Patent Publication Number: US-2011051579-A1

Title: Method for calibrating signal offsets on lightscribe disc

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a disc drive, and more particularly, to a method for calibrating signal offsets of an inner ring and an outer ring in control feature zones of a label side on a lightscribe disc. 
     2. Description of the Prior Art 
     A disc usually has two sides, wherein one side is used as a data side and the other side is used as a label side. A conventional method of producing labels on the disc is to make a mark on the label side by use of a pen or a label sticker as an identification. Recently, a lightscribe label technology has been developed. A user can carve desired patterns or texts on the label side of a lightscribe disc by use of a pick-up head of a disc drive to emit a laser light on the lightscribe disc, such that a beautiful and personalized disc can be produced. 
     Please refer to  FIG. 1  (including  1 A and  1 B), which is a diagram illustrating how a conventional disc drive reads a signal in a control feature zone on a lightscribe disc. As shown in  1 A, a control feature zone  11  of a lightscribe disc  10  includes an outer ring  12  and an inner ring  13  equipped with 400 spokes, wherein these spokes are evenly distributed in the inner ring  13  of the control feature zone  11  with equal angles. An optical encoder  14  is fixed in the disc drive  15 . The optical encoder  14  sends out a beam irradiated on the inner ring  13  in order to produce spoke signals shown in  1 B, and then provides angular dimensions to describe relative positions on the label side  17  during drawing operations to an pick-up head  16 . The outer ring  12  provides related information patterns of the lightscribe disc  10 , such as a media ID field, a saw-tooth mark, or an index mark. The information patterns of the outer ring  12  read by the pick-up head  16  form the information pattern signals shown in  1 B. In the specification of the lightscribe disc  10 , the start position of the spoke signals is set to follow the end of the index mark of the outer ring  12 . For this reason, the disc drive  15  must find out the start position of the spoke signals by use of the signals within the inner ring  13  and the outer ring  12  simultaneously when the lightscribe disc  10  is inserted into the disc drive  15  for drawing marks on the label side  17 . After the start position of the spoke signals is confirmed, the disc drive  15  can know the rotation angle of the lightscribe  10  and the information pattern signals of the outer ring  12  are currently read by the pick-up head  16  as long as the disc drive  15  counts the number of the spoke signals in the inner ring  13  continuously. 
     However, the optical encoder  14  and the pick-up head  16  are two individual components, wherein each component has different electrical signals with different processing speeds to cause a delay or a lead accordingly. As shown in  1 B, the generated information pattern signals of the outer ring and the spoke signals of the inner ring are not synchronized, where an offset “d” is existed. Furthermore, manufacturing errors and manufacturing quality of the lightscribe disc will also lead to a problem that the information pattern signals of the outer ring can not be entirely aligned with the spoke signals of the inner ring defined in the specifications. Warping or irregularities occurred on the disc will also cause the signal offsets between the spoke signals of the inner ring and the information pattern signals of the outer ring more obvious. As a result, the read information pattern signals in the outer ring cannot be decoded successfully, or the pick-up head is unable to accurately achieve the radial calibration, thereby affecting the accuracy of the follow-up label-drawings. Hence, there are still problems to be solved upon calibrations of the signals of the inner ring and the outer ring read by the disc drive. 
     SUMMARY OF THE INVENTION 
     It is one of the objectives of the present invention to provide a method for calibrating signal offsets on a lightscribe disc to solve the abovementioned problems. By measuring all signal offsets between information patterns of the outer ring and spoke signals of the inner ring within a marked area in order to calculate an average signal offset, the signal offsets between the signals of the outer ring and the inner ring can be calibrated by reference to the average signal offset. 
     It is another one of the objectives of the present invention to provide a method for calibrating signal offsets on a lightscribe disc to reduce a total signal offset by using the average signal offset obtained from information patterns of the outer ring and the spoke signals of the inner ring. 
     In order to achieve the abovementioned objectives, the method for calibrating signal offsets on a lightscribe disc disclosed in the present invention includes the following steps: utilizing spoke signals of an inner ring as a counter in order to read information pattern signals of an outer ring in a predetermined marked area; measuring the signal offsets; checking whether a number of the spoke signals of the inner ring exceeds a predetermined value; when the number of the spoke signals of the inner ring does not exceed the predetermined value, continue to measure the signal offsets; when the number of the spoke signals reaches the predetermined value, calculate an average signal offset; and calculating the signal offsets of the information pattern signals of the outer ring by utilizing the average signal offset. 
     In one embodiment of the present invention, the predetermined marked area can be a saw-tooth mark and a media ID mark, a single media ID mark, or a first part or a second part of a saw-tooth mark. 
     In one embodiment, the step of measuring the signal offsets includes the following steps: counting time with a timer, wherein the timer is started after being zeroed; starting the timer when the information pattern signals of the outer ring are generated; stopping the timer when the spoke signals of the inner ring are generated; and calculating the signal offsets by using a time difference between the start of the timer and the stop of the timer. Herein the step of calculating the signal offsets includes the following sub-steps: measuring a unit time of a single spoke signal of the inner ring; comparing the time difference with a half of the unit time; when the time difference is smaller than the half of the unit time, setting the time difference as a leading signal offset; and when the time difference is not smaller than the half of the unit time, setting a delay signal offset by subtracting the time difference from the unit time. 
     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 THE DRAWINGS 
         FIG. 1  (including  1 A and  1 B) is a diagram illustrating how a conventional disc drive reads a signal in a control feature zone on a lightscribe disc. 
         FIG. 2  is a diagram of partial enlargement for a control feature zone on a lightscribe disc. 
         FIG. 3  is a diagram illustrating a delay signal offset of reading a saw-tooth information pattern according to an embodiment of the present invention. 
         FIG. 4  is a diagram illustrating a leading signal offset of reading a saw-tooth information pattern according to an embodiment of the present invention. 
         FIG. 5  is a diagram illustrating the signal offsets between the information pattern signals and the spoke signals according to an embodiment of the present invention. 
         FIG. 6  (including  6 A and  6 B) is a diagram illustrating how to measure the signal offsets of the information pattern signals according to an embodiment of the present invention. 
         FIG. 7  is a flowchart illustrating a method for calibrating signal offsets on a lightscribe disc according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In order to achieve the abovementioned objectives of the present invention, the adopted technical means and effects are described below by using given embodiments together with drawings. 
     Please refer to  FIG. 2 , which is a diagram of partial enlargement for a control feature zone of a lightscribe disc. A control feature zone  20  includes an outer ring  21  and an inner ring  22 , wherein the outer ring  21  includes information patterns  23  in multiple marked areas of the lightscribe disc, and the inner ring  22  has spokes  24  located side by side. In the specification of the lightscribe disc, the start position of each information pattern  23  in the outer ring  21  is set to be aligned with a specific spoke  24  and cover a specific amount of spoke  24  as the signal interpretation area. Take a saw-tooth maker as an example. The saw-tooth maker is divided into a first part and a second part, wherein each part has eight saw-tooth information pattern signals. The saw-tooth information pattern signals of the first part are started from the 64 th  spoke  24 , each saw-tooth information pattern covering eight spokes; while the saw-tooth information pattern signals of the second part are started from the 264 th  spoke  24 , each saw-tooth information pattern covering eight spokes  24 . For this reason, manufacturing errors and manufacturing quality of the lightscribe disc will lead to a problem that the information pattern signals  23  of the outer ring  21  cannot be entirely aligned with the spoke signals  24  of the inner ring  22  to cause a signal offset D, thereby affecting the accuracy of the signal interpretation area. 
     As shown in  FIG. 3 , which is a diagram illustrating a delay signal of reading a saw-tooth information pattern  23  according to an embodiment of the present invention. When reading the saw-tooth information pattern  23 , the lightscribe disc is rotated with a rotation direction R and a beam  25  of the pick-up head is radiated on a line L. When the spoke signal  26  of the inner ring is counted to the (64+8n) th  spoke signal or the (264+8n) th  spoke signal, the beam  25  of the pick-up head reaches the saw-tooth pattern  23  and a read signal with level high is outputted until the beam  25  leaves the saw-tooth pattern  23 . At this time, a signal length “x” corresponding to the high-level signal is calculated by using pulses of the disc drive. As long as the beam  25  of the pick-up head leaves the saw-tooth information pattern  23 , the read signal with level low is outputted until the covered eight spoke signals end. At this time, a signal length “y” corresponding to the low-level signal is calculated by using pulses of the disc drive. A radial movement “h” of the beam  25  for the pick-up head can be calculated as a reference for radial movement calibration by using a ratio of the signal length “x” to the signal length “y”. However, the signal offset “D” is generated because the information pattern  23  cannot be aligned with the spoke signal. The delayed information pattern signal will end after eight spoke signals pass, which results in ending the reading signal to cut off the unfinished low-level signal and thereby reduce the signal length “y” of the low-level signal. As a result, the ratio of the signal length “x” of the high-level signal to the signal length “y” of the low-level signal is wrong, thereby affecting the accuracy of the radial calibration. 
     As shown in  FIG. 4 , which is a diagram illustrating a leading signal of reading a saw-tooth information pattern according to an embodiment of the present invention. However, the leading signal offset “D” is generated because the information pattern  23  cannot be aligned with the spoke signal. After the information pattern  23  ends, the eight spoke signals have not finished, which results in keeping reading the low-level signal to lengthen the low-level signal and thereby increase the signal length “y” of the low-level signal. As a result, the ratio of the signal length “x” of the high-level signal to the signal length “y” of the low-level signal is wrong. As long as the ratio of the signal length “x” of the high-level signal to the signal length “y” of the low-level signal changes, the radial movement “h” also changes, thereby affecting the accuracy of the radial calibration. 
     As shown in  FIG. 5 , which is a diagram illustrating the signal offset between the information pattern signals and the spoke signals according to an embodiment of the present invention. The signal offset “D” between each information pattern and its corresponding spoke signal are different from each other. As long as the information pattern changes, the accuracy will be changed, which results in a problem that sequential labels cannot be aligned. Hence, according to an embodiment of the present invention, all of the signal offsets D 1 , D 2 , D 3 , . . . , and Dn between information patterns and corresponding spoke signals are measured, in order to calculate an average signal offset DA=(D 1 +D 2 +D 3 + . . . +Dn)/n as a reference for calibrating the signal offsets between information patterns and corresponding spoke signals. As a result, the signal length “x” of the high-level signal and the signal length “y” of the low-level signal can be maintained at a certain relationship so as to improve the accuracy of calibration. 
     Please refer to  FIG. 6  (including  6 A and  6 B), which is a diagram illustrating how to measure the leading signal offset or the delayed signal offset of the information pattern signals according to an embodiment of the present invention. First, a unit time “ts” of a single spoke signal is measured. A timer is zeroed before starting to count time. Start the timer when the information pattern signals of the outer ring are generated; and stop the timer when the spoke signals of the inner ring are generated. As shown in  6 A, which indicates a leading signal offset existed in the information pattern signal. First, the timer is zeroed. Start the timer when the information pattern signals of the outer ring are generated; and stop the timer when the spoke signals of the inner ring are generated. Calculate the signal by measuring a time difference between the starting of the timer and the stopping of the timer. Finally, compare the time difference with a half of the unit time “ts” (i.e., ts/2). When the time difference is smaller than ts/2, it indicates a leading signal offset “ta”. As shown in  6 B, which indicates a delayed signal offset existed in the information pattern signal. First, the timer is zeroed. Start the timer when the information pattern signals of the outer ring are generated; and stop the timer when the spoke signals of the inner ring are generated. Calculate the signal offsets by measuring a time difference between the start of the timer and the stop of the timer. Finally, compare the time difference “tb” with a half of the unit time “ts” (i.e., ts/2). When the time difference “tb” is not smaller than the half of the unit time (i.e., ts/2), set a delayed signal offset “td” by subtracting the time difference “tb” from the unit time “ts”, which is expressed as: td=ts−tb. 
     The abovementioned embodiments cite the saw-tooth information pattern as an example for describing features of the present invention, but the present invention is not limited to this only. When reading information patterns in a media ID mark, each square information pattern containing two spoke signals, the high-level signal of the information pattern is viewed as a digital signal “1” and the low-level signal is viewed as a digital signal “0”. If the signal length of the high-level signal is smaller than a predetermined length, it cannot be captured as a valid signal. As a result, the signal offset resulted from a condition that the information pattern cannot be aligned with the spoke signal will cause a change in the signal length of the high-level signal, thereby affecting the accuracy of decoding the media ID mark. In other words, the method for calibrating the signal offsets of a saw-tooth mark is suitable for the media ID mark as well. 
     Please refer to  FIG. 7 , which is a flowchart illustrating a method for calibrating signal offsets on a lightscribe disc according to an exemplary embodiment of the present invention. The detailed steps for calibrating the signals of the outer ring according to the average signal offset are listed below. First, in the step S 1 , start to perform the signal offset calibration upon the lightscribe disc. In the step S 2 , spoke signals of the inner ring are utilized as a counter in order to read information pattern signals of the outer ring in a predetermined marked area; wherein the predetermined marked area can be a first part or a second part of a saw-tooth mark or a media ID mark. In the step S 3 , the timer is used for counting time. The step of counting time can be started after the timer is zeroed, or the step of counting time can be implemented by counting a number of pulses. In the step S 4 , start the timer when the information pattern signals of the outer ring are generated. In the step S 5 , stop the timer when the spoke signals of the inner ring are generated. In the step S 6 , calculate the signal offsets. In the step S 7 , check whether the number of the spoke signals of the inner ring exceeds a predetermined value. If the number of the spoke signals does not exceed the predetermined value, go back to the step S 3 ; and if the number of the spoke signals reaches the predetermined value, go to the step S 8 . In the step S 8 , calculate an average signal offset. Finally, in the step S 9 , the signal offsets of the information pattern signals of the outer ring are calibrated by utilizing the average signal offset during a radial calibration or a decoding calibration. 
     In summary, the present invention provides a method for calibrating signal offsets on a lightscribe disc. By measuring signal offsets between information patterns of the outer ring and corresponding spoke signals of the inner ring within a marked area in order to calculate an average signal offset, the signal offsets between the signals of the outer ring and the inner ring can be calibrated by reference to the average signal offset. As a result, a total signal offset can be reduced, the synchronization of the signals in the outer ring and the inner ring can be improved, and the failure of radial calibration can be avoided, such that the pick-up head can be correctly moved in order to facilitate the label-drawings on the lightscribe disc. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.