Abstract:
A recording power determining method comprises writing data consecutively into a plurality of test blocks of an optical disc while changing recording power in such a manner that the arrangement of recording power values is distributed over the arrangement of the test blocks, reproducing the information recorded in the test blocks written into consecutively, determining an asymmetry value for each of the recording power values on the basis of the information in each of the test blocks reproduced, determining an approximation characteristic of the asymmetry value for a recording power on the basis of the asymmetry value for each of the recording power values, and determining a recording power for realizing a specific target value of the asymmetry value from the obtained approximation characteristic.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-212669, filed Jul. 22, 2005, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a recording power determining method of determining the optimum recording power even if an optical disc has a face deflection or an eccentricity and to an optical disc apparatus. 
   2. Description of the Related Art 
   When data is written onto an optical disc, such as CD-R or DVD-R, the optimum recording power is determined by doing test writing before final writing in order to write data with high quality. 
   To determine a recording power, test writing is done onto a test area set on an optical disc while changing the recording power of the laser beam sequentially. The test-written signal is reproduced, thereby measuring the asymmetry value (or signal quality). 
   If the optical disc has a face deflection or an eccentricity, the power of the laser beam applied to the recording tracks on the optical disc changes. Specifically, a drop in the recording power resulting from a focus shift caused by a face deflection or from a track shift due to an eccentricity makes it impossible to record the signal properly, which impairs the reliability of the determined recording power. 
   The technique for determining the recording power through eliminating the effects of a face deflection and an eccentricity has been disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-171768. 
   In the prior art, test recording is done while changing the recording power sequentially around the disc. After the test recording, the test-recorded signal is reproduced, determining the asymmetry value in each recording power. From the measured value, a linear or quadratic approximation characteristic of the asymmetry value in the recording power is determined. From the determined linear or quadratic approximation characteristic, a recording power to realize a specific target of the asymmetry is found. To complete the test recording on just one round of the disc, the approximation characteristic is designed to be free from the face deflection or eccentricity components when the linear or quadratic approximation characteristic is determined from the measured result. Moreover, a light beam with unrecording power to do no recording is irradiated, thereby detecting the periodic fluctuation components of the reflected light beam due to a face deflection or eccentricity of the disc. The light beam with recording power is corrected so as to cancel the components. 
   However, for example, when a case where a position where the effect of a face deflection of the disc is large overlaps with a position where recording is done with the optimum power is compared with a case where a position where the effect of the face deflection is small overlaps with a position where recording is done with the optimum power, there appears a difference between the determined approximation characteristics, which causes the problem of impairing the reliability of test recording. 
   BRIEF SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, there is provided a recording power determining method comprising: writing data consecutively into a plurality of test blocks of an optical disc while changing recording power in such a manner that the arrangement of recording power values is distributed over the arrangement of the test blocks; reproducing the information recorded in the test blocks written into consecutively; determining an asymmetry value for each of the recording power values on the basis of the information in each of the test blocks reproduced; determining an approximation characteristic of the asymmetry value for a recording power on the basis of the asymmetry value for each of the recording power values; and determining a recording power for realizing a specific target value of the asymmetry value from the obtained approximation characteristic. 
   According to another aspect of the present invention, there is provided a recording power determining method comprising: writing data into a plurality of test blocks arranged consecutively on an optical disc while changing a recording power in such a manner that the recording power values at which two test blocks were written into consecutively are caused to differ from one another by two places in the order in which all of the recording power values used in recording are arranged in ascending order; reproducing the information recorded in the test blocks written into consecutively; determining an asymmetry value for each of the recording power values on the basis of the information in each of the test blocks reproduced; determining an approximation characteristic of the asymmetry value for a recording power on the basis of the asymmetry value for each of the recording power values; and determining a recording power for realizing a specific target value of the asymmetry value from the obtained approximation characteristic. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a block diagram schematically showing the configuration of a recording and reproducing apparatus for an optical disc according to an embodiment of the present invention; 
       FIG. 2  is a flowchart to help explain an OPC (Optimum Power Calibration) operation in the embodiment; 
       FIG. 3  is a diagram to help explain the order of recording power values created in step S 103 ; 
       FIG. 4  is a diagram to help explain the order of recording power values created in step S 104  (in the case of a recordable DVD); 
       FIG. 5  is a diagram to help explain the order of recording power values created in step S 104  (in the case of a recordable CD); 
       FIGS. 6A and 6B  are characteristic diagrams of β values with respect to recording power values; 
       FIG. 7  shows the magnitude of defocus and detrack in a recordable DVD; 
       FIG. 8  shows the degree of the effect of a face deflection and eccentricity on the recording power when OPC is started in the order of recording power values shown in  FIG. 4  from a position where the degree of the effect of a face deflection and eccentricity on the recordable DVD is small; 
       FIG. 9  shows the degree of the effect of a face deflection and eccentricity on the recording power when OPC is started in the order of recording power values shown in  FIG. 4  from a position where the degree of the effect of a face deflection and eccentricity on the recordable DVD is large; 
       FIG. 10  shows the magnitude of defocus and detrack in one OPC in a recordable CD; 
       FIG. 11  shows the degree of the effect of a face deflection and eccentricity on the recording power when OPC is started in the order of recording power values shown in  FIG. 5  from a position where the degree of the effect of a face deflection and eccentricity on the recordable CD is small; 
       FIG. 12  shows the degree of the effect of a face deflection and eccentricity on the recording power when OPC is started in the order of recording power values shown in  FIG. 5  from a position where the degree of the effect of a face deflection and eccentricity on the recordable CD is large; 
       FIGS. 13A and 13B  are characteristic diagrams of β values with respect to recording power values when OPC is made in the order of recording power values shown in  FIG. 4  and  FIG. 5 , respectively; 
       FIG. 14  shows an approximation characteristic of β values with respect to recording power values when OPC is made in the order of recording power values shown in  FIG. 4  and  FIG. 5 ; 
       FIG. 15  is a diagram to help explain the result of examining the repeat accuracy of recording power target values obtained from a recording power versus β value approximation characteristic when OPC is made on a recordable DVD in a conventional order and in a new order; 
       FIG. 16  is a diagram to help explain the result of examining the repeat accuracy of recording power target values obtained from a recording power versus β value approximation characteristic when OPC is made on a recordable CD with a face deflection whose linear speed is 1.2 m/s in a conventional order and in a new order; and 
       FIG. 17  is a diagram to help explain the result of examining the repeat accuracy of recording power target values obtained from a recording power versus β value approximation characteristic when OPC is made on a recordable CD with a face deflection whose linear speed is 1.3 m/s in a conventional order and in a new order. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, referring to the accompanying drawings, an embodiment of the present invention will be explained. 
     FIG. 1  is a block diagram schematically showing the configuration of a recording and reproducing apparatus for an optical disc according to an embodiment of the present invention. 
   The laser diode of an optical pickup head (PUH)  101  irradiates a laser beam onto an optical disc  100 . The reflected light from the optical disc  100  is detected by a photodetector of the optical pickup head  101 , which converts the light into an electric signal. The optical pickup head  101  is composed of a laser diode, an optical system including an objective, a focusing actuator, a tracking actuator, a photodetector, and a lens position sensor. 
   The output signal of the optical pickup head  101  is amplified by an RF amplifier  102 . The signal amplified at the RF amplifier  102  is input to a signal detector  103  and a β detector  104 . The signal detector  103  extracts the wobble component from the input signal. The signal detector  103  detects the address of the optical disc  100  on the basis of the extracted wobble component and supplies the detected address to a CPU  105 . The CPU  105  recognizes the recording position in the radial direction of the optical disc  100  from the input address and outputs a control signal corresponding to the recording position to a recording control circuit  106 . The β detector  104  detects the top peak value A and bottom peak value B of the RF signal and detects a β (asymmetry) value on the basis of the detected values. 
   An encoder  107  modulates the information to be written by a modulation scheme conforming to the format of the optical disc  100 . For example, when the optical disc  100  is a recordable CD, such as CD-R or CD-RW, the encoder  107  subjects the information to eight fourteen modulation (EFM modulation) and outputs the modulated signal to the recording control circuit  106 . 
   On the basis of the modulated signal and the control signal from the CPU  105 , the recording control circuit  106  outputs a driving control signal to a servo circuit  109  and a laser driving circuit  108 . The servo circuit  109  not only controls the rotation of a spindle motor  110  but also sets the focusing position and tracking position of the optical pickup head  101  suitably. The laser driving circuit  108  applies current to the laser diode of the optical pickup head  101  on the basis of the driving control signal, causing the laser diode to irradiate a laser beam onto the optical disc  100 . 
     FIG. 2  is a flowchart to help explain an Optimum Power Calibration (OPC) operation in the embodiment. 
   The ID number recorded on the optical disc  100  is read (step ST 101 ). The target β value corresponding to the ID number read in step ST 101  and the recording speed is read from a table in which prepared internal memory (step ST 102 ). The recording speed has been specified by a host computer or a system controller. 
   The start power and step power for OPC according to the recording speed are read. On the basis of the start power and step power, a table describing the order of recording power values as shown in  FIG. 3  is created (step S 103 ). 
   The recording power values are rearranged according to the recording order, thereby creating a new table (step ST 104 ). For example, when the optical disc  100  is a recordable Digital Versatile Disc (DVD), the recording power values are rearranged as shown in  FIG. 4 . Moreover, when the optical disc  100  is a recordable Compact Disc (CD), the recording power values are rearranged as shown in  FIG. 5 . 
   Using the recording power values in the table obtained by rearranging the recording power values in step ST 104 , test recording is done in a Power Control Area (PCA) (step ST 105 ). 
   The signal recorded in the PCA of the optical disc  100  is reproduced and β (asymmetry) values are calculated on a recording power basis (step ST 106 ). 
   Hereinafter, the calculation of β values will be explained. An RF signal corresponding to the reflected light from the optical disc  100  which received light with the optical pickup head  101  is input to the RF amplifier  102 . The RF amplifier  102  amplifies the input RF signal. The amplified RF signal is input to the β detector  104 . The β detector  104  detects the top peak value A and bottom peak value B of the RF signal input on a recording power basis. The β detector  104  calculates a β (asymmetry) value from the detected two peaks. The β value is determined by substituting the top peak value A and bottom peak value B into the following equation:
 
β=( A+B )/( A−B )
 
   The β values determined on a recording power basis are rearranged with respect to the recording power values so as to provide a β value versus recording power characteristic diagram as shown in  FIG. 6A  (step ST 107 ). The obtained β values are subjected to a smoothing process using a weighted average (the center value=½, the preceding and following values=¼), thereby obtaining an approximation characteristic of β values with respect to recording power values as shown in  FIG. 6B  (step ST 108 ). As shown in  FIG. 6B , the intersection of the target β value obtained in step ST 102  and the approximation characteristic obtained in step ST 108  is calculated, thereby determining the optimum recording power (step ST 109 ). The determined optimum recording power is stored in a memory (step ST 110 ). 
   Next, when data is actually written onto the optical disc  100 , the data is written at the optimum recording power stored in the memory. 
   The operation of finding the β value will be explained in detail. 
   In the prior art, the recording power was changed stepwise as shown in  FIG. 3  and the results were recorded. In the embodiment, the order of recording power values is distributed with respect to the order of recording positions as shown in  FIG. 4  in the case of the recordable DVD and as shown in  FIG. 5  in the case of the recordable CD. Since the number of tracks subjected to one power calibration in the recordable DVD differs from that in the recordable CD, the order of recording power values in the recordable DVD differs from that in the recordable CD. Specifically, the order of recording power values in the recordable DVD is determined, taking into account that about one track (equivalent to one round) is used to make a power calibration once. The order of recording power values in the recordable CD is determined, taking into account that about 1.5 to 1.7 rounds are used to make a power calibration once. Since in the case of the recordable CD, the linear speed in recording differs in the range of 1.2 to 1.4 m/s according to the memory capacity, the number of tracks used in power calibration differs. 
   The order of recording power values shown in  FIGS. 4 and 5  is determined, taking the following points into account: 
   1. To prevent similar recording values from being affected by a face deflection or an eccentricity (in other words, to distribute the affected recording power values), recording is not done using similar recording power values in positions fulfilling the symmetry of a circle. 
   2. As for recording power values with which recording is done in positions where the effect of a face deflection or an eccentricity is large, recording is done in positions where the effect of a face deflection or an eccentricity is small using the preceding or succeeding recording power values. 
   In this way, the effect of a face deflection or an eccentricity exerted in smoothing by a weighted average can be cancelled when the optimum recording power is obtained from an asymmetry versus recording power characteristic. 
   To satisfy the above two conditions, for example, the order of recording power values is set so that the recording power values of adjacent blocks may be separated 2 steps or more from each other. 
     FIG. 7  shows the magnitude of defocus (a shift in the focus) and detrack (a shift in the radial direction) in one OPC of a recordable DVD. The solid line represents a case where recording was started from a position where defocus and detrack were small. The broken line represents a case where recording was started from a position where defocus and detrack were large. 
     FIG. 8  shows the degree of the effect of a face deflection and eccentricity with respect to recording power values when OPC is started in the order of recording power values in the embodiment shown in  FIG. 4  from a position where the degree of the effect of a face deflection and eccentricity on the recordable DVD is small. The solid line represents the degree of the effect with respect to recording power values. The broken line represents the result of linear approximation of the solid line. 
   Similarly,  FIG. 9  shows the degree of the effect of a face deflection and eccentricity with respect to recording power values when OPC is started in the order of recording power values shown in  FIG. 4  as in  FIG. 8  from a position where the degree of the effect of a face deflection and eccentricity on the recordable DVD is large. The solid line represents the degree of the effect with respect to recording power values. The broken line represents the result of linear approximation of the solid line. 
   As described above, in a case where recording is done on a disc with a face deflection or an eccentricity, even if the recording start position is where the degree of the effect of a face deflection or an eccentricity is large or small, the effect is cancelled in the calculated approximation characteristic. Therefore, the approximation characteristic does not depend on the recording start position. 
     FIG. 10  shows the magnitude of defocus (a shift in the focus) and detrack (a shift in the radial direction) in one OPC of a recordable CD. The solid line represents a case where recording was started from a position where defocus and detrack were small. The broken line represents a case where recording was started from a position where defocus and detrack were large. In the case of the recordable CD, the number of tracks used in OPC differs according to the linear speed (capacity).  FIG. 10  shows a case where the recoding CD has a linear speed of 1.3 m/s. Since defocus or detrack occurs in either the plus direction or the minus direction, the asymmetry value goes in a direction in which it becomes smaller with respect to recording power values. 
     FIG. 11  shows the degree of the effect of a face deflection and eccentricity with respect to recording power values when OPC is started in the order of recording power values in the embodiment shown in  FIG. 5  from a position where the degree of the effect of a face deflection and eccentricity on the recordable CD is small. In  FIG. 11 , the result for a linear speed of 1.2 m/s, that for a linear speed of 1.3 m/s, and that for a linear speed of 1.4 m/s are shown, taking into account that the linear speed of the recordable CD is not constant. 
   Similarly,  FIG. 12  shows the degree of the effect of a face deflection and eccentricity with respect to recording power values when OPC is started in the order of recording power values shown in  FIG. 5  from a position where the degree of the effect of a face deflection and eccentricity on the recordable CD is large. As in  FIG. 11 , the results for three linear speeds are shown. 
   As in the recordable DVD, in the recordable CD, adjacent recording power values differ from one another in the degree of the effect of a face deflection or an eccentricity. This acts so as to cancel the effect of a face deflection or an eccentricity in the calculated approximation characteristic of the asymmetry value. Moreover, even in a recording start position where the degree of the effect of a face deflection or an eccentricity is large or small, an approximation characteristic unaffected by the degree of the effect can be obtained. 
   In a disc where the β value changes linearly with respect to the recording power, an approximation characteristic of the β value with respect to the recording power is calculated. The results of the calculations are shown in  FIGS. 13A and 13B .  FIGS. 13A and 13B  show approximation characteristics of the β value with respect to the recording power when OPC is made in the order of recording power values shown in  FIGS. 4 and 5  in a case where the test writing start point is in a position where the degree of the effect of a face deflection or an eccentricity is large and in a case where the degree of the effect is small, respectively. The approximation characteristics were calculated using the weighted average or linear approximation. When the asymmetry changes linearly with respect to the recording power, it has been shown that, even if the recording start position shifts 90° because of the effect of a face deflection or an eccentricity, using the weighted average or linear approximation produces a similar effect. 
   Next, in a disc where the β value changes in a curve with respect to the recording power, an approximation characteristic of the β value with respect to the recording power is calculated. The results of the calculations are shown in  FIG. 14 . The approximation characteristic was calculated using the weighted average.  FIG. 14  shows an approximation characteristic of the β value with respect to the recording power when OPC was made in the order of recording power values shown in  FIGS. 4 and 5 . When the β value changes in a curve with respect to the recording power, the measured value is averaged with weight, which makes it possible to eliminate the effect of a face deflection or an eccentricity in the asymmetry curve according to the characteristic of the disc as described above. 
     FIG. 15  shows the result of examining the repeat accuracy of recording power target values obtained from a recording power versus β value approximation characteristic when OPC was made on a recordable DVD with a face deflection (or disc whose outermost edge deflected about 0.5 mm) in a conventional order ( FIG. 3 ) and in a new order ( FIG. 4 ). 
   Table 1 lists the resulting statistics shown in  FIG. 15 . 
   
     
       
             
             
             
           
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Conventional Order 
               New Order 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Standard 
               1.070762 
               0.530306034 
             
             
                 
               Deviation σ 
             
             
                 
               Average 
               99.58 
               99.62 
             
             
                 
               Error 
               1.075278 
               0.532328884 
             
             
                 
                 
             
           
        
       
     
   
   As shown in Table 1, the statistics in the new order shows better values than those in the conventional order. 
     FIG. 16  shows the result of examining the repeat accuracy of recording power target values obtained from a recording power versus β value approximation characteristic when OPC was made on a recordable CD with a face deflection (or disc whose outermost edge deflected about 0.5 mm) and a linear speed of 1.2 m/s in a conventional order ( FIG. 3 ) and in a new order ( FIG. 5 ). 
     FIG. 17  shows the result of examining the repeat accuracy of recording power target values obtained from a recording power versus β value approximation characteristic when OPC was made on a recordable CD with a face deflection (or disc whose outermost edge deflected about 0.5 mm) and a linear speed of 1.3 m/s in a conventional order ( FIG. 3 ) and in a new order ( FIG. 5 ). 
   Table 2 lists the resulting statistics shown in  FIGS. 16 and 17 . 
   
     
       
             
             
           
             
             
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
               TABLE 2 
             
           
           
             
                 
                 
             
             
                 
               Linear speed 
             
           
        
         
             
                 
               1.2 m/s 
               1.3 m/s 
             
           
        
         
             
                 
               Conventional 
               New 
               Conventional 
               New 
             
             
                 
               Order 
               Order 
               Order 
               Order 
             
             
                 
                 
             
           
        
         
             
               Average 
               69.1 
               69.92 
               67.44 
               67.14 
             
             
               Standard 
               0.994885 
               0.60068 
               1.99141 
               0.926041 
             
             
               Deviation σ 
             
             
               Error 
               1.439776 
               0.859096 
               2.952862 
               1.379268 
             
             
                 
             
           
        
       
     
   
   As shown in Table 2, the statistics in the new order show better values than those in the conventional order. 
   The change of the order of recording power values in OPC shows effects to all of the recording optical discs. Specifically, when a recording power versus asymmetry characteristic is considered in obtaining the optimum recording power, recording is done in such a manner that the recording power is changed so as to cancel the effect of a face deflection or an eccentricity of the disc, taking the linear speed in OPC into account (e.g., considering a case where DVD is used and a case where CD is used), which makes it possible to obtain the optimum recording power with high accuracy even if the recording start position changes according to the degree of the effect of a face deflection or an eccentricity. The same holds true for an optical disc using blue laser. 
   This invention is not limited to the above embodiment and may be embodied by modifying the component elements without departing from the spirit or essential character thereof. In addition, various inventions may be formed by combining suitably a plurality of component elements disclosed in the embodiment. For example, some ones may be removed from all of the component elements constituting the embodiment. Furthermore, component elements used in two or more embodiments may be combined suitably. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.