JPH10268180A - Objective lens drive device for optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens drive device for an optical head, capable of reducing the travel distance of an objective lens beyond an intended position, and keeping the objective lens at the position more quickly at the time of driving the objective lens for a travel to the intended position at high speed. SOLUTION: A zero-cross detection circuit 14 detects the cross of a focus error signal from a focus error detection circuit 12 with a zero level, or the arrival of an objective lens 11b at a focusing position during the high-speed travel thereof to the focusing position, thereby keeping the objective lens 11b at an intended position, depending on the focus error signal. In this case, the focus error signal is time differentiated through a differential compensation circuit 16. A signal for the appearance of a zero level at a time earlier than the arrival of the focus error signal at the zero level is thereby generated, and sent to the zero-cross detection circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for optically writing or reading information on or from an optical disk, and in particular, to traverse the objective lens in the optical axis (focus) direction or the track of the optical disk. The present invention relates to an improvement of an objective lens driving device for driving in a (tracking) direction.

[0002]

2. Description of the Related Art As is well known, as an optical disk as mentioned above, a CD (Compound) on which audio data is recorded has been conventionally used.
Act Disks) and LDs (Laser Disks) in which both moving image data and audio data are recorded are widely used.

In recent years, not only moving image data and audio data but also sub-video data representing, for example, subtitles are compressed and recorded on an optical disk having the same diameter as a CD at a high density. Has also developed an optical disc, commonly known as a DVD, that allows the user to freely select and play back audio and subtitles in a desired language during playback by recording a plurality of types in different languages. Have been.

As a part of the development of this DVD, a DVD-ROM (Read Only Memory) and a D-ROM
Development for use as a VD-RAM (Random Access Memory) is also being promoted.

On the other hand, as a reproducing apparatus for reproducing such an optical disk, a rotary servo unit for controlling the rotation speed of the optical disk, or a method of irradiating a laser beam onto a signal recording surface of the optical disk and photoelectrically converting reflected light thereof is used. And an optical head for reading information recorded on an optical disk. The original information is reproduced by subjecting the signal photoelectrically converted by the optical head to waveform equalization processing, demodulation processing, and the like.

Here, the optical disc reproducing apparatus is provided with an objective lens driving device for controlling the position of the objective lens of the optical head in the focusing direction and the tracking direction. The objective lens driving device includes a focus search function of forcibly moving the objective lens from an initial position in a focus direction, and an objective lens that has reached a position near a focal point by the focus search function so as to converge to the focal point position. It realizes a focus servo function for controlling, a track jump function for moving the objective lens at high speed in the tracking direction, and a tracking servo function for performing position control in the tracking direction so that the objective lens follows the track of the optical disc.

FIG. 6 shows a configuration of a conventional objective lens driving device for realizing a focus search function and a focus servo function. That is, reference numeral 11 in the drawing denotes a focus actuator unit. The focus actuator unit 11 is an electromechanical converter including a magnet (not shown) and a focus actuator coil 11a.
By controlling the direction and magnitude of the current flowing through 1a, a driving force is generated for the objective lens 11b in the focus direction indicated by an arrow in the drawing.

The amount of displacement of the position of the objective lens 11b controlled by the focus actuator unit 11, that is, the amount of displacement of the relative distance between the objective lens 11b and the optical disk, is added to the amount of displacement due to surface deflection caused by rotation of the optical disk. Then, it is supplied to the focus error detection circuit 12. The focus error detection circuit 12 generates a focus error signal corresponding to how much the relative distance between the objective lens 11b and the optical disc deviates from the relative distance at which the objective lens 11b is at the focal point.

The focus error signal is supplied to the first fixed contact 13a of the changeover switch 13 and
The signal is supplied to the zero cross detection circuit 14. The zero-cross detection circuit 14 detects a point at which the focus error signal crosses the zero level, that is, a state where the objective lens 11b has reached the in-focus position, and based on the detection result,
It controls the changeover switch 13 and the oscillation circuit 15 that generates a sine wave signal of a constant frequency. The sine wave signal output from the oscillation circuit 15 is supplied to the second fixed contact 13b of the changeover switch 13.

That is, the zero-cross detection circuit 14
Controls the oscillation circuit 15 in a state where it is not detected that the focus error signal crosses the zero level and switches the common contact 13c of the changeover switch 13 to the second fixed contact 13b. doing. The zero-cross detection circuit 13 stops the oscillation circuit 15 in a state where it has detected that the focus error signal has crossed the zero level, and connects the common contact 13c of the changeover switch 13 to the first fixed contact 13a. The switching is controlled so as to be performed.

The sine wave signal or the focus error signal selected by the changeover switch 13 passes through a differential compensation circuit 16, which will be described in detail later, and then the amplification circuit 1
The amplified signal is supplied to a focus actuator coil 11 a of the focus actuator unit 11. As a result, the objective lens 11b is driven by the sine wave signal output from the oscillation circuit 15 or the focus error detection circuit 12
The position is controlled in the focus direction based on the focus error signal output from.

The operation of the focus search function and the focus servo function in the conventional objective lens driving device having the above configuration will be described with reference to FIG.

FIG. 7A shows the position L of the objective lens 11b, FIG. 7B shows the focus error signal VFE, and FIG. 7C shows the output voltage VDIFF of the differential compensation circuit 16.
FIG. 2D shows the moving speed S of the objective lens 11b, FIG. 2E shows the input voltage VIN to the focus actuator unit 11, and FIG. 2F shows the output from the zero-cross detection circuit 14. 3 shows a switching control signal of the changeover switch 13.

In this case, the switching control signal connects the common contact 13c of the switch 13 to the second fixed contact 13b at H (High) level, and connects the common contact 13c of the switch 13 at L (Low) level. Are connected to the first fixed contact 13a.

First, at time T1, when reproduction of the optical disk is requested, the zero-cross detection circuit 14
And generates an H level switching control signal. Therefore, the sine wave signal output from the oscillation circuit 15 is supplied to the focus actuator unit 11 via the changeover switch 13, the differential compensation circuit 16 and the amplification circuit 17, so that the objective lens 11b is focused from the initial position. The camera is forcibly moved in the focus direction toward the position, and the focus search function is realized here.

With this focus search function, when the objective lens 11b reaches the vicinity of the focal point, the focus error detection circuit 12 generates a focus error signal. If the focus error signal crosses the zero level at time T2, the zero-cross detection circuit 14 stops the oscillation circuit 15 and generates an L-level switching control signal.

For this reason, the focus error detection circuit 12
Is supplied to the focus actuator unit 11 via the changeover switch 13, the differential compensation circuit 16 and the amplifier circuit 17, so that the focus error signal becomes zero level, that is, the objective lens 11b Is controlled to converge to the in-focus position,
Here, the focus servo function is realized.

Next, the reason why the differential compensation circuit 16 is interposed in the above-described objective lens driving device will be described. That is, the focus actuator unit 1
1, the focus actuator coil 11
The transfer function G (S) of the amount of displacement of the objective lens 11b with respect to the current input to a is given by G (S) = Kf × [1 / (mS ² + DS + K)]. Note that Kf is a conversion coefficient from current to force, m is the mass of the movable part, D is viscous resistance (resistance force acting on the movable part in proportion to the speed of the movable part), and K is a spring constant (displacement of the movable part). S is a Laplace operator, a force coefficient acting on the movable part in proportion to the quantity.

FIG. 8A shows the transfer function G
FIG. 6 shows a frequency characteristic based on (S) representing a displacement amount of the objective lens 11b with respect to an input voltage to the focus actuator coil 11a of the focus actuator unit 11. FIG. FIG. 8B shows a frequency characteristic representing a phase delay of displacement of the objective lens 11b with respect to an input voltage to the focus actuator coil 11a of the focus actuator unit 11.

As apparent from FIGS. 8A and 8B,
A peak due to resonance exists around 37 Hz, and in a frequency region lower than the resonance frequency, the amplitude characteristic is flat and the phase delay is asymptotic to 0 deg. In a frequency region higher than the resonance frequency, the amplitude characteristic is -12 dB / OC.
It decreases at T, and the phase lag is approaching -180 deg. In a higher frequency region, the phase of the coil current with respect to the input voltage starts to delay due to the inductance of the focus actuator coil 11a, so that the amplitude characteristic decreases more sharply than -12 dB / OCT, and the phase delay decreases by-
It will be more delayed than 180 deg.

On the other hand, the focus error signal has characteristics as shown in FIG. In FIG. 9, the horizontal axis indicates the relative distance between the objective lens 11b and the optical disk, and the vertical axis indicates the voltage level. As is apparent from this characteristic, the range of the focus error signal that can be used for the focus servo is ± 8 μm (16 μm in total) around the zero level which is the in-focus position. The focus servo controls the input signal of the focus actuator unit 11 by negative feedback so that the focus error signal always becomes zero level.

Here, as described above, the focus actuator unit 11 has a phase delay of -180 deg or more in a frequency region higher than the resonance frequency.
If the focus servo loop is set to have negative feedback in the DC region without the differential compensation circuit 16 inside (by passing through), the phase delay of one round of the servo loop becomes -180d.
If the gain is 1 or more at the frequency at which eg occurs, positive feedback occurs at that frequency and oscillation occurs.

Therefore, in order to perform stable focus servo without such positive feedback of the focus servo loop up to such a high frequency region, the phase delay of one round of the focus servo loop near the cutoff frequency is -1.
It suffices to perform phase lead compensation so as to be less than 80 deg.

The differential compensation circuit 16 performs this phase lead compensation. This differential compensating circuit 16 is configured as shown in FIG.
As shown in FIG.
R6 and a capacitor C.
The transfer function Gd (S) from 8 to the output terminal 19 is R1
= R2, Gd (S) = [(R4 + R5) / R3] × [1+ ｛SC
R4 / (1 + SCR6)}]. The characteristics of the operational amplifiers OP1 and OP2 are ideal characteristics (infinite gain, zero output impedance, etc.). Then, the characteristics of the differential compensation circuit 16 are designed so that the cut-off frequency of the servo loop or the like becomes a desired value.

FIG. 11A shows a frequency characteristic representing an output voltage level with respect to an input voltage level of the differential compensation circuit 16. FIG. 11B shows the differential compensation circuit 1
6 shows a frequency characteristic indicating a phase advance of an output voltage with respect to an input voltage to the input voltage V.6.

When the relative distance between the objective lens 11b and the signal recording surface of the optical disk is out of the range of ± 8 μm from the in-focus position, focus servo cannot be performed. By the above-described focus search, the objective lens 11b is forcibly driven in the focus direction from the initial position, and is switched to the focus servo again when the objective lens 11b reaches the vicinity of the focal point.

[0027]

In the conventional objective lens driving apparatus as described above, the focus servo is switched to the focus servo in a state where the objective lens 11b reaches a focal point at a certain speed by a focus search. By applying a driving force in the opposite direction, the objective lens 11b is made to converge to the focal point. In other words, the objective lens 11b is configured to once overshoot the in-focus position by forced movement by the focus search, and then converge to the in-focus position by the focus servo.

Therefore, in order to shorten the time required for the focus search, if the speed at which the objective lens 11b is forcibly driven in the focus direction from the initial position to the in-focus position is increased, the accompanying speed increases. As a result, the distance over which the objective lens 11b goes too far from the in-focus position increases. When the distance over which the objective lens 11b goes beyond the in-focus position exceeds the area (± 8 μm) provided for the focus servo of the focus error signal characteristic shown in FIG.
As shown in FIG. 12, the objective lens 11b can no longer be converged to the in-focus position by the focus servo. FIGS. 12A to 12F show FIGS.
(F) respectively.

Therefore, the present invention has been made in view of the above circumstances, and when the objective lens is moved at high speed and driven so as to converge at the target position, the distance over which the objective lens passes the target position is reduced. It is another object of the present invention to provide a very good objective lens driving device for an optical head, which allows the objective lens to converge to a target position faster.

[0030]

An objective lens driving device for an optical head according to the present invention includes a moving means for moving an objective lens to a target position at a high speed, and a state in which the objective lens reaches a position near the target position by the moving means. An error signal generating means for generating an error signal corresponding to the deviation of the objective lens from the target position; and an error signal generated by the error signal generating means having a value corresponding to a state where the objective lens has reached the target position. The object of the present invention is to include a detecting means for detecting that the condition has been satisfied, and a control means for converging the objective lens to a target position in response to an error signal based on the detection result of the detecting means.

Then, by subjecting the error signal generated by the error signal generation means to time differentiation processing, a signal in which the error signal appears earlier than the value at which the error signal becomes a value detected by the detection means is generated. And a differentiating means to be provided to the detecting means.

According to the above configuration, a signal in which the error signal is generated and detected at a time earlier than the time when the error signal becomes a value detected by the detecting means by performing the time differential processing on the error signal, is detected. Since the error signal is given to the means, control for converging the objective lens to the target position can be performed earlier than in the conventional method of performing servo after the error signal reaches the value. For this reason, the distance by which the objective lens passes over the target position is reduced, and the objective lens can be converged to the target position more quickly.

Further, the objective lens driving device for an optical head according to the present invention comprises a focus search means for moving the objective lens from the initial position in the focus direction at a high speed, and the focus search means moves the objective lens to a position near a focal point with respect to the optical disk. In the reached state, the focus error signal generating means for generating a focus error signal corresponding to the deviation of the objective lens from the in-focus position with respect to the optical disc, and the focus error signal generated by the focus error signal generating means Detecting means for detecting that a value corresponding to the state of reaching the focus position with respect to the optical disk is obtained, and based on a detection result of the detection means, the objective lens is converged to the focus position with respect to the optical disk in response to a focus error signal. And control means for causing Is the elephant.

Then, by subjecting the focus error signal generated by the focus error signal generation means to time differentiation processing, the value appears earlier than the time when the focus error signal becomes a value detected by the detection means. A differentiating means for generating a signal and applying the signal to the detecting means is provided.

Further, the objective lens driving device for an optical head according to the present invention comprises a track jump means for moving the objective lens at a high speed in the tracking direction of the optical disc, and the track jump means makes the objective lens close to a target track of the optical disc. A tracking error signal generating means for generating a tracking error signal corresponding to a track deviation from a target track of the objective lens, and a tracking error signal generated by the tracking error signal generating means. Detecting means for detecting that the target lens has reached the target track, and converging the objective lens on the target track according to the tracking error signal based on the detection result of the detecting means. For those equipped with control means It is.

Then, by subjecting the tracking error signal generated by the tracking error signal generating means to time differentiation processing, the tracking error signal appears at a time earlier than the value detected by the detecting means. A differentiating means for generating a signal and applying the signal to the detecting means is provided.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as those in FIG. 6 are denoted by the same reference numerals.
That is, the focus error signal output from the focus error detection circuit 12 is supplied to the differential compensation circuit 16. The output signal of the differential compensation circuit 16 is supplied to the first fixed contact 13a of the changeover switch 13 and the zero-cross detection circuit 14, respectively. The changeover switch 13 selects the output signal of the differential compensation circuit 16 and the sine wave signal output from the oscillation circuit 15, and the selected signal is directly supplied to the amplification circuit 17.

The operation of the focus search function and the focus servo function in the above configuration will be described with reference to FIG. In addition, FIG.
(F) corresponds to FIGS. 7 (a) to 7 (f), respectively. First, at time T11, when reproduction of the optical disk is requested, the zero-cross detection circuit 14 drives the oscillation circuit 15 and generates an H-level switching control signal.

For this reason, the sine wave signal output from the oscillation circuit 15 is supplied to the focus actuator section 11 via the changeover switch 13 and the amplification circuit 17, so that
The objective lens 11b is forcibly moved in the focus direction from the initial position to the focus position, and the focus search function is realized here.

When the objective lens 11b reaches the vicinity of the in-focus position by this focus search function, FIG.
As shown in (b), the focus error detection circuit 12 generates a focus error signal. This focus error signal is supplied to the differential compensation circuit 16 and time-differentiated to be converted into a signal having a waveform as shown in FIG. Then, this differential compensation circuit 1
The output signal of No. 6 is supplied to the zero-cross detection circuit 14 to detect that the output signal has crossed the zero level.

In this case, since the output signal of the differential compensation circuit 16 is obtained by time-differentiating the focus error signal, the time T12 at which the waveform crosses the zero level is
The time when the focus error signal crosses the zero level,
That is, the time T when the objective lens actually reaches the focal point position
13 is earlier than time 13 by time Ta. Then, at time T12 when the output signal of the differential compensation circuit 16 crosses the zero level, the zero cross detection circuit 14 stops the oscillation circuit 15 and generates an L level switching control signal.

Therefore, the output signal of the differential compensation circuit 16 is supplied to the focus actuator section 11 via the changeover switch 13 and the amplifier circuit 17 so that the focus error signal becomes zero level, that is, the objective lens 11b Are controlled so as to converge to the in-focus position, and the focus servo function is realized here.

Therefore, according to the above-described first embodiment, the switching from the focus search function to the focus servo function is performed by detecting the zero cross of the signal obtained by time-differentiating the focus error signal.
Switching from the focus search function to the focus servo function can be performed earlier than the time when the focus error signal crosses the zero level. For this reason, the distance over which the objective lens 11b passes the in-focus position, which is the target position, is reduced, and the objective lens 11b can converge to the in-focus position more quickly.

FIG. 3 shows operation waveforms when the moving speed of the objective lens 11b during the focus search is set to the speed described with reference to FIG. In addition, FIG.
(F) corresponds to FIGS. 12 (a) to (f), respectively. As is apparent from FIG. 3, the focus lens is switched from the focus search function to the focus servo function at time T12 earlier by time Ta than time T13 at which the focus error signal crosses the zero level, thereby focusing the objective lens 11b. The position can be converged, and the time required for focus search can be reduced.

FIG. 4 shows a second embodiment of the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals. That is, separately from the differential compensation circuit 16 for compensating the phase advance of the focus servo loop, a differential compensation circuit 20 for time-differentiating the focus error signal output from the focus error detection circuit 12 and leading the signal to the zero-cross detection circuit 14 is provided. Has been installed. According to such a configuration, the two differential compensation circuits 16 and 20 can be set to characteristics suitable for the respective purposes, which is more effective.

FIG. 5 shows a third embodiment of the present invention. The third embodiment is suitable for a case where an objective lens moved at a high speed in a tracking direction by a track jump function is converged on a target track by a tracking servo function.

That is, reference numeral 21 in the drawing denotes a tracking actuator. The tracking actuator unit 21 is an electromechanical conversion unit including a magnet (not shown) and a tracking actuator coil 21a. The tracking actuator unit 21 controls the direction and magnitude of a current flowing through the tracking actuator coil 21a to control the objective lens 21b. To generate a driving force in the tracking direction (the direction of the arrow in the figure).

The amount of displacement of the objective lens 21 b controlled by the tracking actuator section 21 is added to the amount of displacement caused by the track swing caused by the eccentricity of the optical disk, and is supplied to the tracking error detection circuit 22. The tracking error detection circuit 22 generates a tracking error signal corresponding to the displacement of the objective lens 21b with respect to the track.

The tracking error signal is subjected to time differentiation processing by the differential compensation circuit 23, and then supplied to the first fixed contact 24a of the changeover switch 24 and to the zero cross detection circuit 25. The zero-cross detection circuit 25 detects a point where the output signal of the differential compensation circuit 23 crosses the zero level, and based on the detection result, the changeover switch 24 and a TJ signal generation circuit 26 for generating a track jump signal. And control. Note that the track jump signal output from the TJ signal generation circuit 26
Is supplied to the fixed contact 24b.

That is, the zero-cross detection circuit 25
Indicates that the TJ signal generation circuit 2 has not detected that the output signal of the differential compensation circuit 23 has crossed the zero level.
6 is driven, and the common contact piece 24c of the changeover switch 24 is controlled to be connected to the second fixed contact 24b. The zero-cross detection circuit 25 stops the TJ signal generation circuit 26 in a state where it has detected that the output signal of the differential compensation circuit 23 crosses the zero level, and sets the common contact piece 24c of the changeover switch 24 to the first position. Is controlled to be connected to the fixed contact 24a.

The signal for track jump selected by the changeover switch 24 or the differential compensation circuit 2
The output signal of No. 3 is amplified by the amplifier circuit 27 and applied to the tracking actuator coil 21 a of the tracking actuator unit 21. Thereby, the position of the objective lens 21b is controlled in the tracking direction based on the track jump signal or the output signal of the differential compensation circuit 23.

Next, the operation will be described. First, when a track jump is requested, the zero cross detection circuit 25
The J signal generation circuit 26 is driven, and the common contact piece 24c of the changeover switch 24 is controlled to be connected to the second fixed contact 24b. Therefore, the TJ signal generation circuit 26
Is supplied to the tracking actuator section 21 via the changeover switch 24 and the amplifier circuit 27, so that the objective lens 21b
The track is forcibly moved from the current position toward the target track in the tracking direction, and the track jump function is realized here.

When the objective lens 21b reaches the vicinity of the target track by the track jump function, the tracking error detection circuit 12 generates a tracking error signal. Then, the time when the signal obtained by time-differentiating the tracking error signal by the differential compensation circuit 23 crosses the zero level (this is the time when the tracking error signal crosses the zero level, that is, the time when the objective lens 21b reaches the target track) In this case, the zero-cross detection circuit 25 stops the TJ signal generation circuit 26 and controls the common contact piece 24c of the changeover switch 24 to be connected to the first fixed contact 24a.

For this reason, the output signal of the differential compensation circuit 23 is supplied to the tracking actuator section 21 via the changeover switch 24 and the amplifier circuit 27 so that the tracking error signal becomes zero level, that is, the objective lens 21b Is controlled to converge to the target track, and a tracking servo function is realized here.

According to the third embodiment, the switching from the track jump function to the tracking servo function is performed by detecting the zero cross of the signal obtained by time-differentiating the tracking error signal. The switching from the track jump function to the tracking servo function can be performed earlier than the time when the signal crosses the zero level. Therefore, the distance over which the objective lens 21b passes over the target track is reduced, and the objective lens 21b can be made to converge on the target track more quickly. It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the scope of the present invention.

[0056]

As described in detail above, according to the present invention,
When the objective lens is moved at a high speed so as to converge at the target position, the distance over which the objective lens passes the target position is reduced, so that the objective lens can be converged to the target position faster. Thus, an objective lens driving device for an optical head can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a view for explaining the operation of each unit of the first embodiment.

FIG. 3 is a view shown for explaining the operation of each unit of the first embodiment.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

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

FIG. 6 is a block diagram showing a conventional objective lens driving device.

FIG. 7 is a view for explaining the operation of each unit of the conventional device.

FIG. 8 is a diagram showing frequency characteristics of a focus actuator unit in the conventional device.

FIG. 9 is a view showing characteristics of a focus error signal in the conventional device.

FIG. 10 is a block circuit configuration diagram showing details of a differential compensation circuit in the conventional device.

FIG. 11 is a view showing frequency characteristics of the differential compensation circuit.

FIG. 12 is a diagram shown to explain a problem of the conventional device.

[Explanation of symbols]

 11: Focus actuator unit, 12: Focus error detection circuit, 13: Changeover switch, 14: Zero cross detection circuit, 15: Oscillation circuit, 16: Differential compensation circuit, 17: Amplifier circuit, 18: Input terminal, 19: Output terminal, 20: Differential compensation circuit, 21: Tracking actuator section, 22: Tracking error detection circuit, 23: Differential compensation circuit, 24: Changeover switch, 25: Zero cross detection circuit, 26: TJ signal generation circuit, 27: Amplification circuit

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 7/135 G02B 7/11 P 7/20 L

Claims (7)

[Claims] A moving means for moving the objective lens to a target position at a high speed; and a moving means for moving the objective lens near the target position in response to a deviation of the objective lens from the target position. Error signal generating means for generating an error signal, and detecting means for detecting that the error signal generated by the error signal generating means has reached a value corresponding to a state where the objective lens has reached the target position, Control means for converging the objective lens to the target position in accordance with the error signal based on the detection result of the detection means, wherein the error signal is generated by the error signal generation means. By performing the time differential processing on the error signal, at a time earlier than the error signal becomes a value detected by the detection means, An objective lens driving device for an optical head, comprising a differentiating means for generating a signal in which the value appears and supplying the signal to the detecting means. 2. The method according to claim 1, wherein the differentiating unit is configured to determine an error signal corresponding to a deviation of the objective lens from the target position.
2. The objective lens driving device for an optical head according to claim 1, wherein a series of negative feedback servo loops for converging the objective lens to the target position are also used to perform phase lead compensation. 3. The error signal generating means generates an error signal having a zero level when the objective lens reaches the target position, and the detecting means detects a zero cross point of the error signal. 2. The objective lens driving device for an optical head according to claim 1, wherein: 4. The apparatus according to claim 1, wherein the target position of the objective lens is a focus position with respect to an optical disk.
An objective lens driving device for an optical head according to claim 1. 5. The objective lens driving device for an optical head according to claim 1, wherein the target position of the objective lens is a track of an optical disk. 6. A focus search means for moving an objective lens from an initial position in a focus direction at a high speed, and the objective lens is moved to the optical disk in a state where the objective lens reaches a position near a focal point for the optical disk by the focus search means. A focus error signal generating means for generating a focus error signal corresponding to a deviation from the focus position, and a focus error signal generated by the focus error signal generation means, wherein the objective lens has reached a focus position with respect to the optical disc. Detecting means for detecting that a value corresponding to the state has been reached, and control means for converging the objective lens to a focus position with respect to the optical disk in accordance with the focus error signal based on a detection result of the detecting means. Lens driving device for optical head The time difference processing is performed on the focus error signal generated by the focus error signal generation means, so that the focus error signal appears at a time earlier than the value detected by the detection means. An objective lens driving device for an optical head, further comprising a differentiating means for generating a signal to be given to the detecting means. 7. A track jump means for moving an objective lens at a high speed in a tracking direction of an optical disk, and the objective lens reaches the target track of the optical disk by the track jump means. A tracking error signal generating means for generating a tracking error signal corresponding to a track deviation from a track to be set; and a tracking error signal generated by the tracking error signal generating means, wherein the objective lens reaches the target track. Detecting means for detecting that a value corresponding to the state has been reached, and control means for converging the objective lens to the target track in accordance with the tracking error signal based on the detection result of the detecting means. The objective lens drive of the optical head Then, by subjecting the tracking error signal generated by the tracking error signal generating means to time differentiation processing, the value appears at a point earlier than the tracking error signal becomes a value detected by the detecting means. An objective lens driving device for an optical head, comprising a differentiating means for generating a signal and supplying the signal to the detecting means.