JPS61158035A - Device for detecting light information - Google Patents

Abstract

PURPOSE:To enable correct focus drawing by providing a device provided with the first and secod photodetectors that receive more than 1/2 and less than 1/2 of reflected light and obtains timing to draw an objective lens to focal position. CONSTITUTION:The device is provided with photodetectors C, D for detecting off track error that receive more than 1/2 of reflected light from an information recording medium and photodetectors A, B for detecting error between an objective lens and focal position that receives less than 1/2 of reflected light from the information recording medium. Output current of photodetectors A, B is converted to voltage, and a tracking error signal FE of the difference is calculated by a subtracter 19, and output current of photodetectors C, D is converted to voltage and a tracking error signal TE of the difference is calculated by a subtracter 22. The signal FE is subtracted from the signal TE and the result is compared with zero level and thereby a signal is obtained from a comparator 24. A sequence controlling circuit 10 controls a switch 12 and a saw tooth voltage generating circuit 13. When the circuit 10 generates saw tooth voltage in the saw tooth voltage generating circuit 13, the objective lens 5 approaches a disk 6 with increase of the voltage.

Description

[Detailed description of the invention] (Technical field) The present invention relates to an optical information detection device such as an optical disk device.

(Conventional technology) FIG. 2 shows an example of the configuration of a conventional optical pickup.

The light beam from the semiconductor laser is made into parallel light by a coupling lens 2, passed through a polarizing beam splitter 3 and a wave plate 4, and is focused by an objective lens 5 onto an information recording medium 6 as a minute spot of about 1 μm. The reflected light from the information recording medium 6 passes through the objective/zoom 5.4 wavelength plate 4 and the polarizing beam splinter 3, and is condensed by the condenser lens 7, and the light beam b is blocked by the light shielding plate 8 and remains. The light flux of b is received by a plurality of divisions, for example, a half-side light-receiving element 9, spread over the condensing point.

This two-divided light receiving element 9 is composed of two divided light receiving elements A and B, and performs focus detection.

This focus detection method is called a knife method because the light shielding plate 8 acts as a knife, and the principle of focus detection is shown in FIG. That is, when focusing, the amount of light received by light receiving elements A and B is equal, but when the information recording medium 6 is closer to the objective lens 5 than the in-focus position, the amount of light received by light receiving element A is equal to that of light receiving element B.
On the other hand, when the information recording medium 6 moves away, the amount of light received by the light receiving element A becomes smaller than the amount of light received by the light receiving element B. In general, focus detection is performed so that the focus of the objective lens S is located within ±1 μm from the recording surface of the information recording medium 6, and the objective lens 5 is moved in the optical axis direction by a servo system (not shown) based on the detection signal to bring the focus to the focal point. Take control.

Generally, in order to avoid collision with the information recording medium 6, the objective lens 5 is focused away from the information recording medium 6 at the start of rotation and brought closer to the information recording medium 6 at the start of rotation. This is called focus pull-in.

An example of out-of-focus and inspection point detection characteristics using this focus detection method is shown by a solid line in FIG. In this example, the focus shift is 10°.
When it is 0 μm or more, no focus error signal is output. Therefore, in order to perform correct focus pull-in, conventionally, a sum signal of four light receiving element outputs corresponding to the total reflected light amount of the information recording medium 6, which is a disk with recording tracks formed in a concentric or spiral shape, has been used. That is, generally the light shielding plate 8 has a light receiving element C divided into two parts as shown in FIG.
9D is used to receive the reflected light P, and this light receiving element C,
A track error signal is obtained by taking the difference between the outputs of light receiving elements A, B, C, and D, and an information signal Rf (
(reading signal of information signal recorded on disk 6)
I am getting . The relationship between this sum signal Rf and defocus is shown by a broken line in FIG. By comparing the level of this sum signal with a constant voltage, it is detected that the objective lens 5 is within the focus detection range, and the focus servo system is turned on.

By the way, if the focus detection signal (difference signal between the outputs of light-receiving elements A and B) corresponding to the amount of light received by light-receiving elements A and B is called detection sensitivity, then as shown in FIG.
, C, D), the detection sensitivity peaks when the amount of light received by the light receiving elements C and D (shading rate) is 70 to 80%, and it is preferable to set this shading rate to 60 to 90%. I understand.

The layout is shown in FIG. 7, and the light-receiving elements C and D are set so as to receive 10 to 90% of the amount of total reflected light.

In this case, the farther the objective lens 5 is from the disk 6, the more the reflected light is concentrated on the light receiving elements C and D near the optical axis.
As shown in the figure, the sum signal remains almost constant even if the focus is significantly off. However, since it is preferable to take the information signal R/'' near the optical axis, the sum signal of the outputs of light receiving elements C and D is used here. Even if the sum signal of the outputs of light receiving elements A, B, C, and D is used, the tendency is similar.
If it blocks the light beam including the optical axis, it will not be possible to detect from the information signal Rf that the objective lens 5 has entered the focus detection range, and correct focus pull-in will not be possible.

(Objective) It is an object of the present invention to provide an optical information detection device that is a device with high focus detection sensitivity and can perform correct focus pull-in.

(Structure) The present invention includes a first light-receiving element for detecting off-track error, which receives at least b of the reflected light from the information recording medium, and a first light-receiving element which receives at least 4 of the reflected light from the information recording medium. a second light-receiving element for detecting an error between the objective lens and the focal position; and means for obtaining timing for drawing the objective lens to the focal position from output signals of the second light-receiving element and the first light-receiving element. With these, the above objectives are achieved.

FIG. 9 is a diagram illustrating that the tracking error signal TE (difference signal between the outputs of light receiving elements C and D) indicating an off-track error in the apparatus shown in FIG. 7 becomes as shown in FIG. 10. Reflected luminous flux P with respect to the dividing line between light receiving elements C and D
If the optical axis of the disc 6 is shifted by a small amount, the light beam P becomes parallel light at the in-focus position and the tracking error signal becomes zero, but if the disc 6 moves far away from the in-focus position, the light receiving element 8
The magnitude of the luminous flux at the top becomes smaller, and the difference in output between the light receiving elements C and D due to the optical axis shift cannot be ignored. Especially in Figure 9 (
In case C), the reflected light P is focused on the light receiving element 8, and the amount of reflected light is all concentrated on the light receiving element C, so that the tracking error signal becomes maximum. The (α) to (forces in FIG. 10 correspond to the states of (α) to (forces) in FIG. 9.

In addition, since the luminous flux on the light receiving element 8 in the state (α) has a small size, the dividing line between the optical axis and the light receiving element 8 is 1
It has been confirmed that even a deviation of about 0.00 μm has almost no effect on the accuracy of the track error signal.

Next, the structure and operation of the present invention will be explained based on examples.

FIG. 1 shows a first embodiment of the invention.

In this embodiment, in the apparatus shown in FIG. 7, when the 7-can control circuit 10 resets the 7-linop flop 11 and turns off the switch 12, it also sends a signal to the sawtooth voltage generation circuit 13 to generate a sawtooth voltage. This sawtooth voltage is outputted to a power amplifier 15 via an adder 14, and an actuator 16 drives the objective lens 5 in the optical axis direction to bring it closer to the disk 6. In addition, the output currents of the focus detection light receiving elements A and H are converted into voltages by the amplifiers 17 and 18, and a focus error signal FE consisting of the difference is calculated by the subtracter 19, and the track detection light receiving elements C1
The output current of D is converted into voltage by amplifiers 20 and 21, and a tracking error signal TE is calculated from the difference by subtracter 22. As shown in FIG. 10, the tracking error signal TE indicates that the objective lens 5 is about 1 point below the focal position.
The voltage reaches its peak at a distance of 50 μm, becomes unstable because the track signal appears near the zero cross, and as the voltage approaches the disk 6, the voltage reverses. In addition, the 7-occurrence error signal FE indicates that the objective lens 5 is at the focal position, 915
The value of 0 μm gradually increases from a distance, decreases rapidly when the objective lens 5 approaches the focal position by about 10 μm, reaches a zero cross at the focal position, and reaches a peak when the objective lens 5 approaches the disk 6 by about 10 μm. reach Therefore, the focus en-signal FE from the subtracter 19 is subtracted from the tracking error signal TE from the subtracter 22 in the subtracter 23, and the result is compared with the zero level in the comparator 24. A signal such as is obtained from the comparator 24. It is unclear whether the broken line in the figure is a high level or a low level. The sequence control circuit 1o receives the output signal of the comparator 24 and controls the switch 12 and the sawtooth voltage generation circuit 13. . When the sequence control circuit IO causes the sawtooth voltage generation circuit 13 to generate a sawtooth voltage, the objective lens 5 approaches the disk 6 as the voltage increases.

Go. At this time, 7 rig 7 o cup 11 is control 2.
The rising edge of the output signal No. 4 is detected, the output becomes high level, and this is latched. Switch 12 is clip 70
When the latch output of the knob 11 becomes high level, the off state changes to the on state. Therefore, the 7-occurrence error signal FE from the subtracter 19 is sent to the adder 14 via the switch 12 and the servo circuit 25, and the focus servo loop is closed when the objective lens 5 almost reaches the focal position, and the focus servo is closed. The focus is accurately drawn in, eliminating the error of the focus servo locking at a point other than the focus position. Further, in this embodiment, since a threshold level is not set for determination, stable bifocus pull-in can be performed even if there are variations in the signal level.

FIG. 12 shows a second embodiment of the present invention, and FIG. 13 is a timing chart thereof. In this second embodiment, in the first embodiment, the focus error signal FE from the subtracter 19 is compared with the zero level in the comparator 26, and the rising edge of the output signal of the flip-flop 27/parator 26 is detected and the signal is Output. Comparator 2
The output signal of 6 changes from a low level to a high level when the objective lens 5 is exactly at the focal position, and when the objective lens 5 is at a position VC far away from the focal position and the focus error signal is almost zero. At times, the output signal of the comparator 26 changes from a low level to a high level due to noise or the like. The latch 28 latches the high level output signal of the flip-flop 11, and its output α2 allows the output signal of the flip-flop 27 to change from a low level to a high level. The high level output of the flip 70 knob 27 is latched by the latch 29, and the switch 12 is turned on by the output signal h2. Naori lip 70 tube 27
, latch 28°29huff! J Tsubu70ri7”lltof
il is cleared by a clear signal from the sequence control circuit 10.

FIG. 14 shows a third embodiment of the present invention, and FIG. 15 is a signal waveform diagram thereof. In the above embodiment, it was detected that the objective lens entered the focus pull-in range based on the difference between the focus error signal and the tracking error signal, but in the third embodiment, the tracking error signal and the tracking level were detected. By comparison, it is detected that the objective lens has entered the focus pull-in range. That is, in the third embodiment, the tracking error signal from the subtracter 22 in the above embodiment is compared with the thread tour level of the reference power supply 31 in the comparator 30, and its output is input to the flip-flop 11.

(Effects) As described above, according to the present invention, the first light receiving element receives at least b of the reflected light from the information recording medium and 1/1/2 of the reflected light
This device has a high focus detection sensitivity and has a second light receiving element that receives light of 2 or less, and the timing for drawing the objective lens to the focal position is obtained from the output signals of the first and second light receiving elements, so correct focus drawing can be performed. It can be carried out.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the first embodiment of the present invention, FIG. 2 is a diagram showing an example of the configuration of a conventional pink-up, FIG. 3 is a diagram showing the focus detection principle of the pink-up, and FIG. A plan view showing the light receiving element of the same pickup, Fig. 5 is a focus detection characteristic diagram of the same pickup, Fig. 6 is a focus detection characteristic diagram of another pickup, Fig. 7 is a diagram showing the same pickup, and Fig. 8 is a diagram showing the same pickup. A characteristic diagram of the pickup; FIG. 9 is an explanatory diagram of the trunk misalignment error of the same pickup; FIG. 10 is a characteristic diagram of the tracking error signal and focus error signal;
The figure shows the comparator output of the first embodiment.
2 is a block diagram showing a second embodiment of the present invention, FIG. 13 is a timing chart of the second embodiment, FIG. 14 is a block diagram showing a third embodiment of the present invention, and FIG. 15 is a timing chart of the second embodiment. It is a signal waveform diagram of 3rd Example. A, B, C, D...light receiving element, 19.22.
23...Par subtractor, 24.26.3(1...Comparator, 11.27...Flip-flop, 2
8.29...Latch. U/Genzu Z-bacteria most Z-shaku/7f? ■. 2゜

Claims (1)

[Claims] A device that converges a laser beam as a minute spot on an information recording medium through an objective lens, detects the reflected light with a light receiving element through the objective lens, and reads an information signal recorded on a track on the information recording medium. a first light-receiving element for detecting an off-track error, which receives 1/2 or more of the reflected light through the objective lens; A second light-receiving element for detecting an error between the objective lens and the focal position, which receives light, and a timing for drawing the objective lens to the focal position based on the output signals of the second light-receiving element and the first light-receiving element. An optical information detection device characterized by comprising: means for obtaining.