JPH05334687A - Focus setting device - Google Patents

Abstract

PURPOSE:To miniaturize an optical pickup system by decreasing operating distance between an optical disk, an actuator and an objective lens in a focus setting device. CONSTITUTION:The operating distance between an optical disk 50 and the objective lens 53 is selected at a small value, and a focus search signal S1 supplied from a sawtooth wave signal generation circuit 61 is supplied to the driving coil 13 of the actuator 52 sequentially as a signal to increase amplitude.

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 (hereinafter referred to as focus search) device, and more particularly to improvement of a focus search drive signal.

[0002]

2. Description of the Related Art A focus search device such as an optical disk player is designed to perform focus servo within a range in which a focus error signal can be obtained, as disclosed in Japanese Patent Laid-Open No. 54-128708. That is, as shown in FIG. 5, in the optical disc player,
The distance from the laser source of the objective lens to the optical disc d Distant, when the laser beam emitted from the laser source is denoted by the distance d ₁ distance d focused on the optical disc surface, the distance d ₁
When the position of the objective lens is displaced with respect to the center and a focus error occurs, for example, by using a four-division photodetector utilizing astigmatism, the distance d ₁ is used as the center and the displacement amount d ₁ −d It is possible to obtain the focus error signal S _ER having the S-shaped characteristic shown in FIG. 5A in which the voltage changes in the positive direction and the negative direction.

Therefore, the focus error can be corrected by configuring a focus servo circuit for driving and controlling the position of the objective lens so that the focus error signal S _ER becomes 0V.

However, since the focus error signal S _ER has an S-shaped characteristic, the displacement amount from the distance d ₁ (that is, the focus error amount) is between the positive maximum value and the negative maximum value of the S-shaped characteristic. If the range D is exceeded, there is a problem that the focus error cannot be corrected only by the focus servo circuit.

In practice, in an optical disk player, the range D of displacement that can be corrected by the focus servo circuit is only ± several tens of μm with the distance d ₁ as the center.
When the optical disc player is restarted after the vibration is applied, the focus error may not be corrected.

Therefore, in the optical disc player,
By detecting the light amount of the reflected light from the optical disk (that is, the reproduction light including the optical recording information of the optical disk), a focus error in a range that cannot be corrected by the focus servo circuit is corrected.

That is, in response to the focus error signal S _ER shown in FIG. 5A, the light amount I _{RE of the} reflected light shown in FIG. 5B has a maximum value at the position of the distance d ₁ , and when the displacement amount d ₁ -d becomes large, Becomes smaller with

Therefore, in the focus search device,
By utilizing this fact and controlling the drive of the position of the objective lens, even if a large focus error occurs, it can be corrected.

An apparatus for performing such a correction will be described below with reference to FIG. In FIG. 6, reference numeral 1 denotes a focus search device as a whole, and as shown in FIG. 7A, a focus search lock signal S _CK rising at a predetermined cycle T1 is applied to the transistor 3 via the base resistor 2.

The transistor 3 has a capacitor 5 that receives a charging current from the positive power supply line L1 via a resistor 4 connected between the collector and the emitter, and repeats the ON operation and the OFF operation according to the focus search lock signal S _CK. Thus, the charging / discharging of the capacitor 5 is controlled, and a sawtooth signal whose signal level changes at a predetermined change rate determined by the time constants of the resistors 4 and 5 is output from the connection point of the resistors 4 and 5.

The emitter resistance of the transistor 7 constitutes a level shift circuit composed of a parallel circuit with series resistors 8 and 9 and the resistor 10, and outputs a sawtooth signal inputted to the base from between the resistors 8 and 9. As a result, the pull-in drive signal S1 shown in FIG. 7B which changes about 0 V is output to the operational amplifier circuit 12 through the fixed contact c → the movable contact piece a of the selection circuit 11.

The operational amplifier circuit 12 has its output terminals connected to driving transistors 14 and 15 for supplying the emitter output to the drive coil 13 of the focus actuator, and divides the emitter outputs of the transistors 14 and 15 into voltage dividing resistors 16 and 17. By feeding back to the inverting input terminal of the operational amplifier circuit 12 via, the drive amplifiers 12, 14 to 17 which supply the drive coil 13 of the focus actuator with a drive signal corresponding to the pull-in drive signal S1 are configured.

The focus actuator is equipped with an objective lens, and is displaced according to the pull-in drive signal S1 of the drive coil 13, whereby the distance d between the disc surface of the optical disc and the objective lens is displaced.

Therefore, when the movable contact piece a of the selection circuit 11 is switched to the fixed contact c and the pull-in drive signal S1 is continuously supplied, the objective lens approaches the optical disk surface as the signal level of the pull-in drive signal S1 changes. And away from the optical disk surface.

On the other hand, in the cooperator 20, the reproduction RF signal S _RF (light amount detection signal of reflected light) shown in FIG. 6C obtained from the optical disk is supplied to the non-inverting input terminal of the comparator 20, and the voltage dividing resistors 21 and 22 are also provided. The reference divided voltage V _D obtained from the above is supplied to the inverting input terminal of the comparator 20 and these values are compared to obtain the reproduction RF.
7D when the signal level of the signal S _RF becomes higher than the reference divided voltage V _D at time t1 in FIG. 7C (that is, when the light amount of the reflected light exceeds a predetermined value), the logic level rises to the logic “H”. The detection signal S2 shown in is output.

Therefore, when the logical level of the detection signal S2 rises to the logical "H", it is possible to detect that the position of the objective lens is displaced and the amount of reflected light is increased.

The comparator 20 supplies the detection signal S2 to the clear terminal CR of the D-type flip-flop circuit (hereinafter referred to as D-FF) 24 via the diode 23.

Further, the focus error signal S _ER1 shown in FIG. 7E from the comparator circuit 25 is obtained at the clock terminal CK of the D-FF 24, and the detection shown in FIG. 6F falls to the logic level "L" during the period T2. The signal S3 is supplied. The non-inverting input terminal of the comparator 25 is grounded, the focus error signal S _ER1 is supplied to the inverting input terminal, and the D terminal of the D-FF 24 is connected to the power supply line L ₁ .

The output end of the focus error amplifier 30 is connected to the fixed contact b of the switching circuit 11. The focus error amplifier 30 is a phase compensation type operational amplifier 35.
And a phase compensation circuit.

That is, the focus error signal S _ER1 is supplied to the non-inverting input terminal of the operational amplifier 25, the inverting input terminal of which is a series circuit of the resistor 31 and the capacitor 32, and the resistor 33.
Is grounded through a parallel circuit of the same and is phase-compensated by the feedback resistor 34, the focus error signal S _ER1 is phase-compensated, and the drive up 12 is performed via the fixed contact b and the movable contact a of the switch of the selection circuit 11. And the focus search is performed.

Further, when the logic level of the detection signal S2 is logic "H", the logic level of the detection signal S3 is logic "H".
At the time point t2 when the switching signal SC1 shown in FIG.
Output to.

With the above-mentioned structure, initially, the transistor 3, the resistor 4, and the capacitor 5 which form the sawtooth wave generation circuit are provided.
Drive signal S for the actuator shown in FIG. 7B from FIG.
I is supplied to the focus actuator 13 via the fixed contact c → the movable contact piece a of the switching circuit 11, and the focus actuator is swung.

The selection circuit 11 switches the output signal from the pull-in drive signal S1 to the output signal of the focus error amplifier 30 in response to the switching signal SC1.

Thus, at time t2, the state in which the focus error is corrected is detected, and the selection circuit 11 is switched to stop and control the displacement based on the pull-in drive signal S1 of the focus actuator. Call search operation).

As a result, after the time point t2, a focus servo loop is formed in which the focus actuator is drive-controlled according to the focus error signal S _ER1 . Therefore, the focus error can be surely corrected.

Thus, even if the focus servo is deviated due to vibration or the like, the focus error can be corrected promptly.

[0027]

With the conventional structure as described above, the focus search operation before the focus servo can be performed.

Now, in FIG. 8, when the objective lens 53 of the actuator 52 provided on the lower surface of the optical disk 50 rotated by the spindle motor 51 is just focused on the pit row of the optical disk 50, the lower surface of the optical disk 50 and the objective lens 53 are covered. When the distance is d ₁ , the pull-in drive signal S1 is at the zero cross point 75, and the pull-in drive signal S1 is
Is a sawtooth wave, the focus is just at the zero cross point 75 after a period 72 in which the level gradually increases from the minimum distance d _{L at} the minimum level position 71, and the maximum distance d _H at the maximum level position 73 is reached. Period 7 in which the level gradually decreases
An operation waveform signal that reaches the lowest level position 71 via 4 is supplied to the actuator 13 and the actuator 52 swings.

That is, the pull-in drive signal S1 is subjected to focus search with a constant amplitude from the lowest level position 71 to the highest level position 73.

Generally, the working distance (WD) which is the minimum distance d _L between the objective lens 53 and the optical disc 50 as shown in FIG. 8 is about 1.6 mm for a CD or the like, and a recordable magneto-optical disc ( MO) and the like are selected to be about 1.0 mm.

This W. D is determined in consideration of all errors such as unevenness of the thickness of the optical disc, difference in attitude during driving, unevenness of the focus search circuit, unevenness of the objective lens, and mounting error of the objective lens. For example, as shown in FIG.
From the state where gravity is applied to the lens surface of the objective lens 53 as in the normal use in which the optical disk 50 is on the lower side and the optical disk 50 is on the upper side, the lens surface of the objective lens is set in a horizontal posture during driving. The maximum distance d _H naturally changes when gravity is not applied vertically to the objective lens 53. Therefore, it is necessary to take these factors into consideration so that the objective lens 53 does not contact the optical disc 50 during the focus search. W. It was difficult to reduce D.

Thus, W. When D is selected to be larger than a predetermined value, the focal length d ₁ of the objective lens 53 to the optical disc 50 at the time of just focus becomes large, the diameter of the objective lens 53 becomes large, the actuator naturally becomes large, and the entire optical pickup becomes large. There was a problem such as becoming.

The present invention has been made in order to solve the above-mentioned problems, and the object of the present invention is to reduce the W.V. Since D can be minimized, the objective lens 53
It is possible to obtain a focus search device in which the diameter of the optical pickup can be made smaller and the optical pickup as a whole can be made smaller.

[0034]

As shown in FIG. 1, the focus search device of the present invention is designed so that an objective lens 53 provided on a focus actuator 52 is brought into contact with or separated from a surface of a disk 50 by a pull-in drive signal. In the focus pull-in device driven by the above-mentioned method, the focus pull-in drive signal S1 is a drive signal whose amplitude gradually changes in each cycle.

[0035]

According to the focus search device of the present invention, since the focus search signal, that is, the pull-in drive signal S1 is so constructed that its amplitude gradually increases every cycle, the thickness unevenness of the optical disk and the objective lens W. Considering mounting error etc. Since it is not necessary to make D large, it is possible to miniaturize the optical system including the objective lens.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A focus search device of the present invention will be described below with reference to FIG.
4 through FIG.

FIG. 1 is an overall system diagram of the focus search device of the present invention, FIGS. 2 and 4 are waveform explanatory diagrams, and FIG. 3 is a sawtooth wave generation circuit diagram.

Parts corresponding to those of the focus search circuit 1 described in the conventional configuration in FIG.

In FIG. 1, the optical disc 50 is rotationally driven by a spindle motor 51. An optical pickup is arranged on the lower surface of the optical disc 50, and a seek servo for moving the optical disc 50 in the radial direction and a focus servo for focusing the focus actuator 52 incorporated in the optical system 54 on the lower face of the optical disc 50 are performed. Be seen.

An objective lens 53 serving as a final emitting lens of an optical system 54 is provided on the upper end surface of the focus actuator 52, and a laser beam emitted from a laser source 55 such as a laser diode is passed through the optical system 54 to the optical disk 5.
0 is irradiated on the lower surface of the focus actuator 52. At this time, the drive coils 13 and 14 of the drive coil 13 of the focus actuator 52 are irradiated.
To 17 (see FIG. 5), the focus servo signal or the focus pull-in drive signal S1 is supplied.

The focus servo signal controls the distance d between the end surface of the optical disc 50 and the end surface of the objective lens 53 so that the focus actuator 52 can focus on the pit provided on the optical disc 50. The focus distance is d ₁ .

In order to form a reproduction RF signal and a focus error signal S _ER1 by having a laser source 55 such as a laser diode in the optical system 54 constituting the optical pickup and receiving the reflected light reflected by the pits of the optical disk 50. It has a 4-division photo detector 57 and the like.

The surface of the photo detector 57 is divided into four parts A,
Assuming B, C, and D, if these four-divided outputs are supplied to the addition circuit 58, the addition output corresponding to the received light amount of the reflected beam 57a projected on the 4-division surface, that is, the reproduction RF signal S
_RF is obtained. This reproduction RF signal S _RF is supplied to the comparator 2
0 to the clear terminal CR of the D-FF 24.

If the outputs of A and C obtained by dividing the surface of the photodetector 57 divided into four into four are set to + and the outputs of B and D are set to-and supplied to the adder circuit 59, subtraction is performed, and the output of this adder circuit 59. A focus error signal S _ER1 is output to.

The focus error signal S _ER1 is supplied to the inverting input terminal of the comparator 25, and is supplied as the detection signal S _{3 to} the clock terminal CK of the D-FF 24 in the same manner as in FIG. The D terminal of the D-FF 24 is connected to the V _CC source, and the switching signal SC1 of the Q output of the D-FF 24 is supplied to a control circuit (hereinafter CP) of a computer or a microprocessor.
U) 60.

The focus error signal S _ER1 output from the adder circuit 59 is supplied to the focus error amplifier 30. In FIG. 5, reference numeral 30 also includes a phase compensation circuit, but in FIG. 1, the phase compensation circuits 31 to 31 indicated by reference numerals 31 to 33 are shown.
33 is shown separately. The output of this phase compensation circuit is connected to the fixed contact b of the selection circuit 11.

The movable contact piece a of the selection circuit 11 is connected to the input ends of the drive amplifiers 12 and 14 to 17, the output end of the drive amplifier 13 is connected to the drive coil 13, and one end of this drive coil 13 is grounded. ing. Drive coil 1
The focus actuator 52 swings up and down by passing an electric current through 3.

The fixed contact c of the selection circuit 11 is connected to the level shift circuits 8 to 10, and the level shift circuits 8 to 10 are connected to the sawtooth wave signal generation circuit 61. The sawtooth wave signal generation circuit 61 has a focus search clock signal S.
_CK is supplied to form a sawtooth wave and data is exchanged with the CPU 60.

The CPU 60 outputs a control signal S _SEC for switching the movable contact piece a of the selection circuit 11.

The operation of the present example having the above-mentioned configuration will be described with reference to FIGS.

In FIG. 2, in this example, the sawtooth wave signal generation circuit 61 does not oscillate a sawtooth wave having a constant amplitude as shown in FIG. 8, but generates a sawtooth wave whose amplitude changes sequentially. To Preferably, the sawtooth wave generating circuit 61 is configured to generate a sawtooth wave having a constant amplitude and then a sawtooth wave having a constant amplitude.

In this way, the objective lens 5 arranged to face the optical disk 50 rotated by the spindle motor 51.
3 swings up and down as shown by arrows A and B from the position shown by the broken line to the position shown by the solid line in FIG.

At this time, the focus search signal S1 supplied to the drive coil 13 of the actuator 52 has a waveform in which the amplitude of the sawtooth wave gradually approaches the optical disc 50 from the one distant from the optical disc 60 as shown in FIG. The focus can be turned on at the position indicated by the sawtooth wave waveform 62, for example.

In this way, the W.W.D. is taken into consideration in consideration of the thickness unevenness of the optical disc 50, the warp of the disc, the focal length, the focus search circuit, and other errors of the mechanism. It is not necessary to take D sufficiently large.

As a result, W. Since the D can be made small and the focal length of the objective lens can be made small, the diameter of the objective lens can be made small, the aperture of the optical system including the actuator becomes small, and the focus retracting device which can make the optical system lightweight and compact. can get.

The structure and waveform of the sawtooth wave generation circuit 61 of the above-described example will be described with reference to FIGS. 3 and 4.

FIG. 3 shows a system diagram of the mirror integral sawtooth wave generating circuit, and FIG. 4 is a waveform diagram for explaining the same.

Reference numeral 63 in FIG. 3 denotes a clock generator which outputs a constant clock pulse 63a having a period T ₃ as shown in FIG. 4A.

This clock pulse 63a is applied to the counter 64.
Is counted in. The counter 64 first counts and outputs two clock pulses 63a, then counts and outputs three counts, and then counts and outputs four counts, and then outputs every five counts. The counter's output waveform is supplied to the waveform shaping circuit 65 so that the cycle of the sequential negative pulses shown in FIG. 4B is T ₄ ,
A focus search clock signal S _CK that changes as T ₅ , T ₆ , T _7, ... Is obtained, and is supplied to, for example, a mirror integration type sawtooth wave generator 61.

The mirror-integral sawtooth wave generator 61 is an operational amplifier having a gain G in which the phase is inverted, the input impedance is substantially infinite, and the input / output impedance is sufficiently smaller than the resistor R. e / Vo = −G / 1 + (1 + G) JωCR, and if the second term of the denominator is sufficiently larger than 1, the integral characteristic is shown.

Actually, the base of the transistor forming the operational amplifier OP is clamped via a diode or the like and is sufficiently saturated, and T ₄ , T ₅ , T ₆ , T ₇ ...
When the diode is cut off by the negative gate of
The collector voltage of the P transistor starts to rise and is negatively fed back via the emitter follower transistor connected to the collector of this transistor, so that it operates as a Miller integrator and is shown in the focus search signal S1 of FIG. 4C. Linearly the collector voltage is negative gate feedback T ₄ ,
T _5, T _6, T ₇ rises in response to ‥‥, transistor of the negative gate leaves the operational amplifier OP is rapidly saturated, different rising sawtooth wave of sequential amplitude is obtained.

Since the focus search device of the present invention is constructed as described above, the W.V. Since D can be minimized, the diameter of the objective lens can be reduced, and the optical pickup as a whole can be miniaturized.

[0063]

According to the present invention, since the amplitude of the focus search signal is successively increased, the working distance W.W. It becomes possible to make D small, the diameter of the objective lens can be made small, and a focus search device in which the optical system of the optical pickup is made small and lightweight can be obtained.

[Brief description of drawings]

FIG. 1 is an overall system diagram showing an embodiment of a focus search device of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the focus search device of the present invention.

FIG. 3 is a sawtooth wave generation circuit diagram used in the focus search device of the present invention.

4 is a waveform diagram of the sawtooth wave generation circuit of FIG.

FIG. 5 is an explanatory diagram of a conventional S-time characteristic curve.

FIG. 6 is a circuit diagram of a conventional focus search device.

FIG. 7 is a waveform explanatory diagram of a conventional focus search device.

FIG. 8 is an explanatory diagram of a conventional focus search device.

[Explanation of symbols]

 11 Selection Circuit 24 D-FF 50 Optical Disc 52 Actuator 53 Objective Lens 55 Laser Source 60 CPU 61 Mirror Integrating Sawtooth Wave Generator

Claims (2)

[Claims] 1. A focus pull-in device in which an objective lens provided in a focus actuator is driven by a pull-in drive signal so as to move toward and away from a disk surface, and the amplitude of the focus pull-in drive signal gradually changes in each cycle. A focus pull-in device characterized in that it is a drive signal. 2. The focus pull-in device according to claim 1, wherein the focus pull-in drive signal is a sawtooth wave signal whose amplitude gradually increases in each cycle.