JP3861900B2 - Optical information reproducing apparatus and reproducing method - Google Patents

Description

  In order to read information from at least first and second types of information recording media, the present invention provides at least first and second types of light beams corresponding to the types of information recording media. The present invention relates to an optical information reproducing apparatus including an optical pickup having a light source and a reproducing method.

  In the optical information reproducing apparatus, a light beam emitted from a light beam light source is condensed and irradiated on the information recording medium, and information is read from the reflected light. For this purpose, a focus servo device is provided, and focus servo is applied based on the focus error signal extracted from the reflected light so that the focus of the light beam follows the information surface on the information recording medium. Also, a focus pull-in device is provided to perform a focus search and activate the focus servo.

  In recent years, information recording media have been diversified, and compact discs (CD), digital versatile discs (DVD), Blu-ray discs (BD), etc. have been put to practical use. The function to play back is required.

  For example, a laser diode that provides light beams of two types of wavelengths for CD and DVD, for example, is mounted on one optical pickup, and a laser diode that is used in accordance with the type of information recording medium to be reproduced is mounted. Optical pickups that reproduce both CDs and DVDs while being selected have been put into practical use. However, immediately after the information recording medium is mounted as an information reproducing apparatus, the type of the information recording medium is unknown, and an attempt is made to reproduce a CD with the wavelength of the light beam for DVD, or the wavelength of the light beam for CD. There is a possibility that the player tries to play a DVD. In addition, it is conceivable to perform a focus search before reproduction, and to estimate the type of the information recording medium mounted from the state of the reflected light obtained at that time, but the error of the apparatus and the deviation of the information recording medium, In consideration of dirt and the limitation of the estimated time, the type of the information recording medium cannot be determined, and the above-mentioned case is inevitable. When the wavelength to be used and the type of the information recording medium do not match, a focus error signal with an ideal waveform cannot be obtained even if focus search is performed, so that focus pull-in frequently occurs. .

  Here, an even greater problem is that the mechanical movable range of the objective lens of the optical pickup is required to reproduce information recording media of different thicknesses from the disk surface to the information recording surface, such as CD and DVD, with one optical pickup. Considering the allowable range of warpage and surface deflection of the information recording medium, they may collide or come into contact with each other, and if the focus pull-in fails, the information recording medium may be damaged or the objective lens may be damaged. It means that there are things.

  As a method of avoiding this problem, a method of performing a focus pull-in operation only during a focus search in which the objective lens is always driven in a direction away from the information recording medium is known (for example, see Patent Document 1). This conventional example will be described.

  FIG. 7 is a block diagram of a conventional optical information reproducing apparatus. In FIG. 7, 1 is an information recording medium, 2 is an optical pickup, 3 is an objective lens, 6 is a focus actuator, 7 is a focus error signal generating means, 9 is a focus servo means, 16 is a control unit, 17 is a light beam light source, Reference numeral 18 denotes focus search means, 19 denotes a servo changeover switch, 20 denotes focus pull-in means, and 21 denotes focus zero cross detection means.

  The operation of the conventional optical information reproducing apparatus configured as described above will be described below.

  First, the optical pickup 2 includes an objective lens 3, a focus actuator 6, and a light beam light source 17. The light beam emitted from the light beam light source 17 is condensed and irradiated on the information recording medium 1 through the objective lens 3. The reflected light is detected. The focus error signal generation means 7 extracts a focus error signal from the reflected light and supplies it to the focus servo means 9. The focus servo means 9 generates a focus servo signal from the focus error signal.

  The focus search means 18 generates a focus search signal for moving the objective lens 3 closer to or away from the information recording medium 1. The servo changeover switch 19 selects the focus search signal and the focus servo signal in accordance with a command from the focus pull-in means 20 and supplies the selected signal to the focus actuator 6. The focus actuator 6 responds to the applied drive voltage. Then, the objective lens 3 is driven to move the focal point of the light beam in the optical axis direction.

  When the information recording medium 1 is loaded in the optical information reproducing apparatus, the control unit 16 first generates a focus search signal in the focus search means 18 and pulls it to the focus actuator 6 via the servo changeover switch 19. In addition, so-called focus search is performed. The focus zero-cross detection means 21 detects that the focus error signal obtained during the focus search has zero-crossed and transmits a focus zero-cross signal to the control unit 16. At this time, the control unit 16 determines that the focal point of the light beam has reached the information surface of the information recording medium 1 and issues an arrival command to the focus pull-in means 20, and the focus pull-in means 20 The changeover switch 19 is switched to switch the signal to be applied to the focus actuator 6 from the focus search signal to the focus servo signal to perform focus pull-in to activate the focus servo. However, as shown in FIG. 8, depending on the combination of the type of the optical pickup 2 and the type of the information recording medium 1, a fake signal in which the focus error signal crosses zero other than the just focus point may occur. When focus pull-in is performed in response to the fake signal, not only the focus servo activation fails, but also the information recording medium 1 may be damaged or the objective lens may be damaged. Therefore, the direction of the focus search when the focus pull-in operation is performed is a direction in which the fake signal is not output, that is, in the case shown in FIG. 8, the focal position of the light beam is moved away from a state close to the information recording medium 1. By performing the focus pull-in only when the focus search is performed in the direction, the focus servo can be stably activated, and the information recording medium 1 can be prevented from being damaged or the objective lens can be damaged.

A processing procedure of the focus pull-in operation in this case will be described with reference to FIG. In FIG. 9, the focal position of the light beam moves in the optical axis direction with time according to the focus search operation of the focus actuator 6. The focus error signal detected at that time is as shown in the figure. First, the objective lens 3 is moved away from the information recording medium 1, and the focal point of the light beam is moved away from the information surface of the information recording medium 1. Next, the focus search direction is reversed and the focus of the light beam is driven in a direction approaching the information surface of the information recording medium 1. At this time, from the output of the focus zero cross detection means 21, it is unknown whether the focus of the light beam is the just focus point or the fake signal, but it can be detected that the focus has exceeded the vicinity of the focus zero cross. Thereafter, the objective lens 3 is further driven in a direction approaching the information recording medium 1 for a predetermined time (ΔT). Thereafter, the focus search direction of the focus actuator 6 is reversed, and this time the objective lens 3 is driven away from the information recording medium 1. Since the fake signal is not generated in the focus error signal obtained when the focus search is performed in this direction immediately before reaching the just focus point, the focus zero cross detection signal that is the output of the focus zero cross detection means 21 is added. If the focus pull-in is performed accordingly, the focus servo can be started stably.
JP 2001-202632 A (page 7, FIG. 3)

  However, in such an optical information reproducing apparatus, regardless of the type of information recording medium and the wavelength of the light beam light source, in order to perform a focus pull-in operation during a focus search in which the objective lens is always kept away from the information recording medium, A new problem arises.

  First, there is no problem when an ideal focus error signal without a fake signal can be obtained or when a focus error signal as shown in FIG. 8 can be obtained, but the type of the information recording medium 1 and the light beam Depending on the combination of the types of wavelengths of the light sources, the fake signal described above may occur at a position where the objective lens 3 is closer to the information recording medium 1 than the just focus point. In this case, the focus servo is activated. In addition to failure, there is a problem that the information recording medium 1 may be damaged or the objective lens may be damaged. This is because, as an optical information reproducing apparatus, the type of the information recording medium is unknown immediately after the information recording medium is mounted. This is likely to occur when the DVD is played at the wavelength of the beam.

  As a specific example, when an optical pickup has two types of light beam light sources having wavelengths of about 650 nanometers / about 780 nanometers for reproducing information recording media of a DVD system / CD system, a DVD is used. When the type of the information recording medium matches the type of the light beam, such as a DVD disk irradiated with a light beam for reproduction or a CD disk irradiated with a light beam for reproducing a CD, As shown in FIG. 2, an ideal focus error signal without a fake signal is often obtained. Alternatively, depending on the structure of the optical pickup, as shown in FIG. 8, a focus error signal having a fake signal in the direction opposite to the output of the focus error signal in the vicinity of the focus error signal on the side far from the information recording medium may be obtained. However, when the type of information recording medium and the type of light beam are different, such as a CD disk irradiated with a light beam for reproducing a DVD or a DVD disk irradiated with a light beam for reproducing a CD. In the former, for example, as shown in FIG. 3, a fake signal is generated near the focus error signal on the side far from the information recording medium in the same direction as the output of the focus error signal, and in the latter, for example, as shown in FIG. A fake signal is generated in the same direction as the output of the focus error signal in the vicinity of the focus error signal near the recording medium.

  Therefore, in a system that performs a focus pull-in operation during a focus search in which the objective lens is always moved away from the information recording medium, the focus servo is performed using a light beam source of a different type from the information recording medium when the type of the information recording medium is unknown. If it is attempted to be pulled in, not only will the focus servo start fail due to the fake signal, but the information recording medium 1 may be damaged or the objective lens may be damaged.

  In addition, the focus error signal and other signals obtained when the type of information recording medium and the type of light beam are different are not intended for use as an optical pickup. In most cases, there is no standard value of the signal, and no inspection is performed even during production. Therefore, a focus search is performed in advance immediately after the information recording medium is mounted on the optical information reproducing apparatus, the type of the mounted information recording medium is estimated, and the wavelength of the light beam light source to be used is selected accordingly. Thus, even if it tries to avoid the above-mentioned case, it is impossible to completely avoid the erroneous detection of the type of the information recording medium. In the worst case, not only the start of the focus servo fails, but also the information There is a big problem that the recording medium 1 is damaged or the objective lens is damaged.

  Secondly, even when an ideal focus error signal without the fake signal can be obtained, the focus of the light beam is once brought close to the information surface of the information recording medium 1 and moved away from the just focus point. Therefore, there is a problem that it takes an extra time to start the focus servo because the focus search is performed and the focus pull-in is performed.

  Third, when the focus search is performed in the direction in which the objective lens is brought closer to the information recording medium, even if the just focus point is detected, the focus search is continued for a certain time, and the objective lens is moved beyond the just focus point. If the focus search speed is increased in order to reverse the direction of the focus search after the image is moved closer to the information recording medium, the objective lens and the information recording medium are too close, and in the worst case, the two collide. There are challenges.

  On the other hand, if the focus search speed is slowed down to reduce the risk of collision between the two, not only will the time required to start the focus servo be increased, but the information recording medium will be moved up and down due to surface blurring of the information recording medium. However, there is a problem that the focus search speed cannot catch up, and the possibility that the focus servo cannot be started because the focus cannot be pulled in increases.

  As described above, according to the present invention, when the type of the information recording medium is unclear and the wavelength of the light beam light source used for starting the focus servo is different from the type of the information recording medium, Even if a signal was generated, the focus servo could not be activated and the information recording medium could be damaged and the objective lens could be damaged without causing damage to the objective lens. Is. Furthermore, the focus search was made to increase the speed of the focus search and reduce the time required for focus pull-in without increasing the risk of collision between the objective lens and the information recording medium. Is.

In order to solve the above-described problems, an optical information reproducing apparatus according to the first aspect of the present invention is adapted to each type of information recording medium in order to read information from at least first and second types of information recording media. a light beam source of at least two or more wavelengths of longer wavelength than the light beam of the at least a first wavelength corresponding first light beam a second light beam, the light beam emitted from each of said light beam source And a focus actuator that drives the objective lens in the optical axis direction of the light beam, and the focus of the light beam is the information recording medium A focus servo means for controlling the position of the objective lens so that the objective lens is positioned at a just focus point that matches the information recording surface, and the objective lens A first focus search means for approaching the information recording medium, a second focus search means for moving the objective lens away from the information recording medium, and a focus from the first focus search operation during the first focus search. a first focus pull means to switch to the servo operation, the during a second focus search, from the second focus search operation and a second focus pull means for switching the focusing servo operation, said first wavelength The main feature is that when the focus servo is pulled in using the light beam light source, the focus servo is pulled in using the second focus pull-in means.

  In the optical information reproducing apparatus of the present invention, after detecting that switching from the first focus search to the second focus search is in the vicinity of a just focus point during the first focus search, The driving voltage of the actuator is increased by a predetermined value, and the objective lens approaches the information recording medium by a predetermined distance from the vicinity of the just focus point, and then the main characteristic is switched to the second focus search. To do.

In the optical information reproducing method according to the second aspect of the present invention, in order to read information from at least the first and second types of information recording media, at least the first corresponding to each type of the information recording media is used. The information recording is performed by condensing light beams emitted from light beam sources of at least two types of wavelengths, ie, a light beam having a wavelength of 2 and a second light beam having a wavelength longer than that of the first light beam by an objective lens. An optical pickup means for irradiating the medium and driving the objective lens in the optical axis direction of the light beam, and so that the focal point of the light beam is located at a just focus point that matches the information recording surface of the information recording medium, A focus servo means for controlling the position of the objective lens; a first focus search means for bringing the objective lens close to the information recording medium; Second focus search means for keeping the distance from the information recording medium, first focus pull-in means for switching from the first focus search operation to the focus servo operation during the first focus search, and the second focus search means during the focus search, the second has the focus search operation and a second focus pull means for switching the focusing servo operation, when brought into focus servo using a light beam source of the first wavelength, the second The main feature is that the focus servo is pulled in by using the focus pull-in means.

  The optical information reproducing apparatus of the present invention, when the type of the information recording medium to be reproduced is unclear, when the wavelength of the light beam light source used to start the focus servo is different from the type of the information recording medium, Even if a fake signal is generated in the focus error signal, focus pull-in can be performed stably without failing to start the focus servo and damaging the information recording medium or damaging the objective lens. In addition, when the type of the information recording medium is clear, it is possible to quickly perform the optimum focus pull-in operation accordingly. Furthermore, it is possible to increase the speed of the focus search and reduce the time required for focus pull-in without increasing the risk of collision between the objective lens and the information recording medium during the focus search. can get.

  Hereinafter, in order to read information from the first and second types of information recording media according to an embodiment of the present invention, the first and second types of wavelengths corresponding to the types of the information recording media respectively. An optical information reproducing apparatus including an optical pickup provided with a light beam light source will be described as an example with reference to FIGS.

(Embodiment)
FIG. 1 is a block diagram of an optical information reproducing apparatus according to an embodiment of the present invention. In FIG. 1, 1 is an information recording medium, 2 is an optical pickup, 3 is an objective lens, 4 is a light beam light source that emits a light beam of a first wavelength, and 5 is a light beam that emits a light beam of a second wavelength. Light source, 6 focus actuator, 7 focus error signal generating means, 8 just focus point vicinity detecting means, 9 focus servo means, 10 first focus search means, 11 second focus search means, and 12 A search changeover switch, 13 is a servo changeover switch, 14 is a first focus drawing means, 15 is a second focus drawing means, and 16 is a control unit.

  The operation of the optical information reproducing apparatus configured as described above will be described below. First, the optical pickup 2 includes an objective lens 3, a focus actuator 6, a light beam light source 4 that emits a light beam of a first wavelength, and a light beam light source 5 that emits a light beam of a second wavelength. 3, the light beams emitted from the light beam light sources 4 and 5 having the first and second wavelengths are condensed on the information recording medium 1 and irradiated, and the reflected light is detected. The focus error signal generation means 7 extracts a focus error signal from the reflected light and supplies it to the just focus point vicinity detection means 8 and the focus servo means 9. The just focus point vicinity detection means 8 detects from the focus error signal that the focus of the light beam is in the vicinity of the just focus point, and outputs a just focus point vicinity detection signal to the control unit 16. The focus servo means 9 generates a focus servo signal from the focus error signal and supplies it to the servo changeover switch 13. The first focus search means 10 generates a focus search signal for bringing the objective lens 3 closer to the information recording medium 1, and the second focus search means 11 is a focus for moving the objective lens 3 away from the information recording medium 1. Generate a search signal. The search changeover switch 12 switches the signals of the first and second focus search means 10 and 11 according to a command from the control unit 16 and supplies the signal to the servo changeover switch 13. The first focus pull-in means 14 outputs a focus ON signal according to a control signal output from the control unit 16 when pulling in the focus servo according to the output of the just focus point vicinity detection means during the first focus search. This is sent to the servo switch 13. The second focus pull-in means 15 outputs a focus ON signal according to a control signal output from the control unit 16 when pulling in the focus servo according to the output of the just focus point vicinity detection means during the second focus search. This is sent to the servo switch 13. The servo change-over switch 13 selects either the focus search signal or the focus servo signal in accordance with the focus ON signal and supplies it to the focus actuator 6. The focus actuator 6 responds to the applied drive voltage. Then, the objective lens 3 is driven to move the focal point of the light beam in the optical axis direction.

  In the optical information reproducing apparatus configured as described above, it is assumed that the light beam light source 4 having the first wavelength is a light beam light source having a wavelength of about 650 nm for reproducing a DVD-based information recording medium. Assuming that the light beam light source 5 having a wavelength of 2 is a light beam light source having a wavelength of about 780 nanometers for reproducing a CD type information recording medium, the operation thereof will be described below. When the information recording medium 1 is loaded into the optical information reproducing apparatus, it is unclear whether the information recording medium 1 is a DVD-type disc or a CD-type disc. The light beam light source 4 having the first wavelength is turned on. Instead, the light beam light source 5 of the second wavelength may be turned on here, but the following procedure is different from the case of turning on the light beam light source 4 of the first wavelength first. The first focus search means 10 or the second focus search means 11 generates a focus search signal, which is applied to the focus actuator 6 via the search changeover switch 12 and the servo changeover switch 13 so-called. Perform a focus search. The waveform of the focus error signal obtained at that time is that the wavelength of the light beam light source 4 of the first wavelength used and the type of the information recording medium are used if the mounted information recording medium 1 is a DVD disc. Therefore, an ideal waveform focus error signal as shown in FIG. 2 can be obtained. In this case, the focus servo can be stably activated regardless of the direction of the focus search.

  On the other hand, if the mounted information recording medium 1 is a CD-type disc, the wavelength of the light beam light source and the type of the information recording medium are different from each other, so that the fake signal as shown in FIG. 3 is not ideal. It becomes a focus error signal. The fake signal is a signal generated by a combination that is not supposed to be used to reproduce a CD-type disc at a wavelength for DVD reproduction as the optical pickup 2. In general, there is no guarantee about the waveform of the error signal. However, since this fake signal is generated due to a discrepancy between the wavelength of the light beam and the base material thickness of the information recording medium, the position of the objective lens 3 is determined from the position of the objective lens when the just focus point is detected. Occurs when far from Still, since the mounted information recording medium 1 may be scratched or soiled, the information recording medium 1 mounted from the obtained focus error signal is a DVD disk or a CD disk. It is not possible to completely identify whether the disk is a disk. Therefore, the CD disk is input to the optical information reproducing apparatus even though the light beam light source 4 having the first wavelength, which is a light beam light source having a wavelength of about 650 nanometers, for reproducing the DVD disk is used. Then, the direction of the focus search when performing the focus pull-in operation is the direction in which the fake signal is not output, that is, the direction in which the position of the objective lens 3 is away from the state close to the information recording medium 1 shown in FIG. The focus pull-in is performed only during a focus search.

  The information recording medium 1 mounted on the optical information reproducing apparatus is a CD disc by using a light beam source 4 having a first wavelength which is a light beam source having a wavelength of about 650 nanometers for reproducing a DVD disc. The focus pull-in operation in a certain case will be described with reference to FIG. In FIG. 4, the focal position of the light beam rises and falls in the direction of the optical axis with time according to the focus search operation of the focus actuator 6. The focus error signal detected at that time is as shown in FIG. First, the objective lens 3 is moved away from the information recording medium 1 by using the second focus search means 11, and the focal point of the light beam is moved away from the information surface of the information recording medium 1 from the just focus point. Next, the direction of the focus search is reversed using the first focus search means 10, and the focus of the light beam is driven in a direction approaching the information surface of the information recording medium 1. When the focal point of the light beam approaches the information surface of the information recording medium 1, the just focus point vicinity detection means 8 outputs a just focus point vicinity detection signal. However, since the just focus point vicinity detection signal is output by the fake signal when the mounted information recording medium 1 is a CD disc, the first focus pulling means does not pull the focus. 14 does not work. Furthermore, until the focus search signal changes by a predetermined voltage (ΔV), that is, the objective lens 3 approaches the information recording medium 1 by a predetermined distance corresponding to the predetermined voltage (ΔV), Accordingly, the first focus search is continued until the focus of the light beam moves through the information surface. Thereafter, the search changeover switch 12 is switched to switch the focus search signal from the first focus search means 10 to the second focus search means 11, and the objective lens 3 moves away from the information recording medium 1, and accordingly The focus of the light beam is driven in a direction away from the information recording medium 1. At this time, by operating the second focus pull-in means 15 during the second focus search, the focus ON signal is generated by the control signal output from the control unit 16 according to the output of the just focus point vicinity detecting means. Is sent to the servo change-over switch 13 to pull in the focus servo. As a result, the light beam light source 4 having the first wavelength, which is a light beam light source having a wavelength of about 650 nanometers, for reproducing the DVD disc is used, but the optical information reproducing device is mounted on the optical information reproducing device. Since the information recording medium 1 is a CD disc, even when a fake signal as shown in FIG.

  On the other hand, if the DVD disc is mounted on the optical information reproducing apparatus, an ideal focus error signal without a fake signal as shown in FIG. 2 can be obtained as described above. It can be carried out. As described above, when the light beam light source 4 having the first wavelength is used, the focus error signal obtained during the second focus search indicates that the mounted information recording medium 1 is a CD disc. Even if it is a DVD disc, a fake signal is not generated immediately before the focal point of the light beam approaches the just focus point, so that the focus pull-in is stably performed regardless of the type of the information recording medium 1. be able to.

  The predetermined voltage (ΔV) is set to a voltage corresponding to the distance that the focal position of the light beam passes through the information surface of the information recording medium 1 during the first focus search. That is, the objective lens 3 may be set so as not to collide with the information recording medium 1 during the focus search. In this way, by setting the distance that passes as described above with the value of the voltage corresponding thereto, the objective lens 3 is applied to the information recording medium 1 regardless of the speed of the focus search or even when the speed is changed. The direction of the focus search can be stably reversed without increasing the risk of collision. Next, although the light beam light source 5 having the second wavelength, which is a light beam light source having a wavelength of about 780 nanometers, for reproducing the CD disk is used, the optical information reproducing device mounted on the optical information reproducing apparatus is used. When the information recording medium 1 is a DVD disk, a non-ideal focus error signal with a fake signal superimposed as shown in FIG. In general, the fake signal is not guaranteed in the same manner as described above. Similarly, since the fake signal is generated due to a discrepancy between the wavelength of the light beam and the thickness of the base material of the information recording medium, the position of the objective lens 3 is transferred to the information recording medium from the position of the objective lens corresponding to the just focus point. It will occur at near time. Therefore, the information mounted on the optical information reproducing apparatus is used even though the light beam light source 5 having the second wavelength which is a light beam light source having a wavelength of about 780 nanometers for reproducing the CD disc is used. While there is a possibility that the recording medium 1 is a DVD disk, the direction of the focus search when performing the focus pull-in operation is the direction in which the fake signal is not output, that is, the position of the objective lens 3 shown in FIG. However, the focus pull-in is performed only when a focus search is performed in a direction approaching the information recording medium 1 from a distance.

  The focus pull-in operation will be described with reference to FIG. In FIG. 6, the focal position of the light beam rises and falls in the optical axis direction according to the focus search operation of the focus actuator 6. The focus error signal detected at that time is as shown in FIG. First, the objective lens 3 is moved away from the information recording medium 1 by using the second focus search means 11, and the focal point of the light beam is moved away from the information surface of the information recording medium 1 from the just focus point. Next, the direction of the focus search is reversed using the first focus search means 10, and the focus of the light beam is driven in a direction approaching the information surface of the information recording medium 1. When the focus of the light beam comes close to the information surface of the information recording medium 1, the focus error signal fluctuates, and the just focus point vicinity detection means 8 outputs a just focus point vicinity detection signal. When the light beam light source 5 having the second wavelength, which is a light beam light source having a wavelength of about 780 nanometers, for reproducing a CD disk is used, even if the information recording medium 1 is a DVD disk, the CD disk Even so, the focus error signal obtained during the first focus search does not generate a fake signal immediately before the focus of the light beam approaches the just focus point. If the focus pull-in is performed with the point vicinity detection signal, the focus pull-in can be performed stably.

  As described above, according to the present embodiment, the second focus pull-in is always performed when the focus servo is pulled using the light beam light source having the first wavelength regardless of the type of the information recording medium from which information is to be read. By pulling in the focus servo using the means, the fake signal will not be mistakenly detected as the focus error signal, and the focus pull-in can always be performed stably. Various conventional problems that occur can be solved.

  Regardless of the type of information recording medium on which information is to be read, when the focus servo is pulled using the light beam light source having the second wavelength, the focus servo is always pulled using the first focus pulling means. Thus, the conventional problem can be solved similarly.

  Further, after the type of the mounted information recording medium 1 is clarified, the light beam light source 4 having the first wavelength or the light beam light source 5 having the second wavelength may be selected according to the type. As described above, since a focus error signal without a fake signal can be obtained, the first focus pull-in means is activated during the first focus search to perform the focus pull-in. This can solve the problem that it always takes extra time to start the focus servo.

  Furthermore, according to the present invention, the problem of the conventional technique that the objective lens and the information recording medium collide can be solved.

  In addition, this embodiment is an example for demonstrating this invention to the last, and it cannot be overemphasized that this invention is not limited by this Example. Although the first type of information recording medium is a DVD disk and the second type of information recording medium is a CD disk, the present invention is effective even if the reverse is true. The same applies to the light beam light sources having the first and second wavelengths. Further, the present invention can be applied to other types of information recording media, and can be applied by changing the embodiment according to the characteristics of the optical pickup to be used.

  The just focus point vicinity detection means described above is a means for detecting that the focus of the light beam is in the vicinity of the just focus point in response to a change in the focus error signal, but the focus error signal crosses the reference point. It is also possible to use a focus zero cross detecting means for detecting the fluctuation of Alternatively, the vicinity of the just focus point can be detected by a change in the amount of reflected light output from the optical pickup.

  Further, after the type of the mounted information recording medium 1 is clarified, the light beam light source 4 having the first wavelength or the light beam light source 5 having the first wavelength is selected according to the type. For example, since the focus error signal without the fake signal is obtained as described above, the first focus pull-in means is activated during the first focus search, or the second focus during the second focus search. The focus may be pulled in by using a pull-in means. This method is particularly effective when, for example, the type of the information recording medium 1 is a DVD-type disk and a disk having a plurality of information surfaces, and when the focus servo is selectively drawn into one of the information surfaces. It is. Although the case of an optical disk has been described here as an example, the present invention can be similarly applied to a magneto-optical disk and a transmissive optical information reproducing apparatus.

  As described above, the optical information reproducing apparatus according to the present invention may fail to start the focus servo and damage the information recording medium even if the type of the information recording medium from which information is to be read is unclear. Since the focus can be stably pulled in without damaging the objective lens, various information recording media can be used in addition to the compact disc (CD), digital versatile disc (DVD), and Blu-ray disc (BD). In the future, which will be diversified, the optical information reproducing apparatus is required to have a function of reproducing various information recording media with a single apparatus, which brings a great effect.

1 is a block diagram of an optical information reproducing apparatus according to an embodiment of the present invention. Focus error signal waveform (focus error signal waveform without an ideal fake signal) obtained when the first type of information recording medium is applied with the light beam light source 4 of the first wavelength Focus error signal waveform diagram obtained when the second type of information recording medium is applied by the light beam source 4 of the first wavelength Explanatory drawing of the focus drawing-in method by one Embodiment of this invention Focus error signal waveform diagram obtained when the first type of information recording medium is applied by the light beam source 5 of the second wavelength Explanatory drawing of the focus drawing-in method by one Embodiment of this invention Block diagram of a conventional optical information reproducing device Conventional focus error signal waveform diagram with fake signal Explanatory drawing of conventional focus pull-in method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Information recording medium 2 Optical pick-up 3 Objective lens 4 Light beam light source of 1st wavelength 5 Light beam light source of 2nd wavelength 6 Focus actuator 7 Focus error signal generation means 8 Just focus point vicinity detection means 9 Focus servo means 10 First 1 focus search means 11 second focus search means 12 search changeover switch 13 servo changeover switch 14 first focus pull-in means 15 second focus pull-in means 16 controller 17 light beam light source 18 focus search means 19 servo changeover switch 20 Focus pull-in means 21 Focus zero-cross detection means

Claims (9)

In order to read information from at least the first and second types of information recording media, a first wavelength light beam corresponding to each type of the information recording medium and a wavelength longer than that of the first light beam are used . A light beam light source having a wavelength of at least two of the two light beams, an objective lens for condensing the light beam emitted from each of the light beam light sources and irradiating the information recording medium, and the objective lens for the light An optical pickup having a focus actuator for driving in the direction of the optical axis of the beam;
Focus servo means for controlling the position of the objective lens so that the focal point of the light beam is located at a just focus point that matches the information recording surface of the information recording medium;
First focus search means for bringing the objective lens closer to the information recording medium;
Second focus search means for moving the objective lens away from the information recording medium;
First focus pulling means for switching from the first focus search operation to a focus servo operation during the first focus search;
The second in focus search, and a second focus pull means for switching to a focus servo operation from said second focus search operation,
When pulling in the focus servo using the light beam light source of the first wavelength, the focus servo is pulled in using the second focus pull-in means, and the focus servo is performed using the light beam light source of the second wavelength. An optical information reproducing apparatus , wherein the focus servo is pulled in using the first focus pull-in means when pulling in . When it is clear whether the type of the information recording medium from which information is to be read is the first type or the second type, the light beam light source having the first or second wavelength corresponding to the type of the information recording medium, respectively. 2. The optical information reproducing apparatus according to claim 1, wherein the focus servo is pulled in by using the first or second focus pulling means. The information recording medium of the first type is a so-called DVD (Digital Versatile Disc), and the corresponding light beam source of the first wavelength is a wavelength of about 650 nm for reproducing a so-called DVD (Digital Versatile Disc). The optical information reproducing apparatus according to claim 1, wherein the optical information reproducing apparatus is a light beam light source. The information recording medium of the second type is a so-called CD (compact disc), and the corresponding light beam source of the second wavelength has a wavelength of about 780 nm for reproducing a so-called CD (compact disc). 3. The optical information reproducing apparatus according to claim 1, wherein the optical information reproducing apparatus is a light beam light source. When the first focus search is switched to the second focus search, the focus actuator drive voltage is increased by a predetermined value after detecting that it is in the vicinity of the just focus point during the first focus search. 2. The optical information reproducing apparatus according to claim 1, wherein the objective lens is switched to the second focus search after approaching the information recording medium by a predetermined distance from the vicinity of the just focus point. In order to read information from at least the first and second types of information recording media, at least a first wavelength light beam and a longer wavelength than the first light beam respectively corresponding to the type of the information recording medium A light beam emitted from each of the light beam light sources having at least two types of wavelengths of the second light beam is condensed by an objective lens and irradiated to the information recording medium, and the objective lens is irradiated in the optical axis direction of the light beam. Optical pickup means for driving
Focus servo means for controlling the position of the objective lens so that the focal point of the light beam is located at a just focus point that matches the information recording surface of the information recording medium;
First focus search means for bringing the objective lens closer to the information recording medium;
Second focus search means for moving the objective lens away from the information recording medium;
First focus pulling means for switching from the first focus search operation to a focus servo operation during the first focus search;
The second in focus search, and a second focus pull means for switching to a focus servo operation from said second focus search operation,
When the focus servo is pulled in using the light beam light source of the first wavelength, the focus servo is pulled in using the second focus pull-in means, and the light beam light source of the second wavelength is used. An optical information reproducing method , wherein when the focus servo is pulled in, the focus servo is pulled in using the first focus pull-in means . When the type of information recording medium from which information is to be read is clear, a focus servo is pulled in by the first or second focus on signal using a light beam having a wavelength corresponding to the type of the information recording medium. The optical information reproducing method according to claim 6, wherein: According the first information recording medium is a DVD (digital versatile disc), the first light beam source wavelength, characterized by having a wavelength of about 650 nm for reproducing the DVD Item 7. The optical information reproducing method according to Item 6 . The second information recording medium is a CD (compact disk), the optical beam source of the second wavelength, claims, characterized in that it has a wavelength of about 780 nm for reproducing the CD 7. The optical information reproducing method according to 6 .

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