JPS63173232A - Focal error detector - Google Patents

Abstract

PURPOSE:To always execute a stable focus control by changing suitably a gain balance of each photodetector in accordance with a shift in the track scanning direction of a far field image. CONSTITUTION:Each output of photodetectors 1a-1d is denoted by A-D, respectively, a displacement detecting means 3 is provided with two adding means, and A+B and C+D are calculated from each output of a photodetecting means 1. In such a case, if a far field image is positioned on an intersection of parting lines, outputs of both are equal, and if it is displaced, outputs of both are unbalanced by a portion corresponding to its quantity, and A+B<C+D or A+B>C+D depends on the displacement direction of the far field image. Accordingly, the output of the displacement detecting means 3 has information related to the shift direction and the shift quantity of the far field image. A control means 4 generates a control signal (command value) for amplifying the outputs of the photodetectors 1a-1d by the respective different amplification factors in accordance with said information, and variable amplifying means 5a-5d can change the amplification factor in accordance with the control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a focus error detection device for detecting the focal point position of an objective lens actuator in an optical disk device (particularly one having a continuous track).

2. Description of the Related Art In recent years, optical disk devices with large capacity and high information retrieval capabilities have been gradually put into practical use. An optical disk device is capable of recording and reproducing high-density information by irradiating a recording medium with a laser beam focused on a spot with a diameter of 1 to 2 μm using an objective lens.

Optical disk devices are composed of various technical elements, among which focus control technology that always maintains the distance between the objective lens and the recording medium at the focal length of the objective lens records and reproduces high-density information. It is no exaggeration to say that this is the most important technology. Among focus control technologies, focus error detection technology that detects the amount of deviation from focus is a technology that particularly requires high precision and reliability. Up to now, excellent methods with high detection sensitivity have been devised, such as the Astigma method and the Foucault (Naifetsugi) method.

An example of the conventional focus error detection device described above will be described below with reference to the drawings.

FIGS. 5A and 5B are block diagrams of a conventional focus error detection device. In FIG. 5(A),
10 is a recording medium. 1) is a laser light source, 12 is a half mirror, 1) 3 is an objective lens, 14 is a convex lens, 15
is a cylindrical lens.

1 is a light receiving means. The light-receiving means 1 includes four light-receiving elements (light-receiving sections) 1a, as shown in FIG.

It is divided into lb, lc, and ld at right angles, and one of the dividing lines coincides with the track direction provided on the recording medium 10. Furthermore, cylindrical lens 1
5 is installed so that its generatrix is at an angle of 45° to the dividing line (not explicitly shown in the figure).

Reference numeral 2 denotes a focus error detection means for calculating a focus error from the outputs of the light receiving elements 1a to 1d.

The operation of the focus error detection device configured as described above will be explained below.

The focus error is detected by an optical system composed of an objective lens 13, a convex lens 14, a cylindrical lens 15, and a light receiving means l. That is, the relative position between the recording medium 10 and the objective lens 13 can be known by producing astigmatism using the convex lens 14 and the cylindrical lens 15 and detecting the two focal positions obtained from the astigmatism using the light receiving means 1. can. Now, when the recording medium 10 is located at the focal point of the objective lens 13, the reflected light passes through the convex lens 14 and the cylindrical lens 15, and then focuses on two points on the optical axis (meridian image and spherical image). . These two
If the light receiving means 1 is provided near the center of the focal point, the image on the light receiving means 1 will be approximately circular. When the recording medium 10 is displaced from the focal position of the objective lens 13, the two focal points also move on the optical axis accordingly. At this time, the image on the light receiving means 1 becomes an ellipse extending in the diagonal direction, that is, in the 45@ or 145' direction from the dividing line. Light receiving element 1a.

The outputs of lb, lc, and ld are A, B, and C, respectively.

If D, then the focus error signal can be obtained by electrically calculating '(A+C)-(B+D). The focus error detection means 2 is for performing such processing. This method is called the astigmatism method, and is disclosed in Japanese Patent Application Laid-Open No. 53-1003 or Japanese Patent Application Laid-open No. 53
-19806 etc. in detail.

Problems to be Solved by the Invention However, with the above configuration, if the far-field image on the light receiving means 1 is shifted in the track scanning direction due to surface runout of the recording medium 10 or misalignment of parts constituting the optical head, etc. However, there was a problem in that a tracking error component was mixed into the focus error signal as a disturbance.

Figure 4 shows this situation. When the center of the far field image (at the time of focus) is on the intersection of the dividing lines of the light receiving means 1 as shown in FIG. The statue is canceled.

However, when the far field image shifts in the track scanning direction as shown in Figure (B), the trunk image is distributed asymmetrically with respect to the dividing line in the track orthogonal direction, so even if the difference in the diagonal sum is taken, it cannot be canceled, and the tracking error component A part of it will be mixed into the focus error signal.

In digital audio discs and video discs where the tracks are discontinuous, the amplitude of the tracking error signal itself is relatively small, so any interference with the focus control system can often be ignored. However, write-once or record-erase type recording media often have continuous tracks, and the influence of tracking error components on focus control becomes a problem.

In view of the above-mentioned problems, the present invention provides a focus error detection device that is capable of always performing stable focus control, with almost no tracking error components mixed in even if the far field image shifts in the track scanning direction. be.

Means for Solving the Problems In order to solve the above-mentioned problems, the focus error detection device of the present invention includes a displacement detection means for detecting a shift of a far field image in the track scanning direction, and a means for instructing the output of each light receiving element. It is comprised of variable amplification means that amplifies with an amplification factor according to the value, and control means that determines a command value to be given to the variable amplification means from the output of the displacement detection means.

Operation The present invention uses the above-described configuration to electrically cancel the dragging error signal by appropriately changing the gain balance of each light receiving element in accordance with the shift of the far field image in the track scanning direction.

Embodiment Hereinafter, a focus error detection device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of a focus error detection device in a first embodiment of the present invention. In Figure 1,
1 is a light receiving means, 2 is a focus error detecting means, 3 is a displacement detecting means, 4 is a control means, and 5 a +5b, 5c, and 5d are variable amplifying means. The input of the displacement detecting means 3 is connected to the outputs of the light receiving elements la, lb, Ic, and ld constituting the light receiving means 1, and the input of the control means 4 is connected to the output of the displacement detecting means 3. The variable amplification means 5a, 5b, 5c, and 5d amplify the outputs of the light receiving elements 1a, lb, lc, and ld, respectively, and their amplification factors are controlled by the output of the control means 4.

The input of the focus error detection means 2 is the corresponding variable amplification means 5a.
~5d output.

The operation of the focus error detection device configured as described above will be described below.

The light receiving means 1 has exactly the same structure as that described in the conventional example. In this embodiment, the respective outputs of the light receiving elements 1a, lb, 1c, and ld are assumed to be A, B, C, and D, respectively. The displacement detecting means 3 includes two adding means, and calculates A+B and C+D from each output of the light receiving means 1. . Here, if the far field image is located on the intersection of the dividing lines, the outputs of both are equal. If the far field image is displaced in the track scanning direction (in the vertical direction in the figure), the balance between the two outputs will be disrupted by an amount corresponding to the displacement.

Whether A+B<C+D or A+B>C+D depends on the direction of displacement of the far field image. Therefore, the output of the displacement detection means 3 has information regarding the direction and amount of displacement of the far field image.

According to this information, the control means 4 generates a control signal (
It has the function of issuing a command value). Variable amplification means 5a to 5d
can change its amplification factor according to its control signal. In this embodiment, the amplification factors of variable amplification means 5a and 5b and 5
The amplification factors of c and 5d are made equal to each other.

- As an example, consider a case where the far field image shifts as shown in FIG. 4(B). At this time, the output of the displacement detection means 3 becomes A+B=kx (C+D) (k>1). In contrast, the control means 4 has, for example, variable amplification means 5a to 5d.
The amplification factor (Ga-Gd) is Gc (=Gd)=kXG
Send a control signal such that a (=Gb). As a result, the amount of imbalance in the amount of light in the track scanning direction caused by the image shift is electrically corrected. At this time, the amount of unbalance of the track images irradiated onto the light receiving elements 1a, lb, lc, and ld is also alleviated, so that the amount of tracking error signals mixed in is drastically reduced.

However, the function of the control means 4 is not limited to this. For example, an appropriate gain balance f (k):Gc (=Gd)-f (k
)xGa (Gb) can completely eliminate the mixing of tracking error signals.

The reason why Ga=Gb and Gc=Gd in this embodiment is to prevent offset from being added to the focus error detection signal by changing the gain balance. The focus error detection means 2 uses the outputs GaXA and Gb of the variable amplification means 5a to 5d.
Focus error signal FB=Ga from xb, GcXc, and Gdxd
It is obtained by calculating xA+QcxC-(GbxB+GdxD). As mentioned in the conventional example, when the focus is focused, the image on the light receiving means 1 is circular, so if there is no deviation in the direction perpendicular to the track, then when the focus is focused, A=B, C=
It is D. The focus error signal at this time is FE= (
Ga-Gb)xA+ (Gc-Gd)xC, but if Ga=Gb and Gc=Gd, FE=O and no offset occurs.

If there is a deviation in the direction perpendicular to the track, Ga=Gb
=Gc-Gd, resulting in the normal Astigma method.

No offset occurs in this case either (Japanese Patent Application Laid-Open No. 53-100
3, JP-A-53-19806, etc.).

A drawback of the astigma method is that an offset occurs when a shift occurs in the track scanning direction and the orthogonal direction, but this can be alleviated by using the present invention. That is, since the deviation in the trunk scanning direction is electrically corrected, the deviation is substantially only in the direction perpendicular to the track.

A problem in this embodiment occurs when A+B and C+D contain many tracking error components. However, if the duty ratio between the tracks is not extremely different than 1 = 1, the tracking error component included in the re-output is extremely small, and even if it is included to some extent, it will be included in A+B and C+D. Since the tracking error components are in phase with each other, it is also possible to cancel them differentially.

As described above, according to this embodiment, there is provided a displacement detecting means for detecting a shift of a far field image in the track scanning direction, and a variable amplifying means for amplifying the output of each light receiving element with an amplification factor according to a command value. By providing a control means for determining a command value to be given to the variable amplification means from the output of the displacement detection means, it is possible to realize a focus error detection device that does not cause disturbance due to a tracking error signal.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a focus error detection device showing a second embodiment of the present invention. In the figure, the input to the displacement detection means 3 is obtained from the outputs of the variable amplification means 5a to 5d. The following is the same configuration as that shown in FIG. However, in this embodiment, the track scanning direction is left and right due to the layout of the drawings.

The operation of the focus error detection device configured as described above will be described below.

In this embodiment, the amplification factors of the variable amplification means 5a to 5d are determined by a feedback loop.

FIG. 3 is a circuit diagram showing an example of the control means 4. In FIG.

In FIG. 3, 41 and 42 are low-pass filters. 43 and 44 are differential amplifiers, and a reference voltage source 45 is connected to their positive phase input terminals. The response frequency of the feedback loop is a low pass filter 41.42
is determined by the time constant of and the gain of the differential amplifiers 43 and 44. When the feedback loop is configured as described above, the output of the variable amplification means 53 to 5d is always GaXA+
GbXB=Il, +, GcXC+ G d X D
" Eo (Eo: reference voltage value generated by the reference voltage source 45). In this embodiment, as in the previous embodiment, Ga=Gb and Gc=Gd.

As described above, according to this embodiment, the variable amplification means 5a to 5
Since the amplification factor of d is determined by a feedback loop, the control means 4 can be simplified.

Effects of the Invention As described above, the present invention includes a displacement detection means for detecting a shift of a far field image in the track scanning direction, a variable amplification means for amplifying the output of each light receiving element with an amplification factor according to a command value, By providing a control means for determining a command value to be given to the variable amplification means from the output of the displacement detection means, it is possible to realize a focus error detection device that does not cause disturbance due to a tracking error signal.

Further, by configuring the displacement detecting means to obtain the input from the output of the variable amplifying means, it is possible to simplify the configuration of the controlling means.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a focus error detection device in an embodiment of the present invention, FIG. 2 is a block diagram of a focus error detection device in a second embodiment of the present invention, and FIG. 3 is a block diagram of a focus error detection device in a second embodiment of the present invention. Circuit diagrams showing one embodiment of the control means 4, FIGS. 4(A) and 4(B)
) are explanatory diagrams that list the problems of the conventional method, Figure 5 (A) (B)
is a block diagram of a conventional focus error detection device. DESCRIPTION OF SYMBOLS 1... Light receiving means, 2... Focus error detection means, 3... Displacement detection means, 4... Control means, 5a to 5d... ...Variable amplification means. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 1 Figure 2 Figure 3 Figure 4 C (β)t
L:LlblLLlb 1(L/(,1)i/c

Claims (6)

[Claims] (1) An optical means for generating astigmatism and an optical means provided near the imaging point are divided in directions perpendicular to each other, and each divided part functions as four independent light receiving parts. A focus error detection device, further comprising a focus error detection means for outputting a difference between sum signals of two sets of light receiving sections disposed diagonally to each other, the light receiving means displacement detection means for detecting the direction and amount of displacement of the information surface of the recording medium illuminated by the far field image in the direction of one dividing line, and the output of each light receiving element at an amplification factor according to each command value. A focus error detection device comprising: variable amplification means for amplifying the signal; and control means for determining a command value to be given to the variable amplification means from the output of the displacement detection means. (2) The displacement detecting means is provided with two adding means for obtaining the respective sum outputs of two sets of light receiving sections separated by one dividing line.
) The focus error detection device described in section 2. (3) A patent characterized in that the recording medium has a track on the information surface, and the track is arranged so that its scanning direction is mapped parallel to one of the dividing lines of the light receiving means. A focus error detection device according to claim (1). (4) Claims characterized in that the displacement detection means is equipped with two adding means for obtaining the sum output of each of two sets of light receiving sections separated by a dividing line perpendicular to the track scanning direction. The focus error detection device according to item (3). (5) The variable amplifying means output signal is input to the displacement detecting means, and each of the variable amplifying means output signals corresponding to two sets of light receiving sections separated by one dividing line with each light receiving section is The focus error detection device according to claim 2, further comprising two adding means for obtaining a sum output. (6) Claim (1) characterized in that the amplification factors of the two variable amplification means that respectively amplify the outputs of the two light receiving sections adjacent to each other in the direction of one dividing line are equal to each other.
Focus error detection device as described in .