JPH11191223A - Focus controller and method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the collision of an optical head with an optical recording medium even when a distance between the optical head and the optical recording medium becomes very short by increasing the value of NA of an objective lens. SOLUTION: When a loop off deciding circuit 31 decides that a focusing servo loop becomes off, a timer circuit 32 counts prescribed times by starting a timer. A driving voltage generating circuit 33 generates a driving voltage so as to separate an objective lens 14a from an optical recording medium 60 until the completion of counting for the prescribed time interval from the start of the timer of the timer circuit 32. Consequently, a focusing driver 40 performs control operation to separate the objective lens 14a from the optical recording medium 60 based on the driving voltage generated in the driving voltage generating circuit 33 when the focusing loop becomes off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a focus control device and a focus control method for performing focus control of an optical head.

[0002]

2. Description of the Related Art There has been provided an optical recording / reproducing apparatus for recording information on an optical recording medium or reproducing information recorded on the optical recording medium. In the above optical recording / reproducing apparatus, the distance between the objective lens held by a movable part such as a biaxial actuator and the optical recording medium is maintained, and the light beam transmitted through the objective lens and collected on the information surface of the optical recording medium. A focus servo device that controls so as to be a just focus is provided.

In recent years, the capacity of read-only ROM disks and recordable / reproducible RAM disks has been increasing, and accordingly, the wavelength of semiconductor lasers in optical heads has been shortened, and light beams have been focused. N of the objective lens
The value of A (Numerical Aperture) is also large.

[0004]

As the value of the NA of the objective lens increases, the distance between the objective lens and the optical recording medium, the so-called working distance (Working Distance:
Hereinafter, it is referred to as “WD”. ) Becomes smaller. For example,
When an objective lens with NA = 0.85 is used, WD
≒ 100 [μm]. Here, the surface deflection during rotation of the optical recording medium having a radius of 5 inches is substantially 300 [μm].
Considering that there is a certain degree, the objective lens may collide with the optical recording medium after the focus servo has shifted from the on state to the off state, and it may be difficult to record information on the optical recording medium or to reproduce information. is there. Also, in some cases,
The objective lens may be damaged.

The present invention has been proposed in view of such circumstances, and even if the distance between the optical head and the optical recording medium becomes very short due to an increase in the value of the NA of the objective lens, the present invention has been proposed. It is an object of the present invention to provide a focus control device and a focus control method for preventing a head from colliding with an optical recording medium.

[0006]

In order to solve the above-mentioned problems, a focus control apparatus according to the present invention generates a focus error signal based on a laser beam emitted from an optical head and reflected from an optical recording medium. A focus error signal generating unit, a driver that forms a focus loop based on the focus error signal and performs focus control of the optical head, and a focus loop determination unit that determines that the focus loop has been cut off. When the focus loop determining means determines that the focus loop has been broken, the optical head is controlled so as to be separated from the optical recording medium.

In the above focus control device, a focus loop is formed based on a focus error signal to perform focus control of the optical head, and the driver separates the optical head from the optical recording medium when determining that the focus loop has been broken. Control.

Further, according to the focus control method of the present invention, a focus error signal is generated based on a laser beam emitted from an optical head and reflected from an optical recording medium,
A focus loop is formed based on the focus error signal, focus control of the optical head is performed, it is determined that the focus loop has been cut, and when it is determined that the focus loop has been cut, the optical head is separated from the optical recording medium. It is characterized by controlling.

In the above focus control method, a focus loop is formed based on a focus error signal to perform focus control of the optical head. When it is determined that the focus loop has been broken, the optical head is separated from the optical recording medium. To control.

[0010]

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

The present invention can be applied to, for example, a focus control device 1 having the configuration shown in FIG.

The focus control device 1 emits a laser beam for recording / reproducing data, and obtains a detection output of reflected light from the optical recording medium 60.
A focus error signal generation unit 20 that generates a focus error signal from the detection output, a focus loop determination unit 30 that determines whether the focus loop is turned off, a focus driver 40 that controls focusing of the optical head, A spindle motor 50 for rotating the optical recording medium 60 and an FG 51 for detecting the number of rotations of the spindle motor 50 are provided. Note that a spindle servo circuit (not shown) performs the following operations based on the detection result of the FG 51.
The optical recording medium 60 is controlled at a predetermined rotation speed.

The optical head 10 includes a semiconductor laser 11 for emitting a laser beam, a collimator lens 12 for converting the laser beam into parallel light, and a polarizing film 13a for transmitting only the laser beam reflected by the optical recording medium 60. And a lens unit 14 for moving two objective lenses 14a and 14b, which will be described later, in two directions: a direction perpendicular to the track of the optical recording medium 60 (tracking direction) and an optical axis direction (focus direction) of the laser beam. And a condenser lens 15 for condensing the laser beam
And a light receiving element 16 for obtaining a detection output of the focused laser beam.

The laser beam emitted from the semiconductor laser 11 becomes parallel light via a collimator lens 12 and enters a beam splitter 13.

The polarizing film 13a of the beam splitter 13
The laser beam incident from the collimator lens 12 is reflected in the direction of the lens unit 14.

The lens unit 14 has a first objective lens 14a for focusing a laser beam on the optical recording medium 60,
It has a second objective lens 14b, a focus coil 14c for adjusting the focal length of the first and second objective lenses 14a and 14b, a magnet 14d, and a yoke 14e. The focus coil 14c is, for example, a magnet 1
4d and a yoke 14e are disposed in a gap of a magnetic circuit. The first objective lens 14a and the second objective lens 14b are integrally driven in the optical axis direction of the laser beam based on the direction and magnitude of the current flowing through the focus coil 14c.

Here, the lens unit 14 will be described in more detail. Specifically, as shown in FIG. 2, the lens unit 14 includes a first electromagnetic actuator 14f for driving a first objective lens 14a and a second electromagnetic actuator 14g for driving a second objective lens 14b. Prepare. First and second electromagnetic actuators 14f, 1
4g is for adjusting spherical aberration. The second objective lens 14b is mounted on a second electromagnetic actuator 14g movable in the focus direction and the tracking direction, and has a numerical aperture of about 0.5. Further, the first objective lens 14a is mounted on the first electromagnetic actuator 14f above the second objective lens 14b,
It is configured to be controllable to any position on the optical axis. The first objective lens 14a moves integrally with the second objective lens 14b in the tracking direction, and follows the tracking servo. Then, the light beam from the semiconductor laser 11 is applied to the first and second objective lenses 14a and 14b.
, And is condensed on the phase-change information recording surface of the optical recording medium 60. At this time, the effective objective lens numerical aperture of the first and second objective lenses 14a and 14b is about 0.85.

Also, the first and second objective lenses 14a, 14a,
14 b supplies the light reflected from the optical recording medium 60 to the beam splitter 13. The beam splitter 13 transmits the laser beam from the first objective lens 14 a and the like, and supplies the laser beam to the light receiving element 16 via the condenser lens 15.

As shown in FIG. 3, for example, the light receiving element 16 is composed of a photodetector whose light receiving section is divided into four parts A, B, C and D, and the laser of each light receiving section A, B, C and D is provided. The beam detection output is used as a focus error signal generator 20.
To supply.

The focus error signal generating section 20 generates a sum signal based on the detection output of the light receiving element 16 and a focus error generating circuit that generates a focus error signal based on the detection output of the light receiving element 16. The circuit includes a circuit 22, a search signal generating circuit 23 for generating a search signal for searching for a just focus position, a phase compensating circuit 24 for performing phase compensation, a switch control circuit 25, and a switching circuit 26.

The sum signal generation circuit 21 generates a sum signal (= A + B + C + D) by calculating the sum of the detection outputs of the four light receiving portions A, B, C, and D in the light receiving element 16, and switches the sum signal by switch control. The signal is supplied to the circuit 25 and the search signal generation circuit 23.

The focus error generating circuit 22 obtains a difference between the sum of the detection outputs of the light receiving sections A and C of the light receiving element 16 and the sum of the detection outputs of the light receiving sections B and D, for example. = (A + C)-(B
+ D)), and supplies the focus error signal to the phase compensation circuit 24 and the switch control circuit 25.

The search signal generation circuit 23
When 0 is set, as shown in FIG. 4A, the first objective lens 14a and the like are once separated from the optical recording medium 60, and the optical head 10 is gradually approached to the optical recording medium 60, so that the laser A search signal for searching for the just focus position of the beam is generated and supplied to the terminal b of the switching circuit 26.

The phase compensating circuit 24 compensates the phase of the focus error signal supplied from the focus error generating circuit 22, and converts the focus error signal to the switching circuit 2.
6 to the terminal a.

The switch control circuit 25 generates a switch control signal to switch the switching circuit 2.
6 is controlled. Here, the first objective lens 1
As FIG. 4A and the like approach the optical recording medium 60, FIG.
As shown in the figure, the signal level of the sum signal increases. First
When the distance WD between the objective lens 14a and the optical recording medium 60 is within several microns, a focus error signal as shown in FIG. 4C is generated. Therefore, the switch control circuit 25 starts detecting the focus error signal when the sum signal goes from the L level to a predetermined pull-in level or more, and when the focus error signal becomes 0 as shown in FIG. To generate an H level switch control signal. As a result, the focus loop is turned on, and the focus servo is pulled. That is, when the switch control signal is at the L level, the focus loop is off, and when the switch control signal is at the H level, the focus loop is on.

When the switch control signal is at the L level, the switching circuit 26 supplies a search signal to the focus driver 40 via the terminal b. When the switch control signal goes high, the switching circuit 26 outputs a focus error signal via the terminal a to the focus driver 40.
To supply.

Therefore, the focus driver 40
The drive voltage (drive signal) shown in FIG. 4E is supplied to the focus coil 14c. As a result, the focus driver 40 operates the first objective lens 14 based on the search signal.
a is once separated from the optical recording medium 60, and the optical head 10 is gradually moved closer to the optical recording medium 60. When the focus of the laser beam is determined, focus control is performed based on the focus error signal.

The switch control circuit 25 includes:
When the signal level of the sum signal falls below the pull-in level or when the focus error signal cannot be detected, an L-level switch control signal is generated. Thereby, the focus servo is turned off.

Here, the focus loop determination unit 30
The system includes a loop-off determining circuit 31 for determining whether the focus servo loop has been turned off, a timer circuit 32 for measuring a predetermined time, and a drive voltage generating circuit 33 for generating a drive voltage for driving the optical head 10.

The loop-off determining circuit 31 determines whether the switch control signal has changed from the H level to the L level, and when it determines that the switch control signal has changed to the L level, determines that the focus servo loop is off. When the loop-off determining circuit 31 determines that the focus servo loop has been turned off, the timer circuit 32 starts a timer and counts a predetermined time. The drive voltage generation circuit 33
Until the timer of the timer circuit 32 is activated and the clocking of the predetermined time is completed, a drive voltage (drive signal) for separating the first objective lens 14 a and the like from the optical recording medium 60 is generated. Therefore, when the focus loop is turned off, the focus driver 40
The control for separating the objective lens 14a from the optical recording medium 60 is performed based on the drive voltage generated in the step (a).

Therefore, the tracking control device 1
For example, even when the recording / reproduction of the optical recording medium 60 is completed, or when the tracking loop is broken due to a sudden impact, the objective lens 14a is pulled away from the optical recording medium It is possible to prevent the recording medium 60 and the objective lens 14a from being damaged by collision.

[0032]

As described above in detail, according to the focus control apparatus and the focus control method according to the present invention, a focus loop is formed based on a focus error signal to perform focus control of an optical head, and a focus loop When the optical head is determined to be out of control, the optical head is controlled to be separated from the optical recording medium, so that when the distance between the optical head and the optical recording medium is very short due to an increase in the value of NA of the objective lens, the focus can be reduced. Even when the servo loop is broken, it is possible to prevent the optical head from colliding with the optical recording medium.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a specific configuration of a focus control device to which the present invention has been applied.

FIG. 2 is a diagram showing a configuration of a lens unit of the focus control device.

FIG. 3 is a diagram illustrating a configuration of a light receiving element of the focus control device.

FIG. 4 shows a search signal, a focus error signal, a sum signal,
5 is a timing chart illustrating a switch control signal and a driver driving signal.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 focus control device, 10 optical head, 20 focus error signal generator, 30 focus loop determiner, 40 driver

Claims (4)

[Claims] A focus error signal generating means for generating a focus error signal based on a reflected light of a laser beam emitted from an optical head from an optical recording medium; and a focus loop formed based on the focus error signal to form an optical system. A driver for performing focus control of the head; and a focus loop determining means for determining that the focus loop has been broken, wherein the driver is configured to control the optical head when the focus loop determining means determines that the focus loop has been broken. A focus control device for controlling the distance from the optical recording medium. 2. The apparatus according to claim 1, further comprising: a time measuring means for measuring a predetermined time from when the focus loop determining means determines that the focus loop has been broken, wherein the driver controls the optical head while the time measuring means is counting the predetermined time. 2. The focus control device according to claim 1, wherein the focus control is performed so as to be away from the recording medium. 3. A focus error signal is generated based on a reflected laser beam emitted from the optical head from an optical recording medium, and a focus loop is formed based on the focus error signal to perform focus control of the optical head. A focus control method comprising: determining that the focus loop has been broken; and controlling the optical head to be separated from the optical recording medium when determining that the focus loop has been broken. 4. The apparatus according to claim 3, wherein a predetermined time is measured from when it is determined that the focus loop has been broken, and the optical head is controlled to be separated from the recording medium while the predetermined time is measured. Focus control method.