Abstract:
An apparatus and method for automatically controlling the focusing of a compact disc player (CDP) performs more reliable automatic control operation upon abnormal conditions of a disc, such as a scratch and dust. The automatic focus controlling apparatus includes a pickup assembly for reading recorded data from a disc; and RF signal converter for converting the output signal read by the pickup assembly into an RF signal; a signal separator for separating a signal corresponding to a 3T component from the RF signal; a phase comparator for comparing the separated 3T signal with a predetermined frequency to provide a phase difference value; and a controller for controlling a focusing operation of an objective lens based on the phase difference value to provide a focus control signal.

Description:
This application is a continuation-in-part of U.S. Patent application Ser. No. 08/927,016 filed Sep. 16, 1997 now U.S. Pat. No. 6,028,825. Applicants claim hereby claim priority to U.S. Pat. application No. 08/927,016, under 35 U.S.C. § 120 and § 365(c) of any PCT INTERNATIONAL applications designating the United States. Applicants hereby incorporate U.S. Patent application Ser. No. 08/927,016 in its entirety by refernce. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention relates to an automatic focus offset adjustment in a disc player, and more particularly to an automatic focus offset adjusting apparatus and method of a disc player for performing a reliable automatic controlling operation with respect to an abnormal condition of a disc such as a scratch or dust. 
     B. Description of the Prior Art 
     FIG. 1 is a functional block diagram showing a generally conventional compact disc player. Referring to FIG. 1, a pickup assembly  2  reads out data from a disc  1  to provide an electric signal. A RF signal generator  3  receives the electric signal supplied from pickup assembly  2  to produce a RF signal. The RF signal from RF signal generator  3  is amplified by a predetermined level in a RF amplifier  4 , and is waveform-shaped in an analog waveform shaping part  5 . Thereafter, the signal from analog waveform shaping part  5  is supplied to a digital signal processor  6  to be subjected to demodulating and decoding processing, thereby reproducing information recorded on disc  1 . 
     Meanwhile, the output signal from pickup assembly  2  is provided to a focus error detector  7  and a track error detector  8 . Focus error detector  7  detects a focus error signal FE from the signal supplied from pickup assembly  2  to provide the detected focus error signal to a servo controller  9 . Track error detector  8  detects a track error signal TE from the signal supplied from pickup assembly  2  to provide the detected track error signal to servo controller  9 . 
     Then, servo controller  9  receives focus error signal FE and track error signal TE respectively from focus error detector  7  and track error detector  8  to provide a focus control signal FC and a track control signal TC. A motor drive  10  receives focus control signal FC and track control signal TC to drive a slide motor  11 , thereby transferring pickup assembly  2  up and down and side to side. Also, servo controller  9  controls a spindle motor  12  via motor driver  10  to rotate disc  1  at a predetermined speed. 
     FIG. 2 is a view showing a construction of the pickup assembly  2  of FIG.  1 . As shown in FIG. 2, pickup assembly  2  has a laser diode  21  for radiating laser beam, and a collimator lens  22  for converting the diverging beam into parallel rays. In addition, a beam splitter  23  separates incident light and reflected light, and a quarter-wave plate  24  changes a polarized plane of the reflected light by 90 degrees. An objective lens  25  focuses the light, and a photodetector  26  converts the light from beam splitter  23  into an electric signal. Further, a focusing coil and a tracking coil (not shown) are disposed around objective lens  25 . 
     Current flowing through the focusing coil applies a force in conformity with the Fleming&#39;s left hand law, and objective lens  25  attached to the coil is moved up and down to perform the focusing. Also, by current flowing through the track coil, objective lens  25  is moved side to side to perform the tracking. 
     To begin with, the laser beam produced from laser diode  21  is transformed into the parallel rays from the diverging beam by passing through collimator lens  22 . At this time, a beam-splitting diffraction grating (not shown) is interposed between laser diode  21  and collimator lens  22 . When the laser beam generated from laser diode  21  passes through the diffraction grating, three beams consisting of one main spot and two side spots are produced. 
     After this, the parallel rays from collimator lens  22  are focused onto objective lens  25  via beam splitter  23  and quarter-wave plate  24 . Successively, objective lens  25  generates the beam spot to emit it to disc  1 . The beam spot emitted from objective lens  25  is reflected from disc  1  to return to objective lens  25 , and the reflected beam is to changed into parallel rays via objective lens  25 . The parallel rays pass though quarter-wave plate  24  to advance toward beam splitter  23 . Then, beam splitter  23  shifts the advancing direction of the parallel rays by as much as 90 degrees to permit the parallel rays to proceed toward photodetector  26 . 
     FIG. 3 is a block diagram for illustrating a general principle of generating the RF signal, focus error signal FE and track error signal TE. Photodetector  26  includes four light-receiving devices A, B, C and D for receiving the main spot and two light-receiving devices E and F for receiving the side spots. Four light-receiving devices A, B, C and D convert the received light into electric signals and supply them to RF signal generator  3  and focus error detector  7 . RF signal generator  3  sums the signals from light-receiving devices A, B, C and D to provide a sum signal A+B+C+D. The sum signal is used as the RF signal. The signals from light-receiving devices A, B, C and D are also provided as a difference signal (A+C)-(B+D) via focus error detector  7 . The difference signal is used as focus error signal FE. 
     Light-receiving devices E and F receive the side spots to convert them into the electric signals. The signals from light-receiving devices E and F produce a difference signal E-F via track error detector  8 . The difference signal E-F is used as track error signal TE. Thereafter, servo controller  9  receives focus error signal FE and track error signal TE to produce focus control signal FC and track control signal TC. 
     FIG. 4 is a block diagram for illustrating a conventional focus offset adjusting method. As is illustrated, servo controller  9  receives focus error signal FE to generate focus control signal FC. At this time, in order to provide accurate focus control signal FC, a variable resistor VR is manually regulated by a user to adjust a focus offset to generate focus control signal FC. 
     Furthermore, since the specific disc is adjusted only once in its fabricating line, the conventional method has the disadvantage of being incapable of obtaining the accurate focus offset value associated with the kind or state of the disc. 
     SUMMARY OF THE INVENTION 
     The present invention is devised to solve the foregoing disadvantages of the prior art. Therefore, it is an object of the present invention to provide an automatic adjusting apparatus of a focus offset for performing a more reliable automatic controlling operation with respect to abnormal conditions of a disc, such as a scratch and dust. 
     Additional objects 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. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     To achieve the above object of the present invention, according to one aspect of the present invention, an automatic focus offset adjusting apparatus, as broadly defined and embodied herein, includes pickup means for reading recorded data from the disc, means for detecting a focus error signal from an output signal read by the pickup means, means for converting an output signal read by said pickup means into a RF signal, means for separating a specific component from said RF signal, means for comparing the separated specific component from said separating means with a signal having a predetermined frequency to provide a phase difference value, and means for controlling a focus operation of an objective lens by varying a focus offset value within a predetermined range of the phase difference value, setting an optimal focus offset value within the predetermined range, adding the optimal focus offset value to the focus error signal, and providing the added signal as a focus control signal to drive the objective lens. 
     According to another aspect of the present invention, an automatic focus controlling method of a disc player, as broadly defined and embodied herein, includes initializing the focusing operation based on an initial focus offset data stored in memory during a focusing initial operation or reset operation, separating a specific component signal from a RF signal associated with the initial focus offset data, comparing the separated specific signal with a reference signal having a predetermined frequency to provide a phase difference value, varying the focus offset value to allow the phase difference value to have a value within a predetermined range, obtaining an optimal focus offset value within the predetermined range, adding the optimal focus offset value to a focus error signal obtained from the RF signal, and providing the added signal as a focus control signal for controlling the focus operation. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one embodiment of the invention and together with the description, serve to explain the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     The above objects and other advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1 is a functional block diagram showing a generally conventional compact disc player; 
     FIG. 2 is a view showing a construction of the pickup assembly of FIG. 1; 
     FIG. 3 is a block diagram for illustrating a general principle of producing a focus error signal and a track error signal; 
     FIG. 4 is a block diagram for illustrating a conventional focus offset adjusting method; 
     FIG. 5 is a block diagram showing an automatic focus offset adjusting apparatus according to an embodiment of the present invention; 
     FIG. 6 is a flowchart for explaining an automatic focus offset adjusting method according to the embodiment of the present invention; and 
     FIG. 7 is a diagram for explaining selection of an optimal focus offset value. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An automatic focus offset adjusting apparatus according to the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 5 is a block diagram showing the automatic focus offset adjusting apparatus according to the present invention. As shown in FIG. 5, a pickup assembly  502  reads data from a disc  501  to provide an electric signal. A RF signal generator  503  receives the electric signal supplied from pickup assembly  502  to produce a RF signal. The RF signal from RF signal generator  503  is amplified via a RF amplifier  504  to advance toward a signal processor. Also, the signal from RF amplifier  504  is provided into a signal separator  505  which in turn separates only a 3T signal in the RF signal so as to measure the jitter. For reference, a recording unit of the disc is pit, and one pit is; 3T to 11T or so. Here, 3T becomes 744 mm since IT is 258 mm. 
     The signal from signal separator  505  is supplied into a phase comparator  506  which then compares the signal from signal separator  505  with a reference voltage to provide an error signal f O  Thereafter, error signal f O  from phase comparator  506  is provided to a microcomputer  507 . In turn, microcomputer  507  receives error signal (phase difference value) f O , from phase comparator  506 , initial focus offset value fi stored in a memory  508   a  and a signal from a level detector  509  to provide a focus offset value f 1  and switch control signal. At this time, initial focus offset value f i , is a current or voltage value, which is stored in memory  508  at the initial stage, and applied to a focusing coil (not shown). 
     Meanwhile, the electric signal from pickup assembly  502  is supplied into a focus error detector  5 l 1 . After receiving the electric signal from pickup assembly  502 , focus error detector  511  provides a focus error signal FE to a phase compensator  512  and level detector  509 . 
     Phase compensator  512  receives focus error signal FE to generate phase-compensated focus error signal FE. Then, phase-compensated focus error signal FE from phase compensator  512  is supplied into an amplifier  513  to be gain-controlled. Amplifier  513  is connected with an adder  514 . 
     Adder  514  adds a focus offset value f 1  via a closed switch SW from microcomputer  507  to an output of amplifier  513 , i.e., phase-compensated and gain-controlled focus error signal. 
     Additionally, level detector  509  detects the level of focus error signal FE, and provides its output signal f 2  to microcomputer  507 . 
     According to the above construction of this invention, initially, pickup assembly  502  is driven by initial focus offset value f i , stored in memory  508 . 
     RF signal of RF signal generator  503  which is changed according to initial driving of pickup assembly  502  is supplied, via RF amplifier  504  and signal separator  505 , into phase compensator  506  which compares the signal from signal separator  505  with the reference voltage to provide the error signal (phase difference value) f O . Thereafter, the error signal f O  from phase comparator  506  is provided to microcomputer  507 . 
     In turn, microcomputer  507  determines whether the phase difference value f O , is within a predetermined threshold n or not, and if so, varies initial focus offset value f i , by ±Δ. 
     After this, microcomputer  507  obtains a new f O , corresponding to f 1 =f i ±Δ. 
     Then, microcomputer  507  determines whether a level f 2  of focus error signal FE from level detector  509  is lower than a predetermined level, if so, sets a lower limit of f focus offset value f 1  as minimum value a and an upper limit of focus offset value f 1  as maximum value b in accordance with the f O , within the threshold value n, obtains an average value of minimum value a and maximum value b as optimal focus offset value as shown in FIG. 7, and outputs the optimal focus offset value to adder  514  via switch SW to add the optimal focus offset value to phase-compensated and gain-controlled focus error signal. 
     FIG. 6 is a flowchart for explaining an automatic focus offset adjusting method according to the present invention. As illustrated, in step S 601 , microcomputer  507  sits a focus mode, e.g, focusing initial mode or reset mode turns switch SW on and outputs initial focus offset value fi stored in memory  508  as focus offset value f 1 , via switch SW and adder  514 , to motor drive for initial focusing drive. 
     In step S 602 , pickup assembly  502  is moved upward or downward, and the RF signal from pickup assembly  502  is changed. The changed RF signal generates new error signal f O  via signal separator  505  and phase comparator  506 , and output error signal f O  is supplied into microcomputer  507 . 
     In step S 602 , microcomputer  507  controls phase comparator  506  to compare the input 3T signal with reference voltage Vref thereby producing error signal (phase difference value) f O . Then, microcomputer  507  determines, in step S 603 , whether error signal f O  is higher than the predetermined threshold n or not. The program proceeds to) step S 604  when error signal f O  is higher than the threshold n. If not, the program proceeds to step S 605 . 
     In step S 603 , if it is determined that error signal f O  exceeds the threshold n, microcomputer  507  determines that the focusing is impossible and jumps the track in step S 604 . 
     In step S 605 , microcomputer  507  adds a predetermined value ±Δ to initial focus offset value f i , and the obtained value f i ±Δ is provided as a new focus offset value f 1 . Then, in step S 606 , microcomputer  507  obtains a new f O  corresponding to f 1 =f i ±Δ. 
     After that, microcomputer  507  determines whether the new f O  is lower than the threshold n or not. 
     The program proceeds to step S 608  when the new f O  is lower than the threshold n. If not, the program proceeds to step S 609 . In step S 608 , the microcomputer  507  varies ±Δ. Then, the microcomputer  507  proceeds to step S 605  to repeat steps S 605  to S 607 . 
     Additionally, microcomputer  507  controls level detector  509  to detect the level f 2  of focus error signal FE in step S 609 . 
     In step S 610 , microcomputer  507  receives the signal f 2  supplied from level detector  509  to determine whether the signal f 2  has a level below a predetermined value or not. If it is determined that the signal f 2  is below the predetermined level, microcomputer  507  proceeds to step S 611 . Otherwise, it proceeds to step S 605  to repeat steps S 605  to S 610 . 
     Then, in step S 611 , microcomputer  507  sets minimum value a and maximum value b of focus offset value f 1  in accordance with f O , within the threshold value n as shown in FIG.  7 . After that, in step S 612 , microcomputer  507  outputs an average ((a+b) 2  of FIG.7) of minimum value a and maximum value b as focus offset value f 1  and turns switch SW off. Then, the program is finished. 
     As described above, the automatic focus offset adjusting apparatus and method according to the present invention is effective in that the focus offset is automatically adjusted to eliminate the error liable to be incurred during the manual controlling. At the same time, the focus offset is automatically adjusted to be stable with respect to warping of the disc and a mechanical error of the pickup in the disc player. Furthermore, the pickup signal obtained when the disc is in an abnormal condition due to dust or scratch is distinguishable to be advantageous for enhancing reliability of the focus offset adjusting operation. 
     Still furthermore, in detecting of the optimal focus offset level, the present invention can reduce computation time by detecting only maximum &amp; minimum levels and setting an average of the maximum and minimum levels as an optimal focus offset value, compared to prior methods in which computation should be required for all the values of focus bias. 
     Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.