JP2553655B2 - Focus control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for converging a light beam emitted from a light source and irradiating it on a recording medium surface to record or reproduce a signal on the recording medium surface. The present invention relates to a focus control device that controls a converged state of a light beam.

2. Description of the Related Art As a conventional technique for pulling in focus control of an optical information recording / reproducing apparatus, there is a technique described in JP-A-60-121537.

The pull-in operation of the focus control will be described with reference to FIG.

A disk-shaped recording medium (hereinafter referred to as a disk) is rotated by a motor at a specified number of revolutions, and after converging and irradiating a light beam emitted from a light source such as a semiconductor laser, the converging lens is driven to pull in focus control. To start.

The recording material surface of the disc is protected by a transparent protective layer, and since there are irregularities and warps on the surface, the recording material surface,
The surface of the disk becomes a surface wobbling by the rotation and moves up and down as shown in FIGS.

Focus error when the converging lens is moved along the locus shown in FIG. 3c, that is, when the position of the light beam converged by the converging lens (hereinafter referred to as the focus position) moves as shown in FIG. 3c. The signal is shown in Figure 3d.

The focus error signal draws a small S-shape on the surface of the disk having a low reflectance and a large S-shape on the surface of the recording material having a high reflectance, and becomes zero at points C ₁ and C ₂ .

Since the peak values V ₂ and V ₁ of the focus error signal on the recording material surface and the disk surface have a relationship of V ₂ > V ₁ , the focus control pull-in level V ₃ is V ₂ ≧ V ₃ > V _1. And move the focus position,
When the focus error signal exceeds V ₃ , that is, when it reaches the point P, the focus control loop is closed to perform the pull-in operation.

In such focus pull-in control, V ₃ which is the pull-in level is set to a level close to V ₁ in order to reduce the overshoot of the control signal after pull-in and stably pull in.

When the focus control pulling operation is not performed to pull the recording medium surface, the movement is performed again by the same pulling control. For example, the reflectance of the disk surface and the electrical offset in the control system are used. If there is a large variation in gain, gain, or offset due to the position of the optical photodetector, the focus error signal will exceed the pull-in level even near the disk surface, and focus control will be applied not on the recording medium surface but on the disk surface. There is a problem that the surface of the recording medium is not covered even if the startup is repeated.

The present invention has been made in view of the above problems, and provides a highly reliable device that accurately and stably pulls in focus control.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a converging means for converging a light beam emitted from a light source and irradiating it onto a recording medium surface, and a light beam on the recording medium surface. Focus error detecting means for detecting the convergent state, moving means for moving the converging means in a direction substantially perpendicular to the recording medium surface, and driving the moving means according to the output of the focus error detecting means. Focus control means for controlling the light beam on the surface of the recording medium to be in a substantially constant convergence state, comparison means for comparing the output of the focus error detection means with a predetermined comparison value, and the comparison value exceeding the comparison value. When
It is equipped with pull-in control means for driving the moving means to perform focus pull-in control for starting focus control, and comparison value switching means for changing the comparison value, and restarting due to focus pull-in error by the pull-in control means. At this time, the comparison value switching means changes the set comparison value to a comparison value in which the focus pull-in position of the light beam becomes a direction away from the recording medium surface.

Effect The present invention has the above-described configuration, when the focus control is retracted, the focus control loop is closed at a predetermined focus position at the time of startup, and the focus position that closes the loop of the control system is changed at the time of restart due to an error in focus acquisition. Is. As a result, stable focus pull-in can be performed against the influence of the reflectivity of the disk surface and the offset and gain variations electrically and optically in the control system.

Embodiment Hereinafter, a focus control device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of the apparatus. Reference numeral 1 denotes a disk, which is attached to the disk motor 2 and rotates at a predetermined rotation speed. A light beam 4 emitted from a semiconductor laser 3 which is a light source is collimated by a collimator lens 5, reflected by a polarization beam splitter 6 and passed through a quarter wavelength plate 7.
It is converged by the converging lens 8 and is approximately 1 μm on the disc 1.
The light beam is emitted. The focus control detects the converged state and causes the recording material surface to follow the recording material surface with high accuracy even when the disk 1 rotates to move up and down. The accuracy is, for example, ± 0.5 μm or less. .

The light beam 4 reflected by the disc 1 again passes through the converging lens 8, the quarter-wave plate 7, and the polarization beam splitter 6,
The split mirror 10 splits into two directions. One light beam 4
Enters the focus error photodetector 11. The other light beam enters the tracking error photodetector 12.

The focus error photodetector 11 has a two-divided structure, and the output difference between the two areas is calculated by the differential amplifier circuit 13 to obtain a focus error signal 14. The distance between the recording material surface and the focus position of the light beam is detected by this focus error signal, and the focus control is operated so that this distance becomes the minimum. The focus error signal is the phase compensation circuit 25 that compensates the phase of the control system, the changeover switch circuit
A current is caused to flow through the control element 21 that moves the converging lens 8 through the drive circuit 20 to cause the focus position to follow the recording material surface.

The tracking error photodetector 12 also has a two-divided structure, and the tracking error signal is obtained by calculating the output difference between the two regions by the differential amplifier circuit 15.

The tracking error signal detects the amount of deviation between the groove previously formed on the surface of the recording material and the convergent position of the light beam, and it can be detected from this signal that it is on the surface of the recording material.

In this focus control system, the control operation is started by moving the surface of the recording material near the focus position of the light beam. In this focus pull-in control operation,
The microcomputer 17 has a D / A circuit 18 and a changeover switch 1
9, add a drive signal to the control element 21 via the drive circuit 20,
This is performed by moving the converging lens 8.

When the converging lens 8 approaches the disc 1 from a position away from the disc 1, the focus error signal 14 changes as shown in FIG. Point C ₁ is due to reflection on the disk surface, and point C ₂ is due to the recording material surface. In order to draw the focus on the surface of the recording material, the comparison value V ₃ is set by the comparison value setting circuit 22 so that V ₁ <V ₃ ≤ V ₂ and input to the comparison circuit 24 via the comparison value switching circuit 23. Keep it.

When the converging lens 8 is brought closer to the disk, the focus error signal 14 changes when the focus position of the light beam comes near the recording material. When the focus error signal 14 is further approached, the comparison value V ₃ which is the pull-in level is exceeded, and the comparison value ON signal is output from the comparison circuit 24 to the microcomputer 17, and this microcomputer 17 outputs the focus control operation ON / OFF signal. Turns ON 27. At this time, the changeover switch circuit 19 is switched to the phase compensation circuit 25 side,
The focus control loop is closed and the operation is enabled.

Next, the microcomputer 17 starts the operation of the counter circuit 26, and the counter circuit 26 starts the tracking error signal.
The 16 track signals are counted for a predetermined time, it is detected that the number of tracks reaches a predetermined number, and it is detected that the track signal has been pulled to the point C ₂ of the recording material surface of the disc.

Here, the counter circuit 26 that detects the recording material surface
If the detection signal that has detected that the predetermined number has been reached from the microcomputer does not come into the microcomputer within the predetermined time, the changeover switch circuit 19 is controlled to the D / A circuit 18 side, the focus control loop is opened, and the operation is stopped. The comparison value switching circuit 23 is controlled to set the comparison value V ₃ ′, and again the microcomputer 17
Signal is input to the D / A circuit 18 to drive the converging lens 8 to execute the pull-in operation.

In addition, when the converging lens is brought close to the disk in advance during the pulling operation and is pulled toward the recording material surface while moving away from the disc, the pulling level is set to V ₆ or V ₆ ′.

At this time, the pull-in level V ₆ has a relationship of V ₄ > V ₆ ≧ V ₅ with respect to the minimum value V ₅ of the focus error signal on the recording material surface.

The comparison circuit 24 is configured to output a comparison value ON signal to the microcomputer 17 when the focus error signal becomes smaller than the comparison value V ₆ . Microcomputer 17
Responds to the comparison value ON signal of the comparison circuit 24 to switch the changeover switch circuit 19 and close the focus control loop in the same manner as described above to start the focus control. In this way, the focused light beam follows the recording material surface of the disc.

Next, the counter circuit 26 is activated to detect the recording material surface. If it cannot be detected within a predetermined time that the predetermined number has been reached, the comparison value switching circuit 23 is controlled to set the comparison value.
Set V ₆ ′ and execute the pull-in operation again.

Comparison value V ₃ ′ switched by the comparison value switching circuit or
V ₆ ′ is set at a position further away from V ₃ or V ₆ from the focus position where the light beam is in a desired convergence state.

As a result, even if V ₁ of the focus error signal on the disk surface fluctuates, the amount of fluctuation is within V ₃ ′ −V ₁ , or if the converging lens is moved closer to the disk and retracted while moving away, V ₆ ′. If it is within -V ₄ , focus pull-in control can be performed.

Further, the reliability of the focus pull-in can be further enhanced by performing the restarting a plurality of times due to the focus pull-in mistake.

In the above embodiment, the pull-in level to be compared with the focus error signal was switched at the time of restart due to a pull-in error of the focus pull-in control, but the type of the disk, the reflectance, etc. are detected in advance, and it is suitable for that at the time of startup. If the pull-in level is set and executed, more stable focus pull-in can be performed. For example, when using discs having different reflectivities such as a read-only disc, a write-once disc, and a rewritable disc, a cartridge for accommodating the disc is provided with a mark or the like for discriminating the disc type or the reflectivity.
The mark may be detected at the time of start-up to switch the pull-in level to execute the pull-in control.

Moreover, the focus pull-level V ₃ 'to the first startup may be V ₃ to restart by pulling miss. Rebooting, pull-in level at rebooting is V ₃ ′, V ₃ ,
The reliability can be further improved by repeating like V ₃ ′ or increasing the number of pull-in levels set between V ₁ and V ₂ .

As described above, according to the present invention, the reliability of the focus pull-in control is improved, the reflectance of the disk surface, the variation of the electrical offset and the gain in the control system, the offset due to the position of the optical photodetector. It is possible to obtain a device that is stable against the effects of the above.

[Brief description of drawings]

FIG. 1 is a block diagram of a focus control apparatus according to an embodiment of the present invention, FIG. 2 is an operation explanatory view showing a focus control pull-in operation according to this embodiment, and FIG. 3 is a timing chart showing a conventional focus pull-in operation. is there. 1 ... Disc, 2 ... Disc motor, 3 ... Semiconductor laser, 4 ... Light beam, 8 ... Converging lens, 14 ... Focus error signal, 19 ... Changeover switch, 22 ... Comparison value setting circuit, 23 …… Comparison value switching circuit, 24 …… Comparison circuit,
27 …… Focus control operation ON / OFF signal.

Front Page Continuation (72) Inventor Yasuhiro Goto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Koichi Yamada 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

(57) [Claims] 1. Converging means for converging a light beam emitted from a light source and irradiating it onto a recording medium surface; focus error detecting means for detecting a converged state of the light beam on the recording medium surface; Moving means for moving the converging means in a direction substantially perpendicular to the recording medium surface, and driving the moving means in accordance with the output of the focus error detecting means to converge the light beam on the recording medium surface in a substantially constant state. Focus control means for controlling so that the output of the focus error detection means is compared with a predetermined comparison value, and when the comparison value is exceeded, the moving means is driven to start focus control. A pull-in control means for performing focus pull-in control, and a comparison value switching means for changing the comparison value. When restarting due to a mistake in pulling in, the comparison value switching means changes the set comparison value to a comparison value in which the focus pull-in position of the light beam moves away from the recording medium surface. Control device.