Abstract:
A method and related apparatus for data accessing of an optical disk drive. The optical disk drive has a motor for rotating an optical disk and a pickup head. The pickup head is capable of writing data onto the optical disk according to a write-in clock. The method includes: when the pick-up head is seeking to a target position and a rotation speed of the motor is still being adjusted and unstable, making the pickup head slide back and forth within a predefined range, and making the pickup head slide toward the target position when the rotation speed of the motor becomes stable.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention provides a method for accessing data by controlling an optical disc drive and related apparatus, more particularly, to a method that accesses data by performing a pause state to adapt to a change of time for stabilizing a rotational speed of a motor in the optical disc drive and related apparatus. 
     2. Description of the Prior Art 
     Optical discs having small size, low cost, and large memory capacity for recording electronic data and information have become one of the most important memory mediums. The development of recordable optical discs has made the optical disc become one of the most important nonvolatile memory mediums. As a user must use an optical disc drive to access data on the optical disc, optical disc drive technology has become one of the major research topics for industry, with the aim of making optical disc drive data access more correct and efficient. 
       FIG. 1  is a functional diagram of an optical disc drive  10  according to the prior art. The optical disc drive  10  comprises a motor  12 , a sliding track  14  fixed to the optical disc  22 , a pickup head  16  for accessing data on the optical disc  22 , a drive circuit  20 , and a control circuit  18 . The motor  12  is used to drive an optical disc  22 , and the control circuit  18  is used to control the optical disc drive  10 . The optical disc  22  comprises a track  24  around the center of the optical disc  22  used to record data, and the track  24  can be divided into a plurality of tracks along a radial line (DO shown in  FIG. 1 ) of the optical disc  22 . For example, a track  28 A and a track  28 B next to the track  28 A are on the outer circle, and a track  28 C is on the inner circle. The sliding track  14  is fixed along the radial line DO of the optical disc  22 , and the pickup head  16 , sliceable along the sliding track  14 , can slide in both directions along the sliding track  14  so as to access data on the optical disc  22 . The pickup head  16  generates a laser to a lower surface  26  of the optical disc  22 , and the optical disc drive  10  analyzes the data recorded on the optical disc  22  according to the laser reflected to the pickup head  16 . In the recordable optical disc drive, a laser generated by the pickup head  16  to record data onto the tracks  24  is also used. When the motor  12  drives the optical disc  22 , the tracks on the optical disc  22  pass by the pickup head  16  as the optical disc  22  rotates. To access data on different tracks, the pickup head  16  slides along the sliding track  16  to different positions according to the different tracks. 
     The control circuit  18  controls the sliding of the pickup head  16 , and receives the data read by the pickup head  16 . In a recordable optical disc drive, the control circuit  18  also records data onto the optical disc  22  with the pickup head  16 . In addition, the control circuit  18  outputs a drive signal  34  to the drive circuit  20 , and the drive circuit  20  transfers the drive signal  34  to a corresponding signal that controls the rotational speed of the motor  12 , then the motor  12  adjusts the rotational speed according to the corresponding signal outputted by the drive circuit  20 . 
     Because data is recorded on the optical disc with great density, it is necessary to coordinate performance of the mechanical and electronic apparatuses in the optical disc drive  10  before it accesses the data on the optical disc  22 , and especially before it records data onto the optical disc  22 . Furthermore, due to a special coding of the data recorded on the optical disc, even if the operation of the electronic apparatus is not perfect and reads a certain part of the data incorrectly, the optical disc drive  10  performs functions of error checking and recovery so as to analyze erroneous parts of the data according other parts of the data. 
     To control the optical disc drive  10  to record data onto the optical disc  22 , the recordable optical disc is specially designed to assist the coordination between mechanical and electronic apparatus while the optical disc drive  10  records data onto the recordable optical disc. Refer to  FIG. 2  and  FIG. 3 .  FIG. 2  and  FIG. 3  are structure diagrams of a recordable optical disc. As shown in  FIG. 2 , the optical disc comprises the track  24  around the center of the optical disc  22 , and on the recordable optical disc, the track  24  is formed with a data track  30 A and wobble tracks  30 B distributed on both sides of the data track  30 A (as shown in region  1 A of  FIG. 2 ). The data track  30 A and lines  33  of the wobble tracks  30 B spiral around the center of the optical disc  22 . As shown in region  1 A of  FIG. 2 , the wobble tracks  30 B periodically differ from the lines  33  in two regions WT 1  And WT 2  having different lengths. Refer to region  1 B of  FIG. 2  and  FIG. 3 , which is the three-dimensional structure of region  1 B, the data track  30 A is for recording data along discontinues spreading recording marks  32  (pits, for example) with different lengths, the wobble tracks  30 B being formed with a continuous spreading pre-groove. When the track  24  passes the pickup head, the pickup head accesses data on the data track  30 A and sweeps the pre-groove along the lines  33  of the wobble tracks  30 B at the same time. As shown in  FIG. 3 , because the intensities of lasers reflected from high parts and low parts of the pre-groove are different, when the pickup head  16  passes over the pre-groove along the lines  33  of the wobble tracks, it reads out signals with different intensities according to the reflected lasers. The cycle of of strong signals and weak signals is related to the lengths of the regions WT 1  And WT 2 . The optical disc  22  is used to code and record wobble data onto the wobble tracks  30 B according to different lengths of the regions WT 1  And WT 2 . The optical disc drive  10  analyzes the laser signals reflected from the pre-groove so as to read out the wobble data recorded on the wobble tracks  30 B from the cycle of strong signals and weak signals. 
     The data track of a recordable optical disc is used for recording user data, and the wobble data on the wobble tracks is used to record data related to standard of data on the optical disc  22 . For example, the wobble data on the wobble tracks is used to record positions of a plurality of frames, which divide the tracks  24  and are used to record certain data, so as to assist the optical disc drive  10  to correctly record data onto corresponding frames. The data track on a blank recordable optical disc does not initially record with any data, thus, it is necessary for the optical disc drive  10  to read the standard of data from the wobble data recorded on the wobble tracks. When the data track does have recorded data, while the optical disc drive records new data onto the data track, it still has to read the standard of data from the wobble data so as to record new data onto correct frames. When the optical disc drive  10  needs to record data onto certain frame, it has to know the position of the frame and generate a recording clock synchronized with the frame according to the wobble data so as to control the pickup head to record each byte of the data onto the frame. On the data track, the different lengths of the recording marks represent different numbers of bytes. To correctly represent corresponding number of bytes with recording marks with proper lengths, the optical disc drive  10  determines how long the pickup head  16  remains emitting recording laser based on the recording clock. Once the recording clock is synchronized with frames defined by the wobble data, the optical disc drive  10  can record each byte of data with proper length onto the corresponding frame. 
     As stated previously, it is necessary to coordinate performances of mechanical and electronic apparatuses in the optical disc drive  10  before it accesses the data on the optical disc  22 . For example, while a rotational speed of the motor is higher and makes a certain frame pass the pickup head with a higher linear velocity, the optical disc drive  10  controls the pickup head  16  accordingly to output a recording clock with a higher frequency so as to record data onto the frame correctly. To access data on the optical disc  22  smoothly, the optical disc drive  10  coordinates operation of mechanical and electronic apparatuses under a certain procedure. Refer to  FIG. 4 .  FIG. 4  is a flowchart of mechanical and electrical coordination procedure  100  before the optical disc drive  10  begins to record data. The procedure  100  is especially suitable for an optical disc drive operating under a constant linear velocity. The optical disc drive operating under a constant linear velocity controls tracks on the inner circle (ex.  28 A and  28 B of  FIG. 1 ) and on the outer circle (ex.  28 C of  FIG. 1 ) to move past the pickup head  16  with same linear velocity. Therefore, the rotational speed of the motor  12  is faster as the pickup head  16  is accessing tracks on the inner circle (ex.  28 C of  FIG. 1 ), and the rotational speed of the motor  12  is slower as the pickup head  16  is accessing tracks on the outer circle (ex.  28 A of  FIG. 1 ) so as to control tracks on the inner circle and on the outer circle to pass the pickup head  16  with same linear velocity. Because tracks on the inner circle and on the outer circle pass the pickup head  16  with the same linear velocity, the optical disc drive  10  operating under a constant linear velocity accesses data on different tracks with the same transmission rate. Therefore, it is more stable to access data and more correct to read/record data. On the contrary, the mechanical and electronic coordination procedure of the prior art is more complex because the rotational speed of the motor  12  has to change while data on different tracks are accessed under a constant linear velocity. As shown in  FIG. 4 , the procedure  100  of the prior art comprises: 
     Step  102 : Start to trace tracks for recording data. Before a user controls the optical disc drive to slide the optical pickup head  16  to a position (called the “target position” hereafter) corresponding to a certain site on the track  24  and record data onto the optical disc  22 , the user can perform tests, such as pre-recording data onto the inner area of the optical disc. 
     Step  104 : As stated previously, the rotational speed of the motor  12  has to change while data on different tracks are accessed under a constant linear velocity. After determining the certain site for recording data, the motor  12  starts to adjust the rotational speed according to a rotational speed corresponding to the track where the certain site located. Meanwhile, the pickup head  16  remains moving toward the target position corresponding to the certain site. While the motor  12  adjusts the rotational speed, the control circuit  18  monitors stability of the rotational speed of the motor  12 . If the rotational speed is stable then execute step  106 , if the rotational speed is unstable then repeat step  104  until the rotational speed becomes stable. According to the prior art, the optical disc drive  10  starts to adjust the rotational speed of the motor  12  when there is a predetermined distance between the pickup head  16  and the target position, then repeats step  104  to check if the rotational speed of the motor has becomes stable. The control circuit  18  determines the rotational speed of the motor  12  with the drive signal  34  outputted to the drive circuit  20  by the control circuit  18 . 
     Step  106 : Start to synchronize the recording clock with the wobble data. As stated previously, the recording clock has to synchronize with the frame defined by the wobble data so as to record data onto the optical disc  22  correctly. After the rotational speed of the motor  12  is stable, the optical disc drive  10  adjusts a frequency of the recording clock according to the wobble data read from the optical disc  22  so as to remain synchronizing the recording clock with the wobble data. Before executing step  108 , repeat step  106  until the recording clock has synchronized with the frame defined by the wobble data. Meanwhile, the pickup head  16  remains moving toward the target position. 
     Step  108 : Examine if the pickup head  16  overtakes the target position. If it does not, execute step  110 , and if it does, slide the pickup head  16  backward and repeat steps  102 ,  104 , and  106 . 
     Step  110 : Start to record data onto tracks of the optical disc  22  corresponding to the target position with the pickup head  16 . 
     Refer to  FIG. 5 .  FIG. 5  is a diagram of position of the pickup head  16  on the sliding track  14  and sequence of related signals when executing the steps shown in  FIG. 4 . Region  5 A of  FIG. 5  shows different positions of the pickup head  16  on the sliding track  14  at different times, the horizontal direction representing the position of the pickup head. A wave pattern  37  and a wave pattern  34  of  FIG. 5  separately represent a wave pattern of tracking error and a wave pattern of drive signal  34 , horizontal direction of the two wave patterns representing time, the vertical direction of the two wave patterns representing intensity of signal. The wave pattern  37  of tracking error represents how many tracks the pickup head  16  has crossed, for example, a period TO of  FIG. 5  represents that the pickup head  16  has crossed a track. As stated previously, the control circuit  18  of  FIG. 1  controls the drive circuit  20  to change the rotational speed of the motor  12  with the drive signal  34 , and changes the intensity of the drive signal  34  to adjust the rotational speed of the motor  12  according to the read-out data from the pickup head  16 . Therefore, the wave pattern of drive signal  34  can represent the rotational speed of the motor  12 . 
     Assuming a position of the pickup head  16  on the sliding track  14  is a position Pp 0  (shown in  FIG. 5 ) corresponding to the track  28 C of  FIG. 1  when executing step  102 , a user outputs a recording instruction to the optical disc drive  10  to record data onto the track  28 B corresponding to a position Pp 3  (a target position) on the sliding track  14  through a computer. After receiving the recording instruction, the optical disc drive  10  starts to control the pickup head  16  to slide from the position Pp 0  to the position Pp 3 . According to the procedure  100  of the prior art, the optical disc drive  10  begins to execute step  104  and step  106  when there is a predetermined distance between the pickup head  16  and the target position. In this case, the predetermined distance is D 0 . According to the target position Pp 3  and the predetermined distance D 0 , the optical disc drive  10  determines a beginning position Pp 1  where it begins to execute step  104  and  106 . During executing step  102 , the optical disc drive  10  controls the pickup head  16  to slide from the position Pp 0  to the beginning position Pp 1 . The pickup head  16  performs a long distance track crossing when the distance between the position Pp 0  and the beginning position Pp 1  is longer, thus, the wave pattern  37  of tracking error is more concentrated during a period Tp 1 . Then, the pickup head  16  performs a short distance track crossing during a period Tp 2 . Finally, the pickup head  16  performs track crossing between several tracks to slightly adjust its position before it has arrived at the beginning position to complete step  102 , and starts to execute step  104  from the beginning position Pp 1 . 
     The rotational speed of the motor  12  varies to access data on different tracks with the optical disc drive  10  operating under a constant linear velocity. While executing step  102 , the rotational speed of the motor  12  corresponds to the track  28 C and is relatively fast, and while the optical disc drive  10  records data onto the track  28 B, the rotational speed of the motor  12  changes to a corresponding slower speed. When adjusting the rotational speed of the motor  12  during step  104 , the pickup head  16  remains moving toward the target position Pp 3 . As shown in the wave pattern  34 , the control circuit  18  changes the drive signal  34  to reduce the rotational speed of the motor  12  so as to change the rotational speed of the motor  12  to the rotational speed of the track corresponding to the target position Pp 3 . Because the control circuit  18  adjusts the drive signal  34  according to the data read from the pickup head  16 , when the rotational speed of the motor  12  is not stable, the drive signal  34  changes to compensate the change of the rotational speed of the motor  12 . The optical disc drive  10  determines a predetermined range, such as a range between L 1  and L 2  of  FIG. 5 . When the wave pattern of the drive signal  34  remains within the range between L 1  and L 2 , a change of the rotational speed of the motor  12  is close to a tolerant range of speed corresponding to the target position, and thus, the rotational speed of the motor  12  stably changes to a rotational speed corresponding to the target position (the purpose of step  104 ). 
     When executing step  104 , the predetermined distance D 0  is divided into two predetermined distances D 1  and D 2 . The predetermined distance D 1  is for executing step  104  when the motor  12  stably changes to the rotational speed corresponding to the target position Pp 3 , and the predetermined distance D 2  is for executing step  106 . During the period the pickup head  12  slides from the beginning position Pp 1  to the position Pp 2  for the predetermined distance D 1 , the optical disc drive  10  executes step  104  at the same time. If the rotational speed of the motor  12  becomes stable when the pickup head  12  has slid to the position Pp 2 , the pickup head  12  begins to execute step  106  from the position Pp 2 . As shown in  FIG. 5 , because the pickup head  12  slides smoothly along the track  24  toward the position Pp 2  during the period Tp 4  of sliding from the beginning position Pp 1  to the position Pp 2 , the wave pattern  37  remains straight and no track is crossed, and the wave pattern of the drive signal  34  changes to remain in the range between L 1  and L 2 . 
     After the rotational speed of the motor  12  has become stable, the optical disc drive  10  executes step  106  and adjusts the frequency of the recording clock according to the wobble data read out from the optical disc  22  so as to synchronize the recording clock with the wobble data during the period when the pickup head  12  slides from the position Pp 2  to the target position Pp 3 . When the optical disc  22  synchronizes the recording clock with the wobble data as the pickup head  12  arrives at the target position Pp 3 , the step  106  is successfully executed. Hereafter, the optical disc drive  10  executes step  108  and step  110 , and starts to record data onto the target position Pp 3  of the optical disc  22  when executing step  110 . 
     The procedure  100  according to the prior art provides the optical disc drive  10  with predetermined distances D 1  and D 2  for giving more time to the optical disc drive  10  to adjust the rotational speed of the motor  12  and synchronize the recording clock with the wobble data. Generally speaking, the lengths of the predetermined distances D 1  and D 2  are determined according to a pre-written program of the control circuit  18 . It is simple to predict the time for synchronizing during step  106  and the length of the predetermined distance D 2 , because synchronizing is only about the performance of the electronic apparatus when executing step  106 . On the contrary, the time for stabilizing the rotational speed of the motor  12  varies significantly during step  104 , so it is difficult to predict and set the length of the predetermined distance D 1 . This is especially so recently, as electronic apparatuses (ex. control circuit  18 ) and mechanical apparatuses (ex. motor  12 ) of optical disc drives are mainly produced at different factories. It is more difficult for the factories that produce the electronic apparatus to estimate the predetermined distance. If the rotational speed of the motor  12  is not stable after the pickup head  16  has slid the predetermined distance D 1 , the optical disc drive  10  continues to execute step  104  though the pickup head  16  has overtaken the position Pp 2  until the rotational speed of the motor  12  becomes stable. Therefore, step  106  is delayed, and the pickup head  16  has overtaken the target position Pp 3  when the optical disc drive  10  has completed step  106 , thus, the pickup head  16  has to slide backward and repeat steps  102 , 104 , and  106 . 
     Refer to  FIG. 6 , which is similar to  FIG. 5 . As shown in  FIG. 6 , the pickup head  16  is assumed to slide from a position Pp 0  to a target position Pp 3  for recording data while executing step  102 . Likewise, the optical disc drive  10  determines a beginning position Pp 1  based on the target position Pp 3  and predetermined distances D 1  and D 2 . During step  102 , the pickup head  16  crosses tracks to the beginning position Pp 1  after it goes through a period Tp 1  to a period Tp 3 . The optical disc drive  10  executes step  104  as the pickup head  16  starts to slide from the beginning position Pp 1 . However, a wave pattern of the drive signal  34  still exceeds a range of a tolerant value between L 1  and L 2  if the rotational speed of the motor  12  is not stable after the pickup head  16  has slid the distance D 1  and arrived at the position Pp 2  (as shown in  FIG. 6 ). Then, the optical disc drive  10  continues to execute step  104 , and the pickup head  16  will overtake the position Pp 2  and continue to slide toward the target position Pp 3 . If the rotational speed of the motor  12  is not stable until the pickup head  16  has slid to a position Pp 4 , the pickup head  16  continues to slide until step  106  and wait until the control circuit  18  has synchronized the recording clock with the wobble data at the same time. Because the optical disc drive  10  cannot complete step  104  during the period when the pickup head  16  slides for the predetermined distance D 1 , the pickup head slides a distance longer than the predetermined distance D 1  and arrives at a position Pp 4  when the optical disc drive  10  has completed step  104 . Due to the delay of step  104 , the pickup head  16  overtakes the target position Pp 3  and arrives at a position Pp 5  when the optical disc drive  10  has completed step  106  during a period Tp 5 . The optical disc drive  10  determines that the position of the pickup head  16  has overtaken the target position Pp 3  during step  108 . Then, the optical disc drive  10  performs a long distance track crossing and a short distance track crossing, and slightly adjusts the position of the pickup head  16  so as to slide the pickup head  16  to a position Pp 6  before the target position Pp 3 . Again, the optical disc drive  10  repeats step  104  and  106  during the period when the pickup head  16  slides from the position Pp 6  to the target position Pp 3 . 
     According to the prior art, the optical disc drive  10  cannot complete step  104  during the period when the pickup head  16  slides for the predetermined distance D 1 , and wastes significant amounts of time to trace tracks, stabilize the rotational speed of the motor  12 , and synchronize the recording clock with the wobble data. Therefore, the length of the predetermined distance D 1  has to be long enough so as to complete step  104  once. However, as stated previously, the time for stabilizing the rotational speed of the motor  12  varies substantially during step  104 , so it is difficult to predict and set the length of the predetermined distance D 1 . Thus, to make sure the length of the predetermined distance D 1  is long enough, the length of the predetermined distance D 1  is extended as long as possible. However, the actual time (the time “t 0 ” shown in  FIG. 5 ) for completing step  104  might be much shorter than the time (the position “Pp 2 ” shown in  FIG. 5 ) for the pickup head  16  to finish the predetermined distance D 1  hereafter, and the optical disc drive  10  wastes time sliding for the predetermined distance D 1  before it executes step  106 . On the other hand, if the length of the predetermined distance D 1  is too short, the optical disc drives  10  wastes more time because the pickup head  16  overtakes the target position. 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the claimed invention to provide a method for adapting to a change of time for stabilizing a rotational speed of a motor by performing a pause state and related apparatus to solve the above-mentioned problems. 
     According to the claimed invention, a pickup head is slid back and forth in a pause state until a rotational speed of a motor becomes stable, then, the pickup head is slid toward a target position where data is recorded. During the period when the rotational speed of the motor is adjusted, the pickup head slides back and forth only in a range of several tracks, thus, the pickup head will not overtake the target position during the following steps even when it takes more time to adjust the rotational speed of the motor. According to the claimed invention, once the rotational speed of the motor has become stable, an optical disc drive starts to synchronize the recording clock with the wobble data. No matter how long it takes to adjust the rotational speed of the motor, the optical disc drive adapts to this and performs mechanical and electronic coordination with more efficiency so as to ensure that the data will be correctly accessed. 
     These and other objectives of the claimed invention will no doubt 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 functional diagram of an optical disc drive according to the prior art. 
         FIG. 2  and  FIG. 3  are structure diagrams of a recordable optical disc. 
         FIG. 4  is a flowchart of mechanical and electronic coordination before the optical disc drive shown in  FIG. 1  starts to record data. 
         FIG. 5  and  FIG. 6  are diagrams of pickup head positioning and sequence of related signals when executing steps shown in  FIG. 4 . 
         FIG. 7  is a functional diagram of an optical disc drive according to the present invention. 
         FIG. 8  is a flowchart of mechanical and electrical coordination before the optical disc drive shown in  FIG. 7  starts to record data. 
         FIG. 9  is a diagram of pickup head positioning and sequence of related signals when performing steps shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 7 . Being similar to the optical disc drive  10  of  FIG. 1 , an optical disc drive  50  of  FIG. 7  comprises a motor  52  fixed inside the optical disc drive  50 , a sliding track  54  fixed inside the optical disc drive  50 , a pickup head  56  for accessing data on the optical disc  22 , a drive circuit  60 , and a control circuit  58 . The motor  52  is used to drive the optical disc  22 . The pickup head  56  is moveable along the sliding track  54  and can slide in both directions along an arrow A 1  so as to access data on the track  24  of the optical disc  22 . The control circuit  58  is used to control the optical disc drive  50 , control the pickup head  56  to slide along the sliding track  54 , receive the read data from the pickup head  54 , and record data onto a track (ex.  28 A) of the optical disc  22  with the pickup head  56  according to a recording clock. Further, the control circuit  58  outputs a drive signal  64  to the drive circuit  60  so as to control the rotational speed of the motor  52  through the drive circuit  60 . 
     In contrast to the prior art, the present invention provides the optical disc drive  50  with a new procedure for mechanical and electronic coordination so as to solve the problems of the prior art. 
     Refer to  FIG. 8 .  FIG. 8  is a flowchart of mechanical and electrical coordination according to a procedure  200  of the present invention. The procedure  200  comprises: 
     Step  202 : Start to trace tracks for recording data. Before a user controls the optical disc drive  50  to slide the optical pickup head  56  to a target position corresponding to a certain site on the optical disc  22  and record data onto the optical disc  22 , they can pre-record test data onto the inner tracks of the optical disc. 
     Step  204 : Start to adjust a rotational speed of the motor  52  according to a rotational speed corresponding to the track on where the certain site is located. While the motor  52  adjusts the rotational speed, the control circuit  18  monitors a stability of the rotational speed of the motor  52 . If the rotational speed remains unstable, execute step  205  until the rotational speed becomes stable. When the rotational speed becomes stable, execute step  206 . 
     Step  205 : During the period when the rotational speed of the motor is adjusted, the pickup head  56  is controlled to slide back and forth within a predetermined recovering distance until the rotational speed of the motor  56  becomes stable. Step  205  is establishes a pause state. While an ordinary optical disc drive stops to display data on an optical disc for a moment, the pickup head slides back and forth within a track under the present invention pause state until the optical disc drive displays data on the optical disc. Further, according to the present invention, a predetermined time is used during step  205 . When the pickup head  56  slides toward the target position from a beginning position for the predetermined time, the control circuit  58  compares a distance between the pickup head  56  and the beginning position with the predetermined recovering distance. If the distance between the pickup head  56  and the beginning position is longer than the recovering distance and the rotational speed of the motor  52  is not yet stable, slide the pickup head  56  opposite the direction of the target position so as to slide the pickup head back to approximately the beginning position. If the distance between the pickup head  56  and the beginning position is shorter than the recovering distance, the pickup head  56  continues to slide toward the target position even though the rotational speed of the motor  52  is not yet stable. As the predetermined time again elapses, again compare the distance between the pickup head  56  and the beginning position with the predetermined recovering distance. If the distance between the pickup head  56  and the beginning position is longer than the recovering distance and the rotational speed of the motor  52  is not yet stable, slide the pickup head  56  opposite the direction of the target position again so as to slide the pickup head back to the beginning position. 
     Step  206 : After completing step  204 , continue to slide the pickup head  56  toward the target position, meanwhile, synchronize the recording clock with the wobble data so as to synchronize the recording clock with the wobble data read from the optical disc  22 . During step  206 , the control circuit  58  detects if the recording clock remains synchronized with the wobble data. Before executing a step  208 , repeat step  206  until the recording clock remains synchronized with the frame defined by the wobble data. According to the present invention, there is a predetermined distance before the target position, and step  206  is executed while the pickup head  56  slides for this predetermined distance. 
     Step  208 : The pickup head  16  moves toward the target position while executing step  206 . After completion of step  206 , examine if the pickup head  56  overtakes the target position. If it does not, execute step  210 , and if it does, return to step  202 . As stated previously, because synchronizing only concerns the performance of the electronic apparatus when executing step  206 , it is simple to predict the time for synchronizing during step  206 . And, according to the present invention, the pickup head  56  remain sliding within the predetermined distance by performing the pause state while executing step  204 . Therefore, after execution of steps  204  and  206 , the pickup head  56  will not overtake the target position as the prior art does. However, the procedure  200  of the present invention can selectively execute step  208  to check if the position of the pickup head  56  has overtaken the target position after executing step  204  and  206  for the sake of insurance. 
     Step  210 : Start to record data onto tracks of the optical disc  22  corresponding to the target position with the pickup head  56 . 
     For more information on the above process, refer to  FIG. 9 .  FIG. 9  is a diagram of positions of the pickup head  56  on the sliding track  54  and sequence of related signals when executing the procedure  200 . Similar to  FIG. 5 , a wave pattern of tracking error  67  of  FIG. 9  represents how many tracks the pickup head  56  crosses, and a wave pattern of drive signal  64  of  FIG. 9  represents how stable the rotational speed of the motor  52  is. Further, a horizontal axis of the two wave patterns represents time, and a vertical axis of the two wave patterns represents intensity of signal. Region  9 A of  FIG. 9  shows the different positions of the pickup head  56  on the sliding track  54  at different times. Assuming the position of the pickup head  56  is P 0  (a position corresponding to the track  28 C of  FIG. 7 , for example.) when beginning to execute step  202 , and the target position where to record data onto is P 3  (a position corresponding to the track  28 B of  FIG. 7 , for example.) According to the procedure  200 , the optical disc drive  50  executes steps  204  and  206  when the pickup head  56  slides for a predetermined distance D 3 . In this case, the predetermined distance is D 0 . According to the target position P 3  and the predetermined distance D 3 , the optical disc drive  50  determines a beginning position P 1 . During execution of step  202 , the control circuit  58  controls the pickup head  56  to slide to the beginning position P 1  while performing a long distance track crossing of a period T 1 , a short distance track crossing of a period T 2 , and a slight position adjustment of a period T 3 . After the pickup head  56  arrives at the beginning position P 1 , the optical disc drive  50  begins to execute step  204  and  206 . When executing step  204 , the optical pickup head  56  begins to adjust the rotational speed of the motor  56 , meanwhile, the pickup head  56  slides back and forth between the beginning position P 1  and a position P 2 , and the distance between P 1  and P 2  is a recovering distance D 4 . The recovering distance can be a track (for example, D 6  of  FIG. 7 ) or several tracks. During period T 4  when executing step  204 , the discontinuous wave pattern of tracking error  67  represents the pickup head  56  sliding from the position P 2  to the beginning position P 1  for the recovering distance D 4 . As the pickup head  56  slides from the beginning position P 1  to the position P 2 , it slides along the track  24  smoothly and does not have to cross tracks, thus, the wave pattern of tracking error  67  becomes straight similar to the situation of the period Tp 4  of  FIG. 5 . On the contrary, as the pickup head  56  slides from the position P 2  to the beginning position P 1 , it crosses tracks, and thus, the wave pattern of tracking error  67  rises and falls. Further, because the pickup head  56  slides back and forth between the beginning position P 1  and the position P 2 , the straight parts and the oscillating parts of the wave pattern of the tracking error  67  are interlaced, thus, the oscillating parts of the wave pattern of the tracking error  67  are discontinuous. According to  FIG. 9 , the position of the pickup head  56  remains between the beginning position P 1  and the position P 2  no matter how long it takes to execute step  204 . Similar to the prior art, once the drive signal  64  remains between L 1  and L 2 , the change of the rotational speed of the motor  56  is within a range of a tolerant value. After the rotational speed of the motor  56  becomes stable during the period T 4 , the control circuit  58  controls the pickup head  56  to stop sliding between the beginning position P 1  and the position P 2 , and continue to slide toward the target position P 3 . While the pickup head  56  slides for a distance D 5 , the optical disc drive  50  begins to execute step  206  at the same time. After completing step  206  during a period T 5 , the pickup head  56  slides to the target position P 3  and begins to execute step  210  to record data onto the optical disc  22 . 
     According to the prior art, because the pickup head remains sliding toward the target position as the optical disc drive adjusts the rotational speed of the motor, the pickup head needs to slide for the predetermined distance D 1  when the optical disc drive adjusts the rotational speed of the motor (refer to  FIG. 5  and  FIG. 6  and the related description). However, the time for stabilizing the rotational speed of the motor varies substantially during step  104 . As electronic apparatuses (ex. the control circuit) and mechanical apparatuses (ex. the motor) are mainly produced by different factories, it is difficult to predict and set the length of the predetermined distance D 1 . When the predetermined distance D 1  is too long, the optical disc drive  50  wastes too much time on adjusting the rotational speed of the motor and synchronizing the recording clock with the wobble data. When the predetermined distance D 1  is too short, the pickup head overtakes the target position as the rotational speed of the motor becomes stable, and wastes more time in re-execution of the procedure  100 . Compared with the prior art, during the period when the optical disc drive  50  adjusts the rotational speed of the motor  52 , the pickup head  56  slides back and forth within the range of the recovering distance. Therefore, it is totally unnecessary for the present invention to have a predetermined distance for adjusting the rotational speed of the motor. Furthermore, the optical disc drive  50  of the present invention can adapt the changes of the time for adjusting the rotational speed of the motor. If the actual time for adjusting the rotational speed of the motor is shorter, the frequency of the pickup head  56  sliding back and forth between the position P 1  and the position P 2  is less, and if the actual time for adjusting the rotational speed of the motor is longer, the frequency of the pickup head  56  sliding back and forth between the position P 1  and the position P 2  is higher. After completing step  204 , the pickup head  56  can continue to slide toward the target position and execute step  206 . And, because synchronizing only concerns the performance of the electronic apparatus when executing step  206 , it is straightforward to predict an accurate time for synchronizing during step  206  and the length of the predetermined distance D 5 . Therefore, as the pickup head  56  slides for a predetermined distance D 3  (D 3 =D 4 +D 5 ), the optical disc drive  50  completes step  204  and  206  accurately, and the mechanical and electronic coordination is completed just before the pickup head  56  arrives at the target position. Compared with the prior art, the optical disc drive  50  of the present invention adapts the changes of the time for stabilizing the rotational speed of the motor, and thus, provides better performance and stability. 
     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 by the metes and bounds of the appended claims.