JPS6231031A - Focus servo leading-in device of information recording device - Google Patents

Abstract

PURPOSE:To discriminate between the protection layer surface and medium surface of a recording medium and to pull in a focus to the surface of the medium securely by deciding the light reflection surface of the recording medium according to the detection output of a specific component of a signal based upon reflected light from the recording medium. CONSTITUTION:A groove for tracking is formed previously on the medium surface of the disk, so when the focus is pulled in to the medium surface, a tracking error signal is generated and a noise due to dust, etc., sticking on the surface of the protection layer is generated. A signal is passed through a low-pass filter 24 so as to remove the influence of the noise. The output of this filter 24 is peak-held by a peak holding circuit 25 during one turn of the disk and its output is compared with a constant voltage Vo. Then, a discrimination between the medium surface and protection layer surface of the disk is made on the basis of this Vo, and when the protection layer surface is discriminated, the pulling in of the focus is restarted from the beginning.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to focusing servo pull-in of an objective lens of an optical information recording/reproducing device.

(Prior art) A block diagram of a conventional optical information recording/reproducing device of this type is shown in Fig. 3.
As shown in the figure. The light emitted by the semiconductor laser 1 passes through the collimator lens 2 and the beam splitter 3, and is focused on the disk-shaped recording medium 6 by the objective lens 4. The objective lens 4 can be driven by a focus actuator 5 in a direction perpendicular to the surface of the disk 6. The reflected light from the disk is reflected by a beam splitter 3 and guided by a condenser lens 7 onto an analyzer 8. The analyzer 8 is divided into a plurality of detection surfaces, and generates a signal containing focus error information using a known method (not shown) such as the astigmatism method or the Knifezi method. Reference numerals 9 and 10 are amplifiers that amplify the outputs of the respective analyzers 8, and 11 is a differential amplifier that generates a focus error signal by taking the difference between the outputs of the amplifiers 9 and 10. 12 is a phase compensation circuit, and a drive amplifier 13 drives a focus actuator 5. 14 is an adder that adds the outputs of amplifiers 9 and 10 to obtain the amount of total reflection light. 15 is a focus pull-in signal generator; at the time of pull-in, the switch 17 first selects the output of the focus pull-in signal generator 15; when the output of the adder 14 is above a certain level;
The controller 16 detects when the output of the phase compensation circuit 12 generates a zero-crossing signal, and then switches the switch 17 to the output of the phase compensation circuit 12 to complete the focus pull-in using the focus error signal.

FIG. 4 shows a cross-sectional view of the disk-shaped recording medium.

a is a protective layer of the recording medium, and is made of a transparent material such as plastic or glass. b is the recording medium layer, and C is the adhesive layer of the double-sided disc. The output of the focus pull-in signal generator 15 generates a ramp waveform so that the objective lens is gradually brought closer to the disk from a sufficiently far position. Therefore, as shown in FIG. 5(1), the focus error signal first starts at time 1. At t2, a focus error signal is generated based on the reflected light from the surface of the protective layer a, and then at t2, a focus error signal due to the medium surface is generated.

Conventionally, in compact discs, etc., the reflectance of the medium surface is sufficiently larger than the reflectance of the protective layer surface, so the difference between these two focus error signals is that there is a signal that is the sum of the outputs of the analyzer. The one greater than the level Va is the medium surface, Va
The side smaller than Va is distinguished as the protective layer surface, and the focus is drawn to the zero-crossing point of the focus error signal when Va is larger. Alternatively, they were distinguished based on the presence or absence of playback information.

However, the reflectance of a medium that can also be recorded is generally lower than that of a medium that is only used for reading. Therefore, as shown in FIGS. 5(3) and 5(4), depending on the medium, there may be almost no difference in reflectance from the surface of the protective layer.

In this case, the above distinction cannot be made. Furthermore, since there are parts where no information is recorded, it is not possible to distinguish between the presence or absence of reproduced information.

(Purpose) The present invention was made in view of the above points, and an object thereof is to provide a device that can distinguish between the surface of a protective layer of a recording medium and the surface of the medium, and reliably focus on the surface of the medium. shall be.

(Example) FIG. 1 shows a block diagram of an embodiment of the present invention.

The same parts as in FIG. 3 are denoted by the same numbers and the explanation will be omitted. 8
In addition to a signal containing focus error information from the analyzer, a signal containing tracking error information is obtained by a known method (not shown) such as a push-pull method or a three-beam method. Reference numerals 17 and 1.8 are amplifiers that amplify the output of the analyzer 8, and 19 is a differential amplifier that takes the difference between the outputs of 17 and 18 and generates a tracking error signal. A phase compensation circuit 20 drives a tracking actuator 23 using a tracking drive amplifier 22 to drive the focused light in a direction perpendicular to the track. 24 is a low-pass filter for the output of the differential amplifier 19, and 25 is a peak hold circuit. 26 is a tracking vibration signal generation circuit, and 21 is a phase compensation circuit 20. A switch for selecting three states of the tracking vibration signal generation circuit 26: output, tracking, and OFF.

Focus pull-in is performed by a focus pull-in signal generator 15. First, a ramp waveform is generated so that the objective lens 4 is gradually brought closer to the disk 6 from a sufficiently far position. As a result, 1 in Figure 5 (3). A focus error signal is generated from the protective layer surface at t2 and from the medium surface at t2.

Then, the objective lens 4 is brought closer to the disk 6 to a position where no focus error signal is generated even by surface wobbling due to rotation of the disk (t3) - at this position, the working distance of the objective lens is approximately IIQI11.
If the deflection of the disk surface is about 0.5 mm or less, a ramp waveform is generated that moves the zero-order objective lens 4 away from the disk 6, which can be determined from the DC gain of the focus actuator and the drive current of the focus actuator. When the sum signal of the output of the adder 14 is above a certain level (vb) in the focus error signal appearing in , and the focus error signal crosses zero, the switch 17 of the focus control loop is closed to the output side of the phase compensation circuit. The focus is drawn onto the medium surface as it is, but when the surface runout of the medium is abnormally large or due to external vibrations,
The objective lens 4 may be accidentally drawn into the surface of the protective layer beyond the medium surface. For this reason, when tracking control is not performed immediately after focus pull-in, it is determined whether the surface is on the protective layer surface or the medium surface based on the presence or absence of a tracking error signal.

This method will be explained with reference to FIG. The horizontal axis is time and the vertical axis is voltage. Figures 2 (1) and (2) show tracking error signals when the focus is drawn to the medium surface and the protective layer surface, respectively.The disk has tracking grooves formed in advance on the medium surface. Therefore, when the focus is drawn to the medium surface, a tracking error signal is generated, and noise is generated on the protective layer surface due to dust attached to the surface. In order to remove the influence of this noise, it is passed through a low-pass filter 24, with a cutoff of about IKHz, and the outputs are shown in Figure 2 (3) and (4), respectively.
), Figure 2 (3) and (4) are respectively shown in Figure 2 (1
), (2) are the waveforms after passing through the filter 24.

The output of this filter 24 is expressed as the period TO of one rotation of the disk.
During this period, a peak hold circuit 25 holds the peak and its output is compared with a constant voltage vO. That is, since the tracking error signal includes many components that pass through the filter, the output v8 of the peak hold circuit is V1>V.
o, and since noise due to dust etc. does not pass through the low-pass filter, the output v2 of the peak hold circuit becomes v2 minus vo. By comparing the magnitude with this vo, it is determined whether the surface is the medium surface of the disk or the surface of the protective layer, and if it is the surface of the protective layer, the focus is redrawn starting from the surface.

However, if the tracks on the disk are formed concentrically, there is a small probability that no tracking error signal will be generated even if the focus is drawn to the surface of the medium.

This is a case where the light spot traces the track without deviation even if tracking control is not performed. Even at this time, in order to generate a tracking error signal, the optical spot is forcibly vibrated in the tracking direction (perpendicular to the track) by the 26 tracking vibration signal generators. This vibration needs to have a frequency different from the rotation of the disk so that it is not synchronized with the eccentricity of the disk. According to this, when the focus is drawn onto the surface of the medium, a tracking error signal is always generated, and this makes it possible to distinguish whether the surface of the protective layer is the surface of the medium, and when the focus is drawn onto the surface of the protective layer. , try refocusing from the beginning.

In the above explanation, the protective layer surface or the medium surface is distinguished immediately after focus pull-in, but recording and reproduction.

This distinction can be made at any time after an erasure error occurs, or when only focus is controlled and tracking control is not performed, and if the focus is drawn to the surface of the protective layer, the focus is immediately re-started from the beginning. be able to.

(Effects) As explained above, according to the present invention, by distinguishing between the surface of the protective layer of the recording medium and the surface of the medium, even when the focus is drawn to the surface of the protective layer, the focus is reliably drawn to the surface of the medium. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an apparatus to which the present invention can be applied, FIG. S2 is a diagram showing a tracking error signal, FIG. 3 is a block diagram showing a conventional example, and FIG. 4 is a cross-sectional view of a recording medium.
FIG. 5 is a diagram showing a focus error signal. Note that 6 is a recording medium, 8 is an analyzer, 24 is a low-pass filter, and 25 is a peak hold circuit.

Claims (6)

[Claims] (1) In a device that records and reproduces information by focusing a light beam on a recording medium, the light reflecting surface of the recording medium is determined according to the detection output of a specific component of a signal based on the reflected light from the recording medium. A focus servo pull-in device for an information recording apparatus, wherein the focus servo pull-in device for an information recording apparatus is characterized in that the focus pull-in of the light beam to the recording medium is restarted. (2) The focus servo pull-in device for an information recording device according to claim 1, wherein the light reflecting surface is a surface of a protective layer of a recording medium or a surface of the medium. (3) A focus servo pull-in device for an information recording apparatus according to claim 1, wherein the specific component is a low frequency component of a tracking error signal of the recording medium. (4) The focus servo pull-in device for an information recording apparatus according to claim 1, wherein the focus servo pull-in device resumes focus pull-in when the detection output does not exceed a certain level within a predetermined time. (5) A focus servo pull-in device for an information recording device according to claim 4, characterized in that the light beam is vibrated in a direction orthogonal to the track. (6) In claim 1, the focus retraction is such that the objective lens for converging the light beam is gradually brought closer to the medium from a position sufficiently distant from the medium, and the focus error signal is caused by surface vibration of the medium. The focus servo of the information recording device is characterized in that the objective lens is gradually moved away from the medium after the objective lens is brought close to the medium until no error occurs, and the focus is pulled in to a focus error signal that first occurs after the objective lens starts to move away. retraction device.