JPS6282520A - optical disc playback device - Google Patents

Abstract

PURPOSE:To reproduce the information recorded on an optical disk with high accuracy by using a means to change the control characteristics for the relative position of a pickup and/or the correction characteristics of the read signals according to the detected position of the pickup. CONSTITUTION:Both a focus servo circuit 58 and a tracking servo circuit 60 work to reproduce the video signals in a normal way. Then a time base servo circuit 56 supplies the video signals delivered from a video/sound demodulation circuit 54 to a burst separator 56c and a horizontal synchronizing separator 56d respectively and compares the burst signal and the horizontal synchronizing signal with a reference clock by phase comparators 56e and 56f and a lock detector 65g respectively. When it is decided that the horizontal synchronizing signal is temporarily equal to the reference clock, the output of the detector 56g is active to close a switch 56h. As a result, the signal obtained by amplifying the output of the comparator 56e by a compensating amplifier 56i is supplied to a power amplifier 56j which drives a tangential actuator 38.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc reproducing device, and more particularly, to a method for controlling the relative position of a pickup with respect to an optical disc and/or correcting characteristics of a read signal. The present invention relates to an optical disc playback device that can be suitably changed and controlled.

[Prior Art] Conventionally, in an optical disc playback device that reads out a video signal and/or an audio signal recorded on an optical disc using a pickup unit facing the optical disc, it is difficult to detect differences in the linear velocity of the optical disc with respect to the pickup unit. The opening control characteristics are changed between the outer and inner peripheries of the optical disc based on the difference in the amount of information per disc. For example, on a disk with a constant angular velocity (hereinafter referred to as a CAM disk), the size of the pits becomes smaller towards the inner circumference compared to those on the outer circumference. It is known that the drop in high frequencies is greater at the outer periphery than at the outer periphery, and the MTF is used to compensate for this.
Compensation will be required. In addition, in so-called tangential servo that corrects fluctuations on the time axis (jitter components) due to eccentricity of the optical disk, etc., especially in CAM disks, the linear velocity increases toward the outer periphery, so the amount of displacement increases, and the gain of the servo increases. must be made larger.

On the other hand, in a disk with a constant linear velocity (hereinafter referred to as a CLV disk), the horizontal synchronization signal included per revolution increases as it approaches the outer periphery. It was necessary to switch the gain of the so-called spindle motor servo, which suppresses uneven rotation of the optical disk, to a lower value on the outer periphery.

Therefore, in conventional optical disc playback devices, the relative position of the pickup unit with respect to the radial direction of the optical disc is detected using a potentiometer, limit switch, etc. attached to the slider on which the pickup unit is mounted, and each compensation value and gain as described in It was configured to switch.

[Problems to be Solved by the Invention] However, if a configuration using such a potentiometer or the like is adopted, there is a problem that the number of parts increases accordingly, leading to an increase in assembly man-hours and a decrease in reliability.

The present invention has been made with the aim of solving these problems, and focuses on the pre-recorded data on optical discs, and improves at least the control characteristics of the relative position of the pickup and/or the correction characteristics of the read signal. The purpose was to provide an optical disc playback device that can be changed and controlled.

[Means for solving the problems] In order to achieve the above object, the present invention has the following configuration as a means for solving the problems. That is, as shown in FIG. 1, an optical disc M1 on which a control code including address information such as a frame number or program time is recorded together with a video signal @ and/or an audio signal is played back using an optical pickup M2. A playback device,
Signal reading means for controlling the relative position between the pickup M2 and the optical disc M1 and reading signals recorded on the optical disc M1 based on the intensity of light incident from the optical disc M1 to the big-up M2. M3, position detection means M4 for decoding the control code from the read signal and detecting the position of the pickup M2 in the radial direction of the optical disc M1; and reading the signal based on the detected position. This is the configuration of an optical disc reproducing apparatus including a changing means M5 for changing at least the control characteristic of the relative position of the pickup M2 and/or the correction characteristic of the read signal of the means M3.

[Function] The optical disc reproducing apparatus of the present invention having the above-mentioned configuration uses a control code (
(including address information such as a frame number or program time) is decoded by the position detection means M4, the position of the pickup M2 in the radial direction of the optical disc M1 is detected, and based on the thus detected position of the pickup M2, the changing means M5 serves to change at least the control characteristics of the relative position of the pickup M2 of the signal reading means M3 and/or the correction characteristics of the signal read from the optical disc M1.

[Examples] In order to further clarify the structure and operation of the present invention described above, preferred embodiments of the present invention will be described in detail below based on the drawings.

FIG. 2 is a schematic configuration diagram showing an overview of a video disc player as an embodiment of the present invention. The video disc player of this embodiment uses laser light (wavelength: 1%, 780 μm ). Laser light output from the semiconductor laser 7 as linearly polarized light is reflected by a total reflection mirror 8, passes through a diffraction grating 9, and is divided into three separate beams. Of these three beams, the central beam is used for information reading and focus servo, and the two beams on both sides are used for tracking servo. The light beam that has passed through the diffraction grating passes through a collimating lens 11 and further enters a polarizing beam splitter 12. In this embodiment, the laser beam output from the semiconductor laser 7 is not reflected at the boundary surface of the polarizing beam splitter 12 and
and reaches the 1/4 wavelength plate 14. 1/4 wavelength plate 14
The light flux that passes through and is converted into clockwise circularly polarized light is sent to the tracking mirror 16. After being reflected by the tangential mirror 18, the light enters an objective lens 20 disposed opposite the bottom surface of the video disc 5.

The objective lens 20 directs the incident laser light to the video disc 5.
At the same time, reflected light that has been diffracted by the pits on the video disk 5 is input and returned to the tangential mirror 18.

This reflected light follows the above-mentioned path in reverse, passes through the quarter-wave plate 14, and reaches the polarizing beam splitter 12. 1/
When passing through the four-wavelength plate 14, the circularly polarized light beam is converted into linearly polarized light having a polarization direction perpendicular to the polarization plane of the original linearly polarized light beam. Therefore, this light beam is reflected at the boundary surface of the polarizing beam splitter 12, passes through the cylindrical lens 22, and then passes through the cylindrical lens 22.
Split photodetector 24 and two photodiodes 26a
.

The light enters a photodetector equipped with 26b.

The 4-split photodetector 24 receives the central light beam from among the three light beams separated by the diffraction grating 9, and passes it through the objective lens 20.
In addition, the information recorded on the tracks of the video disk 5 is detected based on the presence or absence of pits, that is, the intensity of reflected light. on the other hand,
The two photodiodes 26a and 26b each detect two light beams on both sides of the three separated light beams, and output a so-called tracking error signal.

These signals detected by the photodetector 2B are input to the electronic control device 30. Based on the detection signal of the photodetector 28, the electronic control device 3o, as will be described in detail in Shun,
While reading the information recorded on the video disc 5,
A tracking actuator 3 that controls the rotation speed of the spindle motor 1 and also rotates the tracking mirror 16.
6. A tangential actuator 38 that rotates the tangential mirror 38. The focus motor 40 and the like that drive the objective lens 20 in the vertical direction are controlled.

These tracking actuators 36. The structures of the tangential actuator 38 and the focus motor 40 are already well known and are not related to the gist of the present invention, so a description thereof will be omitted. In addition to the objective lens 20, at least the tangential mirror 18. The tracking mirror 16 is mounted on a slider (not shown), and during playback, is moved together in the radial direction of the video disc 5 by a slider motor (not shown), but a description of this configuration is also omitted here. do.

Next, a servo system such as a focus servo will be explained based on FIG. 3, focusing on the internal configuration of the electronic control unit @30. As shown in the figure, the electronic control device 30 includes a preamplifier 51 that amplifies the signal from the 4-split photodetector 24, and an FM compensator 52 that performs MTF compensation on the output signal.
, a video/audio signal demodulation circuit 54 that demodulates a two-channel audio signal and a video signal from the output signal of the FM compensator 52;
A time base servo circuit 56 further separates a burst signal and a horizontal synchronization signal from the demodulated video signal to drive the tangential mirror 18 and the spindle motor 3.
A focus servo 5B and two photodiodes 26 drive the objective lens 20 based on the difference in the sum signal between the diagonals of the four divided parts of the four-part photodetector 24.
A tracking servo circuit 60 drives the tracking mirror 16 based on the difference between the output signals a and 26b, and a control code such as a frame number and program time separated from the video signal by a code separator 62 is input to each of the above servo circuits. It is configured to include a control circuit 64 and the like that control the following.

The control circuit 64 includes a well-known CPU 71. ROM73, R.A.
It is configured as a logical operation circuit with input/output ports etc. centered around M75 etc. The input ports include 5IO 79 for inputting the serial signal from the code separator 62, and a time base servo circuit 56. Focus servo circuit 58
The input ports 81, etc. input spindle lock signals, focus lock signals, etc. from the servo circuits, etc., and the control output ports 83, etc., which output operating commands to each servo circuit, etc. serve as output ports. There is a correction output port 85 that outputs a correction signal for switching the characteristics (gain, etc.) of the compensation amplifier of each servo circuit, etc., and these are connected to the CPU via a common bus 87.
71. It is interconnected with the ROM 73 and the like.

A video disc 5 is placed on the turntable 1, fixed by a clamper (not shown), etc., and is driven by a spindle motor 3.
starts rotating, the control circuit 64 first sends a focus start signal FSt to the pull-in circuit 5 of the focus servo circuit 58.
It is output to 8a. The switch 58b is closed by the focus start signal @Fst, the focus motor 40 is driven via the power amplifier 58c, and the objective lens 20 moves in the direction of the video disk 5 from its original position. When the laser beam is accurately focused on the video disk 5, the difference between the diagonal sum signals of the 4-split photodetector 24, that is, the output of the differential amplifier 58d (this is called a focus error signal) becomes zero, so the compensation amplifier 58e
outputs a control signal to the power amplifier 58c via the switch 58b to maintain the objective lens 20 in that position relative to the video disc 5. In this state, the lock detector 58f outputs a focus lock signal Flk, assuming that the laser beam is accurately focused on the video disc 5 by the focus servo. Therefore,
This can be known through the control circuit 64 and the cover 81.

When the control circuit 64 receives the focus lock signal,
A tracking start signal TSt is output to the switch 60a of the tracking servo circuit 60.

As a result, from the input signals of the two photodiodes 26a and 26b of the photodetector 28, the differential amplifier 60b
, the difference (this is called a tracking error signal) is detected, which is further amplified by a compensation amplifier 60G, and then sent to a power amplifier 6 via a switch 60a.
0e and output as a drive signal for driving the tracking actuator 36. Therefore, the tracking servo circuit 60 has three parts separated by the diffraction grating 9.
Two of the two light beams on both sides sandwich the track of the video disc 5 and illuminate contrasting positions, so that the central light beam accurately follows the pit row of the track, that is, the tracking error signal is always zero. The angle of the tracking mirror 16 is controlled as follows.

Such focus servo and tracking servo are performed by opening the switch 56a of the time base servo circuit 56 in response to the spindle start signal SSt output from the control circuit 64, supplying power to the spindle motor 3 via the power amplifier 56b, and It starts at the same time as the disk 5 is rotated at a predetermined rotation speed. As a result, when the above-described focus servo circuit 58 and tracking servo circuit 60 operate and the video signal is normally reproduced from the track of the video disc 5, the time base servo circuit 56 operates the video/audio demodulation circuit 54. The video signal output from the is inputted to each of a burst separator 56G and a horizontal synchronization separator 56d, and the separated burst signal and horizontal synchronization signal are input to a reference clock and phase comparators 56e and 56f.
and the lock detector 51 for comparison. When it is determined that the horizontal synchronization signal and the reference clock have become equal, the output Slk of the lock detector 56CJ becomes active and the switch 56h is closed. As a result, the phase comparator 56
A signal obtained by amplifying the output of signal e by the compensation amplifier 561 is input to the power amplifier 56j that drives the tangential actuator 38 and to the adder 56. Therefore, the tangential mirror 18 that displaces the laser beam in the tangential direction of the track of the video disc 5 can highly accurately follow uneven linear velocity caused by eccentricity of the video disc 5, and The relative linear velocity of the video disc 5 is always kept constant.

On the other hand, among the signals corresponding to such rotational unevenness, a relatively slow fluctuation component is added to the phase difference component between the horizontal synchronization signal and the reference clock by an adder 56k. Since the spindle motor 3 is controlled by the signal obtained by amplifying the added signal by the compensation amplifier 561 and the power amplifier 56b, its rotation speed is also stabilized.

In addition, the FM compensator 52 and the compensation amplifiers 561, 561 are as follows:
It is configured as a gain-adjustable amplifier whose gain can be changed externally.

Next, regarding the control performed in the control circuit 64,
This will be explained based on FIG. FIG. 4 is a flowchart showing the process of setting the gain of the compensation amplifier 561 in the control system for keeping the rotation speed of the spindle motor 3 constant in the time base servo circuit 56. The control circuit 64 receives a spindle start signal 3st, a focus start signal Gst, t
'After outputting the racking start signal TSt and starting each servo, when the focus lock signal Flk and spindle lock signal Slk are detected via the input port 81,
The spindle servo gain setting routine shown in Figure 4 is as follows:
Repeat at specified timing. Note that the video disc 5 in this embodiment is a CLV disc.

When this routine is started, in step 100, a process of reading the relative position X of the pickup, that is, the objective lens 20 with respect to the video disc 5 is performed. this is,
This is performed by inputting a control code including the program time separated from the video signal by the code separator 62 from the 5IO 79 and converting the program time into the current position X. In the following step 110, it is determined to which range of the video disc 5 this position X belongs. In other words, among the areas where tracks on which information is recorded exist,
As shown in FIG. 5, it is determined whether the inner range a, the outer range C, or the outer range C is being read.

The process branches to steps 120, 130, and 140 depending on which part the objective lens 20 faces, and when it is in the inner circumference range a, the time base servo circuit 5
6, the maximum value G is applied to the gain Gsp of the compensation amplifier 56I at
max is set in step 120 >, when it is in the range C, the gain Gsp is set to an intermediate value (3mid is set in step 130), and when it is in the range C, the gain Gsp is set to the minimum value G
m1n is set (step 140), and after any processing, the routine is terminated after proceeding to NEXT.

Therefore, in this embodiment configured as above, 1.
When reading a CLV disk, the gain of the servo system can be increased according to the rotational speed of the video disk 5 that increases toward the inner circumference, that is, the rotational speed of the spindle motor 3, and the linear velocity of the video disk 5 increases. Reproduction can be performed while suppressing fluctuations to a substantially constant level or less regardless of the outer circumference or inner circumference. Moreover, according to this embodiment, there is no need to separately provide a detection means such as a potentiometer to detect the position in the radial direction of the video disk 5 such as a slider equipped with the objective lens 20, etc., and the apparatus and configuration can be simplified. It is also possible to reduce assembly man-hours, improve reliability, etc.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment in any way, and the control characteristics of each servo system shown in FIG. A configuration in which the gain etc. of the compensation amplifier 561 of the servo system of the Zenthar mirror 18 is changed according to the position in the radial direction of the optical disk, a configuration in which the magnitude of MTF compensation by the FM compensator 52 is changed, or these are Of course, it can be implemented in various ways, such as a combined configuration. For example, FIG. 6 shows that when playing a CAM disk, the current position X of the pickup is known from the control code such as the frame number (step 200 >
When this is within the inner circumference range A shown in FIG. 7, a large value F1 should be set as the MTF compensation value Fmtf in step 2.
10, 220), and sets a small value F2 when outside the range A (steps 210, 230>).In this case, the The drop in high frequency components in the frequency range is sufficiently compensated for.

In addition, in the example, the relative position of the pickup (objective lens) with respect to the optical disk was divided into three or two divisions, but
It is also conceivable to control the control characteristics and the like in even smaller ranges. Further, in the above description, a video disc was used as the optical disc, but the present invention may also be applied to a digital audio disc player.

[lambda] - As detailed above, according to the optical disc playback device of the present invention, the pickup can read the optical disc without providing a separate detection means for detecting the position of the pickup in the radial direction of the optical disc. The control characteristics of the relative position of the pickup and/or the correction characteristics of the read signal can be changed depending on the position, and the excellent effect is that information recorded on the optical disc can be reproduced with high precision. play. In addition, there is no need to provide a separate means to detect the pickup position, so
It is also possible to reduce the size of the device, reduce the number of assembly steps, and improve reliability.

3 is a block diagram mainly showing the configuration of the electronic control device, FIG. 4 is a flowchart showing the control in the embodiment, and FIG. 5 is a spindle servo diagram. Explanatory diagram showing the range of video discs corresponding to gain switching, Part 6
The figure is a flowchart showing control of another embodiment of the present invention,
FIG. 7 is an explanatory diagram showing the switching range of MTF compensation, similar to FIG. 5.

1... Turntable 3... Spindle motor 5
...Video disk 7...Semiconductor laser 9...
Diffraction grating 12...Polarizing beam splitter 14...174 Wave plate 16...Tracking mirror 18...Tangential mirror 20...Objective lens 24...4-split photodetector 26a, 26b... Photodiode 28...Photodetector 30...Electronic control device 36
...Tracking actuator 3B...Tangential actuator 40...Focus motor 52...FM compensator 56...Time base servo circuit 58...Focus servo circuit 60...Tracking servo circuit 62... ...Code separator 64...Control circuit 71...
・CPtJ

Claims (1)

[Scope of Claims] 1. An optical disc playback device that uses an optical pickup to play back an optical disc on which a control code including address information such as a frame number or program time is recorded together with a video signal and/or an audio signal. , signal reading means for controlling the relative position of the pickup and the optical disk and reading a signal recorded on the optical disk based on the intensity of light incident on the pickup from the optical disk; position detection means for decoding the control code from the signal and detecting the position of the pickup in the radial direction of the optical disk; and based on the detected position, the signal reading means controls the relative position of at least the pickup. an optical disc reproducing device comprising: changing means for changing characteristics and/or correction characteristics of a read signal;