JPH04247331A - Method for deciding focus setting - Google Patents

Abstract

PURPOSE:To decide focus setting without adding external circuits even if an optical recording medium is in a offcenter-less state by injecting a kick back voltage to tracking servo. CONSTITUTION:The tracking servo is put into the off state by controlling a switch 24 and the focus servo is put into the on state by controlling a switch 14. Consequently, the focus servo based on a focus error signal FES starts operating. A detecting circuit 30 detects a peak change of the tracking error signal TES appearing when the optical storage medium is in an offcenter state. The kick back voltage is injected to a limit amplifier 25 by turning on a switch 28 to move an objective lens 4 in a horizontal direction and to generate a pseudo offcenter if the signal TES is not detected. The circuit 30 detects the peak by a fluctuation in the signal TES.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for focusing a laser beam spot onto the surface of a recording medium in an optical recording apparatus or the like. More specifically, the present invention relates to a method that can effectively determine whether focus pull-in has actually been performed even when a recording medium such as an optical disk is mounted in an optical recording apparatus in a non-eccentric state.

0002

[Prior Art] Generally, in an optical recording device, a focus servo is used to focus a laser beam on the surface of an optical disk, and a tracking servo is used to make a laser beam spot follow an information recording track formed on the surface of an optical disk. information is written, read, or erased. When processing such information, it is first necessary to focus the laser beam so that the beam spot is focused on the surface of the optical disk. Conventionally, whether or not focus pull-in has been actually performed has been determined by detecting whether or not a tracking error signal is output. That is, when an optical disc is mounted on a spindle motor of an optical recording device, the optical disc is eccentric due to various error factors. Therefore, when such an optical disk is rotated by a spindle motor, the information recording track is shifted relative to the focused laser beam spot depending on the amount of eccentricity. If focus pull-in is actually performed, this deviation will be detected as a tracking error signal, and focus pull-in can be confirmed. That is, the detection range of the tracking error signal is approximately several micrometers from the focal point of the laser beam to determine whether or not focus pull-in has been performed. Therefore, when the optical disk is set on the spindle motor in an eccentric state, focus pull-in can normally be effectively determined.

By the way, a metal hub is usually provided at the center of an optical disk for attachment to a spindle motor. This hub contacts the cup of the spindle motor and is fixed by magnetic force. At this time, the optical disk is slightly eccentric with respect to the rotation axis of the spindle motor due to deviation of the fixing position of the optical disk, vibration of chucking, deviation of the position of the spindle motor cup, etc. Therefore, when the spindle motor is rotated, this eccentricity causes the track to be displaced relative to the focused laser beam spot, resulting in a tracking error signal. However, sometimes the optical disk is mounted on the spindle motor without eccentricity. At this time, even if the spindle motor is rotated,
Since no track positional deviation occurs, even if focus pull-in is actually performed, no tracking error signal is generated, which may lead to incorrect determination.

Conventionally, in order to effectively determine whether or not focus is being pulled in even in the above-mentioned non-eccentric state, a method has been used in which a tracking error signal is generated by causing so-called pseudo eccentricity. For this purpose, a so-called lens lock servo was used. This lens lock servo is an automatic control mechanism for fixing the objective lens at a predetermined position based on a predetermined reference voltage. When there is no eccentricity, this reference voltage is forcibly changed and the objective lens is swung in the radial direction of the optical disk to create pseudo-eccentricity, and focus pull-in is determined based on whether a tracking error signal is detected at this time. was.

[0005]

[Problems to be Solved by the Invention] However, in the conventional method for determining focus pull-in when there is no eccentricity using a lens lock servo, an external additional circuit such as a DA converter is required to variably control the reference voltage of the lens lock servo. However, there was a problem in that the structure was complicated. Furthermore, if there is no lens lock servo, it is not possible to determine focus pull-in using detection of a tracking error signal. For this reason, it is necessary to eject the optical disc once, chuck it again, bring it into an eccentric state, and then repeat the focus pull-in operation.
There was a problem that the operation was complicated.

In view of the above-mentioned problems of the conventional technology, the present invention utilizes only the tracking servo and focus servo that are originally provided in the optical recording device, without using any external additional circuit, even when there is no eccentricity. The purpose is to enable determination of focus pull.

[0007]

[Means for Solving the Problems] FIG. 1 shows a basic flowchart of a focus pull-in determination method according to the present invention. After loading the optical disk into the optical recording device and starting it up, in step 1, the tracking servo is turned off or put into a resting state. This tracking servo is an automatic control mechanism that allows the laser beam spot to always follow the track. Next, in step 2, the focus servo is turned on. As a result, in step 3, the focus servo performs an automatic focusing operation of the laser beam spot to execute focus pull-in. In step 4, it is detected whether the tracking error signal TES is being output. If detected, it is determined that focus pull-in has been successful. Conversely, if the tracking error signal TES is not detected, a process of injecting a kickback voltage into the tracking servo is performed in step 5. This kickback voltage is originally supplied from a kickback circuit installed in the tracking servo. The kickback circuit is for forcibly moving the laser beam spot in the radial direction of the disk, and is used, for example, when seeking a spiral track formed on the surface of an optical disk, or when rewriting recorded information. It is used when the verification is then performed sequentially. Subsequently, in step 6, it is detected again whether the tracking error signal TES is being output. If the tracking error signal TES is detected, it is confirmed in step 7 that focus pull-in has been executed. Conversely, if the tracking error signal TES is not detected in step 6, it is determined that the focus is out of focus, and a jump is made to another control loop to take appropriate measures.

[0008]

[Operation] After the focus pull-in operation is performed in step 3, if the tracking error signal TES is detected in step 4, it can be confirmed that the focus pull-in has actually been performed. However, even if it is determined NO in the first detection process, it may not necessarily be out of focus. That is, when the optical disk is accidentally chucked with respect to the spindle motor in a non-eccentric state, even though the focus pull-in has been completed,
The tracking error signal TES may not be detected. Therefore, at this time, a kickback voltage is injected in step 5. During the focus pull-in operation, the tracking servo is in an OFF state, so the kickback voltage forcibly moves the objective lens in the radial direction of the disk, that is, in the eccentric direction. This movement of the objective lens causes pseudo-decentering. Therefore, in step 6, the second
When the tracking error signal is detected for the second time and a YES determination result is obtained, it is confirmed that focus pull-in has actually been performed. As described above, according to the present invention, focus pull-in can be effectively determined by simply injecting a kickback voltage even when the optical disk is chucked without eccentricity.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a schematic diagram showing an example of the optical configuration of an optical recording device suitable for implementing the focus pull-in determination method according to the present invention. The optical recording device includes a light source 1 for emitting a laser beam, a collimator lens 2 for converting the laser beam into a parallel beam, and an objective lens 4 for focusing the parallel laser beam on a disk-shaped optical recording medium 3.
Contains. On the surface of the optical recording medium 3, tracks for recording information are formed in a spiral shape.

The objective lens 4 is driven in a direction perpendicular to the optical recording medium 3, as shown by the arrow, to focus the focused laser beam on the track. It is also relatively driven in the horizontal direction, that is, in the direction across the track, as shown by the arrow, causing the focused laser beam spot to follow the track. This focusing and track following are performed via focus servo and tracking servo.

The optical recording device further includes a beam splitter 5, which separates the reflected light from the optical recording medium 3 from the incident light. The separated reflected light is focused by a focusing lens 6 and further split into two by another beam splitter 7. The divided reflected light is transmitted to the first light receiving element 8 and the second light receiving element 9.
The light is received by each. The first light receiving element 8 outputs a photocurrent depending on the amount of light received, and the second light receiving element 9 similarly outputs a photocurrent depending on the amount of light received.

When the focused laser beam incident on the optical recording medium 3 is in focus, the pair of light receiving elements 8 and 9
receive the same amount of divided reflected light, and there is no difference in photocurrent. However, when the light is out of focus, an imbalance occurs in the amount of light received between the pair of light receiving elements 8 and 9, resulting in a difference in the magnitude of the photocurrent. Therefore, by differentially processing the photocurrents output from the pair of light receiving elements 8 and 9, it is possible to obtain a focus error signal FES representing the focusing error of the laser beam spot. This focus error signal is used as a focus servo control signal to automatically focus the laser beam spot.

Furthermore, a tracking error signal TE representing the positional error of the laser beam spot with respect to the track
In order to obtain S, the light receiving surface of at least one of the light receiving elements is actually divided. A tracking error signal TES is obtained by determining the difference between the photocurrents output from each divided portion.

FIG. 3 shows an example of a focus servo built into the optical recording apparatus shown in FIG. The focus servo is
A subtracter 11, an amplifier 12 for amplifying the focus error signal FES, a phase compensation circuit 13, a switch 14 for controlling ON and OFF of the focus servo, and a limit amplifier 15 for preventing overshoot of the focus servo. , a vertical actuator driver 16, a vertical voice coil 17 for driving the objective lens 4 in the vertical direction, and the like. As described above, this focus servo automatically controls the vertical position of the objective lens 4 based on the focus error signal FES, and executes focus pull-in of the laser beam spot and automatic focusing after focus pull-in.

FIG. 4 is a schematic circuit block diagram showing an example of a tracking servo built into the optical recording apparatus shown in FIG. The tracking servo includes a subtracter 21 located at the input stage, an amplifier 22 for amplifying the tracking error signal TES, a phase compensation circuit 23, a switch 24 for controlling ON and OFF of the tracking servo, and a limit amplifier 25. , a horizontal actuator driver 26, and a horizontal voice coil 27 for driving the objective lens 4 in the horizontal direction.

In addition, a kickback voltage generating circuit 29 is connected to the limit amplifier 25 via a switch 28. This kickback voltage generation circuit 29 is for injecting a kickback voltage into the limit amplifier 25 via the switch 28, and is normally used, for example, for verifying information writing to a track or for track seeking.

Furthermore, a detection circuit 3 is installed in the tracking servo.
0 is connected to detect the tracking error signal TES.

Finally, the focus pull-in determination method according to the present invention will be explained in detail with reference to FIGS. 3 and 4. First, after setting the optical recording medium, the tracking servo switch 24 shown in FIG. 4 is controlled to turn off the tracking servo. This is because if the tracking servo is activated, focus pull-in cannot be determined. next,
The switch 14 shown in FIG. 3 is controlled to turn on the focus servo. As a result, the focus error signal FE
Based on S, the focus servo starts operating, drives the vertical voice coil 17 via the vertical actuator driver 16, and executes focusing of the laser beam spot formed by the objective lens 4.

Next, using the detection circuit 30 shown in FIG.
A tracking error signal TES supplied to the input stage of the tracking servo in the OFF state is detected. At this time, if the optical recording medium is set in an eccentric state and focus pull-in is successful, a tracking error signal TES as shown in FIG. 5 is output. In the example shown in FIG. 5, for example, a disk-shaped optical recording medium is
It shows the tracking error signal obtained when rotating by m. In this way, when the track is in an eccentric state, the position of the track changes relative to the horizontally fixed laser beam spot, so the periodic signal TES
appears. The detection circuit 30 determines whether focus pull-in has actually been performed by detecting a peak change or the like of this signal TES.

On the other hand, if the tracking error signal TES is not detected in the above process, there is a possibility that the optical recording medium is not eccentric, and the switch 2 shown in FIG.
8 to inject kickback voltage into the limit amplifier 25. In response to the injected kickback voltage, the horizontal actuator driver 26 drives the horizontal voice coil 27 to forcibly move the objective lens 4 in the horizontal direction, that is, in the eccentric direction, thereby causing pseudo eccentricity. Subsequently, the detection circuit 30 performs a second detection process. If the focus pull-in is successful, a tracking error signal TES appears due to pseudo eccentricity. 7 shows an example of the signal TES according to FIG. 6. As shown in the figure, before the kickback voltage is injected, only a zero level signal appears, but when the kickback voltage is injected, the signal TE
S begins to vary and a peak appears each time the track crosses a fixed laser beam spot. The detection circuit 30 confirms that the focus pull-in is successful by detecting this peak.

[0021]

As explained above, according to the present invention, by simply injecting a kickback voltage to the tracking servo, even when the optical disk is chucked to the spindle motor without eccentricity, It becomes possible to effectively determine focus pull-in, and there is an effect that there is no need to add a complicated external circuit unlike the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing a focus pull-in determination method according to the present invention.

FIG. 2 is a schematic diagram showing an example of an optical recording device suitable for implementing the method according to the invention.

FIG. 3 is a circuit diagram showing an example of a focus servo built into the optical recording device shown in FIG. 2;

FIG. 4 is a circuit diagram showing an example of a tracking servo built into the optical recording device shown in FIG. 2;

FIG. 5 is a waveform diagram showing a tracking error signal that appears when the optical recording medium is eccentric.

FIG. 6 is a waveform diagram showing an example of a tracking error signal obtained when a kickback voltage is injected in a non-eccentric state of the optical recording medium.

[Explanation of symbols]

1 Laser beam light source 3. Optical recording medium 4 Objective lens 8 First light receiving element 9 Second light receiving element 17 Vertical voice coil 24 Switch 27 Horizontal voice coil 28 Switch 29 Kickback voltage generation circuit 30 Detection circuit

Claims (1)

[Claims] 1. A process for placing a tracking servo in a rest state while operating a focus servo to focus a laser beam spot on the surface of an optical recording medium; and a process for detecting whether a tracking error signal is output. , a process of injecting a kickback voltage to the tracking servo when a tracking error signal is not detected, a process of detecting whether a tracking error signal is output again, and a process of injecting a kickback voltage into the tracking servo when a tracking error signal is detected, and a process of injecting a kickback voltage into the tracking servo when a tracking error signal is detected. A method for determining focus pull-in, which includes a process of confirming that pull-in has been executed.