Abstract:
An optical disk drive for accessing data stored on a compact disc has a housing, a sled sliding inside the housing, a driving device for driving the sled, an actuator installed on the sled, a servo device for providing a push force to drive the actuator, a control circuitry for controlling operations of the optical disk drive, an adaptive compensator, and an error signal generation circuit. The actuator can move within a predetermined range on the sled, wherein the predetermined range includes a linear region and a non-linear region. It is desirable to keep the actuator within the linear region of the predetermined range. For this, an adaptive compensator is used to provide a supplementary force to the sled when the actuator is near the non-linear region.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application commonly owned parent application Ser. No. 10/063,311, filed Apr. 10, 2002 U.S. Pat No. 6,717,892. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical disk drive (for example, compact disk drive or DVD drive) capable of reading data stored on an optical disk (for example, CD or DVD). More specifically, the present invention discloses an optical disk drive comprising an adaptive compensator for preventing an actuator from entering a non-linear region. 
     2. Description of the Prior Art 
     In current technology, an optical disk is lightweight, small physical volume, and low cost. In addition, optical disks have a high capacity for information storage, making optical disks an indispensable information-storing medium. 
     Of course, high-density information stored on an optical disk is read out by an optical disk drive for further processing. The high-speed requirements of modern society demand not only a continuous increase of data storage density on the optical disk, but also demand a high speed optical disk drive for reading the data on the optical disk. In order to allow the optical disk drive to read high-density data quickly, the optical disk drive must have a precise control system. Therefore, developing a precise control system for the optical disk drive is an important topic of the information industry. 
     Please refer to  FIG. 1 .  FIG. 1  is a perspective view of an optical disk drive  10  according to the prior art. The optical disk drive  10  reads data stored on an optical disk  14 . The optical disk drive  10  includes a housing  12  and a rotatable base  16  installed on the housing  12 . The housing  12  further comprises a hole  17  that shows a sled  18  inside the housing  12 . The sled  18  inside the housing  12  is capable of sliding left and right so as to scan data stored on the optical disk  14 . When the optical disk  14  is put on the base  16  and rotated by the base  16 , the sled  18  slides left and right along the hole  17  so that the optical disk drive  10  reads data stored on the optical disk  14 . 
     For further illustration of the inner construction of the optical disk drive  10 , please refer to  FIG. 2 .  FIG. 2  is a perspective view of the inner structure of the optical disk drive  10  according to the prior art. In order to clearly show the inner structure of the optical disk drive  10 , a portion of the housing  12  of the optical disk drive  10  is omitted in  FIG. 2 . Inside the optical disk drive  10 , a spindle motor  15  on the housing  12  is capable of rotating the base  16  and further driving the optical disk  14  on the base  16 . For clarity,  FIG. 2  only shows a portion of the optical disk  14 . The sled  18  slides left and right on a path  30  along a direction  34  shown in  FIG. 2 . The sliding of the sled  18  is driven by a driving device  20 . The driving device  20  comprises a driving motor  20   a  installed inside the housing  12 , a gear  20   b  rotated by the driving motor  20   a  and a saw tooth plate  20   c  on the sled  18 . When the driving motor  20   a  rotates the gear  20   b , the saw tooth plate  20   c , engaging with the gear  20   b , pushes the sled  18  to slide left and right along the slide  30 . For reading high-density data stored on the optical disk  14 , the sled  18  controls an actuator  22 , which is capable of moving left and right in a direction  36  within a predetermined range on the sled  18 , as shown in  FIG. 2 . A lens  32  is installed on the actuator  22 , and connects with a light source  26  installed on the sled  18 . Light (for example, a laser) is emitted from the light source  26  and passes through the lens  32  on the actuator  22  optically, and then shines on the bottom surface of the optical disk  14 . The light reflected from the optical disk  14  passes through the lens  32  on the actuator  22 . The light is then sent back to the sled  18 , so that the optical disk drive  10  is capable of reading the data stored on the optical disk  14 . Meanwhile, the actuator  22  slides left and right on the sled  18 , and is driven by a servo device  24  on the sled  18 . The servo device  24  provides a push force to drive the actuator  22  left and right. 
     In order to read the high-density data stored on the optical disk  14  well, the optical disk drive  10  comprises a control system for controlling the operation of the actuator  22  and the sled  18 . Please refer to  FIG. 3 .  FIG. 3  is a diagram of the control system of the optical disk drive  10  according to the prior art. In the current optical disk standard, data is written onto the optical disk  14  along tracks. The optical disk shown in  FIG. 3  shows one of the tracks  46  with data stored therein. For reading data on the track  46 , the sled  18  and the actuator  22  on the optical disk drive  10  must make the lens  32  lock the position of the track  46 . Therefore, the optical disk drive  10  is capable of reading data stored on the track  46  with the rotation of the optical disk  14 . For this purpose, the control system of the optical disk drive  10  comprises a control circuitry  38  for controlling the operation of the optical disk drive  10 . The control circuitry  38  has a compensation device  48  for controlling both the driving device  20  and the servo device  24 . Furthermore, a sensor  28  is installed on the sled  18  and is connected with the actuator  22 . This means that the light emitted from the light source  26  passes through the lens  32  and shines incident onto the optical disk  14 . The light may be reflected from the optical disk  14  into the sensor  28  by passing through the lens  32  on the actuator  22  again. By analyzing the light incident on the sensor  28 , the sensor  28  is capable of sensing whether the lens  32  locks on the track  46 . The result is then transmitted into the control circuitry  38 . According to this result, the control circuitry  38  makes the compensation device  48  to control the driving device  20  and the servo device  24  for adjusting the operation of the sled  18  and the actuator  22  respectively. Therefore, the lens  32  is able to lock the track  46 , and the optical disk drive  10  reads data stored on the track  46  of the optical disk  14  correctly. 
     The control system of the prior optical disk drive  10  is used for locking the track  46 . The control circuitry  38  controls the operation of the sled  18  and the actuator  22  through the driving device  20  and the servo device  24  respectively. Compared with the actuator  22 , the move range of the sled  18  is larger, but the response of the control circuitry  38  is slower. In addition, the movement of the sled  18  is not very accurate, so it can only make a rough locking motion. On the other hand, the move range of the actuator  22  is smaller, but the response is quicker. So the actuator  22  is able to make an accurate locking. The control circuitry  38  controls both the sled  18  and the actuator  22 , so the control circuitry  38  needs to give consideration to both kinds of track locking. The control of the sled  18  and the actuator  22  is not only related with the control circuitry  38 , but also related with the mechanical characteristics of the driving device  20  and the servo device  24 . Please refer to  FIG. 3  again. The servo device  24  provides a pushing force to push the actuator  22  left and right within a predetermined range  40  on the sled  18 , but the relationship between the push force received by the actuator  22  and the displacement of the actuator  22  within the predetermined range may change due to different positions of the actuator  22  in the predetermined range. The predetermined range  40  is divided into a linear region  44  and a non-linear region  42 . In the linear region  44 , the push force, provided by the servo device  24  for pushing the actuator  22 , has a linear relationship with the displacement of the actuator  22 . Relatively, within the non-linear region  42  of the predetermined range  40 , the push force received by the actuator  22  has a non-linear relationship with the displacement of the actuator  22 . 
     In the linear region  44 , the control circuitry  38  provides a push force to the actuator  22  through the servo device  24 . This push force controls the position of the actuator on the sled  18  and keeps the linear relation between the sled  18  and the actuator  22 . Alternatively, in the non-linear region  42 , the control circuitry  38   22  would be unable to control and the position of the actuator  22  on the servo device  24  is unknown. Thus, the control circuitry  38  would be unable to keep the relation of the sled  18  and the actuator  22  in the non-linear region  42 . Once the relation between the sled  18  and the actuator  22  is unknown, the optical disk drive  10  may be unable to lock the track  46  and read data stored on the optical disk  14  correctly. When designing the compensation device  48  of the control circuitry  38 , designers may specially set the relation between the sled  18  and the actuator  22  so as to keep the position of the actuator  22  within the linear region  44  of the predetermined range  40 . 
     In modern industry, there are many components inside an optical disk drive. The driving device  20 , the sled  18 , the servo device  24 , the actuator  22 , and the control circuitry  38  may be from different vendors. The design of the compensation device  48  had better according to the specifications of the hardware device. However, there may be some inevitable errors during production, and the produced hardware device may be some different from the specifications of the original design. Although the compensation device  48  of the control circuitry  38  is designed according to the specifications of the hardware device so as to keep the actuator  22  inside the linear region  44  on the sled  18 , there may be some negative effects on the set relation control in the compensation device  48 . Therefore, the optical disk drive  10  may be unable to lock the track  46  fast and correctly. Of course, a poor design of the compensation device  48  also deteriorates the relationship, and lets the actuator  22  enter the non-linear region  42 , making the actuator  22  difficult to control. Further, the deviation phenomenon caused by poor manufacturing of the optical disk  14  can also deteriorate the relationship. The run-out phenomenon of the optical disk  14  is caused when the rotation axis of the base  16  and the center of the circular optical disk  14  do not match. Ultimately, the run-out phenomenon makes the position of the track  46  on the optical disk  14  unpredictable. In the optical disk drive with high access rate, the rotation speed of the optical disk  14  is especially high, so that the negative effect on tracking caused by the run-out phenomenon is obvious. In this case, the rotation of the track  46  is not circular when the optical disk  14  rotates. Therefore, the sled  18  and the actuator  22  also need to change position quickly so as to lock the track  46 . If the control response of the relation is too slow, then the actuator may unexpectedly enter into the non-linear region. 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the claimed invention to provide an optical disk drive with an adaptive compensator for the driving device to provide a supplementary force to the sled when the sled is near the non-linear region. The supplementary force drives the actuator away from the non-linear region. 
     The claimed invention, briefly summarized, discloses an optical disk drive for accessing data stored on an optical disc. The optical disk drive comprises: a sled, a driving device for driving the sled, an actuator installed on the sled, a servo device for providing a push force to drive the actuator, a control circuitry for controlling operations of the optical disk drive, an adaptive compensator, and an error signal generation circuit. The actuator is capable of moving within a predetermined range on the sled. When the actuator is within a linear region of the predetermined range, a displacement of the actuator on the sled has a linear relationship with the push force, and when the actuator is within a non-linear region of the predetermined range, the displacement of the actuator on the sled has a non-linear relationship with the push force. The control circuitry includes a compensation device for providing a driving force to drive the sled. In addition, the adaptive compensator makes the driving device to provide a supplementary force to the sled so as to prevent the actuator from entering the non-linear region. The error signal generation circuit generates an error signal according to a relationship between the actuator and the optical disc. The adaptive compensator makes the driving device to provide a supplementary force to push the sled according to the error signal so as to prevent the actuator from entering the non-linear region. 
     It is an advantage of the claimed invention that the optical disk drive has an adaptive compensator. When the compensation device does not control well and the magnitude of the error signal is too large, then the adaptive compensator is able to provide a supplementary force through the driving device so as to keep the actuator within the linear region and lock tracks correctly. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an optical disk drive according to the prior art. 
         FIG. 2  is a perspective view of inner structure of the optical disk drive according to the prior art. 
         FIG. 3  is a diagram of the control system of the optical disk drive according to the prior art. 
         FIG. 4  is a diagram of an optical disk drive according to the present invention. 
         FIG. 5  is a diagram of a control system of the optical disk drive according to the present invention. 
         FIG. 6  is a flow chart of a control method of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 4 .  FIG. 4  is a simplified diagram of an optical disk drive  60  according to the present invention. 
     The optical disk drive  60  comprises a housing  62 , a rotatable base  66  on the housing  62  for rotating an optical disk  64 . A sled  68  slides inside the housing  62 . A hole  67  on the housing  62  is able to let the sled  68  slide left and right so as to read data stored on the optical disk  64 . 
     In order to read data stored on the optical disk  64  effectively, the optical disk drive  60  comprises a control system. Please refer to  FIG. 5 .  FIG. 5  is a simplified diagram of the control system of the optical disk drive  60 . The sled  68  of the optical disk drive  60  is driven by a driving device  70  so as to slide left and right (along a direction  84 ) on a path  80 . The actuator  72  accepts a push force provided by a servo device  74  and moves left and right (along a direction  86 ) within a predetermined range  90  on the sled  68 . The driving device  70  of the optical disk drive  60  is not limited by the description of the invention. A lens  82  is installed on the actuator  72 . A light source  76  and a sensor  78  installed on the sled  68  are optically coupled with the actuator  72 . Light (always a laser) is emitted from the light source  76  and then optically passed through the lens  82  on the actuator  72 . Then light shines on the optical disk  64 . The light reflected from the optical disk  64  also passes through the lens  82  to the actuator  72 . A portion of the reflected light is provided to the sled  68  for reading data stored on the optical disk  64  and another portion of it is incident to the sensor  78 . In order to make the lens  82  to focus on tracks  96  on the optical disk  64 , the sensor  78  is able to analyze the received light and judge whether the light, emitted from the light source  76  and passed through the lens  82 , is focused on the track  96  of the optical disk  64  correctly or not. If the actuator  72  is unable to lock the position of the track  96  correctly, then the light is unable to focus on the track  96 . The sensor  78  generates an error signal. If the position of the actuator  72  away from the position of the correct track  96  is farther, the magnitude of the error signal may be greater. A control circuitry  88  inside the optical disk drive  60  receives the error signal, which is generated by the sensor  82 . In order to control the sled  68  and the actuator  72  to lock the position of the track  96  correctly, the control circuitry  88  comprises a compensation device  98  for making the driving device  70  to provide a driving force to drive the sled  68 . Besides the above control circuitry  88  and the compensation device  98 , an adaptive compensator  100  is added. The compensation device  98  keeps the relation between the actuator  72  and the sled  68 . The adaptive compensator  100  is to supplement the compensation device  98  to control the relation. 
     As discussed before, the prior optical disk drive  10  comprises a compensation device  48  for controlling the relation between the sled  18  and the actuator  22  by controlling the driving device  20  and the servo device  24 . Nevertheless, in the event of low quality hardware devices in the optical disk drive  10 , bad design of the control circuitry  38 , or run-out of the optical disk  14 , the relation is hard to be maintained. In order to supplement the compensation device  98 , the optical disk drive  60  further comprises the adaptive compensator  100  so as to keep the actuator  72  within the linear region  94  of the predetermined range  90 . The operation of the adaptive compensator  100  is described as below. First, the adaptive compensator  100  reads the error signal. According to the error signal, the adaptive compensator  100  judges whether the actuator  72  is near the non-linear region  92  of the predetermined range  90  or not. An embodiment of the decision rule is accordance with whether the magnitude of the error signal is greater than a predetermined value or not. In a general situation when the compensation device  98  is able to control the relation between the actuator  72  and the sled  68  so as to keep the actuator  72  within the linear region  94  and to lock the position of the track  96 , the magnitude of the error signal should be small. On the other hand, if the magnitude of the error signal is greater than a predetermined value, the compensation device  98  is unable to control the relation between the actuator  72  and the sled  68 . This means the actuator  72  is unable to lock the track  96  and that the actuator  72  is near the non-linear region  92 . In the non-linear region  92 , the position of the actuator  72  has a non-linear relationship with the push force provided by the servo device  74 . Therefore the control module designed for the linear relationship in the compensation device  88  loses effectiveness, and the relation between the actuator  72  and the sled  68  is unable to maintain. 
     The adaptive compensator  100  of the optical disk drive  60  is able to prevent the actuator  72  from entering into the non-linear region  92 . When the adaptive compensator  100  decides that the actuator  72  is near the non-linear region  92  (as described before, this means the magnitude of the error signal is greater than a predetermined value), then it makes the driving device  70  to provide a supplementary force to drive the sled  68 . The supplementary force combines with the original driving force, which the compensation device  98  uses to control the driving device  70 , so as to push the sled  68 . Once the sled  68  is moved away from this original position by the supplementary force provided by the adaptive compensator  100 , the compensation device  98  uses the new position of the sled  68  to adjust the position of the actuator  72  again. This keeps the position of the actuator  72  away from the nonlinear region  92 . When the actuator  72  comes back to the linear region  94  again, the control module of the compensation device  98  becomes effective again. The control module is then able to use the relation between the sled  68  and the actuator  72  to lock the track  96  and reduce the magnitude of the error signal. Since the magnitude of the error signal is reduced, the adaptive compensator  100  judges that the actuator  72  already come back to the linear region  94  and is far away from the non-linear region  92 . The adaptive compensator  100  no longer makes the driving device  70  to provide the supplementary force to the sled  68  as the compensation device  98  is able to control the relation and lock the track  96  effectively. 
     In general, the error signal generated by the sensor  78  is not only capable of representing the degree of the actuator  72  deviation from the target track position, but also capable of representing the actuator  72  deviation to the left or right side of the target track position by positive or negative symbol. The adaptive compensator  100  of the present invention is able to use the magnitude and the symbol of the error signal to set the magnitude and the direction of the supplementary force. This allows the sled  68  to move for the purpose of reducing the error signal. The compensation device  98  could then adjust the position of the actuator  72  again according to the new position of the sled  68 . 
     As the embodiment of the present invention stated before, the adaptive compensator  100  judges if the actuator  72  is already near the non-linear region  92  according to whether the magnitude of the error signal is greater than a predetermined value. In general, the demarcation line between the linear region  94  and the non-linear region  92  is not especially clear, and it may change due to a change of the mechanical characteristics of the servo device  74  and the actuator  72 . Therefore, it is possible to adjust the predetermined value smaller so as to prevent the actuator  72  from entering the non-linear region  92 . Thus, if the actuator  72  has a small deviation range relative to the correct locking position inside the linear region  94 , the magnitude of the error signal is greater than the predetermined value. Then the adaptive compensator  100  makes the actuator  72  away from the non-linear region  92 . Further, the magnitude of the predetermined value also has a relationship with the time domain response. If the time domain response is slower, then the movement response of the sled  68  and the actuator  72  may be longer. If the response is too slow, the actuator  72  may enter the non-linear region  92 . To prevent the above situation, it is also possible to adjust the predetermined value to a smaller value. Therefore, the adaptive compensator  100  could provide the supplementary force through the driving device  70  faster. 
     In conclusion, the spirit of the present invention is to use an additional adaptive compensator  100  inside an optical disk drive  60 . When the actuator  72  is already near the non-linear region  92  but the compensation device  98  is unable to provide enough driving force to push the sled  68  so that to force the actuator  72  far away from the non-linear region  92 , the adaptive compensator  100  is able to provide a supplementary force through the driving device  70 . The position of the sled  68  is adjusted again so as to make the actuator  72  capable of locking the track  96  correctly. To see a summary of the control method of the optical disk drive used in the present invention, please refer to  FIG. 6 .  FIG. 6  is a flow chart of a control method according to the present invention, which comprises the following steps. 
     Step  200 : The control method begins. 
     Step  202 : The error signal is read. 
     Step  204 : The driving force is generated to drive the driving device, and then the method jumps to step  216 . 
     Step  206 : The error signal is read. 
     Step  208 : A low pass filter is used to filter the error signal so as to exclude the interfere noise of the error signal. 
     Step  210 : It is checked that the magnitude of the error signal is greater than a predetermined value or not. If yes, the method jumps to step  212 , otherwise to step  214 . 
     Step  212 : A non-zero supplementary force is generated to control the sled, and the method jumps to step  216 . 
     Step  214 : A zero supplementary force is generated, i.e., a supplementary force is not generated. 
     Step  216 : The driving force and the supplementary force are combined to control the sled. 
     Step  218 : The control method is terminated. 
     The control method as above may be repeated in the optical disk drive, so as to control the operation of the optical disk drive correctly. 
     In the above discussion, the optical disk drive for reading data stored on the optical disk is only exemplificative. 
     Since the adaptive compensator  100  is used for preventing the actuator  72  from entering into the non-linear region  92 , the principle and the spirit of the invention is also suitable for a recordable/re-writable optical disk drive for writing data onto the optical disk. 
     The prior art optical disk drive  10  includes the compensation device  48  for controlling the relation between the sled  18  and the actuator  22 . However, the optical disk drive  60  according to the present invention additionally comprises the adaptive compensator  100  installed in the compensation device  98 . When the compensation device control is insufficient for compensation and the magnitude of the error signal is too large, the adaptive compensator  100  is able to provide a supplementary force through the driving device  70  so as to keep the actuator  72  within the linear region  94  and lock the track  96  correctly. The control method of the prior art optical disk drive only simply generates a driving force to control the sled  18 . 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only be the metes and bounds of the appended claims.