JPH0677321B2 - Focus control device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention is an optical system which enables recording or reproduction by setting an appropriate state even when there are variations in the optical system of a pickup or the reflectance of a disc. The present invention relates to a focus control device for a recording / reproducing device.

[Technical Background of the Invention and Problems Thereof] In recent years, the progress of information industries such as computers has been remarkable, and the amount of information to be 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)
When recording or reproducing in, 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 the focus state can be maintained, and then the focus is adjusted. A method of holding the focus state by activating the servo is adopted.

As a conventional example of this type of device, 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 provides a focus control device that can be pulled into the focus servo area even when the optical system of the optical pickup or the reflectance of the disc varies. The purpose is to

[Outline of the Invention] The present invention drives the optical system of the 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, the focus servo is performed. By setting a threshold for discrimination when the loop is turned on, it is possible to reliably perform autofocus without being affected 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 an output waveform of a focus error signal with respect to a distance between a focusing optical system and a disk. FIG. 3 shows a flow chart of one embodiment, and FIG. 4 shows a flow chart in the case of 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 (just) in a spot shape on the disc 3.

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 (A specific optical system may be, for example, one described in JP-A-56-7246.) The photodiode D ₁ in the four-division photodetector 6
The outputs of D ₂ ; 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 a DC addition signal S _DC and a focus error signal S _FER by an adder 9 and a subtractor (differential amplifier) 10, respectively, and the A / D converter of the CPU 13
It is designed to be input to 12.

The focus error signal S _FER is obtained by the objective lens 2 by the critical angle method (for example, shown in Japanese Patent Laid-Open No. 56-7246).
As the distance from the disk 3 approaches the focus position (JUST FOCUS) L _J as shown in FIG.
After that, within the focus pull-in range W that includes the focus position L _J in the approximate center, the output waveform is characterized by a sharp rise, a sharp fall after reaching the maximum point, and a slow increase through the valley portion. Is.

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

By the way, the CPU 13 reads the program data written in the ROM (not shown), decodes the program contents, and executes them sequentially.

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 is output to the focus coil 5. Is applied with a signal for gradually moving the objective lens 2 away from the disk 3.

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 via the A / D converter 12 and stored in the memory 1.
Sequentially stored in 6. Therefore, the amount of digital data output from the I / O port B14 can be covered by the focus pull-in range W in FIG.
By setting the number of steps and the step width appropriately, the digital data DS _FER corresponding to the characteristics shown in FIG. 2 is sequentially stored in the memory 16.

Focus error signal S _{FER at} each minute displacement position
Data DS _FER of the focus error signal S output from the photodetector 6 when the digital data DS from the I / O port B14 is increased (or decreased) and output.
_{Since the FER} is simply stored in a digital quantity through the A / D converter 12 and stored sequentially, it can be performed at a very high speed.

This process is shown in the flowchart of FIG.

That is, the data content output from the I / O port B14 is cleared by the start of the level setting, and the objective lens 2 is positioned at the initial position. Then, when the step variable (index) I corresponding to moving the objective lens 2 by a minute pitch amount is set to 0 and this variable I is changed, A /
The digital data DS _FER of the focus error signal S _{FER fetched} through the D converter 12 is made to correspond to the level setting error signal data DS _FER (I). Then I / O
The digital data DS for moving the objective lens output from the port B14 is increased by one step, and the index I is increased by one in response to this, and the digital data DS _{FER fetched} through the A / D converter 12 at that time has an error. The signal data DS _FER (I) is sequentially written in the memory 16. When this process is repeated and the number of data output from the I / O port B14 reaches the specified number of steps (I / O
Port B is marked as FULL. ) Ends the data acquisition process.

When the above data acquisition is completed, index I = 0
The objective lens 2 is returned to the initial position by outputting the data. Then, the CPU 13 determines that the data D in the memory 16 is
_SFER is read and arithmetic operation logic unit (denoted as ALU) 17
The maximum value of data DS _FERMAX ,
Perform processing such as _{obtaining the} minimum value DS _FERMIN and the average value DS _FERAV .

This process is shown in FIG. 3 (b).

That is, the index I is cleared to 0, and the memory data DS _FER in this case is substituted into the registers for storing the maximum value DS _FERMAX , the minimum value DS _FERMIN , and the total sum value DS _FERTOT , respectively.

Then, the index I is increased by one, and if the memory data DS _FER (I) (I = 1 in this case) in that case is larger than the maximum value DS _FERMAX in the register, it is replaced with this large value, and it is smaller. If not, do not replace. If this memory data DS _FER (1) is smaller than the minimum value DS _FERMIN in the register, it is replaced with this value, and if not, it is not replaced. This is repeated by increasing the index I value by one. The memory data subjected to the processing such as comparison and replacement is added to _obtain the value of the total sum value DS _FERTOT . This process is index I
The index I is incremented by one until it reaches the maximum number (eg, 255), and when the maximum number is reached, the above total sum value DS _FERTOT is _added to the total number of steps (I = 0. It becomes the number +1.)
The average value DS _FERAV is obtained by dividing by.

Further, the digital data corresponding to the minimum value and the maximum value of the focus error signal waveform in FIG. 2 can be obtained by the above-mentioned processing such as comparison and replacement.

Then, as shown in FIG. 3C, the digital amount DSb of the discrimination level Sb in the case of focus servo is set to, for example, the average value DSb = DS _FERAV, and the digital amount of the discrimination level a is set.
Set DSa to DSa = S _FERAV + S _FERMIN ) / 2.

When the above levels Sa, Sb are required, these levels Sa, Sb
Since Sb is obtained based on the actual focus error signal S _FER , it is appropriately set according to the disc 3 even when the disc 3 is exchanged and the reflectance changes. Also, when the optical system of the optical pickup or the photoelectric conversion efficiency of the photodetector 6 is different for each product,
Focus error signal output by the photodetector
Since it is set based on _SFER , it is hardly affected by the optical system of the optical pickup or the photodetector.

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 level becomes equal to or higher than the level Sb, and the focus loop is executed. 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 taken into the CPU 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, 40 A / s for each step
D conversion is performed, 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. In addition, it is desirable that the movement step width at the time of detecting the level Sb be smaller than that at the level Sa.

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 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 pass through the CPU 13 but through the low pass filter (LPF) 19 and the phase compensation network (PCN) 20. The switch 21 for analog or the like is turned on, and the signal is 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. A correction signal, which is taken into the register of the CPU 13 through the converter 12 at an appropriate interval and moves the objective lens 2 in a direction in which the value becomes larger than the preceding data, 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 the objective lens 2 is moved in the direction closer to the disc 3 to focus. The level may be set.

In this case, the level Sa outside the focus pull-in range W
It is desirable to use it for the determination for focus search of another level Sd between the level Sc and the level Sc in addition to the level Sc corresponding to the above for more reliable autofocus.

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

The present invention is not limited to optical recording / reproducing devices such as optical discs, but can be widely applied to recording / reproducing devices such as magnetic discs.

Further, it is desirable that the discrimination threshold value setting means of the present invention is carried out prior to actual focus search.
The focus search is not necessarily performed before the focus search but may be performed regularly or the like. Further, the discriminating level can be held by a backup power source even when the power is off, and can be corrected or replaced with an updated value when the level is updated.

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

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. Prior to the above, the optical system of the optical pickup is moved, the values of the actual focus error signals detected at least in the focus servo pull-in range are sequentially stored at that time, and the reference value is determined based on the stored value. Therefore, even if the photoelectric conversion efficiency of the optical system of the optical pickup or the photodetector 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 with respect to a distance between a disc and a focusing optical system. FIG. 3 is a characteristic diagram showing an output waveform, FIG. 3 is a flowchart for explaining the operation of the first embodiment, and FIG. 4 is a flowchart for focus search. 1 ... Optical recording / reproducing apparatus 2 ... Objective lens, 3 ... Disk 4 ... Focus driver 5 ... Focus coil, 6 ... Photodetector 7,8,9 ... Adder, 10 ... Subtractor 12 …… A / D converter, 13 …… CPU 15 …… D / A converter, 16 …… Memory

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 support is detected by the detection means. Focus control unit calculates the average value of the values of the focus error signal detected in the ball pull-in range, and having a reference value determining means for determining the reference value based on this value.