Title of Invention

"ADAPTIVE FOCUSING METHOD FOR AND APPARATUS"

Abstract

A method for adaptively focusing an optical disc, said method comprising the steps of adaptively focusing a static part by a method in which an optical disc is not driven and a pickup head operates in an optical disc drive followed by adaptively focusing a dynamic part by a method in which a focus is deviated when both a disc drive and a pickup head operate in an optical disc drive of an optical disc and an apparatus for performing the aforesaid adaptive focusing method.

Full Text

Field of the Invention: The present invention relates to an adaptive focusing method for an optical disc and an apparatus thereof. The present invention relates to the field of controlling an optical disc drive, and more particularly, to an adaptive focusing method and apparatus to control an optical disc drive using an adaptive focus search algorithm. Description of the Related Art: An optical disc is a mass storage medium that can hold up to several tens gigabytes of binary data in an inexpensive plastic disc. Due to a large capacity of the optical disc, the optical disc is widely used as a major data storage medium in the computer field and multimedia devices. An optical disc drive includes a large number of component parts including motors, actuators and optical and electronic components. Many control algorithms are used to control motors and actuators to move a pickup head in a proper way so as to access a recording layer on a disc surface. One of problems of the control algorithms is to focus a laser beam onto the surface of the optical disc. More particularly, the control algorithms have a problem with detecting and adjusting an optimal focus point of the pickup head. In conventional optical pickup heads, a laser diode is used to generate the laser beam to be radiated onto a data area (i.e. the recording layer) of the optical disc. A photo sensor, which generates opto-electrical signals representing focusing/tracking errors in the optical pickup heads, detects the laser beam reflected from the surface of the optical disc. The photo sensor includes a number of separate light sensitive areas. Some of the iignt sensitive areas is used to generate a focusing error signal (FES). The FF5 is used in servo controi algorithms to detect and adjust the pickup head to correct a focusing position A control signal of a focus actuator is referred to as a focus drive signal (FOD,). FIG. 1 is a time diagram illustrating a process includir~g a general focusing algorithm used in the optical disc drive. At an initial stage, the pickup head moves from a central position 0.0 (0-state) toward a lowermost position (1-state). When the pickup head reaches the owermost position (1-state), the pickup head goes to the uppermost position (2-state) to make a saw-tooth pulse movement. When the pickup head arrives at the uppermost position (2-state), the pickup head goes back to the lowermost position (1-state) and then repeats the process of going to the 2-state and back to the 1-state until the pickup head stably achieves focusing. This procedure is called a focus search. FODTOPMARGN' is a constant to define a maximum value of the FOD during a focus search and FODBOTMARGN' is a constant to define a minimum value of the FOD during the focus search. 'FODMAGNSTEP' and FODTIMESTEP' are constants to determine a velocity of the focus actuator, i.e., constants to define fixed distance intervals for a smallest change in the FOD and time intervals between closest changes in the FOD, respectively. When the pickup head approaches the focus point, the FES changes like S-curves shown in FIG. A center of the S-curves corresponds to the focus point of the pickup head and a number of S-curves is equal to a number of layers of an optical disc. However, a high-density optical disc uses an objective lens having a small numerical aperture (NA) and has a small gap between the surface and a recording layer of the high-density optical disc. Thus, a focal length of the objective lens decreases and an allowance of a vertical distortion of the high-density optical disc increases. As a result, when the general focusing algorithm presented in FIG. 1 is used, the objective lens is highly likely to scratch or damage the surface of the high-density optical disc. A searching time is long until the stable focusing is attained in an initial search for a focus point and after losing the focus due to dirt on and damage to the surface of the high-density optical disc. Documents describing conventional focusing algorithms include International Patent Application No. WO 02/59888, entitled 'Optical Disk Drive with Digital Focus and Tracking Servo System. US. Patent Application No 6.192,010, entitled Apparatus and Method for Adjusting Pickup I-lead of Optical Disc Drive to Optimal Focus Point, and U.S. Patent Application No. 6,392,971 entitled 'Focus control Method and Optical Disc Recording/Reproducing Apparatus'. SUMMARY OF THE INVENTION According to an aspect of the present invention, there is provided an adaptive focusing method and apparatus of a high-density optical disc where a gap between a surface and a recording layer is small. According to an aspect of the present invention, there is also provided an adaptive focusing method and apparatus to prevent an objective lens of a pickup head from scratching or damaging a surface of an optical disc during a search for a focus point. According to an aspect of the present invention, there is also provided an adaptive focusing method and apparatus to search for a focus point within a short period of time right before focusing or in an initial state. According to an aspect of the present invention, there is also provided an adaptive focusing method and apparatus to search for a focus point within a short period of time after a focus point loosing event during a focus search. Additional aspects and/or 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. According to an aspect of the present invention, there is provided an adaptive focusing method for a static part in which an optical disc is not driven and a pickup head operates in an optical disc drive. The pickup head falls from the optical disc to a minimum value of a focus drive signal during a focus search operation. When the pickup head reaches the minimum value of the focus drive signal, the pickup head rises close to the optical disc and then to a maximum allowable value of the focus drive signal when a signal reflected from the optical disc is detected. When the pickup head reaches the maximum allowable value of the focus drive signal, the pickup head falls from the optical disc to a minimum allowable value of the focus drive signal. Field of the Invention: The present invention relates to an adaptive focusing method for an optical disc and an apparatus thereof. The present invention relates to the field of controlling an optical disc drive, and more particularly, to an adaptive focusing method and apparatus to control an optical disc drive using an adaptive focus search algorithm. Description of the Related Art: An optical disc is a mass storage medium that can hold up to several tens gigabytes of binary data in an inexpensive plastic disc. Due to a large capacity of the optical disc, the optical disc is widely used as a major data storage medium in the computer field and multimedia devices. An optical disc drive includes a large number of component parts including motors, actuators and optical and electronic components. Many control algorithms are used to control motors and actuators to move a pickup head in a proper way so as to access a recording layer on a disc surface. One of problems of the control algorithms is to focus a laser beam onto the surface of the optical disc. More particularly, the control algorithms have a problem with detecting and adjusting an optimal focus point of the pickup head. In conventional optical pickup heads, a laser diode is used to generate the laser beam to be radiated onto a data area (i.e. the recording layer) of the optical disc. A photo sensor, which generates opto-electrical signals representing focusing/tracking errors in the optical pickup heads, detects the laser beam reflected from the surface of the optical disc. The photo Statement of the Invention: Accordingly, the present invention provides an adaptive focusing method for an optical disc, said method comprising the steps of adaptively focusing a static part by a method such as herein described in which an optical disc is not driven and a pickup head operates in an optical disc drive followed by adaptively focusing a dynamic part by a method such as herein described in which a focus is deviated when both a disc drive and a pickup head operate in an optical disc drive of an optical disc. The present invention also provides an apparatus for implementing the adaptive focusing method for an optical disc, comprising: a disc driver rotating the optical disc; a pickup head; a focus servo controller that moves the pickup head to an optimal focus point; a reflected signal detecting a signal reflected from the optical disc by the pickup head; and a signal processor preventing spikes between a surface of the optical disc and the pickup head in response to the signal reflected and generating a focus drive signal for the focus servo controller using an adaptive focus search algorithm comprising a static part and a dynamic part to reduce a focus search time. According to another aspect of the present invention, there is provided an adaptive focusing method of a dynamic part in which a focus is deviated when both a disc driver and a pick head operate in an optical disc drive. A pickup head rises from a lowermost position from a surface of an optical disc and then to a maximum allowable value of a focus drive signal when a signal reflected from the optical disc is detected. When the pickup head reaches the maximum allowable value of the focus drive signal, the pickup head falls from the optical disc to a minimum allowable value of the focus drive signal. According to still another aspect of the present invention, there is provided an adaptive focusing apparatus of an optical disc drive including a focus servo controller that moves a pickup head to an optimal lbcus point and a disc driver that rotates an optical disc. The adaptive focusing apparatus includes a reflected signal detector that detects a signal rellected from the optical disc by the pickup head and a signal processor that prevents spikes between a swihee of the optical disc and the pickup head in response to the reflected signal and generates a focus drive signal fir the focus servo controller using an adaptive focus search algorithm including a static part and a dynamic part to reduce a focus search time. STATEMENT OF THE INVENTION A method for adaptively focusing an optical disc, said method comprising the steps of adaptively focusing a static part by a method such as herein described in which an optical disc is not driven and a pickup head operates in an optical disc drive followed by adaptively focusing a dynamic part by a method such as herein described in which a focus is deviated when both a disc drive and a pickup head operate in an optical disc drive of an optical disc. BRIEF DESCRIPTION OF THE DRA WINGS These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the exemplary aspccts taken in conjunction with the accompanying drawings in which: FIG. 1 is a time diagram of a general focusing algorithm; FIG. 2 illustrates a PBS curving in an S shape when a pickup head approaches a focus point: FIG. 3 is a schematic block diagram of an optical disc drive to which an adaptive focusing method is applied, according to an aspect of the present invention: FIG. 4 is a time diagram of an adaptive focus search algorithm, according to an aspect of the present invention; and FIG. SA through 3D are time diagrams of the adaptive focus search algorithm, according to another aspect of the present invention. DETAILED DESCRITPlON OF THE PREFERRED EMBODIMEN~I'S Reference wHi now be made in detaiI to the aspects of the presert ivention, examples of which are Ilustratec ~n the accompanying drawings, wnere~ hke reference numerals refer to the Ike elernents throughout. The aspects are deschbed below to expiain the present nvention by referring to the figures. FiG. 3 is a schematic block di3gram of an optical disc drive to which ~n adaptive focusing method is applied, according to the present invention. Reference numeral 100 denotes a disc, reference numeral 110 denotes a pickup unit, which can also be referred to as a pickup head, including an optical system ricluding a laser diode, an objective lens, a photo sensor, and the like, and reference numeral 120 denotes a reflected signal detector whicfl detects a reflected signal from the photo sensor. Reference numeral 130 denotes a signal processor which generates a signal to drive the optical disc drive using an adaptive focus search aigortthm, including a static part and a dynamic part, that prevents spikes from a surface of the disc 100 and the objective lens and reduces a focus search time. Reference numeral 140 denotes a focus servo controfler including a focus actuator, which keeps a gap between the objective lens and a recording layer of the disc 100 in a focus-in state, and so forth. Reference numeral 150 denotes a disc driver including a spindie motor, which rotates the disc 100, and the like. The adaptive focus search algorithm, which can be reaiized as software in a controller (not shown) of the signal processor 130or in the signal processor 130, is divided into two parts. The first part is the static part used before starting focusing or in nitiaiization. In the static part, for iflustrative purposes, the spindle motor of the disc driver 150 is motionless and the focus actuator of the focus servo controller 140 has an adaptive swing margin. A swing margin of the focus actuator can be caicufated every pass of the pickup head depencing on an actual position of a center of S-curves or a focus point and may be an absolute swing margin to prevent damage to the opticai system in the absence of an FES feedback signaL The static part does not allow the rotation of the spindle motor and is proposed to check a Pipe of disc and a number of layers and to adjust an FES gain coefficient. The second part is the dynamic part, wHch sriould be used only wnen the disc lOG rotates r~ synchronization with a velocity of the spindle motor of the disc driver 150 and when a focus is suddenly deviated due to outer disturbances, an unstable operation of the optical beam reflected from the surface and the recording layer of the disc 1 00. The photo sensor has a number of separate light sensitive areas and the reflected signal detector 120 detects a portion of the reflected laser beam as the FES or detects the sum signal (i.e., the RF signal) to use the FES signal or the sum signal in the adaptive focus search algorithm. The signal detector 130 analog-to-digitalconverts the reflected signal (FES) detected by the reflected signal reflector 1 20 to obtain an actual value of the FES and low-pass filters the actual value of the FES, so that the controller can check whether the disc 100 is loaded, a type of disc, a number of layers of the disc 100 and adjust an FES gain coefficient using the actual value of the FES. The controller digital-to-analogoonverts the FOD value calculated by variables and constants used in the adaptive focus search algorithm presented in FIG. 4 and, then, provides the FOD value to the focus servo controller 140. The prevention of the spikes between the disc 100 and the objective lens of the pickup unit 110 is achieved by checking a rising part period of the S-curves of the FES. In an existing focus search algorithm, a result thereof marked with dotted lines in FIG. 4, a rising region of an FOD depends on a constant FODTOPMARGN. In the adaptive focus search algorithm, according to an aspect of the present invention, the ascending region of the FOD rises up to a maximum allowable value FOUT_MAX of the FOD, which corresponds to a maximum focus search voltage. The maximum allowable value FOUT_MAX exists within the constant FODTOPMARGN. When the pickup head reaches the maximum allowable value FOUT_MAX of the FOD, the descending region of the FOD is formed. In the existing focus search algorithm, the descending region of the FOD depends on a constant FODBOTMARGN. In the adaptive focus search algorithm, according to an aspect of the present invention, the descending region of the FOD is formed to a minimum allowable value FOUT_MIN (which corresponds to a minimum focus search voltage). The minimum allowable value FOUT_MIN exists within a constant FODBOTMARGN. When the pickup head reaches the minimum allowable value FOUT_MIN of the FOD, the ascending region of the FOD is re-formed. A number of times the descending region (i.e., the 1-state) with the ascending region of the FOD and the ascending region (i.e., the 2-state) with the descending region of the FOD are repeated after the reflected signal is detected is determined in consideration of the stability of focusing. After the reflected signal is detected, a section Ta representing an amount of the movement of the pickup head, i.e., a section ranging from a rising part of an S-curve to the maximum allowable value FOUT_MAX (which corresponds to a focus point) or from the maximum allowable value FOUT_MAX to a falling pan of the S-curve, may be set to be a fixed value. The section Ta may be adaptively set in proportion to a time interval from the reflection of the signal from the surface of the disc 1 DO to the reflection of the signal from the recording layer of the disc 100 or may be adaptively set using a peak-to-peak time of the FES with the S-curves. The set section Ta contributes to the prevention of the pickup head's touching the surface of the disc 100 and a reduction in the time required to search for the focus point using an adaptive margin of the FOD. At the bottom of FIG. 4, a focus point access time according to the general focus search algorithm and the focus point access time, according to an aspect of the adaptive focus search algorithm of the present invention, are shown. A time interval TO necessary to obtain a first S-curve is the same in both the general focus search algonthm and the adaptive focus search algorithm. An access time between the first S-curve and a third S-curve is T2 in the general focus search algorithm, but Ti in the adaptive focus search algorithm, where Ti FIGS. SA through 5D are time diagram5 of the adaptive focus Search algorithm according to another aspect of the present invention, i.e., a time diagram of a profile of the FES and the FOD when Performing the dynami0 part in which the disc 1oo and the Pickup head operate, a timing diagram of driving clock pulses of the spindle motor, and a timing diagram of the vertical deviation of the disc 100. The focus search algorithm will be described with reference to the Optical disc drive shown in FIG. 3. FIG. 5A shows a profile of the vertical deviation of the disc 100 during the rotation of the disc 100, and FIG 5B shows the driving clock pulses of the spindle motor generated by the disc driver 150, which rotates the disc 100 FIG. SC is the timing diagram of the FOD, and FIG. SD is the timing diagram of the FES. According to the dynamic part Of the adaptive focus search algorithm althoug focusing deviates during the operation of the disc 100 due to outer disturbances, the verticles deviation (FIG. 5A) of the disc 100 can be predicted. Thus, the FOD. wnich is referred to as a focus search voltage, is adjusted so that the disc 100 enters a closest focus position. Four states of the FOD. i.e., the 0-state, the 1-state, the 2-state, and a 3-state, will be described below. In the 0-state, a time delay is created to prevent false conditions caused by possible false S-curves of the FES due to the unpredictable relative positions of the pickup head and the surface of the disc 100. A current output ESOUT of the FOD is initialized and the maximum allowable value FOUT_MAX of the FOD is set to be an initial margin. V other words, an initial value of the maximum allowable value FOUT_MAX of the FOD is equal to a variable FOUT_MIN_GLOB and depends on a previous state of a focus servo system of the optical disc drive. When the previous state of the focus servo system is an on-focus state, the variable FOUT_MIN_GLOB has a minimum filtered FOD value, which corresponds to a lowermost position of the surface of the disc 100. When the previous state of the focus servo system is not the on-focus state, the variable FOUT_MIN_GLOB has a constant FODBOTMARGN to prevent the touching of the disc 100. In FIG. 50, FOUT_MIN_GLOB_C is a constant to define a fixed distance interval for an initial position of the FOD in a starting portion of the dynamic part of the adaptive focus search algorithm. The 1-state forms a slowly ascending region of the FOD with a rising velocity of at least predetermined times (e.g., 10 times) less than the rising velocity of the pickup head. A vertical rising velocity of the pickup head is set to be less than a vertical deviation velocity of the surface of the disc 100 shown in FIG. 5A. If the S-curve of the FOD is found, the voltage FSOUT of the FOD is stored and a time uSTIME to keep a latest moment an S-curve is found is stored. Further, a new top margin FOUT_MAX is calculated as a focus point A*FODTIMESTEP, and the 1-state is switched to the 2-state. When no S-curves are found, the 1-state is switched to the 0-state so as to start the dynamic part from an initial state. The 2-state forms the ascending region of the FOD. During the 2-state, the FES having the S-curves is checked. When the S-curve is found, the new top margin FOUT_MAX is calculated as the focus point A*FODMAGNSTEP, where A is a constant. In this calculation, the time and the distance of the movement of the pickup head are fixed in the 2-state. The 3-state forms the descending and flat horizontal regions of the FOD. The descending region quickly moves the pickup head from a dangerous area to a safe position and the flat region keeps the pickup head in a stand-by state. A stand-by state duration is calculated by uSTIME (a last instant of time when an S-curve is found) + uREVTlME (revolution interval of the spindle motor) — (A+B)*FODTIMSTEP. Here, B is a constant to define a fixed distance interval to keep the pickup head below the lowermost position of the surface of the disc 100. After the 3-state, the 3-state is switched to the 2-state, and then the states are repeated in the order of the 2-state, the 3-state, the 2-state, the 3-state, etc. to search for the focus. Accordingly, the dynamic part of the focus search algorithm uses information about a revolution time of the spindle motor, a current time, and a moment of a safe lower most position of the surface of the disc 100 to synchronize the moment of getting the S-curves and the lowermost position of the surface of the disc 100, which leads to a safe, unbreakable focus search algorithm. Also, the focus search time required to enter the safe focus state can be reducel As described above, according to an aspect, the present invention is suitable for a high-density optical disc in which a gap between a surface and the recording layer is narrow. Also, an objective lens of a pickup head can be prevented from scratching or damaging the surface of the high-density optical disc during a search for a focus point. A time required to search for the focus point can be reduced right before starting focusing or in an initial state. Moreover, after losing the focus point in a normal operation, the search for the focus point is possible within a short period of time. As a result, stability and reliability of an optical system may be improved. A focus search algorithm proposed in the present invention is suitable for a high-density optical disc and can be realized in a digital signal processor, a microprocessor, or the like without any additional hardware cost. Although a few aspects 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 this aspect without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents. WE CLAIM: A method for adaptively focusing an optical disc, said method comprising the steps of adaptively focusing a static part by a method such as herein described in which an optical disc is not driven and a pickup head operates in an optical disc drive followed by adaptively focusing a dynamic part by a method such as herein described in which a focus is deviated when both a disc drive and a pickup head operate in an optical disc drive of an optical disc. 2. The method as claimed in claim 1, wherein the adaptive focusing method for focusing the static part comprises: allowing the pickup head to rise close to the optical disc and to a maximum allowable position corresponding to a maximum allowable value of the focus drive signal when a signal reflected from the optical disc is detected and when the pickup head reaches a minimum allowable position corresponding to a minimum value of the focus drive signal; and allowing the pickup head to fall from the optical disc to a minimum allowable position corresponding to a minimum allowable value of the focus drive signal when the pickup head reaches the maximum allowable position. 3. The method as claimed in claim 2, wherein the maximum allowable position corresponding to the maximum allowable value of the focus drive signal is set within a maximum value of the focus drive signal during the focus search operation, and the minimum allowable position corresponding to the minimum allowable value of the focus drive signal is set within the minimum value of the focus drive signal during the focus search operation. 4. The method as claimed in claim 2, comprising repeating the rise of the pickup head to the maximum allowable position and the fall of the pickup head to the minimum allowable position after the fall of the pickup head to the minimum allowable position. 5. The method as claimed in claim 2, wherein a vertical deviation of the pickup head to the maximum allowable position after the reflected signal is detected is set fixed. 6. The method as claimed in claim 2, wherein a vertical deviation of the pickup head to the maximum allowable position is set in proportion to a time interval from the reflection of the signal from a surface of the optical disc to the reflection of the signal from a recording layer of the optical disc. 7. The method as claimed in claim 2, wherein the reflected signal is a focus error signal that is a portion of a signal detected by the pickup head. 8. The method as claimed in claim 2, wherein the reflected signal is a sum signal of signals detected by the pickup head. 9. The method as claimed in claim 5, wherein a vertical deviation of the pickup head to the maximum allowable position is set by detecting a peak-to-peak time of the focus error signal. 10. The method as claimed in claim 2, wherein the static part performs the focus search operation prior to a start of focusing or an initialization operation, and checks whether the optical disc is loaded, a type of optical disc, a number of layers of the optical disc and adjust a gain coefficient of the focus error signal, using the signal reflected. 11. The method as claimed in claim 1, wherein the adaptive focusing method for focusing the dynamic part compnses: allowing the pickup head to rise from a lowermost position of a surface of the optical disc to a minimum allowable position corresponding to a maximum allowable value of a focus drive signal when a signal reflected from the optical disc is detected; andallowing the pickup head to fall from the optical disc to a minimum allowable position corresponding to a minimum allowable value of the focus drive signal when the pickup head reaches the maximum allowable position. 12. The method as claimed in claim 11, comprising allowing the pickup head to stand-by at the minimum allowable position for a predetermined period of time before the rise of the pickup head to the maximum allowable position. 13. The method as claimed in claim 12, wherein when a previous state of the optical disc drive is not an on-focus state, the pickup head stands-by at the minimum allowable position corresponding to the minimum allowable value of the focus drive signal so as not to touch the optical disc. 14. The method as claimed in claim 11, wherein the lowermost position of the surface of the optical disc corresponds to the minimum allowable position. 15. The method as claimed in claim 11, wherein the maximum allowable position corresponding to the maximum allowable value of the focus drive signal is within a maximum value of the focus drive signal during a focus search operation, and the minimum allowable position corresponding to the minimum allowable value of the focus drive signal is within a minimum value of the focus drive signal during the focus search operation. 16. The method as claimed in claim 11, wherein a vertical deviation of the pickup head to the maximum allowable position after the reflected signal is detected is fixed. 17. The method as claimed in claim 11, wherein a vertical deviation of the pickup head to the maximum allowable position is set in proportion to a time interval from the reflection of the signal from the surface of the optical disc to the reflection of the signal from a recording layer. 18. The method as claimed in claim 11, wherein the reflected signal is a focus error signal that is a portion of a signal detected by the pickup head. 19. The method as claimed in claim 11, wherein the reflected signal is a sum signal of signals detected by the pickup head. 20. The method as claimed in claim 11, wherein a vertical deviation of the pickup head to the maximum allowable position is adaptively set by detecting a peak-topeak time of the focus error signal. 21. The method as claimed in claim 11, wherein the rise of the pickup head to the maximum allowable position comprises: allowing the pickup head to rise at a slower speed than a vertical deviation speed of the optical disc; andallowing the pickup head to rise to the maximum allowable position corresponding to the maximum allowable value of the focus drive signal when the signal reflected from the optical disc is detected. 22. The method as claimed in claim 11, wherein the fall of the pickup head to the minimum allowable position comprises: allowing the pickup head to fall from the optical disc to the minimum allowable position corresponding to the minimum allowable value of the focus drive signal when the pickup head reaches the maximum allowable position; and allowing the pickup head to stand-by at the minimum allowable position for a predetermined period of time when the pickup head reaches the minimum allowable position. 23. The method as claimed in claim 22, comprising repeating the rise of the pickup head to the maximum allowable position when the signal reflected from the optical disc is detected, the fall of the pickup head to the minimum allowable position when the pickup head reaches the maximum allowable position of the focus drive signal, and the stand-by of the pickup head at the minimum allowable position when the pickup head reaches the minimum allowable position, after the rise of the pickup head to the maximum allowable position. 24. An apparatus for implementing the method of adaptively focusing an optical disc as claimed in claims I to 23, comprising: a disc driver rotating the optical disc; a pickup head; a focus servo controller that moves the pickup head to an optimal focus point; a reflected signal detecting a signal reflected from the optical disc by the pickup head; and a signal processor preventing spikes between a surface of the optical disc and the pickup head in response to the signal reflected and generating a focus drive signal for the focus servo controller using an adaptive focus search algorithm comprising a static part and a dynamic part to reduce a focus search time. 25. The apparatus as claimed in claim 24, wherein the disc driver comprises a spindle motor and the focus servo controller comprises a focus actuator, and wherein the static part is applied before a focusing starts or in an initialization operation, and during the static part, the spindle motor of the disc driver is motionless and a swing margin of the focus actuator is adaptive. 26. The apparatus as claimed in claim 24, wherein the static part allows the pickup head to fall from the optical disc to a minimum position corresponding to a minimum value of a focus drive signal during a focus search operation, allows the pickup head to rise close to the optical disc when the pickup head reaches the minimum position and to a maximum allowable position corresponding to a maximum allowable value of the focus drive signal when the signal is reflected from the optical disc, and allows the pickup head to fall from the optical disc to a minimum allowable position corresponding to a minimum allowable value of the focus drive signal when the pickup head reaches the maximum allowable position. 27. The apparatus as claimed in claim 26, wherein the allowing of the pickup head to rise to the maximum allowable position and the allowing of the pickup head to fall to the minimum allowable position are repeated a predetermined number of times in consideration of a stability of the focusing. 28. The apparatus as claimed in claim 26, wherein a vertical deviation of the pickup head to the maximum allowable position corresponding to the maximum allowable value of the focus drive signal after the reflected signal is detected is set fixed. 29. The apparatus as claimed in claim 26, wherein, after the signal reflected is detected, a vertical deviation of the pickup head to the maximum allowable position corresponding to the maximum allowable value of the focus drive signal is set in proportion to a time interval from the reflection of the signal from the surface of the optical disc to the reflection of the signal from a recording layer. 30. The apparatus as claimed in claim 26, wherein the reflected signal is a focus error signal that is a portion of a signal detected by the pickup head. 31. The apparatus as claimed in claim 26, wherein the reflected signal is a sum signal of signals detected by the pickup head. 32. The apparatus as claimed in claim 30, wherein a vertical deviation of the pickup head to the maximum allowable position after the reflected signal is detected is set by detecting a peak-to-peak time of the focus error signal. 33. The apparatus as claimed in claim 25, wherein the swing margin is set to be an absolute margin to prevent damage to the optical disc drive. 34. The apparatus as claimed in claim 25, wherein the swing margin is calculated every pass of the pickup head depending on an actual position of a center of Scurves of the signal reflected or an actual position of a focus point. 35. The apparatus as claimed in claim 25, wherein in the static part, the signal processor does not allow the spindle motor to rotate, and checks a type of optical disc, a number of layers and adjusts a gain coefficient of a focus error signal. 36. The apparatus as claimed in claim 24, wherein the dynamic part is used when the optical disc rotates in synchronization with a speed of the spindle motor of the disc driver and when a focus is deviated due to outer disturbances in a normal operation, instability of the optical disc drive, or damage to the optical disc. 37. The apparatus as claimed in claim 36, wherein the pickup head moves to an initial position being a lowermost position of the surface of the optical disc to search for a focus point, where an actual value of the focus drive signal is the lowermost position of the surface of the optical disc. 38. The apparatus as claimed in claim 37, wherein the dynamic part allows the pickup head to rise from the initial position and to a maximum allowable position corresponding to a maximum allowable value of the focus drive signal when the signal reflected from the optical disc is detected, and allows the pickup head to fall from the optical disc to a minimum allowable position corresponding to a minimum allowable value of the focus drive signal when the pickup head reaches the maximum allowable position. 39. The apparatus as claimed in claim 38, wherein the dynamic part allows the pickup head to stand-by at the minimum allowable position for a predetermined period of time before the rise of the pickup head. 40. The apparatus as claimed in claim 38, wherein the dynamic part allows the pickup head to stand-by at the minimum allowable position when the pickup head reaches the minimum allowable position after the fall of the pickup head. 41. The apparatus as claimed in claim 24, wherein the dynamic part of the focus search algorithm uses information about a revolution time of a spindle motor, a current time, and a moment of a safe lowermost position of the surface of the disc to synchronize the moment of S-curves and the lowermost position of the surface of the disc. 42. The apparatus as claimed in claim 24, wherein the dynamic part of the adaptive focus search algorithm comprises a 0-state, a 1-state, and a 2-state, and a 3-state, wherein in the 0-state, a time delay is created to prevent false conditions caused by false S-curves of a focusing error signal (FES) due to unpredictable relative positions of the pickup head and the surface of the disc, the 1-state forms a slowly ascending region of a focus drive signal (FOD) with a rising velocity of at least predetermined times less than a rising velocity of the pickup head, the 2-state forms an ascending region of the FOD, and the 3-state forms descending and flat horizontal regions of the FOD. 43. The apparatus as claimed in claim 43, wherein after the 3-state, the 3-state is switched to the 2-state, and the states are repeated in an alternating order to search for the focus point. 44. A method for adaptively focusing an optical disc substantially as herein described with reference to the accompanying drawings. 45. An apparatus for adaptively focusing an optical disc substantially as herein described with reference to the accompanying drawings.

Documents:

1235-del-2003-abstract.pdf

1235-del-2003-claims.pdf

1235-del-2003-correspondence-others.pdf

1235-del-2003-correspondence-po.pdf

1235-del-2003-description (complete).pdf

1235-del-2003-drawings.pdf

1235-del-2003-form-1.pdf

1235-del-2003-form-19.pdf

1235-del-2003-form-2.pdf

1235-del-2003-form-26.pdf

1235-del-2003-form-3.pdf

1235-del-2003-form-5.pdf

1235-del-2003-petitiion-137.pdf

1235-del-2003-petitiion-138.pdf

abstract.jpg