Patent Publication Number: US-2005141361-A1

Title: Apparatus for preventing damage of actuator coil in optical disc system and method for the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the priority of Korean Patent Application No. 2003-100639, filed on Dec. 30, 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 an optical disc reproducing and recording system, and more particularly, to an apparatus to prevent damage of an actuator coil installed in a pickup and a method for the same.  
      2. Description of the Related Art  
      Commonly, an optical disc reproducing system reproduces information recorded on various optical discs such as compact discs (CDs), compact disc-read only memories (CD-ROMs), laser discs (LDs), mini discs (MDs), and digital video discs (DVDs). The optical disc reproducing system adapts various kinds of servo controls including a mechanical driving control to substantially exactly pick up RF signals from a disc. There are basically  4  servo controls: a spindle servo control, a focusing servo control, a tracking servo control, and a sled servo control.  
      In a servo control apparatus used in a conventional optical disc reproducing system, an optical pickup generates RF signals converted into electrical signals by optically picking up information recorded on a disc. In this case, the optical pickup includes a focusing actuator and a tracking actuator. The focusing actuator moves an object lens in an optical axis direction in response to a focusing control signal that is output from a focusing compensation filter. Meanwhile, the tracking actuator traces a track by moving the object lens in a radial direction of a disc in response to a tracking control signal that is output from a tracking compensation filter.  
      The servo control apparatus is designed so that oscillation is not substantially generated in focus or tracking servo control signals for a stable servo operation.  
      However, in a conventional optical disc reproducing system, a sensitivity deviation of a pickup is generated due to a reflexibility of a disc or to mechanical characteristics of an actuator. At this time, oscillation of servo control signals may be continuously generated due to the sensitivity deviation of the pickup. These continuous servo oscillation signals may destroy a focus or tracking actuator coil and an object lens connected to the coil by flowing an over current to the focusing or tracking actuator coil.  
     SUMMARY OF THE INVENTION  
      The present invention provides a pickup damage preventing apparatus of an optical disc system, which prevents an actuator coil and an object lens from being destroyed by stopping a servo operation for a predetermined time when a servo error signal in an oscillation status is detected from a focus/tracking servo operation, and a method for the same.  
      According to an aspect of the present invention, there is provided a method of preventing damage of an actuator coil in an optical disc system, the method comprising: generating a servo control signal from focus and tracking error signals generated from an optical pickup; detecting a peak value of the generated servo control signal; determining whether an oscillation status of the focus/tracking error signal is in effect by comparing the detected peak value of the servo control signal with a threshold value; and if the servo control signal is determined to be in the oscillation status for a first predetermined time, cutting off a servo operation for a second predetermined time by generating a servo off command.  
      According to another aspect of the present invention, there is provided an apparatus to prevent damage of an actuator coil in an optical disc system. The apparatus comprises: an RF amplifier to extract focus and tracking error signals by amplifying an RF signal reflecting from a disc; a servo signal processing unit to generate a level/phase-compensated servo control signal from the focus and tracking error signals amplified by the RF amplifier and to turn a servo loop on/off in response to a servo on/off command; a peak value detector to detect a peak value of the servo control signal generated by the servo signal processing unit; a comparator to determine whether an oscillation status is in effect by comparing the peak value of the servo control signal detected by the peak value detector with a threshold value; and a microprocessor to output a servo off command to the servo signal processing unit if a logic signal corresponding to the oscillation status is input from the comparator for a predetermined time.  
      Additional and/or other aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
       FIG. 1  is a block diagram of an apparatus for preventing damage of an actuator coil in an optical disc system according to an exemplary embodiment of the present invention;  
       FIG. 2  is a front view of a pickup of  FIG. 1 ;  
       FIG. 3  is a graph showing a waveform of a correct servo control signal and a waveform of an oscillating servo control signal;  
       FIG. 4  is an equivalent circuit diagram of a peak value detector of  FIG. 2 ; and  
       FIG. 5  is a flowchart of a method of preventing damage of an actuator coil in an optical disc system according to an exemplary embodiment of the present invention.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
       FIG. 1  is a block diagram of an apparatus to prevent damage of an actuator coil in an optical disc system according to an exemplary embodiment of the present invention. 
    
    
      Referring to  FIG. 1 , an optical pickup  110  is driven by a tracking actuator (not shown) to control servo tracking and a focusing actuator (not shown) to control servo focusing. The optical pickup converts information that is recorded on a surface of a disc  100  into an electrical RF signal by optically picking up the information. Referring to an optical pickup structure shown in  FIG. 2 , an object lens  112  emits a laser beam that is condensed on a signal surface of the disc  100 . A focusing actuator coil  116  drives the object lens  112  so that the signal surface of the disc  100  is placed within a focus depth of the laser beam. A tracking actuator coil  114  drives the object lens  112  so that a laser beam to be used in optical pickup may exactly trace along a track of the disc  100 .  
      The RF amplifier  120  amplifies the RF signal output from the optical pickup  110 . At this time, the RF amplifier  120  generates a focus error signal (FES) and a tracking error signal (TES) from the amplified RF signal by including a focus error detecting circuit (not shown) and a tracking error detecting circuit (not shown).  
      A servo signal processing unit  130  includes a focus servo control loop (not shown) and a tracking servo control loop (not shown) and generates a focus servo control signal, a tracking servo control signal, and a sled feed servo control signal from the FES and the TES generated by the RF amplifier  120  using gain/phase-compensated filtering. Also, the servo signal processing unit  130  cuts off the servo control signals in response to a servo on/off command output from a processor  170  for a predetermined time and then turns on the servo control signals.  
      An actuator driving unit  140  drives the focusing actuator and the tracking actuator in the pickup  110  using the focus servo control signal and the tracking servo control signal generated by the servo signal processing unit  130 .  
      A disc motor  105  rotates the disc  100  with a constant linear velocity (CLV) method or a constant angular velocity (CAV) method using a disc driving signal output from a disc motor driving unit (not shown).  
      A feed motor  108  moves the optical pickup using the sled feed servo control signal generated by the servo signal processing unit  130 .  
      A peak value detector  150  detects a peak value of the focus/tracking servo control signal that is generated by the servo signal processing unit  130  when a servo error signal is oscillated due to a pickup sensitivity deviation. That is, as shown in  FIG. 3 , the servo signal processing unit  130  generates a relatively smooth servo control signal  310  when performing a normal servo operation and a continuously oscillating servo control signal  330  when performing an abnormal servo operation. Therefore, the peak value detector  150  detects a peak value of the oscillating servo control signal  330 . In a normal servo error signal without oscillation, an error voltage V p  is maintained with a very low value except for a moment, and in an oscillating servo error signal, the error voltage V p  is continuously maintained with a very high value.  
       FIG. 4  is an example of the peak value detector  150 , and the peak value detector  150  includes a rectifier  154  and a smoother  156 . The rectifier  154  half wave rectifies a focusing/tracking servo control signal V p  with an oscillating pattern using a diode D. The smoother  156  holds the signal that is half wave rectified by the rectifier  154  using a capacitor C and a register R.  
      A comparator  160  determines an oscillation status is in effect by comparing the peak value V peak  of the servo control signal detected by the peak value detector  150  to a threshold value V th . That is, if the peak value V peak  is larger than or equal to the threshold value V th , the comparator  160  outputs a logic “high” signal indicating that the servo control signal is in the oscillation status, and otherwise, the comparator  160  outputs a logic “low” signal indicating that the servo control signal is in a normal status.  
      The microprocessor  170  outputs a servo on/off command and a phase compensation filter coefficient to the servo signal processing unit  130 . The microprocessor  170  outputs a servo on command to the servo signal processing unit  130  when performing a normal servo operation, and if the microprocessor  170  receives a logic high signal from the comparator  160 , the microprocessor  170  recognizes that the servo control signal is in the oscillation status and outputs a servo off command to the servo signal processing unit  130 .  
       FIG. 5  is a flowchart of a method of preventing damage of an actuator coil in an optical disc system according to an exemplary embodiment of the present invention.  
      A count register, such as a timer that is coupled to the microprocessor  170 , is initialized in operation  510  so as to begin counting a time lapse from the start of the method of preventing damage of an actuator coil in the optical disc system.  
      A peak value of a focus/tracking servo control signal is detected in operation  520 .  
      The peak value V peak  of the servo control signal is compared with a threshold value V th  in operation  530 . At this time, if the peak value V peak  of the servo control signal is smaller than the threshold value V th , this process returns to operation  510 , and whenever the peak value V peak  of the servo control signal is larger than or equal to the threshold value V th , a count value is increased by 1 in operation  540 .  
      Whether the count value is a value T corresponding to the predetermined time is checked in operation  550 . At this time, if the count value is the value T, a servo off command is generated in operation  560 , and otherwise, this process returns to operation  520 .  
      Eventually, if an oscillation status of a servo error signal is sensed for more than the predetermined time, by generating a servo off command, a continuous maintenance of the oscillation status is made possible. Also, the destruction of an actuator coil and an object lens connected to the actuator coil is prevented.  
      As is described above, according to the present invention, an actuator coil and an object lens installed in a pickup are prevented from being destroyed by stopping a servo operation for a predetermined time when an oscillation status is detected from a focus or tracking servo.  
      Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.