Abstract:
With a high-density optical disc drive, although it is necessary to correct spherical aberrations which depend on a disc substrate thickness error, operation of an aberrations correction element takes time and therefore easy correction according to a disc radius degrades the operability of the apparatus. 
     The present invention comprises an optical pickup unit including an objective lens and an aberrations correction lens, a focus actuator, a tracking actuator, a aberrations correction motor, a seek motor, an aberrations correction lens control module, a radius information detecting module, and a system control module.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an optical disc drive. 
         [0002]    A background art of the present technical field is disclosed, for example, in Japanese Patent Laid-open No. 2005-108334. The above-mentioned patent gazette describes “providing an apparatus which corrects spherical aberrations caused by a difference between discs” as an object and “performing writing or reading by controlling a spherical aberrations control mechanism based on control signal data by radius position stored in a storage means” as a solving means. 
       SUMMARY OF THE INVENTION 
       [0003]    With a high-density optical disc, although numerical aperture is increased as a means for improving the recording density, it becomes impossible to ignore an effect of spherical aberrations caused by a disc cover layer thickness error. The disc cover layer thickness means a layer between a disc surface and an information side or a space layer between information sides of a multilayer disc. Therefore, control of a high-density optical disc is such that spherical aberrations may be reduced according to a disc cover layer thickness error by use of a spherical aberrations correction element. 
         [0004]    A method for correcting such spherical aberrations is disclosed in Patent Reference 1. As shown in Japanese Patent Laid-open No. 2005-108334, a method for changing the amount of spherical aberrations correction according to a disc radius position is effective to ensure optimal read/write performance because the method can reduce spherical aberrations caused by variation in cover layer or space layer thickness in the radial direction of the disc. 
         [0005]    However, the spherical aberrations element generally requires time to change the amount of correction, arising a subject that performing frequent correction operation will take much time, resulting in degradation of the operability of an apparatus. 
         [0006]    Therefore, an object of the present invention is to provide an optical disc drive having excellent operability. 
         [0007]    The above-mentioned object can be accomplished by a configuration described, for example, in Claims. 
         [0008]    In accordance with the present invention, it is possible to provide an optical disc drive having excellent operability. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein: 
           [0010]      FIG. 1  is a diagram showing components of the present embodiment. 
           [0011]      FIG. 2  is a diagram showing an interpolation operation for spherical aberrations correction. 
           [0012]      FIG. 3  is a diagram showing a flow chart of an interpolation operation for spherical aberrations correction. 
           [0013]      FIG. 4  is a diagram showing a change operation for spherical aberrations correction. 
           [0014]      FIGS. 5A and 5B  are diagrams showing a change operation for spherical aberrations correction in read/write operation. 
           [0015]      FIGS. 6A and 6B  are diagrams showing a change operation for spherical aberrations correction in seek operation. 
           [0016]      FIGS. 7A and 7B  are diagrams showing spherical aberrations correction in read/write operation. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]    An embodiment of the present invention will be described below. 
       Embodiment 1 
       [0018]    First, a configuration of an optical disc drive of the present embodiment will be described below with reference to  FIG. 1 . 
         [0019]    Referring to  FIG. 1 , the optical disc drive includes a disc  1 , an objective lens  2 , a focus actuator  3 , a tracking actuator  4 , a spherical aberrations correction lens  5 , and a spherical aberrations correction motor  6 . The focus actuator  3  drives the objective lens  2  in the rotating axis direction of the disc  1 . The tracking actuator  4  drives the objective lens  2  in the radial direction of the disc  1 . The spherical aberrations correction motor  6  drives the spherical aberrations correction lens  5  in the optical axis direction. Further, the optical disc drive includes an optical pickup unit  7 , a seek motor  8 , a detector  9 , a focusing error signal generator  10 , a focus control signal generator  11 , and a focus actuator drive unit  12 . The optical pickup unit  7  includes the objective lens  2  and the spherical aberrations correction lens  5 . The seek motor  8  drives the optical pickup unit  7  in the radial direction of the disc  1 . The focusing error signal generator  10  generates a signal of error in the focus direction between the disc  1  and the objective lens  2 . The focus control signal generator  11  controls the focus actuator  3  so that a focal spot may be positioned on a writing surface or a reading surface of the disc  1 . The focus actuator drive unit  12  drives the focus actuator  3 . Further, the optical disc drive includes a tracking error signal generator  13 , a tracking control signal generator  14 , a tracking actuator drive unit  15 , a seek motor controller  16 , a seek motor drive unit  17 , and a spherical aberrations correction lens controller  18 . The tracking error signal generator  13  generates a signal of error in the tracking direction between the disc track and the objective lens  2 . The tracking control signal generator  14  controls the tracking actuator  3  so that a focal spot may be positioned at a predetermined disc track. The tracking actuator drive unit  15  drives the tracking actuator  3 . The seek motor controller  16  controls the seek motor  8 . The seek motor drive unit  17  drives the seek motor  8 . The spherical aberrations correction lens controller  18  controls the position of the spherical aberrations correction lens  5 . Further, the optical disc drive includes a spherical aberrations correction lens drive unit  19 , a system controller  20 , a radius information detecting unit  21 , a spindle motor  22 , a frequency generator  23 , and a motor controller  24 . The spherical aberrations correction lens drive unit  19  drives the spherical aberrations correction lens  5 . The system controller  20  manages apparatus conditions and operations and gives operational instructions suitable for the apparatus conditions and operations. The radius information detecting unit  21  detects a disc radius position of the focal spot. The spindle motor  22  rotates the disc  1 . The frequency generator  23  generates a signal according to the rotating speed of the spindle motor  22 . The motor controller  24  controls the spindle motor  22  to rotate at a predetermined speed. 
         [0020]    Operation overview of each block and the relationship between blocks will be described below. 
         [0021]    In  FIG. 1 , the focus actuator  3  moves the objective lens  2  in the rotating shaft direction of the disc, and the tracking actuator  4  moves the objective lens  2  in the radial direction of the disc. Further, the seek motor  8  moves the optical pickup unit  7  in the radial direction of the disc, and the spherical aberrations correction motor  6  moves a spherical aberrations correction lens  5  in the optical axis direction. The detector  9  converts reflected light into an electrical signal and then sends the converted signal to the focusing error signal generator  10 , the tracking error signal detecting unit  13 , the spherical aberrations correction lens controller  18 , and the radius information detecting unit  21 . The focusing error signal generator  10  generates a focusing error signal based on the signal sent from the detector  9  and then sends the generated signal to the focus control signal generator  11 . The focus control signal generator  11  generates focus control signals based on the signals sent from the focusing error signal generator  10  and the system controller  20  and then sends the generated signal to the focus actuator drive unit  12 . The focus control signals mean a feedback control signal for performing feedback control based on the focusing error signal, a focus pull-in control signal for performing feedback control pull-in, and a focus jump control signal. The focus actuator drive unit  12  drives the focus actuator  3  based on the signal sent from the focus control signal generator  11 . The tracking error signal generator  13  generates a tracking error signal based on the signal sent from the detector  9  and then sends the generated signal to the tracking control signal generator  14 . The tracking control signal generator  14  generates tracking control signals based on the signals sent from the tracking error signal generator  13  and the system controller  20  and then sends the generated signal to the tracking actuator drive unit  15  and the seek motor controller  16 . The tracking control signals mean a feedback control signal for performing feedback control based on the tracking error signal and a seek-and-tracking-jump control signal. The tracking actuator drive unit  15  drives the tracking actuator  4  based on the signal sent from the tracking control signal generator  14 . The seek motor controller  16  generates a seek motor control signal based on the signals sent from the system controller  20  and the tracking control signal generator  14  and then sends the generated signal to the seek motor drive unit  17 . The seek motor drive unit  17  drives the seek motor  8  based on the signal sent from the seek motor controller  16 . The radius information detecting unit  21  calculates information about the radius position of the disc currently irradiated with a focal spot from a physical address of the disc based on the signal sent from the detector  9 , then sends the calculated information to the spherical aberrations correction lens controller  18 . The spherical aberrations correction lens controller  18  generates a motor control signal for spherical aberrations based on the signals sent from the system controller  20 , the detector  9 , and the radius information detecting unit  21 , and then sends the generated control signal to the spherical aberrations correction lens drive unit  19 . The spherical aberrations correction lens drive unit  19  drives the spherical aberrations correction motor  6  based on the signal sent from the spherical aberrations correction lens controller  18 . The spindle motor  22  drives a disc  1 . The frequency generator  23  converts information about the rotating speed of the spindle motor  22  into an electrical signal and then sends the converted signal to the motor controller  24 . The motor controller  24  controls the disc motor  21  based on the signal sent from the frequency generator  23  so that the disc  1  rotates at a predetermined rotating speed. 
         [0022]    A spherical aberrations correction method will be described below. 
         [0023]    Calculation of a spherical aberrations correction value is performed for each disc insertion during a time interval after the disc is inserted until writing or read operation starts. First, as shown in  FIG. 2 , the spherical aberrations correction lens controller  18  moves the focal spot to an inner circumference of the disc at a radius position r 0 , measures a read signal ( 102  in  FIG. 3 ), and detects the position of the spherical aberrations correction lens  5  at which the read signal is maximized. This position is regarded as an optimal spherical aberrations correction position x 0  of the spherical aberrations correction lens  5  in the inner circumference of the disc ( 103  in  FIG. 3 ). In the same manner, the controller  18  moves the focal spot to an outer circumference of the disc at a radius position r 8  ( 104  in  FIG. 3 ), measures a read signal, and detects the position of the spherical aberrations correction lens  5  at which the read signal is maximized. This position is regarded as an optimal spherical aberrations correction position x 8  of the spherical aberrations correction lens  5  in the outer circumference of the disc ( 105  in  FIG. 3 ). Then, the controller  18  calculates x 2 , x 4  and x 6  in each zone, as shown in  FIG. 2 , by performing linear interpolation of the spherical aberrations correction positions x 0  and x 8  which have previously been detected with respect to change positions for spherical aberrations correction, r 1 , r 3 , r 5 , and r 7 , obtained in advance by splitting the disc into eight in terms of the radius ( 106  in  FIG. 3 ). The change positions r 1 , r 3 , r 5 , and r 7  are physical addresses of the disc: r 1 =PA 1 , r 3 =PA 3 , r 5 =PA 5 , and r 7 =PA 7 , respectively. 
         [0024]    Then, the spherical aberrations correction lens controller  18  minutely changes a change address for spherical aberrations correction according to the moving direction of the focal spot. This is done to prevent the spherical aberrations correction lens from being moved unnecessarily when the focal spot frequently moves within a minute range in verification operation and Walking OPC. Specifically, the change position for spherical aberrations correction is set to either of different values, addresses PA 1   n  and PA 1   p , depending on whether the spot moves from inner to outer circumferences of the disc or vice versa. For example, as shown in  FIG. 4 , when the focal spot is following up a disc track, the spherical aberrations correction position is changed from x 0  to x 1  after it exceeds the change address PA 1   p ; when the focal spot is moving in the inner circumferential direction because of track jump or the like, the spherical aberrations correction position is changed from x 1  to x 0  after it exceeds the change address PA 1   n . The addresses PA 1   p  and PA 1   n  are set so that the difference between them is larger than the capacity to be written and read in one cycle so that the spherical aberrations correction lens does not unnecessarily move at the time of verification. When the capacity and the number of the addresses to be written and read in one cycle change according to a disc radius position, the difference between the above-mentioned change addresses (for example, PA 1   p  and PA 1   n ) also changes according to the radius. 
         [0025]    Write, read, and seek operations, and an operation for changing the spherical aberrations correction position will be described below. When a spot reaches the change position PA 1   p  during writing from inner to outer circumferences, write operation is once stopped as shown in  FIG. 5A , the aberrations correction motor  6  is driven to change the spherical aberrations correction position from x 0  to x 1 . After that write operation is started. This operation can prevent the degradation of the writing quality due to optical axis shift of the spherical aberrations correction lens  5  involved in driving of the aberrations correction motor  6 . 
         [0026]    On the other hand, when the spot reaches the change position PA 1   p  during reading from inner to outer circumferences, the aberrations correction motor  6  is driven to change the spherical aberrations correction position from x 0  to x 1  while continuing read operation as shown in  FIG. 5B . This operation can prevent read operation delay. Retrial read operation for reading the relevant address again may cope with the above-mentioned degradation of read performance due to optical axis shift of the spherical aberrations correction lens  5  involved in driving of the aberrations correction motor  6 . 
         [0027]    As shown in  FIG. 6A , when the spot moves between the above-mentioned zones in seek operation, the spherical aberrations correction lens  5  is changed in position to a spherical aberrations correction position corresponding to a target position during seek operation. For example, (1) in  FIG. 6B  indicates coarse seek in which the seek motor  8  is driven by a predetermined amount to move the optical pickup unit  7 , (2) in  FIG. 6B  indicates close seek in which the optical pickup unit  7  is driven at a constant speed based on the period of the tracking error signal, and (3) in  FIG. 6B  indicates track jump in which acceleration and deceleration voltages are applied to the tracking actuator to move the focal spot to a nearby track. It is preferable that the spherical aberrations correction position be changed using (1) coarse seek together, in order not to be affected by the degradation of the tracking error signal due to optical axis shift of the spherical aberrations correction lens  5  during coarse seek. 
         [0028]    The present embodiment, when the spot reaches a change position during reading, drives the aberrations correction motor  6  to change the spherical aberrations correction position while continuing read operation, but the present invention is not limited. Specifically, it would be possible that the spherical aberrations correction position for a relevant zone is changed when amplitude reduction of the read signal is detected. It would also be possible that the spherical aberrations correction position for a relevant zone is changed if a data read error or address read error occurs. 
         [0029]    The present embodiment calculates information about the radius position of the disc currently irradiated with a focal spot from a physical address of the disc, but the present invention is not limited thereto. Specifically, it would be possible that the radius information detecting unit  21  detects radius information from the moving distance of the seek motor. For example, when the seek motor is a stepping motor, a radius position of the disc can be calculated with the number of drive steps from the reference position with reference to a predetermined inner circumferential position. 
         [0030]    The present embodiment performs spherical aberrations correction according to the radius information of the disc without depending on the writing and reading speeds guaranteed for media, but the present invention is not limited thereto. Specifically, with a writing speed of Vw or a reading speed of Vr at which write performance margin or read performance margin against variation in disc substrate thickness can sufficiently be ensured, it would be possible to use a correction value detected in the inner circumference of the disc without performing spherical aberrations correction according to the radius information of the disc. Therefore, depending on a disc used, when the maximum writing speed is Vw or lower and the maximum reading speed is Vr or lower, detection of an optimal spherical aberrations correction position x 8  at the above-mentioned outer circumferential position r 8  is not performed. 
         [0031]    The present embodiment performs spherical aberrations correction according to the radius information of the disc by use of the same value both for reading and writing, but the present invention is not limited thereto. Specifically, when the write performance margin or read performance margin against variation in disc substrate thickness is different, it would be possible to set a spherical aberrations correction value as shown by solid lines in recording and dotted lines in writing, as shown in  FIG. 7A . In this case, reading for verification is based on the spherical aberrations correction position in writing. Further, as shown in  FIG. 7B , it would be possible to set a spherical aberrations correction position according to operating conditions by detecting and interpolating the spherical aberrations correction position at disc radius positions r 0  and r 8  independently for each of writing and reading. 
         [0032]    As mentioned above, by independently setting a radius position for changing the amount of spherical aberrations correction according to the moving direction of the focal spot and allowing the amount of spherical aberrations correction with respect to the radius position to draw a hysteresis loop, spherical aberrations caused by disc substrate thickness error can be corrected without degrading the operability, thus realizing the reliability of the apparatus. 
         [0033]    While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible to changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications as fall within the ambit of the appended claims.