signals photoelectrically converted according to the irradiation light intensity of the partial spot lights "mouth" and "ho" of the light beam 2a, which are irradiated on the light receiving element part B and the same above, respectively. By doing so, a focus error signal corresponding to this output level difference can be obtained. Moreover, the polarity of the focus error signal (=.

+), polarity information about the distance between the disk recording surface 28 and the objective lens 5 can also be obtained.

For example, in the above state ① (when the objective lens 5 is too fast relative to the disk recording surface 28), since the optical field @a shown in FIG. 2(A) is obtained on the light receiving surface 27a, The amount of light irradiated by the partial spotlight "mouth" is smaller than the amount of light irradiated by the partial spotlight "ho" on the light receiving element part B, and the photoelectrically converted signal obtained from the light receiving element part B is given by 1 from the light receiving element part E. Its level is lower than that of the photoelectrically converted signal, and by comparing both signal outputs, a corner focus error signal is obtained.

A negative focus error signal is obtained by polarizing the objective lens 5 closer to the recording surface 28 of the disk, so when the actuator that moves the objective lens 5 is actuated in accordance with this, the focus F1 of the light beam 2a will be on the light receiving surface 27a. , and as a result, the light beam irradiated onto the light-receiving surface 27a gradually approaches
The size of a becomes small, and when all of this is accumulated in the light receiving element parts B and E, the output difference between the signal from the light receiving element part B and the signal from the light receiving element part E disappears, and the focal point The error signal will be zero.

In this way, the state (2) described above (when the focus of the objective lens 5 matches the disk recording surface 28) is achieved.

In the above condition (■) (when the objective lens 5 is too close to the disk recording surface 28), a focus error signal with a polarity opposite to that described in the above condition (■ (when the objective lens 5 is too fast with respect to the disk recording surface 28)) is generated. Needless to say, you can obtain

Since the optical image irradiated onto the light-receiving surface 27a is small in the above state (when the focus of the objective lens 5 is aligned with the disk recording surface 28), the light-receiving element portions B and E are Therefore, there is no focus error signal.

In this way, the focus error of the objective lens 5 is detected based on the size and shape of the optical image a-C irradiated onto the light-receiving element portion A-E constituting the light-receiving surface 27a of the light-receiving element 27, and the focus error is detected. Depending on the signal level and its polarity,
By operating the actuator that moves the objective lens 5 in the focus direction, focus error (focal shift) can be avoided.
can be removed.

What has been described above is the light-receiving element portion B that constitutes the light-receiving surface 27a8.
, E has been described to remove the focus error using the signals obtained from the light-receiving element parts A, C, and E.
In D and F, the relationship is opposite to that of the light-receiving element portions B and E (if the objective lens 5 is far from the disk recording surface 28, the light-receiving element portion B is smaller than the light-receiving element portion E, and at the same time, (light-receiving element portion A + light-receiving element portion Portion C)> (light-receiving element portion F), and if the light-receiving element portion is close to the light-receiving element portion F), the opposite is true.Therefore, focus error signals can also be obtained from the light-receiving element portions A, C, D, and F.

], and since the same signal can be obtained from this, it can also be used. In fact, all of the photoelectrically converted signals obtained from the light receiving element portions A to F can be used.

In the focus error detection method according to the present invention described above,
Since the signal generated according to the magnitude relationship of the light amount obtained from each light receiving element portion A to F forming the light receiving surface 27a can be obtained no matter how far the focus is, the focus error signal disappears from -■ to +■ There's nothing to do. Moreover, the sensitivity is low when the focus is far away, and the sensitivity increases as you get closer to the focus, making it an ideal principle to achieve accurate focus alignment.

Furthermore, in the focus error detection method according to the present invention, since the cylindrical lens 9 is not interposed between the half prism 3 and the light receiving probe 27, the polarity signal can be obtained directly from the disk recording surface 28.

Although the above was explained using a compact disc as an example, the method of the present invention is not limited to this.
Of course, the present invention can also be similarly applied to reproduction using an optical recording medium such as a video disc.

(Effects of the Invention) As described above, the focus error detection method of the present invention is as follows:
The drawbacks of conventional focus error detection methods are that the astigmatism method requires a large number of components, is expensive, and is troublesome to adjust, and the beam size method cannot detect the dynamic focus error signal. It can eliminate the drawback of not being able to get a large range, (9
The focus error signal obtained is directly obtained including not only the amplitude but also the polarity, and the dynamic range of the signal is very large.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the principle of the focus error detection method according to the present invention, and FIG. 2 is a diagram showing an optical image formed on the light-receiving surface 27a of the light-receiving element 27 shown in FIG. In the same figure (A), the focus F1 of the light beam 2a is located in front of the light receiving surface 27a.
The figure (B) shows the optical image Bb when the focal point Fo of the light beam 2a is on the light-receiving surface 27a, and the figure (C) shows the optical image a when the light beam 2a is focused behind the light-receiving surface 27a. Focus F2
FIG. 3 is a diagram showing the optical image C when
FIG. 4 is a diagram showing an example of the light receiving element 27 shown in FIG.
It is a diagram showing the state seen from the optical axis Ih direction, and the same figure (A)
is the light-receiving surface 27a of the light-receiving element 27 shown in FIG.
) is the partial spot light weight ~ which is obtained by dividing the spot light of the light beam 2a incident on the light receiving surface 27a' into six parts, and (C) is the same as the point S, S= of the light receiving element 27 shown in FIG. Figure (B
5 is a diagram showing a state in which the spot lights A and A shown in FIG. 5 are superimposed on each other. 6 is a diagram showing another embodiment of the light receiving element portions A to F constituting the light receiving surface 27a of the light receiving element 27 shown in FIG. 3, FIG. 7 is a diagram for explaining the principle of playing a compact disc, FIG. 8 is a diagram for explaining the astigmatism method; FIG. is a diagram for explaining the beam size method.
B) is a diagram showing a photodetector 17 using a light receiving element consisting of a concentric photodiode 22, and FIG. 2a... Light beam, 27... Light receiving element, I... Partial spot light, A-F... Light receiving element portion, ■... Optical axis. ? 7 Roo Figure 6-p7 Figure CA)

Claims (1)

[Claims] A light receiving element is tilted at a predetermined angle with respect to the optical axis of the light beam and placed on the optical path of the light beam, and the light intensity of the partial spot light of the light beam irradiated onto the plurality of light receiving element parts forming the light receiving element is determined. A focus error detection method characterized by detecting a focus error of an optical pickup.