Abstract:
A method for measuring an eccentricity of an optical disk is provided. The method includes steps of: rotating the optical disk with a spindle motor; irradiating a light beam emitted from an optical pickup on the optical disk; detecting the light beam reflected from the optical disk with a detector; generating tracking error signals; receiving electronic signals from the spindle motor; calculating a quantity of tracks traversed by the light beam during determined revolutions of the optical disk based on the tracking error signals and the electronic signals from the spindle motor; and determining the eccentricity of the optical disk based on the quantity of the tracks.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to methods and devices for measuring eccentricities and, more particularly, to a method for measuring an eccentricity of an optical disk and a device implementing the same. 
         [0003]    2. Description of related art 
         [0004]    To record or reproduce information on or from an optical disk, a light beam needs to be projected accurately on data tracks on the optical disk. 
         [0005]    The optical disk is generally designed to have a symmetrical shape. However, practically, the optical disk may not be the ideal shape. Mechanical positional deviation and/or plastic deformation and etc. introduce an eccentricity of the optical disk. When the eccentricity is too great, tracking servo operations following up the track deviation fails to proceed. This leads to a problem that the light beam cannot be projected accurately on a desired track. 
         [0006]    Therefore, a method for measuring an eccentricity of an optical disk and a device implementing the method are desired. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, a method for measuring an eccentricity of an optical disk is provided. The method includes steps of: rotating the optical disk with a spindle motor; irradiating a light beam emitted from an optical pickup on the optical disk; detecting the light beam reflected from the optical disk with a detector; generating tracking error signals; receiving electronic signals from the spindle motor; calculating a quantity of tracks traversed by the light beam during determined revolutions of the optical disk based on the tracking error signals and the electronic signals from the spindle motor; and determining the eccentricity of the optical disk based on the quantity of the tracks. 
         [0008]    In another aspect, a method for measuring an eccentricity of an optical disk is provided. The method includes steps of: locating the optical disk onto a spindle motor; driving the spindle motor to rotate the optical disk; irradiating a light beam emitted from the optical pickup on the optical disk; detecting the light beam reflected from the optical disk and generating electronic signals in terms of the light beam with a detector; generating tracking error signals with a tracking servo circuit; outputting electronic signals from the spindle motor to a signal processing circuit; and determining in the signal processing circuit the eccentricity of the optical disk in accordance with a quantity of tracks traversed by the light beam during determined revolutions of the optical disk based on the tracking error signals and the electronic signals from the spindle motor. 
         [0009]    In still another aspect, a device for measuring an eccentricity of an optical disk is provided. The device includes a spindle motor, an optical pickup, a detector, a tracking servo circuit, and a processor. The spindle motor locates the optical disk thereon and rotates the optical disk. The optical pickup emits a light beam to irradiate the optical disk. The detector receives the light beam reflected from the optical disk and generates electronic signals in terms of the light beam. The tracking servo circuit receives the electronic signals and produces tracking error signals in a sinusoidal waveform. The processor determines and outputs the eccentricity based on the tracking error signals. The processor has a shaping circuit configured for transforming the tracking signals from the sinusoidal waveform to a pulse waveform, a counter configured for receiving the tracking error signals in the pulse waveform, counting a quantity of tracks traversed by the light beam; and an operation circuit configured for calculating the eccentricity in accordance with the quantity of the tracks. 
         [0010]    Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a block diagram of a device for measuring an eccentricity of an optical disk in accordance with an exemplary embodiment; and 
           [0012]      FIG. 2  is a flow chart illustrating a method for measuring an eccentricity of the optical disk of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Reference will now be made to the drawings to describe the exemplary embodiment of the device and the method, in detail. 
         [0014]    Referring to  FIG. 1 , a device  10  for measuring an eccentricity of an optical disk  20  in accordance with an exemplary embodiment is illustrated. The device  10  includes a spindle motor  30 , an optical pickup  40 , a focusing servo circuit  50 , a tracking servo circuit  60 , a system control circuit  70 , and a signal processing circuit  80 . 
         [0015]    The spindle motor  30  is configured for supporting the optical disk  20  thereon and driving the optical disk  20  to rotate at a predetermined rotational speed. 
         [0016]    The optical pickup  40  is electronically connected to and controlled by the focusing servo circuit  50  and the tracking servo circuit  60 . The optical pickup  40  includes a detector  42 , a light source (not shown), and a plurality of optical lenses (not shown) therein. The light source is capable of emitting a light beam  44 . The optical lenses are capable of focusing the light beam  44  on the optical disk  20 . The detector  42  may be a photo diode and configured for detecting the light beam  44  reflected from the optical disk  20  and outputting electronic signals based on the received light beam  44 . 
         [0017]    The focusing servo circuit  50  includes a focusing error signal generator  52 , a focusing compensation circuit  54 , a switch  56 , and a focusing drive circuit  58 . The focusing error signal generator  52  is electronically connected to the detector  42  for receiving the electronic signals and generating focusing error signals. The focusing compensation circuit  54  is electronically connected to the focusing error signal generator  52  for receiving the focusing error signals and outputting focusing compensation signals based on the focusing error signals. The focusing drive circuit  58  is electronically connected to the focusing compensation circuit  54  via the switch  56 . The switch  56  is turned on/off in accordance with signals outputted from the system control circuit  70 . If the switch  56  is turned on, the focusing drive circuit  58  is capable of receiving the focusing compensation signals from the focusing compensation circuit  54  and sending out focusing drive signals to adjust/move/drive the optical pickup  40 , that is, a focusing servo operation for moving the light beam  44  along a direction Y perpendicular to the optical disk  20  is performed. If the switch  56  is turned off, the focusing compensation signals from the focusing compensation circuit  54  cannot be fed to the optical pickup  40  thus, the focusing servo operation is not performable. 
         [0018]    The tracking servo circuit  60  includes a tracking error signal generator  62 , a tracking compensation circuit  64 , a switch  66  and a focusing drive circuit  68 . The tracking error signal generator  62  is electronically connected to the detector  42  for receiving the electronic signals and generating tracking error signals. The tracking compensation circuit  64  is electronically connected to the tracking error signal generator  62  for receiving the tracking error signals and outputting tracking compensation signals. The tracking drive circuit  68  is electronically connected to the tracking compensation circuit  64  via the switch  66 . The switch  66  is turned on/off in accordance with signals output from the system control circuit  70 . If the switch  66  is turned on, the tracking drive circuit  68  is capable of receiving the tracking compensation signals and sending out tracking drive signals to adjust/move/drive the optical pickup  40 , that is, a tracking servo operation for moving the light beam  44  along a direction X parallel to the optical disk  20  is performed. If the switch  66  is turned off, the signals from the tracking compensation circuit  64  cannot be applied to the optical pickup  40  so that the tracking servo operation is inactive. 
         [0019]    The signal processing circuit  80  includes a shaping circuit  82 , a first counter  84 , a second counter  86 , and an operation circuit  88 . The shaping circuit  82  is electronically connected to the tracking error signal generator  62  for receiving the tracking error signals in a sinusoidal waveform and transforming the tracking error signals in the sinusoidal waveform to a rectangle waveform. The first counter  84  is electronically connected to the shaping circuit  82 , and configured for counting a tracking error signal pulse count. The second counter  86  is electronically connected to the spindle motor  30  for receiving and counting an electronic signals pulse count of the electronic signals sent by the spindle motor  30 . A quantity of tracks traversed by the light beam  44  is determinable by the first counter  84 , and a number of revolutions that the spindle motor  30  rotates is determinable by the second counter  86 . The operation circuit  88  is electronically connected to the counter  84  for calculating an eccentricity of the optical disk  20  based on the quantity of tracks traversed and the number of revolutions (e.g., the quantity of tracks traversed per revolution) and outputting a result signal to the system control circuit  70 . The memory  90  is electronically connected to the operation circuit  88  and configured for storing a reference value. The eccentricity of the optical disk  20  can be compared with the reference value. The reference value can be changed in accordance with different precision requirements. 
         [0020]    Referring also to  FIG. 2 , the device  10  can be operated as follows. 
         [0021]    First, in step S 10 , the optical disk  20  is placed onto the spindle motor  30 . 
         [0022]    Second, in step S 12 , the optical disk  20  is rotated at a predetermined rotational speed by the spindle motor  30 . 
         [0023]    Third, in step S 14 , the system control circuit  70  signals the switch  56  to turn on and signals the switch  66  to turn off; thus, the focusing servo operation is activated and the tracking servo operation is inactivated. 
         [0024]    Fourth, in step S 16 , the detector  42  detects the light beam  44  reflected from the optical disk  20 , and outputs electronic signals transformed from light signals in the reflected light beam  44 . The focusing error signal generator  52  receives the electronic signals from the detector  42  and outputs focusing error signals to the focusing compensation circuit  54 . The focusing compensation circuit  54  outputs the tracking compensation signals to the focusing drive circuit  58  via the switch  56 . The focusing drive circuit  58  adjusts the optical pickup  40 . The light beam  44  emitted from the optical pickup  40  is thus projected on the optical disk  20 . 
         [0025]    Fifth, in step S 18 , the tracking error signal generator  62  processes the electronic signals from the detector  42  and outputs the tracking error signals in the sinusoidal waveform to the shaping circuit  82 . 
         [0026]    Sixth, in step S 20 , the shaping circuit  82  transforms the tracking error signals in the sinusoidal waveform to the rectangle waveform and outputs the tracking error signals in the rectangle waveform to the counter  84 . 
         [0027]    Seventh, in step S 22 , the first counter  84  counts the tracking error signals pulse count to determine the quantity of tracks traversed by the light beam  44 , and outputs signals to the operation circuit  88 . 
         [0028]    Eighth, in step S 24 , the second counter  86  counts the electronic signals pulses count of the electronic signals from the spindle motor  30  to determine the quantity of revolutions the optical disk  20  rotates, and outputs signals to the operation circuit  88 . 
         [0029]    Ninth, in step S 26 , the operation circuit  88  calculates the eccentricity of the optical disk  20  based on the quantities of the tracks and the revolutions. The eccentricity of the optical disk  20  can be easily calculated. For example, the eccentricity approximately equals to the number of the tracks traversed by the light beam  44  in one revolution divided by a constant. The eccentricity can be also described by deviating distance of the tracks relative to a center of the optical disk  20  and can be easily calculated because widths of the adjacent tracks and track pitches are known from published specifications of the optical disk  20 , and the number of the tracks traversed by the light beam  999  on the optical disk  20  in one revolution can be counted. 
         [0030]    Tenth, in step S 28 , the operation circuit  88  compares the eccentricity of the optical disk  20  with a reference value stored in the memory  90  to analyze the eccentricity of the optical disk  20 . If the eccentricity of the optical disk  20  is greater than the reference value, the optical disk  20  is identified as an eccentric disk (step  30 ), and the system control circuit  70  outputs a signal to turn on the switch  66  (step S 32 ). The tracking drive circuit  68  can thus receive the tracking error correction signal and output electronic signals to adjust the optical pickup  40  to moving the light beam  999  to a correct track. If the eccentricity of the optical disk  20  is less than the reference value, the disk  20  is identified as a regular disk (step S 30 ). 
         [0031]    The eccentricity of the optical disk  20  can thus be simply measured and adverse effects due to the eccentricity can be greatly reduced. 
         [0032]    The embodiments described herein are merely illustrative of the principles of the present invention. Other arrangements and advantages may be devised by those skilled in the art without departing from the spirit and scope of the present invention. Accordingly, the present invention should be deemed not to be limited to the above detailed description, but rather by the spirit and scope of the claims that follow, and their equivalents.