JP2006134466A - Focus control apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus control apparatus which is satisfactory even in occurrence of periodical wobbling or accidental mixture of noise while being capable of focus search operation with irreducibly minimum amplitude centering on a focal point. <P>SOLUTION: The apparatus comprises: an area determination means 14 for determining that a focus error signal is between a first threshold and a second threshold when setting a focus error signal value set so as to prevent an objective lens from colliding in a direction of approaching the side of a recording surface to be the first threshold and setting a focus error signal value set so as to prevent the objective lens from being separated too much in a direction of moving away from a recording surface to be the second threshold; a lens control means 16 for carrying out focus control so that the focus error signal may be between the first threshold and the second threshold based on an area determination signal outputted from the area determination means; and an amplitude measurement control means 21 for controlling the gain of the focus error signal by correcting the disturbance of an area determination signal caused by reverse movement of the objective lens caused in wobbling and detecting the maximum amplitude value of the focus error signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention moves the objective lens of an optical pickup used in an optical information recording medium such as an optical disc apparatus or the like in an apparatus for recording and reproducing information in the focus direction, thereby adjusting the focal position (focus point) of the objective lens. The present invention relates to a focus control device that detects and controls the moving direction of an objective lens.

In general, in an apparatus for recording or reproducing information with respect to an optical information recording medium, for example, an optical disk, as a process before pulling in the focus servo, the direction in which the objective lens of the optical pickup is orthogonal to the disk surface, That is, a focus search operation is performed in which the objective lens focal position (also referred to as a focal point) is searched by moving in the focus direction.
In this case, the objective lens is fixed so that the focal position of the objective lens can be detected even if the distance from the neutral position to the focal point of the objective lens varies due to the warp or surface deflection of the optical disc, the mounting accuracy of the lens actuator or disc motor, etc. The focus search operation is performed by moving the lens in the focus direction with a large amplitude (see, for example, Patent Document 1).

The state at this time will be described with reference to FIG. FIG. 9 is a graph showing the positional relationship between the disk surface and the tip of the objective lens during the focus search operation. FIG. 9 shows an example of focusing on a high density optical disk when there are a low density optical disk and a high density optical disk.
When the focus search operation starts, the objective lens approaches the disc surface from a neutral position far away from the disc surface, passes through the focal point for the high-density optical disc, and gets closer to the disc surface before reversing the direction of movement of the objective lens. And move away from the disk surface. During this time, the disk surface is irradiated with laser light through the objective lens and reflected by the disk surface, and this reflected light is detected by an optical sensor (not shown) to continuously obtain a focus error signal. Therefore, it can be recognized that the tip of the objective lens has passed the focal point for the high-density optical disc.
Thereafter, focus servo is performed by recognizing the position of the focal point, and the movement of the objective lens is controlled based on the focus error signal, and the objective lens moves so as to straddle the focal point. Will go.
JP-A-10-55546

By the way, the light spot formed on the information recording surface of the optical disc is determined by the NA (Numerical Aperture) of the objective lens and the wavelength of the laser beam, and the size of the light spot is proportional to the wavelength / NA, so In order to increase the density, it is necessary to adopt a laser beam having a short wavelength or increase the NA in order to obtain a minute light spot.
Further, in order to reduce the influence of the inclination of the disk surface with respect to the optical axis of the objective lens, the thickness from the light incident surface to the information recording surface is reduced in a high-density optical disk. Along with this, the distance from the tip of the objective lens to the disk surface, so-called working distance (WD), has also become shorter. For example, as shown in FIG. 9, in the case of a conventional optical disk, WD1, which is the distance from the focal point to the disk surface, is large, but WD2 in the case of a high-density optical disk is considerably small.

Further, since it is necessary to form a light spot on the information recording surface with high accuracy, the sensitivity of the focus error in the vicinity of the in-focus point has been increased. That is, as shown in FIG. 9, in the case of a high-density optical disc, the time width of the S-curve characteristic in the time axis direction of the focus error signal near the focal point is short.
Therefore, when the working distance is narrowed as described above, the conventional focus search method for detecting the focal position of the objective lens by moving the objective lens of the optical pickup largely with a constant amplitude in the direction perpendicular to the disk surface. Then, as shown in FIG. 9, there is a possibility that the objective lens and the high density optical disk collide.

In addition, in order to pull the focus servo stably, the temporal change rate of the focus error signal at the in-focus point needs to be a predetermined level or lower. The error change rate increases and the focus servo cannot be pulled in stably.
In order to solve this problem, it is possible to reduce the moving speed of the objective lens of the actuator in order to pull the focus servo stably by the conventional method, but this is used because it increases the time required for focus search I can't do it.

  The present invention has been devised to pay attention to the above problems and to effectively solve them. An object of the present invention is to provide a focus control device capable of performing a focus search operation with a necessary minimum amplitude centering on a focal point, and in particular, there is periodic surface shake on an optical disc during rotation, It is an object of the present invention to provide a focus control device capable of good focus control even when sudden noise is mixed in a focus error signal.

The present invention has the following configuration as means for solving the above problems. That is,
The irradiation light is focused on the recording surface of the optical information recording medium via the objective lens, and the objective lens collides with the optical information recording medium based on a focus error signal obtained from the return light from the recording surface. In the focus control apparatus for preventing the above, the objective lens exceeds the in-focus position with the focus error signal value at a focus position where the objective lens focuses the irradiation light on the recording surface as a reference value. The focus error signal value set in a direction approaching the recording surface side so that the objective lens does not collide with the optical information recording medium is set as a first threshold value, and the objective lens exceeds the in-focus position. The focus error signal value set in a direction away from the recording surface and set so that the objective lens is not too far from the optical information recording medium. When the threshold value is set, an area determination unit that determines and outputs that the focus error signal is between the first threshold value and the second threshold value, and an area determination signal output from the area determination unit The focus error signal returns to the in-focus position when the focus error signal approaches the recording surface exceeding the first threshold, or when the focus error signal exceeds the second threshold and moves away from the recording surface, the focus error signal Is controlled to be between the first threshold value and the second threshold value, and the lens control means for controlling the focus without causing the objective lens to collide with the optical information recording medium, and the objective lens is in focus. A plurality of rectangular amplitude measurement section signals are generated from the amplitude values of the region determination signals at a plurality of positions separated from the position by a predetermined distance, and a high level period and a low level period of the amplitude measurement section signal are generated. Amplitude measurement control means for detecting a maximum value and a minimum value of the focus error signal for each bell period, obtaining a maximum amplitude value as a difference between the maximum value and a minimum value, and controlling a gain of the focus error signal based on the maximum amplitude value And a focus control device.

According to the focus control device of the present invention, the following excellent effects can be exhibited.
The direction in which the objective lens is located closer to the disc surface than the focal point or away from the focal point based on the order of change in the level of the focus error signal. The objective lens is moved in the direction of approaching when it is far away, so that the objective lens can always perform a focus search operation with a small amplitude around the focal point.
Therefore, as in the conventional focus search method, the objective lens is moved in the focus direction in consideration of the variation of the focal position from the neutral position of the objective lens due to the warp and surface blur of the optical disc, the mounting accuracy of the lens actuator and disc motor, etc. It is not necessary to search for the focal position of the lens by moving a large distance, and even when the WD (working distance) is narrow, collision between the objective lens and the optical information recording medium when the focus servo is pulled in can be prevented.
In addition, even if there is inconvenience when the period of the optical disc surface shake and the period of the ramp-like signal coincide, or when there is sudden noise mixing in the focus error signal, it is possible to perform good focus control that eliminates these effects. is there.

Hereinafter, an embodiment of a focus control device according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a main part of an optical pickup including a focus control device according to the present invention, and FIG. 2 is a block diagram showing an area determination circuit of the focus control device.
In FIG. 1, an optical disk D, which is an example of an optical information recording medium, is rotationally driven by a spindle motor M. An optical pickup 2 is provided so as to be movable relative to the optical disc D. This optical pickup 2 has an objective lens 6 that is moved forward and backward by the actuator 4 in the surface direction (optical axis direction) of the optical disc D, and recording / reproducing laser light emitted by a laser element (not shown) is received. A light spot is formed by irradiating the disk surface through an optical system (not shown) and an objective lens 6. Here, the description of the actuator in the tracking direction is omitted.

The optical sensor 8 detects reflected light from the disk surface (recording surface). The focus error detection circuit 10 generates and outputs a focus error signal FS based on the signal from the optical sensor 8. At this time, the output level of the focus error signal FS varies depending on various variations such as the constant of the detection circuit, the intensity of the laser beam, the reflectance of the optical disk, etc., so that the gain is increased by the gain control signal from the amplitude measurement control circuit 21 described later. It is controlled and output. The tracking error detection circuit and the like are not shown.
This focus error signal FS is then input to the focus control device 12. The focus control device 12 includes an area determination circuit 14 that determines whether the objective lens 6 is positioned closer to or far from the disk surface than the focal point based on the focus error signal FS, and the area determination circuit. And a lens control circuit 16 for controlling the moving direction of the objective lens 6 according to the determination result of 14.

The lens control circuit 16 delays an output from the area determination circuit 14 by a predetermined time Td (see FIG. 4), and an actuator that forms a control signal for the actuator 4 based on the output of the delay circuit 18. A control circuit 19 is included. Then, the output of the actuator control circuit 19 is input to the driver 20, where an actuator driver signal DS is output.
As shown in FIG. 2, the region determination circuit 14 includes two comparator circuits 22 and 24, two rising edge detection circuits 26 and 28 each composed of a logic circuit individually connected to these outputs, and both rising edges. An output of the detection circuits 26 and 28 is constituted by an RS flip-flop 30 that is input to the S input and the R input, respectively. The RS flip-flop 30 outputs an area determination signal AS.
Threshold values + TH1 and -TH2 are input to the comparator circuits 22 and 24 as reference values, respectively. Each of the rising edge detection circuits 26, 28 inputs delay element circuits 26A, 28A for delaying a part of the outputs of the comparator circuits 22, 24, and outputs the outputs of the comparator circuits 22, 24 to one pin. These pins are negative logic pins and are composed of AND circuits 26B and 28B for inputting the outputs of the delay element circuits 26A and 28A.

Next, the operation of the apparatus configured as described above will be described.
First, the operation of the region determination circuit 14 will be described with reference to FIGS. FIG. 3 is a timing chart showing the relationship among the lens position, focus error signal, region determination signal, and set (including reset) signal.
Normally, when the objective lens 6 (see FIG. 1) passes through the focal point in a direction approaching the disk surface from a distance, the focus error signal FS is zero (for example, period h1) → positive (for example, period h2) → negative (for example, period) h3) → zero (for example, period h4), and when passing through the focal point in a direction away from the disk surface, zero (for example, period h5) → negative (for example, period h6) → positive (for example, period h7) → zero (for example, Period h8) changes.
The period of h2-h3 and h6-h7 is called an S-curve period.

  First, when the focus search operation starts and the objective lens 6 approaches the focal point (periods h1 and h2), the level of the focus error signal FS input to the comparator circuits 22 and 24 of the area determination circuit 14 shown in FIG. Changes from zero to the positive direction, and exceeds the positive threshold value + TH1 at time t1 in FIG. At this time, the output of the comparator circuit 22 changes from L (low) to H (high), and a positive pulse having a width corresponding to the delay amount d of the delay element circuit 26A is set in the RS flip-flop 30 by the rising edge detection circuit 26. Although output to the input (S), since the RS flip-flop 30 is set to the H level (high level) at the start of the focus search, the area determination signal AS remains at the H level and does not change (time t1).

Next, when the objective lens 6 passes through the in-focus point P1, the focus error signal FS changes from zero to the negative direction (period h3) and then returns to the zero direction again. At time t2 in FIG. Exceeded (focus error signal is negative). At this time, the output of the comparator circuit 24 changes from L to H, a positive pulse having a delay amount d is output from the rising edge detection circuit 28 to the reset input (R) of the RS flip-flop 30, and the region determination signal AS is L and it is determined that the objective lens 6 is in a region closer to the disc surface than the focal point (time t2).
When the objective lens 6 passes through the focal point and moves to a region close to the disk surface (period h4), the actuator control circuit 19 (see FIG. 1) controls the objective lens 6 to return to the focal point. Reverses the direction of movement at point P2 and starts to return to the focal point (period h5).

  When the objective lens 6 approaches the focal point from the area close to the disk surface, the level of the focus error signal FS changes from zero to the negative direction and then changes to the positive direction, and exceeds -TH2 at time t3 in FIG. 3 (period h6). At this time, the output of the comparator circuit 24 changes from L to H, and a positive pulse is output from the rising edge detection circuit 28 to the reset input (R) of the RS flip-flop 30, but the RS flip-flop 30 is already at the L level (low level). The area determination signal AS remains at the L level and does not change (time t3).

  Next, when the objective lens 6 again exceeds the in-focus point P3, the focus error signal FS changes from zero to the positive direction and then returns to the zero direction again and exceeds + TH1 at time t4 in FIG. 3 (period h7). At this time, the output of the comparator circuit 22 changes from L to H, a positive pulse is output from the rising edge detection circuit 26 to the set input (S) of the RS flip-flop 30, the area determination signal AS becomes H, and the objective lens 6 is turned on. It is determined that the region is far from the focal point. Thereafter, the same process is repeated.

Now, after understanding the basic operation of the region determination circuit 14 as described above, the focus search operation will be described with reference to FIGS. FIG. 4 is a timing chart showing the relationship among the lens position, the region determination signal, the delay circuit output, and the actuator drive signal.
First, the reflected light from the optical disk D is converted into an electrical signal by the optical sensor 8 in the optical pickup 2 via the objective lens 6 and output to the focus error detection circuit 10. This focus error detection circuit 10 is based on the electric signal converted by the optical sensor 8, and a region determination circuit 14 that forms a focus error signal FS corresponding to the in-focus position of the light spot of the laser light that forms part of the focus control device 12. Output to.

Based on the level change order of the focus error signal FS, the area determination circuit 14 determines whether the objective lens 6 is closer to the disk surface than the in-focus position or away from the focal point as described above. The determination signal AS is output.
The region determination signal AS, which is the output of the region determination circuit 14, is output to the actuator control circuit 19 with a delay of a predetermined time Td by the delay circuit 18.
Based on the determination result of the region determination circuit 14, the actuator control circuit 19 separates the disk and the objective lens 6 when the objective lens 6 is closer to the disk surface than the focal point, and when it is far from the focal point. The actuator 4 is moved so as to approach the disk.

First, at the start of the focus search operation, the state of the area determination circuit 14 is set to the H level (a state away from the focal point). Then, the output (region determination signal) of the region determination circuit 14 is output to the actuator control circuit 19 by the delay circuit 18 after being delayed by a predetermined time Td (see FIG. 4). The actuator control circuit 19 changes the voltage (actuator drive signal) applied to the actuator 4 in a ramp shape (tilt shape) so that the moving speed of the objective lens 6 is constant. This operation can be realized by performing integration processing in the delay circuit 18 on the output AS of the delayed region determination circuit 14.
Since the area determination signal AS that is the output of the area determination circuit 14 is in the H level until the focal point is first reached, the voltage applied to the actuator 4 changes in a ramp shape in the positive direction in proportion to the passage of time. The lens 6 approaches the focal point at a constant speed.

Here, when the objective lens 6 passes the focal point, the region determination signal AS which is the output of the region determination circuit 14 changes to L level (a state closer to the disk surface than the focal point), and the input of the actuator control circuit 19 is also a predetermined value. It changes to L level with a delay of time Td. Accordingly, the voltage applied to the actuator 4 changes in a ramp shape in the negative direction in proportion to the passage of time with a delay of Td from the time when the objective lens 6 passes through the focal point, and the objective lens 6 once passes at a constant speed. Go closer to the focus.
Thereafter, every time the objective lens 6 passes through the focal point, the area determination signal AS, which is the output of the area determination circuit 14, changes in a direction to bring the objective lens 6 closer to the focal point, so that the actuator 4 moves the objective lens 6 to the focal point. Move to the center in the focus direction and repeat the focus search operation.

  The width of the focus search centered on the focal point can be controlled by the temporal change rate (integrator constant) of the voltage applied to the actuator 4 and the delay time Td. FIG. 5 is a diagram for comparing the locus of the objective lens during the focus search of the present invention and the focus search of the conventional apparatus. As is clear from this figure, the focus search operation of the conventional apparatus may cause the objective lens to collide with the high-density optical disk. However, according to the apparatus of the present invention, the movement amplitude of the objective lens centering on the focal point is marked. Thus, the objective lens can be prevented from colliding with the high-density optical disk.

Next, the amplitude measurement control circuit 21 that performs processing when there is inconvenience when the period of the optical disc surface shake and the period of the ramp-like signal used for the focus search match or when there is sudden noise in the focus error signal will be described. To do.
As described above, in the focus search operation of the apparatus of the present invention, the movement amplitude of the objective lens around the in-focus point can be remarkably reduced, but this makes the movement amplitude of the objective lens and the amplitude of the surface shake of the optical disc comparable. At this time, if the periods of the two coincide with each other, a state occurs in which the objective lens does not pass the focal point, and the S-curve period is not detected correctly, resulting in inconvenience in the focus search operation. First, this state will be described with reference to FIG.

In FIG. 6, (A) shows the in-focus position (solid line) having the surface blur and the locus (dashed line) of the objective lens in the focus search operation, and (B) shows the focus error FS at this time. It is shown.
Taking the left end of (A) as an example, the objective lens gradually approaches the in-focus point from below, but the in-focus point moves upward due to surface blurring and the objective lens cannot cross the in-focus point. ing. The focus error FS at this time cannot obtain a normal S-curve characteristic because the error values before and after the focal point are not point-symmetric as shown at the left end of (B).
As described above, when the period of the disk shake and the period of the ramp-like signal used for the focus search coincide with each other, there may occur a phenomenon that the objective lens returns without being able to pass through the focal point. As for the focus error FS, the maximum error output of the correct S-curve is not obtained.

FIG. 3C shows the detection state of the focus error FS. The reverse period that does not exist when the disk is not shaken is included twice in the circumference of the disk. When the focus error FS shown in (C) is input to the area determination circuit 14 shown in FIG. 1, the area determination signal AS shown in (D) is obtained, and a narrow pulse is generated in the reverse period. .
Originally, when there is no disc surface blur, the area determination signal AS has one S-curve period in both the H level period and the L level period as described with reference to FIG. Accordingly, in both the H level period and the L level period, the maximum amplitude value of the S-shaped curve can be obtained every time by detecting the maximum value and the minimum value of the focus error FS and taking the difference therebetween.
As described above, the maximum amplitude value originally obtained in the H level period and the L level period can be used as a gain control signal to the focus error detection circuit 10 in FIG. 1, but FIG. When the reverse period shown in FIG. 6 occurs, the S-curve period does not always exist in the H level period or the L level period. Therefore, the maximum amplitude value obtained in the H level period or L level period using the region determination signal AS as it is cannot be used for gain control.

  FIG. 7 is a block diagram showing the inside of the amplitude measurement control circuit 21. This circuit corrects the inconvenience of the area determination signal AS when there is a disk shake, creates an amplitude measurement section signal in which an S-shaped curve period always exists in the H level period and the L level period, and sets the maximum amplitude value. As shown in FIG. 1, the focus error signal FS from the focus error detection circuit 10 and the area determination signal AS from the area determination circuit 14 are input as input signals to generate a gain control signal, as shown in FIG. The focus error detection circuit 10 is configured to send it to the focus error detection circuit 10. The operation will be described below with reference to FIG. 7 and FIG. 8 showing signal timing.

In FIG. 7, the focus error amplitude measurement circuit 32 obtains the maximum amplitude value by measuring the maximum and minimum values of the focus error FS that first passed through the S-curve period when the focus search is started, and sets the next bandwidth. The circuit 34 obtains an amplitude value of T% which is a predetermined ratio with respect to the maximum amplitude value, and supplies this to the next focus error bandwidth range detection circuit 40 as bandwidth information.
The focus error bandwidth in-range detection circuit 40 identifies whether the amplitude of the input focus error signal FS is within or out of the bandwidth, and enables (counts) a first counter 42 and a second counter 44 described later. Yes) Supply a signal.

In FIG. 8, (A) shows the focus error signal FS and the set bandwidth range. The next (B) is an out-of-band signal obtained by pulsing a portion where the focus error signal FS exceeds the bandwidth range inside the focus error bandwidth in-range detection circuit 40.
(C) shows the input area determination signal AS, and (D) shows the timing pulse at the edge of the area determination signal AS.
Next, (E) shows a period during which the first counter 42 is counting, and (F) shows a period during which the second counter 44 is counting.

The purpose of the operation of the first counter 42 is to measure the time from when the focus error signal FS enters the bandwidth range after the area determination signal AS is inverted, and when it stays there for a predetermined time. Outputs a latch signal. The fact that this focus error is within the bandwidth for a predetermined time means that the S-curve period has not been detected, and this indicates that the objective lens is sufficiently out of focus. If the potential of the region determination signal AS is latched at this position, it is possible to obtain a signal in a form in which the reverse pulse is removed from the region determination signal AS.
The operation purpose of the second counter 44 is to prevent the first counter 42 from malfunctioning due to a narrow pulse such as noise superimposed on the focus error signal FS.

Next, the operation of the first and second counters will be mainly described.
The bandwidth measurement section signal shown in (G) rises in the bandwidth measurement section signal circuit 38, starting from the falling edge signal shown in FIG. 8D created by the edge detection circuit 36. The enable of the first counter 42 shown in (E) is started at the falling edge of the out-of-band signal (B) coming after this rising edge, and the first shown in (F) at the rising edge of the out-of-band signal (B). 2 Enable the counter 44. Both counters start measuring time when each enable signal rises.
The first counter 42 starts measuring time when the enable signal (E) rises, stops counting when it reaches the predetermined time N, generates a latch signal at that timing, outputs it to the latch circuit 42, and outputs a bandwidth measurement interval signal. Cut (G). However, if the following “disable signal of the first counter” is output from the second counter 44 before the predetermined time N, the enable signal (E) is cut, and the measurement is stopped and reset. The predetermined time N is set as a time necessary for the objective lens to be sufficiently separated from the focal point.
The second counter 44 starts measuring time when the enable signal (F) rises, stops measuring when counting up to a predetermined time P, and outputs a “disable signal of the first counter” at that timing, as described above. The measurement of the first counter 42 is stopped. However, if there is a falling part in the out-of-band signal (B) before the predetermined time P, the enable signal (F) is cut and measurement is stopped and reset. The predetermined time P is set to be longer than the maximum width time of noise that is suddenly mixed.

  With the above configuration and operation, the first counter 42 outputs a latch signal at a position where the objective lens is sufficiently away from the focal point. As a result, the amplitude measurement section signal (H) output from the latch circuit 46 is The pulse generated by the retrograde included in the area determination signal AS (C) is removed, and an amplitude measurement section signal having an S-shaped curve period in the H level period and the L level period is always obtained. The amplitude measurement section signal (H) is indicated by (E) in FIG.

  Returning to FIG. 7, the amplitude measurement section signal output from the latch circuit 46 is then supplied to the amplitude measurement circuit 48, where the focus error signal FS is maximized for each of the H level period and the L level period of the amplitude measurement section signal. The value and the minimum value are detected, and the maximum amplitude value that is the difference value is obtained. This maximum amplitude value is input to the next gain control signal generation circuit 50, where a predetermined coefficient is calculated and supplied to the focus error detection circuit 10 of FIG. 1 as a gain control signal.

  With the above configuration, in the focus control apparatus according to the present invention, even if there is inconvenience when the period of the optical disc surface shake and the period of the ramp-like signal coincide with each other, or sudden noise is included in the focus error signal, the influence thereof is also affected. In the state where the error is removed, fluctuations in the focus error due to various variations in the constant of the detection circuit of the focus error detection circuit 10, the intensity of the laser beam, the reflectance of the optical disk, and the like can be prevented, and stable focus control becomes possible.

1 is a block configuration diagram showing a main part of an optical pickup including a focus control device according to the present invention. It is a block block diagram which shows the area | region determination circuit of a focus control apparatus. It is a timing chart which shows the relationship between a lens position, a focus error signal, a region determination signal, and a set (including reset) signal. It is a timing chart which shows the relationship between a lens position, an area | region determination signal, a delay circuit output, and an actuator drive signal. It is a figure for comparing the objective-lens locus | trajectory at the time of the focus search of this invention and the focus search of a conventional apparatus. It is a figure which shows the area | region determination signal generation | occurrence | production when there exists a surface blur. It is a block diagram of an amplitude measurement control circuit. It is a figure which shows the signal waveform and timing of each part of an amplitude measurement control circuit. It is a graph which shows the positional relationship of the disc surface at the time of a focus search operation | movement, and the front-end | tip of an objective lens.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Optical pick-up, 4 ... Actuator, 6 ... Objective lens, 8 ... Optical sensor, 10 ... Focus error detection circuit, 12 ... Focus control apparatus, 14 ... Area determination circuit, 16 ... Lens control circuit, 18 ... Delay circuit, 19 ... Actuator control circuit, 20 ... Driver, 21 ... Amplitude measurement control circuit, 22, 24 ... Comparator circuit, 26, 28 ... Rising edge detection circuit, 30 ... RS flip-flop, 32 ... Focus error amplitude measurement circuit, 34 ... Bandwidth Setting circuit 36 ... Edge detection circuit 38 ... Bandwidth measurement interval signal generation circuit 40 ... Focus error bandwidth in-range detection circuit 42 ... First counter 44 ... Second counter 46 ... Latch circuit 48 ... Amplitude Measurement circuit, 50... Gain control signal generation circuit.

Claims (1)

The irradiation light is focused on the recording surface of the optical information recording medium via the objective lens, and the objective lens collides with the optical information recording medium based on a focus error signal obtained from the return light from the recording surface. In the focus control device for preventing
Using the focus error signal value at the in-focus position where the objective lens focuses the irradiation light on the recording surface as a reference value, the objective lens moves in the direction approaching the recording surface side beyond the in-focus position. The focus error signal value set so that the objective lens does not collide with the optical information recording medium is set as a first threshold value, and the objective lens is in a direction away from the recording surface beyond the in-focus position. When the focus error signal value set so that the objective lens is not too far from the optical information recording medium is set as the second threshold value, the focus error signal is between the first threshold value and the second threshold value. An area determination means for determining that it is contained and outputting,
When the focus error signal exceeds the first threshold and approaches the recording surface based on the region determination signal output from the region determination means, or when the focus error signal exceeds the second threshold and moves away from the recording surface The focus control is performed without causing the objective lens to collide with the optical information recording medium by controlling the focus error signal to be between the first threshold value and the second threshold value. Lens control means;
A plurality of rectangular amplitude measurement section signals are generated from the amplitude values of the region determination signals at a plurality of positions where the objective lens is separated from the in-focus position by a predetermined distance, and a high level period and a low level of the amplitude measurement section signal are generated. Amplitude measurement control means for detecting a maximum value and a minimum value of the focus error signal for each period, obtaining a maximum amplitude value as a difference between them, and controlling a gain of the focus error signal based on the maximum amplitude value; ,
A focus control device comprising:

Images