Abstract:
A method and apparatus for eliminating errors in a seek operation on a recording medium are provided. Given a target address on a recording medium, a reading device is moved to seek the target address, and it is determined whether or not a signal is read out at the location to which the reading device has been moved. If the expected signal is not available at that location, by extending a variable frequency range of an oscillator clock of a PLL circuit or by increasing a track gap between the target address and the track to which the reading device jumps initially to seek the target address, the oscillator clock can be phase-synchronized to EFM signal from the recording medium reliably, resulting in reduction of the seek errors.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to method and apparatus for eliminating errors in a seek operation on a recording medium. 
     2. Background of the Related Art 
     In a disk apparatus, such as a disk drive, an optical pickup is moved to a target address on an optical disk loaded therein to read out data from the target address. This is called a seek operation.  FIG. 1  shows a flow chart of a related art seek operation. 
     Specifically, given a target address, the present address of the optical pickup is obtained, in step S 0 , and the number of tracks to move or jump is calculated, in step S 1 . In step S 1 , the number of tracks to move is calculated based on a difference between the present track and the first inner track of a target track containing the target address (hereinafter, referred to as the “pre-target track”). If the number of tracks to move is zero, in step S 2 , it is determined that the optical pickup has reached the pre-target track. Otherwise, the seek operation continues so that the optical pickup is moved by the re-calculated number of tracks and then address information, such as sub-Q, is read out again at that address on the optical disk, in step S 3 . 
     If the target address has not been sought for a predetermined period of time, a seek retry counter, ‘SEEKRetryCnt’ is increased by 1, in step S 4 . And then, if ‘SEEKRetryCnt’ is smaller than a predetermined seek retry number of times, ‘SEEK_RETRY_LIMIT’, in step S 5 , steps S 0  and S 1  are repeated; otherwise, it is determined that a seek error occurs, in step S 6 . The seek operation error may be caused by a servo-control error or a delay of phase-locking of a phase-locked loop (PLL) circuit by which a clock of a PLL circuit is phase-synchronized to a signal read out from the optical disk. The latter case is described below in detail with reference to  FIG. 2 . 
     Given a target address CT, on the track # 21  in  FIG. 2 ), the optical pickup is moved to the pre-target track (track # 22  in  FIG. 2 ). A laser beam of the optical pickup is positioned on the pre-target track and then reaches near the target address by performing a tracking operation along the spiral track. During the tracking operation, eight-to-fourteen modulation (EFM) signals are read out from those tracks. By phase-locking a clock of the PLL circuit to the EFM signal, sub-Q data can be read out and used to determine whether or not the target address is sought. 
     Phase synchronization between the clock of the PLL circuit and the EFM signal may fail during the pickup transition from the pre-target track to the target address (T 1  in  FIG. 2 ), which is caused mainly by a large phase difference between them. If this occurs, and thus if the phase synchronization is completed on other tracks passing the target address (for example, track # 23 ), the same operations as before are executed once so as to seek the target address by moving the optical pickup to the pre-target track and performing the phase synchronization of the PLL clock. 
     If phase synchronization between the clock of the PLL circuit and the EFM signal fails again during the pickup transition to the target address, the same seek operations including the optical pickup movement and the PLL clock phase-locking are repeated until the target address is sought. A seek error occurs if the seek operation is not made for a predetermined number of times or a predetermined period of time. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
     In order to achieve at least the above objects, in whole or in part, and in accordance with the purposes of the invention, as embodied and broadly described herein, there is provided a method of eliminating errors in a seek operation on a recording medium in accordance with an embodiment of the invention that includes moving a reading device to a target location on a recording medium, checking whether or not a signal is read out at the target location to which the reading device has been moved, and extending a variable frequency range of a synchronization clock of a PLL circuit based on the checking result, the synchronization clock being phase-synchronized to an output signal of the reading device. 
     To further achieve at least the above objects, in whole or in part, and in accordance with the purposes of the invention, as embodied and broadly described herein, there is provided an apparatus for reading, reproducing, or recording a recording medium in accordance with an embodiment of the invention that includes a servo-controller configured to move a reading device to a target location on a recording medium, a signal processor configured to check whether or not a signal is read out at the target location to which the reading device has been moved, and a controller configured to extend a variable frequency range of a synchronization clock of a PLL circuit based on the checking result, the synchronization clock being phase-synchronized to an output signal of the reading device. 
     To further achieve at least the above objects, in whole or in part, and in accordance with the purposes of the invention, as embodied and broadly described herein, there is provided a method of eliminating errors in a seek operation on a recording medium in accordance with an embodiment of the invention that includes moving a reading device a predetermined first track gap to a target track, checking whether or not a signal is read out at the target track to which the reading device has been moved, and moving the reading device to another inner track of the target track based on the checking result, the another inner track being located on an inside of the target track by a second predetermined track gap that is larger than the first predetermined track gap. 
     To further achieve at least the above objects, in whole or in part, and in accordance with the purposes of the invention, as embodied and broadly described herein, there is provided an apparatus for reading, reproducing, or recording a recording medium in accordance with an embodiment of the invention that includes a servo-controller configured to move a reading device a predetermined first track gap to a target track, a signal processor configured to check whether or not a signal is read out at the target track to which the reading device has been moved, and a controller configured to move the reading device to another inner track of the target track based on the checking result, the another inner track being located on an inside of the target track by a second predetermined track gap that is larger than the first predetermined track gap. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
         FIG. 1  is a flow chart of a related art seek operation; 
         FIG. 2  illustrates a seek error that occurs due to delay of phase-locking in a PLL circuit in the seek operation of  FIG. 1 ; 
         FIG. 3  is a partial block diagram of a disk drive in accordance with an embodiment of the invention; 
         FIG. 4  is a flowchart of a seek error elimination method according to an embodiment of the invention; 
         FIG. 5  illustrates a relation between the frequency of output clock and input voltage in a voltage-controlled oscillator; and 
         FIG. 6  is a flowchart of a seek error elimination method according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Now, a method and apparatus for eliminating errors in a seek operation on a recording medium in accordance with embodiments of the invention will be described in detail with reference to the drawings, in which like reference numerals have been used to designate like elements. The invention is shown implemented in an optical disk drive. However, it may also be implemented in other apparatus for reading, reproducing, or recording a recording medium. 
       FIG. 3  is a partial block diagram of a disk drive according to an embodiment of the invention. The disk drive comprises an optical pickup  31  for reading out signals from an optical disc loaded therein, an RF circuit  32  for producing an EFM signal from a signal that is read out by the optical pickup and producing both a tracking error (TE) signal and a focusing error (FE) signal, a PLL circuit  50  for producing a synchronization clock that is phase-locked to the EFM signal, a DSP  33  for demodulating the EFM signal into digital data by using the synchronization clock; an interface  34  for communicating with an external device such as personal computer (PC), a servo  35  for servo-controlling the objective lens attached to the optical pickup, disk rotation, and movement of the optical pickup; and a microcomputer  40  for processing the reproduction and seek operation. 
     The PLL circuit  50  comprises a phase detector (PD)  51  that detects a phase difference between the EFM signal and a voltage-controlled oscillator (VCO) clock and produces a signal in proportion to the phase difference, a loop filter  52  for producing a low-pass component of the phase difference-proportionate signal; a VCO  53  for generating and producing a clock whose frequency is proportional to the input voltage, and a frequency divider  54  for frequency-dividing the VCO clock. The microcomputer  40  adjusts a gain of the phase detector  51  by using a gain control signal, as needed, so that the range of the phase difference that can be locked by the PLL circuit is extended. 
       FIG. 4  is a flowchart of a seek error elimination method according to an embodiment of the invention and will be described below in detail with reference to the partial block diagram of the disk drive shown in  FIG. 3 . The flowchart and corresponding method of  FIG. 4  is applicable to other disk-related apparatus other than the disk drive shown in  FIG. 3 , such as DVD players and audio CD players. 
     Given a jump command via the interface  34 , in step S 09 , the microcomputer  40  initializes seek operation-related variables, such as ‘SEEKRetryCnt’ and ‘Gain_Adjusted’ (these variables will be described later in detail) to zeros, in step S 10 , and then detects the current address on an optical disk by reading out MM:SS:FF values contained in sub-Q frame data, in step S 11 . Then, the microcomputer  40  calculates the number of tracks to move based on the current address and the target address that has been specified by the jump command, in step S 12 . The number of tracks to move is calculated based on a difference between the current track and the first inner track of the target track containing the target address. 
     Based on the number of tracks to move calculated in step S 12 , the optical pickup  31  is moved by the servo  35 , in step S 13 . If the number of tracks to move is smaller than a predetermined number of tracks, the objective lens is controlled so that the laser beam of the optical pickup  31  reaches the target track. 
     After the pickup transition, the microcomputer  40  determines if a ‘Read_OK’ signal is input from the DSP  33 , in step S 14 . The ‘Read_OK’ signal is a signal that is produced when a VCO clock in the PLL circuit  50  is phase-synchronized to the EFM signal produced by the RF circuit  32 . Specifically, the ‘Read_OK’ signal is produced only when a frame synchronization signal has been detected from the EFM signal consecutively a predetermined number of times, which implies that the EFM signal are demodulated to a bit train successfully by using the phase-locked synchronization clock. 
     Receiving the ‘Read_OK’ signal, the microcomputer  40  determines the current address based on data frame interpreted by the DSP  33 , in step S 15 , and then examines whether or not the current address is the target address, in step S 16 . If another pickup transition is required to seek the target address, ‘SEEKRetryCnt’ is increased by 1 signifying the number of seek retrials up to now, in step S 17 , and it is then determined whether or not ‘SEEKRetryCnt’ is larger than a predetermined maximum number of times, or ‘SEEK_RETRY_LIMIT’, in step S 18 . If it is smaller than ‘SEEK_RETRY_LIMIT’, the microcomputer  40  calculates the number of tracks to move again, as in step S 12 , and then performs the subsequent steps S 13  through S 14  according to the conditions. 
     If a ‘Read_OK’ signal is not generated in step S 13 , the microcomputer  40  examines if a defect signal is produced from the RF circuit  32  and at the same time, examines if the current state is a tracking ON state, in step S 19 . The defect signal is a signal that is produced from the RF circuit  32  when RF signals are not detected for a predetermined period of time due to disk surface defects, such as fingerprints or scratches thereon. 
     If there is no defect signal in the tracking ON state, the microcomputer  40  determines that the reason why a ‘Read_OK’ signal is not generated is that the VCO clock signal has not been phase synchronized to the EFM signal read out from the disk, and thus increases the gain of the phase detector  51  in the PLL circuit  50 , in step S 20 . Since a large value of the gain increases the degree to which an output voltage is proportional to the phase difference, a range of voltage that is applied to the VCO  53  via the loop filter  52  is increased by ‘ΔV 1 +ΔV 2 ’, as shown in  FIG. 5 . As a result, a frequency range of the VCO clock is, in turn, extended by ‘Δf 1 +Δf 2 ’, as shown in  FIG. 5 . Hence, the EFM signal and the VCO clock signal that would be impossible or take considerable amount of time for phase synchronization therebetween with a frequency range Δfp can be phase-synchronized to each other in a shorter period of time. 
     Once the gain is adjusted, a ‘Gain_Adjusted’ variable is set to 1 so as to indicate that the gain has been varied. Then, ‘SEEKRetryCnt’ is increased by 1, in step S 21 , and it is examined whether or not ‘SEEKRetryCnt’ is smaller than ‘SEEK_RETRY_LIMIT’, in step S 22 . If the condition is met, the microcomputer  40  goes back to step S 14  to wait for ‘Read_OK’ signal. If ‘SEEKRetryCnt’ becomes equal to ‘SEEK_RETRY_LIMIT’, the microcomputer  40  informs the external device through the interface  34  that a seek error has occurred, in step S 30 . Then, the microcomputer  40  examines the value of ‘Gain_Adjusted’, in step S 31 , and if ‘Gain_Adjusted’ is equal to 1, the gain of the phase detector  51  is reset to the initial value, in step S 32 . By doing this, the VCO clock frequency is prevented from being varied sensitively due to high gain of the phase detector  51 , even to noise of the EFM signals that often occur in the normal condition. 
     On the other hand, if it is determined that the number of tracks to move is zero, in step S 16 , in a normal or high value of the gain, the microcomputer  40  examines the value of ‘Gain_Adjusted’, in step S 31 , and if ‘Gain_Adjusted’ is equal to 1, the gain of the phase detector  51  is reset to the initial value, in step S 32 . 
     A seek error elimination method according to another embodiment of the invention will be described below in detail with reference to  FIG. 6 .  FIG. 6  is a flowchart of another embodiment of the invention that is applicable to the disk drive of  FIG. 3 . In this embodiment, the microcomputer  40  does not use the gain control signal to eliminate the seek errors. 
     Given a jump command via the interface  34 , in step S 39 , the microcomputer  40  initializes ‘SEEKRetryCnt’ to  0  and ‘Track_gap’ to 1, in step S 40 , and then detects the current address on an optical disk by reading out MM:SS:FF values contained in sub-Q frame data, in step S 41 . Next, the microcomputer  40  calculates the number of tracks to move based on the current address and the target address that has been specified by the jump command, in step S 42 . The number of tracks to move is calculated based on a difference between the current track and one inner track that is located on the inside of the target track by the value of ‘Track_gap’. By setting ‘Track_gap’ to 1, the number of tracks to move is calculated initially on the basis of the first inner track of the target track. 
     Based on the number of tracks calculated in step S 42 , the optical pickup  31  is moved by the servo  35 , in step S 43 . If the number of tracks to move is smaller than a predetermined number of tracks, the objective lens is controlled so that the laser beam of the optical pickup  31  reaches the target track. After the pickup transition, the microcomputer  40  determines if a ‘Read_OK’ signal is input from the DSP  33 , in step S 44 . 
     Receiving the ‘Read_OK’ signal, the microcomputer  40  determines the current address based on data frame interpreted by the DSP  33 , in step S 45 , and then examines whether or not the current address is the target address, in step S 46 . If another pickup transition is required to seek the target address, ‘SEEKRetryCnt’ is increased by 1, signifying the number of seek retrials up to now, in step S 47 , and it is then determined whether or not ‘SEEKRetryCnt’ is larger than a predetermined maximum number of times, or ‘SEEK_RETRY_LIMIT’, in step S 48 . If it is smaller than ‘SEEK_RETRY_LIMIT’, the microcomputer  40  calculates the number of tracks to move again, as in step S 42  and then performs the subsequent steps S 43  through S 44  according to the conditions. 
     If a ‘Read_OK’ signal is not generated after step S 43 , the microcomputer  40  examines if a defect signal is produced from the RF circuit  32  and at the same time, examines if the current state is a tracking ON state, in step S 49 . If the defect signal is not produced in the tracking ON state, the microcomputer  40  determines that the reason why a ‘Read_OK’ signal is not generated is that the VCO clock signal has not been phase synchronized to the EFM signal read out from the disk, and thus sets ‘Track_gap’ to 2 or 3, in step S 50 , so that the number of tracks to move will be calculated based on a more inside track, in step S 42 , in the subsequent seek retry. By doing this, it takes two or three times the amount of time taken for the optical pickup to reach the target address than that of ‘Track_gap’ = 1 . Hence, the EFM signal and the VCO clock signal that would be otherwise impossible or require considerable amount of time for phase synchronization can be phase-synchronized to each other during the extended pickup transition time. 
     After step S 50 , ‘SEEKRetryCnt’ is increased by 1, in step S 51 , and then it is examined whether or not ‘SEEKRetryCnt’ is smaller than ‘SEEK_RETRY_LIMIT’, in step S 52 . If it is equal to ‘SEEK_RETRY_LIMIT’, the microcomputer  40  informs an external device through the interface  34  that a seek operation error has occurred, in step S 60 . Regardless of whether a seek operation error occurs or the target address is sought successfully, ‘Track_gap’ is reset to 1, which enables rapid phase synchronization for the pickup transition between tracks whose phase difference is relatively small by alleviating an unnecessary long transition by a large value of ‘Track_gap’. 
     The method and apparatus according to embodiments of the invention provide at least the following advantages. 
     The method and apparatus according to embodiments of the invention eliminate errors in the seek operation on a recording medium due to the time delay in phase synchronization of a PLL circuit. The method and apparatus according to embodiments of the invention further provide an effective way of eliminating errors in seek operations caused by the time delay of a PLL circuit phase-locking that occurs because the PLL circuit has been tuned initially inappropriately. 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the invention. The present teaching can be readily applied to other types of apparatuses. The description of the invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.