JP2008140442A - Optical disk drive and focus control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk drive which can perform a stable focus operation by surely performing the distinction of a board surface and the information recording surface of an optical disk, and to provide a focus control method. <P>SOLUTION: When detecting a focus sum signal by a substrate surface, a detection signal of the focus sum signal by return light from the surface output from an RF amplifier turns into a big signal and can be surely detected by setting an amplification factor of the RF amplifier as a first amplification factor which is a large amplification factor compared with a normal amplification factor. After determining it being a surface, an information recording surface is detected by setting the amplification factor as a second amplification factor which is the normal amplification factor, and the operation to draw a focus point of a laser beam to the information recording surface can be stably performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus that handles CD, DVD, HD DVD, and the like, and a focus control method.

  A plurality of types of recording density optical disks called CD (Compact Disc) standards and DVD (Digital Versatile Disk) standards are already widely used. In recent years, by recording information using laser light of a blue-violet wavelength, In addition, an ultra-high density optical disk HD DVD (High Density Digital Versatile Disk) with a further increased recording density has been put on the market.

  Some of the optical disks described above have a low reflectance of laser light on the information recording surface, and there are optical disks that have a small difference from the reflectance on the substrate surface outside the optical disk. In such a case, it is difficult to determine whether the focal point of the laser beam is on the substrate surface or the information recording surface, and there is a possibility that the focusing operation is erroneously performed on the substrate surface, which is an obstacle to recording and reproduction. As a method for dealing with such a problem, the following technique has been proposed (for example, see Patent Document 1).

In Patent Document 1, the peak timing of the focus sum signal and the zero cross timing of the focus error signal are compared, and when these timings substantially coincide with each other, the recording / reproduction surface is determined and the focusing operation is performed.
JP 2003-272183 A

  However, in Patent Document 1, when both the focus difference signal and the focus difference signal on the substrate surface and the information recording surface are small, it becomes difficult to compare the timing of the peak of the focus sum signal and the timing of the zero crossing of the focus error signal. There is a risk of misjudgment.

  The present invention has been made in view of the circumstances as described above, and provides an optical disc apparatus and a focus control method capable of reliably distinguishing between a substrate surface and an information recording surface of an optical disc and performing a stable focusing operation. The purpose is to do.

  In order to achieve the above object, an optical disc apparatus according to the present invention includes an objective lens for condensing laser light on an information recording surface of an optical disc and a divided light receiving portion for receiving reflected light from the optical disc. An optical pickup having a photodetector, signal processing means for generating a focus error signal and a focus sum signal from an output signal of the photodetector, and the focus error signal and the focus sum signal generated by the signal processing means A focus control means for generating a focus control signal for controlling the position of the objective lens in the focus direction; and a step of drawing the focus of the laser beam onto the information recording surface of the optical disc; Set the signal amplification factor when the sum signal is generated, and the objective lens The first amplification factor is set at a position farther from the surface than the position on the objective lens side surface of the optical disc, and the objective lens gradually moves in the direction of the optical disc to focus on the surface. And a gain setting means for setting a second gain after detecting a focus sum signal due to the reflected light from the surface at the position.

  The focus control method of the present invention includes an objective lens for condensing laser light on an information recording surface of an optical disc, and a photodetector having a divided light receiving portion for receiving reflected light from the optical disc. An optical pickup, a signal processing means for generating a focus error signal and a focus sum signal from the output signal of the photodetector, and a focus direction of the objective lens from the focus error signal and the focus sum signal generated by the signal processing means An optical disc having a focus control means for generating a focus control signal for controlling the position of the lens and an amplification factor setting means for setting a signal amplification factor when a focus error signal and a focus sum signal are generated by the signal processing means The focal point of the laser beam is drawn into the information recording surface of the optical disc in the apparatus. In the focus control method, the step of setting the amplification factor to a first amplification factor, and the step of moving the objective lens to a position away from the surface from a position focusing on the surface of the optical disc on the objective lens side; A step of gradually moving the objective lens in the direction of the optical disc, and a focus sum signal by reflected light from the surface at a position where the objective lens is focused on the surface and a preset first threshold value. In comparison, when it is determined that the focus sum signal is greater than the first threshold value, the step of determining that the focus sum signal is a focus sum signal due to reflected light from the surface; Setting the amplification factor to a first amplification factor after being determined to be a focus sum signal due to reflected light from The objective lens is gradually moved in the direction of the optical disc, and a focus sum signal by reflected light from the information recording surface at a position where the objective lens is focused on the information recording surface and a preset second threshold value And when it is determined that the focus sum signal is greater than the second threshold, the focus sum signal is determined to be a focus sum signal due to reflected light from the information recording surface; And a step of drawing the focal point of the laser beam onto the information recording surface after it is determined that the signal is a focus sum signal by reflected light from the information recording surface.

  According to the present invention, by reliably distinguishing between the optical disc substrate surface and the information recording surface, it is possible to prevent erroneous focus operation on the optical disc surface, shorten the optical disc recognition operation time, and stabilize and shorten the focus operation. It is possible to provide an optical disc apparatus capable of performing the recording / reproducing operation.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an internal configuration of an optical disc apparatus 1 according to the present invention. The optical disc apparatus 1 records and reproduces information on an optical disc 2 as an information recording medium such as a DVD (Digital Versatile Disc). The optical disc 2 has grooves concentrically or spirally. The concave portion of the groove is called a land, the convex portion is called a groove, and one round of the group or land is called a track. User data is recorded on the optical disc 2 by irradiating intensity-modulated laser light along the tracks (grooves only or grooves and lands) to form recording marks.

  Data reproduction is performed by irradiating a laser beam with a weaker read power (Read Power) than at the time of recording along a track and detecting a change in reflected light intensity caused by a recording mark on the track. The recorded data is erased by irradiating a laser beam with erase power (Erase Power) stronger than the read power along the track to crystallize the recording layer.

  The optical disk 2 is rotationally driven by a disk motor 3. A rotation angle signal is output from a rotary encoder 3 a (not shown) attached to the disk motor 3 to the disk motor drive circuit 4. When the disk motor 3 rotates once, the rotation angle signal is generated, for example, 5 pulses. Thus, the disk motor control circuit 5 can determine the rotation angle and the rotation speed of the disk motor 3 based on the rotation angle signal input from the rotary encoder 3a via the disk motor drive circuit 4. The disk motor 3 is controlled by a disk motor control circuit 5.

  Information is recorded on or reproduced from the optical disc 2 by the optical pickup 5. The optical pickup 5 is provided with an objective lens 6 supported by a wire or a leaf spring (not shown). The objective lens 6 can be moved in the focusing direction (the optical axis direction of the lens) by driving the focus actuator 7, and can be moved in the tracking direction (the direction orthogonal to the optical axis of the lens) by driving the tracking actuator 8. Is possible.

  The optical pickup 5 is connected to a thread motor 9 via a gear and a screw shaft (not shown). The thread motor 9 is driven by a thread motor drive circuit 10. The sled motor 9 is rotated by the sled motor driving current supplied from the sled motor driving circuit 10, so that the optical pickup 5 moves in the radial direction of the optical disc 2. The sled motor driving circuit 10 outputs a sled motor driving current in accordance with a control signal sent from the sled motor control circuit 11.

  The laser diode 12 emits laser light in accordance with the drive current supplied from the laser drive circuit 13. The laser drive circuit 13 is supplied with a control signal corresponding to the reproduction, recording or erasing operation from the laser control circuit 14 and supplies a drive current to the laser diode 12 based on the control signal.

  The modulation circuit 15 modulates user data supplied from the host device 33 via the interface circuit 32 during information recording, and provides the modulated recording data to the laser control circuit 14. The modulation method is, for example, 8-16 modulation in the case of a DVD system, and EFM modulation in the case of a CD system. The laser control circuit 14 supplies a control signal for writing to the laser drive circuit 13 based on the modulated recording data supplied from the modulation circuit 15 at the time of recording information on the optical disc 2 (at the time of mark formation). The drive circuit 13 supplies a drive current to the semiconductor laser diode 12 in the optical pickup 5.

  Laser light emitted from the laser diode 12 is irradiated onto the information recording surface of the optical disc 2 through the optical component 16 in the optical pickup 5 and the objective lens 6. The reflected light from the optical disk 2 is guided to the photodetector 17 through the objective lens 6 and the optical component 16.

  The photodetector 17 is composed of, for example, a quadrant photodetection cell, generates a detection signal, and outputs the generated detection signal to the RF amplifier 18. The RF amplifier 18 having a function as a signal processing means processes a detection signal from the photodetector 17 and generates a focus error signal (FE) indicating an error from the just focus, a laser beam spot center and a track center. A tracking error signal (TE) indicating an error and a full addition signal or reproduction signal (RF) of the detection signal are generated, and the generated focus error signal (FE), tracking error signal (TE), and full addition signal or reproduction are generated. The signal (RF) is supplied to the A / D / D / A converter 19.

  The focusing control circuit 20 generates a focus control signal according to the focus error signal (FE) fetched by the DSP 29 from the RF amplifier 18 via the A / D / D / A converter 19 and the generated focus control signal Is supplied to the focus actuator drive circuit 21. The focus actuator drive circuit 21 supplies a focus actuator drive current for driving the focus actuator 7 to the focus actuator 7 in the focusing direction based on the focus control signal supplied from the focusing control circuit 20. Thereby, focus servo is performed in which the laser beam is always just focused on the information recording surface of the optical disc 2.

  The track king control circuit 22 generates and generates a track control signal according to the tracking error signal (TE) A / D converted by the A / D / D / A converter 19 from the RF amplifier 18 and captured by the DSP 29. The track control signal is supplied to the tracking actuator drive circuit 23. Based on the tracking control signal supplied from the tracking control circuit 22, the tracking actuator driving circuit 23 supplies a tracking actuator driving current for driving the tracking actuator 8 to the tracking actuator 8 in the tracking direction. As a result, tracking servo is performed in which the laser beam always traces the track formed on the optical disc 2.

  By performing such focus servo and tracking servo, the reproduction signal (RF) obtained by adding the detection signal from the light detector 17 (each light detection cell) is recorded on the track of the optical disc 2 corresponding to the recording information. Changes in reflected light from pits and the like formed in are reflected. This reproduction signal is A / D converted via an A / D / D / A converter 19 and supplied to a data reproduction circuit 24. The data reproduction circuit 24 generates a binary signal of 1 or 0 according to the reproduction signal supplied from the A / D / D / A converter 19, and sends the generated binary signal to the error correction circuit 29. Output. The data recovery circuit 19 outputs the binarized signal to the error correction circuit 29, and at the same time, calculates the phase difference between the recovered clock signal supplied from the PLL (Phase Locked Loop) circuit 25 and the binarized signal. The phase comparison signal is generated, and the generated PLL phase comparison signal is output to the PLL circuit 25.

  A DSP (Digital Signal Processor) 29 is a focus error signal (FE) and a tracking error which are output from the RF amplifier 18 and then converted into a digital signal by A / D conversion via an A / D / D / A converter 19. Various arithmetic processes are performed on the digital signal such as the signal (TE) to control the disk motor control circuit 5, the thread motor control circuit 11, the focusing control circuit 20, and the tracking control circuit 22.

  Disk motor control circuit 5, thread motor control circuit 11, laser control circuit 14, modulation circuit 15, A / D / D / A converter 19, focusing control circuit 20, tracking control circuit 22, PLL circuit 25, error correction circuit 29 Is controlled by a CPU (Central Processing Unit) 28 via a bus 27. The RF amplifier 18 is controlled by the CPU 28 by a signal D / A converted via the A / D / D / A converter 19.

  The CPU 28 follows an operation command supplied from the host device 33 via the interface circuit 32 and also follows a program stored in a ROM (Read Only Memory) 31 and a program loaded from the ROM 31 to a RAM (Random Access Memory) 30. Various processes are executed, various control signals are generated, and are supplied to the respective units, whereby the optical disc apparatus 1 is comprehensively controlled.

  FIG. 2 is a diagram showing the positional relationship between the optical disc 2 and the objective lens 6 and the relationship between the focus error signal and the focus sum signal. The positional relationship between the objective lens side surface 2b of the optical disc 2 and the objective lens 6 will be described in three stages (A, B, C).

  A is a case where the objective lens 6 is located at a position farther from the surface 2b than the position where the objective lens 6 is focused on the surface 2b on the objective lens side of the optical disc, and the focal point of the laser light does not reach the surface 2b. In the step of focusing the laser beam on the information recording surface of the optical disc, the objective lens is first set at such a position or further away from the surface 2b.

  B is a position where the objective lens gradually moves in the direction of the optical disk and the surface 2b is focused on the laser beam. A focus error signal is detected before and after focusing on the surface 2b. When the surface 2b is focused, the focus sum signal detected almost at the same time becomes the maximum. The focus sum signal may be a full addition signal or a reproduction signal (RF) of the photodetector 17.

  C is a position where the objective lens further gradually moves in the direction of the optical disc, and the laser beam is focused on the information recording surface 2a. A focus error signal is detected before and after focusing on the information recording surface 2a. Further, when focusing on the information recording surface 2a, the focus sum signal detected almost at the same time becomes the maximum.

  B and C indicate that the signal amplitude of the focus error signal and the focus sum signal is small because the reflectance of the surface 2b is smaller than the reflectance of the information recording surface 2a. When the reflectivity of the information recording surface 2a is reduced, the reflectivity of the surface 2b is approached, and when the speed at which the objective lens gradually moves is increased, it becomes difficult to distinguish the signal from the surface 2b and the signal from the information recording surface 2a.

  FIG. 3 is a diagram showing the positional relationship between the optical disc 2 and the objective lens 6 according to the present invention and the relationship between the focus error signal, the focus sum signal, and the amplification factor of the RF amplifier. The difference from FIG. 2 is that the signal amplification factor when the focus error signal and the focus sum signal are generated by the signal processing means is variable depending on the position of the objective lens.

  When at the position A, the signal amplification factor when the focus error signal and the focus sum signal are generated by the RF amplifier 18 is set to the first amplification factor, and at the position B, the focus sum by the reflected light from the surface 2b is set. After the signal is detected, the second amplification factor is set. The second amplification factor is an amplification factor when the focus servo is operated on the information recording surface to turn on the focus, that is, a normal amplification factor. The first amplification factor is a larger amplification factor than the second amplification factor. At the second amplification factor, the detection signal of the focus error signal and the focus sum signal from the surface 2b is a small value and there is a possibility of erroneous detection. However, by setting the first amplification factor, The detection signal of the focus error signal and the focus sum signal from the output surface 2b becomes a large signal and can be reliably detected.

  In this way, when the objective lens 6 is gradually brought closer to the optical disc 2, the signal due to the reflected light from the surface 2b to be detected first can be reliably detected. The amplification factor is set by the CPU 28 setting the amplification factor of an amplifier (not shown) in the RF amplifier 18 by a signal D / A converted via the A / D / D / A converter 19.

  If the focus error signal and the focus sum signal due to the reflected light from the information recording surface 2a are detected while maintaining the first amplification factor, the focus servo may oscillate in some cases, and the focus servo for operating the focus on the information recording surface 2a is operated. In this case, there is a possibility that the oscillation may not be performed properly due to oscillation, so that a step for returning the amplification factor to the normal amplification factor is required. Accordingly, the magnitude of the focus sum signal on the surface 2b is compared with a predetermined first threshold value set in advance, and when it is determined that the focus sum signal is large, the focus sum signal is reflected by the reflected light from the surface 2b. It is determined that it is a signal. Then, by changing to the second gain after the determination, the focus servo can be operated on the information recording surface 2a.

  In the detection of the focus error signal and the focus sum signal by the reflected light on the information recording surface 2a, the focus sum signal by the reflected light from the information recording surface 2a at the position where the objective lens 6 is focused on the information recording surface 2a is set in advance. And when the focus sum signal is determined to be larger than the second threshold value, the focus sum signal is a focus sum signal generated by reflected light from the information recording surface 2a. judge.

  The reflectivity of the information recording surface 2a differs depending on the difference between the CD system, the DVD system, the HD DVD system, and the reproduction-only type and the recordable type. Accordingly, the second threshold value is set to a threshold value corresponding to the information recording surface 2a. After the optical disk 2 is loaded in the optical disk apparatus 1, the type of the optical disk 2 is determined in the initial operation. The CPU selects an appropriate setting value from various setting values stored in the ROM 31 based on the determination result, and sets it as the second threshold value in the RAM 30.

  FIG. 4 is a flowchart of the process of drawing the focal point of the laser beam onto the information recording surface 2a of the optical disc 2. In S <b> 1, the CPU 28 sets the signal amplification factor of the RF amplifier 18 when the focus error signal and the focus sum signal are generated in the RF amplifier 18 to the first amplification factor.

  In S2, the CPU 28 sends a signal to the focusing control circuit 20, and moves the objective lens 6 in a direction away from the surface 2b to a position where the focal point of the laser beam does not reach the surface 2b of the optical disc 2. In S3, the CPU 28 sends a signal to the focusing control circuit 20 to gradually move the objective lens 6 in a direction approaching the surface 2b.

  In S4, the CPU 28 compares the focus sum signal that may be due to the reflected light from the surface 2b with a preset first threshold value, and when it is determined that the focus sum signal is greater than the first threshold value. In S5, it is determined that the focus sum signal is a focus sum signal generated by the reflected light from the surface 2b. That is, it is determined that the surface 2b has been detected. When it is determined that the value is smaller than the first threshold value, the process returns to S3 and the objective lens 6 is gradually moved in a direction approaching the surface 2b.

  In S6, the CPU 28 sets the signal amplification factor of the RF amplifier 18 to the second amplification factor. In S7, the CPU 28 sends a signal to the focusing control circuit 20, and gradually moves the objective lens 6 in a direction closer to the surface 2b.

  In S8, the CPU 28 compares the focus sum signal that may be due to the reflected light from the information recording surface 2a with a preset second threshold value, and determines that the focus sum signal is greater than the second threshold value. In S9, the focus sum signal is determined to be a focus sum signal by reflected light from the information recording surface 2a. That is, it is determined that the information recording surface 2a has been detected. When it is determined that the value is smaller than the second threshold value, the process returns to S7 and the objective lens 6 is gradually moved in a direction closer to the surface 2b. In S10, the CPU 28 starts a focus pull-in operation with respect to the information recording surface 2a.

  As described above, when detecting the focus error signal and the focus sum signal from the surface 2b, the amplification factor of the RF amplifier 18 is set to the first amplification factor that is larger than the normal amplification factor. Thus, the detection signal of the focus error signal and the focus sum signal due to the reflected light from the surface 2b output from the RF amplifier 18 becomes a large signal and can be reliably detected, and it can be determined that the surface 2b. After detecting the surface 2b, the information recording surface 2a is detected by setting the amplification factor to the second amplification factor which is a normal amplification factor, and the focus of the laser beam is drawn on the information recording surface 2a. It can be performed. In this way, by distinguishing between the surface 2b of the optical disc 2 and the information recording surface 2a, stable focus control is possible.

1 is a block diagram showing an internal configuration of an optical disc apparatus according to the present invention. The figure which shows the positional relationship of an optical disk and an objective lens, and the relationship of a focus error signal and a focus sum signal. The figure which shows the positional relationship of the optical disk and objective lens concerning this invention, and the relationship of a focus error signal, a focus sum signal, and the amplification factor of RF amplifier. The flowchart of the process of drawing in the focus of a laser beam on the information recording surface of an optical disk.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 2 Optical disk 2a Information recording surface 2b Surface 6 Objective lens 7 Focus actuator 12 Laser diode 13 Laser drive circuit 14 Laser control circuit 17 Photo detector 18 RF amplifier 19 A / D / D / A converter 20 Focusing control circuit 21 Focus actuator drive circuit 28 CPU
30 RAM
31 ROM
32 Interface circuit 33 Host device

Claims (5)

An optical pickup having an objective lens for condensing laser light on the information recording surface of the optical disc and a photodetector having a divided light receiving portion for receiving the reflected light from the optical disc;
Signal processing means for generating a focus error signal and a focus sum signal from the output signal of the photodetector;
Focus control means for generating a focus control signal for controlling the position of the objective lens in the focus direction from the focus error signal and the focus sum signal generated by the signal processing means;
In the step of drawing the focus of the laser beam onto the information recording surface of the optical disc, a signal amplification factor is set when the focus error signal and the focus sum signal are generated by the signal processing means, and the objective lens is the optical disc of the optical disc. A first amplification factor is set at a position farther from the surface than a position focusing on the surface on the objective lens side, the objective lens gradually moves in the direction of the optical disc, and the position at the position focused on the surface An optical disc apparatus comprising: an amplification factor setting unit that sets a second amplification factor after detecting a focus sum signal by reflected light from the surface.   When a focus sum signal by reflected light from the surface at a position where the objective lens is focused on the surface is compared with a preset first threshold, and the focus sum signal is greater than the first threshold 2. The optical disk apparatus according to claim 1, further comprising a determining unit that determines that the focus sum signal is a focus sum signal generated by reflected light from the surface when it is determined.   A focus sum signal by reflected light from the information recording surface at a position where the objective lens is focused on the information recording surface is compared with a preset second threshold value, and the focus sum signal is 3. The optical disk apparatus according to claim 1, further comprising a determining unit that determines that the focus sum signal is a focus sum signal generated by reflected light from the information recording surface when it is determined that the focus sum signal is greater than a threshold value.   4. The optical disc apparatus according to claim 1, wherein the first amplification factor is larger than the second amplification factor. An optical pickup having an objective lens for condensing laser light on the information recording surface of the optical disc and a photodetector having a divided light receiving portion for receiving the reflected light from the optical disc;
Signal processing means for generating a focus error signal and a focus sum signal from the output signal of the photodetector, and controlling the position of the objective lens in the focus direction from the focus error signal and the focus sum signal generated by the signal processing means. Of the optical disc in the optical disc apparatus, comprising: a focus control means for generating a focus control signal for the signal; and an amplification factor setting means for setting a signal amplification factor when a focus error signal and a focus sum signal are generated by the signal processing means. In the focus control method for drawing the focal point of the laser beam onto the information recording surface,
Setting the amplification factor to a first amplification factor;
Moving the objective lens to a position away from the surface from a position focusing on the objective lens side surface of the optical disc;
Gradually moving the objective lens in the direction of the optical disc;
When a focus sum signal by reflected light from the surface at a position where the objective lens is focused on the surface is compared with a preset first threshold, and the focus sum signal is greater than the first threshold Determining that the focus sum signal is a focus sum signal due to reflected light from the surface when determined;
Setting the gain to a first gain after it is determined that the focus sum signal is a focus sum signal from reflected light from the surface;
The objective lens is gradually moved in the direction of the optical disc, and a focus sum signal by reflected light from the information recording surface at a position where the objective lens is focused on the information recording surface and a preset second threshold value And when it is determined that the focus sum signal is greater than the second threshold, the focus sum signal is determined to be a focus sum signal due to reflected light from the information recording surface;
And a step of drawing the focus of the laser beam onto the information recording surface after it is determined that the focus sum signal is a focus sum signal due to reflected light from the information recording surface.

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