Patent Publication Number: US-8125864-B2

Title: Information processing device and method, program, and recording/reproducing device

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. JP 2008-092186, filed in the Japanese Patent Office on Mar. 31, 2008, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an information processing device and method, program, and recording/reproducing device, and specifically, relates to an information processing device and method, program, and recording/reproducing device which enable an initial value to be compensated in a more suitable manner with a control system for controlling the operation of an object of control to direct the angle or position thereof toward a target value. 
     2. Description of the Related Art 
     Heretofore, with an optical disc recording/reproducing device, servo control has been performed to condense a laser beam to a fixed position. Specifically, focus servo control for correcting condensed position shift in a disc-vertical direction, and tracking servo control for correcting condensed position shift in a disc-radial direction are performed. A servo controller is realized generally by the following filter for emphasizing low-frequency components, and performing phase shift compensation at a high frequency. Specifically, a filter is employed, which emphasizes the low-frequency components of an error signal to suppress low-frequency position shift, performs compensation of phase shift at a high frequency, thereby operating a control system in a stable manner. 
     This error signal is generated under reflected light from an optical disc, but a detection region whereby a normal error signal can be detected is limited. Therefore, for example, with the focus servo control, a lens mounted on an actuator is driven to a detection region, and confirmation is made whether or not the lens is in the detection region, following which a servo control operation is started. Also, with the tracking servo control, the detection region is relatively swung as to the lens in a stationary state due to disc eccentricity, and accordingly, a servo control operation is started while considering a point in time wherein relative speed is slow. 
     As described above, at a point in time where a servo control operation is started, the relative position and relative speed of the actuator as to a target position are frequently not zero. At this time, the relative position or relative speed is sufficiently small, and the actuator position converges at the target position through transient response. However, if the relative position or relative speed is great (not sufficiently small), the actuator position protrudes from the detection region due to saturation of actuator thrust during transient response, or the like, and consequently, the actuator position does not converge at the target position in some cases. 
     In order to suppress occurrence of such a situation, techniques have been generally employed, such as a servo control operation being started at a position where the relative position is as small as possible, speed servo control being performed before a servo control operation is started to reduce the relative speed, or the like. 
     Also, a technique has been proposed wherein a transient response correction value is charged in a capacitor within an integrator of a servo controller before start of the servo control, and with this as an initial value of the integrator, the servo control is started, thereby reducing transient response (e.g., see Japanese Unexamined Patent Application Publication No. 1-138666). Further, a technique has also been proposed wherein compensation quantity corresponding to the properties of an object of control is obtained, or the initial settings of a servo controller are performed by obtaining a coefficient to compute an initial value, thereby performing a positioning operation in a stable manner (e.g., see U.S. Pat. No. 2,685,622). In this way, techniques have been proposed wherein stable transient response is obtained by setting the initial value of the servo controller to a suitable value to perform initial value compensation. 
     SUMMARY OF THE INVENTION 
     However, though the relative position and relative speed are set based on an error signal, in a case of an optical disc, according to the properties of optical elements, an error signal is not necessarily proportional to the relative position with the entire detection region. Specifically, an error signal is frequently detected to be small as to the relative position around the limit of a detection range. Therefore, in the case of employing an initial value compensation method which employs the value of an error signal as the relative position without being subjected to any correction, compensation of the initial value is performed based on the error signal detected to be smaller than the actual relative position, there has been a possibility that the assumed advantage might not be obtained. In order to suppress occurrence of such a situation, an arrangement can be conceived wherein the detected error signal is corrected to perform compensation of the initial value, but it takes time to calculate correction thereof, and consequently, there is a possibility that compensation of the initial value might not be in time. Also, a new circuit for correction has to be provided, which increases the circuit scale, and accordingly, there is a possibility that development costs, manufacturing costs, operational costs, and so forth might increase. 
     There has been recognized demand to enable compensation of the initial value of a control system for controlling the angle or position of an object of control to direct toward a target value in a more readily suitable manner. 
     According to an embodiment of the present invention, an information processing device includes: a correction coefficient holding unit configured to hold a correction coefficient which is a ratio between the position of an object of control at a start time of control operation, and a detection signal indicating the control result of the object of control, with a control system for controlling the operation of the object of control so as to direct the angle or position thereof toward a target value; an initial value compensation matrix holding unit configured to hold an initial value compensation matrix for performing compensation of the initial value of a control computing unit for computing control output for controlling the object of control from the detection signal based on the position and speed of the object of control; and an initial value generating unit configured to correct the position and speed of the object of control at a start time of control operation with the correction coefficient, and employ the position and speed of the object of control after correction, and the initial value compensation matrix to generate an initial value compensation value for compensating the initial value of the control computing unit. 
     The information processing device may further include a speed generating unit configured to generate from the position of the object of control at a start time of control operation the speed of the object of control at the start time of control operation, with the initial value generating unit employing the speed generated by the speed generating unit to generate the initial value compensation value. 
     The speed generating unit may generate the speed based on the position of the object of control at a start time of control operation, and the position of the object of control one sample ahead from the start time of control operation. 
     The speed generating unit may generate the speed based on the position of the object of control at a start time of control operation, and the position of the object of control a plurality of samples ahead from the start time of control operation. 
     The correction coefficient holding unit may hold a correction coefficient for position for correcting the position of the object of control, and a correction coefficient for speed for correcting the speed of the object of control. 
     According to an embodiment of the present invention, an information processing method includes the steps of: holding a correction coefficient which is a ratio between the position of an object of control at a start time of control operation, and a detection signal indicating the control result of the object of control, with a control system for controlling the operation of the object of control so as to direct the angle or position thereof toward a target value; holding an initial value compensation matrix for performing compensation of the initial value of a control computing unit for computing control output for controlling the object of control from the detection signal based on the position and speed of the object of control; and correcting the position and speed of the object of control at a start time of control operation with the correction coefficient, and employing the position and speed of the object of control after correction, and the initial value compensation matrix to generate an initial value compensation value for compensating the initial value of the control computing unit. 
     According to an embodiment of the present invention, a program, which, in order to process information, causes a computer to function as: a correction coefficient holding unit configured to hold a correction coefficient which is a ratio between the position of an object of control at a start time of control operation, and a detection signal indicating the control result of the object of control, with a control system for controlling the operation of the object of control so as to direct the angle or position thereof toward a target value; an initial value compensation matrix holding unit configured to hold an initial value compensation matrix for performing compensation of the initial value of a control computing unit for computing control output for controlling the object of control from the detection signal based on the position and speed of the object of control; and an initial value generating unit configured to correct the position and speed of the object of control at a start time of control operation with the correction coefficient, and employ the position and speed of the object of control after correction, and the initial value compensation matrix to generate an initial value compensation value for compensating the initial value of the control computing unit. 
     According to an embodiment of the present invention, a recording/reproducing device includes: a recording/reproducing element configured to perform writing or reading of data as to a disc-shaped recording medium; a driving unit configured to drive the recording/reproducing element in the horizontal direction or vertical direction as to a recording face of the disc-shaped recording medium; an error signal detecting unit configured to detect an error signal which is proportional to the difference between a position to be recorded/reproduced by the recording/reproducing element and the actual position; a control computing unit configured to employ a control parameter to perform control calculation as to the detection signal detected by the error signal detecting unit, and calculate control output for reducing the absolute value of the error signal; and an initial value compensation value generating unit configured to generate an initial value compensation value for compensating the initial value of the control computing unit at a start time of control operation with a servo control system including the driving unit, the error signal detecting unit, and the control computing unit, with the initial value compensation value generating unit including a correction coefficient holding unit configured to hold a correction coefficient which is a ratio between the position of the recording/reproducing element at a start time of control operation, and the error signal, an initial value compensation matrix holding unit configured to hold an initial value compensation matrix for performing compensation of the initial value of the control computing unit based on the position and speed of the recording/reproducing element at a start time of control operation, and an initial value generating unit configured to correct the position and speed of the object of control at a start time of control operation with the correction coefficient, employ the position and speed of the object of control after correction, and the initial value compensation matrix to generate the initial value compensation value. 
     With the above embodiment of the present invention, with a control system for controlling the operation of the object of control so as to direct the angle or position thereof toward a target value, a correction coefficient is held, which is a ratio between the position of an object of control at a start time of control operation, and a detection signal indicating the control result of the object of control, an initial value compensation matrix is held, which performs compensation of the initial value of a control computing unit for computing control output for controlling the object of control from the detection signal based on the position and speed of the object of control at a start time of control operation, the position and speed of the object of control at a start time of control operation is corrected with the correction coefficient, and the position and speed of the object of control after correction, and the initial value compensation matrix are employed to generate an initial value compensation value for compensating the initial value of the control computing unit. 
     With the above embodiment of the present invention, there are provided a recording/reproducing element configured to perform writing or reading of data as to a disc-shaped recording medium, a driving unit configured to drive the recording/reproducing element in the horizontal direction or vertical direction as to a recording face of the disc-shaped recording medium, an error signal detecting unit configured to detect an error signal which is proportional to the difference between a position to be recorded/reproduced by the recording/reproducing element and the actual position, a control computing unit configured to employ a control parameter to perform control calculation as to the detection signal detected by the error signal detecting unit, and calculate control output for reducing the absolute value of the error signal, and an initial value compensation value generating unit configured to generate an initial value compensation value for compensating the initial value of the control computing unit at a start time of control operation with a servo control system including the driving unit, the error signal detecting unit, and the control computing unit, wherein a correction coefficient is held, which is a ratio between the position of the recording/reproducing element at a start time of control operation, and the error signal, an initial value compensation matrix is held, which performs compensation of the initial value of the control computing unit based on the position and speed of the recording/reproducing element at a start time of control operation, the position and speed of the object of control at a start time of control operation is corrected with the correction coefficient, and the position and speed of the object of control after correction, and the initial value compensation matrix are employed to generate an initial value compensation value. 
     According to an embodiment of the present invention, an information processing device includes: a corrected initial value compensation matrix holding unit configured to hold a correction coefficient which is a ratio between the position of an object of control at a start time of control operation, and a detection signal indicating the control result of the object of control, and a corrected initial value compensation matrix which is a multiplication result of an initial value compensation matrix for performing compensation of the initial value of a control computing unit for computing control output for controlling the object of control from the detection signal based on the position and speed of the object of control at a start time of control operation, with a control system for controlling the operation of the object of control so as to direct the angle or position thereof toward a target value; and an initial value generating unit configured to employ the position and speed of the object of control at a start time of control operation, and the corrected initial value compensation matrix to generate an initial value compensation value for compensating the initial value of the control computing unit. 
     The information processing device may further include a speed generating unit configured to generate from the position of the object of control at a start time of control operation the speed of the object of control at the start time of control operation, with the initial value generating unit employing the speed generated by the speed generating unit to generate the initial value compensation value. 
     The speed generating unit may generate the speed based on the position of the object of control at a start time of control operation, and the position of the object of control one sample ahead from the start time of control operation. 
     The speed generating unit may generate the speed based on the position of the object of control at a start time of control operation, and the position of the object of control a plurality of samples ahead from the start time of control operation. 
     The corrected initial value compensation matrix holding unit may hold a multiplication result obtained by multiplying the initial value compensation matrix by a correction coefficient for position for correcting the position of the object of control, and a correction coefficient for speed for correcting the speed of the object of control, as the corrected initial value compensation matrix. 
     According to an embodiment of the present invention, an information processing method includes the steps of: holding a correction coefficient which is a ratio between the position of an object of control at a start time of control operation, and a detection signal indicating the control result of the object of control, and a corrected initial value compensation matrix which is a multiplication result of an initial value compensation matrix for performing compensation of the initial value of a control computing unit for computing control output for controlling the object of control from the detection signal based on the position and speed of the object of control at a start time of control operation, with a control system for controlling the operation of the object of control so as to direct the angle or position thereof toward a target value; and employing the position and speed of the object of control at a start time of control operation, and the corrected initial value compensation matrix to generate an initial value compensation value for compensating the initial value of the control computing unit. 
     According to an embodiment of the present invention, a program, which, in order to process information, causes a computer to function as: a corrected initial value compensation matrix holding unit configured to hold a correction coefficient which is a ratio between the position of an object of control at a start time of control operation, and a detection signal indicating the control result of the object of control, and a corrected initial value compensation matrix which is a multiplication result of an initial value compensation matrix for performing compensation of the initial value of a control computing unit for computing control output for controlling the object of control from the detection signal based on the position and speed of the object of control at a start time of control operation, with a control system for controlling the operation of the object of control so as to direct the angle or position thereof toward a target value; and an initial value generating unit configured to employ the position and speed of the object of control at a start time of control operation, and the corrected initial value compensation matrix to generate an initial value compensation value for compensating the initial value of the control computing unit. 
     According to an embodiment of the present invention, a recording/reproducing device includes: a recording/reproducing element configured to perform writing or reading of data as to a disc-shaped recording medium; a driving unit configured to drive the recording/reproducing element in the horizontal direction or vertical direction as to a recording face of the disc-shaped recording medium; an error signal detecting unit configured to detect an error signal which is proportional to the difference between a position to be recorded/reproduced by the recording/reproducing element and the actual position; a control computing unit configured to employ a control parameter to perform control calculation as to the detection signal detected by the error signal detecting unit, and calculate control output for reducing the absolute value of the error signal; and an initial value compensation value generating unit configured to generate an initial value compensation value for compensating the initial value of the control computing unit at a start time of control operation with a servo control system including the driving unit, the error signal detecting unit, and the control computing unit, with the initial value compensation value generating unit including a corrected initial value compensation matrix holding unit configured to hold a correction coefficient which is a ratio between the position of the recording/reproducing element at a start time of control operation, and the error signal, and a corrected initial value compensation matrix which is a multiplication result of an initial value compensation matrix for performing compensation of the initial value of the control computing unit based on the position and speed of the recording/reproducing element at a start time of control operation, and an initial value generating unit configured to employ the position and speed of the object of control at a start time of control operation, and the corrected initial value compensation matrix to generate the initial value compensation value. 
     With the above embodiment of the present invention, with a control system for controlling the operation of the object of control so as to direct the angle or position thereof toward a target value, a correction coefficient which is a ratio between the position of an object of control at a start time of control operation, and a detection signal indicating the control result of the object of control, and a corrected initial value compensation matrix which is a multiplication result of an initial value compensation matrix for performing compensation of the initial value of a control computing unit for computing control output for controlling the object of control from the detection signal based on the position and speed of the object of control at a start time of control operation are held, the position and speed of the object of control at a start time of control operation, and the position and speed of the object of control after correction, and the corrected initial value compensation matrix are employed to generate an initial value compensation value for compensating the initial value of the control computing unit. 
     With the above embodiment of the present invention, there are provided a recording/reproducing element configured to perform writing or reading of data as to a disc-shaped recording medium, a driving unit configured to drive the recording/reproducing element in the horizontal direction or vertical direction as to a recording face of the disc-shaped recording medium, an error signal detecting unit configured to detect an error signal which is proportional to the difference between a position to be recorded/reproduced by the recording/reproducing element and the actual position, a control computing unit configured to employ a control parameter to perform control calculation as to the detection signal detected by the error signal detecting unit, and calculate control output for reducing the absolute value of the error signal, and an initial value compensation value generating unit configured to generate an initial value compensation value for compensating the initial value of the control computing unit at a start time of control operation with a servo control system including the driving unit, the error signal detecting unit, and the control computing unit, wherein a correction coefficient which is a ratio between the position of the recording/reproducing element at a start time of control operation, and the error signal, a corrected initial value compensation matrix which is a multiplication result of an initial value compensation matrix for performing compensation of the initial value of the control computing unit based on the position and speed of the recording/reproducing element at a start time of control operation are held, the position and speed of the object of control at a start time of control operation, and the corrected initial value compensation matrix are employed to generate an initial value compensation value. 
     According to embodiments of the present invention, the control system can be operated in a stable manner. Specifically, compensation of the initial value of the control system for controlling the angle or position of the object of control to direct toward a target value can be performed in a readily suitable manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration example of an optical disc recording/reproducing device according to the related art; 
         FIG. 2  is a diagram describing an example of a push-pull signal; 
         FIG. 3  is an enlarged view of the push-pull signal shown in  FIG. 2 ; 
         FIG. 4  is a diagram describing an example of the situation of tracks formed on an optical disc; 
         FIG. 5  is a diagram illustrating an example of the situation of an error signal and controller output at the time of track jumping; 
         FIG. 6  is a block diagram illustrating another example of a digital control model; 
         FIG. 7  is a diagram representing the control model shown in  FIG. 6  with a status spatial expression; 
         FIG. 8  is a block diagram of a control system including an initial value compensation value generating unit; 
         FIG. 9  is a block diagram illustrating a principal configuration example of an optical disc recording/reproducing device to which an embodiment of the present invention has been applied; 
         FIG. 10  is a block diagram illustrating a detailed example of a configuration relating to pickup position control; 
         FIG. 11  is a flowchart describing an example of the flow of initial value compensation value generating processing; 
         FIG. 12  is a block diagram illustrating another example of a configuration relating to pickup position control; 
         FIG. 13  is a flowchart describing another example of the initial value compensation generating processing; 
         FIG. 14  is a diagram illustrating a relation between a lens position and an error signal with focus servo control; and 
         FIG. 15  is a block diagram illustrating a configuration example of a personal computer to which an embodiment of the present invention has been applied. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The details of the present embodiment will be described below with the tracking servo control with an optical disc recording/reproducing device as an example. First, the tracking servo control thereof will be described. 
       FIG. 1  is a block diagram illustrating a principal configuration example of a tracking servo control system of an optical disc recording/reproducing device according to the related art. An optical disc recording/reproducing device  10  shown in  FIG. 1  is a device which performs reading or writing of data as to an optical disc  21 . The tracking servo control system of this optical disc recording/reproducing device  10  performs the servo control by following a circumferential track formed on the surface of the optical disc  21  which swings due to disc eccentricity or the like, and driving a lens unit  33  of a recording/reproducing element  11  in the horizontal direction with electromagnetic actuators  13 A and  13 B to condense laser on the track. As shown in  FIG. 1 , the optical disc recording/reproducing device  10  includes a recording/reproducing element  11 , control unit  12 , and electromagnetic actuators  13 A and  13 B. 
     The recording/reproducing element  11  to be controlled is an element which performs writing or reading of data as to the optical disc  21  which is a recording medium. The recording/reproducing element  11  includes a laser light source  31 , light separating unit  32 , lens unit  33 , and light receiving unit  34 . The recording/reproducing element  11  performs writing or reading of data by focusing a laser beam on each recording layer. The condensed position of the laser beam output from the recording/reproducing element  11  is controlled by the electromagnetic actuator  13 A or  13 B which is driven in accordance with the control of the control unit  12 . 
     The laser beam emitted from the laser light source  31  is refracted by the light separating unit  32 , and is focused on the recording face of the optical disc  21  by the lens unit  33 . Also, the laser beam thereof is reflected off the optical disc  21 . The reflected light thereof is changed to parallel light by the lens unit  33 , and is guided to the light receiving unit  34 . The light receiving unit  34  receives the return light thereof, and subjects this to photoelectric conversion, and supplies the obtained error signal to the control unit  12 . 
     The control unit  12  includes an error signal detecting circuit  41 , A/D conversion circuit  42 , tracking servo control computing circuit  43 , D/A conversion circuit  44 , and actuator driving circuit  45 . The error signal supplied from the light receiving unit  34  is detected by the error signal detecting circuit  41 , supplied to the A/D conversion circuit  42  as a tracking error signal which is proportional to shift quantity between a laser condensed position and a track center, and subjected to A/D (Analog/Digital) conversion. The digitized tracking error signal (hereafter, also referred to as “digital tracking error signal”) is supplied to the tracking servo control computing circuit  43 . The tracking servo control computing circuit  43  performs predetermined control calculation regarding the digital tracking error signal thereof to generate a control signal which is a digital signal for performing control so as to reduce the tracing error (hereafter, referred to as “digital control signal”). The generated digital control signal is subjected to D/A (Digital/Analog) conversion at the D/A conversion circuit  44 , and supplied to the actuator driving circuit  45  as an analog-converted control signal (hereafter, referred to as “analog control signal”). The actuator driving circuit  45  drives the electromagnetic actuators  13 A and  13 B to perform the position control of the lens unit  33  in the horizontal direction as to the recording face of the optical disc  21  based on the analog control signal thereof. 
     The lens unit  33  is moved in the horizontal direction as to the recording face of the optical disc  21  by the electromagnetic actuators  13 A and  13 B so as to reduce the error signal. The lens unit  33  has lightness in weight, and is capable of high-speed driving, so the optical disc recording/reproducing device  10  can basically have this tracking servo follow the condensed position as to track direction position shift due to disc eccentricity. 
     Description will be made below regarding an example wherein, with the control system such as shown in  FIG. 1 , when a laser beam is reflected on the recording face of the optical disc  21  as an error signal, a push-pull signal is employed, which is obtained from a portion where ± first order and zero order generated from the track provided on the recording face are overlapped, to perform initial value compensation at the time of track jumping. 
     Description will be made first regarding the push-pull signal. The push-pull signal at the time of a spot condensed by the lens unit  33  traversing multiple tracks becomes generally such as shown in  FIG. 2 . A range shown in A 0  in  FIG. 2  is employed as a detection region. At regions A 1  and A −1  adjacent to the detection region the polarity turns to the opposite, and the inclination of the signal is inverted. Further, the outer sides A 2  and A −2  thereof become the detection regions of the adjacent tracks. 
     Upon a spot  52  positioned over the current track  51  moving in the horizontal direction such as shown in both arrows  53 , a push-pull signal  54  becomes a vibration wave such as a sine function as shown in  FIG. 2 .  FIG. 3  enlarges the push-pull signal  54  within the detection region A 0  thereof. When comparing a relative position s between the track  51  and spot  52 , and output p of the push-pull signal  54 , the waveform of the push-pull signal  54  can be regarded as a rough linear curve at the center portions in the detection regions. That is to say, the movement distance of the spot  52  is generally proportional to the value of the push-pull signal output p. On the other hand, the difference between the movement distance of the spot  52  and the push-pull signal output p increases at the regions in the vicinity of the edges of the detection regions. That is to say, it becomes difficult to consider that the movement distance of the spot  52  is proportional to the value of the push-pull signal output p. In general, the push-pull signal p approximates to the sine function of the relative position s such as the following Expression (1). 
     
       
         
           
             
               
                 
                   
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     In a case where the accurate value of the relative position s has to be calculated from the push-pull signal s, for example, back-calculation is performed such as shown in the following Expression (2). 
     
       
         
           
             
               
                 
                   
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     Next, track jumping will be described. With the optical disc  21 , in general, as shown in  FIG. 4 , a track  51  is formed in a spiral shape from the inner circumference to the outer circumference. Accordingly, with a still operation wherein the same track (one round worth of track) is reproduced repeatedly, track jumping has to be performed once per one round, thereby moving the spot  52  to the inner circumference (having the spot  52  perform track jumping).  FIG. 5  is a diagram illustrating an example of a situation of an error signal e and controller output u at the time of track jumping thereof. As shown in  FIG. 5 , with a track jumping period shown in both arrows C, the servo controller does not perform a servo control operation, outputs a jump pulse during a period  61 , and outputs a brake pulse during a period  62 . Thus, the spot  52  is forcibly moved to a track adjacent to the inner circumferential side. At this time, the spot  52  passes through the outside of the detection region, and the error signal e has the opposite inclination, and accordingly, as shown in  FIG. 5 , the waveform of the error signal e becomes a diphasic waveform having peaks upward and downward. Upon the spot  52  moving to the adjacent track, a servo control operation is started again. Starting a servo control operation at the time of the spot  52  reaching the detection region center increases overshoot, so in general, as shown in  FIG. 5 , a servo control operation is frequently started at a position where the error signal e takes a certain degree of great value. That is to say, a servo control operation is started at a region where the difference as to the relative position s is great. 
     As described above, a servo control operation is started for each track jumping at the time of a still operation wherein the same track is reproduced, and in a case where the push-pull signal is employed as an error signal, and a servo control operation is frequently started at a region where the difference as to the relative position s is great. 
     Next, initial value compensation will be described. The digital control system of the optical disc recording/reproducing device  10  such as shown in  FIG. 1  is generally represented with the block diagram shown in  FIG. 6 . In  FIG. 6 , K(z) represents a servo controller, and P(z) represents the operation of an object of control (actuator).  FIG. 7  is a diagram representing each of the controller K(z) and object of control P(z) of this control system by employing status spatial expressions. The overall control system is represented with status spatial expressions, such as shown in the following Expressions (3) and (4). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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                                       cz 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       k 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       X 
                                       pz 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       k 
                                       ) 
                                     
                                   
                                 
                               
                             
                             ] 
                           
                           + 
                           
                             
                               [ 
                               
                                 
                                   
                                     
                                       B 
                                       cz 
                                     
                                   
                                 
                                 
                                   
                                     
                                       
                                         B 
                                         pz 
                                       
                                       · 
                                       
                                         D 
                                         cz 
                                       
                                     
                                   
                                 
                               
                               ] 
                             
                             ⁢ 
                             
                               r 
                               ⁡ 
                               
                                 ( 
                                 k 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         ≡ 
                           
                         ⁢ 
                         
                           
                             
                               A 
                               z 
                             
                             · 
                             
                               
                                 X 
                                 mz 
                               
                               ⁡ 
                               
                                 ( 
                                 k 
                                 ) 
                               
                             
                           
                           + 
                           
                             
                               B 
                               z 
                             
                             · 
                             
                               r 
                               ⁡ 
                               
                                 ( 
                                 k 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         
                           y 
                           ⁡ 
                           
                             ( 
                             k 
                             ) 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             ( 
                             
                               
                                 
                                   0 
                                 
                                 
                                   
                                     C 
                                     
                                       p 
                                       z 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           ⁡ 
                           
                             [ 
                             
                               
                                 
                                   
                                     
                                       X 
                                       cz 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       k 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       X 
                                       pz 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       k 
                                       ) 
                                     
                                   
                                 
                               
                             
                             ] 
                           
                         
                       
                     
                   
                   
                     
                       
                         ≡ 
                           
                         ⁢ 
                         
                           
                             C 
                             z 
                           
                           · 
                           
                             
                               X 
                               mz 
                             
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Initial value vectors representing the initial values of the controller and object of control are represented with the following Expression (5) in which X cz (0) denotes the initial value of the controller, and X pz (0) denotes the initial value of the object of control. That is to say, the initial vectors become the initial value compensation values of this control system. 
     
       
         
           
             
               
                 
                   
                     Initial 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     value 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     vectors 
                   
                   = 
                   
                     [ 
                     
                       
                         
                           
                             
                               X 
                               cz 
                             
                             ⁡ 
                             
                               ( 
                               0 
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             
                               X 
                               pz 
                             
                             ⁡ 
                             
                               ( 
                               0 
                               ) 
                             
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     At this time, a transfer function between an actuator position y of the control system and the initial value vectors is represented with Expression (6). 
     
       
         
           
             
               
                 
                   y 
                   = 
                   
                     
                       C 
                       z 
                     
                     · 
                     
                       
                         ( 
                         
                           zI 
                           - 
                           
                             A 
                             z 
                           
                         
                         ) 
                       
                       
                         - 
                         1 
                       
                     
                     · 
                     z 
                     · 
                     
                       ( 
                       
                         
                           
                             
                               
                                 X 
                                 cz 
                               
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                           
                         
                         
                           
                             
                               
                                 X 
                                 pz 
                               
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     With initial value compensation, the initial value X cz (0) of the controller is given with a function of the initial value X pz (0) of the object of control, such as shown in the following Expression (7).
 
 X   cz (0)=α X   pz (0)   (7)
 
     Thus, the transfer function of Expression (6) can be changed, and accordingly, a desired initial value response can be given to the above-mentioned control system. 
     In general, with the controller of a disc device, as shown in  FIG. 6 , a second order filter made up of a low-frequency emphasis filter and a high-frequency phase advance filter. The above Expression (7) is specifically represented such as the following Expression (8) in which the register value of the low-frequency emphasis filter is x L (k), the register value of the high-frequency phase advance filter is x H (k), and the states of the actuator which is an object of control are a position x(k) and speed v(k). 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             
                               x 
                               L 
                             
                             ⁡ 
                             
                               ( 
                               0 
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             
                               x 
                               H 
                             
                             ⁡ 
                             
                               ( 
                               0 
                               ) 
                             
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               k 
                               11 
                             
                           
                           
                             
                               k 
                               12 
                             
                           
                         
                         
                           
                             
                               k 
                               21 
                             
                           
                           
                             
                               k 
                               22 
                             
                           
                         
                       
                       ) 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             
                               x 
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                           
                         
                         
                           
                             
                               v 
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     As shown in Expression (8), α of Expression (7) can be represented with a matrix, so this α will be referred to as an initial value compensation matrix. 
     Further, {C z ·(ZI−A z ) −1 ·z} within Expression (6) is written specifically such as the following Expression (9). 
     
       
         
           
             
               
                 
                   
                     
                       C 
                       z 
                     
                     · 
                     
                       
                         ( 
                         
                           zI 
                           - 
                           
                             A 
                             z 
                           
                         
                         ) 
                       
                       
                         - 
                         1 
                       
                     
                     · 
                     z 
                   
                   ≡ 
                   
                     
                       1 
                       
                         det 
                         ⁡ 
                         
                           ( 
                           
                             zI 
                             - 
                             
                               A 
                               z 
                             
                           
                           ) 
                         
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             ω 
                             1 
                           
                           ⁡ 
                           
                             ( 
                             z 
                             ) 
                           
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           
                             ω 
                             2 
                           
                           ⁡ 
                           
                             ( 
                             z 
                             ) 
                           
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           
                             ω 
                             3 
                           
                           ⁡ 
                           
                             ( 
                             z 
                             ) 
                           
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           
                             ω 
                             4 
                           
                           ⁡ 
                           
                             ( 
                             z 
                             ) 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     According to the above Expressions (7) through (9), the transfer function can be represented with the following Expression (10). 
     
       
         
           
             
               
                 
                   
                     
                       
                         y 
                         = 
                         
                           
                             1 
                             
                               det 
                               ⁡ 
                               
                                 ( 
                                 
                                   zI 
                                   - 
                                   
                                     A 
                                     z 
                                   
                                 
                                 ) 
                               
                             
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   ω 
                                   1 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   z 
                                   ) 
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   ω 
                                   2 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   z 
                                   ) 
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   ω 
                                   3 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   z 
                                   ) 
                                 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   ω 
                                   4 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   z 
                                   ) 
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   α 
                                 
                               
                               
                                 
                                   1 
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             
                               X 
                               pz 
                             
                             ⁡ 
                             
                               ( 
                               0 
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               ( 
                               
                                 
                                   
                                     
                                       
                                         
                                           
                                             ω 
                                             1 
                                           
                                           ⁡ 
                                           
                                             ( 
                                             z 
                                             ) 
                                           
                                         
                                         ⁢ 
                                         
                                           k 
                                           11 
                                         
                                       
                                       + 
                                       
                                         
                                           
                                             ω 
                                             2 
                                           
                                           ⁡ 
                                           
                                             ( 
                                             z 
                                             ) 
                                           
                                         
                                         ⁢ 
                                         
                                           k 
                                           21 
                                         
                                       
                                       + 
                                       
                                         
                                           ω 
                                           3 
                                         
                                         ⁡ 
                                         
                                           ( 
                                           z 
                                           ) 
                                         
                                       
                                     
                                   
                                 
                                 
                                   
                                     
                                       
                                         
                                           
                                             ω 
                                             1 
                                           
                                           ⁡ 
                                           
                                             ( 
                                             z 
                                             ) 
                                           
                                         
                                         ⁢ 
                                         
                                           k 
                                           12 
                                         
                                       
                                       + 
                                       
                                         
                                           
                                             ω 
                                             2 
                                           
                                           ⁡ 
                                           
                                             ( 
                                             z 
                                             ) 
                                           
                                         
                                         ⁢ 
                                         
                                           k 
                                           22 
                                         
                                       
                                       + 
                                       
                                         
                                           ω 
                                           4 
                                         
                                         ⁡ 
                                         
                                           ( 
                                           z 
                                           ) 
                                         
                                       
                                     
                                   
                                 
                               
                               ) 
                             
                             ⁢ 
                             
                               ( 
                               
                                 
                                   
                                     
                                       x 
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                                 
                                   
                                     
                                       v 
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                               ) 
                             
                           
                           
                             det 
                             ⁡ 
                             
                               ( 
                               
                                 zI 
                                 - 
                                 
                                   A 
                                   z 
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     According to Expression (10), it can be understood that the initial value response y is determined by the root of the denominator expression which is the pole of the control system, and the root of the numerator expression which is equivalent to the zero point of Expression (10). Therefore, the position of the zero point is adjusted by changing the values of the coefficients k 11 , k 12 , k 21 , and k 22  of these expressions, whereby the satisfactory initial value response y can be obtained. 
     In general, the coefficients k 11 , k 12 , k 21 , and k 22  are determined beforehand so as to cancel out a late pole or vibration point with the zero point, a servo control operation is performed with the x L (0) and x H (0) calculated with the above Expression (8) from the actuator position x(0) and actuator speed v(0) when the servo is turned on, as controller initial values. 
     Note that, with the common optical disc recording/reproducing device  10 , a digitized error signal e(k) between the object position and the actuator position is detected, but it is difficult to detect the actuator position x(k) and actuator speed v(k). 
     Therefore, let us say that the digitized error signal e(k) which corresponds to the relative position between the object position and the actuator position is employed instead of the actuator position x(k). Also, digitized relative speed e v (k) between the object position and the actuator position is represented with such as Expression (11) with sampling time as T. 
     
       
         
           
             
               
                 
                   
                     
                       e 
                       v 
                     
                     ⁡ 
                     
                       ( 
                       k 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         e 
                         ⁡ 
                         
                           ( 
                           k 
                           ) 
                         
                       
                       - 
                       
                         e 
                         ⁡ 
                         
                           ( 
                           
                             k 
                             - 
                             1 
                           
                           ) 
                         
                       
                     
                     T 
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     In the event of employing this digitized relative speed e v (k) between the object position and the actuator position instead of the actuator speed v(k), the above Expression (8) can be represented with such as the following Expression (12). An initial value compensation value can be calculated from the digitized error signal e(k) between the object position and actuator position by employing Expression (12). 
     
       
         
           
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             
                               x 
                               L 
                             
                             ⁡ 
                             
                               ( 
                               0 
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             
                               x 
                               H 
                             
                             ⁡ 
                             
                               ( 
                               0 
                               ) 
                             
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               k 
                               11 
                             
                           
                           
                             
                               k 
                               12 
                             
                           
                         
                         
                           
                             
                               k 
                               21 
                             
                           
                           
                             
                               k 
                               22 
                             
                           
                         
                       
                       ) 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             
                               e 
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                           
                         
                         
                           
                             
                               
                                 e 
                                 v 
                               
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
       FIG. 8  is a block diagram of the control system including an initial value compensation value generating unit for realizing such initial value compensation. Specifically, the control system shown in  FIG. 8  is a control system obtained by adding an initial value compensation value generating unit  91  to the control system shown in  FIG. 6 . The operation of this control system will be described here. The digitized error signal e(k) is input to the initial value compensation value generating unit  91 , there digitized relative speed e v (k) is generated in accordance with Expression (11). An initial value compensation value is calculated in accordance with Expression (12) to set this in the controller K(z) wherein the value of the digitized error signal is e(0), and the value of the digitized relative speed is e v (0), when a servo control start request is received. Simultaneously, a switch connected to the controller output is turned on in accordance with the servo control start request, and a servo control operation is started with the calculated initial value compensation value as a controller initial value. 
     In a case where such initial value compensation is performed at the time of start of the servo control after track jumping, a servo control operation is frequently started at a position where the error signal e takes a certain degree of a great value as described above. As shown in the graph in  FIG. 3 , if the push-pull signal p employed as the error signal e takes a certain degree of great value, the error with the relative position s increases in some cases. In the event of a servo control operation being started in such a region, the relative position and relative speed of the spot detected by the push-pull signal p as to the object position decrease as compared to the actual position and speed, and accordingly, the advantage of initial value compensation is not sufficiently obtained in some cases. 
     In order to suppress occurrence of such a situation, an arrangement can be conceived wherein the obtained push-pull signal value p is subjected to correction of the above Expression (2) within a one sampling period. However, the load of calculating the inverse trigonometric function of Expression (2) is great, and accordingly, it is difficult to perform this calculation within one sampling period. Also, there are possibilities such as increase in a circuit scale, and increase in development costs and manufacturing costs. 
     Therefore, with the present invention, an arrangement is made wherein the ratio K p  between the relative position s and push-pull signal p at a position where a servo control operation is started is calculated beforehand, and this correction coefficient K p  is employed to correct the digitized error signal e(0) and digitized relative speed ev(0) in a simple manner. Thus, the simply corrected initial value compensation value is calculated, and an advantage more similar to assumption can be obtained. 
     This arrangement will be described below in detail.  FIG. 9  is a block diagram illustrating a principal configuration example of the optical disc recording/reproducing device to which an embodiment of the present invention has been made. The optical disc recording/reproducing device  100  shown in  FIG. 9  is a device which performs reading and writing of information as to an optical disc  107  mounted on a predetermined position. The optical disc recording/reproducing device  100  includes a system controller  101 , spindle motor driving circuit  102 , spindle motor  103 , servo control unit  104 , data processor  105 , and optical head unit  106 . 
     The system controller  101  is a control unit which controls the operation of each unit within the optical disc recording/reproducing device  100 . A CPU (Central Processing Unit)  111  of the system controller  101  executes various types of processing in accordance with a program stored in ROM (Read Only Memory)  112  or program loaded into RAM (Random Access Memory)  113 . The RAM  113  also stores data for the CPU  111  executing various types of processing, and so forth as appropriate. 
     The spindle motor driving circuit  102 , which is controlled by the system controller  101 , controls the rotation of the spindle motor  103  for rotating the optical disc  107 . The servo control unit  104 , which is controlled by the system controller  101 , controls the condensed position of an optical pickup (optical head unit  106 ). The data processor  105 , which is controlled by the system controller  101 , performs information processing with information read out by the optical disc  107 , or information written in the optical disc  107  as an object of processing. The optical head unit  106 , which is controlled by the system controller  101 , irradiates a laser beam to the optical disc  107  to read out or write information. 
       FIG. 10  is a block diagram illustrating a detailed example of the configuration relating to the position control of the pickup, of the various configurations of the optical disc recording/reproducing device  100  shown in  FIG. 9 . As shown in  FIG. 10 , the optical disc recording/reproducing device  100  includes a recording/reproducing element  121 , control unit  122 , electromagnetic actuators  123 A and  123 B, and initial value compensation value generating unit  124 . 
     The recording/reproducing element  121  is an element which performs writing or reading of data as to the optical disc  107  which is a recording medium. The recording/reproducing element  121  performs writing or reading of data by focusing a laser beam on each recording layer of the optical disc  107  to be subjected to rotation operations. Therefore, the control unit  122  employs the electromagnetic actuators  123 A and  123 B to control the condensed position of the laser beam output from the recording/reproducing element  121  in the horizontal direction as to the recording face of the optical disc  107 . 
     The recording/reproducing element  121  performs reading or writing of data by irradiating a laser beam to the optical disc  107 , and generates an error signal to supply this to the control unit  122  by detecting the return light reflected off the recording face of the optical disc  107 . The control unit  122  controls the electromagnetic actuators  123 A and  123 B based on the error signal thereof. 
     The recording/reproducing element  121  includes a laser light source  131 , light separating unit  132 , lens unit  133 , and light receiving unit  134 . The laser light source  131  emits a laser beam having a predetermined wavelength toward the light separating unit  132 . The light separating unit  132  refracts the laser beam emitted from the laser light source  131  to guide this to the optical disc  107  side (lens unit  133 ), and also transmits the laser beam reflected off the optical disc  107  to guide this to the light receiving unit  134 . The lens unit  133  condenses the laser beam from the light separating unit  132  to focus this on each recording layer of the optical disc  107 , and also changes the return light from the optical disc  107  to parallel light to supply this to the light separating unit  132 . The light receiving unit  134  is made up of a photoelectric conversion element employing, for example, a CMOS (Complementary Metal Oxide Semiconductor) sensor, CCD (Charge Coupled Device), or the like. The light receiving unit  134  receives the return light from the optical disc  107  supplied through the light separating unit  132  to subject this to photoelectric conversion, and supplies the obtained error signal to the control unit  122 . 
     Note that  FIG. 10  illustrates the single laser light source  131 , single light separating unit  132 , single lens unit  133 , and single light receiving unit  134  respectively, but the number of each unit may be two or more. Also, the position relation of each unit shown in  FIG. 10  is an example, and accordingly, each unit may be disposed in any way. It goes without saying that the shape and size of each unit are arbitrary. 
     The control unit  122  includes an error signal detecting circuit  141 , A/D conversion circuit  142 , tracking servo control computing circuit  143 , D/A conversion circuit  144 , and actuator driving circuit  145 . The error signal detecting circuit  141  detects the error signal generated at the light receiving unit  134 , thereby generating a tracking error signal to supply this to the A/D conversion circuit  142 . The A/D conversion circuit  142  subjects the tracking error signal generated at the error signal detecting circuit  141  to A/D conversion, and supplies the digitized tracking error signal (hereafter, also referred to as “digital tracking error signal”) to the tracking servo control computing circuit  143 . 
     The tracking servo control computing circuit  143  performs predetermined control computation regarding the digital tracking error signal supplied from the A/D conversion circuit  142  to generate a control signal which is a digital signal (hereafter, referred to as “digital control signal”) for performing control so as to reduce a tracking error. The tracing servo control computing circuit  143  employs the initial value compensation value supplied from the initial value compensation value generating unit  124  to perform this control computation to generate a digital control signal, and supplies this to the D/A conversion circuit  144 . The D/A conversion circuit  144  subjects the digital control signal supplied from the tracking servo control computing circuit  143  to D/A conversion to supply the analog-converted control signal (hereafter, referred to as “analog control signal”) to the actuator driving circuit  145 . The actuator driving circuit  145  drives the electromagnetic actuators  123 A and  123 B based on the analog signal supplied from the D/A conversion circuit  144 . 
     The electromagnetic actuators  123 A and  123 B control the position in the horizontal direction as to the recording face of the optical disc  107 , of the recording/reproducing device  121 , in accordance with the control signal supplied from the control unit  122 . Hereafter, in a case where description does not have to be made distinguishing the electromagnetic actuators  123 A and  123 B one from another, these are collectively referred to as “actuator  123 ”. 
     The initial value compensation value generating unit  124  is a processing unit for generating an initial value compensation value to be provided to the tracking servo control computing circuit  143 . The initial value compensation value generating unit  124  includes an initial value generating unit  151 , relative speed generating unit  152 , correction coefficient holding unit  153 , and initial value compensation matrix holding unit  154 . 
     The initial value generating unit  151  calculates an initial value compensation value within one sampling period based on the digitized error signal e(0) at the time of a servo control start request being received, which is supplied from the tracking servo control computing circuit  143 , the digitized relative speed e v (0) at the time of a servo control start request being received, which is supplied from the relative speed generating unit  152 , and the correction coefficient K p  supplied from the correction coefficient holding unit  153 , and the initial value compensation matrix α supplied from the initial value compensation matrix holding unit  154 , and supplies this to the tracking servo control computing circuit  143 . 
     The relative speed generating unit  152  calculates a digitized relative speed e v (0) at the time of a servo control start request being received, which is supplied from the tracking servo control computing circuit  143 , and supplies this to the initial value generating unit  151 . 
     The correction coefficient holding unit  153  holds the ratio K p  between the relative position s and push-pull signal p at a position where a servo control operation is started, which is calculated beforehand, and supplies the ratio K p  thereof to the initial value generating unit  151  based on a request from the initial value generating unit  151 . The initial value compensation matrix holding unit  154  holds the initial value compensation matrix α, and supplies the initial value compensation matrix α thereof to the initial value generating unit  151  based on a request from the initial value generating unit  151 . 
     This operation will be described in detail. Let us say that a servo control operation start signal level p s  is the magnitude of the error signal when a servo control operation is started at the time of track jumping. The actual track jumping waveform varies depending on a subtle conditional difference at each time, so the actual servo control operation start signal level p(0) becomes a different value at each time, but let us say that a servo control operation start signal level e s  here is a representative value based on the actual measured value such as the mean value of the actual servo control operation start signal level p(0), or a representative value to be derived logically. According to Expression (2), the original relative position s s  corresponding to this servo control operation start signal level p s  can be obtained such as shown in the following Expression (13). 
     
       
         
           
             
               
                 
                   
                     
                       s 
                       s 
                     
                     = 
                     
                       
                         p 
                         max 
                       
                       ⁢ 
                       
                         
                           sin 
                           
                             - 
                             1 
                           
                         
                         ( 
                         
                           
                             p 
                             s 
                           
                           
                             p 
                             max 
                           
                         
                         ) 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         - 
                         
                           p 
                           max 
                         
                       
                       &lt; 
                       
                         p 
                         s 
                       
                       &lt; 
                       
                         p 
                         max 
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     Now, let us say that the ratio between the s s  and p s  is K p  such as shown in the following Expression (14). 
     
       
         
           
             
               
                 
                   
                     K 
                     p 
                   
                   = 
                   
                     
                       
                         s 
                         s 
                       
                       
                         p 
                         s 
                       
                     
                     = 
                     
                       
                         
                           p 
                           max 
                         
                         ⁢ 
                         
                           
                             sin 
                             
                               - 
                               1 
                             
                           
                           ( 
                           
                             
                               p 
                               s 
                             
                             
                               p 
                               max 
                             
                           
                           ) 
                         
                       
                       
                         p 
                         s 
                       
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
     At this time, the push-pull signal can be corrected in the vicinity of p s  approximately such as shown in Expression (15).
 
 s ( k )= K   p   p ( k )   (15)
 
     Originally, it is desirable to set e(0)=S(0) at the time of calculating an initial value compensation value based on Expression (12), but actually, there is no method for measuring the relative position s itself, so the push-pull signal p is employed to set e(0)=P(0). In order to suppress the error between the relative position s(0) and push-pull signal p(0), it is logically desirable to employ the above Expression (2) to perform correction, but actually, this method is difficult from a point of view of a circuit scale or computation time as described above. 
     Therefore, the initial value generating unit  151  employs Expression (15) which is an approximation to suppress the error by setting e(0)=K p p(0). Similarly, by employing Expression (15), the relative speed e v (0) can be represented such as shown in the following Expression (16). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             e 
                             v 
                           
                           ⁡ 
                           
                             ( 
                             0 
                             ) 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             
                               s 
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                             - 
                             
                               s 
                               ⁡ 
                               
                                 ( 
                                 
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                           
                           T 
                         
                       
                     
                   
                   
                     
                       
                         ≈ 
                           
                         ⁢ 
                         
                           
                             
                               
                                 K 
                                 p 
                               
                               ⁢ 
                               
                                 p 
                                 ⁡ 
                                 
                                   ( 
                                   0 
                                   ) 
                                 
                               
                             
                             - 
                             
                               
                                 K 
                                 p 
                               
                               ⁢ 
                               
                                 p 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                           
                           T 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               K 
                               p 
                             
                             ⁢ 
                             
                               
                                 
                                   p 
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                                 - 
                                 
                                   p 
                                   ⁡ 
                                   
                                     ( 
                                     
                                       - 
                                       1 
                                     
                                     ) 
                                   
                                 
                               
                               T 
                             
                           
                           = 
                           
                             
                               K 
                               p 
                             
                             ⁢ 
                             
                               
                                 p 
                                 v 
                               
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
         
       
     
     This Expression (16) is applied to the above Expression (12), whereby an initial value compensation value can be represented such as the following Expression (17). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           ( 
                           
                             
                               
                                 
                                   
                                     x 
                                     L 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     x 
                                     H 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                               
                             
                           
                           ) 
                         
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     k 
                                     11 
                                   
                                 
                                 
                                   
                                     k 
                                     12 
                                   
                                 
                               
                               
                                 
                                   
                                     k 
                                     21 
                                   
                                 
                                 
                                   
                                     k 
                                     22 
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   
                                     e 
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       e 
                                       v 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     k 
                                     11 
                                   
                                 
                                 
                                   
                                     k 
                                     12 
                                   
                                 
                               
                               
                                 
                                   
                                     k 
                                     21 
                                   
                                 
                                 
                                   
                                     k 
                                     22 
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   
                                     
                                       K 
                                       p 
                                     
                                     ⁢ 
                                     
                                       p 
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       K 
                                       p 
                                     
                                     ⁢ 
                                     
                                       
                                         p 
                                         v 
                                       
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
           
         
       
     
     That is to say, as shown in Expression (17), the initial value generating unit  151  corrects the push-pull signal p(0) when a servo control start request is received, the relative speed p v (0) calculated from the push-pull signal p(0) at the relative speed generating unit  152  with the correction coefficient K p  obtained from the correction coefficient holding unit  153  to calculate the digitized error signal e(0) and digitized relative speed e v (0). Subsequently, as shown in Expression (17), the initial value generating unit  151  employs the initial value compensation matrix α obtained from the initial value compensation matrix holding unit  154  to calculate an initial value compensation value (initial value vector) from the calculated digitized error signal e(0) and digitized relative speed e v (0). 
     The initial value generating unit  151  supplies the initial value compensation value thus calculated to the tracking servo control computing circuit  143 . 
     An example of the flow of initial value compensation value generating processing having the above-mentioned content will be described with reference to the flowchart shown in  FIG. 11 . Upon receiving a servo control start request, the initial value compensation value generating unit  124  starts the initial value compensation value generating processing. 
     Upon the initial value compensation value generating processing being started, in step S 1  the initial value generating unit  151  and relative speed generating unit  152  obtain the push-pull signal p(0) and p(−1) from the tracking servo control computing circuit  143 . The p(0) is the value of the push-pull signal when a servo control start request is supplied, and the p(−1) is the value of the push-pull signal one sampling ahead thereof. 
     Description will be made here assuming that the tracking servo control computing circuit  143  holds the value of the past push-pull signal, the push-pull signals p(0) and p(−1) are supplied to the initial value generating unit  151  and relative speed generating unit  152  at timing wherein a servo control start request is supplied. It goes without saying that the tracking servo control computing circuit  143  may supply the push-pull signal p(k) to the initial value generating unit  151  and relative speed generating unit  152  for each sampling regardless of whether or not a servo control start request is supplied. In this case, the initial value generating unit  151  and relative speed generating unit  152  hold at least the push-signal one sampling ahead. 
     In step S 2 , the relative speed generating unit  152  employs the push-pull signals p(0) and p(−1) to calculate the relative speed p v (0) at the timing wherein a servo control start request is supplied in accordance with the above Expression (16). 
     In step S 3 , the initial value generating unit  151  reads out the correction coefficient K p  from the correction coefficient holding unit  153 , and in step S 4  corrects the push-pull signal p(0) and relative speed p v (0) with the correction coefficient K p  thereof in accordance with the above Expression (16). 
     Also, in step S 5 , the initial value generating unit  151  reads out the initial value compensation matrix α from the initial value compensation matrix holding unit  154 , and in step S 6  calculates an initial value compensation value from the initial value compensation matrix α, and the push-pull signal p(0) and relative speed p v (0) which have been corrected by the processing in step S 4 , in accordance with the above Expression (16) in step S 6 . 
     In step S 7 , the initial value generating unit  151  supplies the initial value compensation value calculated by the processing in step S 6  to the tracking servo control computing circuit  143 , and in step S 8  causes the tracking servo control computing circuit  143  to start the servo control. Upon completing the processing in step S 8 , the initial value generating unit  151  ends the initial value compensation generating processing. 
     An initial value compensation value is obtained in such a way, whereby the initial value generating unit  151  can suppress influence due to the error even in a case where the push-pull signal initial value p(0) is relatively great, and the error as to the original relative position s(0) is great, and accordingly, a sufficient advantage of initial value compensation can be obtained with the control system. That is to say, the initial value generating unit  151  can readily calculate a more appropriate initial value compensation value, and provide this to the control system. In other words, the initial value compensation generating unit  124  can readily perform the initial value compensation of the control system in a more appropriate manner. 
     Note that description has been made so far wherein the initial value compensation value generating unit  124  calculates and holds the correction coefficient K p  and initial value compensation matrix α beforehand, and at the time of a servo control start request, the initial value generating unit  151  employs the correction coefficient K p  and initial value compensation matrix α thereof to generate an initial value compensation value, but the present invention is not restricted to this, for example, an arrangement may be made wherein the initial value compensation matrix α is corrected with the correction coefficient K p  beforehand, and at the time of a servo control start request, an initial value compensation value is generated by the corrected initial value compensation matrix α 1 . 
     The above Expression (17) can be transformed such as shown in the following Expression (18). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           ( 
                           
                             
                               
                                 
                                   
                                     x 
                                     L 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     x 
                                     H 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                               
                             
                           
                           ) 
                         
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     k 
                                     11 
                                   
                                 
                                 
                                   
                                     k 
                                     12 
                                   
                                 
                               
                               
                                 
                                   
                                     k 
                                     21 
                                   
                                 
                                 
                                   
                                     k 
                                     22 
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   
                                     
                                       K 
                                       p 
                                     
                                     ⁢ 
                                     
                                       p 
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       K 
                                       p 
                                     
                                     ⁢ 
                                     
                                       
                                         p 
                                         v 
                                       
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     
                                       k 
                                       11 
                                     
                                     · 
                                     
                                       K 
                                       p 
                                     
                                   
                                 
                                 
                                   
                                     
                                       k 
                                       12 
                                     
                                     · 
                                     
                                       K 
                                       p 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       k 
                                       21 
                                     
                                     · 
                                     
                                       K 
                                       p 
                                     
                                   
                                 
                                 
                                   
                                     
                                       k 
                                       22 
                                     
                                     · 
                                     
                                       K 
                                       p 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   
                                     p 
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       p 
                                       v 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             α 
                             1 
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 
                                   
                                     p 
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       p 
                                       v 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
           
         
       
     
     In Expression (17), the correction coefficient K p  is multiplied by the initial value compensation matrix α. Specifically, the initial value compensation matrix α is corrected with the correction coefficient K p , and the corrected initial value compensation matrix α 1  is calculated. As shown in Expression (17), the initial value generating unit  151  can readily calculate an initial value compensation value from the push-pull signal p(0) and relative speed p v (0) by employing such corrected initial value compensation matrix α 1 . That is to say, the initial value generating unit  151  can reduce computation processing the load of computing an initial value compensation value at the time of a servo control start request. 
       FIG. 12  is a block diagram illustrating a detailed example of the configuration relating to the position control of the pickup, of the relative configurations of the optical disc recording/reproducing device  100  shown in  FIG. 9  in this case. That is to say,  FIG. 12  is a diagram corresponding to  FIG. 10 . As shown in  FIG. 12 , the configuration of the control system in this case is basically the same in the case of  FIG. 10 , but includes an initial value compensation value generating unit  224  instead of the initial value compensation value generating unit  124  shown in  FIG. 10 . 
     The initial value compensation value generating unit  224  has basically the same configuration as the initial value compensation value generating unit  124  shown in  FIG. 10 , but includes a corrected initial value compensation matrix holding unit  254  instead of the correction coefficient holding unit  153  and initial value compensation matrix holding unit  154  shown in  FIG. 10 . 
     The corrected initial value compensation matrix holding unit  254  holds the corrected initial value compensation matrix α 1  which has been calculated beforehand. The corrected initial value compensation matrix α 1  is, as shown in the above Expression (18), obtained by multiplying the initial value compensation matrix α and correction coefficient K p . 
     The initial value generating unit  151  can readily calculate an initial value compensation value from the push-pull signal p(0) and relative speed p v (0) at the time of a servo control start request by employing the corrected initial value compensation matrix α 1 . 
     An example of the flow of the initial value compensation value generating processing in this case will be described with reference to the flowchart shown in  FIG. 13 . In this case as well, each piece of processing is performed basically in the same way as in the case described with reference to the flowchart shown in  FIG. 11 . 
     Specifically, in step S 21  the initial value generating unit  151  and relative speed generating unit  152  obtains the push-pull signals p(0) and p(−1) in the same way as in the case in step S 1  in  FIG. 11 . In step S 22 , the relative speed generating unit  152  calculates the push-pull signals p(0) and p(−1), and relative speed p v (0) in the same way as in the case in step S 2  in  FIG. 11 . 
     Unlike the case of steps S 3  through S 6  in  FIG. 11 , in step S 23  the initial value generating unit  151  reads out the corrected initial value compensation matrix α 1  from the corrected initial value compensation matrix holding unit  254 , and in step S 24  employs the corrected initial value compensation matrix α 1  thereof to calculate an initial value compensation value in accordance with the above Expression (18). 
     In the same way as in the case of steps S 7  and S 8  in  FIG. 11 , in step S 25  the initial value generating unit  151  supplies the initial value compensation value calculated by the processing in step S 24  to the tracking servo control computing circuit  143 , and in step S 26  causes the tracking servo control computing circuit  143  to start the servo control. Upon completing the processing in step S 26 , the initial value generating unit  151  ends the initial value compensation value generating processing. 
     An initial value compensation value is obtained in such a way, whereby the initial value generating unit  151  can readily calculate an initial value compensation value to provide this to the control system, as compared to the case in  FIG. 10 . In other words, the initial value compensation value generating unit  224  can further readily perform the initial value compensation of the control system, as compared to the case of the initial value compensation value generating unit  124 . 
     Note that the relative speed e v (0) may be calculated such as shown in the following Expression (19) by taking a difference between the current sample and the sample n samples ahead to reduce noise influence. 
     
       
         
           
             
               
                 
                   
                     
                       e 
                       v 
                     
                     ⁡ 
                     
                       ( 
                       0 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         s 
                         ⁡ 
                         
                           ( 
                           0 
                           ) 
                         
                       
                       - 
                       
                         s 
                         ⁡ 
                         
                           ( 
                           
                             - 
                             n 
                           
                           ) 
                         
                       
                     
                     nT 
                   
                 
               
               
                 
                   ( 
                   19 
                   ) 
                 
               
             
           
         
       
     
     At this time, tentatively, if Expression (15) might hold for the value n samples ahead as well, the initial value compensation value can be calculated in the same way as described above in accordance with Expression (17). 
     On the other hand, in a case where the relative position s(−n) is sufficiently greater than the relative position s(0), and Expression (15) does not hold, K v  satisfying the following Expression (20) is selected. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             e 
                             v 
                           
                           ⁡ 
                           
                             ( 
                             0 
                             ) 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             
                               s 
                               ⁡ 
                               
                                 ( 
                                 0 
                                 ) 
                               
                             
                             - 
                             
                               s 
                               ⁡ 
                               
                                 ( 
                                 
                                   - 
                                   n 
                                 
                                 ) 
                               
                             
                           
                           nT 
                         
                       
                     
                   
                   
                     
                       
                         ≈ 
                           
                         ⁢ 
                         
                           
                             K 
                             v 
                           
                           ⁢ 
                           
                             
                               
                                 p 
                                 ⁡ 
                                 
                                   ( 
                                   0 
                                   ) 
                                 
                               
                               - 
                               
                                 p 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     - 
                                     n 
                                   
                                   ) 
                                 
                               
                             
                             nT 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             K 
                             v 
                           
                           ⁢ 
                           
                             
                               p 
                               v 
                             
                             ⁡ 
                             
                               ( 
                               0 
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   20 
                   ) 
                 
               
             
           
         
       
     
     The above Expression (12) can be represented such as shown in the following Expression (21) by applying this K v  thereto. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           ( 
                           
                             
                               
                                 
                                   
                                     x 
                                     L 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     x 
                                     H 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                               
                             
                           
                           ) 
                         
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     k 
                                     11 
                                   
                                 
                                 
                                   
                                     k 
                                     12 
                                   
                                 
                               
                               
                                 
                                   
                                     k 
                                     21 
                                   
                                 
                                 
                                   
                                     k 
                                     22 
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   
                                     e 
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       e 
                                       v 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     k 
                                     11 
                                   
                                 
                                 
                                   
                                     k 
                                     12 
                                   
                                 
                               
                               
                                 
                                   
                                     k 
                                     21 
                                   
                                 
                                 
                                   
                                     k 
                                     22 
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   
                                     
                                       K 
                                       p 
                                     
                                     ⁢ 
                                     
                                       p 
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       K 
                                       v 
                                     
                                     ⁢ 
                                     
                                       
                                         p 
                                         v 
                                       
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   21 
                   ) 
                 
               
             
           
         
       
     
     That is to say, the initial value generating unit  151  can calculate an initial value compensation value by employing this Expression (21). 
     Note that the configuration of the initial value compensation value generating unit in this case is basically the same as in the case of  FIG. 10 , and accordingly, the block diagram in  FIG. 10  can be applied thereto. However, the relative speed generating unit  152  employs the value n samples ahead to generate relative speed in accordance with the above Expression (19). Also, the correction coefficient holding unit  153  also holds K v  for speed as well as the K p  as a correction coefficient. As shown in Expression (21), the initial value generating unit  151  corrects the push-pull signal p(0) and relative speed p v (0) by employing the correction coefficients K p  and K v  to calculate an initial value compensation value. 
     However, in  FIG. 10 , in the same way as in the case of the push-pull signal value p(−1) one sample ahead, at least the push-pull signal value p(−n) n samples ahead has to be held by either the tracking servo control computing circuit  143  or relative speed generating unit  152 . 
     Also, the flow of the initial value compensation value generating processing in this case is basically the same as the flow described with reference to the flowchart in  FIG. 11 . However, in this case, in step S 1  the push-pull signal value p(−n) n samples ahead is obtained instead of the push-pull signal value p(−1) one sample ahead. Also, in step S 2  the relative speed p v (0) is calculated by employing the push-pull signal value p(−n) n samples ahead thereof. Further, in step S 3  the correction coefficient K v  for speed is also read out as well as the correction coefficient K p , and in step S 4  the relative speed p v (0) is corrected by employing the correction coefficient K v  for speed thereof. 
     Thus, an initial value compensation value is calculated by employing the above Expression (21), whereby the initial value compensation value generating unit  124  can reduce influence due to the error, and obtain a sufficient advantage of initial value compensation at the control system, even in a case where the push-pull signal value p(−n) n samples ahead is relatively great, the error as to the original relative position s(n) is great, and a sufficient advantage is not obtained with the initial value compensation value calculated based on the above Expression (17). 
     Also, in the same way as in the case where the relative speed p v (0) is calculated by employing the push-pull signal value p(−1) one sample ahead, the initial value compensation matrix can also be corrected with the correction coefficient beforehand in this case. That is to say, in the same way as in the case of the above Expression (18), the above Expression (21) can be transformed such as shown in the following Expression (22). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           ( 
                           
                             
                               
                                 
                                   
                                     x 
                                     L 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     x 
                                     H 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     0 
                                     ) 
                                   
                                 
                               
                             
                           
                           ) 
                         
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     k 
                                     11 
                                   
                                 
                                 
                                   
                                     k 
                                     12 
                                   
                                 
                               
                               
                                 
                                   
                                     k 
                                     21 
                                   
                                 
                                 
                                   
                                     k 
                                     22 
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   
                                     
                                       K 
                                       p 
                                     
                                     ⁢ 
                                     
                                       p 
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       K 
                                       v 
                                     
                                     ⁢ 
                                     
                                       
                                         p 
                                         v 
                                       
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     
                                       k 
                                       11 
                                     
                                     · 
                                     
                                       K 
                                       p 
                                     
                                   
                                 
                                 
                                   
                                     
                                       k 
                                       12 
                                     
                                     · 
                                     
                                       K 
                                       v 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       k 
                                       21 
                                     
                                     · 
                                     
                                       K 
                                       p 
                                     
                                   
                                 
                                 
                                   
                                     
                                       k 
                                       22 
                                     
                                     · 
                                     
                                       K 
                                       v 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 
                                   
                                     p 
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       p 
                                       v 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             α 
                             2 
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 
                                   
                                     p 
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       p 
                                       v 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   22 
                   ) 
                 
               
             
           
         
       
     
     Like this Expression (22), an initial value compensation value can be readily calculated by employing the corrected initial value compensation matrix α 2  which has been corrected with the correction coefficient. 
     Note that the configuration of the initial value compensation value generating unit in this case is also basically the same as in the case of  FIG. 12 , and accordingly, the block diagram in  FIG. 12  can be applied thereto. However, the relative speed generating unit  152  employs the value n samples ahead to generate relative speed in accordance with the above Expression (19). Also, the corrected initial value compensation matrix holding unit  254  holds the corrected initial value compensation matrix α 2  beforehand. As shown in Expression (22), the initial value generating unit  151  calculates an initial value compensation value from the push-pull signal p(0) and relative speed p v (0) by employing the corrected initial value compensation matrix α 2 . 
     However, in this case as well, at least the push-pull signal value p(−n) n samples ahead has to be held by either the tracking servo control computing circuit  143  or relative speed generating unit  152 . 
     Also, the flow of the initial value compensation value generating processing in this case is basically the same as the flow described with reference to the flowchart in  FIG. 13 . However, in this case, in step S 21  the push-pull signal value p(−n) n samples ahead is obtained instead of the push-pull signal value p(−1) one sample ahead. Also, in step S 22  the relative speed p v (0) is calculated by employing the push-pull signal value p(−n) n samples ahead thereof. Further, in step S 23  the corrected initial value compensation matrix α 2  is read out, and in step S 24  an initial value compensation value is calculated by employing the corrected initial value compensation matrix α 2  thereof. 
     Thus, an initial value compensation value is calculated in accordance with the above Expression (22), whereby the initial value compensation value generating unit  224  can reduce influence due to the error, and obtain a sufficient advantage of initial value compensation at the control system, even in a case where the push-pull signal value p(−n) n samples ahead is relatively great, the error as to the original relative position s(n) is great, and a sufficient advantage is not obtained with the initial value compensation value calculated based on the above Expression (18). That is to say, the initial value compensation value generating unit  224  can further readily calculate an initial value compensation value as compared to the cased of calculating an initial value compensation value in accordance with Expression (21). 
     Description has been made so far regarding the case where the push-pull signal is employed as an error signal with the tracking servo control, but the present invention is not restricted to this, for example, may be applied to the focus servo control as well. 
       FIG. 14  is a diagram illustrating the relation between a lens position and an error signal with the focus servo control. As shown in  FIG. 14 , in general, it has been understood that, with the focus servo control as well, an error signal exhibits the S&#39;th order curve as to the lens position. That is to say, there is a possibility that an error signal is detected to be smaller than the original relative position in the same way as the case of the above-mentioned tracking servo control. Accordingly, the present invention may be applied to a case where the initial value compensation method is applied at the time of start of the operation of such a focus servo control system, in the same way as in the case of the above-mentioned tracking servo control. 
     Additionally, the present invention may be applied to other than the above-mentioned control system, as long as initial value compensation is performed as to a control system such that a signal indicating the state of an object of control causes an error as to the actual state at the time of start of control. That is to say, as long as the device includes such a control system, the present invention is not restricted to an optical disc recording/reproducing device, and may be applied to any kind of device. 
     Such a device may be, for example, an optical disc reproducing device which reads out data recorded in an optical disc to reproduce this, and does not perform writing of data to an optical disc, or an optical disc recording device which performs writing of data to an optical disc, and does not perform reading. Alternatively, such a device may be a device completely different from these, for example, such as a digital camera or the like. 
     It goes without saying that an object of control may be other than a recording/reproducing element. Also, an object of control may be provided separately, for example, with the example shown in  FIG. 10 , the control unit  122  and initial value compensation value generating unit  124  may be integrated to a single control device  125  which controls the recording/reproducing element  121  (electromagnetic actuator  123 ) which is an external object of control. Obviously, the electromagnetic actuator  123  may be included in the control device  125 . Further, the initial value compensation value generating unit  124  may be a single device (initial value compensation value generating device) which provides an initial value compensation value to the external control unit  122 . 
     The case in  FIG. 12  is also the same, and the control unit  122  and initial value compensation value generating unit  224  may be the control device  225 , or the initial value compensation value generating unit  224  may be a single device (initial value compensation value generating device). 
     The above-mentioned series of processing can be executed not only by hardware but also by software. In this case, for example, the above-mentioned series of processing may be configured as a personal computer such as shown in  FIG. 15 . 
     In  FIG. 15 , a CPU (Central Processing Unit)  301  of a personal computer  300  executes various types of processing in accordance with a program stored in ROM  302 , or a program loaded into RAM  303  from a storage unit  313 . Data or the like used by the CPU  301  to execute various types of processing is also stored in the RAM  303  as appropriate. The CPU  301 , ROM  302 , and RAM  303  are mutually connected through a bus  304 . An input/output interface  310  is also connected to the bus  304 . 
     The input/output interface  310  is connected with an input unit  311  made up of a keyboard, mouse, and so forth, an output unit  312  made up of a display configured of CRT (Cathode Ray Tube), LCD (Liquid Crystal Display), or the like, speaker, and so forth, a storage unit  313  configured of a hard disk or the like, and a communication unit  314  configured of a modem or the like. The communication unit  314  performs communication processing through a network including the Internet. 
     The input/output interface  310  is also connected with a drive  315  as appropriate, on which a removable medium  321  such as a magnetic disk, optical disc, magneto-optical disk, semiconductor, or the like is mounted as appropriate, and a computer program read out therefrom is installed into the storage unit  313  as appropriate. 
     In a case where the above-mentioned series of processing is executed by software, a program making up the software thereof is installed from a network or recording medium. 
     The recording medium is not restricted to being configured of, separately from the device main unit such as shown in  FIG. 15 , the removable medium  321  made up of a magnetic disk (including a flexible disk), optical disc (including CD-ROM (Compact Disc-Read Only Memory), DVD (Digital Versatile Disc)), magneto-optical disk (including MD (Mini Disc)), semiconductor memory, or the like wherein a program to be distributed to a user is recorded, but also may be the ROM  302 , a hard disk included in the storage unit  313 , or the like, wherein a program to be distributed to a user in a state built into a device main unit beforehand has been recorded. 
     Note that, with the present Specification, steps describing a program to be recorded in a recording medium include not only processing performed in time series along a described order but also processing executed in parallel or individually even though not necessarily performed in time series. Also, with the present Specification, the term “system” represents the entirety of equipment configured of multiple devices. 
     Note that the configuration described above as a single device may be configured as multiple devices. Conversely, the configuration described above as multiple devices may be configured as a single device collectively. Also, a configuration other than the above configuration may be added to the configuration of each device. Further, if the configuration and operation as the entire system are substantially the same, a part of the configuration of a certain device may be included in another device. That is to say, embodiments of the present invention are not restricted to the above-mentioned embodiment, and various changes can be made without departing from the essence and spirit of the present invention. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.