JPS60202549A - Optical information reproducer - Google Patents

Abstract

PURPOSE:To attain the stable focus control regardless of the presence or absence of a read signal by performing the focus control in accordance with a composite focus error signal obtained from addition of the 1st focus error signal extracted from the phase difference of output signals fed from plural photodetecting cells and the 2nd focus error signal obtained by menas of astigmatism. CONSTITUTION:The output signals Sa-Sd fed from photodetecting cells 16a- 16d are supplied to the 1st focus error detecting means consisting of adders 20 and 21, a phase comparator 25 and an LPF26, to the 2nd focus error detecting means consisting of adders 22 and 23, subtractor 24 and an LPF27. The 1st focus error detecting means detects the 1st focus error from the phase difference between (Sa+Sb) and (Sc+Sd); while the 2nd focus error detecting means makes use of the astigmatism of a light spot 17 to detect the 2nd focus error respectively. An adder 28 adds the 1st and 2nd focus error signals to output a composite focus error signal. Then the focus control is executed by the 1st focus error signal with a normal reproduction and by the 2nd focus error signal when the read signal is erased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information reproducing device for optically reproducing information from an information record carrier.

Conventional configurations and their problems In recent years, devices that optically reproduce information from information recording carriers on which information is recorded at high density have been commercialized, and video disc players that can reproduce television signals and digital audio signals have been commercialized. It is already on sale as a playable compact disc player (trademark of Philips Corporation). Information is recorded in these at extremely high density, and highly accurate focus control is generally performed during reproduction. As a focus control method, a method has already been proposed in which a focus error signal is extracted from the phase difference between the output signals of two photodetectors arranged substantially along an information track. (For example, see Japanese Patent Publication No. 53-13122.) Hereinafter, focus control in a conventional optical information reproducing device will be explained with reference to the drawings, and in particular, focus control means using a phase difference between output signals of a plurality of photoelectric detectors. . FIG. 1 is an enlarged view of the main parts of the optical head of a conventional optical information reproducing device, where 1 is a light beam, 2 is a converging optical system, 3 is a detection optical system,
4 is a photoelectric detector, 4a and 4b are light receiving cells included in the photoelectric detector 4, 5 is an information recording surface, 6a is an information recording surface when in focus, and esb and 6C are when out of focus. This shows each information recording surface.

FIG. 2 is a signal waveform diagram for explaining the operation.

The operation of the conventional optical information reproducing apparatus configured as described above will be described below. When the information recording surface 6a moves in the length direction of the information track when the focusing optical system 2 is correctly focused, the light receiving cell 4a of the photoelectric detector 4
At the same time, the amount of light incident on the light receiving cell 4a and the light receiving cell 4b suddenly changes, and the output signal Sa from the light receiving cell 4a and the output signal sb from the light receiving cell 4b become as shown in FIG. There is no phase difference between 8a and sb.However, when the information recording surface 5b moves in the length direction of the information track when the focus is shifted, the amount of light incident on the light receiving cells 4a and 4b of the photoelectric detector 4 gradually decreases. Moreover, the change in the amount of light incident on the light receiving cell 4a is delayed in phase, and the change in the amount of light incident on the light receiving cell 4b is advanced in phase.

Therefore, the output signal Sa from the light receiving cell 4a and the output signal sb from the light receiving cell 4b are as shown in FIG. 2(b). Further, when the information recording surface 5b moves in the length direction of the information track when the focus is shifted in the opposite direction to the above, the phase shift becomes opposite to the above, and the output signal Sa from the light receiving cell 4a and the output signal Sa from the light receiving cell 4b are The output signals sb are as shown in FIG. 2(C). (Therefore, the light receiving cell 4a
By detecting the phase shift of the output signal Sa from the light receiving cell 4b and the output signal sb from the light receiving cell 4b, the magnitude and direction of the focus error of the converging optical system 2 can be detected.

The above is the principle of the focus error detection means that detects a focus error from the phase difference between respective read signals from a plurality of light receiving cells. Strictly speaking, the above explanation is valid only when there is no unevenness on the information recording surface, or when information is recorded with unevenness, the optical phase depth is an integral multiple of π. When information is recorded at an optical phase depth that deviates from an integral multiple of π, even when the focusing optical system 2 is correctly focused, the output signals Sa and sb
has a predetermined phase difference depending on the optical phase depth. However, even in this case, the focus error can be detected by comparing the phase difference between the output signals Sa and sb with a predetermined phase difference, and there is essentially no difference from the case where there is no unevenness on the information recording surface. None. This method of detecting focus errors using phase difference has high accuracy because it directly detects focus errors from the relationship between the light spot formed on the information recording surface by the convergent optical system and the information recording surface. Since the read signals from each light-receiving cell can also be AC amplified to a predetermined level and then compared in phase, this method has the advantage of being less susceptible to circuit offsets, temperature drifts, and the like.

However, with this method of using the read signal from the information record carrier, there are cases where the focus error greatly exceeds the depth of focus, or where the recorded information on the information record carrier has disappeared for some reason. In some cases, the focus error cannot be detected, so the focus control pull-in range is extremely narrow, and the focus control may not function in large defects or areas where no information is recorded on the information recording carrier. Ta.

OBJECTS OF THE INVENTION It is an object of the present invention to accurately detect a focus error based on the phase difference of each read signal of a plurality of light receiving cells, and to
An object of the present invention is to provide an optical information reproducing device that can widen the pull-in range of focus control and perform stable focus control regardless of the presence or absence of a read signal.

Structure of the Invention The optical information reproducing apparatus of the present invention comprises: a light source that emits a light beam; a converging optical system that guides and converges the light beam onto the information recording surface of an information recording carrier on which information is recorded; and the information recording carrier. a photoelectric detector having a plurality of light-receiving cells that receive reflected light from the information recording carrier and output an electric signal; a detection optical system that guides the reflected light from the information recording carrier to the photoelectric detector; a first focus error detection means for obtaining a first focus error signal by comparing the phase of the sum of output signals from one or more light receiving cells and the sum of output signals of one or more other light receiving cells; , the level of the sum of output signals from a predetermined one or more light receiving cells of the photoelectric detector and the sum of output signals of one or more other light receiving cells is compared, and a second
a second focus error detection means for obtaining a focus error signal; and a focus control means for controlling the focus of the converging optical system in accordance with a composite focus error signal obtained by adding the first and second focus error signals. However, in a frequency band below a predetermined frequency lower than the gain intersection of the focus control, the first focus error detection means has higher detection sensitivity than the second focus error detection means,
At least one of the first and second focus error detection means is configured such that in a frequency band exceeding the predetermined frequency, the second focus error detection means has a detection sensitivity υ higher than that of the first focus error detection means. Because it is configured to include a filter element, focus control during normal playback is accurate and has a wide pull-in range, making it possible to perform stable control at any location regardless of the presence or absence of recorded information. It is what it is.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a perspective view of the main parts of an optical head of an optical information reproducing apparatus according to an embodiment of the present invention, in which 10 is a light source;
is the flux emitted from the light source, 12 is an information record carrier,
13 is a converging lens, 14 is a beam splitter, 16 is a cylindrical lens, 16 is a photodetector, 16a, 16b, 16c
and 16d, a light receiving cell included in the photoelectric detector 16;
7 is a light spot formed on the photoelectric detector 16.

FIG. 4 is a block diagram of the circuit portion of the focus control means in this embodiment, in which 20, 21, 22, 23 and 28 are adders, 26 is a phase comparator, 26 and 27 are low-pass filters, and 29 is a control It is a circuit.

Further, FIG. 6 is a frequency characteristic diagram of the detection sensitivity of the first focus error detection means and the second focus error detection means.

The operation of the optical information reproducing apparatus configured as above will be explained below with reference to the drawings. The converging lens 13 constitutes a converging optical system, and converges the light beam 11 emitted from the light source 10 onto the information recording carrier 12. The reflected light from the information recording carrier 12 is guided onto a photoelectric detector 16 by a converging lens 13, a beam splitter 14, and a cylindrical lens 15, which constitute a converging optical system, to form a light spot 17. As shown in the figure, the photoelectric detector 16 has four light receiving cells 1ea, 1eb, 1ea and 1ed divided by a straight line substantially parallel to the information track and a straight line perpendicular to the information track, and the focus of the converging lens 13 is correct. It is arranged approximately midway between the front focal line and the rear focal line of the detection optical system when they are aligned.

The main axis of the cylindrical lens 16 is placed on the information track of the information recording carrier 12 with a rotation of approximately 46 degrees, and the optical spot 1
7 is inverted symmetrically from the front focal line of the detection optical system to the straight line including this front focal line, so that the information track is projected onto the photoelectric detector 16 in the direction of arrow T in the figure. From the light receiving cells 16a, 1ab, 16a and 16d, ? The output signals Sa, Sb, Sc and Sd are sent to the adder 20
,21. A first focus error detection means consisting of a phase comparator 25 and a low-pass filter 26, and adders 22 and 23.
, a subtractor 24 and a second focus error detection means consisting of a low-pass filter 27. As is clear from the description of the conventional example, the first focus error detection means (Sa+
A focus error is detected from the phase difference between Sb) and (Sa+Sd). That is, the phase comparator 25 compares the phase difference between the output signal from the adder 20 and the output signal from the adder 21 with a predetermined value, and detects a focus error from the difference. Furthermore, the output signal of the phase comparator 25 is filtered through a low-pass filter 25.
After passing through, it is output as a first focus error signal. Fifth
Figure A shows the frequency characteristics of the detection sensitivity of the first focus error detection means. Note that the detection sensitivity here means the gain of the focus error signal with respect to the focus error.

The second focus error detection means is configured to detect a focus error using astigmatism of the light spot 17. A method of detecting focus error using astigmatism is already known (
For example, see Japanese Patent Application Laid-open No. 50-99561),
The operation will be briefly explained below. When there is no focus error in the converging optical system, the light spot 17 with astigmatism is the light receiving cell 16a.

Since the photoelectric detector 16 is installed so as to span almost equally over 16b, 160 and 16d, Sa, Sb, g
o and Sd are both approximately equal. However,
When the focus of the converging lens 13 shifts, the position of the focal line of the detection optical system moves back and forth along the optical axis, so that the light spot 1
7 has an elliptical shape with its long axis or short axis parallel to the main axis of the cylindrical lens 16, so that (Sa+Sc) and (Sb+Sd) are unbalanced. Furthermore, since the magnitude relationship between (Sa+Sc) and (Sb+Sd) is reversed depending on the direction of focus deviation of the converging lens 13, the direction and magnitude of the focus error can be detected by calculating (Sa+5a)-(Sb+8d). Fourth
In the figure, the adder 22 calculates (Sa+Sc), the adder 23 calculates (Sb+ad), and the subtracter 24 calculates (Sb+Sd) - (Sa + Sc) to detect the focus error. do. Low pass filter 2
7 removes the noise caused by the recorded information signal from the output signal of the subtracter 24 and outputs a second focus error signal. As shown by B in the figure, the characteristics are almost flat. The adder 28 adds the first focus error signal and the second focus error signal to output a compound focus error signal, and the control circuit 29 adds the above-mentioned first focus error signal and second focus error signal to output a compound focus error signal. ,
Focus control means is configured to drive the actuator to cancel the focus error. As shown in Figure 6, the frequency F
In a frequency band lower than t (Ft is lower than the gain intersection of focus control), the first focus error detection means has a larger gain than the second focus error detection means, so during normal playback, within the above band, the first focus error detection means has a larger gain than the second focus error detection means. Highly accurate focus control is performed using the focus error signal.

Furthermore, the disadvantage that the first focus error detection means stops functioning when the read signal disappears can be overcome by the second focus error detection means, and the pull-in range can be widened. The second focus error detection means is a light beam 1
However, the frequency of the offset and temperature drift is generally extremely low, so during normal playback, the first focus error signal It will not be a problem as it will be compensated by. Further, when no read signal is obtained, very precise control is not required, so the offset and the like hardly pose a problem in this case as well. Note that the low-pass filter 26 may be an integrator, and in this case, the frequency characteristic of the detection sensitivity of the first focus error detection means will be as shown in FIG. 6C.

Note that, instead of including the low-pass filter 26, the first focus error detection means may be configured to include a lead-lag filter such that the detection sensitivity of the second focus error detection means decreases at low frequencies. .

FIG. 6 is a perspective view of the main parts of an optical head of an optical information reproducing apparatus according to still another embodiment of the present invention, in which 41 is a photoelectric detector, and 41a, 41b, 41c, and 41d are included in the photoelectric detector 41. A light receiving cell 42 is a light spot formed on the photoelectric detector 41. The process up to the point where the light beam 11 is converged onto the area of the information recording carrier 12 is the same as in the previous embodiment, but the reflected light from the information recording carrier 12 is transmitted to the photoelectric detector 41 by a detection optical system consisting of a converging lens) and a beam splitter 14. The light is guided upward to form a light spot 42. Since the photoelectric detector 41 is installed in front of the focal point of the detection optical system, this light spot 42 becomes a blurred image (far-field image) and the information trunk is projected in the direction of arrow T in the figure. The photoelectric detector 41 is connected to the arrow T as shown in the figure.
A light receiving cell 41 divided into four by parallel lines perpendicular to the direction of
a.

41b, 41d, and 41c, which are arranged in that order, and output signals Sa, Sb, Sa, and Sd according to the incident light to each. In this case, clearly (Sa-1-8b) and (Sc
A first focus error signal can be obtained by comparing the phases of +Sd).

The second focus error detection means can detect from the size of the light spot. A method for detecting a focus error using the size of this light spot is already known (for example,
18247), its operation will be briefly explained below. When the converging lens 13 is correctly focused on the information record carrier 12, the light spot 42
The photoelectric detector 41 is installed so that the same amount of light enters the three light receiving cells 41a, 41b, 41a and 41d, and in this case, (Sa-1-8c) and (Sb-1-
8d) are equal. However, for example, information recording carrier 1
2 moves away from the converging lens 13 and a focus error occurs, the light spot 42 becomes smaller (sb-1-8
d) is larger than (Sa-)-8a).

Conversely, when the information recording carrier 12 approaches the converging lens 13 and a focal error occurs, the optical spot 42 becomes larger and (Sa+Sc) becomes larger than (Sb-1-8d). Therefore, the direction and magnitude of the focus error can be detected from the difference between (Sa+sc) and (Sb+Sd).

The circuit portion of the focus control means using the first and second focus error signals described above can be realized in the same manner as in the above embodiment by the configuration shown in FIG. 4, and the same effects as in the above embodiment can be obtained. can.

It should be noted that the second focus error detection means is not limited to the above two embodiments, and may be of any type as long as it detects a focus error by differential outputs of a plurality of light receiving sets. There is no problem.

Effects of the Invention As is clear from the above description, the present invention comprises: a light source that emits a luminous flux; a converging optical system that guides and converges the luminous flux onto the information recording surface of an information recording carrier on which information is recorded; a photoelectric detector having a plurality of light receiving cells that receive reflected light from the information recording carrier and output an electrical signal; a detection optical system that guides the reflected light from the information recording carrier to the photoelectric detector; and the photoelectric detector. A first focus error that obtains a first focus error signal by comparing the phase of the sum of output signals from a predetermined one or more light receiving cells and the sum of output signals of another one or more light receiving cells. a detection means and a predetermined one of the photoelectric detectors;
The sum of the output signals from one or more light receiving cells and the other one
a second focus error detection means for obtaining a second focus error signal by comparing the levels of the sum of the output signals of the one or more light receiving cells; and a compound focus error that is obtained by adding the first and second focus error signals. and a focus control means for controlling the focus of the converging optical system according to a signal, and in a frequency band below a predetermined frequency lower than the gain intersection of the focus control means, the first focus error detection means The second focus error detection means has a higher detection sensitivity than the first focus error detection means in a frequency band exceeding the predetermined frequency. By configuring at least one of the second focus error detection means to include a filter element, highly accurate focus control is performed using the phase difference between the read signals from the plurality of light receiving cells during normal playback, and the readout The effect is that focus control can be performed regardless of the presence or absence of a signal.

Furthermore, by configuring the first focus error detection means to include a low-pass filter or an integrator, it is possible to obtain the effect that the necessary focus control gain can be easily ensured even if there is no read signal.

[Brief explanation of the drawing]

FIG. 1 is an enlarged view of the main parts of the optical head of a conventional optical information reproducing device, FIG. 2 is a signal waveform diagram for explaining the operation of the focus control means of the conventional optical information ζ main device, and FIG. The figure is a perspective view of the main parts of the optical head of an optical information reproducing device according to an embodiment of the present invention, FIG. 4 is a block diagram of the circuit portion of the focus control means in the embodiment of the present invention, and FIG. FIG. 6 is a frequency characteristic diagram of the first and second focus error detection means in the embodiment of the present invention, and FIG. be. 10... light source, 13... converging lens,
14... Beam splitter, 16...
Cylindrical lens, 16°41...Photoelectric detector, 16
a, 16b, 16c. 16d, 41a', 41b, 41C, 41d...-
・Light receiving cell, 20, 21. 22, 23, 28...
・Adder, 24...Subtractor, 26...
Phase comparator, 26... Reducing pass filter, 29
...control circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 Figure 5 Inkyushu Moat Maki

Claims (2)

[Claims] (1) A light source that emits a luminous flux, a converging optical system that guides and converges the luminous flux onto the information recording surface of the information recording carrier on which information is recorded, and an electrical signal that receives reflected light from the information recording carrier. a photoelectric detector having a plurality of light-receiving cells that output
a detection optical system that guides reflected light from the information recording carrier to the photoelectric detector; a sum of output signals from one or more predetermined light receiving cells of the photoelectric detector; and one or more other light receiving cells. a first focus error detection means for obtaining a first focus error signal by comparing the phase of the sum of the output signals of the photoelectric detector; A second focus error signal is obtained by comparing the level of the sum of the output signals of one or more light receiving cells.
The focus error detection means adds the first and second focus error signals and calculates
+Kaiyoshi Senkyu ^ Focus control means for controlling the object point,
In a frequency band below a predetermined frequency lower than the gain intersection of the focus control, the first focus error detection means has higher detection sensitivity than the second focus error detection means, and in a frequency band exceeding the predetermined frequency, the first focus error detection means has a higher detection sensitivity than the second focus error detection means. At least one of the first and second focus error detection means includes a filter element so that the second focus error detection means has a higher detection sensitivity than the first focus error detection means. information reproducing device. (2) The optical information reproducing device according to claim (1), wherein the first focus error detection means includes a low-pass filter or an integrator.