JP3041121B2 - Focus servo device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus servo device used for a write-once optical disk drive, a rewritable optical disk drive, and the like.

[0002]

2. Description of the Related Art There are two types of laser diodes used in a write-once optical disk drive or a rewritable optical disk drive, such as output during reproduction and output during recording, that is, a relatively low output and a relatively high output. Using the output of For this reason, the laser oscillation wavelength differs between reproduction and recording, and a focus shift occurs due to chromatic aberration of the optical system. When the output of the laser diode changes from reproduction to recording, or from recording to reproduction, a larger focus shift occurs due to a change in the oscillation wavelength of the laser than the focus shift caused by the surface deflection of the recording medium, and the laser returns to the in-focus position. However, there was a problem that the time required for this was long.

Therefore, an invention as shown in Japanese Patent Application No. 2-203426 has been made. Hereinafter, a conventional example will be described with reference to the drawings. 4 and 5 relate to a conventional example, FIG. 4 is a block diagram showing a configuration of a focus servo device, and FIG. 5 is a timing chart showing timings of main signals of the focus servo device.

In FIG. 4, reference numeral 31 denotes a relatively low drive current which is output to the laser diode 31 when data written on the medium is read, and a relatively high drive current is output to the laser diode 31 when data is written on the medium. The laser diode 31 is a read / write switching unit.
As shown in FIG. 5A, a beam having an output corresponding to the drive current from the read / write switching unit 31 is emitted, and the lens 38 is turned on.
Converges this beam and irradiates the medium surface with spot light.

Reference numeral 33 denotes a focus error detector which outputs a focus error signal indicating the amount of focus position deviation of the spot light applied to the medium surface, as shown in FIG. 5C, by the light reflected from the medium surface. , 34 are focus error detectors 3
The focus servo control unit outputs a drive signal to the lens drive mechanism 37 via the changeover switch 36 so that the focus error signal from the controller 3 becomes zero, that is, a spot light is focused on the medium surface.

As shown in FIG. 5B, when the read / write switching unit 31 switches from a relatively low driving current to a relatively high driving current, the lens 35 suddenly accelerates in a direction away from the medium surface. In addition, when the read / write switching unit 31 switches from a relatively high drive current to a relatively low drive current, the lens 38 is moved with rapid acceleration and rapid deceleration in a direction approaching from the medium surface. The switch 36 selectively outputs a drive signal from the focus servo controller 34 or an acceleration pulse from the acceleration pulse generator 35 in response to a switching signal from the read / write switch 31. Is output to the lens drive mechanism 37.

Next, the operation of the above conventional example will be described.

First, when the read / write switching unit 31 is outputting a relatively low drive current to the laser diode 32 in order to read data written on the medium, the switch 36 is turned on by the focus servo control unit 34. Is output to the lens drive mechanism 37.

In this case, the focus error signal is as shown in FIG.
As shown in FIG. 5C, the signal 41 has a relatively small fluctuation according to the surface deflection of the medium. Therefore, as shown in FIG. 5D, the spot light is focused on the medium surface.

In this state, in order to write data on the medium, the read / write switching unit 31 switches from a relatively low drive current to a relatively high drive current to switch the laser diode 32.
In this case, since the oscillation wavelength of the laser diode 32 shifts to a slightly longer wavelength, the spot light is focused on a position far from the medium surface, as shown in FIG.

In this case, the focus error signal is as shown in FIG.
As shown in (c), the signal 42 has a relatively large fluctuation of a minus level corresponding to the chromatic aberration of the lens 38.

Therefore, the changeover switch 36 is turned on by the changeover signal of the read / write changeover section 31 so that the acceleration pulse generator 35
Is switched to output the acceleration pulse from the lens drive mechanism to the lens drive mechanism, the lens 38 moves with rapid acceleration and rapid deceleration in a direction away from the medium surface, and therefore, as shown in FIG. Focusing on the medium surface in time (focus error signal 43).

After the time t during which the acceleration pulse is output, when the changeover switch 36 is switched so as to output the drive signal from the focus control section 34 to the lens drive mechanism 37, the focus error signal becomes as shown in FIG. As shown in FIG. 7, a signal 44 having relatively small fluctuation according to the surface runout of the medium.
Therefore, as shown in FIG. 5D, the spot light is focused on the medium surface.

On the other hand, in this state, in order to read the data written on the medium, the read / write switching unit 31 switches to a relatively low drive current, and the oscillation wavelength of the laser diode 32 shifts to the original short wavelength. , FIG. 5 (d)
As shown in (1), the spot light is focused on a position close to the medium surface, and a large focus shift occurs.

Therefore, when the changeover switch 36 is switched to output the acceleration pulse from the acceleration pulse generator 35 to the lens driving mechanism 37 in response to the switching signal from the read / write switcher 31, the lens 38 moves in the direction approaching the medium surface. 5 with rapid acceleration and rapid deceleration.
As shown in (d), the spot light is focused on the medium surface in a short time (focus error signals 46 and 47).

[0016]

However, in general, in a focus servo apparatus, there is a case where the dispersion of the optical system and the oscillation wavelength of the laser at the time of switching the drive current differ depending on the individual difference of the laser diode. That is, the amount of focus shift caused by the chromatic aberration of the optical system caused by a change in the output of the laser diode differs for each device. Therefore, the effect of correcting the focus shift in a short time when the output of the laser diode of the conventional focus servo device is switched is maximized, that is, the chromatic aberration of the optical system caused by the output change of the laser diode in the shortest time is reduced. In order to correct the resulting focus shift amount, it is necessary to adjust the amplitude or time of the acceleration pulse for each device. Further, even if the amplitude or time of the acceleration pulse is adjusted for each device, there is a problem that it is difficult to maintain the above-mentioned effect to the maximum because the amount of focus shift changes due to aging of the laser diode or the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is capable of always correcting a focus shift when switching the output of a laser diode in a short time without performing any adjustment or the like. It is intended to provide.

[0018]

A focus servo device according to the present invention comprises a laser diode for irradiating a medium with spot light through an optical lens, a relatively low drive current and a relatively high drive current for the laser diode. Driving means for selectively supplying the optical lens, and when the driving means switches from a relatively low driving current to a relatively high driving current, the optical lens is moved at a rapid acceleration and a rapid deceleration in a direction away from the medium surface. On the other hand, when the driving means switches from a relatively high driving current to a relatively low driving current, an acceleration means for generating a signal for moving the lens at a rapid acceleration and a rapid deceleration in a direction approaching from the medium surface. And detecting a focus error signal indicating an amount of deviation of a spot light irradiated on the medium from the focus position by the laser diode. A focus servo device comprising a step and the drive means switching from a relatively low drive current to a relatively high drive current and / or the drive means switching from a relatively high drive current to a relatively low drive current. Setting means for setting a signal generated by the acceleration means according to the focus error signal in the case.

[0019]

The focus error signal when the drive means switches from a relatively low drive current to a relatively high drive current and / or when the drive means switches from a relatively high drive current to a relatively low drive current. The setting means sets a signal generated by the acceleration means, the acceleration means generates a signal set by the setting means, and the driving means switches from a relatively low driving current to a relatively high driving current. When, the optical lens is moved with rapid acceleration and rapid deceleration in a direction away from the medium surface,
On the other hand, when the drive means switches from a relatively high drive current to a relatively low drive current, the lens is moved with rapid acceleration and rapid deceleration in a direction approaching from the medium surface.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 relate to an embodiment of the present invention. FIG. 1 is a block diagram showing a configuration of a focus servo device, FIG. 2 is a timing chart showing timings of main signals of the focus servo device, and FIG. It is a waveform diagram explaining an acceleration pulse.

As shown in FIG. 1, a focus servo device 1 of this embodiment includes a laser diode 2 for generating a light beam, a light beam from the laser diode 2 condensed, and a medium is irradiated with spot light. A lens 3 to be input and reflected light from an optical recording medium (hereinafter, referred to as a medium) such as a write-once optical disk, a rewritable optical disk, a magneto-optical disk, or an optical card are input via a half mirror 4,
A focus detection unit that outputs a focus error signal indicating a focus position shift amount of the spot light applied to the medium surface;
And a focus servo control unit 6 described later, a read / write switching unit 8, an acceleration pulse generation unit 9, and a controller 10.

The focus servo control unit 6 controls the drive signal so that the focus error signal from the focus detection unit 5 via the changeover switch SW1 becomes zero, that is, a drive signal such that the spot light is focused on the medium surface. Is output to the lens driving mechanism 7 for driving the lens 3 via the changeover switch SW2.

The read / write switching section 8 outputs a relatively low drive current to the laser diode 2 when reading data written on the medium, and outputs a relatively high drive current when writing data on the medium. It outputs to the diode 2 and controls the changeover switch SW2 and the acceleration pulse generator 9.

When the read / write switching unit 8 switches from a relatively low drive current to a relatively high drive current, the acceleration pulse generator 9 performs rapid acceleration and deceleration in a direction to move the lens 3 away from the medium surface. When the read / write switching unit 8 switches from a relatively high drive current to a relatively low drive current, an acceleration pulse for moving the lens 3 at a rapid acceleration and a rapid deceleration in a direction approaching from the medium surface is output. Is to occur.

When the read / write switching section 8 switches from a relatively low drive current to a relatively high drive current, or switches from a relatively high drive current to a relatively low drive current, An acceleration pulse calculation unit 11 that detects a focus error signal from the focus detection unit 5 and calculates, for example, the amplitude of the acceleration pulse and transmits a set value of the amplitude of the acceleration pulse to the acceleration pulse generation unit 9; ON / OFF control of the changeover switch SW1 by the control of the acceleration pulse calculation unit 10 by the latch timing signal, and the acceleration pulse correction control unit 12 by which the read / write switching unit 8 is controlled by the control signal. Have been.

The acceleration pulse generator 10 has means for storing a set value of the amplitude of the acceleration pulse from the acceleration pulse calculator 11, and generates an acceleration pulse based on the set value. I have.

The acceleration pulse calculator 11 detects a focus error signal from the focus detector 5 and calculates, for example, the amplitude of the acceleration pulse. The read / write switching unit 8 does not affect the acceleration pulse generation unit 9 and the changeover switch SW2 during the period when the signal is transmitted. That is, during this period,
The acceleration pulse does not enter the focus servo system.

Next, the operation of setting the amplitude of the acceleration pulse in the above embodiment will be described. The other operations are the same as those of the conventional example, and the description is omitted.

When the focus servo device 1 is started up, for example, when the power is turned on or at the time of initial operation such as when a medium is inserted, the focus switches are set to the a side by setting the changeover switches SW1 and SW2 to the focus error detecting section 5, and The focus servo system including the servo control unit 6, the lens driving mechanism 7, and the lens 3 is closed. At this time, the read / write switching unit 8 outputs a relatively low drive current. In this case, the focus error signal is as shown in FIG.
As shown in (c), the signal 13 has a relatively small fluctuation according to the surface deflection of the medium.

A first detection area for detecting an amount of focus shift caused by chromatic aberration of the optical system caused by a change in output of the laser diode 2, for example, in the case of a magneto-optical disk,
After the medium moves to the ALPC (auto laser power control) area, which is a total reflection area in the ISO (International Organization for Standardization) sector format (FIG. 2A), the acceleration pulse correction control unit 12 outputs a timing signal 14 (FIG. 2
(D)), the changeover switch SW1 is set to the b side to open the focus servo system, and the control signal is controlled so that the read / write switching unit 8 outputs a relatively high drive current. The ALPC area can be used repeatedly, and by using the ALPC area, there is an effect that the ALPC area can be used for servo control other than the intended use of the ALPC area. Further, not only in the magneto-optical disk but also in other optical recording media, for example, by providing such an area, the amount of defocus is detected.

The output of the laser diode 2 is changed from read power to write power by the drive signal from the read / write switching section 8 (FIG. 2B), the oscillation wavelength of the laser diode 2 is changed, and focus is caused by chromatic aberration of the optical system. The error signal becomes a relatively large signal 15 (FIG. 2C).
The acceleration pulse correction control unit 12 converts the latch timing signal 16 (FIG. 2E) having a delay sufficient for changing the focus error signal into a relatively large signal 15 with respect to the timing signal 14 from the acceleration pulse calculation unit. 11, and the acceleration pulse calculating section 11 outputs a relatively large focus error signal 15 based on the latch timing signal 16.
Latch the peak of

After that, the acceleration pulse correction control unit 12
The timing signal 17 (see FIG.
(D)), the changeover switch SW1 is switched to the a side, and the focus servo system is closed. As a result, as shown in FIG. 2C, the focus error signal becomes a signal 18 having a relatively small fluctuation according to the surface deflection of the medium. Subsequently, the acceleration pulse correction control unit 12 switches the read / write switching unit 8 according to the control signal so as to output a relatively low drive current.

The acceleration pulse calculator 11 calculates the set amplitude of the acceleration pulse from the latched relatively large focus error signal 15 by a method described later, and sets the result in the acceleration pulse generator 9.

When the acceleration pulse generator 9 generates the set acceleration pulse, the read / write switching unit 8 switches the read / write switching unit 8 from a relatively low drive current to a relatively low drive current at the time of reading and writing, as in the conventional example. When the lens 3 is moved at a rapid acceleration and a rapid deceleration in a direction away from the medium surface when switching to a high driving current, and when the read / write switching unit 8 switches from a relatively high driving current to a relatively low driving current. Then, the lens 3 is moved with rapid acceleration and rapid deceleration in a direction approaching from the medium surface, and the focus shift when the output of the laser diode 2 is switched is corrected in a short time.

When detecting the amount of focus shift due to the chromatic aberration of the optical system caused by a change in the output of the laser diode 2, the switch SW1 is set to the b side to open the focus servo system. The detection may be performed with the focus servo system closed with SW1 kept on the a side.

Next, a method of calculating the amplitude of the acceleration pulse will be described.

The focus error detector 5 sets the detection sensitivity to G (F
ES) [V / m], and the acceleration sensitivity of the lens drive mechanism 7 is A (L
ENS) [m / s · s / V], and the time of the acceleration pulse is t
[S], if the focus error signal when the focus servo is open is E (FES) [V] and the set value of the acceleration pulse amplitude is Ep [V], then Ep = E (FES) / ｛G ( FES) · A (LENS) · t ² 、, and the amplitude of the acceleration pulse is calculated and set.
Here, Ep and t of the acceleration pulse are defined as shown in FIG. Further, since G (FES) and A (LENS) hardly change, they can be treated as predetermined constants. Therefore, by measuring E (FES), it is possible to calculate the amplitude of the acceleration pulse. it can.

As described above, the focus servo device 1 according to the present embodiment, when the focus servo device 1 starts up,
Since the amount of focus shift due to a change in the output of the laser diode is detected, and the acceleration pulse is corrected based on the detected amount of focus shift, it is not necessary to adjust the acceleration pulse for each device. Even if the focus shift amount changes due to changes, etc.,
It is possible to always correct the focus shift when switching the output of the laser diode in a short time.

In the above embodiment, the acceleration pulse time is fixed and the amplitude of the acceleration pulse is calculated and set. However, the present invention is not limited to this. For example, the acceleration pulse time is fixed and the acceleration pulse time is fixed. That is, the pulse width t
(The amplitude Ep and the pulse width t of the acceleration pulse are defined by FIG. 3 similarly to the above embodiment). That is, the pulse width t can be obtained as t = [E (FES) / {G (FES) · A (LENS) · Ep}] ^1/2. By measuring E (FES), the acceleration is calculated by the above calculation. The time of the pulse can be calculated.

The detection of the amount of focus shift due to the chromatic aberration of the optical system caused by the change in the output of the laser diode 2 is performed by changing the output of the laser diode 2 from read power to write power by a drive signal from the read / write switching unit 8. The focus error signal becomes a relatively large signal 15 due to a change in the oscillation wavelength of the laser diode 2 and the chromatic aberration of the optical system. However, the present invention is not limited to this. For example, as shown in FIG. The output of the laser diode 2 changes from write power to read power by the drive signal from the read / write switching unit 8, the oscillation wavelength of the laser diode 2 changes, and the focus error signal is relatively large due to chromatic aberration of the optical system. (Figure 2
(C)), the amount of defocus is detected, and
The acceleration pulse calculation unit 1 is operated based on the defocus amount.
The acceleration pulse may be calculated by 1 (the absolute value of the signal 19 is substantially equal to the absolute value of the signal 15).

Further, the detection of the amount of defocus caused by the chromatic aberration of the optical system caused by the change in the output of the laser diode 2 is performed by detecting the above-mentioned signals 15 and 19, and the acceleration pulse calculator 11 calculates the absolute value of the signal 15 The average of the absolute value of the signal and the signal 19 may be obtained to calculate the acceleration pulse.

Further, the detection of the focus shift amount caused by the chromatic aberration of the optical system caused by the change in the output of the laser diode 2 is performed, for example, by detecting a plurality of ALPCs on one track.
Over the region, a plurality of signals 15 and / or 19 are detected, and the acceleration pulse calculation unit 11 calculates the absolute value of the plurality of signals 15 and the average of the absolute values of the signals 19 or any one of them. The average of one of the signals may be obtained to calculate the acceleration pulse. In this way, for example, even if there is a defect in a specific ALPC area, the average is obtained over a plurality of ALPC areas. Thus, the amount of defocus can be reliably detected.

[0044]

As described above, according to the present invention, the focus servo device of the present invention always corrects the focus shift when switching the output of the laser diode in a short time without performing any adjustment or the like. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a focus servo device according to one embodiment.

FIG. 2 is a timing chart showing timings of main signals of the focus servo device according to one embodiment.

FIG. 3 is a waveform diagram illustrating an acceleration pulse according to one embodiment.

FIG. 4 is a block diagram illustrating a configuration of a focus servo device according to a conventional example.

FIG. 5 is a timing chart showing timings of main signals of a conventional focus servo device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Focus servo device 2 ... Laser diode 5 ... Focus error detection part 6 ... Focus servo control part 7 ... Lens drive mechanism 8 ... Read / write switching part 9 ... Acceleration pulse generation part 11 ... Acceleration pulse calculation part 12 ... Acceleration pulse correction control Department

Claims (1)

(57) [Claims] 1. A laser diode for irradiating a medium with spot light via an optical lens; a drive unit for selectively supplying a relatively low drive current and a relatively high drive current to the laser diode; When the means switches from a relatively low drive current to a relatively high drive current, the optical lens is moved at a rapid acceleration and a rapid deceleration in a direction away from the medium surface, while the drive means is moved at a relatively high drive current. An acceleration means for generating a signal for moving the lens at a rapid acceleration and a rapid deceleration in a direction approaching from the medium surface when switching to a relatively low drive current; and irradiating the laser diode on the medium. Detecting means for detecting a focus error signal indicating the amount of deviation from the focused position of the spot light, the focus servo device, The focus error signal when the drive means switches from a relatively low drive current to a relatively high drive current and / or when the drive means switches from a relatively high drive current to a relatively low drive current; A focus servo device comprising a calculating means for calculating a signal generated by the means.