Patent Document

This application claims the priority of Korean Patent Application No. 2003-83615, filed on Nov. 24, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a data storage device and a method of tracking data stored in the data storage device, and more particularly, to a method of finely tracking a position of data recorded in a data storage medium using scanning probe microscopy (SPM) technology. 
     2. Description of the Related Art 
     Generally, a high-density data storage device using SPM technology includes a data storage medium, a probe, an x-y stage, a controller, and a signal processor. Data can be stored in or erased from the data storage medium. The probe includes a tip for recording or reproducing data and a cantilever on which the tip is mounted. The x-y stage moves the data storage medium, and the controller issues commands to control the data storage device. To record or reproduce high-density data, a method of tracking data with high precision is required. 
     Three different types of conventional methods of tracking a position of data have been employed to record data on or reproduce data from such a high-density data storage device using SPM technology. 
     First, the position of data can be tracked using a mechanical or electric signal of a data storage medium by distinguishing a signal of recorded data from a signal of reproduced data. This method is proposed in U.S. Pat. Nos. 5,132,934, 5,396,483, 5,856,967, and 6,370,107. The foregoing patents disclose a method of forming metal patterns or mechanical grooves on a data storage medium, but it is difficult to form sufficiently fine patterns or grooves on the data storage medium. Also, since the mechanical grooves themselves serve as a mechanism for recording and reproducing data, the practical applications of this method are limited. 
     Second, there is a method of modulating a central position of data recorded in a data storage medium by oscillating a probe or the data storage medium, as disclosed in U.S. Pat. No. 5,404,349. This method is based on a principle of modulation and demodulation by oscillating the data storage medium in a high frequency range. However, it is difficult to oscillate the data storage medium in the high frequency range. In addition, a circuit for detecting the oscillation of the data storage medium becomes complicated and detection is delayed owing to the principle of modulation and demodulation. 
     Third, a method of using a central position of data stored in a data storage medium and a relative displacement of a probe for recording or detecting the data is disclosed in U.S. Pat. Nos. 5,202,879 and 6,195,313, for example. Unfortunately, this method necessarily requires very precise recording of data patterns in the data storage medium. In particular, the method proposed in U.S. Pat. No. 5,202,879 cannot serially track data. Accordingly, the data can only be tracked at a relatively low speed. Thus, a data tracking process becomes very sensitive to the external environment. 
     SUMMARY OF THE INVENTION 
     The present invention provides a data storage device and a method of tracking data stored in the data storage device. The method can serially detect off-track errors of data in a data storage medium using a tip of a probe for recording or reproducing data, and compensate for the off-track errors through a simple compensation algorithm without the need of precise patterns. 
     According to an aspect of the present invention, there is provided a method of tracking data stored in a data storage device comprising a data storage medium on which data can be recorded and erased, a plurality of probes for scanning the data storage medium to detect data, a scanner for driving the data storage medium or the probes, and a controller for applying a control signal to the scanner. The method includes (a) oscillating the probe or the data storage medium; (b) detecting an off-track error of the probe on the data storage medium by the oscillation; and (c) adjusting a scanning position of the probe on the data storage medium to compensate for any off-track error. 
     In operation (a), the probe or the data storage medium may be oscillated according to a low-frequency generated by the controller. 
     Operation (b) may include detecting data stored on the data storage medium using the probe; generating a signal synchronized with a data position pattern of the data storage medium; and detecting an off-track error of the probe using the synchronized signal. 
     Operation (c) may include shifting a direct current level of a low-frequency signal in the controller based on a detected off-track error and applying the shifted low-frequency signal to the scanner to drive the probe. 
     According to another aspect of the present invention, there is provided a data storage device comprising a data storage medium on which data can be recorded and erased, a plurality of probes for scanning the data storage medium to detect data, a scanner for driving the probes, and a controller for controlling the scanner. Herein, the controller includes a synchronizer, which generates a signal synchronized with a data pattern of the data storage medium that is detected by one of the probes; an off-track detector, which detects an off-track error of the probe using the data pattern and the synchronized signal; a compensator, which transmits a value that is compensated for the off-track error detected by the off-track detector to the scanner; and an oscillation signal generator, which applies an oscillation signal to the scanner. 
     The data storage device may further include an interruption generator, which is connected to the synchronizer and controls operational timing of the oscillation signal generator and the off-track detector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1A  shows a data storage device; 
         FIGS. 1B and 1C  show a data region and a servo region, respectively, of the data storage device of  FIG. 1A ; 
         FIG. 1D  is a partial view of data bits in data or servo unit cells; 
         FIG. 2  illustrates a method of tracking data stored in a data storage device according to the present invention; 
         FIG. 3  shows a detailed construction of the data storage device of  FIG. 1A ; and 
         FIG. 4  shows a waveform obtained when a probe scans data bits to record data on or reproduce data from a data storage medium using the data tracking method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
       FIG. 1A  shows an example of a data storage device. Referring to  FIG. 1A , the data storage device includes a data storage medium  10  and probes  11 . The data storage medium  10  stores data, and each of the probes  11  is disposed near the data storage medium  10  and includes a tip for recording and reading data. The data storage medium  10  is positioned on a stage  12  which is driven by a scanner  13  that receives a signal from a controller  14 . Here, the scanner  13  may drive the probes  11  instead of the stage  12  to record to or reproduce data from the data storage medium  10 . 
     The data storage medium  10  is divided into N×M data regions A on which data can be recorded and H servo regions B which store information on positions of the data regions A. N×M probes  11  are provided in the data regions A, respectively, and H probes  11  are provided in the servo regions B, respectively. Generally, each of the probes  11  includes the tip ( 11   a  of  FIG. 3 ), which is in contact with a recording surface or is spaced a predetermined distance apart from the recording surface, and a cantilever ( 11   b  of  FIG. 3 ) for supporting the tip. 
       FIG. 1B  shows the data region A of  FIG. 1A , and  FIG. 1C  shows the servo region B of  FIG. 1A . Referring to  FIG. 1B , the data region A includes n×m data unit cells. Referring to  FIG. 1C , the servo region B includes n×m servo unit cells. A probe  11  moves over the data unit cells and the servo unit cells to read from or record data to the respective unit cells. 
       FIG. 1D  is a partial view of the data or servo unit cells. Referring to  FIG. 1D , a unit cell  22  includes data bits “ 0 ” or “ 1 ”  21 , each of which has a radius R. It is assumed that the unit cell  22  has a length of  4 R and a width of  2 R.  FIG. 1D  shows a set of unit cells  22  in 3 rows (m 1 , m 2 , and m 3 ). Here, data bits  21  in adjacent rows (m 1  and m 2  or m 2  and m 3 ) have a phase difference of 180°. 
     Hereinafter, a method of tracking data stored in a data storage device according to an embodiment of the present invention will be described in detail with reference to  FIG. 2 .  FIG. 2  illustrates a method of tracking data stored in a data storage device according to the present invention. 
       FIG. 2  also shows the data bits  21  in 3 rows (m 1 , m 2 , and m 3 ) included in the data or servo unit cells  22  as shown in  FIG. 1D . The tip  11   a  of the probe  11  positioned on each of the data regions A and the servo regions B scans the data or servo unit cells  22  in the rows (m 1 , m 2 , and m 3 ) to record or reproduce data. A data bit “ 0 ” or “ 1 ” is recorded on the unit cell  22  in accordance with a certain rule. Reference character  21   a  (shaded) denotes a data bit “ 1 ” and reference character  21   b  (unshaded) denotes a data bit “ 0 ”. 
     The tip  11   a  of the probe  11  scans data bits in the direction of row m 2 . In spite of an external environment, the tip  11   a  oscillates and scans the data bits in the row m 2  between the upper and lower rows m 1  and m 3  to precisely track data. Here, to oscillate the tip  11   a  with respect to the data storage medium  10 , the data storage medium  10  may be oscillated using the scanner  13  of  FIG. 1A , or the probe  11  may be oscillated on its own. That is, the controller  14  transmits a signal to the scanner  13  such that the data storage medium  10  or the probe  11  is oscillated at a low frequency. Actually, initial oscillation of the tip  11   a  is equal to the sum of the low-frequency oscillation driven by the scanner  13  and oscillatory motion resulting from external disturbance of the data storage device. As shown in  FIG. 2 , the cycle of a scanning wave of the tip  11   a  is 8 R, i.e., 8 times the radius R of the data bit  21 . The cycle and amplitude of oscillation of the tip  11   a  can be changed according to specific characteristics of the data storage medium  10  and the probe  11 . 
     As shown in  FIG. 2 , when the tip  11   a  scans data bits “ 1 ”, a probe signal is detected by the tip  11   a . Here, the tip  11   a  may cross over into the lower row m 3  due to an external disturbance. Thus, off-track signal  24  is detected from the probe signal. If the off-track signal  24  is detected, the controller  14  adds a compensation signal to the probe signal. Here, the magnitude of the off-track signal  24  varies according to the displacement of the tip  11   a , and a compensation signal having a predetermined magnitude is applied to the data storage medium  10  or the probe  11  through the scanner  13  in consideration of the magnitude of the off-track signal  24 . It can be confirmed from the probe signal of  FIG. 2  that a compensation signal is applied from a position where the off-track signal  24  is detected. Accordingly, from this moment on, the oscillation (W)  23  of the tip  11   a  becomes equal to the sum of a chopping wave with magnitude W o  and a compensation signal with magnitude W c . Here, an off-track check region is in a position of data bits in the upper and lower rows m 1  an m 2 , in a direction in which the tip  11   a  scans data bits in the row m 2 . A scan position of the tip  11   a  is moved upward by the compensation signal with magnitude W c . 
     Likewise, if the tip  11   a  crosses over into the upper row m 1  due to an external disturbance during scanning of the row m 2 , the same process described above is performed. Specifically, data recorded in the data bit  21  is detected using the tip  11   a  while scanning row m 2 . Here, if the tip  11   a  scans a data bit in row mi above row m 2 , information regarding the size of the violated region can be determined from the probe signal. Thus, based on the information from the incursion, the controller  14  applies a compensation signal for the off-track signal to the data storage medium  10  or the probe  11 . In response to the compensation signal, the scanner  13  reduces an oscillation position of the data storage medium  10  or the probe  11 . In summary, at the outset, the probe  11  or the data storage medium  10  is oscillated, an off-track error of the probe  11  or the data storage medium  10  is detected from the oscillation, and, if necessary, compensation of the scan position of the probe  11  is provided by the scanner  13  based on the off-track error. 
     The data storage device (especially, the controller  14 ) will be described in detail with reference to  FIG. 3 , which shows a detailed construction of the data storage device of  FIG. 1 . In a left servo region, the tip  11   a  attached to the cantilever  11   b  of the probe  11  can scan and reproduce data bits “ 1 ” (shaded)  21   a  in a row direction. Also, in a right data region, the tip  11   a  attached to the cantilever  11   b  of the probe  11  can scan and reproduce data bits “ 0 ” (unshaded)  21   b  in a row direction. To record or reproduce data, a scanning signal generator generates a signal and outputs the signal to a scanner to drive the data storage medium  10  or the probe  11 . Here, the same displacement occurs between a probe in the servo region and a probe in the data region. 
     If data in the left servo region is reproduced (or detected), a synchronizer generates a signal which is synchronized with the patterns of the data and transmits the generated signal to an interruption generator. In response to the generated signal, operational timings of an off-track detector, an oscillation signal generator, and a recording/reproduction controller are controlled. That is, if the off-track detector detects any off-track error of the tip  11   a , a compensator shifts a direct current (DC) level of a low-frequency oscillation signal and applies the shifted low-frequency oscillation signal to the scanner  13 . Here, the oscillation signal generator applies a signal along with the low-frequency oscillation signal to the scanner  13 , thereby varying the oscillation range of the tip  11   a . As a result, the probe  11 , which scans the data region, enables the recording/reproduction controller to record and reproduce data in the data region. 
       FIG. 4  shows a waveform obtained when a probe scans data bits to record or reproduce data on a data storage medium using the data tracking method according to the present invention. Referring to  FIGS. 2 and 4 , in the absence of a compensation signal (refer to reference numeral  45 ), the tip  11   a  oscillates over data bit  21  in the row m 2  due to external disturbances. Here tip  11   a  sometimes scans beyond the radius R of the data bit  21 . That is, the tip  11   a  crosses over to the data bits in the upper row m 1  (refer to  41 ) and the lower row m 3  (refer to  42 ). In this case, a scanning process of the tip  11   a  can be adjusted by adding a compensation signal (refer to  44 ) to the probe signal so that the tip  11   a  scans nearer to the center of the data bits in the row m 2 . 
     The present invention can serially detect off-track errors of data in a data storage medium using a tip of a probe for recording or reproducing data, and compensate for off-track errors through a simple compensation algorithm without the need for precise patterns. Consequently, data can be reliably recorded on and reproduced from the data storage medium.

Technology Category: 7