JPH0565936B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a recording medium drive device that optically records, reproduces, or erases information signals on a recording medium;
The present invention also relates to a focus pull-in method for pulling the focus into the linear region of the focus servo means in this recording medium drive device.

[Conventional technology]

As a conventional recording medium drive device and focus pull-in method, there is a focus servo method in an optical reproducing device disclosed in Japanese Patent Application Laid-open No. 10701/1983.

Hereinafter, a conventional example will be explained with reference to the drawings.

FIG. 5 is a block diagram showing the focus servo system of a conventional optical disc playback device; FIG. 6A,
B is a waveform diagram for explaining each operation.

In FIG. 5, the light emitted from the laser source 4 passes through the beam splitter 39, the half mirror 40, and the reading lens 9 as shown by solid lines, and passes through the disk (X ₀ , X ₁ , and X ₂ indicate the positions). ) and is reflected. The reflected light passes through the reading lens 9 again, is bent by the half mirror 40, and then enters the photodetectors D ₁ , D ₂ , and D ₃ . Therefore, in order to make the incident light on the photodetector D ₁ equal to the incident light on the photodetector D ₂ , the difference is calculated by the differential amplifier 18 and then passed through the servo amplifier 41 and the output level limiting circuit 42 . If a focus servo system is configured to move the actuator 10 using the drive circuit 22, the laser beam indicated by the solid line will always form a condensing spot on the _X0 plane. However, the range in which the laser beam enters the photodetectors D ₁ and D ₂ is narrow, and the error signal S ₁ for configuring the focus servo system is
As shown in Figure A, it can only be detected partially. (The horizontal axis is the distance between the disk and the reading lens, and the X ₀ position is d _0. ) Conventionally, in order to operate the servo system in this detectable area, initially In the figure, the servo loop is closed until the focus servo lock-in after the power is turned on.
Although not shown, a sweep voltage is added to the drive circuit 22 to move the photodetector D ₂ closer to the disk.
When light is incident on the beam (that is, when S ₁ rises as shown in FIG. 2A), the sweep voltage is made zero, the servo is locked in, and the condensing spot is locked on the X ₀ plane.

However, in this state, when the laser beam disappears, S ₁
(for example, a photodetector)
When the variation in dark current (D ₁ , D ₂ ) becomes positive, the reading lens approaches the disk and collides with it. Therefore,
Conventionally, for example, the sweep voltage was made slightly negative, so that the focal spot was locked slightly closer to X ₁ than X ₀ , but when the laser light disappeared, the reading lens moved away from the disk. .

In addition, if the reading lens approaches the disk beyond the servo error signal detection area due to disturbance etc. without considering that the laser beam will disappear,
When the laser beam is in the dangerous area in Figure B), the solid line laser beam enters the photodetector D ₃ (or D ₃ ′, D ₃ ″), so it is detected and transmitted by the comparator 43 and the multivibrator 44. A configuration was adopted in which the gate of the output level control circuit 42 was opened to open the servo loop for a certain period of time, and a certain negative voltage was applied to the drive circuit 22 to forcibly separate the reading lens 9 from the disk. In the figure, d ₃ and d ₃ ' are the distances at which the light enters the photodetectors D ₃ and D ₃ ', respectively, and S ₂ is the detection signal thereof.

[Problem that the invention seeks to solve]

Since the conventional recording medium drive device and its focus pull-in method are constructed as described above, a complicated optical system and electric circuit system are required to prevent collisions. Furthermore, when the recording medium has a transparent protective layer, there is a high possibility of malfunction. In other words, generally the recording medium is exposed, and light is focused on it to record.
Reproducing or erasing data has problems in terms of preservation and reliability of recorded information.
Usually, a protective layer made of PMMA, PC, epoxy, glass, etc. is provided, and recording, reproduction, or erasing is performed on the recording medium through this layer. in this case,
Due to the difference in refractive index between air and the surface of the protective layer, this surface has a reflectance of about 4%, so the focus servo system has a stable point on the surface of this protective layer in addition to the recording medium surface. Therefore, if the objective lens is moved toward the disk from a distance with the servo closed as in the conventional method, the S-shaped characteristic due to reflection on the surface of the protective layer will first appear.
It may lock into the surface of the protective layer. In particular, for write-once type and erasable type optical disks that also record, automatic correction of focus detection sensitivity is performed to avoid fluctuations in servo gain due to changes in the power of the light source used for recording. Since it operates in the same way even if the protective layer is used, there is no difference in the S-shaped characteristics of the focus detection signal between the surface of the protective layer and the recording medium.

Furthermore, when the light condensing spot by the reading lens passes through the surface of the protective layer and approaches the surface of the recording medium, the auxiliary beam reflected from the surface of the protective layer eventually enters D ₃ and is considered to have come too close to the disk. In some cases, the reading lens is moved away from the disk, and the light condensing spot may not reach the surface of the recording medium. In particular, if the reflectance of the recording medium is low and difficult to distinguish from the reflectance of the surface of the protective layer,
It becomes a problem.

As described above, in order to perform focus pull-in on a disk with a protective layer, it is necessary to simultaneously solve the following two problems.

The first is to prevent accidental locking into the surface of the protective layer.

Second, the tip of the condensing lens for recording, reproducing, or erasing is prevented from colliding with the surface of the protective layer.

The present invention was made to solve the above two problems at the same time and in a simple way.It is a recording medium that does not lock into the surface of the protective layer and does not collide with the tip of the condensing lens. An object of the present invention is to provide a driving device and a focus pulling method thereof.

[Means for solving problems]

The recording medium drive device according to the present invention is arranged so that the surface runout position of the recording medium is outside the movable range of the optical system that creates the condensing spot and is within the movable range of the condensing spot. This sets the positional relationship of the optical system.

In addition, a focus pull-in method in a recording medium drive device according to another aspect of the present invention includes recording, reproducing, or erasing information signals by irradiating a focused spot from an optical system onto the surface of the recording medium while following the surface deflection of the recording medium. When performing this, the positional relationship between the recording medium and the optical system is adjusted in advance so that the surface runout position of the recording medium is outside the movable range of the optical system and within the movable range of the light focusing spot. a step of arranging the movable part of the optical system at a position closest to the recording medium to set it as a pulling-in operation starting point; a step of moving the optical system away from the optical system; in this moving step, the movable part of the optical system is stopped in the first linear region in which the servo means for causing the condensing spot to follow the surface deflection of the recording medium operates, and the retracting operation is completed; This process involves a process of

[Effect]

The recording medium drive device according to the present invention controls the amount of surface runout of the recording medium and the recording medium so that the position of the surface runout of the recording medium is outside the movable range of the optical system and within the movable range of the condensing spot. The positional relationship between the medium and the optical system and the focal length of the optical system are set, so even if retraction fails, the movable part of the optical system will collide with the recording medium, damaging the optical system and preventing recording, playback, etc. There will be no loss of information on the recording medium.

Furthermore, using a device configured as described above, the movable part of the optical system is brought closest to the recording medium in advance, and when it is gradually moved away from this point,
By always closing the servo and performing the pull-in operation in the sensor detection area of the first servo, stable focus pull-in is possible regardless of the surface of the protective layer of the recording medium.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 1 is a disk, 1a is a recording medium, 1b is a disk protective layer made of glass or plastic, and 1c is the surface of the disk protective layer. Recording is performed on the recording medium through the protective layer. 2 is a turntable on which a disk is placed, and 3 is a disk motor that rotates the turntable.

For example, 4 is a light source made of a semiconductor laser (hereinafter abbreviated as LD), 5 is a collimating lens that converts the diffused light from the LD into parallel light, 6 is a prism that bends the collimated light beam by 90 degrees, and 7 is a polarizing beam splitter. , (hereinafter abbreviated as PBS), 8 is a quarter wavelength plate, which is used to bend the returning light beam by 90 degrees at PBS. 9 is a condensing lens, 10 is an actuator that moves the condensing lens, and 11 is a PBS.
a condenser lens that reconverges the light beam bent by the
2 is a shielding plate that blocks half of the condensed light beam, 13 is a two-split photodetector with its dividing line at the focus of the condensing lens, and 14 is 4, 5, 6, 7, 8, 9, 10, 1.
An optical head on which optical system components consisting of 1, 12, and 13 are placed, 15 a linear motor for driving the optical head, and 16 a base for supporting the disk motor 3, the optical head 14, and the linear motor 15.

Next, the operation will be explained using FIGS. 1 and 2.

A disk 1 is placed on a turntable 2 and rotated by a disk motor 3.
The disc motor connects to the base 1 through its flange.
6 is supported. At this time, the distance a between the flange surface of the disk motor 3 and the top surface of the turntable 2, and the distance b between the reference surface of the base 16 and the flange surface of the disk motor. Also, the center value of each
Let a ₀ , b ₀ be the tolerances Δa and Δb. If the amount of surface runout of the disk is Δx, then the reference surface of the base 16 and the disk protective layer surface 1c
The distance C from the above can be expressed as C=a+b±Δx=a ₀ +b ₀ ±Δa±Δb±Δx (1).

On the other hand, inside the optical head 14, the diffused light emitted from the LD 4 is collimated by the collimator lens 5, becomes parallel light, and the optical path is bent by 90 degrees by the prism 6. The light passes through the wavelength plate 8 and is again focused by the condensing lens 9 to form a condensing spot.

In the figure, the dotted line of the condensing lens 9 indicates the position furthest from the disk, and the solid line indicates the closest position, and the range between these is the movable range of the condensing lens 9. At this time, if the distance from the reference plane of the base 16 to the tip of the condensing lens when it is closest to the disk 1 is d, the center value is d ₀ , and the tolerance is Δd, then in conjunction with equation (1), , d=d ₀ ±Δd<c=a ₀ +b ₀ ±Δa ₀ ±Δb ₀ ±Δx In other words, for a, b, Δx, Δd so that max(d)<min(c) , by setting d ₀ so that d ₀ <a ₀ +b ₀ −Δa ₀ −Δb ₀ −Δx−Δd (2), the tip of the condenser lens collides with the surface 1c of the disk protective layer. Never.

Also, if the distance from the tip of the condensing lens to the condensing spot is f and the movable distance of the condensing lens is l, the movable distance of the condensing spot is similarly l,
If the thickness of the disk protective layer is t, min(c+t)max(d)-l+f max(c+t)min(d)+f...(3) In other words, if e=c+t, min(e)max(d)- By setting l and f so that l + f max (e) min (d) + f, the recording medium 1a of disk 1 is always included in the movable range of the light focusing spot from d + fl to d + f. becomes possible.

Note that the amount of surface runout of the recording medium can be reduced by reducing the diameter of the disk and controlling the injection molding process even if the substrate is made of plastic. For example, at the present time (April 1, 1986)
For a 130cm write-once type optical disk, the proposed surface runout amount is 0.6mmp-pMAX, which is higher than the conventional
30cm video disc specifications 1/3 of 2mm p-p
It is as follows.

Further, as for the parameters of the optical system such as f, by increasing the focal length, a distance between the condensing spot and the tip of the lens is ensured. By increasing the focal length,
In order to secure the necessary NA (NA = 0.5) to obtain a small focal spot, the diameter of the objective lens must be increased, but this can be done by using an aspherical lens or by performing high-precision aberration correction. , are now readily available.

Additionally, the distance between the disk and the condensing lens varies depending on the positional tolerances of the turntable on which the disk is placed and the optical system (optical head), but this can also be reduced by reducing the tolerances. .

Therefore, as described above, it is possible to ensure that the position of the surface runout of the recording medium is always outside the operating range of the movable part of the optical system, that is, the tip of the condensing lens, and within the movable range of the condensing spot. This makes it possible to configure a recording medium drive device in which the tip of the condensing lens does not collide with the disk.

Next, a description will be given of a focus servo means for causing a light condensing spot to follow the surface runout of a recording medium, and a method of drawing the light into a linear region in which the servo means operates.

In FIG. 1, when the condensing spot is located on the surface of the protective layer or the surface of the recording medium, it is reflected at the boundary surface and returned to the original parallel light by the condensing lens 9. The reflected light beam whose round-trip phase is shifted by 1/2 by the quarter-wave plate 8 has a polarization plane rotated by 180 degrees with respect to the incident light beam to the condenser lens, so the PBS 7
It is bent by 90 degrees and enters the sensor lens 11.
Further, half of the light flux is blocked by the shielding plate 12, and the remaining light is focused on the dividing line of the two-split photodetector 13. By taking the difference between the outputs of this two-split photodetector, the relative distance between the light spot position and the surface of the disk recording medium or disk protective layer can be detected only when the light spot is located near each surface. can.

In other words, if the recording medium surface is taken as the origin, the condensing lens direction is taken as positive, the light spot position is taken as the horizontal axis, and the photodetector output is taken as the vertical axis, the photodetector 13a, The amount of light received by 13b changes as shown in FIGS. 2a and 2b, respectively.

By converting this into a voltage signal and creating a difference signal and a sum signal, signals as shown in FIG. 2c and d are obtained, respectively. The difference signal is a signal that controls the sensor part of the servo, but it has a linear detection area only in a range of several microns near the interface between the recording medium surface and the surface of the disk protective layer.

Therefore, in the recording medium drive device configured as described above, in order to perform focus pull-in to prevent the focus from accidentally locking into the surface of the protective layer, the following steps must be taken in advance when pulling the focus into the linear range of the focus sensor. The state in which the movable part of the optical system is moved to the point closest to the recording medium is defined as the retraction operation start point, and when the movable part of the optical system is moved in the direction away from the recording medium from this point, the first servo means The focus servo loop may be closed in the linear region of , and the pull-in operation may be completed.

In other words, in the traditional focus attraction method,
When the condensing lens was moved as far as possible in the direction toward the disk, there was a possibility that the tip of the condensing lens would collide with the surface of the recording medium or protective layer of the disk.
Therefore, in order to reliably detect the recording medium surface and lock-in the servo before collision, a method is used in which the condensing lens is fully retracted in the direction away from the disk and then gradually moved out. Therefore, it must pass through the surface of the protective layer. Therefore, it is necessary to distinguish the surface of this protective layer from the recording medium surface by some means. However, with the configuration of the present invention, even if the condenser lens is moved to the maximum in the direction approaching the disk, the tip of the condenser lens
It will not collide with the disk. Therefore, if the condensing lens is moved in a direction away from the disk from this position, the recording medium surface will always come first, so there is no need for any means to avoid the protective layer surface.

Next, a difference signal, which is a servo sensor signal, is generated from the photodetector 13, the loop gain is automatically adjusted, the actuator 10 is feedback-controlled, and a pull-in operation is performed to close the servo loop in this narrow linear region. The configuration and operation of the servo system circuit section will be explained.

In FIG. 3, 17a and 17b are preamplifiers that convert the output currents from the photodetectors 13a and 13b, respectively, into voltage signals, 18 is an arithmetic unit that creates a difference signal, 19 is an arithmetic unit that creates a sum signal, and 20 is an arithmetic unit that creates a sum signal. Difference signal
21 is a filter that performs phase compensation of the servo loop, 22 is a drive circuit that drives the actuator 10, 23 is a resistor, 24 is a switch (ON at H), 25 is a comparator, 26 is a 27 and 28 are resistors that provide hysteresis characteristics to the comparator; 29 is a D-type flip-flop; 30 is an inverter; 23, 24, 2
5, 26, 27, 28, and 29 constitute a detection circuit 31 that detects the linear region of the servo. 32 is a power supply, 33 is a switch (ON at H), 34 is a resistor that determines the charging time constant, 35 is a charging/discharging capacitor,
36 is a resistor that determines the discharge time constant, and 32,3
3, 34, 35, and 36 constitute an actuator drive circuit 37 for servo retraction. 38
is a switch (ON at H) that closes or opens the servo loop.

Next, the servo operation will be explained using FIGS. 2 and 3.

The light received by the two-split photodetector 13 is converted into electric current. After converting this into voltage signals as shown in FIG. 2 a and b by the preamplifier 17, the arithmetic unit 1
8 and 19, a difference signal X and a sum signal Y as shown in FIG. 2c and d are generated. As shown in FIG. 2, the linear region of the difference signal as a sensor for detecting the relative distance between the recording medium surface and the light spot is very narrow, several microns. Furthermore, the sensitivity changes depending on the power fluctuation of the light source and the reflectance of the recording medium. Therefore,
Sensitivity can be kept constant by dividing the difference signal by a sum signal that changes at a similar rate. This operation is performed by the divider 20. If the detected servo error signal is sent directly as negative feedback to the actuator, since the characteristics of the actuator are second-order, the phase will rotate 180 degrees and a frequency region will occur where positive feedback will occur. The system becomes unstable. Therefore, the phase is advanced by that portion using the filter 21 to perform phase compensation.

The servo loop is opened and closed by a switch 38, and when it is closed, the actuator drive circuit 22 drives the actuator 10 using the servo error signal, and when it is opened and the retraction control system is activated, the retraction drive signal is used. do.

Next, the operation of the pull-in control system will be explained using FIGS. 3 and 4.

As shown in FIG. 4, when the pull-in control signal becomes "H", the switch 33 closes and the voltage E of the power supply 32
1, capacitor 35 is charged through resistor 34, and the input voltage V1 to the drive circuit changes. At this time, the input voltage V5 of the detection circuit 31 is "L", so the actuator is driven by the voltage V1, and the condensing lens approaches the disk as much as possible, and on the way, the difference signal X shows that the condensing spot is A linear region of the sensor appears where it passes through the surface of the recording medium. However, since the switch 24 is open, the input V2 to the comparator 25 for detecting the linear region remains zero. Next, when the pull-in control signal becomes "L", the switch 33 opens, and the electric charge charged in the capacitor 35 is gradually discharged through the resistor 36, and the voltage V1 gradually decreases as shown in FIG. . Therefore, the condensing lens also slowly moves away from the state where it is as close as possible to the disk, and eventually, as the condensing spot approaches the recording medium, the linear region of the sensor appears at X. At this time, the switch 24 is also open, so this X signal is input to the comparator 25 through the resistor 23.
When the input voltage V2 of the comparator becomes equal to or higher than the reference voltage V3, the output voltage V4 of the comparator 25 becomes "L", and V3 also
It changes by the amount of hysteresis. Next, V2
When it enters the linear region and the condensing spot almost coincides with the surface of the recording medium, it becomes less than the changed V3, and V returns again.
4 becomes “H”. At this time, flip-flop 2
9 operates, V5 becomes H, the switch 38 is closed, the servo loop is closed, and the retracting operation is completed.

In the above example, a spherical lens was used as the optical system for creating the light spot, but any lens that can condense light could be used as the lens, such as an aspheric lens, Fresnel lens, hologram, or grating. But that's fine.

Further, although the optical system is constructed by a combination of individual optical components, it may be a gray scale integrated with these components.

In addition, whether the recording medium is a read-only one such as a compact disc or video disc, or an additional write type optical disc such as a write-once optical disc, erasable optical discs that utilize phase change or magneto-optical technology can be used. Even in the case of a disk, its positional relationship with the optical system may be set so that its surface runout position is outside the movable range of the optical system and within the movable range of the condensing spot.

In addition, the media shape is not limited to disk shape, but also drum shape, card shape, tape shape, etc. depending on the position.
If the distance to the optical system changes, there is no need for rotation.

In addition to the above-mentioned Foucault method, there are also sensor signal extraction methods such as the astigmatism method, if the linear region is limited and the range is small compared to the amount of change in the position of the recording medium. , any method may be used.

〔Effect of the invention〕

As described above, according to the present invention, the recording medium and the optical system are arranged such that the surface runout position of the recording medium is outside the movable range of the movable part of the optical system and within the movable range of the optical spot. Since the positional relationship is set, collisions can be mechanically prevented, and even if trouble occurs in the electrical system, the optical system will not collide with the disk, resulting in high reliability. Further, there is an effect that a complicated optical system or electric circuit system for collision prevention is not required. Furthermore, according to another aspect of the present invention, when performing focus pull-in in the apparatus configured as described above, the movable part of the optical system is moved to the point closest to the recording medium in advance, and then the pull-in operation is performed. As a starting point, when moving the movable part of the optical system in the direction away from the recording medium, the focus servo loop was closed in the linear region of the first servo means to complete the retraction operation, so that the surface of the recording medium Malfunctions due to reflections on the surface of the upper protective layer can be prevented, and the focus servo can be reliably pulled onto the recording medium, thereby improving reliability.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram showing an optical disk recording and reproducing apparatus according to an embodiment of the present invention, FIG.
b, c, and d are waveform diagrams for explaining their operations, FIG. 3 is a block diagram showing the focus servo means of an optical disk recording/reproducing apparatus according to an embodiment of the present invention, and FIG. 4 is a diagram showing its operation. FIG. 5 is a block configuration diagram showing a focus servo system of a conventional optical disk reproducing apparatus, and FIGS. 6A and 6B are waveform diagrams for explaining the operation of the conventional apparatus. 1... Disk, 1a... Recording medium, 1b...
Disk protective layer, 4...Light source, 9...Condensing lens, 10...Actuator, 12...Hair shielding plate, 13...Two-split photodetector, 14...Optical head, 16...Base. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. An optical system for recording an information signal on the surface of a recording medium having a protective layer, or for creating a light converging spot for reproducing or erasing the recorded information signal; and a focus servo means for pulling the recording medium into a linear region in which the servo means operates, wherein the surface runout position of the recording medium is outside the movable range of the optical system, and In order to achieve the movable range of the light condensing spot, the distance from the base on which the recording medium is installed to the surface of the recording medium is e, the movable distance of the condensing lens that creates the condensing spot on the surface of the recording medium is l, The distance from the base to the tip of the condensing lens closest to the recording medium is d, the distance from the tip of the condensing lens to the condensing spot is f, and the distance from the base to the protective layer is When the distance is c, the positions of the recording medium and the optical system are set so that min(e)≧max(d)−l+f max(e)≦min(d)+f max(d)<min(c) A recording medium drive device characterized in that a relationship is set. 2. When recording, reproducing, or removing an information signal by irradiating a focused spot from an optical system onto the surface of the recording medium to follow the surface wobbling of the recording medium, the position of the surface wobbling of the recording medium is determined in advance by the optical system. a step of setting the positional relationship between the recording medium and the optical system so that the movable part of the optical system is outside the movable range of the system and within the movable range of the condensing spot; a step of moving the movable part of the optical system in a direction away from the recording medium from the start point of the retracting operation; A focus pull-in method in a recording medium drive device, comprising: stopping a movable part of the optical system in a first linear region in which a servo means for following the surface runout of the recording medium operates, and completing a pull-in operation. 3. The distance from the base on which the recording medium having a protective layer is installed to the surface of the recording medium is e, the movable distance of the condensing lens that creates a condensing spot on the surface of the recording medium is l, and the distance from the base to the recording medium is The distance to the tip of the condensing lens when it is closest is d, the distance from the tip of the condensing lens to the condensing spot is f, the distance from the base to the protective layer is c, min(e )≧max(d)−l+fmax(e)≦min(d)+fmax(d)<min(c) A focus pull-in method in the recording medium drive device described in 2.