JPH02254635A - Pregroup crossing signal detector - Google Patents

Abstract

PURPOSE:To surely detect a pregroup crossing signal even when the reflectance of an optical recording medium varies and a light quantity to irradiate is widely fluctuated by comparing mean value detected with a mean value detecting means and the output signal of a photodetector element. CONSTITUTION:The detector is equipped with the mean value detecting means to detect the mean value of the output signal from a photodetector 9 and a comparing means to compare the detected mean value with the output signal from the photodetector 9. For the mean value detecting means, it is composed of, for example, sample holding circuits 16 and 17 to obtain the maximum value and minimum value, respectively, of the output from the photodetector 9 and a mean value arithmetic circuit 18 to obtain the mean value from the output signals. Thus, by always comparing the output signal from the photodetector 9 with the mean value, the pregroup crossing signal can be obtained, and even when the reflectance of the optical recording medium and the light quantity of a focused light to irradiate the optical recording medium are widely fluctuated, the pregroup crossing signal can be always correctly obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention optically records/reproduces information or records/reproduces information by irradiating an optical recording medium such as an optical disk with a focused beam of a semiconductor laser, gas laser, etc. Detection of pregroove crossing signals used in optical recording and reproducing devices that perform playback and erasure!
Regarding equipment.

[Prior Art] Conventionally, as an optical recording medium used in the above-mentioned optical recording/reproducing apparatus, there is one as shown in FIG. 6, for example. This optical recording medium 100 is of a type having a recording layer on one side, and includes a transparent substrate 102 provided with a pregroove 101, a recording layer 103 provided on the entire surface of this transparent substrate 102, and this recording layer. 103 and a protective layer 104 provided on the entire surface thereof, the main part thereof is constituted. In the figure, 10
5 indicates a bit.

In order to reproduce the information recorded on the optical recording medium 100, as shown in FIG. The recorded information is reproduced by inputting it to the element.

By the way, call the target track of the optical recording medium,
When reproducing the recorded information recorded in the pregroove of the target track, the optical head 106 is moved across the pregroove 101 as shown in FIG. A signal crossing 101 is detected. Then, the number of these pregroove crossing signals is counted, and the optical head 106 is moved to the desired pregroove 10.
Move it to 1.

A device for detecting this pregroove crossing signal is C.
There is one as shown in Fig. 9. That is, this pregroove crossing signal detection device uses the semiconductor laser 110
The laser beam emitted from the collimator lens 11
1 into parallel light, and the parallelized beam is shaped into a circular beam by a beam shaping prism 112.

Then, this circular beam is passed through a beam splitter 113 and a quarter-wave plate 114, and is focused by an objective lens 115 into a circular beam having a diameter slightly larger than the width of the pregroove 101, as shown in FIG.
Irradiate to 0.

Next, the reflected light from the optical recording medium 100 is returned through the same optical path as above, reflected laterally by the beam splitter 113, and the reflected beam is passed through the lens 116 and the cylindrical lens 117 to the four-part light receiving element 11.
8. Then, as shown in FIG. 11, a signal obtained by processing the output signal from the four-division light receiving element 118 is a signal 119 that changes in accordance with a change in the amount of reflected light caused by the optical head 106 crossing the pregroove 101. Become.

Therefore, as shown in FIG. 12, the signal 119 is
Compared with the reference voltage VR by the comparator 120,
A method is adopted in which the position of the optical head 106 is controlled by detecting a pregroove crossing signal 121 generated when the optical head 106 crosses the pregroove 101 and counting the number of detected pregroove crossing signals 121. ing.

However, in this case, the reflected light from the pregroove 101 of the optical recording medium 100 is converted into an electrical signal 119 by the four-part light receiving element 118, and this signal 119 is
Since the pregroove crossing signal 121 is detected by comparing '1120'QN quasi'af pressure VR and
- If the intensity etc. of 110 fluctuates, the optical recording medium 10
The intensity of the reflected light from 0 changes. Therefore, the output signal 119 from the quadrant light receiving element 118 is 1. As shown in FIG. 13, when the voltage is lower than the reference voltage VR, even if this signal 119 is passed through the comparator 120, the pregroove crossing signal 121 cannot be obtained, and the optical head 106
Therefore, there is a problem in that the crossing of the pregroove 101 cannot be detected.

Therefore, as a method that can solve this problem, there is a method as disclosed in Japanese Patent Application Laid-open No. 171637/1983 (FIG. 3 of the same publication). Rather than directly comparing the output signal of the two-split light receiving element with a reference voltage using a comparator, the sum of the output signal of the two-split light receiving element is passed through a peak holder circuit to obtain its peak value. A difference signal is obtained between the peak value of the output signal of the sum of the elements and the output signal of the sum of the two-split light-receiving elements. By comparing this difference signal with a reference voltage using a comparator, it is possible to reliably detect the lateral opening signal of the pregroove even if the reflectance of the optical recording medium changes. be.

[Problems to be Solved by the Invention] However, the above-mentioned prior art has the following problems. In other words, since the difference signal between the peak value of the sum output signal of the two-split light-receiving element and the sum output signal of the two-split light-receiving element itself is obtained, the difference signal corresponding to the peak value of the sum output signal of the two-split light-receiving element It is possible to detect a change in the output signal of the sum of the two divided light-receiving elements using a portion of the optical recording medium with a high reflection intensity as a reference. Therefore, even if the reflection intensity of the optical recording medium varies or the intensity of the light irradiated onto the optical recording medium fluctuates, it can be accommodated to some extent, but the intensity of the light irradiated onto the optical recording medium will vary. In cases where there is a large fluctuation, the difference signal between the peak value of the sum output signal of the two-split light receiving element and the sum output signal of the two-split light receiving element itself may be lower than the reference voltage, and the difference signal may become lower than the reference voltage. There was a problem that the signal could not be detected accurately.

[Means for Solving the Problems] Therefore, the present invention has been made to solve the above-mentioned problems of the prior art. , a pre-groove crossing signal detection giI that can reliably detect a pre-groove crossing signal even when the amount of light from a light source irradiating an optical recording medium varies greatly! Our goal is to provide the following.

That is, in the present invention, an optical recording medium is irradiated with focused light, the reflected light from the optical recording medium is received by a light receiving element via an optical system, and the focused light is detected by an output signal from the light receiving element. In a pregroove crossing signal detection device for detecting a signal when crossing a pregroove, average value detection means detects an average value of output signals from the light receiving element.

The apparatus is configured to include a comparison means for comparing the average value detected by the average value detection means and the output signal from the light receiving element.

The average value detecting means may include, for example, a sample-and-hold circuit that calculates the maximum and minimum values of the output signal from the light-receiving element, and an average value calculation circuit that calculates the average value from the output signal of this sample-and-hold circuit. used. However, the present invention is not limited to this, and as the average value detection means, a low-pass filter or the like may be used to determine the DC component of the output signal from the light receiving element, that is, the average value.

Further, as the comparison means, for example, a normal comparator is used.

[Operations] This invention includes an average value detecting means for detecting the average value of the output signal from the light receiving element, and a comparing means for comparing the average value detected by the average value detecting means and the output signal of the light receiving element. Since the output signal from the light receiving element is always compared with its average value, the pregroove crossing signal can be obtained, and the reflectance of the optical recording medium and the focus irradiated onto the optical recording medium can be determined. Even when the amount of light fluctuates greatly, the pregroove crossing signal can always be accurately determined.

[Example 1 The present invention will be explained below based on illustrated embodiments.

FIG. 3 shows an optical recording/reproducing apparatus to which the pregroove crossing signal detection apparatus according to the present invention is applied.

This optical recording/reproducing device 1 includes a semiconductor laser 2 and an elliptical beam L emitted from the semiconductor laser 2.
A collimator lens 3 that converts the laser beam L8 into parallel light, a beam shaping prism 4 that shapes the laser beam L8 into light with a circular cross section, a beam splitter 5 that splits the beam LB, and linearly polarized light and circularly polarized light. mutually convert 1/
A four-wavelength plate 6, an objective lens 7, a condensing lens 8 that condenses the beam separated by the beam splitter 5, a cylindrical lens SL, and four light receiving elements 9a and 9b.
, 9C19d.

The optical disc 10 as an optical recording medium on which information is recorded and reproduced by the optical recording and reproducing device a1 has a fourth
As shown in FIG.
13, and a protective layer 14 provided on the entire surface of this recording layer 13.
The main part is composed of.

In the device 1, the elliptical laser beam L8 emitted from the semiconductor laser 2 is collimated by the collimator lens 3, and then shaped into a circular beam IB by the beam shaping prism 4. Thereafter, this beam LB passes through a beam splitter 5 and a quarter wave root 6, is focused by an objective lens 7, and is irradiated onto an optical disk 10.

The reflected light from the optical disk 10 returns along the same optical path as above, is reflected by the beam splitter 5, and is imaged on the two-split light receiving element 9 by the condenser lens 8.

The optical head H moves across the pregroove 11 of the optical disc 10 during a seek operation to move the optical head H to a target track.

FIG. 1 shows an electrical circuit of a pregroove crossing signal detection device. In the figure, reference numeral 15 indicates four light receiving elements 9a, 9b, and 9c of the quadrant light receiving element 9.

9d, two adjacent light receiving elements 9a, 9b and 90.
16 is a sample hold circuit for detecting the maximum value of the output signal from the differential amplifier 15; 17 is the output from the differential amplifier 15; A sample and hold circuit 18 for detecting the minimum value of the signal calculates an average value from the maximum and minimum values of the difference signals of the output signals from the quadrant light receiving element 9 held in both sample and hold circuits 16 and 17. An average value calculation circuit 19 compares the average value of the difference signal of the output signal from the four-division light receiving element 9 calculated by the average value calculation circuit 18 with the difference signal itself of the output signal from the four-division light reception element 9. A comparator 20 is a comparator for detecting the timing at which the tracking error signal, which is a difference signal of the output signal from the quadrant light receiving element 9, passes the O level.21 is a comparator for detecting the rising edge of the output signal from the comparator 2o and sample a mono multivibrator for detecting sample and hold timing by a hold circuit 16 and outputting a short width pulse;
22 is a mono-multivibrator for detecting the falling edge of the output signal from the comparator 20, detecting the timing of sampling and holding by the sample-and-hold circuit 17, and outputting a short-width pulse.

In the above configuration, the pregroove crossing signal detection device according to this embodiment detects the pregroove crossing signal as follows.

That is, during a seek operation to move the optical head H to a target track, as shown in FIG.
is moved from the outside in the radial direction of the optical disc 10 toward the inside, or from the inside in the radial direction toward the outside by a driving means (not shown).

At this time, since the optical disc 10 is rotating, when viewed from the coordinates fixed on the optical disc 10, the optical head H moves the pregroove 11 formed on the optical disc 13 obliquely, as shown in FIG. It will cross. In the figure,
p indicates a bit recorded within the pregroove 11.

In this manner, when the optical head H crosses the pregroove 11 of the optical disc 10, the semiconductor laser 2 emits a laser beam L8 for detecting a pregroove crossing signal, as shown in FIG. This semiconductor laser 2
The beam LB emitted from the collimator lens 3 becomes a parallel beam of light, and the beam LB that has become this parallel beam of light
is shaped into a beam having a circular cross section by the beam shaping prism 4. Thereafter, this circular beam LB passes through the beam splitter 5 and the quarter-wave plate 6, is focused by the objective lens 7, and is irradiated onto the optical disc 10.

Then, as shown in FIG. 3, the reflected light from the optical disk 10 is condensed by the objective lens 7, passes through the same path as above, and is passed through the beam splitter 5 to the four-split light receiving element 9.
The light is irradiated upward and converted into an electrical signal by this four-part light receiving element 9.

Four light receiving elements 9a of the above-mentioned four-division light receiving element 9.

Among the output signals from 9b, 9c, and 9d, the difference signal between the sums of the two adjacent light receiving elements 9a, 9b and 9c, 9d is sent to the differential amplifier 15 as shown in FIG. The respective difference signals a (FIG. 2(a)) are determined by the following.

The maximum value and minimum value of the signal a representing the difference between the output signals from the four-division light receiving element 9 are sampled and held by sample and hold circuits 16 and 17, respectively. This sample and hold operation is performed as follows.

That is, as shown in FIG. 2(f), the tracking error signal i, which is the difference signal between the output signals from the four-division light-receiving element 9, is the difference signal a between the output signals from the four-division light-receiving element 9.
This is a signal that has a phase difference of 90 degrees and also crosses the zero point. Therefore, the tracking error signal i, which is the difference signal between the output signals from the quadrant light receiving element 9, is input to the comparator 2o, as shown in FIG. 1, and is compared with 0■ by the comparator 20. As shown in FIG. 2 (0), the output from the comparator 20 rises when the tracking error signal i crosses the zero point from minus to plus, and rises when the tracking error signal i crosses the zero point from plus to minus. A falling pulse signal jIfi is obtained.

The output signal j of this comparator 20 is input to mono multivibrators 21 and 22, respectively. As shown in FIG. 2(h), the mono-multivibrator 21 is triggered by the rising edge of the output signal @j of the comparator 20, and outputs a short timing pulse k. The timing at which this timing pulse k is output is shown in Fig. 2 (f
), this timing coincides with the timing at which the tracking error signal i changes from negative to positive, and as is clear from Fig. 2(a), this timing coincides with the timing at which the tracking error signal i is 90 degrees out of phase with the tracking error signal i. This corresponds to the peak position of the difference signal a between the output signals from the different four-division light receiving elements 9, that is, the position of the maximum value.

Furthermore, as shown in FIG. 2(i), the mono-multivibrator 22 is triggered by the fall of the output signal j of the comparator 20, and outputs a timing pulse 1 with a short width. The timing at which this timing pulse 1 is output coincides with the timing at which the tracking error signal 1 changes from positive to negative as shown in FIG. 2(f), and this timing is the same as that shown in FIG. 2(a). As is clear from the above, it corresponds to the bottom position, that is, the position jδ of the minimum value, of the difference signal a of the output signal from the quadrant light-receiving element 9, which has a phase difference of 90 degrees from the tracking error signal i.

Therefore, the sample hold circuits 16 and 17, whose sampling timings are determined by the mono multivibrators 2 and 22, receive the output signal from the quadrant light receiving element 9, as shown in FIGS. 2(b) and 2(C). difference signal a
The maximum and minimum values of will be held.

Output signal e from the sample and hold circuits 16 and 17 above
, f, the average value is calculated by the average value calculation circuit 18.

The output signal q from this average value calculation circuit 18 is compared with the difference signal a itself between the output signals from the quadrant light receiving element 9 by a comparator 19, as shown in FIG. As shown in (e), a pregroove crossing signal is obtained.

In this way, the average value q of the difference signal of the output signal from the four-division light receiving element 9 is obtained, and the average value fig of the difference signal @a of the output signal from this four-division light receiving element 9 and the difference signal from the four-division light receiving element 9 are calculated. The comparator 19 compares the output signal with the difference signal a itself to detect a pregroove crossing signal.

Therefore, there may be variations in the reflectance of the optical disc 10, or the laser beam L emitted from the semiconductor laser 2 may
[Even if the intensity of 3 fluctuates greatly, the output signal a from the quadrant light receiving element 9 is always compared with its average fliQ, so that when the 1 northern beam LE3 crosses the pregroove 11 of the optical disc 10, it periodically The pregroove crossing signal can be accurately detected from the fluctuating signal a.

In this way, the average value detection means includes a sample and hold circuit that calculates the maximum and minimum values of the output signal from the light receiving element, respectively, and an average value calculation circuit that calculates the average value from the output signal of this sample and hold circuit. When using such a method, the response is fast, and there is no need to consider the time delay due to the value of the CR constant, unlike when a low-pass filter or the like is used as the average value detection means.

[Effects of the Invention] As described above, the present invention includes an average value detection means for detecting the average value of the output signal from the light receiving element, and an average value detected by the average value detection means and the output signal of the light receiving element. Since it is configured to include a comparison means for comparing the
Even if there are variations in the reflectance of the optical recording medium or the amount of light from the light source irradiating the optical recording medium varies greatly, the signal crossing the brig groove can be reliably detected.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the pregroove crossing signal detection device according to the present invention, FIGS. 2(a) to (i) are waveform diagrams showing the operation, and FIG. FIG. 4 is an explanatory diagram showing an optical disk; FIG. 5 is an explanatory diagram without showing the moving path of the optical head; FIG. 6 is an optical recording FIG. 7 is a perspective view showing a beam irradiated to the optical recording medium; FIG. 8 is a perspective view showing a reproduction operation; FIG. 9 is a configuration showing a conventional pregroove crossing signal detection device. Figure 10 is an explanatory diagram showing an optical recording medium.
1(a) and 1(b) are waveform diagrams showing the operation of a conventional pregroove crossing signal detection device, FIG. 12 is a circuit diagram showing a conventional pregroove crossing signal detection device, and FIG. 13 (
FIGS. 8A and 8B are waveform diagrams showing different detection states of the pregroove crossing signal. [Explanation of symbols] 9... Quadrant light receiving element 10... Optical disk 11... Pregroove 15... Summing amplifier 16.17... Sample hold circuit 18... Average value calculation circuit 19...・Comparator LB...Laser beam permission application Person: Fuji Xerox Co., Ltd. Patent attorney
Tomohiro Nakamura (1 other person) Fig. Fig. Laser beam Fig. Fig. 7 Fig. 10 Fig. 12 Fig. 13

Claims (1)

[Claims] An optical recording medium is irradiated with focused light, and the reflected light from this optical recording medium is received by a light receiving element via an optical system, and the focused light is pregrooved by the output signal from this light receiving element. The pregroove crossing signal detection device detects a signal when crossing a pregroove, comprising an average value detection means for detecting an average value of the output signal from the light receiving element, and an average value detected by the average value detection means. A pregroove crossing signal detection device comprising: comparison means for comparing the output signal from the light receiving element.