Abstract:
A method and apparatus for controlling a maximum rotational speed of a recording medium, are discussed. The method according to an embodiment of the present invention includes determining an imbalance error of the recording medium, and variably setting a maximum rotational speed of the recording medium based on the determined imbalance error.

Description:
This application claims the benefit of the Korean Patent Application No. 10-2005-0023257 filed on Mar. 21, 2005 in Republic of Korea, the entire contents of which are here by fully incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for controlling a spindle in an optical disc device, and more particularly to a method and apparatus for controlling a maximum rotational speed of an optical disc based on an imbalance error of the optical disc. 
   2. Description of the Related Art 
     FIG. 1  is a block diagram of a general optical disc device. For example, a variety of types of optical disc devices such as DVD players may comprise an optical disc  10 , an optical pickup  11 , an RF processor  12 , a digital signal processor  13 , a spindle motor  14 , a sled motor  15 , a microcomputer  16 , a motor drive  17 , a servo controller  18 , and a memory  19  as shown in  FIG. 1 . The components are operatively coupled. 
   The optical disc  10  may have a variety of structural errors which cause vibration and noise and exert adverse effects on a servo associated with playback and recording operations. Examples of such errors include an eccentric error caused by mismatch between the center of tracks formed on the optical disc and the center (i.e., a central hole) of the optical disc, and an imbalance error caused when the optical disc is bent asymmetrically in one direction from the center of the disc, e.g., due to the incorrect positioning of the optical disc on the optical disc device. 
   Generally the eccentric errors exert adverse effects on the servo over a range of low to high disc rotational speeds, almost regardless of the rotational speed of the optical disc. However, generally the imbalance errors exert no noticeable effect on the servo when the spindle motor  14  rotates the optical disc at a low speed while exerting an adverse effect on the servo when the optical disc rotates at a high speed. Thus, the eccentric and imbalance errors are different. 
     FIG. 2  is a flow chart of a method for controlling a spindle in an optical disc device according to a related art. 
   When an optical disc  10  is inserted into an optical disc device such as a DVD player, the microcomputer  16  controls the servo controller  18  to perform an operation for setting the maximum spindle/rotational speed of the disc  10 . 
   The microcomputer  16  turns the spindle motor on to rotate the optical disc  10  and turns the focusing servo on while turning the tracking servo off (S 10 ). 
   The microcomputer  16  rotates the spindle motor  14  at a preset low speed (for example, 3,000 RPM) (S 11 ) and counts track cross signals detected by the optical pickup  11  while the optical disc  10  rotates once at the preset low speed (S 12 ). The track cross signal count represents the number of tracks which a laser beam irradiated by the optical pickup  11  crosses, and corresponds to the eccentric error of the optical disc  10 . 
   The microcomputer  16  compares the number of track crossings counted in the above manner with a first preset reference value (S 13 ). If the track crossing count is equal to or exceeds the first reference value, the microcomputer  16  determines that the optical disc has a large eccentric error and sets the maximum spindle speed of the optical disc to a low spindle speed (for example, ×16) (S 17 ). 
   On the other hand, if the track crossing count is less than the first reference value, the microcomputer  16  rotates the spindle motor  14  at a preset high speed (for example, 4,300 RPM) (S 14 ) and counts track cross signals detected during one rotation of the optical disc  10  (S 15 ). This track cross signal count corresponds to both the eccentric and imbalance errors of the optical disc  10 . 
   The microcomputer  16  then compares the number of track crossings counted in the above manner with a second preset reference value (S 16 ). If the track count is equal to or exceeds the second reference value, the microcomputer  16  determines that the optical disc has large eccentric and imbalance errors and sets the maximum spindle speed of the optical disc  10  to a low spindle speed (for example, ×16) (S 17 ). 
   On the other hand, if the track crossing count is less than the second reference value, the microcomputer  16  determines that the optical disc  10  has small eccentric and imbalance errors which are within an acceptable range and thus sets the maximum spindle speed of the optical disc  10  at a high speed (for example, ×32) (S 18 ). 
   The count of the track cross signals (track crossings) detected when the optical disc rotates at a high speed corresponds to the combination of eccentric and imbalance errors of the optical disc. Thus, for a given disc, if the imbalance error (which exerts an adverse effect only when the optical disc rotates at a high speed) is small and the eccentric error is relatively large, the error (i.e., mostly an eccentric error) detected when the optical disc rotates at a low speed may be larger than the first reference value, but at the same time, an error (i.e., the sum of eccentric and imbalance errors) detected when the optical disc rotates at a high speed is less than the second reference value. In this case, the related art method unnecessarily and unconditionally reduces the maximum spindle speed (S 17 ) based on the eccentric error detected when the optical disc rotates at a low speed, even though the high speed test for the same disc indicates that the maximum spindle speed can and should be maintained. 
   SUMMARY OF THE INVENTION 
   Therefore, the present invention has been made in view of the above and other problems, and it is an object of the present invention to provide a method for adjusting the maximum spindle speed to an optimal level. 
   It is another object of the present invention to provide a method for detecting an imbalance (or unbalance) error of an optical disc, which affects a servo when the optical disc rotates at a high speed, and for adjusting the maximum spindle speed based on the detected imbalance error. 
   It is another object of the present invention to provide a method and apparatus for controlling a maximum rotational speed of a recording medium (e.g., an optical disc such as a DVD), which addresses the limitations and disadvantages associated with the related art. 
   In accordance with one aspect of the present invention, there is provided a method for controlling a maximum rotational speed of a recording medium, the method comprising: determining an imbalance error of the recording medium; and variably setting a maximum rotational speed of the recording medium based on the determined imbalance error. 
   In accordance with another aspect of the present invention, there is provided an apparatus for controlling a maximum rotational speed of a recording medium, the apparatus comprising: a controller to determine an imbalance error of the recording medium, and to variably set a maximum rotational speed of the recording medium based on the determined imbalance error. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram of a general optical disc device in which the present invention can be applied; 
       FIG. 2  is a flow chart illustrating a method for controlling a spindle in an optical disc device according to a related art; 
       FIG. 3  is a flow chart illustrating a method for controlling a spindle in an optical disc device according to an embodiment of the present invention; and 
       FIG. 4  illustrates an example of adjusting the maximum spindle speed according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present invention is directed to a method for controlling a spindle in an optical disc device and the optical disc device. The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     FIG. 3  is a flow chart illustrating a method for controlling a spindle in an optical disc device according to an embodiment of the present invention. The method according to the present invention can be applied to the optical disc device constructed as described above with reference to  FIG. 1 , or to other apparatus/system.  FIG. 4  also shows an example of a maximum spindle speed adjustment operation according to an embodiment of the present invention. 
   Referring to  FIGS. 1 and 3 , if a recording medium such as an optical disc  10 , e.g., a CD or DVD, is inserted into the optical disc device, the microcomputer  16  controls the servo controller  18  to perform a series of operations for setting a maximum spindle speed. 
   The microcomputer  16  turns the spindle motor  14  on to rotate the optical disc  10  and turns the focusing servo on while turning the tracking servo off (S 30 ). 
   The microcomputer  16  rotates the spindle motor  14  at a preset low speed (for example, 3,000 RPM) (S 31 ) and counts track cross signals detected by the optical pickup  11  during one rotation of the optical disc  10 , and temporarily stores the track cross signal count as an eccentric error value A (S 32 ). The track cross signal count represents the number of tracks which a laser beam irradiated by the optical pickup  11  crosses. 
   The amount of eccentricity may be detected based on the number of tracks which a laser beam irradiated by the optical pickup  11  crosses while the optical disc rotates half a turn. However, it is more desirable to detect the number of tracks which the laser beam crosses while the optical disc rotates one turn since an imbalance error to be detected is associated with an error of the optical disc when the optical disc is bent asymmetrically. 
   Thereafter, the microcomputer  16  rotates the spindle motor  14  at a preset high speed (for example, 4,300 RPM) (S 33 ). The speed of 4,300 RPM is a rotational speed at which the imbalance error of the optical disc is detected remarkably well; however, other high speed may be used. This rotational speed can be set based on experimental results and can be changed to a different level. 
   The microcomputer  16  counts track cross signals detected by the optical pickup  11  while the optical disc  10  rotates once at the preset high speed and temporarily stores the track cross signal count as an eccentric and imbalance error value B (S 34 ). 
   The microcomputer  16  then calculates an imbalance error value C by subtracting the stored eccentric error value A detected when the optical disc  10  rotates at the low speed at step S 32  from the eccentric and imbalance error value B detected when the optical disc  10  rotates at the high speed at step S 34  (i.e., C=B−A) (S 35 ), and compares the imbalance error value C with a preset reference value Ref_C (S 36 ). In the example of  FIG. 4 , the imbalance error value C_Value is obtained by subtracting the eccentric error value A_Value from the eccentric and imbalance error value B_Value. 
   When the result of the comparison indicates that the calculated imbalance error value C exceeds the reference value Ref_C (S 36 ), the microcomputer  16  determines that the optical disc  10  has an imbalance error larger than the reference value and sets the maximum spindle speed to a preset level (for example, ×16 in  FIG. 4 ) (S 37 ). As a variation, if the calculated imbalance error value C exceeds the reference value Ref_C at step S 36 , the microcomputer  16  at step S 37  may set the maximum spindle speed to a speed obtained by subtracting a value that is proportional to the difference (C−Ref_C) between the detected imbalance error value and the reference value from a maximum spindle speed supported by the optical disc device. That is, at step S 37 , the maximum spindle speed can be adjusted proportional to the difference (C−Ref_C). For instance, if the difference (C−Ref_C) is large, then the maximum spindle speed of the optical disc device can be lowered more, whereas if the difference is small, then the maximum spindle speed can be lowered less. This proportional adjustment can be done using a look-up table, which can provide the exact maximum spindle speed adjustment for each difference value, so as to provide an optimal maximum spindle speed adjustment operation. 
   On the other hand, if the calculated imbalance error value C does not exceed the reference value Ref_C at step S 36 , the microcomputer  16  determines that the current optical disc has an imbalance error less than the reference value and maintains the current maximum spindle speed supported by the optical disc device (for example, ×32 in  FIG. 4 ) (S 38 ). 
   As described above, the present invention calculates an imbalance error value, which causes a servo error only when the optical disc rotates at a high speed, and adjusts the maximum spindle speed based on the calculated imbalance error value. Accordingly, for example, even when an eccentric and imbalance error value B_Value of an optical disc having a small imbalance error C_Value is detected at the same level as that of an optical disc having a large imbalance error C_Value when they rotate at a high speed as shown in  FIG. 4 , the maximum spindle speed is prevented from being unnecessarily adjusted down when the optical disc has a small imbalance error or from being unconditionally adjusted down based only on the eccentric error value detected when the optical disc rotates at a low speed. 
   As is apparent from the above description, a method for controlling a spindle in an optical disc device according to the present invention easily and efficiently detects an imbalance error of an optical disc, adjusts the maximum spindle speed to be suitable for the imbalance error of the optical disc, and also minimizes vibration and noise caused by the imbalance error when the optical disc rotates at a high speed while preventing the maximum spindle speed from being unnecessarily adjusted down based on an eccentric error of the optical disc. 
   Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.