JPH06101123B2 - Focus control device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention enables to set to an appropriate state and record or reproduce even when the optical system of a pickup or the reflectance of a disc varies. The present invention relates to a focus control device for an optical recording / reproducing device.

[Technical Background of the Invention and Problems Thereof] In recent years, the progress of industries related to information such as computers has been remarkable, and the amount of information handled has dramatically increased.

Therefore, in place of the conventional magnetic head, laser light is used to optically record information on a disk-shaped recording medium at high density,
There is a situation where an optical recording / reproducing apparatus capable of reproducing at high speed is drawing attention.

By the way, the above disk-shaped recording medium (hereinafter referred to as a disk)
In the case of recording or reproducing, it is necessary to set the optical system of the optical pickup, which is an objective lens system or the like, to a focus state and maintain the focus state. Therefore, in general, the error signal of the photodetector whose output changes according to the distance from the disc is used to set the optical system of the optical pickup within the focus servo area where focus can be maintained, and then the focus servo is set. A method of holding the focus state by operating it is adopted.

As a conventional example of this type of apparatus, there is, for example, JP-A-56-7246.

As disclosed in this conventional example, by using the critical angle method, the error signal output of the photodetector changes in a substantially sinusoidal shape with distance in the vicinity of the focus,
When the focus servo is actuated when entering the area that changes in a sine wave shape, the focus state can be set to approximately the center of the waveform.

However, when there are variations in the optical system part of the optical pickup, the photodetector, or the like, or when the reflectance or transmittance of the disc varies from product to product,
Since the output level or the output waveform of the error signal changes, there is a problem that the autofocus cannot be set correctly.

[Object of the Invention] The present invention has been made in view of the above points, and is for an optical recording / reproducing apparatus that can be pulled into the focus servo area even when the optical system of the optical pickup or the reflectance of the disk varies. An object of the present invention is to provide a focus control device.

[Outline of the Invention] The present invention drives the optical system of an optical pickup before actually operating the autofocus to take in the error signal output of the photodetector in each state, and based on the error signal, focus servo control is performed. By setting a threshold for discrimination when the loop is turned on, it is possible to reliably perform autofocus without being influenced by variations in the optical pickup, reflectance of the disc, and the like.

Embodiments of the Invention The present invention will be specifically described below with reference to the drawings.

1 to 4 relate to one embodiment of the present invention, FIG. 1 shows a main part of one embodiment, and FIG. 2 shows a focus error signal output waveform with respect to a distance between a focusing optical system and a disc. FIG. 3 shows a flow chart of one embodiment, and FIG. 4 shows a flow chart for focus search.

The main part of an optical recording / reproducing apparatus 1 having one embodiment of the present invention has the configuration shown in FIG.

The laser light (not shown) is focused by the objective lens 2 onto the disk 3 as an optical recording medium that is rotationally driven so that it can be irradiated in a spot shape.

The laser light is used in a high energy density state during recording, and is used in a weak energy density during reproduction.

The objective lens 2 is driven by the drive signal level applied to the focus coil 5 via the focus driver 4,
The distance from the disc 3 is changed, and in the normal use state, the laser beam is focused on the disc 3 in a spot form (just).

The light reflected by the disk 3 is made into a parallel light flux by the objective lens 2, and then the optical path is changed by the action of the λ / 4 plate and the polarization beam splitter, and the light is incident on the four-division photodetector 6 used for focus setting. It (Specifically, for example, the one described in JP-A-56-7246 may be used.) The photodiodes D ₁ , D ₂ , in the four-division photodetector 6 described above.
The outputs of D ₃ and D ₄ are added by adders 7 and 8, respectively. Then, the outputs of the adders 7 and 8 are further converted into the DC addition signal S _DC and the focus error signal S _FER by the adder 9 and the subtractor (differential amplifier) 10, respectively, and are input to the A / D converter 12 of the CPU 13. Is done.

The focus error signal S _FER is obtained by the critical angle method.
As the objective lens 2 moves away from the disk 3, the focus position (JUST FOCU)
S) As it approaches L _J , the output level once drops to a valley, then rises sharply within the focus pull-in range W that includes the focus position L _J in the approximate center, and then rises sharply again after reaching the maximum point. It is characteristic that it shows an output waveform that drops and gradually increases through a valley portion.

Therefore, in the recording / reproducing apparatus 1 according to the first embodiment, the objective lens 2 is set in advance to a distance state close to the disc 3 in FIG. 2, then the objective lens 2 is moved away, and the level Sa in the middle of falling into the first valley is reached. Is detected, and then the focus servo is operated when the level Sb is detected within the focus pull-in range W, for example, at a position sufficiently close to the focus position L _J , so that a (just) focus state can be set in a short time thereafter. I am doing it.

By the way, the CPU 13 reads, for example, program data written in a ROM (not shown), decodes the program content, and sequentially executes the program data.

That is, the CPU 13 sequentially changes the digital data output DS for setting the focus level via the I / O port B (reference numeral 14), and this output is converted into an analog amount by the D / A converter 15, and the focus coil 5 A signal for gradually moving the objective lens 2 away from the disc 3 is applied.

Then, the focus error signal S _FER detected at each position of the objective lens 2 moved by a small amount is converted into digital data DS _FER by the A / D converter 12, and is converted by the arithmetic operation logic unit (ALU) 17 into the first data. The arithmetic processing according to the flowchart shown in FIG. 3 is performed. When each arithmetic processing is performed, the next digital data DS _FER is sequentially input, and the same arithmetic processing is performed.

In other words, when the level setting process for discrimination starts, I / O
The memory data for driving the objective lens 2 output from the port B14 is cleared, and the maximum value S _FERMAX and the minimum value S _FERMIN of the focus error signal S _FER are respectively stored in the ALU17 register of the CUP 13 or another register (or an attached memory). Digital data DS _FERMAX and DS _FERMIN are set to 0 and 255, for example. These 0 and 255 are good if the A / D conversion level at the time of moving the objective lens 2 has variations in the reflectance or the like of the disk 3 as long as it is within this range. Then, the data for driving (moving) the objective lens 2 output from the I / O port B14 is increased by one step (for example, 1 bit), output from the photodetector 6 at this time, and converted by the A / D converter 12. The digital data DS _{FER of} the focus error signal S _{FER generated} is compared with the maximum value data DS _FERMAX to determine whether this digital data is DS _FER > DS _FERMAX . If the above determination is YES, The data DS _FER is replaced by the maximum value data DS _FERMAX , otherwise the following decision DS _FER <DS _FERMIN is made. That is, DS _FER <
If the determination of DS _FERMIN is YES, the replacement is performed, and if not, the digital data of the I / O port B14 is incremented again. By increasing by this step, the objective lens 2 is moved by a small amount from the disk 3, and the focus error signal S is passed through the A / D converter 12 in that case.
_FER digital data DS _FER is above as determined DS _FER> DS _Fermax by ALU17 of, DS _FER <DS _FERMIN are sequentially performed, DS _Fermax according to the determination, substitution DS _FERMIN is performed.

In example FIG. 2, an objective lens 2 at the stage of step 0 is the distance from the disk is set to L _0, the digital data DS _FER = DS _CO of the focus error signal S _FER level S _CO in this state is captured, DS _FER (that is, DS _CO )> 0
And DS _FER (that is, DS _CO ) <255, DS _FERMAX =
_{Replaced by} DS _CO , DS _FERMIN = DS _CO .

In the next step 1, the objective lens 2 is moved by a small amount,
The focus error signal in this state is set to L ₁ , and the same determination as described above is performed. If the determination is YES, replacement is performed.

The maximum value data DS _{FERMX is} obtained by sequentially performing this arithmetic processing at least for the range including the servo _pull-in range W.
Is set to the maximum value level S _MAX in Fig. 2 and the minimum value data
DS _FERMIN will be set to the digital data corresponding to the minimum value level S _MIN .

In this way, maximum value data DS _FERMAX and minimum value data
When DS _FERMIN is obtained, the digital data DSb, DSa of the discrimination reference levels Sb, Sa are obtained by the arithmetic operation shown in FIG. 3 (b), (c) or (d).

In Fig. 3 (b), the level Sb is the maximum value S _MAX and the minimum value.
It is set to the average value of S _MIN , and level Sa is the minimum value with level Sb.
Set by the average value of S _MIN .

Not limited to the one shown in FIG. 3 (b), the same figure (c),
The levels Sb and Sa may be set as in (d).
In addition, "128" in the same figure (d) means the maximum data of digital conversion data.

These levels Sa and Sb are the actual focus error signal S
Since it is obtained based on _FER , it is properly set according to the disc 3 even when the disc 3 is exchanged and the reflectance changes. Further, even when the optical system of the optical pickup or the photoelectric conversion efficiency of the photodetector 6 is different for each product, it is set based on the focus error signal S _FER output by the photodetector. There is almost no influence on the optical system or the photodetector.

According to the first embodiment, the level value for discrimination can be obtained with almost no need for a memory for storing data.

When the focus level is set as described above, the focus search is performed according to the flowchart shown in FIG. 4, and after passing through the level Sa, the focus servo is turned on when the focus becomes equal to or higher than the level Sb. A loop is formed and the focus state is quickly set.

That is, after the focus search is started and the data contents of the I / O port B14 are cleared, the I / O port B14 is cleared.
Output data sequentially increases in step width, and this output data is converted into an analog amount through the D / A converter 15 and applied to the focus coil 5 through the focus driver 4 so that the objective lens 2 is sequentially moved away from the disc 3. To Then, at the position where the objective lens 2 is being moved, the digital data of the focus error signal S _FER output from the photodetector 6 through the A / D converter 12 is captured by the CUP 13 and corresponds to the level Sa. The ALU 17 compares whether the digital data is larger than the digital data. The acquisition of each A / D conversion data is performed, for example, 40 times in each step. Then, when compared, when it is larger than the level Sa (the digital data DSa of the level Sa), 4
If it does not reach 0 times, the A / D conversion data is continuously fetched, and if it reaches 40 times, the output data of the I / O port B14 is increased by one step width, and then the A / D conversion data continues. And the comparison with the digital data DSa of the level Sa are repeated.

Through this process, the objective lens 2 moves away from the disc 3 in a stepwise manner or continuously, so that the focus error signal S _FER becomes smaller than the level Sa. Then, when it becomes smaller than the level Sa, the output data of the I / O port B14 is increased by one step, and this time, the digital data DS _{FER of the fetched} focus error signal S _FER.
Is compared with the digital data DSb of the level Sb. Similarly, for example, 40 for each step
The A / D conversion is performed once, and the comparison with the digital data DSb of the level Sb is repeated with the A / D converted data 40 times at each step.

When 40 comparisons were made for each of the above steps, the level
If Sb is not exceeded, the output of I / O port B14 is successively increased by the step width.

By the above focus search, the objective lens 2 is gradually moved away from the disc 3, so that it will soon cross almost the focus position L _J of the level Sb, and the level Sb will be reached at this position.
Get bigger. Then, the signal data for turning on the focus servo is output from the I / O port A18, and the output of the focus error signal S _FER does not go through the CUP 13 but goes through the low pass filter (LPF) 19 and the phase compensation network (PCN) 20. The switch 21 such as analog is turned on and output to the focus driver 4.

This focus error signal S _FER causes the objective lens 2
Is almost held at the focus position L _J with respect to the disc 3. That is, this focus error signal S _FER
When the distance from the focus position L _J increases, the polarity of the signal output returns to the focus position L _J, and when it gets too close, the polarity changes to the direction returning to the focus position L _J. Acts to hold on.

Further, this focus error signal S _FER is held at a position slightly deviated from the focus position L _J when there is an influence of temperature drift of the differential amplifier 10 or the like, but the direct current addition signal S _DC is A / D. After passing through the converter 12 into the register of the CPU 13 at an appropriate interval, the preceding data is compared and a correction signal for moving the objective lens 2 in the direction in which the value becomes larger is output, and this signal is added to the focus drive output. Since it is output, the focus state is always maintained without being affected by the temperature drift and the like.

Although the objective lens 2 is moved in the direction away from the disc 3 to set the focus level in the above description, the present invention is not limited to this, and is moved in the direction closer to the disc B. Alternatively, the focus level may be set.

In this case, the level Sa outside the focus pull-in range
It is desirable to use another level on the opposite side to the determination for the focus search for more reliable autofocus.

Note that the above-described setting formulas for the levels Sa, Sb, etc. are not limited to those described above.

Further, the present invention is not limited to optical recording / reproducing devices such as optical disks, but can be widely applied to recording / reproducing devices such as magneto-optical disks.

Further, it is desirable that the discrimination threshold value setting means of the present invention is carried out prior to the actual focus search, but it is not necessarily carried out before the focus search, and it is carried out periodically or the like. Is also good. Further, the control level can be held by the backup power source even when the power is turned off, and can be corrected or replaced with an updated value when the level is updated.

The maximum value of the peak value can be detected through the hold circuit, or the minimum value can be detected through the peak value hold circuit through the inversion circuit.

Further, although the critical angle method has been described in the embodiment, it can be applied to other focus detection methods such as the astigmatism method.

When the reference level is set while the disc is rotated, the data may be captured in synchronization with the rotation so that the reflected or transmitted signal is always captured from the same location.

As described above, according to the present invention, in the focus control device that operates the focus servo loop when the focus error signal reaches a predetermined reference value of the focus servo pull-in range, the operation of the focus servo loop is performed. The optical system of the optical pickup is moved prior to the above, and the reference value is determined from the actual focus error signal detected at least in the focus servo pull-in range at that time. Even if the photoelectric conversion efficiency or the reflectance of the disc varies, the reference value corrected according to the influence can be obtained. As a result, it becomes possible to reliably perform autofocus.

Further, when the focus search is performed, the focus state can be set surely and in a short time.

[Brief description of drawings]

1 to 4 relate to an embodiment of the present invention. FIG. 1 is a configuration diagram showing a main part of the embodiment, and FIG. 2 is a focus error signal output with respect to a distance between a disc and a focusing optical system. FIG. 3 is a characteristic diagram showing waveforms, FIG. 3 is a flow chart of one embodiment, and FIG. 4 is a flow chart in the case of focus search. DESCRIPTION OF SYMBOLS 1 ... Optical recording device, 2 ... Objective lens 3 ... Disk 4 ... Focus driver 5 ... Focus coil 6 ... 4-division photodetector, 7,8 ... Adder 12 ... A / D converter, 13 ... CPU 14, 18 ... I / O port 17 ... ALU (Arithmetic operation logic unit) 21 ... Switch

Claims (1)

[Claims] 1. An optical pickup for recording or reproducing information by condensing and irradiating light of a light source in a spot shape on an optical recording medium by using a focusing optical system, and the optical system. On the other hand, a focus search means for moving the optical system to set the focus state from the defocus state, a focus error signal detection means corresponding to a deviation from the focus state when the focus search is performed, and the focus error In a focus control device having focus servo means for activating a focus servo loop when a signal reaches a predetermined reference value in the focus servo pull-in range, the optical system is moved prior to the operation of the focus servo loop, At that time, at least the focus server is detected by the detecting means. Focus control apparatus characterized by the maximum value and the minimum value of the focus error signal detected in the pull-in range determined from these maximum and minimum values that have been determined with a reference value determining means for determining the reference value.