JPH1049894A - Focus pull-in apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a focus pull-in apparatus by which the pull-in of a focus is stabilized by making an MPU detect the level and the zero cross of a focus control signal, and compensate control gain to be constant irrespective of the distance up to the focal point of an objective lens. SOLUTION: A focus control signal Af is changed into a phase compensation signal by a phase compensator 201 so as to be supplied to an AF driver 210, and the focus of an objective lens 212 is controlled. A comparator 202 detects the prescribed level and the zero cross of the focus control signal Af so as to be reported to an MPU 203. An A/D converter 213 inputs a focus quantity-of- light signal to the MPU 203 at every definite time, and an A/D converter 214 converts the signal into an analog signal so as to be input to a phase compensator 206. At this time, the MPU 203 has a function to compensate the control gain to be constant irrespective of the distance up to the focal point of the objective lens 212. Thereby, a corrected control value is supplied to a position control loop via the A/D converter 214 so as to stabilize the pull-in of a focus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus pull-in device for focusing a light beam on a medium surface of an optical information recording medium.

[0002]

2. Description of the Related Art Conventionally, various types of recording media for optically recording information and reading recorded information, such as a disk, a card, and a tape, are known. These optical information recording media include those that can be freely recorded and reproduced, those that can be additionally recorded and reproduced, and those that can only be reproduced. In particular, it is considered that the use of an optical card as a recording medium will be expanded due to features such as ease of manufacture, portability, and accessibility. Various optical information recording / reproducing apparatuses for this optical card are provided.

In such an optical information recording / reproducing apparatus, information is recorded and reproduced while always performing auto-tracking and auto-focus control. In addition, information is recorded on the recording medium by modulating according to the recording information and scanning the information track with a light beam narrowed down into a minute spot, and a series of information is recorded as an optically detectable information pit row. Is done. In reproducing information from a recording medium, a light beam spot with a low power that does not record on the medium scans the information pit row of the information track and detects reflected light or transmitted light from the recording medium. The recorded information is reproduced based on the obtained detection signal.

FIG. 7 is a diagram showing an example of the configuration of an optical system of a conventional optical information recording / reproducing apparatus. In FIG. 7, 101
Denotes a semiconductor laser as a recording and reproducing light source. The luminous flux emitted from the semiconductor laser 101 is transmitted to the collimator lens 1
After being collimated at 02, the light is split into a plurality of light beams by the diffraction grating 103. The split light beam is supplied to the polarizing beam splitter 10.
The light passes through the quarter-wave plate 105 and is focused on the optical card 107 by the objective lens 106 as a minute light spot. The reflected light from the optical card 107 is transmitted to the objective lens 10
6, 1/4 wavelength plate 105, polarizing beam splitter 10
4. Photodetector 109 via toric lens 108
The information reproduction signal and the tracking and focus control signals are generated by the detection signal of the photodetector 109. Of the light beams split by the diffraction grating 103, recording, reproduction, and focus control (hereinafter, referred to as AF) are performed using the 0th-order diffracted light, and tracking control (hereinafter, referred to as AT) is performed using ± 1st-order diffracted light. Is called).
In this case, AF is an astigmatism method, and AT is a three-beam method.

FIG. 8A is a schematic plan view of an optical card. A number of information recording / reproducing tracks are arranged in parallel on the optical card 107, and some of them are shown as T1, T2, T3,. This track is divided into tracking tracks tt1 to tt4. Tracking tracks tt1-tt4 are grooves or tracks T1-T4.
T3 is formed of a material having a different light reflectance, and is used as a guide for obtaining a tracking signal. FIG. 8A shows an example in which information is recorded or reproduced on the track T3. The 0th-order diffracted light 110 for recording, reproduction and AF is placed on the track T3 and the ± 1st-order diffracted lights 111 and 112 for AT.
Are applied to tracking tt3 and tt4, respectively.
Here, a tracking control signal is obtained from the reflected lights from the diffracted lights 111 and 112, and the 0th-order diffracted light 110 is controlled so as to scan the track T3 correctly. The diffracted lights 110, 111, and 112 are scanned left and right on the information track of the optical card 107 by a mechanism (not shown) while maintaining the same positional relationship under AF and AT control.

The scanning method includes a method of moving an optical system and a method of moving an optical card. In either method, the optical system and the optical card reciprocate relative to each other.
Non-constant speed parts occur at both ends of the optical card. This state is shown in FIG. The horizontal axis in FIG. 8B represents the horizontal direction of the optical card, and the vertical axis represents the relative scanning speed between the optical system and the optical card. Normally, a constant-speed scanning area at the center of the optical card 107 is used as a recording area.

FIG. 9 shows each of the diffracted lights 110 to 11 in FIG.
2 is a partially enlarged view of FIG. The 0th-order diffracted light 110 for recording, reproduction and AF is located at the center of the ± first-order diffracted lights 111 and 112 for AT and scans the center of the track T3. The shaded portions 113a, 113b, and 113c are recording rows by the 0th-order diffracted light 110 due to the strong power of the semiconductor laser 101, and are generally called pits. Since the pits 113a, b, and c have different reflectivities from the periphery of the other recording rows, when scanning is performed again with the weak light spot 110, the reflected light of the zero-order diffracted light 110 is modulated by the pits 113a, b, and c, and a reproduction signal is obtained. Can be The ± first-order diffracted lights 111 and 112 for AT are applied to the periphery of the recording row and the tracking tracks tt3 and tt4.
A tracking control signal is obtained by the reflected light.

FIG. 10 is a circuit diagram showing details of the photodetector 109 of FIG. 7 and a signal processing circuit. In FIG. 10, the photodetector 109 includes a four-division optical sensor 114 and an optical sensor 11
It is composed of 5,116 optical sensors in total.
Further, the light spots 110a, 111a, and 112a are respectively the diffracted lights 110, 111, and 110 in FIGS.
The light reflected from the optical card 112 is shown. The light spot 110a is condensed on the four-divided optical sensor 114, and the light spots 111a and 112a are
6 are collected. Sensor outputs in the diagonal directions of the four-divided sensor 114 are added by adders 117 and 118, respectively.

The outputs of the adders 117 and 118 are also added by the adder 121 and reproduced as an information reproduction signal RF. That is, the information reproduction signal RF is transmitted to the four-division optical sensor 11.
4 corresponds to the sum total of the light spots 110a condensed at 4. Further, the outputs of the adders 117 and 118 are subtracted by the differential circuit 120 to become a focus control signal _Af . That is, the focus control signal _Af is a difference between the sums of the four divided optical sensors 114 in the diagonal directions. Since the astigmatism method is well known in the literature, the description is omitted here. Optical sensor 115, 1
16 output is subtracted by the differential circuit 119, a tracking control signal A _t. Normally, the tracking control signal A _t is controlled so as to become zero, this tracking control for scanning to follow the light spot on the information track by is performed. The outputs of the addition circuits 117 and 118 are added by the addition circuit 122, and the focus light amount signal P
becomes _f . The focus light amount signal is a four-divided sensor 114,
Light spot 110 condensed on optical sensors 115 and 116
a, 111a, and 112a.

FIG. 11 is a diagram showing a focus pull-in device of a conventional optical information recording / reproducing device. 11 performs the pull-in of the focus using the focus light quantity signal P _f and a focus control signal A _f created in FIG. Hereinafter, a specific description will be given. First, reference numeral 201 denotes a phase compensation circuit for performing phase compensation of a focus control signal;
Is a comparator for comparing the level of the focus control signal with a predetermined value to binarize it. Comparator 202
Detects zero cross or a predetermined level of the focus control signal A _f, as will be described later, and outputs the MPU 203. Also, 204 is a differential amplifier, detects a difference between the output of the target position signal generating circuit 205 for generating a focus intensity signal P _f and the focus target position signal of FIG.

The output signal of the differential amplifier 204 is output to the X terminal of the switch SW 207 via the phase compensator 206.
On the other hand, the output signal of the phase compensator 201 is input to the W end of the switch SW 207, and the switch SW 207 switches to W or X based on a command from the MPU 203. Switch SW20
7 is connected to the Y terminal of the switch SW 208, and the Z terminal is connected to the output of the AF pull-in pulse generation circuit 209. The AF pull-in pulse generation circuit 209 is an MPU 203
Is a circuit that outputs a pull-in pulse necessary for pulling in the focus based on the control of (1). The switching SW 208 is an MP
It is switched to the Y or Z end by the command of U203. The output of the switching SW 208 is input to an AF coil driver 210 that drives the AF coil 211, and the objective lens 212 is configured to move in the direction perpendicular to the surface of the record carrier (optical card) by driving the AF driver 210.

FIG. 12A is a diagram showing a change in a focus light amount signal with respect to a distance x when the objective lens is driven in a direction perpendicular to the optical card surface. In FIG. 12A, first, x = 0 indicates the focus position, and the negative side of the distance x indicates the direction in which the optical card is located. A distance x is closer to the optical card surface, and a distance x on the positive side is far from the optical card surface. Here, when the objective lens is moved from the negative side of the distance toward the in-focus position, the focus light amount signal P _f gradually increases at first, but increases rapidly to the point x _L as it approaches the in-focus position. doing. Then, the rate of increase of the focus light amount signal decreases, and gradually decreases after the in-focus position.

FIG. 12B is a diagram showing a change of the focus control signal _{Af with} respect to the distance similarly to FIG. 12A. Similarly, when the objective lens is moved from the negative side of the distance toward the in-focus position, the focus control signal _Af temporarily becomes negative near the in-focus point and becomes 0 at the in-focus point. After passing through the focal point, it becomes positive once, and then converges to 0 as the objective lens moves away.

Next, a conventional focus pull-in operation will be described. First, when pulling in the focus, the MPU 203 outputs a pull-in start command signal to the target position signal generation circuit 205 in order to move the objective lens toward the focus position. In response to this, the target position signal generation circuit 20
3 outputs to the differential amplifier 204 a target light amount signal P _fT that increases with time. Outputting an output signal proportional to the difference of the differential in the amplifier circuit 204 focus the light quantity signal P _f and the target light quantity signal P _fT to the phase compensator 206, a phase compensator 206
Then, the signal after the phase compensation is output to the X terminal of the switching SW 207.

In this case, the switching SW 207 is set to the MPU 203
The switch SW208 is also switched to the X terminal side by the command of
The output signal of the phase compensator 206 is supplied to the AF coil driver 210 via the changeover switches 207 and 208, being connected to the Y terminal side according to the command of No. 3. Thereby, the AF coil 211 is driven by the function of the position control loop, and the objective lens gradually moves toward the in-focus position. At this time, as the focus approaches as shown in FIG.
The focus control signal increases to the negative side, and when the focus control signal reaches a predetermined level A _L , the comparator 20
2 sends a timing signal to the MPU 203. MPU
When the timing signal 203 is received, the switch SW 208 is switched to the Z terminal, and the AF pull-in pulse generation circuit 2 is switched.
09 is instructed to generate an AF pull-in pulse. This is an open control pulse that drives the objective lens from the position of x _L in FIG. 12A toward the focal point.

When approaching the in-focus position, the focus control signal _Af crosses zero at the in-focus point as shown in FIG.
The comparator 202 detects this zero cross,
The MPU 203 is notified of the timing of the zero cross. M
PU203 is a switch SW207 at the timing of zero cross.
Is switched to the W terminal side, and the switch SW208 is switched to the Y terminal side, thereby turning on the focus control loop and pulling in the focus. Thereafter, a focus servo state is established by the focus control signal _Af . Conventionally, focus pull-in is performed in this manner.

[0017]

However, FIG.
In the focus light amount signal of (a), the distance x between the optical card and the objective lens is not necessarily proportional. Here, on the negative side of the horizontal axis in FIG. 12A, when the distance is far from the focal point 0 (the objective lens is close to the optical card surface), the rate of change of the focus light amount signal with respect to the distance x is small. As the focus approaches 0, the rate of change of the focus light amount signal sharply increases up to the vicinity of the point x _L.

In such a case, if the position of the objective lens is controlled with a driving force proportional to the difference between the target light amount signal and the focus light amount signal as described above, the control is performed at a position where the distance x is far from the negative focal point. The gain decreases. That is, in such a position, the change of the light amount signal with respect to the distance change Δx is ΔP _fA as shown in FIG. 12A, whereas the change of the light amount signal with respect to the same Δx near the focal point is ΔP _fB. And even if the same distance Δx, ΔP _fA is Δ
It is smaller than P _fB . Therefore, especially as described above, the distance x
At a position distant from the negative focal point, the control gain decreases, and the driving force of the objective lens decreases. Therefore, when external vibration is applied to the apparatus in a state where the control gain is lowered at the time of focus pull-in, there is a problem that the position control of the objective lens is easily released, and the focus cannot be pulled because the control becomes impossible.

In view of the above problems, the present invention has an object to provide a focus pull-in device which can stably pull in a focus even when external vibration is applied. is there.

[0020]

An object of the present invention is to provide a position control loop for controlling an objective lens for converging a light beam of a light source on a recording medium according to a difference between a focus light amount signal and a predetermined target signal, Means for outputting a gradient of a focus light amount signal from a value of the focus light amount signal in a focus pull-in device for moving the objective lens toward a focus position by a control operation of the position control loop at the time of focus pull-in; Means for calculating a gain correction coefficient from the calculated inclination and the inclination of the focus light amount signal previously obtained at a predetermined position of the objective lens, and means for multiplying the control value of the position control loop by the calculated gain correction coefficient. This is achieved by a focus pull-in device.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows the first embodiment of the present invention.
FIG. 2 is a block diagram showing an embodiment. In FIG. 1, the same portions as those of the conventional device of FIG. 11 are denoted by the same reference numerals, and detailed description is omitted. That is, in FIG.
1. The switching SW 207, the switching SW 208, the AF coil driver 210, and the AF coil 211 are the same as those in FIG. The focus control signal _Af generated by the signal processing circuit of FIG. 10 is input to the phase compensator 201, and the phase-compensated signal is supplied to the AF driver 210 to drive the objective lens 212 in the focus direction and perform focus control. Do. In this case, although not shown in FIG. 1, the optical system shown in FIG. 7 is actually provided, and the light beam from the semiconductor laser 101 is collimated by the collimator lens 10.
2. It is assumed that the light is irradiated onto the optical card 107 through the diffraction grating 103, the objective lens 212 (corresponding to the objective lens 106 in FIG. 7), and the like.

The comparator 202 and the phase compensator 2
06, AF pull-in pulse generation circuit 209, MPU 203
Are the same as those in FIG. Comparator 202 detects the zero cross of the focus control signal a predetermined level of A _f A _L and the focus control signal A _f, and notifies the MPU 203. In the present embodiment, the A / D converter 2
13, D / A converter 214 is provided, focus light quantity signal P _f is taken into MPU203 at regular intervals during the focus pull-in A / D converter 213. The focus light amount signal _Pf is a signal generated by the signal processing circuit of FIG. D / A converter 214 is MP
The control value from U203 is converted into an analog signal and output to phase compensator 206. In the present embodiment, as will be described in detail later, the MPU 203 has a function of correcting the control gain to be constant irrespective of the distance to the focal point of the objective lens 212, and outputs the corrected control value via the D / A converter 214. By supplying the focus to the position control loop, the focus is pulled in stably.

Next, the principle of the control gain correcting method according to the present invention will be described with reference to FIG. First, FIG. 2A is a diagram showing the inclination (rate of change) of the focus light amount signal. The horizontal axis represents the focus light amount signal P _f , and the vertical axis represents the differential value of the focus light amount signal of FIG. x '. FIG. 2B shows the relationship between the amplitude of the focus light amount signal and the distance of the objective lens to the optical card surface. That is, in FIG. 2B, the horizontal axis represents the focus light amount signal P _f , and the vertical axis represents the negative distance in FIG. 12A, that is, the distance −x in the direction in which the objective lens approaches the optical card surface from the focal point. It is. In FIG. 2 (b), x = f (P f) is the distance indicates that the function of the focus intensity signal P _f, a distance -x is found knowing the value of the focus intensity signal P _f. In FIG. 2A, the gradient x 'is x' = f '
(P _f ) = g (P _f ), and when the value of the focus light amount signal P _f is known, the slope x ′ can be obtained.

Here, the position of the objective lens in the x direction is measured by any method, and if the relationship with the focus light amount signal P _f is known, x ′ = g (P _f ) can be obtained. In the present embodiment, it is assumed that the relationship between the position of the objective lens and the focus light amount signal is known in advance, and the function g (P _f ) is known. Note that f (P _f ) is the minimum when the focus light amount signal P _f = P _fN as shown in FIG. 2, and corrects the control gain between P _f = P _{fN and} P _fL as described later in detail. It is.

Specifically, first, as shown in FIG.
The slope at the focus light amount signal P _f = P _fL at _L is x
It is calculated as _L ′ = g (P _fL ). x _L is shown in FIG.
Corresponding to x _L of (a), a focus control signal A _f shown in FIG. 12 (b) corresponds to the distance when it comes to A _L. That is, it corresponds to the distance of the final position when controlling the position of the objective lens. However, x _L is not limited to this, and may be near the final position of the position control. In this way, the value of x _L ′ is obtained in advance and stored in the memory. Next, the slope is calculated as x ′ = g (P _f ) from the value of the focus light amount signal P _f for each control cycle, and the gain correction coefficient is calculated as K from the obtained value of x ′ and the previous value of x _L ′. =
It is calculated as x '/ x _L'. Then, the control value of the position control loop is multiplied by the gain correction coefficient K for each control cycle. By doing so, even when the distance between the objective lens and the focus light amount signal is not in a proportional relationship as shown in FIG. 12A, the control gain can be corrected so that the control gain is constant at each position of the objective lens. Insufficient driving force due to a decrease in control gain when the objective lens is far from the focal point can be compensated.

The broken lines in FIGS. 2A and 2B show the inclination of the focus light amount signal and the distance between the objective lens when the offset ΔP _N occurs in the focus light amount signal. As described above, the gradient x 'when the focus light amount signal has an offset is x' as shown by the broken line in FIG.
= G (P _f −ΔP _N ), and the slope can be obtained by subtracting ΔP _N from P _f and substituting it for the function g.

Next, the specific operation of this embodiment will be described with reference to FIG.
A description will be given based on FIG. FIG. 3 is a flowchart showing the focus pull-in operation, and FIG. 4 is a diagram showing signals of various parts at the time of focus pull-in. First, when the focus is pulled in, the MPU 203 sets the switch SW 207 in FIG.
4D, the switching SW 208 is connected to the Y end as shown in FIG. 4E, and the position control loop of the objective lens 212 is turned on. In FIG. 4, and on the position control loop at time t _0, to start focus pull-in operation.

In this state, the focus light amount signal _Pf becomes A
Is sampled by the / D converter 213 (S1), and M
It is taken into the PU 203. The focus light amount signal is taken into the MPU 203 by the A / D converter 213 at regular time intervals. The MPU 203 monitors the output signal of the comparator 202 and determines that the level of the focus control signal _Af is A
determining whether the _f ≦ A _L (S2). That is,
The comparator 202 compares the level of the focus control signal _Af with the predetermined level A _L , and the MPU 203 determines whether the focus control signal A _f has reached the predetermined level A _{L based} on the output signal.

In this case, since the focus pull-in operation has just started, the objective lens 21
4 is a predetermined distance away from the focal point, and FIG.
As shown in (b), the focus control signal _Af is at the 0 level. Therefore, No is determined in S2, and MPU2
03 determines in S3 whether it is the first sampling. In this case, since the MPU203 is first sampling, it is determined YES, and the process proceeds to S4, [Delta] P offset amount [Delta] P _N of the focus intensity signal P _{f N} = P
Calculate as _{f- PfN} . P _f is a value of the focus light amount signal sampled in S1, and P _fN is a known value.
The value of the focus light amount signal at a position sufficiently close to the in-focus position when there is no offset as shown in FIG. That is, in the S4, and far enough away from the focus position in the first sample, the value of the focus intensity signal P _f is the minimum, by calculating the amount of deviation between the P _fN, the offset amount [Delta] P _N Have gained. In S4, MP
U203 is the value P _{f of} the focus light amount signal obtained in S1.
_Is set as the target light amount signal P _fT .

[0030] Then, MPU 203 adds the value of the predetermined a target light quantity signal P _fT obtained (S5), followed by calculating the slope x 'of the focus light quantity signal at that time (S
6). The slope x ′ is x ′ = g (P _f
−ΔP _N ). Further, the function g is known as described above, and may be obtained by using a polynomial of the focus light amount signal _Pf , or may be read in a table in a memory in advance. Subsequently, the MPU 203 uses the obtained value of x 'to calculate a gain correction coefficient K as K = x'.
/ X _L ′ (S7). As described with reference to FIG. 2, x _L ′ is the slope of the focus light amount signal when x = x _L and is a known value. Then, MPU 203 calculates a control value V ₀ which is the position control loop (S8).

The control value V ₀ is given by: V ₀ = (P _fT -P _f ) × G
× K. P _fT is the value of the target light amount signal of S5, P
_f is the value of the focus intensity signal P _f of S1, K is a gain correction factor obtained in S7. G is a gain constant required when the inclination is x _L ′ at x = x _L , and is a known value. MPU203 outputs a control value V ₀ which is calculated to the D / A converter 214 (S9). The control value V ₀ is D /
The signal is converted into an analog value by the A converter 214 and supplied to the phase compensator 206. The phase compensator 206 performs phase compensation. The signal after the phase compensation is supplied to the AF driver 210 through the switching switches 207 and 208. Here, the control value V ₀ is a value obtained by multiplying the difference between the target light amount signal P _fT and the focus light amount signal P _{f by} a gain constant, as described above, and controls the AF coil 211 according to the difference from the target. Works, and the objective lens 212 is controlled to a position corresponding to the target light amount signal.

The exit first control above, the focus light quantity signal P _f is sampled at a fixed time after again S1, MPU 203 performs the same processing. However, in the second control, since the determination is No in S3, the process proceeds to S5 without passing through S4, and a is added to the previous target light amount signal P _fT to set the target light amount signal. S6 ~ S
9 is performed. Hereinafter, the MPU 203 repeats the processing of S1 to S3 and S5 to S9 at regular time intervals and performs position control while increasing the target light amount signal P _fT by a, thereby gradually bringing the objective lens 212 closer to the focal point. Go. FIG. 4A shows the focus light amount signal P _{f at} this time,
The broken line indicates the target light amount signal _PfT . Target light signal P
_fT increases linearly because they increase a increments every fixed as described above time, and follows the target light quantity signal P _fT by the action of the control as described hereinabove focus intensity signal P _f.

The position control is performed as described above, and S
2, the level of the focus control signal _Af is _Af ≦ A
_When the value becomes _L (YES in S2), the MPU 203 proceeds to S6 without passing through S5, and performs the same processing thereafter. That is,
As shown in FIG. 4B, the focus control signal _Af changes at time t _L1
After A _f ≤ A _L , the MPU 203 executes S1 to S
2. The processing of S6 to S9 is repeated, and the target light amount signal P
The same position control is performed with _fT fixed. Thereby, the focus light amount signal _Pf becomes constant as shown in FIG. 4A, and the objective lens 212 is stopped. MPU2
03 performs position control in a state where the target light amount signal is fixed for a fixed time T. It waits for the objective lens 212 at the position of A _f ≦ A _L is to stabilize stopped, in order to detect the current of the AF coil 211 at the time of stopping by the current detection circuit (not shown). That is, the drive current of the AF coil 211 necessary for stopping the objective lens 212 against the gravity is detected.

At time t _L2 after the lapse of time T, MP
U203 switches the switch SW208 to the Z end as shown in FIG. As a result, the position control loop is turned off and switched to open control. Simultaneously with this switching, the MPU 203 controls the AF pull-in pulse generation circuit 209 as shown in FIG.
It is supplied to the coil driver 210. The AF pull-in pulse at this time is obtained by adding the current value detected during the previous time T to
Further, a driving pulse corresponding to a driving current value obtained by adding a current necessary for pulling up the objective lens 212 is designated by the MPU 203, and the AF pull-in pulse generation circuit 20
The AF pull-in pulse as shown in FIG.
It is supplied to the AF coil driver 210 through 208. As a result, the above-described drive current is supplied to the AF coil 211, and the objective lens 212 further moves toward the focal point by open driving.

At this time, the MPU 203 sets the comparator 2
02, the focus control signal _Af becomes 0 level as shown in FIG.
When a zero cross is detected in MPU2, the MPU 203
As shown in (d) and (e), the switching SW 207 is switched to the W end and the switching SW 208 is switched to the Y end. As a result, the focus control loop is turned on, and the focus is pulled.
With the above, the focus pull-in is completed, and thereafter, the state becomes the focus servo state by the focus control loop. Also,
After that, by turning on the tracking servo,
It becomes possible to record and reproduce information on the optical card.

As described above, in the present embodiment, the slope is calculated from the value of the focus light amount signal, the gain correction coefficient is calculated from this slope and the slope at a predetermined position obtained in advance, and the obtained gain correction coefficient is calculated. Since the control value is multiplied, when the distance between the focus light amount signal and the objective lens is not in a proportional relationship, a change in the control gain can be corrected to be constant. Therefore, especially when the objective lens is away from the in-focus position, a decrease in control gain can be corrected, so that a shortage of driving force can be compensated for, and even if external vibrations are applied, control can be prevented from being lost. Can be. Further, since the offset amount of the focus light amount signal is removed, the position of the objective lens can be controlled more accurately without being affected by the offset.

FIG. 5 is a block diagram showing a second embodiment of the present invention. In the first embodiment, the focus light amount signal is sampled by the A / D converter 213 and the MPU is sampled.
Although the inclination and the gain correction coefficient are calculated in 203, in the present embodiment, a function generator 215 is provided to calculate the inclination and the gain correction coefficient. That is, the function generator 215 generates the function of x '= g (P _f ) described in the first embodiment from the input focus light amount signal P _f . Further, inside the function generator 215, the gain correction coefficient K is calculated from K ′ and x _L ′ which is known in advance as K = x ′.
/ X _L ′, a difference between the target light quantity signal P _fT output from the differential amplifier 204 and the focus light quantity signal P _f (P _fT −P _f ), and a gain correction coefficient K, described in the first embodiment. And a circuit for multiplying the gain multiplier G.

The differential amplifier 204 and the target position signal generation circuit 205 are the same as those shown in FIG. 11, and the target position signal generation circuit 205 increases the target position which increases at a fixed rate with respect to time based on an instruction from the MPU 203. The signal P _fT is output. Other configurations are the same as those in FIG. With this configuration, the control value V ₀ = (P _{fTT) is supplied} from the function generator 215 to the phase compensator 206 at the time of focusing.
−P _f ) · K · G is output, and correction can be performed so that the control gain becomes constant irrespective of the position of the objective lens just like the embodiment of FIG.

In the above embodiment, the target light amount signal is increased at a fixed rate with respect to time, but the distance may be increased at a fixed rate. In addition, the position control is performed until the level of the focus control signal becomes A _L , and thereafter, the mode is switched to the open control. However, depending on the waveform of the focus light amount signal, the position control is performed up to the zero cross point of the focus light amount signal, and the position is controlled at the zero cross point. Focus pull-in may be performed. Further, since the focus light amount signal may cause a difference due to an instrument difference depending on the sensitivity of the optical sensor, the light emission intensity of the semiconductor laser, the characteristics of the signal processing circuit, and the like, it is desirable to correct as follows.

FIG. 6 shows the difference between the focus light quantity signals. The horizontal axis represents the distance between the objective lens and the optical card x, the vertical axis represents the focus light quantity signal P _f indicating the intensity of the amount of light incident on the light sensor. Indicates a standard value of the focus light amount signal, and x = f (P _f ). Indicates a focus light amount signal having a different level due to a difference between apparatuses. Here, as shown in FIG. 6, when the focus light amount signal changes due to the machine difference, x = f (P
_f) is a similar figure to the direction of the amplitude of the focus intensity signal P _f. Therefore, the maximum and minimum values of the focus light quantity signal P _f was measured in the standard state of the difference (amplitude) as the standard amplitude value a, when the amplitude value in the case of by machinery difference variation to is b, both similar X in the case of
Can be represented by x = f [(a / b) · P _f ]. a is fixed as a standard value. Also, when assembling and adjusting the device, the value of b is measured and EE
It is stored in the PROM.

In the MPU 203, the focus light amount signal P _f sampled by the A / D converter 213
_Is corrected as P _fC = (a / b) · P _f . Thereafter, the MPU 203 performs the above-described control using the corrected value. This makes it possible to correct the machine-to-machine variation, and to perform more accurate position control. In addition, by measuring the focus light amount signal every time the optical card is loaded or at regular time intervals, and correcting the focus light amount signal using the value, it is possible to cope with not only variations among the devices but also environmental changes and temporal changes.

[0042]

As described above, according to the present invention, by correcting the control gain to be constant according to the position of the objective lens, the control gain when the objective lens is away from the in-focus position is corrected. Insufficient driving force due to the decrease can be compensated for, and even when external vibrations are applied, the focus can be stably pulled in without deviating from the control. Further, by removing the offset from the focus light amount signal, it is possible to more accurately control the position.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a focus pull-in device according to the present invention.

FIG. 2 is a diagram for explaining the principle of control gain correction according to the present invention.

FIG. 3 is a flowchart showing an operation of the embodiment of FIG. 1;

FIG. 4 is a time chart showing signals of respective units when the focus is pulled in the embodiment of FIG. 1;

FIG. 5 is a block diagram showing a second embodiment of the present invention.

FIG. 6 is a diagram showing focus light quantity signals having different amplitudes due to the difference between the apparatuses.

FIG. 7 is a diagram showing a configuration of an optical system of a conventional optical information recording / reproducing apparatus.

FIG. 8 is a diagram showing a relationship between a recording surface of an optical card and a scanning speed with respect to an area thereof.

9 is an enlarged view of a part of the optical card of FIG. 8;

10 is a diagram showing a photodetector of the optical system of FIG. 7 and a signal processing circuit for processing an output signal thereof.

FIG. 11 is a diagram showing a conventional focus pull-in device.

12 is a diagram showing a focus light amount signal and a focus control signal used for focus pull-in of the apparatus of FIG. 11;

[Explanation of symbols]

 Reference Signs List 101 semiconductor laser 107 optical card 109 photodetector 201, 206 phase compensator 202 comparator 203 MPU 207, 208 switching SW 209 AF pull-in pulse generation circuit 210 AF coil driver 211 AF coil 212 objective lens 213 A / D converter 214 D / A converter

Claims (4)

[Claims] 1. A position control loop for controlling an objective lens that converges a light beam of a light source on a recording medium in accordance with a difference between a focus light amount signal and a predetermined target signal, and controls the position control loop when a focus is pulled in. In operation, in a focus pull-in device that moves the objective lens toward a focus position, a unit that outputs a gradient of a focus light amount signal from a value of the focus light amount signal,
Means for calculating a gain correction coefficient from the output inclination and the inclination of the focus light amount signal previously obtained at a predetermined position of the objective lens; and means for multiplying the control value of the position control loop by the calculated gain correction coefficient. A focus pull-in device comprising: 2. The focus pull-in device according to claim 1, wherein the tilt output means subtracts an offset from the focus light signal and outputs a tilt from the value of the focus light signal from which the offset has been removed. Focus focusing device. 3. The focus pull-in device according to claim 1, wherein the value of the focus light amount signal is corrected based on a predetermined standard amplitude value of the focus light amount signal and a predetermined amplitude value of the focus light amount signal. A focus pull-in device, comprising: a correction unit that performs correction. 4. The focus pull-in device according to claim 1, wherein the position control loop moves the objective lens to near a focal point at the time of focus pull-in.