JPH04372726A - Optical disk device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical disc device that records and reproduces information by irradiating a recording medium with a laser beam spot and receiving and detecting reflected light. The present invention relates to a focus pull-in method.

0002

2. Description of the Related Art Generally, in an optical disc device, a focusing servo is used to focus a laser beam spot on an optical recording medium, such as an optical disc, and a tracking servo is used to direct the laser beam spot to an information recording track formed on the optical disc. Information is written, read, or erased in accordance with the information. When processing such information, it is first necessary to focus the laser beam to bring the spot into focus on the optical disc.

Conventionally, this focus pull-in operation has been performed using a focus position error signal FES of a laser beam spot. The error signal FES is a signal obtained by differentially processing a plurality of photocurrents obtained by receiving reflected light from an optical disk in a divided manner, and is normally used as an input signal for a focusing servo. That is, in the focusing servo, the position of the laser beam spot is controlled so that the error signal FES becomes zero. When performing a focus pull-in operation, the laser beam spot is linearly approached to the optical disk surface while the focusing servo is stopped and the error signal FES is monitored. When the error signal FES becomes 0, the approach operation is stopped and at the same time, the focusing servo is enabled to forcibly bring the laser beam spot into focus.

0004

By the way, optical discs generally have a multilayer structure in which a substrate is coated with an optical recording medium layer and a protective layer in this order. The protective layer has a light reflective surface, and the information recording surface of the optical recording medium layer is covered with the protective layer. When a laser beam spot is brought close to an optical disc having such a multilayer structure during focus pull-in, reflection occurs first on the optical disc surface and then on the recording surface. Therefore, the error signal FES becomes 0 when reflected from the surface, and subsequently becomes 0 when reflected from the recording surface. That is, the error signal FES includes false focus information caused by optical disk surface reflection and true focus information caused by recording surface reflection. If the focusing servo is erroneously activated in response to false focusing information, the laser beam spot will be focused on the optical disk surface, resulting in a problem that normal information recording and reproduction cannot be performed. Furthermore, if the focusing servo is applied while the optical disk surface is in focus, there is a problem that the servo circuit will malfunction.

[0005] In order to prevent erroneous focus pulling,
One possibility is to utilize the difference in reflectance between the surface of the protective layer and the recording surface. Generally, the reflectance of the surface of the protective layer is smaller than the reflectance of the recording surface, so there is a difference in the total photocurrent amount at the time of both reflections. This difference is detected using a circuit and processed using software to distinguish between false focus information and true focus information included in the error signal FES. However, such an identification method requires complicated circuitry and software, and has problems in that it is not reliable.

[0006]

[Means for Solving the Problems] In view of the above-mentioned problems and problems of the conventional technology, the present invention uses a simplified circuit to distinguish between false focus information and true focus information to ensure reliable recording of optical discs. The purpose is to draw focus to a surface.

[0007] In order to achieve the above object, an optical disc device according to the present invention has the following means or structure. That is, an optical disk device includes a laser light source that emits a laser beam, an objective lens that focuses the laser beam as a spot, and an actuator that focuses the spot on the recording surface through the reflective surface of the recording medium. It is equipped with. A light-receiving element is disposed on the reflected optical path, and has a multi-divided surface that can receive the reflected light from the recording medium in a divided manner, and outputs a detection signal for each divided surface. AG in the light receiving element
A circuit C is connected to the error signal FES, which processes the detection signal and outputs an error signal FES including false focus information caused by the reflection of the spot on the surface of the recording medium and true focus information caused by the reflection on the recording surface. A servo circuit is connected to the AGC circuit, and normally performs a servo operation to control the actuator and maintain the focused state of the spot according to the error signal FES. Furthermore, a bias circuit is incorporated as a feature of the present invention, and by adding a predetermined amount of bias component to each detection signal, true focus information is kept valid while false focus information is invalidated. . Finally, a control circuit consisting of a CPU, etc. is provided, which drives the actuator with the servo operation stopped when focusing, brings the spot close to the recording surface through the reflective surface, and disables false focusing. While the information is ignored, the true focus information that remains valid is detected and the servo operation is activated to bring the spot into focus on the recording surface.

Preferably, the control circuit includes means for controlling the bias circuit to stop supplying the bias component and increase the gain of the error signal FES in the servo operation after the focusing of the spot on the recording surface is completed. Contains.

[0009]

[Operation] Generally, the error signal FES is obtained by differentially processing the detection signal or photocurrent output from the multi-split plane of the light receiving element using an AGC circuit, and is a small S-shaped signal representing false focusing information. It includes a large S-shaped waveform representing the waveform and true focus information. By adding a bias component to each photocurrent during focus pull-in, the amplitude value of the S-time waveform can be reduced. By appropriately setting the magnitude of the bias component, it is possible to reduce the amplitude of a small S-shaped waveform to a negligible extent while still maintaining the amplitude of a large S-shaped waveform at an effective level that can be detected. In this way, by using the amplitude-modulated error signal FES, only true focus information can be reliably detected and the spot can be correctly focused on the recording surface.

In addition, after the focus pull-in is completed,
By stopping the supply of the bias component, the amplitude of the S-shaped waveform returns to its original level, and the error signal F in servo operation
It is possible to increase the gain of ES.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the electrical configuration of an optical disc device according to the present invention, and best represents the features of the present invention. Further, FIG. 2 shows the optical configuration of the optical disc device, and FIG. 3 shows the operation of the optical disc device. In order to facilitate understanding of the present invention, first, the optical configuration will be briefly explained with reference to FIG. 2, and then the configuration of the present invention will be explained in detail with reference to FIG. 1, and finally with reference to FIG. The focus pull-in operation of the optical disc device will now be explained.

As shown in FIG. 2, the optical disk device includes a laser light source 1 that emits a laser beam, a collimator lens 2 that converts the laser beam into a parallel beam, and an optical disk 3.
and an objective lens 4 for converging the parallel beam to form a spot. The optical disc 3 has a multilayer structure in which a substrate 5 is coated with an optical recording medium layer 6 and a protective layer 7 in this order. The protective layer 7 has a reflective surface 8 whose reflectance is, for example, about 5%. Further, the optical recording medium layer 6 has a recording surface 9 on which tracks for recording information are formed. The reflectance of the recording surface 9 is, for example, about 20%. The objective lens 4 is driven vertically and horizontally with respect to the optical disk 3 by a biaxial actuator 10 as shown by the arrows, and performs focusing of the laser beam spot and tracking of the information recording track. Let's do it.

The optical disc device further includes a beam splitter 11, which separates the reflected light from the optical disc 3 from the incident light. The separated reflected light is converged by a converging lens 12 and further divided into two beams by another beam splitter 13. One of the light beams is received by the servo light receiving element 14. The other light beam is received by the information reproducing light receiving element 15.

Next, the electrical configuration of the optical disc device will be explained in detail with reference to FIG. The servo light receiving element 14 has multi-divided surfaces A, B, C, and D that can receive reflected light from an optical disk (not shown) in a divided manner, and detects a detection signal, that is, photocurrent IA, IB, for each divided surface. , IC and ID. In this example, a four-part plane is used, but the present invention is not limited to this, and for example, a two-part plane may be used. In this example, an astigmatism method is used to detect the focal position of the laser beam spot. That is, the optical structure shown in FIG. 2 includes an astigmatism optical system, and the light receiving spot J in the focused state is approximately circular, and the light is received approximately equally by the quarter plane. On the other hand, when the light receiving spot N is located in front of the focal point, the light receiving spot N has a flat shape tilted to the left, for example, due to astigmatism. On the other hand, the light-receiving spot F beyond the focused point has a flattened shape tilted to the right due to astigmatism.

An AGC circuit 16 is connected to the light receiving element 14. The AGC circuit 16 outputs photocurrents IA to I
D is differentially processed according to a predetermined calculation formula and a focal position error signal FES of the laser beam spot is output. This error signal FES includes false focus information due to reflections on the optical disk surface 8 and true focus information due to reflections on the recording surface 9. The AGC circuit 16 further differentially processes the photocurrents IA to ID according to a predetermined calculation formula, and also outputs a track position error signal TES of the laser beam spot. The AGC circuit 16 performs automatic gain control of the error signals FES and TES in response to fluctuations in the amount of reflected light during information recording and information reproduction, so that the subsequent servo circuit can always operate optimally.

A focus servo circuit 17 is connected to the AGC circuit 16, and controls the actuator 10 according to the error signal FES to perform a servo operation to maintain the focused state of the spot. The focus servo circuit 17 is
It is composed of a phase compensation circuit 18, a switch circuit 19 for switching between stopping and activating the servo operation, an amplifier circuit 20, and a drive circuit 21 for driving the actuator 10. Although not shown, the other error signal TE
S is also input to the tracking servo circuit and similarly performs tracking servo operation.

The optical disk device further includes a bias circuit 22, which is a characteristic component of the present invention. This bias circuit 22 is for adding a predetermined amount of bias component, ie, bias current IX, to each photocurrent IA to ID, and prevents false focusing information while keeping true focusing information contained in the error signal FES valid. The purpose is to invalidate it. The bias circuit 22 includes a constant current source 23 for supplying or injecting the bias current IX, and a switching circuit 24 for selectively stopping the injection or supply of the bias current IX.

Finally, the optical disc device is equipped with a control circuit 25 consisting of a CPU and the like. The control circuit 25 controls the switch circuit 19 of the servo circuit 17 during focus retraction to stop the servo operation, and also injects a forced signal into the amplifier circuit 20 to drive the actuator 10 to move the objective lens 4 linearly in the vertical direction. move it. As a result, the laser beam spot approaches the recording surface 9 through the reflective surface 8 of the optical disc 3. At this time, control circuit 2
5 makes the switching circuit 24 of the bias circuit 22 conductive;
Bias current IX is injected into each of photocurrents IA to ID. This is to invalidate false focus information included in the error signal FES. In this state, the control circuit 25 outputs the error signal F.
The ES is monitored to detect true focus information that remains valid while ignoring invalidated false focus information. At the time of detection, the focus servo operation of the servo circuit 17 is activated via the switch circuit 19, and the laser beam spot is brought into focus on the recording surface 9. The control circuit 25 also monitors the tracking error signal TES. When correct focus pull-in is completed, the laser beam spot is maintained in focus by the action of the servo circuit 17. On the other hand, the tracking servo circuit is still in a stopped state and the spot following operation for the information track is not performed, so that a significant tracking error signal TES is output. By detecting this error signal TES, completion of focusing of the laser beam spot is confirmed and injection of bias current IX is stopped.

Finally, the operation of the optical disc device will be explained in detail with reference to FIG. As described above, the AGC circuit 16 outputs the error signal FES according to a predetermined calculation formula. This calculation formula follows the astigmatism method and is expressed, for example, as follows. FES={(IA+IC)-(IB+ID)}/(
IA+IB+IC+ID) As is clear from this equation, IA+IC increases before the in-focus point, IB+ID increases beyond the in-focus point, and both terms become equal at the in-focus point. Therefore, the error signal FES generally has an S-shaped waveform near the in-focus point.

In order to facilitate understanding of the following explanation, the above-mentioned arithmetic expression will be transformed into the following arithmetic expression. FES=ΔI/I Here, ΔI represents the difference between the former term IA+IC and the latter term IB+ID, and I represents the total photocurrent sum. Here, the error signal output when the surface is reflected is FES1=ΔI1/I1, and the error signal output when the recording surface is reflected is FES2=Δ
When I2/I2, the value of ΔI1 is considerably smaller than the value of ΔI2 due to the difference in reflection characteristics on both sides, while the value of the total current sum I1 is reduced to a relatively small extent compared to I2. Therefore, the S-curve S1 of FES1 is
Its amplitude is smaller than that of the S-curve S2 of No. 2. However, as is clear from FIG. 3, when no bias current is injected, even the small S-shaped waveform S1 has a detectable amplitude level.

On the other hand, when the bias current IX is injected according to the present invention, the error signal at the time of reflection on the optical disk surface becomes FES
1=ΔI1/(I1+4IX), and the error signal at the time of reflection on the recording surface is FES2=ΔI2/(I2+4IX)
becomes. In either case, the numerator difference term is unaffected by the bias current injection, while the denominator total photocurrent sum term increases by the injection. Originally, the difference ΔI1
is considerably smaller than the difference ΔI2, it is greatly affected by the bias current injection, and FES1
The amplitude of the S-shaped waveform S1X at the time of injection becomes extremely small and becomes below the detection level, so it is invalidated. On the other hand, the S-shaped waveform S at the time of injection included in the error signal FES2 at the time of reflection from the recording surface
2X is not significantly affected by the injection of bias current, the amplitude is kept at a detectable level, and is still effective. That is, when a bias current is injected, a small S-shaped waveform representing false focus information is invalidated like S1X, and a large S-shaped waveform representing true focus information is kept valid like S2X.

In this way, the amplitude modulated error signal FES
By performing the focus pull-in operation using the laser beam, the laser beam spot can always be correctly focused on the recording surface of the optical disc. This focus pull-in operation is performed by moving the objective lens close to the optical disk while the servo circuit is stopped. Next, the large S-shaped waveform S2X
The focus servo operation is activated at the zero-crossing point to ensure the focus-in state. At this time, the slope, that is, the gain, of the S-shaped waveform S2X when the bias current is injected is gentler than the slope of the S-shaped waveform S2 when the bias current is not injected. Therefore, the focus-in state can be more easily achieved than in the past. That is, if the gain of the error signal FES is too high, the focus servo operation will work too much, and the surface runout of the optical disk and the linear movement of the objective lens will act synergistically, causing the objective lens to be pushed away from the in-focus position. In this regard, according to the present invention, the gain of the error signal FES during the focus pull-in operation is suppressed to be lower than that of the prior art, so that the focus servo works gently to achieve a reliable focus-in state.

Finally, when the focus-in state is reached,
A tracking error signal TES is now output from the AGC circuit 16. By detecting this error signal TES, the control circuit 25 stops injection of bias current. As a result, the S-shaped waveform of the focus error signal FES becomes like S2, and the gain increases. By performing an autofocus operation near the zero-crossing point of this S-shaped waveform S2, the focused state of the laser beam spot can be continuously maintained.

[0024]

[Effects of the Invention] As explained above, according to the present invention, by injecting a bias current into the photocurrent, false focus information is disabled while validly maintaining true focus information included in the focus position error signal. This has the effect of reliably focusing the laser beam spot on the recording surface. Furthermore, since the gain of the position error signal can be suppressed to some extent when true focus information is maintained effectively, there is an effect that focus pull-in can be performed more easily than in the past. In addition, by stopping the injection of bias current after the focus pull-in is completed, the gain of the focus position error signal is increased and an effective autofocus operation can be performed as in the conventional method.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing the electrical configuration of an optical disc device according to the present invention.

FIG. 2 is a block diagram showing the optical configuration of the optical disc device according to the present invention.

FIG. 3 is a waveform diagram for explaining the operation of the optical disc device according to the present invention.

[Explanation of symbols]

1 Laser light source 3. Optical disc 4 Objective lens 6 Optical recording medium layer 7 Protective layer 8. Reflective surface 9 Recording surface 10 Two-axis actuator 14 Light receiving element for servo 16 AGC circuit 17 Focus servo circuit 22 Bias circuit 23 Constant current source 24 Switching circuit 25 Control circuit

Claims (2)

[Claims] 1. A laser light source that emits a laser beam, an actuator that includes an objective lens that focuses the laser beam as a spot and focuses the spot on a recording surface via a reflective surface of the recording medium, and a recording medium. A light-receiving element has a multi-divided surface that can receive the reflected light from the surface separately and outputs a detection signal for each divided surface, and a light-receiving element that processes the detection signal and detects false focusing caused by spot reflection on the recording medium surface. An AGC circuit for outputting an error signal including true focus information caused by information and recording surface reflection, and a servo circuit for controlling an actuator according to the error signal and performing servo operation to maintain a spot in focus. , a bias circuit for invalidating false focus information while keeping true focus information valid by adding a predetermined amount of bias component to each detection signal, and an actuator that maintains true focus information valid while invalidating false focus information, and drives the spot to approach the recording surface through the reflective surface, ignores the invalidated false focus information, detects the true focus information that remains valid, activates the servo operation, and moves the spot toward the recording surface. An optical disc device comprising a control circuit for executing focus pull-in. 2. The control circuit includes means for controlling the bias circuit to stop supplying the bias component and increase the gain of the error signal in the servo operation after the focusing of the spot on the recording surface is completed. The optical disc device according to claim 1.