Abstract:
This invention provides method and apparatus for controlling reproduction speed of an optical disk, which detects the magnitude of a disk vibration after initial operation of an optical disk and adjusts the disk rotation speed based upon the vibration magnitude. The method according to this invention comprises the steps of rotating an installed optical disk; detecting the quantity of signal derived from tracking error signals which are combined from signals reproduced from the optical disk when the rotation speed reaches to a predetermined speed; and deciding whether to increase the rotation speed above the predetermined speed based upon the detected quantity of the signal. This invention is able to reproduce an optical disk at the possible maximum speed within allowable speed limit through detecting accurate disk vibration magnitude at the initial operation stage and adjusting the reproduction speed to higher speed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to method and apparatus for controlling reproduction speed of an optical disk, which detects the magnitude of a disk vibration after initial operation for an optical disk and adjusts the disk rotation speed based upon the vibration magnitude. 
     2. Description of the Related Art 
     As media for recording digital information, a Compact Disk (referred as “CD” hereinafter) or a Digital Versatile Disk (referred as “DVD” hereinafter) series are generally used. Such kinds of optical disks can record enormous quantity of information such as long-time moving pictures, and these recording media are continuously developed for higher speed to reproduce or record more data within shorter time. 
     However, this high-speed reproduction inevitably causes disk vibration because of weight or eccentricity of a disk. Such a disk vibration at high speed generates a loud noise and increase difficulties of servo controls such as a tracking control, a focussing control and a sled control, thus might cause an error in searching a recording or reproduction point. These situations, if occurred, make it impossible to record or reproduce data accurately. 
     Accordingly, for high-speed reproduction, a vibration magnitude should be detected first. To do this, the vibration magnitude may be detected based upon reproduced signals and then a rotation speed is decreased if the vibration magnitude exceeds a certain critical level. For these speed adjusting processes, a conventional art equips a shock sensor for detecting a magnitude of disk vibration while a disk is rotating. The shock sensor outputs electric energy proportional to a vibration magnitude. However, this method causes rise in cost due to the equipment of a shock sensor. 
     To reduce the cost, several apparatuses for reproducing an optical disk which can detect disk vibration magnitude based upon reproduced signals without an additional sensor during high-speed reproduction and adjust a rotation speed depending upon the detected vibration magnitude have been invented, and they have been filed with the Korean patent application No. 98-54951, 98-54952 and 99-176, respectively. 
     The method according to the Korea patent application No. 98-54951 detects both vibration and eccentricity of a disk using a tracking error signal and controls a spindle motor. For this process, it detects disk vibration depending upon how many times a tracking error signal exceeds a predetermined standard slice level for a given time, samples and holds the peak and bottom level of the tracking error signal, computes the difference between peak and bottom, and checks whether there is an eccentricity by comparing the difference with a standard level. After then, it does not decrease a current rotation speed in case that there is an eccentricity even though the detected disk vibration exceeds the predetermined level. 
     The method according to the Korea patent application No. 98-54952 (also filed in the U.S. Patent and Trademark Office) detects an unbalance magnitude of an optical disk and controls a rotation speed according to the detected magnitude. This method computes the unbalance magnitude using the difference between A and B of a photo diode in which A and B are signals converted from a reflected main beam, and adjusts a driving voltage applied to a spindle motor depending upon the computed unbalance magnitude. 
     The method according to the Korea patent application No. 99-176 rotates an installed optical disk at a predetermined initial reproduction speed, measures how much the optical disk vibrates based upon levels of a high-frequency signal reproduced from the rotating optical disk, and controls the reproduction speed depending upon the measured disk vibration. 
     The above conventional methods detect a vibration of an optical disk based upon levels detected from an optical disk as explained above. However, they are not able to guarantee an accuracy in calculating vibration magnitude since the signal level to use in detecting disk vibrating magnitude is very sensitive, therefore, the reproduction cannot be performed under the optimal maximum speed since it is difficult to detect the vibration magnitude in precision even though the vibration magnitude exceeds a certain level. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide apparatus and method for controlling reproduction speed of an optical disk, capable of detecting the magnitude of disk vibration caused by a high-speed rotation, and adjusting its reproduction speed based upon the detected vibration magnitude. 
     It is another object of the present invention to subdivide the magnitude of disk vibration based on respective rotation speeds and to adjust the reproduction speed of an optical disk depending upon the detected vibration magnitude and a current speed range. 
     The reproduction speed control apparatus according to this invention comprises a driving means for rotating an inserted optical disk; a counting means for counting a prescribed signal derived from a tracking error signal of the rotating optical disk; and a controlling means for controlling a reproduction speed of the optical disk based on the counted value. 
     The method according to this invention comprises the steps of: rotating an installed optical disk; detecting the quantity of a prescribed signal derived from a tracking error signal which are combined from signals reproduced from the optical disk when the rotation speed reaches to a predetermined speed; and deciding whether to increase the rotation speed above the predetermined speed based upon the detected quantity of the prescribed signal. 
     In the present invention, the driving means drives an inserted optical disk to rotate, and the counting means counts the prescribed signal derived from the tracking error signal of the optical disk being rotated by the driving means. 
     After that, the controlling means calculates the magnitude of disk vibration from the value counted by the counting means, and increases the rotation speed of the optical disk if the vibration magnitude is allowable at the current speed range. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the present invention. 
     In the drawings: 
     FIG. 1 is a schematic block diagram of a preferred embodiment of an apparatus for controlling reproduction speed of an optical disk according to the present invention; 
     FIG. 2 is a flowchart showing a preferred method controlling disk reproduction speed according to the present invention; 
     FIG. 3 showes experimental count values of pulse signals for various reproduction devices and optical disks, which are counted at respective predetermined rotation speeds; 
     FIG. 4 is a graph showing the relation between the disk vibration magnitude detected from a tracking error signal after initial operation of an optical disk and rotating speed adjusting process; 
     FIG. 5 showes an example of a tracking error signal and pulse signals Cout generated from the tracking error signal; and 
     FIG. 6 showes an example of pulse signal Cout form for the disk characteristics. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In order that the invention may be fully understood, preferred embodiments thereof will now be described with reference to the accompanying drawings. 
     FIG. 1 is a schematic block diagram of a reproduction apparatus embodying the present invention, which comprises a pickup  20  radiating a lazor beam onto an optical disk  10  and detecting recorded signals from a reflected beam; a sled motor  30  moving the pickup  20  to the radial direction of the optical disk  10 ; a spindle motor  31  rotating the optical disk  10 ; a driver  60  driving the sled motor  30  and the spindle motor  31 ; an R/F unit  40  for equalizing and shaping the signal detected by the pickup  20 ; a servo unit  50  controlling the driver  60  against the rotation speed variation of the optical disk  10  and a focussing error (F.E) signal and a tracking error (T.E) signal produced by the pickup  20  from signals detected from the optical disk  10 ; a digital signal processor  70  decoding signals outputted from the R/F unit  40  into original data and generating/outputting pulse signals Cout, which is derived from the tracking error signal, representing track-cross of the pickup  20 ; a memory  81  storing predetermined reference values of the pulse signals Cout for various rotation speeds of an optical disk; a timer  82 ; and a microcomputer  80  counting the pulse signals Cout outputted from the digital signal processor  70  and adjusting the rotation speed of the optical disk  10  based upon the counted value. 
     FIG. 2 showes a flowchart of a preferred method controlling disk reproduction speed embodying the present invention. 
     The preferred embodiment of the reproduction speed control method of FIG. 2 will be described in detail together with an explanation for the operation of the reproduction apparatus of FIG.  1 . 
     The many experimental data shown in FIG. 3 considered, the memory  81  has stored reference count values of the pulse signals, for example 8000 and 9500, etc., for each predetermined rotation speeds, for example 4000 rpm and 5000 rpm, etc. The reference count values are to be used as boudaries to decide whether the disk vibration is allowable and they are chosen from many experimental results obtained for several reproduction apparatuses as FIG. 3 showes 
     In those experiments, a clamper (not figured) with No. 4 cavity whose diameter is larger was used to reduce variation of clamping angle, and rubber of 40 in hardness was equipped into a tray (not figured). 
     When the optical disk  10  is inserted and installed onto a tray (S 10 ) of the reproducing apparatus shown in FIG. 1, the optical disk  10  is fixed by a clamper. 
     When the inserted optical disk  10  is fixed in the tray, the microcomputer  80  drives the spindle motor  31  through the servo unit  50  and the driver  60  to rotate the optical disk  10  in order to control the reproduction speed according to speed control procedure of FIG.  4 . At initial step, the microcomputer  80  forces the driver  60  to apply a driving voltage corresponding to 1st speed, i.e., 4000 rpm to the spindle motor  31 . 
     When the rotation speed of the optical disk  10  reaches to 4000 rpm, the microcomputer  80  temporarily deactivates the tracking servo control, which makes an object lens equipped in the pickup  20  trace the center of a current track, with the focussing servo control activated. The activated focussing servo control moves the object lens up and down to maintain exact focusing distance to the disk  10 . 
     The reason why to deactive the tracking servo control is to detect the difference of mangnitude of an actuator&#39;s shake caused by mechanical vibration by a rotating disk. 
     The microcomputer  80  also controls the timer  82  to count elapsing time after the tracking servo control is deactivated, and begins to accomplish the vibration detecting operation to adjust the current reproduction speed of the optical disk  10 . 
     Meantime, the digital signal processor  70  produces pulse signals Cout representing track cross of a incident main beam of the pickup  20  based upon a tracking error signal (TE) outputted from the pickup  20  as shown on FIG. 5, and outputs the pulse signals to the microcomputer  80  (S 12 ). In this process, if a object lens equipped in the pickup  20  is located around the area of the optical disk  10  where the tracking error signal is reversed in phase (A of FIG.  5 ), the period of the pulse signals Cout becomes longer, that is, a low frequency characteristic is revealed. On the contrary, if the object lens is located around the center of a track (B of FIG.  5 ), the period of the pulse signals Cout becomes shorter, that is, a high frequency characteristic is revealed. 
     The frequency characteristics are shown for 1.0 G, 0.5 G, and a normal disk in FIG.  6 . FIG. 6 showes that the pulse densities are different each other. That is, a disk to cause large quantity of vibration is to generates pulses with small density which means that the number of pulses decreases. 
     The microcomputer  80  counts the pulse signals Cout outputted from the digital signal processor  70  (S 13 ), and the counting operation is proceeded until the time elapsing in the timer  82  reaches to the predetermined time, for example 0.52 seconds of the interval ‘a’ of FIG.  4 . 
     In the process of counting the pulse signals Cout, the microcomputer  80  checks whether the time elapsing in the timer  82  reaches to the predetermined 0.52 seconds, and if 0.52 seconds elapsed the microcomputer  80  stops the timer  82 . 
     Then, the microcomputer  80  compares the number of pulse signals counted during the predetermined time with the 1st reference value 8000 among the reference values which are pre-stored in the memory  81  (S 14 ), and checks how much the disk vibration is. If the number of the counted pulse signals is greater than the 1st reference value (S 20 ), the microcomputer  80  distinguishes that the optical disk  10  is a 1.0 G (Gauss: a unit for indicating the weight variation of a disk. It indicates mass per a fixed distance, i.e., ‘g/cm’, from the cente hole) disk, which means that the quantity of current vibration due to rotation of the optical disk  10  exceeds an allowabe range at the current rotation speed. In the contrary, if the number of the counted pulse signals is less than the 1st reference value (S 20 ), the microcomputer  80  tentatively distinguishes the optical disk  10  as a normal disk, which means that the quantity of the disk vibration is acceptable at the current rotation speed. 
     Then, the microcomputer  80  controls the rotation speed (reproduction speed) of the optical disk  10  according to the above distinguishment. If the optical disk  10  is distinguished as a 1.0 G disk since the disk vibration exceeds the allowable range, the microcomputer  80  maintains the present rotation speed 4000 rpm (S 30 ), and if the optical disk  10  is tentatively distinguished as a normal disk since the disk vibration is allowable, the microcomputer  80  increases the driving voltage to the spindle motor  31  so that it may be rotated at the higher speed of 5000 rpm (S 22 ). 
     After the optical disk  10  is distinguished as a normal disk and the rotation speed is changed to 5000 rpm, the microcomputer  80  restarts the timer  82 , and counts pulse signals Cout outputted from the digital signal processor  70  during the predetermined time 0.52 sec of the interval ‘b’ of FIG.  4 . When the predetermined time is passed in the timer  82 , the microcomputer  80  compares again the number of pulse signals counted during 0.52 seconds and the 2nd reference value 9500 pre-stored in the memory  81  (S 23 ). 
     After the comparison, if the number of counted pulse signals is greater than the 2nd reference value (S 24 ), the microcomputer  80  distinguishes the optical disk  10  as a 0.5 G disk, and if not, it definitely distinguishes the optical disk  10  as a normal disk. 
     If the optical disk  10  is distinguished as a 0.5 G disk, the microcomputer  80  re-controls the rotation speed of the optical disk  10  to be adjusted below 5000 rpm as dotted in FIG. 4 (S 40 ). If the optical disk  10  is definitely distinguished as a normal disk, the microcomputer  80  maintains the increased rotation speed of 5000 rpm (S 30 ) and starts a detecting/reproducing TOC (Table of Contents) data in the lead-in area of the optical disk  10  to accomplish user data reproduction or record. 
     The above-explained apparatus and method for controlling a reproduction speed of an optical disk are able to reproduce and/or record an optical disk at allowable maximum speed through detecting the quantity of vibration more exactly at the initial operation stage. 
     Although the preferred embodiment of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as recited in the accompanying claims.